Session BG3.4

[Programme]

BG3.4 | Forest under pressure: the need to understand causes, mechanisms and forest adaptive management of dieback forests to improve their resilience

Forest under pressure: the need to understand causes, mechanisms and forest adaptive management of dieback forests to improve their resilience

Convener: Francesco Ripullone | Co-conveners: Tamir Klein, Giovanna Battipaglia, Michele ColangeloECSECS, Simona Altieri

Orals

| Fri, 28 Apr, 16:15–18:00 (CEST)

Room N2

Posters on site

| Attendance Fri, 28 Apr, 10:45–12:30 (CEST)

Hall A

Posters virtual

| Attendance Fri, 28 Apr, 10:45–12:30 (CEST)

vHall BG

The majority of world forest ecosystems are subject to a number of natural disturbances (e.g. wildfires, pests, diseases, adverse weather events). These can severely affect their health and vitality by causing tree mortality or by reducing their ability to provide the full range of goods and services. Understanding and quantifying forest vulnerability to such disturbances and the underlying driving mechanisms is crucial to assess climate impacts and develop effective adaptation strategies.
This session will cover aspects ranging from observed and projected climate change to consequences for forest ecosystems and forest assessment, spanning a range of scales and conditions. In particular, we welcome submissions on the following subjects:

• Forest mortality and die-back phenomena under global warming.
• Evaluation of the effects of natural and anthropogenic disturbances on forest health and growth.
• Vulnerability of old-growth forests and mountainous forest ecosystems to climate change.
• Multidisciplinary approaches towards monitoring and modelling tree vulnerability at the local, regional and global scale.
• Estimation of resistance, resilience and recovery of forests in drought-prone areas.
• Interdisciplinary forestry research covering not only ecological but also economic and social aspects.
• Effects of forest adaptive management on forest health and vulnerability.
• Methods and tools for decision support and adaptation support in the forestry sector.
• Modelling growth at different scales: wood, tree, forest.

Orals: Fri, 28 Apr | Room N2

Chairpersons: Francesco Ripullone, Tamir Klein, Giovanna Battipaglia

16:15–16:20

5-minute convener introduction

16:20–16:30

EGU23-17180

ECS

On-site presentation

Quantifying the response of shrubs and trees to drought as a tool to detect vulnerable forests in Spain

Antonio Gazol

Climate change is expected to increase the duration and severity of heatwaves and droughts in the Mediterranean region. In this climate change hotspot, drought and heat stress have triggered the occurrence of forest mortality events over the past decades. It is thus important detecting those regions in which drought-induced forest mortality events are occurring to advance in the knowledge of why some species and populations are more vulnerable to heat and drought than others.

If localized on time, these declining forests are valuable natural laboratories to attribute potential factors triggering mortality. However, detecting and identifying drought-impacted forest is challenging because forest mortality events in the Mediterranean region are spatially heterogeneous and have a local extent.

Here I summarize the main findings of several studies performed in forests that have been impacted by drought events over the past years aiming to detect how: i) the vitality and growth of shrubs and trees varied between species, and ii) between individuals within species. Further, I discuss how these results can help to increase our capacity in detecting forest mortality hotspots.

How to cite: Gazol, A.: Quantifying the response of shrubs and trees to drought as a tool to detect vulnerable forests in Spain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17180, https://doi.org/10.5194/egusphere-egu23-17180, 2023.

16:30–16:40

EGU23-3564

ECS

On-site presentation

Linking remotely sensed ecosystem resilience with forest mortality across the continental United States

Xiaonan Tai, Anna Trugman, and William Anderegg

Episodes of forest mortality have been observed worldwide associated with climate change, impacting species composition and ecosystem services such as water re- sources and carbon sequestration. Yet our ability to predict forest mortality remains limited, especially across large scales. Time series of satellite imagery has been used to document ecosystem resilience globally, but it is not clear how well remotely sensed resilience can inform the prediction of forest mortality across continental, multi-biome scales. Here, we leverage forest inventories across the continental United States to systematically assess the potential of ecosystem resilience derived using different data sets and methods to predict forest mortality. We found high resilience was as- sociated with low mortality in eastern forests but was associated with high mortality in western regions. The unexpected resilience–mortality relation in western United States may be due to several factors including plant trait acclimation, insect popula- tion dynamics, or resource competition. Overall, our results not only supported the opportunity to use remotely sensed ecosystem resilience to predict forest mortality but also highlighted that ecological factors may have crucial influences because they can reverse the sign of the resilience–mortality relationships.

How to cite: Tai, X., Trugman, A., and Anderegg, W.: Linking remotely sensed ecosystem resilience with forest mortality across the continental United States, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3564, https://doi.org/10.5194/egusphere-egu23-3564, 2023.

16:40–16:50

EGU23-8249

On-site presentation

Towards species-level forecasts of drought-induced tree mortality risk

Martin De Kauwe, Manon Sabot, Belinda Medlyn, Andy Pitman, Patrick Meir, Lucas Cernusak, Anna Ukkola, Sami Rifai, and Brendan Choat

Australia is the driest inhabited continent. Annual rainfall is low and is accompanied by marked inter-annual variability, leading to multi-year droughts. n particular, South-East Australia has recently experienced two of the worst droughts in the historical record (2000–2009 and 2017–2020). Predicting species-level responses to drought at the landscape scale is critical to reducing uncertainty in future terrestrial carbon and water cycle projections. We embedded a stomatal optimisation model in the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model and parameterised the model for 15 canopy-dominant eucalypt tree species across South-Eastern Australia (mean annual precipitation range: 344–1424 mm yr^-1). We carried out three experiments: applying CABLE to the recent drought; a theoretical future drier drought (20% reduction in rainfall); and a future drier drought (20% reduction in rainfall) with a doubling of atmospheric carbon dioxide (CO₂). The drought's severity was highlighted as at least 25% of their distribution ranges, and 60% of species experienced leaf water potentials beyond the water potential at which 50% of hydraulic conductivity is lost due to embolism. We identified areas of severe hydraulic stress within species’ ranges, but we also pinpointed resilience in species found in predominantly semiarid regions. The importance of the role of CO₂ in ameliorating drought stress was consistent across species. Our results represent an important advance in our capacity to forecast the resilience of individual tree species, providing an evidence base for decision-making around the resilience of restoration plantings or net-zero emission strategies.

How to cite: De Kauwe, M., Sabot, M., Medlyn, B., Pitman, A., Meir, P., Cernusak, L., Ukkola, A., Rifai, S., and Choat, B.: Towards species-level forecasts of drought-induced tree mortality risk, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8249, https://doi.org/10.5194/egusphere-egu23-8249, 2023.

16:50–17:00

EGU23-4614

ECS

Virtual presentation

Can process-based BGC models simulate drought-induced tree mortality worldwide?

Nanghyeon Jo, Casimir Agossou, Eunsook Kim, Jong-Hwan Lim, and Sinkyu Kang

Drought-induced tree mortality has been increasing worldwide under climate change; therefore, forests will become more vulnerable as warming continues. With growing interest in tree decline due to increased climate variability, ecophysiological roles and dynamics of non-structural carbohydrates (NSCs) have drawn wide attention recently. Accordingly, a lot of field data have been collected, but these achievements were not well incorporated in process-based vegetation models yet, where NSCs ecophysiology was implicitly applied or ignored. In this study, we addressed five key modeling issues in simulating spatial and temporal patterns of NSCs dynamics across different scales as follows: (1) interconversion between dual NSCs pools (i.e., rapid soluble sugar and slown starch pools), (2) incorporation of the sink-limited growth allocation strategy, (3) hydraulic limitation of NSCs transports between organs, (4) feedback mechanisms between tree NSCs and root symbionts, and (5) large-scale simulations of NSCs dynamics. In addtion, we applied key issues (1) and (2) of NSCs to the BIOME-BGC model and evlauated across biomes. As a result, modified BGC model (BGC-NSCs) successfully simulated vegetation traits across different biomes, such as seasonal and interannual variations of St (mean R² of, 0.55, 0.62), and site-specific SS-to-St ratios, while the model did not simulate the SS temporal variation well. Nevertheless, in the factor analysis of several variables for the global tree mortality data, physiological variables such as NSCs and PLC (Percent loss of conductivity) produced in the BGC-NSCs model were important. Despite limitations of the current BGC modeling and simple assumptions of mortality mechanisms, this study demonstrated a potential to use key ecophysiological variables for simulating widespread drought-induced mortality across different biomes and climate regions.

How to cite: Jo, N., Agossou, C., Kim, E., Lim, J.-H., and Kang, S.: Can process-based BGC models simulate drought-induced tree mortality worldwide?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4614, https://doi.org/10.5194/egusphere-egu23-4614, 2023.

17:00–17:10

EGU23-2903

ECS

Virtual presentation

Mega-Disturbances and forest decline in the Sierra Nevada of California, USA: Insights for managing disturbance dynamics

Zack Steel, Gavin Jones, Brandon Collins, Rebecca Green, Alex Koltunov, Kathryn Purcell, Sarah Sawyer, Michele Slaton, Scott Stephens, Peter Stine, and Craig Thompson

Mature forests characterized by high cover of tall trees and complex understories are important habitat for native plant and wildlife species and support critical ecosystem functions globally. In California’s Sierra Nevada a combination of a century of fire exclusion and worsening climate change has led to increasingly severe wildfires and extreme drought that threaten habitats of sensitive species. Using spatially explicit datasets of forest structure and the Ecosystem Disturbance and Recovery Tracker, we quantified the loss of conifer forest cover in the southern Sierra Nevada between 2011 and 2020, a decade and region characterized by unprecedented mega-disturbances. Due to the combination of wildfires, drought, and drought-associated beetle kill, 30% of conifer forest extent was lost (fell below 25% canopy cover) during this period. Of the spatially limited mature forest habitats, 56% of moderate density (40-60% canopy cover) and 84% of high density (>60% canopy cover) forests were degraded. Drought and beetle-kill caused greater cumulative degradation than areas where wildfire mortality overlapped with the other disturbances. However, burned areas resulted in larger patches of forest loss and greater forest fragmentation on average. These results highlight that current conservation approaches are failing to protect mature forest habitats within disturbance-prone ecosystems like the conifer forests of California. We emphasize the need to switch from a static approach to conservation toward one focused on managing healthy disturbance dynamics, especially using frequent low-severity fire to increase forest resilience to future mega-disturbances. Without rapid management interventions, remaining mature forest habitat in the Sierra Nevada may be susceptible to complete loss in the coming decades.

How to cite: Steel, Z., Jones, G., Collins, B., Green, R., Koltunov, A., Purcell, K., Sawyer, S., Slaton, M., Stephens, S., Stine, P., and Thompson, C.: Mega-Disturbances and forest decline in the Sierra Nevada of California, USA: Insights for managing disturbance dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2903, https://doi.org/10.5194/egusphere-egu23-2903, 2023.

17:10–17:20

EGU23-4068

ECS

On-site presentation

Drought resistance enhanced by tree species diversity in global forests

Dan Liu, Tao Wang, Josep Peñuelas, and Shilong Piao

Restoring species diversity is proposed as a strategy to improve ecosystem resistance to extreme droughts, but the impact of species diversity on resistance has not been evaluated across global forests. Here we compile a database that contains tree species richness from more than 0.7 million forest plots and satellite-based estimation of drought resistance. Using this database, we provide a spatially explicit map of species diversity effect on drought resistance. We found that higher species diversity could notably enhance drought resistance in about half of global forests but was spatially highly variable. Drought regimes (frequency and intensity) and climatic water deficit were important determinants of differences in the extent that species diversity could enhance forest drought resistance among regions, with such benefits being larger in dry and drought-prone forests. According to a predictive model of species diversity effect, the conversion of current monoculture to mixed-species tree plantations could improve drought resistance, with the large increase in dry forests. Our findings provide evidence that species diversity could buffer global forests against droughts. Restoration of species diversity could then be an effective way to mitigate the impact of extreme droughts on large scales, especially in dry and drought-prone regions.

How to cite: Liu, D., Wang, T., Peñuelas, J., and Piao, S.: Drought resistance enhanced by tree species diversity in global forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4068, https://doi.org/10.5194/egusphere-egu23-4068, 2023.

17:20–17:30

EGU23-13234

ECS

On-site presentation

Global analysis of deviations in climate sensitivity of tree-growth after extreme drought events

Christopher Leifsson, Allan Buras, Anja Rammig, and Christian Zang

In the course of climate change, forests around the globe will be exposed to more frequent and more severe extreme drought events. Direct and lagging impacts of drought events on forests, so-called drought legacies, are often estimated from tree-ring derived secondary growth measurements which easily translate into biomass and are available globally. However, secondary growth is a result from multiple internal mechanisms and therefore does not reveal potential impacts on the underlying physiology, such as hydraulic dysfunction, repair mechanisms and altered carbon allocation. Instead, the carbon demand of these impacts translates to less carbon being available for secondary growth which therefore results in temporarily altered relationships between climate and growth.

Here, we advance the concept of drought legacies by additionally quantifying simultaneous “functional legacies” as climate sensitivity deviations (CSD) of secondary growth. We quantified legacies in both growth and climate sensitivity after extreme drought events using linear mixed-effects models on a global-scale, multi-species tree-ring dataset. We further differentiated the responses by clade, site aridity and hydraulic safety margins in order to determine common factors which convey heightened or lessened vulnerability to extreme drought events.

Our results show that while depressed growth was common after droughts across most of the analysed groups, although with varying legacy lengths, post-drought climate sensitivity deviations were more nuanced. The climate sensitivity of growth was decoupled for gymnosperms with small hydraulic safety margin, i.e. those with a more risk-prone hydraulic growth strategy. In comparison, the climate sensitivity of growth tightened for angiosperms growing in arid sites, a response which occurred in conjunction with a post-drought growth overshoot. These responses are consistent with current understanding of impaired hydraulic function and increased carbon allocation towards xylogenesis, respectively. In conclusion, climate sensitivity deviations reveal physiological responses not discernible from growth legacies alone and therefore serves as a promising avenue for a more comprehensive identification of drought impacts on tree growth at large scales.

How to cite: Leifsson, C., Buras, A., Rammig, A., and Zang, C.: Global analysis of deviations in climate sensitivity of tree-growth after extreme drought events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13234, https://doi.org/10.5194/egusphere-egu23-13234, 2023.

17:30–17:40

EGU23-12250

ECS

Highlight

On-site presentation

‘The application of a novel IoT driven biosensing platform, the TreeTalker®, for coppice forest monitoring in central Italy’.

Jim Yates, Shahla Asgharinia, and Riccardo Valentini

Coppicing forest management systems represent the oldest systematic silvicultural practice across the European continent. This simplistic yet sustainable system is well defined by several silvicultural applications which are in general designed to provide a woody crop within a relatively short rotational period. Additionally, the treatment and maintenance of such forests continue to provide a variety of functions and thus ecosystem services. Although the extension of coppice forests is estimated at approximately 20 million hectares across Europe, they are often poorly utilised, undermanaged or altogether abandoned. In systems where management activity is enduring, threats from climate induced mortality remain prevalent. This coupled with poor management, which often promotes over stocking on one hand and unregulated coppice sprout management inducing stool exhaustion on the other, threaten this historical management approach. Consequently, novel monitoring efforts for these forest types and systems merits attention. This study aims to investigate the application of a novel biosensing platform, the TreeTalker, toward the continuous monitoring of individual sprouts on coppice stools and selected standards across three plots in a historically coppiced forest located in central Italy. The TreeTalker is an IoT driven device integrated platform aiming to monitor well established tree ecophysiological processes such as sap flow, stem radial growth and light canopy interactions in quasi real time via LoRa architecture and an inhouse multi sensor infrastructure. We present the results of a two year consecutive monitoring campaign using these devices. Evidently, we observed that competition among sprouts on the same stool is clearly detectable via the TreeTalkers sensors, particularly the radial dendrometer expressing different results both across the seasons monitored and among individuals. Strong signals in reduced stem radial growth across the very dry 2022 season were also observed. The results suggest that the TreeTalker provides high fidelity data on the ecophysiological behaviour of trees throughout the vegetative season. Data from these devices offers an exciting new frontier in forest monitoring. For coppice forests specifically, silvicultural activities such as timing of thinning intervention and sprout selection for standard recruitment can be guided by retrieved information in addition to real time monitoring of stem health. Scaling via more TreeTalker device installation and subsequent spatial and temporal requirements requires further investigation.

How to cite: Yates, J., Asgharinia, S., and Valentini, R.: ‘The application of a novel IoT driven biosensing platform, the TreeTalker®, for coppice forest monitoring in central Italy’., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12250, https://doi.org/10.5194/egusphere-egu23-12250, 2023.

17:40–17:50

EGU23-12540

ECS

On-site presentation

Climate-driven variations in functional strategies of temperate forest ecosystems

Daijun Liu, Adriane Esquivel-Muelbert, Jonas Fridman, Ruiz Benito Paloma, Zavala Girones Miguel Ángel, Julen Astigarraga, Suvanto Susanne, Andrzej Talarczyk, Emil Cienciala, Georges Kunstler, Mart-Jan Schelhaas, Jon Sadler, Tom Matthews, Chris Woodall, Nezha Acil, Chao Zhang, and Thomas Pugh

Tree functional strategies play a crucial role regulating the fitness and ability of forests to cope with water stress. However, current understanding on community-level functional strategies of forest ecosystems and how they vary with geographic patterns is still limited. We combined eight functional traits (e.g. leaf nitrogen content, xylem conductivity, leaf area to sapwood area ratio, leaf mass area, xylem water potential at 50% loss of conductivity, slope for the curve between P50-P88, leaf turgor loss point and wood density) with forest inventory data across the USA and Europe (12,332 0.25° gridcells) to identify functional strategies with respect to water stress and to analyse their relationships with climate factors and across functional groups. Principal components analysis suggests that functional strategies at species-level could be captured at community-level. Acquisitive-conservative strategies loaded along the first dimension, while the water storage and isohydricity strategies loaded along the second dimension. Spatial patterns of community-level strategies showed more explanatory power with temperature than aridity. Multiple community-level strategies at a grid cell were observed at water-limited sites, which were broadly captured by broad functional groups based on leaf type and phenology. Our findings promote the understanding of forest adaptation to drought and provide a basis for improving the ability of ecosystem models to predict the patterns of tree mortality and forest biomass accumulation.

How to cite: Liu, D., Esquivel-Muelbert, A., Fridman, J., Benito Paloma, R., Miguel Ángel, Z. G., Astigarraga, J., Susanne, S., Talarczyk, A., Cienciala, E., Kunstler, G., Schelhaas, M.-J., Sadler, J., Matthews, T., Woodall, C., Acil, N., Zhang, C., and Pugh, T.: Climate-driven variations in functional strategies of temperate forest ecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12540, https://doi.org/10.5194/egusphere-egu23-12540, 2023.

17:50–18:00

EGU23-15805

On-site presentation

Drought resilience of a mixed beech-spruce forest - an experimental study linking responses from the rhizosphere to the canopy, from physiology to morphology, and from hours to years

Thorsten Grams

This paper addresses the knowledge gaps on what determines tree responses to drought, their recovery, and survival following drought release, integrating physiological and morphological responses from the rhizosphere to the canopy of mature trees. I summarize 10 years of research on an experimentally induced drought and subsequent recovery in a maturing beech-spruce forest in southern Germany. Study objects 70- to 80-year-old trees that are readily accessible via canopy crane and grow in either mono-specific or mixed stands. We studied about 100 trees in 12 plots of roughly 150 m2 each. Tress were exposed to experimentally induced summer drought for five consecutive years by complete throughfall exclusion during the growing season (Kranzberg forest ROOF experiment, kroof.wzw.tum.de).

During the first two drought summers, when both species were not yet acclimated, drought stress intensity peaked with pre-dawn leaf water potentials near -2.0 MPa and concomitant severe declines in physiological (e.g. leaf gas exchange, phloem transport) and morphological (e.g. growth) responses. After overcoming the critical first two years of drought, significant morphological acclimation in the following three years, e.g. by adjustment of leaf area or rooting depths, resulted in relaxation of physiological stress, as evidenced, for example, by increased stomatal conductance and pre-dawn leaf water potential. Reduced water consumption of spruce and thus higher water availability, also for neighboring beech trees, significantly alleviated drought stress in the trees.

After a total of five years of experimentally induced summer drought, drought release was initiated in early summer 2019 by controlled watering. Physiological parameters such as stomatal conductance or xylem sap flow recovered with hours or days after drought release, including resilience of C allocation, e.g. sugar transport along the stems, as an important prerequisite for the recovery of tree functionality and productivity. Restored coupling between canopy and rhizosphere significantly supported spruce root growth, which recovered within a few days. In contrast, other morphological responses (e.g., leaf area recovery) took years to recover. With future increases in the frequency of drought events under ongoing climate change, tree species that recover more quickly will be favored.

How to cite: Grams, T.: Drought resilience of a mixed beech-spruce forest - an experimental study linking responses from the rhizosphere to the canopy, from physiology to morphology, and from hours to years, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15805, https://doi.org/10.5194/egusphere-egu23-15805, 2023.

Posters on site: Fri, 28 Apr, 10:45–12:30 | Hall A

Chairpersons: Giovanna Battipaglia, Tamir Klein, Francesco Ripullone

A.208

EGU23-6143

ECS

Dieback events of Scots pines caused by lack of rain in mid and late summer

Stefan Hunziker, Michael Begert, Simon C. Scherrer, Andreas Rigling, and Arthur Gessler

Same as other parts of Europe, the inner-Alpine Swiss Rhône valley has been increasingly affected by Scots pine (Pinus sylvestris L.) dieback events since the 1990s. Such events were not confined to years of extreme heat and drought across Switzerland and Europe such as 2003 or 2018, and the severity and frequency of sudden tree mortality varied on relatively small spatial scales. Which are the relevant parameters that changed in time and which factors triggered these dieback events?

We found that sudden mortality events occurred exclusively after periods of below average precipitation between July and September. During this time of the year, soil moisture regularly drops to a minimum while the atmospheric water demand is high. Further factors such as insect infestation or spring frost may increase the magnitude of tree mortality, but they were neither a required contributor nor were they found to trigger dieback events. Consequently, the region with lowest summer precipitation within the Swiss Rhône valley outlines the area most affected by Scots pine dieback.

However, the amount and frequency of the highly variable summer precipitation did not decrease since the 1980s, but the atmospheric water demand in spring and summer increased continuously. As a result of the higher water loss to the atmosphere, the period of low soil moisture has been prolongated and intensified. Therefore, Scots pines have become more dependent on (temporary) water stress relief by precipitation events during mid and late summer.

Many Scots pine died (most likely due to hydraulic failure) within months following severe summer water stress. The effects of such periods appeared faster on tree crown defoliation (i.e., the proportion of needles that should be present on a tree, but which have been lost) than on mortality, as some trees died only after a year or two. We found that these Scots pines exceeded a defoliation threshold of about 75 % and were unable to recover. In such strongly defoliated trees, stress-related metabolites increase in needles, but get depleted in roots, indicating that mortality is linked to belowground carbon starvation negatively affecting functions central for tree survival.

How to cite: Hunziker, S., Begert, M., Scherrer, S. C., Rigling, A., and Gessler, A.: Dieback events of Scots pines caused by lack of rain in mid and late summer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6143, https://doi.org/10.5194/egusphere-egu23-6143, 2023.

A.209

EGU23-4657

ECS

Integration of TreeTalker proximal data with remote sensing for monitoring seasonal phenological dynamics at the species level in Italy

Alexander Cotrina-Sánchez, Gaia Vaglio Laurin, Jerzy Piotr Kabala, Francesco Niccoli, Jim Yates, Riccardo Valentini, and Giovanna Battipaglia

Over the years, remote sensing and spectroscopy have contributed significantly to vegetation monitoring, primarily to understand the interaction of plants with solar radiation. However, due to spatial and temporal heterogeneity, light availability below and within tree canopies is challenging to estimate or time-consuming. Therefore, it is essential to know the structure of the tree canopy through vertical light transmission profiles, which will allow estimating plant development, biophysical properties throughout the canopy and the seasonal phenology of the species.

Currently, technologies based on the Internet of Things (IoT) are constituted as efficient and low-cost tools for monitoring forest ecology at the individual and species levels. A device applied to ecology and based on IoT is the "TreeTalker" (TT +), which allows measuring in semi-real time, in addition to water transport in trees, diametrical growth, the spectral transmittance of light through the canopy in 12 spectral bands, using spectrometers in the visible range (VIS) between 450 – 650 nm and 610 – 860 nm in the near-infrared (NIR). These parameters are acquired and stored by each TT+ every hour, sent to a node (TT-Cloud), and transmitted and stored on a server.

In this context, our study integrates remote sensing data and those obtained through IoT to evaluate the variability of the spectral response at the population level in forest species: Quercus cerris, Fagus Sylvatica and Pinus pinaster. Cloud computing was used through Google Earth Engine (GEE) to extract multitemporal values from the Sentinel 2 satellite and its subsequent integration with data from the TreeTalker spectrometer, devices installed in trees of 05 plots located in central and southern Italy, precisely in the Rocarespampani sector in Viterbo, Vesuvio National Park and Matese Regional Park in Campania Region.

Preliminary results show the ability of the TT+ spectrometer to store daily information at different wavelengths during the year. The spectral response of the near-infrared (NIR) bands is the most susceptible to foliage changes for deciduous species, mainly in the summer and spring seasons. In the case of visible bands (VIS), it is more susceptible to energy input in coniferous species and in the winter and autumn seasons. Finally, a higher correlation was obtained between the NIR bands of Sentinel 2 and TT+, mainly for the deciduous species Q. cerris and F. Sylvatica.

The seasonal assessment of the species will be continued during the following years at local and regional scales to understand their responses to climate change. Also, light transmission through the forest canopy will contribute to identifying and complementing knowledge of forest-climate interactions, allowing a more detailed understanding of the ecophysiological parameters of forest vegetation and phenological changes at the species and ecosystem level.

How to cite: Cotrina-Sánchez, A., Vaglio Laurin, G., Kabala, J. P., Niccoli, F., Yates, J., Valentini, R., and Battipaglia, G.: Integration of TreeTalker proximal data with remote sensing for monitoring seasonal phenological dynamics at the species level in Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4657, https://doi.org/10.5194/egusphere-egu23-4657, 2023.

A.210

EGU23-6819

ECS

Biodiversity threatened by increasing mountain forest loss

Xinyue He, Zhenzhong Zeng, Joseph Holden, and Dominick Spracklen

A.211

EGU23-13210

ECS

Highlight

What future for pollinators in the understorey vegetation under the impact of climate change ?

Benjamin Lanssens, Louis François, Alain Hambuckers, Merijn Moens, Tim Anders, Merja Tölle, Arpita Verma, and Laura Remy

Although understorey biomass is negligible in comparison to overstorey biomass, understorey vegetation supports the majority of biodiversity within forests. The diversity of plant species in the understorey is important for pollinators, such as bees and butterflies, which use the available resources for food and shelter. However, the future of understorey vegetation is uncertain due to the impact of climate change and human activities. Climate change and forest management are known to be among the most important factors affecting the diversity and abundance of understorey plant species. Most studies on understorey vegetation has often been limited in scope, either focusing on a small number of specific plant species or large-scale studies of plant functional types. In this study, we take a more comprehensive approach by combining the results of a species distribution model with a dynamic vegetation model to simulate the evolution of understorey vegetation at the species level. We select a set of 30 species important for pollinators. In order to cover a large climatic gradient, simulations are performed over the Walloon region in Belgium and the Eisenwurzen region in Austria. The climate dataset is provided by the regional climate model COSMO-CLM, which has a 3 km spatial resolution and covers the period from 1980 to 2070 under different greenhouse gas concentration scenarios (RCP 2.6 and RCP 8.5). Additionally, we investigate the effect of different forest management practices (thinning and clear-cutting) on overstorey and how they impact understorey vegetation. Overall, the study aims to provide new insights into the current and future state of understorey vegetation with a focus on the impact of climate change and forest management on key pollinator resources.

How to cite: Lanssens, B., François, L., Hambuckers, A., Moens, M., Anders, T., Tölle, M., Verma, A., and Remy, L.: What future for pollinators in the understorey vegetation under the impact of climate change ?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13210, https://doi.org/10.5194/egusphere-egu23-13210, 2023.

A.212

EGU23-8720

ECS

Fusion of European forest inventories with Sentinel-1 and Sentinel-2 data for improving scalability in estimating forest variables

Milto Miltiadou, Stuart Grieve, Julian Tijerín Triviño, Julen Astigarraga, Harry Owen, Paloma Ruiz Benito, and Emily Lines

Large scale forest inventory plot data are key to monitor forest ecosystems, but while they provide very detailed information at tree level they are limited in resolution in both space and through time. Earth Observation (EO) data offer the opportunity for scaling up plot data and improving the temporal resolution of monitoring. However, there are significant challenges to this, including small field plot sizes, pre-processing and potential GPS errors in aligning the data, whilst the huge amount and variety of EO data introduce substantial challenges of high dimensionality, in addition to the noise of training and testing data, within any AI system. In this work, we fuse plot and Earth Observation data, demonstrating the value of embedding existing and newly EO derived metrics, and selecting the most important features to improve monitoring of forest properties at large scales.

In this work we work with Sentinel-1 (SAR) and Sentinel-2 (optical) and inventory data from close to 10,000 plots in Spain, measured from onwards. SAR data require substantial pre-processing due to noise and acquisition, topographic and moisture effects. We used pre-processed SAR data, and filtered for non-shaded slopes, removed plots close to surface water and data collected on days with high precipitation. We masked out clouds from our optical data. After fusing the EO data, we removed disturbed areas using the Global Forest Change Collection and plots with high variability of pixels around them to reduce uncertainty due to the small sizes of the plots. As well as using standard indices (e.g., NDVI, RVI), we derive new metrics of the phenological cycle of the forest from monthly averages of indices and bands by selecting features from peaks and troughs. We reduce dimensionality using principal component analysis and random forest to select the most important features. Chosen features are used for training and evaluating a customized AI system to estimate forest variables such as total basal area, stem density, mean diameter at breast height and forest type. The code implemented in Google Earth Engine JavaScript and Python will be released as open source.

How to cite: Miltiadou, M., Grieve, S., Tijerín Triviño, J., Astigarraga, J., Owen, H., Ruiz Benito, P., and Lines, E.: Fusion of European forest inventories with Sentinel-1 and Sentinel-2 data for improving scalability in estimating forest variables, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8720, https://doi.org/10.5194/egusphere-egu23-8720, 2023.

A.213

EGU23-12291

ECS

Ecophysiological and mechanistic post-fire strategies of Pinus pinaster Aiton growing in an area prone to multi-stress conditions.

Francesco Niccoli, Marçal Argelich Ninot, Kabala Jerzy Piotr, Giovanna Battipaglia, Eric Verrecchia, and Pierre Vollenweider

The health of Mediterranean forests is seriously threatened by the effects of progressive climate change. Frequent droughts and heat waves induce heavy stress and favor the ignition of large wildfires causing decline in tree growth and mortality. Although trees are often able to survive the impact of fire thanks to their adaptive traits, partial injuries, such as crown defoliation, could compromise their physiology and resilience amplifying pre-existing climatic/site-specific stresses.

Expanding knowledge on the physiological and mechanistic dynamics of burned forests in areas prone to multi-stress conditions is crucial to identify the most resilient species capable of countering future rates of climate change.

In this context, our research aimed to understand the resilience of Pinus pinaster Aiton plantations located in the Vesuvius National Park, a particularly warm and dry area of southern Italy, affected by a large wildfire in 2017, which led to a progressive defoliation of trees in the post-fire years, reaching 50% in 2020. We selected different study sites along a wildfire severity gradient (control, low and medium burning intensity) and we applied a multi-parametric approach studying in the post-fire years (2017-2020): tree growth, intrinsic water use efficiency of the trees, morphological traits and needle nutrients in foliage, as well as the forest soil properties.

Morpho-anatomical analyses of foliage showed that although the burned stands suffered severe defoliation, resilience reactions already started in burned trees during weeks following wildfire, with the formation of larger but also more xeromorphic and defensive foliage (i.e. needles with higher linear weight and increased percentage area of resin ducts) than at the control site. On another hand, the needle nutrient content indicated for all sites severe deficiencies of main macro and micro-nutrients (especially N, P, K). Accordingly, soil analyzes highlighted a forest soil particularly poor in nutrients, and in burned sites the fire seems to have worsened the dystrophy by burning the nutrient pool in topsoil humus layer. Finally, the stem growth never recovered: tree-growth was steadily in decline in the burned versus control sites in the post fire years. Similarly, the intrinsic water use efficiency was reduced in burned stands indicating higher transpiration costs for assimilated carbon. The higher conductance, confirmed by the increase in the density of the stomatal lines found in needles, suggested the need of the burned trees to attempt a higher carbon uptake and counteract the carbon starvation in the stem triggered by the crown reduction.

Our results suggest that the studied burned stands are unlikely to recover their pre-fire performance. Carbon starvation will be difficult to reverse due to carbon retention in foliage to form new, heavier, and more defensive needles, also given the foliar nitrogen concentrations below deficiency level, further impeding assimilation. Therefore, the forest ecosystem reached a high vulnerability, not as a direct consequence of forest wildfire but due to the synergic effect of several stress factors: poor soil nutritional condition (exacerbated by the wildfire), an environment prone to drought stress and partial defoliation due to the fire (that lowered the tree photosynthetic capacity).

How to cite: Niccoli, F., Argelich Ninot, M., Jerzy Piotr, K., Battipaglia, G., Verrecchia, E., and Vollenweider, P.: Ecophysiological and mechanistic post-fire strategies of Pinus pinaster Aiton growing in an area prone to multi-stress conditions., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12291, https://doi.org/10.5194/egusphere-egu23-12291, 2023.

A.214

EGU23-9237

ECS

How late spring frosts affect tree-ring growth and wood anatomical traits of European beech in Mediterranean mountain forests?

Enrico Tonelli, Alessandro Vitali, Julio J. Camarero, Michele Colangelo, Davide Frigo, Francesco Ripullone, Marco Carrer, and Carlo Urbinati

Xylem anatomical traits in series of annual tree rings, allow establishing structure-function relationships and assessing species sensitivity to environmental variability. Extreme events such as late spring frosts (LSF) and drought spells are among the main climate-induced disturbances affecting European beech (Fagus sylvatica L.) forests, especially in the Mediterranean region. In this study we aimed to i) compare chronologies of tree-ring widths and vessel traits of beech trees located along an elevation gradient and ii) determine the variability of tree-ring traits before and after LSF occurrence. The study sites, located in the Italian Apennines and Spanish Pyrenees, were hit by severe LSF in recent years. We investigated how tree growth and vessel traits varied in relation to indicators of spring frost occurrence, i.e., mean minimum temperatures, accumulated degree days and temperatures anomalies. Then, we checked vessel traits in rings formed right after the frost events and compared them to those measured in non-affected trees. Radial growth reductions ranged from 36 % to 84 % and this negative effect of LSF on radial growth was only detected during the same LSF year. Growth fully recovered within 1–2 years after the LSF. We found a decrease of vessels diameter and surface area, and higher vessel density with increasing elevations. Vessel traits did not provide added values for detecting spring frost sensitivity. In fact, LSF caused the formation of very narrow rings but no-significant differences in vessels traits. Our results indicate a good recovery capacity of European beech and no legacy effects caused by LSFs. However, other xylem proxies (e.g., fiber cell wall) could better detect LSF impacts on wood formation.

How to cite: Tonelli, E., Vitali, A., Camarero, J. J., Colangelo, M., Frigo, D., Ripullone, F., Carrer, M., and Urbinati, C.: How late spring frosts affect tree-ring growth and wood anatomical traits of European beech in Mediterranean mountain forests?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9237, https://doi.org/10.5194/egusphere-egu23-9237, 2023.

A.215

EGU23-14520

Stress response and transformation processes initiated by the summer drought 2018 – a multi-scale study from the Hainich forest

Franziska Koebsch, Martina Mund, Anne Klosterhalfen, Steffen Dietenberger, Laura Donfack, Marius Heidenreich, Christian Markwitz, David Montero, Christian Thiel, Frank Tiedemann, and Alexander Knohl

More frequent and intense drought events pose one of the greatest threats to forests under climate change with substantial consequences for tree growth, ecosystem stability, and climate change mitigation. A better understanding of drought-related stress response and adaptation mechanisms is paramount to assess the adaptative capacity of forest ecosystems and deduce supportive management actions.

Here, we report on the stress effects and transformation processes initiated by the 2018 summer drought in the Hainich Nationalpark, an old-growth beech-dominated forest in Central Germany (DE-Hai). We deploy a multi-scale approach encompassing long-term eddy covariance measurements for stand-level CO₂ exchange, concurrent surveys of tree increments, and satellite imagery that covers the core zone of the National Park. Thus, we can provide a comprehensive picture of the response mechanisms that occur in a mixed old-growth forest in the wake of a severe drought.

After a 15-year reference period of relatively stable net CO₂ uptake of 535±73 g m² yr^-1on average, the summer drought 2018 persistently lowered the forest’s CO₂ sink function down to 333-395 g m² yr^-1 (2019-2021). The lowered CO₂ sequestration was primarily due to a sustained reduction in photosynthetic CO₂ uptake and went along with an increase in tree mortality from 1 to 6%. We observed a substantial shift in growth patterns among the surviving trees: Fraxinus excelsior, which in its role as competitor tree had contributed substantially to stand-level growth for a long time, showed significantly lower increments from 2018. At the same time, increments of Fagus sylvatica increased markedly after 2018. Especially younger, suppressed Fagus individuals benefitted in the post-drought period and pushed stand-level growth to a new record in 2021. On larger spatial scale encompassing the National Park core zone, drought response was overprinted by topographic effects that reflect landscape water availability, particularly altitude and routing of waterways.

Tree growth response to extreme water stress in a mixed, old-growth forest varies with regard to species-specific drought tolerance levels and/or the tree’s role in the forest structure. The natural growth dynamics emanating from drought events in unmanaged forests are modulated locally by landscape water availability, and can cumulate into profound structural change. At the early stage of transformation captured by our study, a reduction in productivity and climate change mitigation potential must be expected.

How to cite: Koebsch, F., Mund, M., Klosterhalfen, A., Dietenberger, S., Donfack, L., Heidenreich, M., Markwitz, C., Montero, D., Thiel, C., Tiedemann, F., and Knohl, A.: Stress response and transformation processes initiated by the summer drought 2018 – a multi-scale study from the Hainich forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14520, https://doi.org/10.5194/egusphere-egu23-14520, 2023.

A.216

EGU23-7456

ECS

Resilience and synergism in larch-beech-spruce mixed forests

Viktória Pipíšková, Jan Světlík, and Soham Basu

The current environmental conditions in Central Europe negatively affect tree growth and forest vitality. Mixing tree species may stabilize or even increase stand productivity and mitigate the effects of drought caused by climate change. However, the effects of mixing European larch (Larix decidua Mill.) with other species have not been assessed by systematic empirical studies. Accordingly, we studied the growth response of larch trees growing in middle-aged mixed stands with European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) in the highlands of the Czech Republic - Drahanská vrchovina (around 500 m a.s.l.). Four research sites with similar environmental conditions were selected to observe various forest mixtures: larch-beech-spruce, larch-beech, larch-spruce, and pure larch. 10 wood cores were collected at breast height from each tree species at the site (a total of 80 samples). Cores were measured and cross-dated by the dendrochronological software Past4. The radial increment of target trees with respect to the competition of the 10 nearest neighbouring trees was evaluated. Positions were measured with a Filed-Map system (IFER, Czech Republic). The competition indexes were calculated as the ratio between the DBH of the target tree and of the competitor divided by the distance between them. The resistance (growth reduction during the extreme year), recovery (growth response after the extreme year), and resilience (capacity to reach pre-disturbance growth) of target trees were calculated.

The even-aged stands with a different proportion of larch, beech, and spruce exhibited a different growth response under the same climatic conditions. In 2018 (the year with the most stressful climatic conditions in the last decade), a decrease in the tree-radial increment of spruces and beeches was observed. This did not occur in larches. They had a similar (only marginally better) growth response in monoculture compared to mixed stands. Tree resistance to the environmental conditions in 2018 was lower than a value of 1 for all tree species. However, beeches growing in the triple mixed stand were the most resistant. Surprisingly, larches in a monoculture exhibited a higher resistance compared to mixed stands. The highest recovery after the extreme conditions of 2018 was observed in larches growing in all variations of mixed stands. On the other hand, larches in a monoculture demonstrated nearly their lowest growth in the period 2019 - 2021. Only larches growing with beeches had a wood increment as high as prior to 2018 (higher resilience of larches growing with beeches). The other tree species reached their previous (2015 – 2017) increment in all stands with larches, so we can assume a positive effect of larch presence (increases the resilience of other tree species). We determined that the larches are not significantly influenced by competition with their neighbours. Furthermore, larches in monoculture are more resistant and larches growing in mixtures are more resilient with superior recovery.

Key words: competition, stem increment, recovery, resilience, resistance, tree-rings, wood cores

How to cite: Pipíšková, V., Světlík, J., and Basu, S.: Resilience and synergism in larch-beech-spruce mixed forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7456, https://doi.org/10.5194/egusphere-egu23-7456, 2023.

A.217

EGU23-5947

ECS

Responses of Fagus sylvatica growing in Southern Italy to climate change: insight from sap flow continuous monitoring

Jerzy Piotr Kabala, Francesco Niccoli, and Giovanna Battipaglia

The ongoing climate change, with altered precipitation regimes and altered evaporative demand due to the increase in temperature are affecting hydrological conditions in most forest sites in Europe. This change has strong consequences on the distribution, composition and ecological functioning of forest species . Fagus sylvatica is one of the most important species in Europe, spanning from southern Scandinavia to the Mediterranean region. Species distribution models forecast a reduction of the area of distribution of F. sylvatica in Italy under the climate change scenarios. The hydraulic behaviour and transpiration responses of the beech to climate conditions have been studied in central Europe. However, this has been scarcely addressed in the southernmost part of its distribution area, where this knowledge might be critical in understanding the physiological responses of this species to climate change, and then its capability to persist in the area.

This study aims to understand the responses of the transpiration of a Fagus sylvatica forest to meteorological variables in the southern Apennines (Matese Regional Park, Italy). The forest stand has been continuously monitored for 2 years with the TreeTalker devices, that record sap flux data at an hourly scale, along with several microenvironmental parameters. The monitoring period encompasses the droughty 2022 year, with high temperatures and precipitations well below the average.

The forest stand studied varies its sap flux in response to the environmental conditions, by reducing its transpiration in late summer, when VPD is high, but water availability is low. This conservative hydraulic behaviour seems to protect the trees from immediate damage due to drought periods, as no tree mortality has been observed. These results suggest that even if in the past Fagus sylvatica has been considered an anisohydric species, the southern ecotypes show a more isohydric behaviour than expected. The prosecution of this monitoring might provide further information about long-term trends in the ecophysiology of this forest.

How to cite: Kabala, J. P., Niccoli, F., and Battipaglia, G.: Responses of Fagus sylvatica growing in Southern Italy to climate change: insight from sap flow continuous monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5947, https://doi.org/10.5194/egusphere-egu23-5947, 2023.

A.218

EGU23-12037

Thermodynamic Approach to Assessing Ecosystem Integrity of Gwangneung Old-Growth Forest Biosphere Reserve in Korea

Joon Kim, Hyunyoung Yang, Minseok Kang, and Jung-Hwa Chun

Biodiversity and integrity are the key indicators representing ecosystem’s state. Much attention has been given to the former while less to the latter. This is because (1) the definition of integrity is ambiguous, (2) theoretical framework is lacking for quantitative assessment, and (3) observation data for quantification and validation are in paucity. The review of literature funnels down the definition of integrity to twofold perspectives: normative and thermodynamic. Accordingly, we define integrity as a state of ecosystem whose structure and function self-organize to an extent comparable to its reference state. Here, system’s self-organization can be expressed holistically based on non-equilibrium thermodynamics by quantifying the system’s thermodynamic entropy balance. We have tested this definition and the theoretical framework to assess the integrity of Gwangneung old-growth forest in Korea (GDK), which has been designated as one of the UNESCO’s Biosphere Reserves since 2010. Long-term observation (from 2005 to 2020) of energy, matter (water vapor and carbon dioxide) and information flows in and out of GDK were divided into the reference period (2006-2010) and the test period (2011-2020). These dataset emcompasses a wide range of environmental conditions and disturbances to examine ecosystem response and adaptability. GDK's self-organization was estimated in terms of entropy production (σ) and entropy transfer (J). Also, using information-theoretic approach, the behaviors of σ and J were analyzed in terms of the balance between informational emergence (flexibility) and self-organization (order, thus related to resilience). These results were compared and scrutinized by associating with the analyses of (1) linear cause and effect relationships between key variables representing ecosystem structure and function (e.g., energy capture, energy dissipation, biomass production, respiration, biodiversity) and (2) transfer entropy-based dynamic process network (of subsystems at various spatio-temporal scales, feedback types/loops and delay). Granting the necessity of further test and improvement, we argue that thermodynamic and information-theoretic frameworks are complementary and shed a light to development of more holistic and operational indicators for ecosystem integrity such as maximum complexity and antifragility.

How to cite: Kim, J., Yang, H., Kang, M., and Chun, J.-H.: Thermodynamic Approach to Assessing Ecosystem Integrity of Gwangneung Old-Growth Forest Biosphere Reserve in Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12037, https://doi.org/10.5194/egusphere-egu23-12037, 2023.

A.219

EGU23-14740

ECS

Assessing Resilience Components in Maritime Pine Provenances Grown in Common Gardens

Concetta Lisella, Serena Antonucci, Giovanni Santopuoli, Marco Marchetti, and Roberto Tognetti

Knowledge acquisition on the response of tree species to drought in the Mediterranean hotspot is an important step to guide adaptation strategies to climate change impacts, e.g., assisted migration.We assessed the resilience components - i.e., resistance, recovery, and resilience - to drought
in 2003 in five provenances of maritime pine planted in four common gardens in Sardinia, and analysed the possible influence of climate variables on these indices. The provenances showed differences in growth rate but not in the components of resilience. Among the provenances, Corsica
was the most productive, while Tuscany was the least. One of the two provenances from Sardinia (Limbara) showed good performance in terms of tree growth in the comparatively drier site. The resilience components were influenced by prevailing environmental conditions at the common garden
sites. In the relatively drier sites, trees showed the lowest resistance but the highest recovery values. However, two sites - which had the lowest stand density - showed the opposite trend during the drought year, probably due to moderate thinning. Predictive models showed different probability in
the response of resilience components to climate variables. Resistance and resilience had a similar pattern, both being positively related to temperature, while recovery showed an opposite trend. The models’ results indicate a noticeable adaptation of maritime pine to the drought conditions of Sardinia, though the age factor should be considered as well. Despite only minor differences among provenances being found, environmental conditions and management practices at the common gardens were important in determining tree growth patterns. This study suggests that the provenance of Corsica may provide appropriate material for forest plantations in Mediterranean conditions with mitigation purposes.

How to cite: Lisella, C., Antonucci, S., Santopuoli, G., Marchetti, M., and Tognetti, R.: Assessing Resilience Components in Maritime Pine Provenances Grown in Common Gardens, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14740, https://doi.org/10.5194/egusphere-egu23-14740, 2023.

A.220

EGU23-1418

ECS

Highlight

Digital forest inventory based on UAV imagery

Steffen Dietenberger, Marlin M. Mueller, Felix Bachmann, Markus Adam, Friederike Metz, Maximilian Nestler, Sören Hese, and Christian Thiel

Data on forest parameters defining the structure, health and condition of a forest stand is essential for forest management and conservation. The increasing frequency of forest changes, such as those caused by climate change-related drought and heat events, highlight the importance of having a forest database with high spatial and temporal resolution. Automated forest parameter extraction based on unmanned aerial vehicle (UAV) imagery is a cost-effective way to address the need for accurate and up-to-date forest data.

The aim of this project is to develop user-friendly tools based on optical data from UAVs that can be applied to accurately and efficiently conduct digital forest inventories. We are using spectral and geometric information from UAV data to create methods for automated derivation of forest parameters such as diameter at breast height (DBH), tree stem positions, individual tree crown delineation, and coarse wood debris. These methods are being designed with the practical needs of potential users from the forestry sector in mind. Different flight configurations, such as nadir and oblique camera angles, as well as different acquisition times, were combined to generate structure from motion (SfM) data products (dense 3D point clouds, orthomosaics and height models) containing both ground and canopy information. For a study site within the Hainich National Park, Germany, we analyzed how leaf-off and leaf-on data can be combined to improve the derivation of stand parameters, such as tree stem positions and individual tree crowns, using point- and raster-based algorithms. Additionally, DBH on an individual tree basis was derived for the same study site using the cast shadows of tree trunks. To do so, a deep learning model was trained to identify stem shadows based on an orthomosaic of only ground points acquired during sunny and leaf-off conditions.

How to cite: Dietenberger, S., Mueller, M. M., Bachmann, F., Adam, M., Metz, F., Nestler, M., Hese, S., and Thiel, C.: Digital forest inventory based on UAV imagery, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1418, https://doi.org/10.5194/egusphere-egu23-1418, 2023.

A.221

EGU23-17203

ECS

Wildfire impacts on soil characteristics in two Pinus halepensis Mill. stands within a Natura 2000 site (Southern Italy)

Luigi Marfella, Rossana Marzaioli, Gaetano Pazienza, Paola Mairota, Helen Catherine Glanville, and Flora Angela Rutigliano

Forest fires are a complex disturbance linked to several factors, such as climate conditions, vegetation types and human activities. Their frequency and intensity/severity have increased in recent decades and this trend is projected to continue because of climate change. Particularly critical are wildfires that frequently affect natural areas. In 2020 across Europe about 131474 hectares of surface within the Nature 2000 Network (N2K) were burnt. In addition to causing damage to vegetation, fire can affect soil characteristics influencing the functioning of the whole forest ecosystem. Understanding the influence of fire on the soil system provides information on its resilience and can be a useful tool for supporting forest management.

This research complements a larger multidisciplinary research project monitoring the conservation status, sensu Habitat Directive 92/43/EEC, of the Habitat of Priority Interest 2270*-Wooded dunes with Pinus pinea and/or Pinus pinaster, within the Special Areas of Conservation (SAC) IT9130006-Pinewoods of the Ionian Arch. Here, we explore the relationships between soil and vegetation as a function of different fire conditions considered capable of triggering multiple successional pathways, potentially leading to habitat degradation. In this context, the specific objective of this work was to evaluate the long-term effects of wildfires on the soil properties in two Aleppo pine stands within the “Romanazzi” and “Marziotta” sections of the SAC that have been influenced by fires between 1997-2006 and 2000-2012, respectively. In both stands, three sites were identified: double-fire, single-fire and unburnt (control) sites. In March 2021, a synchronic sampling across sites, covering a period of 9-24 years post-fires, was performed. In each of them, the weight and organic carbon content of the organic layer (O-layer) were measured alongside the physicochemical and biological properties of the underlying topsoil (0-10 cm depth, n=5).

Our results show the absence of the O-layer in double-fire sites, indicating a loss of this organic carbon pool. On the contrary, in both single-fire sites, this layer had successfully recovered. Our data suggest that the recovery in the O-layer in single-fire plots might be independent of the time elapsed since the wildfire. Regarding soil properties, compared to control sites, both single and double-fire sites for each stand exhibited significant alterations in specific soil chemical properties, i.e., pH, electrical conductivity, content in total organic carbon (C_org), extractable organic carbon, nitric and ammoniacal nitrogen, as well as decreases in soil microbial biomass (C_mic), respiration, and C_mic/C_orgratio. Of particular interest was a significant alteration in the N-cycle with increased mineralization and nitrification rates in all burnt sites at both stands. Principal component analysis showed that the impact of multiple fires may not depend only on frequency or time since the last fire, but also on frequency-time interaction.

In conclusion, the burnt sites have not recovered to control levels for many soil characteristics, especially for N-cycle processes. The increase in N mineralization, nitrification and, consequently, in N availability could induce shifts in the plant, fungi, and pedofauna community structure, thus affecting the successional pathways with consequences on the resilience of the target forest ecosystem.

How to cite: Marfella, L., Marzaioli, R., Pazienza, G., Mairota, P., Catherine Glanville, H., and Rutigliano, F. A.: Wildfire impacts on soil characteristics in two Pinus halepensis Mill. stands within a Natura 2000 site (Southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17203, https://doi.org/10.5194/egusphere-egu23-17203, 2023.

A.222

EGU23-2212

Is growth of Swiss stone pine at the alpine treeline impaired or enhanced by competition with N2-fixing green alder?

Walter Oberhuber, Ethan Salino, Lena Obexer, Gerhard Wieser, and Andreas Gruber

Green alder (Alnus alnobetula (Ehrh.) K. Koch = Alnus viridis (Chaix) DC) is a nitrogen-fixing pioneer species that is widely distributed at high altitude and latitude in the northern hemisphere. Due to changes in land management green alder is currently the most expanding shrub in the European Alps. It forms dense, tall thickets that are thought to impair establishment and growth of trees. The main focus of this study therefore was (i) to compare annual increments of Swiss stone pine (Pinus cembra L.), which is the dominant tree species at high elevation in the Central Eastern Alps, with that of green alder, and (ii) to determine radial growth of Swiss stone pine in competition and in absence of competition with green alder. The study area is situated within the treeline ecotone stretching from c. 1950 up to 2200 m in the Central Tyrolean Alps (Mt. Patscherkofel: 47.21 N, 11.46 E; Kühtai: 47.22 N, 11.04 E). A comparison of radial growth between similar aged stems (c. 20 yrs) revealed that annual increments of Swiss stone pine (2311 ± 628 µm) were more than four-times larger than those of green alder (519 ± 92 µm). This finding can be explained by different carbon allocation strategies, i.e., favouring vertical stem growth in single stemmed Swiss stone pine over preference of horizontal spreading in multi-stemmed green alder. This interpretation is supported by aerial photographs, which show that green alder stands are spreading vigorously within the treeline ecotone on Mt. Patscherkofel, amounting to c. 450 m² ha⁻¹ decade⁻¹. Radial growth measurements of Swiss stone pine occurring inside and outside green alder thickets (canopy height 2–3 m) revealed that Swiss stone pine individuals with a comparable height to green alder (tree height: 2.9 ± 0.8 m) showed significantly lower growth inside green alder stands than outside, while Swiss stone pine trees taller than green alder thickets (tree height: 6.1 ± 1.6 m) grew better inside than outside green alder thickets. We explain these findings by source limitation of Swiss stone pine growth at low tree height, whereas with increasing tree height carbon assimilation is no longer a limiting factor and the higher N₂ availability within green alder thickets can be exploited for stem growth. We conclude from this study that due to its horizontal competition strategy and dense cover of its foliage green alder is able to strongly impede the establishment and growth of co-occurring late-successional Swiss stone pine. Hence, spreading of green alder due to land abandonment and decrease in grazing pressure causes a delay in the development of closed forest stands, and also hampers climate warming induced advance of the alpine treeline.

This research was funded by the Austrian Science Fund (FWF), P34706-B.

How to cite: Oberhuber, W., Salino, E., Obexer, L., Wieser, G., and Gruber, A.: Is growth of Swiss stone pine at the alpine treeline impaired or enhanced by competition with N2-fixing green alder?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2212, https://doi.org/10.5194/egusphere-egu23-2212, 2023.

Posters virtual: Fri, 28 Apr, 10:45–12:30 | vHall BG

Chairpersons: Giovanna Battipaglia, Tamir Klein, Francesco Ripullone

vBG.2

EGU23-12088

Assessment of changes in wood anatomical traits to forecast drought-induced dieback in Mediterranean oak forests

Michele Colangelo, Angelo Rita, Marco Borghetti, J. Julio Camarero, Raúl Sánchez-Salguero, Luis Matias, Osvaldo Pericolo, and Francesco Ripullone

Some tree species have shown to be very vulnerable to drought and heat waves in the Mediterranean Basin, causing a loss of important socio-economic and ecosystem forest services. In this regard, oaks are important but vulnerable species which are showing losses in terms of productivity and growth and rising mortality rates. Dendroecological studies using retrospective analysis of wood anatomical traits and tree rings have demonstrated their potential to assess long-term patterns of growth and vigor in several Mediterranean oak species. Moreover, the long-term reconstruction of wood anatomical traits such as transversal lumen area, allows investigating hydraulic adjustments of trees through time.

In this study, we reconstructed changes in wood anatomy for a 38-year long period (1980-2017) to investigate how drought impacted the hydraulic functionality and triggered dieback in five ring-porous oak species from Italy and Spain (Quercus robur, Quercus frainetto, Quercus cerris, Quercus canariensis, Quercus pubescens). We compared non-decaying (ND) and decaying (D) coexisting trees of each species showing low and high defoliation levels, respectively. We analyzed earlywood anatomical traits (vessel area, hydraulic diameter, vessel density, theoretical hydraulic conductivity, etc.) in these species and analysed them considering a ranking of increasing drought tolerance: Q. robur, Q. frainetto, Q. cerris, Q. canariensis, and Q. pubescens.

We observed differing growth patterns and xylem conduit area responses in D trees compared with ND trees. The D trees formed narrower EW vessels than ND and the Dh were lower in D trees compared with ND trees. We discuss the relationships between radial growth, changes in wood anatomy and hydraulic functioning of trees focusing on those proved more sensitive to growth decline and mortality in order to highlight the climatic triggers of dieback in ring-porous oak species as related to hydraulic failure.

How to cite: Colangelo, M., Rita, A., Borghetti, M., Camarero, J. J., Sánchez-Salguero, R., Matias, L., Pericolo, O., and Ripullone, F.: Assessment of changes in wood anatomical traits to forecast drought-induced dieback in Mediterranean oak forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12088, https://doi.org/10.5194/egusphere-egu23-12088, 2023.

vBG.3

EGU23-9998

ECS

Structural overshoot and post-drought recovery depend on site and species-specific characteristics in Mediterranean mixed forests

Santain Settimio Pino Italiano, Jesús Julio Camarero, Angelo Rita, Michele Colangelo, Marco Borghetti, and Francesco Ripullone

Increasing drought severity can affect the healthy status of forests and determine changes in structural and ecophysiological responses to such extreme climate events. Reduced canopy cover, productivity and tree growth and recent dieback phenomena are widespread responses to drought. However, favourable climatic conditions can improve the post-drought recovery capacity of forests, but also make them vulnerable to drought damage through structural overshoot by altering the root to shoot ratio due to wet conditions. Due to the lack of integrated and retrospective field data, the patterns and responses of forests to wet-dry climate variability are still poorly understood. In this work we used remote sensing data (NDVI) to characterise the canopy conditions and combined them with field and tree-ring width data to assess the effects of the summer 2017 drought on Mediterranean tree species in southern Italy (Fraxinus ornus, Quercus pubescens, Acer monspessulanum, Pinus pinaster). By comparing radial growth and resilience indices we found that growth responses to drought depended not only on tree species but also on site conditions. Overall, the growth decline due to drought was followed by a rapid recovery, while negative legacies to drought were found at lower quality sites, which corresponded to sites with the lowest NDVI values. Indeed, trees at these sites showed high growth rates before drought, in response to wet winter-spring conditions, and then suffered more from drought stress. Our results demonstrated how structural overshoots predisposes to drought damage and induced negative legacies. Specific knowledge on the effects of drought overshoot over time is important for analysing and understanding current forest responses and dynamics.

How to cite: Italiano, S. S. P., Camarero, J. J., Rita, A., Colangelo, M., Borghetti, M., and Ripullone, F.: Structural overshoot and post-drought recovery depend on site and species-specific characteristics in Mediterranean mixed forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9998, https://doi.org/10.5194/egusphere-egu23-9998, 2023.