The assessment of forest vulnerability and resilience in the sight of global ecological, social and economic changes is a relevant issue. In recent decades, forest vulnerability is rapidly increasing worldwide and forecasting changes in tree health is becoming a challenge. Forest dieback episodes have been recorded in all biomes affecting different tree and shrub species. These dieback cases are revealing the high vulnerability of some species, particularly conifers, manifested as a loss in tree vigour, growth decline and sometimes tree death. Tree mortality commonly involves multiple, interacting factors, ranging from drought to insect pests and diseases, often making the determination of a single cause unrealistic. The need of understanding and predicting changes in tree mortality, growth and recruitment in response to dieback is essential to improve vegetation and C cycle models.
There is a common agreement on the key role of interdisciplinary research and the combined use of complementary tools to improve the monitoring and projection of forest vulnerability and dieback.
This session focuses on efforts to improve our understanding on: i) causes and mechanisms related to forest vulnerability and dieback; ii) potential changes in tree species composition, forest structure and extent of dieback under current and future climate change scenarios; iii) evaluation of which functional anatomical and hydraulic traits make some tree species or stands and tree populations more prone to environmental-induced dieback and decline IV) assessment of the role and interaction of insect disease and other abiotic factors on mortality; V) possible contribution of novel methods and approaches in quantitative wood anatomy to evaluate plant adaptive capability and identify early-stress indicators; VI) how trees die from drought and how to quantitatively assess tree mortality rates and the magnitude of tree mortality episodes associated to climate change events.
Contributions will focus on an integrated multi-scale (from cells to plant communities, ecosystems and global approaches), multi-temporal (from tree-ring series analysis to xylogenesis and long-term forecasting) and interdisciplinary (microscopy and individual plant physiology to remote sensing) frameworks.

Convener: Francesco Ripullone | Co-conveners: Giovanna Battipaglia, Jesus Julio Camarero, Veronica De Micco, Angelo Rita
| Attendance Tue, 05 May, 14:00–15:45 (CEST)

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Chat time: Tuesday, 5 May 2020, 14:00–15:45

Chairperson: Francesco Ripullone
D663 |
Tamir Klein

The Mediterranean basin is a mosaic of human and natural landscapes, many of which are important forests and woodlands. Among global biomes, it has been under the longest anthropogenic stress, and today, in addition to the ongoing warming, it experiences drying. In my talk I will give examples from new research on the impacts of these processes on Mediterranean forests, as well as opportunities for increasing their sustainability under intensifying change.

Aleppo pine is perhaps the single most important forest tree species for the region, and has been grown for decades in common garden plots of provenances from around the region. Forest scientists from Spain, Italy, Greece and Israel, teamed up to synthesize the results of these provenance trials. Together, we produced the temperature and precipitation growth sensitivity profiles for Aleppo pine. Next, these profiles were applied on future climate maps, to show the potential expansion of this key species northward, as well as its extinction in many southern locations. In a seven decades-long tree mortality study across Israel, this mortality pattern is already occurring, driven by hotter and longer drought periods.

My current research is focused on finding new avenues to ensure the long-term existence of forests and trees in the Mediterranean. Examples include: (1) Mixed forests, with native broadleaf and conifer species coexisting, have high resilience, thanks to interspecific niche partitioning; (2) Native fruit trees have higher drought resistance than their cultivated relatives, and should be protected and integrated into local agriculture; (3) Native savannah trees from the southern fringes of the region are becoming more important, and offer new resilience strategies; and (4) Variations among Aleppo pine ecotypes give hope for the future suitability of this species across the Mediterranean.

How to cite: Klein, T.: Forest vulnerability and tree mortality in the Mediterranean: Impacts and Opportunities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2522, https://doi.org/10.5194/egusphere-egu2020-2522, 2020.

D664 |
Enric Batllori Presas and Francisco Lloret Maya

Forest mortality related to extreme drought has been reported worldwide, affecting all biomes and plant types (angiosperm vs. gymnosperms, evergreen vs. deciduous). The forecasted increased frequency and intensity of drought events as a consequence of anthropogenic climate change could promote an increasingly widespread drought-induced mortality in the future. However, little understanding exists on ecological trajectories or the replacement processes after drought-induced mortality events. We assess (through a collaborative initiative) the extent of short-term self-replacement patterns in temperate forest ecosystems worldwide (N = 131 sites) in relation to: species traits, the major bioclimatic characteristics of reporting sites, and past management and disturbance legacies in the affected sites. We found that alternate species replaced pre-drought dominant tree species in ~70% of the examined cases, whereas in ~10% of the study sites there was no replacement by woody vegetation. Replacement was influenced by management intensity, and post-drought shrub dominance was higher when pathogens acted as co-drivers of tree mortality. No significant replacement patterns were found in relation to the bioclimatic characteristics of the reporting sites (environmental location) or of the dominant species (bioclimatic ‘niche’). Shifts to both more xeric and to moister communities were observed. These changes were driven by species with higher limits of tolerance to dry conditions and by species with wider bioclimatic ranges, respectively. Overall, our findings highlight the potential for major forest ecosystem reorganization in the coming decades.

How to cite: Batllori Presas, E. and Lloret Maya, F.: Forest dynamics after drought-induced mortality: a global assessment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9316, https://doi.org/10.5194/egusphere-egu2020-9316, 2020.

D665 |
Cornelius Senf, Allan Buras, Christian Zang, Anja Rammig, and Rupert Seidl

Drought has been suggested as major driver of large-scale forest diebacks, but quantitative evidence covering large spatial and long temporal scales is rare for Europe. Combining spatially explicit maps of canopy mortality (i.e., partial or full loss of the dominant tree canopy) generated from Landsat satellite data for the period 1986-2016 and gridded drought indices (0.5° resolution; including vapor pressure deficit, climatic water balance, and precipitation deficit), we report a consistent link between pulses of above-average tree mortality and drought conditions as measured in all three drought indices. As such, we deliver first quantitative evidence that drought conditions can trigger large-scale forest diebacks across Europe’s forests. A future increase in the severity and intensity of droughts as predicted for Europe might thus have unforeseen consequences for Europe’s forests, with large-scale forest diebacks likely becoming more common in the future.

How to cite: Senf, C., Buras, A., Zang, C., Rammig, A., and Seidl, R.: A consistent link between drought and forest diebacks across Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5679, https://doi.org/10.5194/egusphere-egu2020-5679, 2020.

D666 |
Stefan Hunziker, Michael Begert, and Arthur Gessler

Forest decline has been attributed to climatic changes in many parts of the world. Although climate conditions are an undisputed crucial factor affecting tree vitality, open questions remain regarding the relative roles of evaporative demand versus precipitation and the relative importance of individual climate variables.

In recent decades, there was a pronounced decline of Scots pines (Pinus sylvestris) at lower elevations in the inner-alpine Rhône valley in Switzerland. Similar observations were made in other inner-alpine valleys. Tree vitality was not continuously decreasing: single events of strong decrease in tree vitality and high mortality rates were observed in between phases of largely constant vitality levels. However, trees were hardly able to recover from such events in recent decades, resulting in a pronounced decrease in living Scots pines.

Climate-trend signals in the Rhône valley from 1981 to 2018 vary between the seasons. The clearest changes occurred in spring, when a strong climatic shift towards drier conditions was detected with significantly increasing evapotranspiration, decreasing precipitation sums and frequency of precipitation events, increasing duration of dry spells at lower elevations, and increasing diurnal temperature ranges. Relative trends of evapotranspiration are elevation dependent with the highest increase at low elevations. Temperature trends are the main driver towards higher evapotranspiration rates, but humidity and sunshine duration are important drivers too. For seasonal evapotranspiration anomalies, anomalies of temperature, humidity, and sunshine duration are of similar importance.

In previous works on Scots pine mortality in the Rhône valley, mortality events were attributed to prolonged periods of water deficits. However, the occurrence and magnitude of mortality events cannot be explained by droughts only. In case of Scots pines at low elevations in the Rhône valley, factors such as insect infestation and spring frost may strongly impact tree vitality and increase mortality rates.

In summary, climatic conditions changed markedly in the Swiss Rhône valley within the last approximately 40 years, especially in spring and at lower elevations. Hence, the less favorable climatic background conditions result in decreased resilience and recuperative power of the Scots pines to various disturbances, leading to the observed forest decline.

How to cite: Hunziker, S., Begert, M., and Gessler, A.: Effects of changing evapotranspiration and precipitation patterns on Scots pine vitality and mortality, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4758, https://doi.org/10.5194/egusphere-egu2020-4758, 2020.

D667 |
Adriane Esquivel‐Muelbert, Thomas Pugh, Timothy Baker, Kyle Dexter, Simon Lewis, David Galbraith, and Oliver Phillips and the RAINFOR Network

Tree mortality is the principal mechanism whereby forests lose living biomass. This process has been observed to have increased across the Amazon forest over recent decades. Greater tree mortality rates have been attributed largely to an increase in the frequency and intensity of droughts, and to the intensification of competition, as a consequence of greater tree growth stimulated by higher CO2concentrations. Analysing the trends in mortality for different taxa allows us to test the contribution of these different drivers to the rise in tree mortality. Droughts are expected to kill wet-affiliated, large, and low wood density taxa. Increased competition is likely to affect slow growth, understory taxa. We assess data from over 30 years of forest monitoring across the Amazon to investigate the changes in mortality across different taxa, providing a greater understanding of the drivers of increased tree mortality across the basin and the vulnerability of these forests to water stress. We observed that the proportion of dead trees across different taxa has changed across the Amazon forest. We show an increase in the mortality of drought-vulnerable trees, particularly in those areas where dry climatic events have intensified over the last 30 years. However, the proportion of large taxa within the dead trees has not changed over the length of this study. We also observed indications of increasing competition-driven mortality represented by a decrease in abundance of slow-growth shade-tolerant species. A suite of mechanisms, varying regionally in importance, are acting synchronically to drive recent increases in tree death across Amazonia. The patterns and mechanisms observed here are amenable to incorporation within the latest generation of global vegetation models and Earth system models, providing a basis for improved simulations of forest dynamics in one of the world’s most carbon-dense ecosystems.

How to cite: Esquivel‐Muelbert, A., Pugh, T., Baker, T., Dexter, K., Lewis, S., Galbraith, D., and Phillips, O. and the RAINFOR Network: Vulnerability of Amazonian tree communities to global change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18729, https://doi.org/10.5194/egusphere-egu2020-18729, 2020.

D668 |
Paolo De Angelis, Dario Liberati, Diego Giuliarelli, Loredana Oreti, and Andrea Vannini

Forests play a key role in the climate system thanks to their large carbon uptake and storage. On the other hand, forests are vulnerable to climate extremes and pest attacks, causing early tree mortality which in turn could reduce their carbon uptake capacity.

Early tree mortality is often associated to a complex interaction of predisposing stress factors (poor site quality, unfavourable stand conditions), inciting factors (frost, drought, mechanical damage) and contributing factors (fungi, insect borers).

In this context, the aim of the present work was to investigate the processes underlying the tree mortality observed in an evergreen mixed forest stand dominated by Quercus ilex, located in the Circeo National Park (central Italy).

The forest has the typical structure of an old-coppice not more managed (actual rotation time about 2 times that the normal), and was recently (2016) affected by an outbreak of Asian ambrosia beetle (Xylosandrus compactus) and Granulate ambrosia beetle (Xylosandrus crassiusculus) that caused an extensive trees crown browning. In 2019, plots were set in the area to monitor the beetle population dynamic and their impact on tree mortality. In each plot, species, dimension (DBH), stage of dieback, stem origin (resprouts after coppicing or from seed), presence of epicormic shoots and subcortical fungi stroma, were recorded for each woody plant.

The plot survey revealed a high frequency of stems classified in a declining stage or dead, on average 42% of the standing stems, with significant differences among the species: 97%, 85%, 74% and 47% for Arbutus unedo, Quercus ilex, Phyllirea latifolia and Fraxinus ornus respectively.

The higher stem mortality of Q. ilex was recorded in the smaller diameter classes, suggesting that the self-thinning process played an important role on the observed mortality as typical in the old not more managed coppices.

To disentangle the role of the interruption of the management from the climatic and biological drivers, time trends on NDVI index were constrained with the duration of the summer dry seasons and comparing our forest with similar Q. ilex forest coppices in the region and regularly managed.

Furthermore, the contribution of recent ambrosia beetles attack was assessed identifying the presence of twigs with signs of previous beetle attack on healthy, declining and dead plants.

Our findings point towards complex tree mortality dynamics, in which the competition generated by the stand abandonment predisposed the forest to the insect attack, leading to the general decline of the forest stand.

How to cite: De Angelis, P., Liberati, D., Giuliarelli, D., Oreti, L., and Vannini, A.: Environmental, biological and human drivers of the dieback of an evergreen Mediterranean forest , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21728, https://doi.org/10.5194/egusphere-egu2020-21728, 2020.

D669 |
Günter Hoch, Nikita Häfeli, and Ansgar Kahmen

Hot summer droughts are becoming increasingly frequent in temperate biomes world-wide. In summer 2018, several weeks of drought paired with constantly high temperatures led to significant forest decline and mortality in mature trees in central Europe. In many regions, European beech was one of the most drought-sensitive tree species in 2018 with many trees showing partial or complete crown dieback by the end of the year, preceded by early leaf browning in mid-summer. So far it is disputed, if these symptoms were solemnly driven by a direct drought effect from dried-out soils, or if they were additionally amplified by hot mid-day temperatures and high atmospheric vapor pressure deficits (VPD).

In a recent study we therefore aimed to disentangle the effects of soil drought, air temperature and VPD on beech seedlings in a full-factorial experiment. Two-year old beech saplings were exposed to either cooler (daily max. temperature 24°C) or warmer (daily max. temperature 35°C) temperatures in walk-in phytotrons. Within each temperature treatment, half of the saplings were grown at either high or low relative humidity resulting in the same low or high mid-day VPD in both temperature treatments (0.7 vs. 2 kPa).Finally, half of the saplings from each temperature-VPD treatment combination where exposed to drought by stopping irrigation in July, with only compensatory water addition among pots to ensure the same dry-out rate among treatments (i.e. no faster soil drying at high VPD). Across all temperature-VPD treatment combinations, drought led to very similar decreases of stomatal conductance, photosynthesis and pre-dawn leaf water potential. There was only a tendency for an approximately 1 week earlier decline of Fv/Fm (leaf fluorescence) under drought at high VPD conditions, pointing at slightly faster stress occurrence at the leaf-level at very low air humidity. Neither high temperatures, nor high VPD induced stress symptoms at the leaf or whole-tree level in well-irrigated saplings. Overall, air temperature and VPD had no significant effect on the saplings' survival time under drought, with saplings from all temperature-VPD combinations dying on average after about 100 days into drought. Therefore, at the same decreasing rate of soil water availability, we did not find additional negative effects of warm temperatures or high VPD on tree survival, indicating that European beech is per se quite robust against heat and high VPD stress.

How to cite: Hoch, G., Häfeli, N., and Kahmen, A.: Experimentally disentangling drought from heat stress effects in European beech trees, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10084, https://doi.org/10.5194/egusphere-egu2020-10084, 2020.

D670 |
Riccardo Valentini

Climate variability and extremes are observed with increasing amplitude and frequency in almost any continent and extensive tree mortality and widespread forest dieback is an increasing and emergent global concern although direct attribution of extensive tree mortality to warming or drying episodes is still under debate (IPCC AR5). Although tree dieback is a combination of causes, including pathogen/pest invasions, genetic responses and management factors, still climate anomalies, even at shorter time scales, can trigger predisposition factors that may lead to irreversible tree decline and dieback.  Despite there are a number of methods for addressing simultaneously tree functions such as photosynthesis and transpiration at leaf level or at canopy scale the same information at high temporal frequency and at individual tree scale is not yet widely diffused. Taking advantage of new technology and latest developments in sensor science, (e.g Internet of Things) we have developed a new device able to measure simultaneously important tree parameters. The parameters are: 1) tree radial growth, as indicator of photosynthetic carbon allocation in biomass; 2) sap flow, as indicator of tree transpiration and functionality of xylem transport; 3) xylem moisture content as indicator of hydraulic functionality 3) light penetration in the canopy in terms of fractional absorbed radiation and 4) light spectral components related to foliage dieback and physiology, 5) tree stability parameters to allow real time forecast of potential tree fallings. We will present a synthesis of data coming from different forest locations including natural, urban and artificial plantations and discuss the capabilities to extend such network at global scale. Examples of AI machine learning application to ecophysiological data will presented. Finally we discuss the possibility of using the TreeTalker network in large scale phenomics applications for individual tree responses to climate change impacts and identification of plant traits.

How to cite: Valentini, R.: New approaches in tree phenomics using IoT technologies and AI machine learning : the TreeTalker network, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12895, https://doi.org/10.5194/egusphere-egu2020-12895, 2020.

D671 |
Eryuan Liang, Xiaoming Lu, Yafeng Wang, Flurin Babst, Steven W. Leavitt, and J. Julio Camarero

Alpine biomes are climate change hotspots, and treeline dynamics in particular have received much attention as visible evidence of climate-induced shifts in species distributions. Comparatively little is known, however, about the effects of climate change on alpine shrubline dynamics. Here, we reconstruct decadally resolved shrub recruitment history (age structure) through the combination of field surveys and dendroecology methods at the world’s highest juniper (Juniperus pingii var. wilsonii) shrublines on the south-central Tibetan Plateau. A total of 1,899 shrubs were surveyed at 12 plots located in four regions along an east-to-west declining precipitation gradient. We detected synchronous recruitment with 9 out of 12 plots showing a gradual increase from 1600 to 1900, a peak at 1900–1940, and a subsequent decrease from the 1930s onward. Shrub recruitment was significantly and positively correlated with reconstructed summer temperature from 1600 to 1940, whereas it was negatively associated with temperature in recent decades (1930–2000). Recruitment was also positively correlated with precipitation, except in the 1780–1830 period, when a trend toward wetter climate conditions began. This apparent tipping point in recruitment success coincides with a switch from positive to negative impacts of rising temperatures.  Warming-induced drought limitation has likely reduced the recruitment potential of alpine juniper shrubs in recent decades. Continued warming is thus expected to further alter the dynamics of alpine shrublines on the Tibetan Plateau and elsewhere.

How to cite: Liang, E., Lu, X., Wang, Y., Babst, F., Leavitt, S. W., and Camarero, J. J.: Past the climate optimum: Recruitment is declining at the world’s highest juniper shrublines on the Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3830, https://doi.org/10.5194/egusphere-egu2020-3830, 2020.

D672 |
Nikolaus Obojes, Jennifer Klemm, Ruth Sonnenschein, Francesco Giammarchi, Giustino Tonon, Ulrike Tappeiner, and Marc Zebisch

To prevent further erosion of pastures along the south slopes of the Vinschgau/Val Venosta (South Tyrol/Italy) about 900 ha of non-native black pine (Pinus nigra) have been afforested there between 1900 and the 1960s. This drought-tolerant Mediterranean species was supposed to be able to cope with the dry climate at degraded soils in the inner-alpine dry valley. Nevertheless, black pine in the Vinschgau has been affected by reoccurring tree vitality decline and diebacks in the last 20 years linked to repeated droughts and heat waves. Observing growth trends via tree ring analysis is usually restricted to single stands. On the other hand, remote sensing data to track tree vitality was not available in sufficient spatial and temporal resolution to be applied to complex mountain terrain until recently. This has changed with the launch of the Sentinel-2 A and B satellites in 2015 and 2017 with a spatial resolution of 10 to 20 m and a revisiting period of 5 days. To analyse the accordance of remote sensing-based vegetation indices to tree-ring based growth data, we compared twelve sites across the Vinschgau/Val Venosta with a differing degree of vitality loss in 2017 for a four-year period from 2015 to 2018. In general, less vital sites were located at lower elevation and on steeper slopes. Radial tree growth was positively correlated to spring precipitation and strongly decreased during earlier hot and dry years such as 1995 and 2003. We found high and statistically significant correlations between site-average basal area increment as well as tree ring width indices and multiple vegetation indices (Normalized Difference Vegetation Index NDVI, Green Normalized Difference Vegetation Index GNDVI, Normalized Difference Infrared Index NDII, Moisture Stress Index MSI) especially for the dry 2017 growing season and the 2018 recovery year, which had large gradients in tree vitality between sites. Overall, these results show that remote sensing-based vegetation indices can be used to scale up stand level growth data also in complex mountain terrain.

How to cite: Obojes, N., Klemm, J., Sonnenschein, R., Giammarchi, F., Tonon, G., Tappeiner, U., and Zebisch, M.: Combining tree ring analysis and remote sensing to assess the 2017 black pine dieback in Vinschgau/Val Venosta (Italy) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19551, https://doi.org/10.5194/egusphere-egu2020-19551, 2020.

D673 |
Jakob Wernicke, Christian Torsten Seltmann, and Michael Körner

The combined negative effects of climate change and adverse forest structures currently result in large amounts of random timber use all over Central Europe. Particularly Norway spruce (Picea abies [L.] Karst) is threatened by summer droughts and secondary pests. Hence, achieving insights in the drought tolerance of spruce is highly relevant to reduce the vulnerability of forest systems under climate change. Especially long-living spruce individuals witness several periods of drought in their ring-width variability. A common measure of trees drought tolerance is referred to resistance, resilience and recovery ability. Besides forest management and site characteristic, the ecological memory of trees might distinctly affect spruce drought tolerance.

Therefore we investigate the spatio-temporal variability of the ecological memory effect from more than 1500 individual ring-width time series of spruce trees collected from the managed forests of Central-East Germany. The memory effect is examined via time series first to third autocorrelation. We are particularly interested in the question: ‘can trees with a ‘good memory’ cope better with climate extremes than trees with a ‘bad memory’? If so, is it possible to influence the memory of trees via specific thinning strategies? Finally, how can autocorrelation improve the assessment of site productivity, taking the climate change induced displacement of growth areas into consideration? The study results reveal crucial insights in the drought vulnerability of spruce dominated forests in relation to forest structure and management strategies.

How to cite: Wernicke, J., Seltmann, C. T., and Körner, M.: Ecological memory effects in Norway spruce ring-width chronologies across managed forests of Central-East Germany: Implications for modelling and planning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20690, https://doi.org/10.5194/egusphere-egu2020-20690, 2020.

D674 |
Phillip Papastefanou, Christian Zang, Thomas Pugh, Daijun Liu, David Lapola, Katrin Fleischer, Thorsten Grams, Thomas Hickler, and Anja Rammig

Plant hydraulics are crucial to understand impacts of droughts on single plants and whole forest ecosystems. The complex interplay of hydraulic mechanisms still poses challenges for vegetation modellers, regarding development and parameterization. Here, we apply a new hydraulic module developed for the dynamic global vegetation model LPJ-GUESS to the Amazon Basin. Special focus is given to the newly developed mortality process based on hydraulic-failure and to differences in hydraulic behaviour of plants.  The implemented hydraulic-failure process can explain observed mortality patterns at rainfall exclusion experiments in the Amazon. Modelled vegetation carbon is most sensitive to two of the hydraulic processes: The xylem vulnerability to water stress and the plant specific hydraulic behaviour, i.e. how plants regulate their water potential under drought stress. Applied to the whole Amazon Basin, our model shows a strong impact of the 2005 drought event across a wide margin of modelled species and parameters, which is in good agreement with empirical studies. We highlight the hydraulic behaviour of plants, for which little is known in the Amazon rainforest, and its relevance for ecosystem model development. Considering only one single plant functional type does not sufficiently capture the complex response of the Amazon rainforest to drought, hence future modelling studies should take the interaction and competition of different hydraulic strategies into account.

How to cite: Papastefanou, P., Zang, C., Pugh, T., Liu, D., Lapola, D., Fleischer, K., Grams, T., Hickler, T., and Rammig, A.: Hydraulic strategy drives Amazon forest modelled response to drought, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10908, https://doi.org/10.5194/egusphere-egu2020-10908, 2020.

D675 |
Patricia María Rodríguez-González, Juan Guerra-Hernández, Ramón Alberto Díaz-Varela, and Juan Gabriel Álvarez-González

Expansion of damaging pests and pathogens is a reality which, together with rapid global change, is arguably the greatest contemporaneous challenge to sustainable forestry and the continuing function of forest ecosystems. Alnus glutinosa (black alder) woodlands are priority riparian forests for conservation at European Scale (Habitat 91E0* of Habitat Directive 43/92/CEE), due to their key ecological functions (such as N fixation, wildlife habitat) and ecosystem services provision (e.g. improvement of water quality). Recently, substantial declines in alder stands have been observed along streams in Europe. A major driver has been the invasive oomycete pathogen Phytophthora alni species complex, with damages widespread across Europe and even in some parts of North America. This is critical, not only due to disproportionate ecological importance of riparian forests in relation to their surface area extent but also due potential impacts to other forest species. Proper management requires accurate assessment of forest status and novel remote sensing devices offer increasing opportunities to overcome high labour costs and time-consuming travels, typical of field based monitoring. The mapping of the defoliation caused by the disease is particularly challenging in high density ecosystems with high spectral variability due to canopy heterogeneity. The use of Unmanned Aerial Vehicle (UAV) data for such tasks might be particularly advisable due to its high resolution, acquisition flexibility and cost efficiency in the field. In this study, Alnus glutinosa decline was assessed by classifying four different health condition levels (healthy, dead, and defoliation under and below a 50% threshold), previously attributed through individual tree field sampling. A combination of multispectral Parrot Sequoia and RGB-UAV-data were analysed using Random Forest (RF) and a simple and robust three-step logistic modelling approaches to identify the most relevant predictors and keep the models parsimonious. A total of 34 remote sensing (RS) variables were included in the study, including a set of vegetation indices (VI), texture features from NDVI and DSM (Digital Surface Model), topographic and DAP (Digital Aerial Photogrammetry)-derived structural from Digital Surface Model (DSM) at crown level. The four level health condition classification achieved an overall classification accuracy of 67%. On the other hand, the confusion matrix computed from the three logistic models using leave-out cross-validation method achieved an overall accuracy of 76% when using four level health condition classification. Our results offer an alternative robust classification method to forest and conservation managers for the rapid and effective assessment of areas affected by the disease in their planning of control and restoration measures aimed at reducing these forests vulnerability and black alder mortality with potential application to other species.

How to cite: Rodríguez-González, P. M., Guerra-Hernández, J., Díaz-Varela, R. A., and Álvarez-González, J. G.: Combining multispectral and texture imagery features to assess health condition in priority riparian forests by means of unmanned aerial systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9680, https://doi.org/10.5194/egusphere-egu2020-9680, 2020.

D676 |
Thorsten Grams

This contribution summarizes the outcome of a five-year experiment on mature (60-80 years old) trees in a Central European forest. We studied roughly 100 trees of European beech and Norway spruce, two tree species of contrasting foliage (i.e. deciduous vs. evergreen) and stomatal sensitivity to drought (i.e. anisohydric vs. isohydric behavior). Trees were exposed to experimentally induced summer droughts from 2014 to 2018 with precipitation throughfall being completely excluded during the growing seasons. The throughfall-exclusion study was established on 12 plots with trees readily accessible by canopy crane (Kranzberg forest roof experiment, southern Germany). We aimed at bringing trees to the edge of survival to studying trees’ capability for acclimation under repeated, severe summer droughts as expected more frequently in future climate scenarios. Results come from a multidisciplinary approach focusing on mechanisms of acclimation, eventually reducing trees’ vulnerability to drought during the five-year study period. Presented data integrate responses from the level of soil/microbial interactions over tree organs and whole-tree morphology to responses at the stand level.

During the first two years, restrictions caused by drought were most prominent, exemplified by pre-dawn leaf water potentials of down to -2.5 MPa and reductions in photosynthesis and growth by up to 50 and 80 % in European beech and Norway spruce, respectively. Nevertheless, percentage loss of conductivity in branch xylem was hardly affected. Likewise, concentrations of non-structural carbohydrates (sum of soluble sugars and starch) in tree organs remained largely unaffected, but translated to significantly lower carbohydrate pool sizes in view of strongly reduced tree growth. Nevertheless, two spruce trees died from drought, in the absence of bark beetle or pathogen interactions. During the fourth and fifth year of summer drought, trees showed clear signs of drought acclimation with e.g. some recovery of stomatal conductance, reductions of whole-tree leaf area, changes in rooting depth and acclimation of associated soil microbial communities. Accordingly, stem diameter growth recovered during the last years of the stress treatment, indicating reduced vulnerability of trees towards the end of the five-year drought treatment.

How to cite: Grams, T.: Five years of experimental summer drought – Anatomical and physiological acclimation of mature beech and spruce, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12858, https://doi.org/10.5194/egusphere-egu2020-12858, 2020.

D677 |
Xiyan Xu, Gensuo Jia, Xiaoyan Zhang, and Ying Xue

Amazon wildfire surge in 2019 once again raised the alarm about the fate of the Earth’s most biodiverse forest. Climate change and deforestation lead to greater vegetation water stress and susceptibility to fires. We use multiple satellite and climate reanalysis data to explore fire susceptibility in response to shifted climate regime due to global climate change and forest loss in Amazon regions. We found that climate in Amazon has been shifting to increased frequency of extreme conditions with increased drought extent and severity. The tropical vegetation that has adapted to its surrounding climate are less resilient under stress of climate change and highly susceptible to fire.  The fire susceptibility has been expanding through the transition season and northward to the tropical rain and seasonal forests. These results highlighted the links between fire risk, climate change and human activities in Amazon regions.

How to cite: Xu, X., Jia, G., Zhang, X., and Xue, Y.: Fire susceptibility and transitional climate regime in Amazon tropics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1414, https://doi.org/10.5194/egusphere-egu2020-1414, 2020.

D678 |
Zhongdian Zhang, Mingbin Huang, Yingnan Yang, and Xiaofang Zhao

Extensive afforestation with exotic species like Robinia pseudoacacia on the Chinese Loess Plateau are facing high drought-induced mortality risk due to the large fluctuations in annual precipitation and severe soil desiccation. The aim of this study was to assess the risk of drought-induced mortality for R. pseudoacacia plantations on the Loess Plateau based on plant hydraulics. We modified the routines of soil-plant-atmosphere water transfer in the Biome BioGeochemistry model (Biome-BGC) using a plant hydraulic model based on the supply-demand theory. The modified model efficiently captured the dynamics of canopy transpiration, soil moisture, leaf water potential, and regional variation in leaf area index in R. pseudoacacia stands on the Loess Plateau. We simulated the 50-year (1968-2017) plant hydraulic dynamics at 14 sites along a precipitation gradient on the Loess Plateau. The results indicated that annual average percentage loss of whole-plant hydraulic conductance (APLK) showed strong temporal variation due to climatic variability, which was positively correlated with annual potential evapotranspiration (PET) and the aridity index (the ratio of PET to annual precipitation). Along the precipitation gradient, the maximum APLK increased linearly with decreasing mean annual precipitation (MAP) and could exceed 60% at sites with MAP <446.1 mm. The sustainable growth of R. pseudoacacia plantations at these sites would face a severe threat. We analyzed the effect of soil desiccation on drought-induced mortality risk further. Soil desiccation increased the sensitivity of plant hydraulic safety to precipitation variability considerably, and the effect was more significant in areas with lower MAP. These quantitative findings should be helpful for evaluating and promoting the sustainability of plantation forests on the Loess Plateau.

How to cite: Zhang, Z., Huang, M., Yang, Y., and Zhao, X.: Evaluating drought-induced mortality risk for Robinia pseudoacacia plantations along the precipitation gradient on the Loess Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1786, https://doi.org/10.5194/egusphere-egu2020-1786, 2020.

D679 |
Zuoqiang Yuan

Although large trees explain the most variation in biomass and structure of forests, but little is known about whether and how large trees can explain variation of forest dynamics (forest productivity and biomass loss). To shed light on the effects of large trees on forest dynamics we analyzed repeated forest inventory data on 74,300 adult trees spread across 700 quadrats of temperate mixed forest in northeastern China. Here, using piecewise structural equation modeling we examined how top 1% high-biomass, 99% remaining-biomass trees, functional trait diversity (FD) and composition (CWM), climate and soil conditions influence forest dynamics in temperate old growth forests. We found that top 1% high-biomass and top 1% large-diameter trees highly increased forset dynamics and biomass stock rather their relevant 99% remaining trees, FD and CWM supporting big-size trees hypothesis. In addition, climate is more important determinant of forest productivity rates than soil nutrients. Moreover, forest productivity and biomass stock declined with CWM traits. Hence, we highlight top 1% trees overruled the effect of 99% remaining trees, FD and CWM on forest dynamics and biomass stock. We argue that including site variation and the big trees to the integrative ecological modeling help better understanding of ecological mechanisms and drivers of forest dynamics.   

How to cite: Yuan, Z.: Few large trees drive the carbon dynamics of temperate forests, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2110, https://doi.org/10.5194/egusphere-egu2020-2110, 2020.

D680 |
Veronica De Micco, Katarina Cufar, and Angela Balzano

Survival of forest tree species in semi-arid environments such as the Mediterranean area is threatened by the increase in harsh drought conditions. Therefore, better knowledge of the eco-physiology of Mediterranean species and their growth responses to climatic factors is needed to develop strategies for sustainable management.

The studies of cambial activity and wood formation can provide information on tree growth and physiological responses to variations in intra-annual climatic parameters, helping to answer questions related to tree performance and plasticity under changing environmental conditions.

Our aim was to investigate cambium production in holm oak (Quercus ilex L.) as one of the most widespread evergreen oaks in Southern Italy. We studied the response of cambium activity throughout the particularly dry year 2017. We collected tissues from tree stems every two weeks by sampling microcores containing phloem, cambium and xylem. For the analyses, thin cross sections of the microcores were analysed under a light microscope to identify the timing of cambial production, xylogenesis and phloem formation. We detected the period in which the cambium was active, as well as the period in which the cambium was not productive. We interpreted the cambial response to climatic conditions at the site during the period of observation.

The observed pattern of xylogenesis differed from the expected bi-modal pattern typical for Mediterranean species which usually results in Intra-annual Density Fluctuations (IADFs) in tree-rings. In Q. ilex we observed only one peak of cambial activity, likely due to the low water availability during the year 2017.

The obtained results provide useful information supporting the forecasting of the wood-growth responses to expected climate change. Moreover, we gained technical experience on optimal preparation of thin sections of problematic tissues, which is especially challenging in Q.ilex due to high hardness of the peculiar wood structure making the investigations of xylogenesis very challenging in this species.

How to cite: De Micco, V., Cufar, K., and Balzano, A.: Cambium production pattern in Q. ilex growing at a dry site in Southern Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6169, https://doi.org/10.5194/egusphere-egu2020-6169, 2020.

D681 |
Ana Carolina Moreira Pessôa, Liana O. Anderson, Rafael Suertegaray Rossato, Victor Marchezini, Bruna Maria Pechini Bento, Sacha Maruã Ortiz Siani, Ane Auxiliadora Costa Alencar, Isabel de Castro Silva, and Torfinn Harding

Providing scientific subsidies for public policies is a compromise that is beyond the boundaries created by the academic universe, requiring scientists to respond to the challenges posed by increasingly complex societies, both socially and environmentally. Considering this, the objective of this work was to build a pilot project for rapid assessment of Tefé National Forest (TNF) land use zoning and evaluate its relevance as a tool to support actions and influence discussions in protected area management councils.

The assessment considered remote sensing data on deforestation and fire from 2005 to 2015. Deforestation maps (PRODES-INPE) and active fire (MODIS) information were overlapped with TNF land use zoning. Although National Forest, in general, has its land use rules provided by law, each protected area defines on its Management Plan their own land use zoning, with specific rules.

The study showed that in 2015, 97% of TNF was covered by forest, and although no deforestation was recorded in the same year, the number of active fires was 1.8 times higher than the average from 2005 to 2014. This demonstrates the vulnerability of this area to the extreme drought which affected the region this year. The Population Zone, where 44% of the TNF population lives, recorded the highest rates of deforestation and fire. The Preservation Zone, on the other hand, showed to be fulfilling its function, presenting no active fires and only one deforestation event during the whole analyzed period.

These results were presented at the 20th TNF Council Meeting, in 2017. The TNF manager pointed out the great importance of spatial and temporal diagnoses, which can exert in prioritize actions to tackle specific problems in most threatened zones. Community leaders participating in the meeting contributed to the completion of the results with in situ day-to-day reports, offering hypotheses for some phenomena observed on the assessment, such as the deforestation observed in 2010. After that, it became clear that actions directly focused on the Population Zone, and mainly related to the use of fire in years of extreme drought, can improve the conservation outcome for this protected area. Integrated socio-environmental diagnosis, such as this pilot project, can be an important tool, allowing a broader version of the monitoring strategies.

How to cite: Moreira Pessôa, A. C., O. Anderson, L., Suertegaray Rossato, R., Marchezini, V., Pechini Bento, B. M., Maruã Ortiz Siani, S., Costa Alencar, A. A., de Castro Silva, I., and Harding, T.: Supporting decision makers through rapid assessments of remote sensing data: the case of Tefé National Forest, Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6175, https://doi.org/10.5194/egusphere-egu2020-6175, 2020.

D682 |
Jaeuk Kim, Huicheul Jung, Insang Yu, and Sung-Hun Lee

In South Korea, national parks occupy the largest area among the protected areas designated to protect biodiversity and ecosystem. Among the 17 mountainous national parks, the vegetation in alpine and sub-alpine regions are very vulnerable to climate change. The objective of this study is to estimate the impact of climate change on sub-alpine vegetation considering uncertainties of future climate and the species distribution method. Observation data were gridded to 3 km spatial resolution from 1981 to 2010 using the Improved GIS-based Registry Model(IDW-IGISRM) based on the Inverse distance weighting(IDW). To reduce future uncertainty of climate change, future climate scenarios of RCP 4.5 and RCP 8.5 of CMIP5 GCM were utilized. In order to increase the spatial resolution of the GCM, Simple Quantile Mapping, one of the various bias correction and downscaling techniques, was applied. Bioclim DB, a bioclimatic variable considering temperature and moisture conditions, was established using monthly maximum temperature, minimum temperature and precipitation data among detailed GCM data. Impact assessment was held using Biomod2 of R package, for endangered sub-alpine vegetation in the National Forest Inventory(NFI). Verification of the species distribution models were carried out using AUC(Area Under the Curve) and TSS(True Skill Statistics). The result of this study is expected to be utilized for protected area management measures for biodiversity conservation in forests.

※ This work was supported by Korea Environment Industry & Technology Institute(KEITI) through Climate Change Correspondence Program, funded by Korea Ministry of Environment(MOE)(2018001310004).

How to cite: Kim, J., Jung, H., Yu, I., and Lee, S.-H.: Climate change impact assessment of sub-alpine vegetation in national park using CMIP5 GCMs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6701, https://doi.org/10.5194/egusphere-egu2020-6701, 2020.

D683 |
Devin Noordermeer, Vera Velasco, and Ingo Ensminger

In the next several decades, warming in the northern hemisphere will result in asynchronous phasing between the temperature and photoperiod signals that evergreen conifers rely upon for cold hardening during autumn. Our study investigated intraspecific variation in photosynthetic and photoprotective mechanisms in Douglas-fir (Pseudotsuga menziesii) originating from contrasting climates during simulated summer and autumn conditions, as well as how autumn warming affects downregulation of photosynthesis and development of cold hardening. Following growth under long days and summer temperature (LD/ST; 16 h photoperiod; 22 °C/13 °C day/night), Douglas-fir seedlings from two interior and two coastal provenances were acclimated to simulated autumn conditions with short days and either low temperature (SD/LT; 8 h photoperiod; 4 °C/-4 °C day/night) or high temperature (SD/HT; 8 h photoperiod; 19 °C/11 °C day/night). Exposure to low temperature induced increase in size and de-epoxidation of the xanthophyll cycle pigment pool, development of sustained nonphotochemical quenching, and downregulation of photosynthetic activity. SD/HT seedlings exhibited no downregulation of photosynthesis, corresponding with no change in xanthophyll cycle pigment de-epoxidation and no development of sustained nonphotochemical quenching. However, freezing tolerance development for all provenances was not impaired under SD/HT relative to SD/LT. Interior Douglas-fir provenances developed greater freezing tolerance relative to coastal provenances under both temperature treatments. Our findings suggest that short photoperiod alone is insufficient to induce downregulation of photosynthesis in autumn for Douglas-fir. However, this prolonged period of photosynthetic activity does not appear to bear a trade-off of impaired freezing tolerance.

How to cite: Noordermeer, D., Velasco, V., and Ensminger, I.: Autumn warming delays downregulation of photosynthesis and does not increase risk of freezing damage in interior and coastal Douglas-fir seedlings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8568, https://doi.org/10.5194/egusphere-egu2020-8568, 2020.

D684 |
Kasia Zieminska, Emily Rosa, Sean Gleason, and N. Michele Holbrook

Water released from storage into the transpiration stream (termed: capacitance) can play an important role in tree every day hydraulic functioning as well as in tree drought response. However, anatomical underpinnings of capacitance and water storage remain unclear, impeding better understanding of capacitance mechanisms. Across 30 temperate angiosperm tree species, we measured in natura twig wood diurnal capacitance and water content, wood density and anatomical properties: vessel dimensions, tissue fractions and vessel-tissue contact fractions (proportion of vessel circumference in contact with other tissues). We found that wood density and predawn lumen volumetric water content (proportion of wood volume that is occupied by water in lumen) together were the strongest predictors of capacitance (radj2=0.44***). Vessel-tissue contact fractions—vessel-ray, vessel-axial parenchyma and vessel-fibre—each explained an additional ∼10% of variation in capacitance. Parenchyma fraction did not correlate with capacitance challenging the common assumption that parenchyma acts as the main source of capacitance water. Anatomical structure, water content and capacitance relationships differed significantly between diffuse-porous and ring-porous species. Predawn relative water content (water in a fresh sample relative to saturated sample) was on average 0.65±0.13 implying that parts of wood were devoid of water.

How to cite: Zieminska, K., Rosa, E., Gleason, S., and Holbrook, N. M.: Wood diurnal capacitance, water storage and their anatomical drivers across 30 temperate angiosperm tree species. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10517, https://doi.org/10.5194/egusphere-egu2020-10517, 2020.

D685 |
Georgeta Mihai, Alin-Madalin Alexandru, Marius-Victor Birsan, Ionel Mirancea, Paula Garbacea, and Emanuel Stoica

European silver fir (Abies alba Mill.) is among the most important forestry species in Europe. In Romanian Carpathians, it covers about 5% of the forests area and almost two-thirds of its distribution is located in Eastern Carpathians, which is the southeastern edge of its distribution in Europe.
The most recent climate change scenarios for Europe suggest increases in mean annual temperature of 1-4 °C by the end of this century (Meinshausen et al. 2011). In the context of global warming, the populations living at the edge of the species distribution will be the first facing the climate change effects. In these regions, as the southeastern Europe, the main constrains are increasing the temperature, extended drought events and water availability. Forest species are particularly sensitive to climate change because the long life-span of trees does not allow for rapid adaptation to environmental changes (Lindner et al. 2010). 
In this context, the aim of this study was to analyze the drought response of 51 European silver fir populations from: Romanian Carpathians (26), Austria (4), Germany (3), France (3), Italy (4), Slovakia (3), Czech Republic (3), Poland (1) and Bulgaria (4)  to strong drought events which have occurred in this region, in the last 30 years. The populations are tested in three provenances trials established in Romania, in 1980; two of them being located outside and one within the optimum climatic of species. The most drought years, with severe or extreme drought periods, have been identified based on the standardized precipitation index (McKee et al. 1993). The growth response of the silver fir populations to the drought events was evaluated by calculating four parameters, namely: resistance, recovery, resilience, relative resilience (Lloret et al. 2011). Results reveled that the general trend was towards decrease the stem radial growth of silver fir during the last 30 years. The provenance x year interaction was not significant which means high provenances stability over time. Significant differences were found among silver fir provenances in terms of ring width, latewood proportion, resistance, recovery and resilience in drought years. There are provenances which have highlighted high productivity and high tolerance to drought, which could be used in reforestation work, breeding and conservation programs. The radial growth of silver fir provenances was negative affected by the temperature increase during vegetation period and positive by previous autumn-spring precipitations. Therefore, the forest management strategy to mitigate negative impacts of climate change should be based on the knowledge of the intraspecific genetic variation and selection of the best performing and adapted planting stock for each region.

How to cite: Mihai, G., Alexandru, A.-M., Birsan, M.-V., Mirancea, I., Garbacea, P., and Stoica, E.: Mitigating climate change effects on forest growth using planting stock with high adaptive genetic capacity: results from Abies alba (Mill.) provenance trials at the southeastern distribution limit, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10851, https://doi.org/10.5194/egusphere-egu2020-10851, 2020.

D686 |
Maria Floriana Spatola, Angelo Rita, Marco Borghetti, Francesco Ripullone, Agostino Ferrara, and Angelo Nolè

The disturbance and recovery of European Forest ecosystems are greatly affected by wildfires, requiring continued monitoring to observe vegetational structure altered over time. One of the most important parameters is “fire severity” defined as magnitude of environmental change caused by wildfires. Due to correlation between severity and post-fire recovery vegetation, fire severity is an  important indicator to define operations in the burned areas. Satellite based-data is becoming a key information for near real-time mapping and monitoring burned area after wildfire disturbances. Moderate resolution Imaging Spectroradiometer (MODIS) time-series data allows for both the capture of the initial disturbance and the ability to monitor the subsequent vegetation regeneration with spectral vegetation indices. In this study, the Google Earth Engine (GEE) platform, was used to analyse post-fire spectral recovery of European forests through the Normalized Difference Vegetation Index (NDVI) and the Relative Recovery Indicator (RRI) based on the Normalized Burn Ratio (NBR). We assessed Normalized Burn Ratio time series in order to determine trends in the short term rates of spectral recovery for three forest land cover classes and European Biogeographic regions disturbed by wildfire (2004-2013), using a series of 5-year post-disturbance time window. NBR pattern of mixed forests showed a lower variability than broadleaved and coniferous forest, indicating high resilience to environmental disturbances. Results indicate different trends of forest recovery according to different spectral indices analysed for European forest ecosystems. During the analysis period (2004-2013) we found that post-fire spectral recovery rates decreased over ten years of observation in each land cover classes and Biogeographic regions. These trends could be related to on-going climate changes affecting the Mediterranean region.

Keywords: Fire severity, Forest, Google Earth Engine, Modis (time series), Recovery, Spectral index, Wildfire.


How to cite: Spatola, M. F., Rita, A., Borghetti, M., Ripullone, F., Ferrara, A., and Nolè, A.: Multi-temporal analysis of post-fire vegetation spectral recovery over European forests, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15175, https://doi.org/10.5194/egusphere-egu2020-15175, 2020.

D687 |
Maria Castellaneta, Angelo Rita, J. Julio Camarero, Michele Colangelo, Angelo Nolè, and Francesco Ripullone

Several die-off episodes related to heat weaves and drought spells have evidenced the high vulnerability of Mediterranean oak forests. These events consisted in the loss in tree vitality and manifested as growths decline, elevated crown transparency (defoliation) and rising tree mortality rate. In this context, the changes in vegetation productivity and canopy greenness may represent valuable proxies to analyze how extreme climatic events trigger forest die-off. Such changes in vegetation status may be analyzed using remote-sensing data, specifically multi-temporal spectral information. For instance, the Normalized Difference Vegetation Index (NDVI) measures changes in vegetation greenness and is a proxy of changes in leaf area index (LAI), forest aboveground biomass and productivity. In this study, we analyzed the temporal patterns of vegetation in three Mediterranean oak forests showing recent die-off in response to the 2017 severe summer drought. For this purpose, we used an open-source platform (Google Earth Engine) to extract collections of MODIS NDVI time-series from 2000 to 2019. The analysis of both NDVI trends and anomalies were used to infer differential patterns of vegetation phenology among sites comparing plots where most trees were declining and showed high defoliation (test) versus plots were most trees were considered healthy (ctrl) and showed low or no defoliation. Here we discuss: i) the likely offset in NDVI time-series between test- versus ctrl- sites; and ii) the impact of summer droughts  on NDVI.

Keywords: climate change, forest vulnerability, time series, remote sensing.

How to cite: Castellaneta, M., Rita, A., Camarero, J. J., Colangelo, M., Nolè, A., and Ripullone, F.: Assessing and monitoring the vulnerability to drought and climate anomalies of Mediterranenan oak forests by using NDVI, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17113, https://doi.org/10.5194/egusphere-egu2020-17113, 2020.

D688 |
Christian Torsten Seltmann, Jakob Wernicke, Rainer Petzold, Martin Baumann, Kristian Münder, and Sven Martens

In forest management and sience it is important to determine the drivers of tree growth and to quantify their relative importance with regard to forest site characteristics. The growth of individual trees depends on complex interactions between biotic and environmental drivers. Forest management can make use or buffer the effects of biotic drivers, e. g. through thinning strategies. However, large uncertainties emerge from environmental drivers and its effects on tree growth.

The aim of this study is to quantify the relative importance of environmental drivers (climate, soil, and terrain attributes) on the growth of Norway spruce trees (Picea abies (L.) Karst.). For that purpose we distinguished three common soil types of Saxony and Thuringia, Germany (Cambisols, Podzols and water-influenced soils, i.e. Gleysol, Planosol, Stagnosol). We used national forest inventory data, regionalized climate data and terrain inferred parameters with a Boosted Regression Tree (BRT) approach. The approach is particularly suitable, since BRT quantify the relative predictor importance, considering non-linearities and interactions among predictors.

The results of this study clearly demonstrate the importance of soil properties on the growth of Norway spruce trees. Terrain attributes and temperature are similarly important for Norway spruce growth on Cambisols and Podzols, whereas spruce growth is mainly influenced by the relative sand content of the soil, the available field capacity and terrain attributes on water-influenced soils. Interactions among environmental drivers are most relevant on Cambisols and Podzols but not on water-influenced soils. Thus, the implementation of the results in growth models of high spatial resolution will support decision making in forest management.

How to cite: Seltmann, C. T., Wernicke, J., Petzold, R., Baumann, M., Münder, K., and Martens, S.: The relative importance of environmental drivers on the growth of Norway spruce depends on soil types: A case study from Saxony and Thuringia, Germany, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17320, https://doi.org/10.5194/egusphere-egu2020-17320, 2020.

D689 |
Luca Belelli Marchesini, Riccardo Valentini, Lorenzo Frizzera, Mauro Cavagna, Isaac Chini, Roberto Zampedri, and Damiano Gianelle

The increased frequency and severity of extremes climatic events determined by the current and predicted scenarios of global climate changes have a large potential impact on the functionality of forest ecosystems and on their capacity of providing ecosystem services. These include climate warming mitigation capacity of forests which is exerted through carbon sequestration, carbon storage and the regulation of the energy balance by allocating incoming solar energy into transpiration rather than thermal energy. Assessing the size of the effects of increasing atmospheric temperature and climate anomalies on the functionality of forests, both in the short and mid-term, as well as their resilience capacity, is therefore of utmost importance in ecological research. European beech (Fagus sylvatica L.) forests, extensively represented over the continent, are known to be particularly vulnerable to late frosts, which limit their distribution into continental areas, and droughts, especially in the southernmost area of their geographical distribution.

The object of this study is an alpine mixed forest at the site of Cembra (46.20N; 11.12E, 1250 m a.s.l) in the Trentino province (Italy). In May 2019 the forest experienced a late spring frost during the early development stage of beech leaves with resulting damage to canopies differing remarkably among individual plants. The ecological monitoring of beech trees started in June 2019 and has been since then carried out by means of clusters of traditional and Internet of Things based devices (Valentini et al. 2019) recording trees radial growth, sap flow density and characterizing the forest microclimatic space. The adopted experimental design consisted in the formation of two groups of trees (n=18) featuring contrasting damaged/undamaged canopies, all selected from the dominant or subdominant layer of the forest canopy structure.

Here we present the rates and the seasonal patterns of beech trees stem radial growth and transpiration from June to November 2019, highlighting the differences among plants directly dependent on the damage conditions and interpreting the total observed tree level variability in relation to microclimate, surrounding forest structure and microtopography. The functional recovery dynamics of transpiration and stem growth in damaged plants will be addressed as an initial evaluation of short-term resilience capacity of the beech forest .

How to cite: Belelli Marchesini, L., Valentini, R., Frizzera, L., Cavagna, M., Chini, I., Zampedri, R., and Gianelle, D.: Impact of climate anomalies on the functionality of beech trees in a mixed forest in the Italian south-eastern Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17762, https://doi.org/10.5194/egusphere-egu2020-17762, 2020.

D690 |
Michele Colangelo, Angelo Rita, Marco Borghetti, Jesus Julio Camarero, Tiziana Gentilesca, Osvaldo Pericolo, and Francesco Ripullone

Increased forest vulnerability to drought and heat spells is being reflected as more widespread and severe dieback events. In this regard, the Mediterranean Basin is revealing a high susceptibility to these phenomena across several tree taxa with a high ecological and socio-economic importance, particularly pines and oaks. For instance, oaks are particularly vulnerable to spring-summer droughts with important losses in term of growth and productivity accompanied by rising mortality rates and declining growth rates, despite some of these species are theoretically considered well-adapted to tolerate drought stress. Dendroecological studies using retrospective analysis of wood anatomical traits and tree-rings have demonstrated their potential to supply useful information on the long-term patterns of forest dieback in several oak species.  

In this study, we explored the xylem anatomical plasticity through time by performing a long-term (1980-2017) reconstruction of wood anatomical traits, aiming at investigate the drought stress effects on dieback of oak species.To this aim, we carried out some field experiments in Italy on four oak species differing in drought tolerance, i.e. Quercus robur, Quercus cerris, Quercus frainetto and Quercus pubescens, considered to have low to high tolerance, respectively, but showing recent decline phenomena. We cored asymptomatic (ND) and symptomatic (D) coexisting trees showing low and high defoliation levels, respectively, and for all sampled species we measured the following anatomical traits in the xylem: vessel area, Dh, vessel density.

Climate-traits relationships over the last century explained the recent growth divergence observed between D and ND trees because D trees were more sensitive[U1]  to drought stress and summer warm temperatures leading to high evapotranspiration rates. Here, we discuss: i) the relationships between radial growth, changes in wood anatomy and hydraulic functioning of trees to highlight the triggers of oak dieback; ii) the associations between climate, growth and anatomy data to explain likely the differences in acclimation/plasticity to short/long-term changes in environmental conditions.

How to cite: Colangelo, M., Rita, A., Borghetti, M., Camarero, J. J., Gentilesca, T., Pericolo, O., and Ripullone, F.: Drought-induced decline in oak Mediterranean forests: insights from wood anatomical traits , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18443, https://doi.org/10.5194/egusphere-egu2020-18443, 2020.

D691 |
Sabine Rosner, Klara Voggeneder, and Sebastian Nöbauer

Global warming calls for fast and easily applicable methods to measure hydraulic vulnerability in conifers since they are one of the most sensitive plant groups regarding drought stress. Classical methods to determine P50, i.e. the water potential resulting in 50% conductivity loss, are labor intensive and prone to errors. In this study, the empirical relationship between percent loss of hydraulic conductivity and relative water loss in sapwood of six conifer species was used to establish a novel proxy for P50. Our new proxy P25W, defined as 25% of relative water loss induced by air injection, is easy and fast to measure and correlates strongly with P50 (r = 0.95) as well as with functional wood traits such as the tracheid wall/lumen ratio (r = -0.87). The method is regarded as a strong new phenotyping tool for screening trees for drought sensitivity.

How to cite: Rosner, S., Voggeneder, K., and Nöbauer, S.: A novel approach for fast prediction of hydraulic vulnerability in conifers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19446, https://doi.org/10.5194/egusphere-egu2020-19446, 2020.

D692 |
Aikaterini Dounavi, Frederike Caroline Creyaufmüller, Isabelle Chassignet, Ludger Leinemann, Horst Delb, Oliver Gailing, Juergen Kreuzwieser, Julia Teply-Szymanski, and Barbara Vornam

In view of climate change the risk of biotic stressors in the forests is expected to be enhanced in addition to severe abiotic stress events, like drought. One biotic stress considered to be increased for oak regeneration is the root feeding of young plants from cockchafer. The cockchafers (Melolontha spp.) belong to the scarab beetles (Scarabaeidae) and are widespread pest species throughout Central Europe. In Germany, the most common species is the European cockchafer (Melolontha melolontha Linnaeus), whereby the forest cockchafer (Melolontha hippocastani Fabricius) is also present, mainly on sandy soils. Specifically, in south-western Germany both European and forest cockchafers cause economic losses in agricultural and forest areas. Besides drought, the feeding of roots from cockchafer larvae, act as an additional stress factor for young oak plants. In the present case study, geographically distant oak stands are infested with different intensity.

In the present study, population genetic analysis was used to differentiate the two cockchafer species and was used to estimate population dynamics, as well as possible consequences of climatic changes to the life cycle of forest cockchafer. Additionally, seedlings of two distant oak provenances were exposed to forest cockchafer larvae in a greenhouse experiment and their population genetic and root-based VOC profiles were studied. Larvae preferences for the different plants/populations were estimated and terpene synthase gene expression of the plants was measured.

Chloroplast haplotypes showed patterns of migration from different refugial regions. However, no clear association between genetic constitution of the different provenances and the abundance of cockchafer populations on site was observed. TPS gene expression patterns in response to larval feeding revealed geographic variation rather than genotypic variation. Our results support the assumption that root-released VOC are influencing the perception of roots by herbivores.

How to cite: Dounavi, A., Creyaufmüller, F. C., Chassignet, I., Leinemann, L., Delb, H., Gailing, O., Kreuzwieser, J., Teply-Szymanski, J., and Vornam, B.: Feeding preference of cockchafer populations and response of oak regeneration: a case study in Germany, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20097, https://doi.org/10.5194/egusphere-egu2020-20097, 2020.

D693 |
Simona Castaldi, Serena Antonucci, Shahla Asgharina, Giovanna Battipaglia, Luca Belelli Marchesini, Mauro Cavagna, Isaac Chini, Claudia Cocozza, Damiano Gianelle, Tommaso La Mantia, Antonio Motisi, Francesco Niccoli, Arturo Pacheco Solana, Giovanna Sala, Giovanni Santopuoli, Giustino Tonon, Roberto Tognetti, Roberto Zampedri, Ilaria Zorzi, and Riccardo Valentini

The  Italian TREETALKER NETWORK (ITT-Net) aims to respond to one of the grand societal challenges: the impact of climate changes on forests ecosystem services and forest dieback. The comprehension of the link between these phenomena requires to complement the most classical approaches with a new monitoring paradigm based on large scale, single tree, high frequency and long-term monitoring tree physiology, which, at present, is limited by the still elevated costs of multi-sensor devices, their energy demand and maintenance not always suitable for monitoring in remote areas. The ITT-Net network will be a unique and unprecedented worldwide example of real time, large scale, high frequency and long-term monitoring of tree physiological parameters. By spring 2020, as part of a national funded project (PRIN) the network will have set 37 sites from the north-east Alps to Sicily where a new low cost, multisensor technology “the TreeTalker®” equipped to measure tree radial growth, sap flow, transmitted light spectral components related to foliage dieback and physiology and plant stability (developed by Nature 4.0), will monitor over 600 individual trees. A radio LoRa protocol for data transmission and access to cloud services will allow to transmit in real time high frequency data on the WEB cloud with a unique IoT identifier to a common database where big data analysis will be performed to explore the causal dependency of climate events and environmental disturbances with tree functionality and resilience.

With this new network, we aim to create a new knowledge, introducing a massive data observation and analysis, about the frequency, intensity and dynamical patterns of climate anomalies perturbation on plant physiological response dynamics in order to: 1) characterize the space of “normal or safe tree operation mode” during average climatic conditions; 2) identify the non-linear tree responses beyond the safe operation mode, induced by extreme events, and the tipping points; 3) test the possibility to use a high frequency continuous monitoring system to identify early warning signals of tree stress which might allow to follow tree dynamics under climate change in real time at a resolution and accuracy that cannot always be provided through forest inventories or remote sensing technologies.

To have an overview of the ITT Network you can visit www.globaltreetalker.org


How to cite: Castaldi, S., Antonucci, S., Asgharina, S., Battipaglia, G., Belelli Marchesini, L., Cavagna, M., Chini, I., Cocozza, C., Gianelle, D., La Mantia, T., Motisi, A., Niccoli, F., Pacheco Solana, A., Sala, G., Santopuoli, G., Tonon, G., Tognetti, R., Zampedri, R., Zorzi, I., and Valentini, R.: The Italian TREETALKER NETWORK (ITT-Net): continuous large scale monitoring of tree functional traits and vulnerabilities to climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20591, https://doi.org/10.5194/egusphere-egu2020-20591, 2020.

D694 |
Iduna Arduini, Roberto Cardelli, and Andrea Bertacchi

The forest of San Rossore, extending for approximately 3,500 ha along the coast of Tuscany (central Italy), is the heart of the “Selve costiere di Toscana”, included in the World Network of Biosphere Reserves (UNESCO). This forest is a mosaic of patches of mixed hygrophilous broadleaves, Mediterranean sclerophyllous and conifers, and old stone pine plantations. With its more than 600 plant species this forest system is a recognized reservoir of high landscape and biological value, nevertheless it is highly vulnerable to antrophogenic disturbance and climate change. The primary reason is that it grows on a succession of old sand dunes alternated with wet hollows and, therefore, the soil is characterized by a very thin organic layer which is prone to erosion and mineralization once the integrity of the vegetation cover is disturbed. Secondly, the forest is surrounded by a highly urbanized area and undergoes touristic pressure, both facilitating the introduction of alien species into the natural vegetation. Investigations demonstrated that the soil seed bank is generally poor and contains an appreciable proportion of alien species. Forest clearings are often invaded by alien trees, first by Ailanthus altissima (Mill.) Swingle, whereas Amorpha fruticosa L. diffuses along channels and ditches.

In the foregone decades the forest of San Rossore underwent several threats: i) the progressive dieback of the forest front nearest to the seashore caused by both the massive coastal erosion and the foliar deposition of marine aerosol-borne pollutants, and ii) the attack of Leptoglossus occidentalis Heidemann and Matsucoccus feytaudi Ducasse, two insect pests that caused a diffuse decay of Pinus pinea L. and Pinus pinaster Aiton stands, respectively. In addition to the above damages on the standing plants, a high density of ungulates impairs the regeneration of forest trees, primarily that of broadleaves.

In recent years, an increased crash down of isolated trees belonging to both the hygrophilous and the Mediterranean forest associations, and the dieback of entire Fraxinus angustifolia Auct. patches were observed. While the former events can be attributed to windstorms, which increased frequency and strength is associated with climate change, the latter are still unexplained, but multiple, interacting factors can be hypothesized. Among these, the infiltration of saline rich seawater in consequence of coastal erosion, the accumulation of pollutants in the soil, the attack of a specific pathogen, but also changes in the seasonal fluctuations of soil humidity, due to either changes in the amount and distribution of rainfall or to changes in forest management. The forest of San Rossore is, indeed, crossed by a system of artificial channels which provided to drain the soil of stone pine plantations in the past, but are no more maintained today. This could have reduced the water flux in the subsurface water table causing soil hypoxia, which weakens the root systems and reduces tree vigor, thus increasing their susceptibility to diseases and crash down.

The forest of San Rossore is a model for complex forest systems subjected to several pressures, which health conservation urgently needs the joint effort of multidisciplinary knowledge.

How to cite: Arduini, I., Cardelli, R., and Bertacchi, A.: The forest of San Rossore (Tuscany, Italy): a call for its conservation through a multidisciplinary approach , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20738, https://doi.org/10.5194/egusphere-egu2020-20738, 2020.

D695 |
Giulia Silvia Giberti, Giustino Tonon, Francesco Giammarchi, Alessio Giovannelli, Kamil Bielak, Ana Martín Ariza, Cristobal Ordóñez Alonso, Felipe Bravo, Ben du Toit, Enno Uhl, and Wellstein Camilla

Forest ecosystems are known to be vulnerable to climate change. Climate extremes, such as drought
events, are expected to increase in duration and frequency in many areas across the globe. Unexpected
and prolonged drought events already caused forests dieback all over the world in the last decades,
leading to dramatic consequences, such as biodiversity loss, ecosystem services alteration and reduction
of carbon sequestration potential. Indeed, in Central Europe, monocultures consisting mostly of 
secondary conifer forests, showed low resistance to such events, and their viability is further threatened
by the interaction with other biotic and abiotic factors. In this context, the need of a deeper understanding
of the physiological mechanisms behind the tree response to extreme drought eventsis fundamental. The
present study, developed under the network of the CARE4C Project (Carbon smart forestry under climate
change GA 778322), aims at investigating Pinus sylvestris xylem plasticity in response to extreme drought.
We selected P. sylvestris pure forests in contrasting climatic zones of Europe, i.e. continental (Poland) and
Mediterranean (Spain), to study P. sylvestris xylem plasticity to extreme drought events under different
climatic conditions. Contemporarily, this study aims at comparing the xylem plasticity of P. sylvestris in
mono-specific and mixed forests. In the latter, the admixture is with Quercus petraea and Quercus
pyrenaica, in Poland and Spain respectively. The responses of P. sylvestris wood anatomical traits, such as
tracheid lumen area, cell wall thickness and parenchyma ray area, will be quantified along the entire treering chronologies. Short-term and legacy effects of extreme drought on P. sylvestris wood anatomical
traits will be evaluated in order to provide insights about the vulnerability of this speciesin a future climate
scenario. Locally, the comparison between P. sylvestris wood anatomical traitsin mono-specific and mixed
forests will highlight whether the mixing of species with different ecological needs can affect P. sylvestris
performance, ameliorating the resilience of this species to extreme drought events.

How to cite: Giberti, G. S., Tonon, G., Giammarchi, F., Giovannelli, A., Bielak, K., Ariza, A. M., Alonso, C. O., Bravo, F., du Toit, B., Uhl, E., and Camilla, W.: The effect of extreme drought events on Pinus sylvestris (L.) xylem plasticity in pure and mixed forests and contrasting climatic conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22307, https://doi.org/10.5194/egusphere-egu2020-22307, 2020.

D696 |
Maria del Carmen Calderon-Ezquerro, Adriana Guerrero Parra, and Benjamin Martinez-Lopez

Coffee rust is the most destructive disease for coffee crops and the most economically important worldwide. This disease causes the premature fall of the leaves, as well as the weakening of the trees, which translates into significant decreases in the production of coffee beans, representing thus a serious danger for the coffee activity of Mexico, which is the ninth world producer. The aggressiveness of the disease is related to the meteorological conditions that favor, or not, the germination, development, and production of the spores of the fungus causing this disease, as well as its transport in the air inside and outside of the canopy of coffee crops. The objective of this work was to determine the meteorological conditions that modulate the development, release, and transport of spores by using aerobiological methods at two locations with different orographic conditions in the center of the state of Veracruz, Mexico, during the years of 2014 and 2015. In both locations, Pacho Viejo and Teocelo, spores were detected in passive traps placed at 1.5, 3, 6 and 9 meters high, registering the highest concentrations in July and August of both years, coinciding with the period of rainfall decrease known as the Canicula. The spore concentrations in Teocelo increased considerably in 2015, probably due to a decrease in temperature during the months of February and March, which led to preconditioning of the spores favoring their germination in the subsequent months. During July and August 2015, high spore concentrations were present in Teocelo at 9 m high, but not in Pacho Viejo. An analysis of the winds of the region, suggests that wind conditions of 2015 favored the dispersion of the spores above the canopy in Teocelo.

How to cite: Calderon-Ezquerro, M. C., Guerrero Parra, A., and Martinez-Lopez, B.: Metereological factors modulating coffee rust in the central area of Veracruz, Mexico , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22572, https://doi.org/10.5194/egusphere-egu2020-22572, 2020.