Displays

Following natural forest disturbances, additional anthropogenic disturbance may alter community recovery and successional trajectories by affecting the occurrences of species, functional groups and evolutionary lineages. However, our understanding is limited of whether rare, common, or dominant species, functional groups, or evolutionary lineages are most strongly affected by an additional disturbance, such as salvage logging. Here, we used a generalized diversity concept based on Hill numbers to quantify the community differences of vascular plants, bryophytes, lichens, wood-inhabiting fungi, saproxylic beetles, and birds following disturbances and experimental salvage logging. Most species groups showed no significant changes in dissimilarities between logged and unlogged plots over the first years of succession, indicating that salvage logging did not contribute to an accelerated decrease of initial dissimilarities. These dissimilarities between communities of were mainly driven by rare species. Trends in species dissimilarities only partially match the trends in dissimilarities of functional groups and evolutionary lineages, with little significant changes in successional trajectories. This talk highlights that salvage logging following natural disturbances can alter successional trajectories in early stages of forest succession following natural disturbances and that those changes persist over time. However, community changes over time may differ remarkably in different taxonomic groups and are best detected based on taxonomic, rather than functional or phylogenetic dissimilarities.

How to cite: Thorn, S.: Salvage logging cause short- and mid-term changes of successional trajectories following forest disturbance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2344, https://doi.org/10.5194/egusphere-egu2020-2344, 2020.

The vast majority of temperate and much of the boreal forest have been completely transformed by human activities, changing forest composition and disturbance regimes. Whilst our capability to observe this transformed state has improved dramatically in recent years, we have precious little information on the state of these forests in the absence of management. To what extent do our forests currently suffer from a surplus or a deficit of disturbance relative to their natural state? What are the implications of this for carbon turnover? Using a novel fusion of satellite observations of stand-replacing disturbances in 80 protected areas, statistical analysis and dynamic vegetation modelling, we generated wall-to-wall estimates of disturbance frequency across northern hemisphere temperate and boreal forests. Analysis of disturbance events in the protected areas revealed that the probability of disturbances from agents including fire, wind-throw and bark beetles was related to community mean functional traits and climate. We used the LPJ-GUESS dynamic vegetation model, which explicitly simulates plant functional types covering different successional stages, to simulate forest functional composition in the absence of human management. We interactively coupled this simulation to a new disturbance probability module to generate estimates of natural disturbance probability across all northern-hemisphere temperate and boreal forests. Disturbance frequency ranged from ca. one stand-replacing event per hundred years in parts of the boreal to less than one per thousand years in broadleaved temperate forests. In many regions the unmanaged disturbance frequencies differed dramatically from those observed in reality over the last two decades, with both disturbance surplus and deficits being recorded. In addition to providing the first quantitative continental-scale assessment of human impact on forest disturbance regimes, our results also provide a lightweight modelling approach for the inclusion of natural disturbances in large-scale vegetation models. They thus facilitate simulation of forest structure, a crucial driver of ecosystem function, from carbon uptake to biodiversity.

How to cite: Pugh, T., Senf, C., and Seidl, R.: What is the natural rhythm of temperate and boreal forest disturbances in the absence of human management?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2910, https://doi.org/10.5194/egusphere-egu2020-2910, 2020.

Bark beetle (Ips typographus) epidemics in Europe are typically triggered by excessive availability of freshly dead trees and trees with compromised defense, which often occur after windstorms or droughts. Subsequently, enlarged beetle populations migrate to the surrounding forests, which were not affected by the primary disturbance. Removal of windfelled trees (salvage or sanitation logging) is therefore a frequent management response to prevent the build-up of bark beetle populations. Yet, the effectivity of the removal remains poorly understood, particularly when the outbreaks are amplified by faster beetle development cycles and reduced tree defense under climate change conditions.

Moreover, diverse ownership, management objectives and limited resources often restrict salvaging operations, and the final effect on bark beetle populations is thus even less clear. To better understand the interplay between climate, management, bark beetle populations, and host trees, we use the process-based forest landscape and disturbance model iLand. We studied differences between the removal of windfelled trees applied evenly across the landscape, focused on the vicinity of roads (scenario of limited logging resources) and concentrated in a contiguous block (scenario of spatially diversified management objectives) on a 16 050 ha forest landscape in Central Europe. We found that the removal of >80% of all windfelled trees is required to substantially reduce bark beetle disturbances. Focusing on the vicinity of roads created a “fire break effect” on bark beetle spread, and was moderately efficient in reducing landscape-scale bark beetle disturbance. Block treatments substantially reduced outbreaks in treated areas. Leaving parts of the landscape untreated (e.g., conservation areas) had no significant amplifying effect on outbreaks in managed areas. Our research suggests that the management of interacting disturbances from wind and bark beetles requires much more complex considerations than are currently practiced.

How to cite: Dobor, L., Hlásny, T., Rammer, W., Zimová, S., and Seidl, R.: How to manage windthrows in Central Europe to prevent bark beetle outbreaks?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3030, https://doi.org/10.5194/egusphere-egu2020-3030, 2020.

It has been recently demonstrated that large-scale mechanisms interact with Amazon deforestation to delay the onset and decrease the duration of the rainy season in Southern Amazonia. A short rainy season increases the exposure of the rainforest to drought and possibly fires, but also increases the climate risk to the intensive double cropping (soy/maize) agriculture system practiced in the region, which requires at least 200 days of rains. Here we show that areas in Southern Amazonia that have more than 20% deforestation, i.e., areas that have not respected the maximum deforestation allowed by Brazil´s Forest Code, have increased climate risk for agriculture when compared to areas that have less than 20% deforested. These results show how environmentally sensible the Brazilian Forest Code is. The legislation, if strictly followed, supports the climate regulation service provided by the rainforest, in a way that benefit the farmers that collectively respect the legislation by anticipating the onset and increasing the duration of the rainy season and decreasing the climate risk to the double cropping systems. These results introduce a new paradigm for conservation of the Amazon, in which there are economic and social reasons to preserve the native vegetation, and it is in the best interest of the agribusiness, local governments and people, to conserve and restore the remaining natural vegetation.

How to cite: Heil Costa, M.: Onset of the rainy season: a paradigm shift for conservation of the Amazon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4112, https://doi.org/10.5194/egusphere-egu2020-4112, 2020.

On July 15, 2006, heavy rainstorm-triggered debris flow destroyed mature riparian forests and altered the channel geomorphology along the Hangye stream, Mt. Seorak National Park, Republic of Korea. We examined the effect of the topographic site condition on the initial establishment and growth of pine trees (Pinus densiflora) as one a dominant species of riparian vegetation along transects on new debris flow terraces formed along the Hangye stream. In the 2019 field investigation, the tree age and internode length of all P. densiflora seedlings were measured in each 25-m² plot placed at 5-m intervals for a total of 19 cross-section lines marked by a topographic survey using an auto level. For data analysis, stream channel morphology was classified into two typical types: a single channel segment with only the main channel (type A; total of 14 cross-section lines) and divergent channel segment with the main and several secondary channels (type B; total of 5 cross-section lines). The height (Hq) and distance (Dq) of each surveyed plot from the thalweg line of the main channel were considered as topographic site conditions with reference to the establishment and growth of riparian vegetation. As a result, the mean Hq and mean Dq were all greater in plots with the appearance of pine trees than in those without in both type A and type B segments, showing statistical significances at the 1% level. This study also showed that the mean age and mean annual growth rate of P. densiflora seedlings were positively correlated with Hq in type A segments but not in type B segments. Dq showed no correlation with the mean age and mean annual growth rate of P. densiflora seedlings in both type A and type B segments. These results demonstrate that the initial establishment and growth of riparian vegetation were affected by the height above the channel bed associated with the flood frequency and divergent flood flows.

Acknowledgement: This work was supported by the National Research Foundation (NRF) grant funded by the Korea government (MSIT) (No. NRF-2017R1C1B5076781).

How to cite: Kim, S. W., Lee, J. U., Lim, Y. H., Nam, S., Chun, K. W., and Kim, M. S.: Topographic effects on the initial establishment and growth of pine trees as a riparian vegetation after debris flow-induced disturbance in a mountain stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7429, https://doi.org/10.5194/egusphere-egu2020-7429, 2020.

How to cite: Sebald, J., Thrippleton, T., Rammer, W., Bugmann, H., and Seidl, R.: The role of alpha and beta diversity in buffering the effects of intensifying natural disturbance regimes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8248, https://doi.org/10.5194/egusphere-egu2020-8248, 2020.

As disturbances are predicted to increase both in terms of frequency and severity due to global changes, it is important to improve our knowledge on their natural regimes in order to adopt an appropriate management to enhance the resilience of forest stands. In this context, the assessment of disturbance regimes in old-growth forests is becoming increasingly important because these ecosystems are considered as reference systems that developed without significant human impact for long periods of time. In the temperate zone of Europe only few fragments of mountain forests perhaps succeeded to persist despite millennia-long anthropogenic land-use pressure. However, few studies support their long-term stability and continuity in a changing landscape. Our study focuses on one of the largest and well-preserved old-growth forests in the Balkans. It is situated in the Biogradska Gora National Park reserve, whose extension (c. 6000 ha) is large enough to recognize the natural range of variability of disturbance processes. Under informal protection (hunting reserve) since 1878, the area became National Park in 1952. At present the forest is dominated by beech, silver fir and Norway spruce. We assume that the old-growth forest stands dominated by coniferous trees, which are currently confined to the inner part of the reserve, were more widespread in the past, and that their area was strongly reduced due natural disturbances and land-uses (e.g. grazing activities, fires, forest exploitation) that may have promoted the spread of beech. We used orthorectified high-resolution Pléiades satellite images (0.5-2 m) and field surveys of forest structures and composition to assess the spatial patterns of successional stages of forest development, thereby indirectly tracing the recent disturbance regime. However, such datasets are unable to unfold longer-term trends and to identify the type of disturbances. Moreover, carrying out dendrochronological research both on living and dead biomass is banned in the reserve area. Thus, we reconstructed longer-term changes in species composition, and disturbance and land use histories using pollen, plant-macrofossils, and charcoal analyses from sediments spanning the past 1000 years. Sediments were collected from a small forest hollow situated on the edge of the present old-growth forest reserve. We found that on the edges of the reserve forest cover dominated by conifers (mainly Abies) was reduced due to land-use activities (agriculture, cattle grazing), as suggested by Cerealia-type pollen and Sporormiella spores. The expansion of beech populations, which are dominant around the forest hollow today, occurred very recently. What emerges with the current level of detail achieved in our study is that tree cover and composition changed substantially over time on the edge of the old-growth forest reserve. This suggests that the edges of the reserve were disturbed and consequently not characterized by long-term stability and continuity of vegetation. Expected results will advance awareness of the legacies of past environmental changes and forest-management on current ecosystems. This multidisciplinary study, in a poorly explored area as the Balkans, will permit to anticipate biotic responses of these important mountain ecosystems in front of future environmental changes, providing useful information for their management and conservation.

How to cite: Cagliero, E., Morresi, D., Paradis, L., Marchi, N., Meloni, F., Curovic, M., Spalevic, V., Bentaleb, I., Motta, R., Finsinger, W., Garbarino, M., and Lingua, E.: Exploring the long-term vegetation and fire-disturbance history of the Biogradska Gora old-growth forest (Montenegro), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9910, https://doi.org/10.5194/egusphere-egu2020-9910, 2020.

Wildfires pose a great threat to the wildland-urban interface (WUI), the zone of contact between wildland vegetation and the human-settled environment. In these areas, high fuel loads often coexist with high value assets, which are more exposed to ignition than equivalent structures in an urban context. At the WUI, wildfires can quickly exhaust the resources normally available to urban firefighters, and the value of assets do not allow the use of large-scale, resource-saving techniques common in wildland fires management.

Mapping the WUI represents a first important step in wildfire risk management due to the primary importance of prevention in a setting that is difficult to defend in the face of emergencies. In addition, as the WUI is not only a possible target for wildfires, it is often a source of them, prevention of fire in these areas is a critical part of risk management.

Several methods are currently available to detect and map the WUI, differing according to the scale and the scope of the analysis. Pioneering methods mainly used aggregated data (e.g. census data, large scale vegetation maps) while recent techniques are increasingly using high precision remote sensing data to identify single structures and local changes in topography and vegetation.

In the context of the UE Interreg project Italia-Slovenija CROSSIT SAFER, a new methodology will be described to analyse and map wildfire risk at the WUI relying on state-of-the-art data and technologies. Specifically, high precision LiDAR data and segmentation processes are used to characterise wildland fuel precisely and efficiently.

How to cite: Taccaliti, F., Marzano, R., Rizzolo, R., Bell, T., Fischetti, D., and Lingua, E.: New methodology for mapping wildfire risk in the wildland-urban interface, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10583, https://doi.org/10.5194/egusphere-egu2020-10583, 2020.

Due to climate change suitable forest management measures are required to mitigate the proposed exacerbating drought events as already observed in central Europe in summer 2003, 2015, 2018, and 2019. This contribution summarizes the findings of two long-term field experiments studying different forest management measures aiming at mitigating drought in forest stands.

The first study investigated the potential of mixing tree composition for mitigating drought stress in Norway spruce (Picea abies [L.] Karst.). To this end, a five-year study with repeated summer droughts, experimentally induced via throughfall-exclusion (TE), was performed. The study objects were mature (60-80 years) old stands of Norway spruce in monoculture and mixture with European beech (Fagus sylvatica (L.). The impacts of repeated summer droughts were assessed on about 100 trees distributed on 12 plots and accessible via canopy crane (Kranzberg forest ROOF experiment in southern Germany). Predawn leaf water potentials of Norway spruce reached minima of -1.8 MPa, but were not affected by species mixture. Nevertheless, daily xylem sapflow density was increased up to 40% in mixture compared to pure strands. Likewise, stem growth, i.e. relative basal area increment, showed significantly higher drought resistance in mixture compared to monocultures.

While altering forest stand composition seems to be promising on the long-term, the conversion from monocultures is often economically not suitable for young stands in the short- to medium-term. Therefore, reducing intraspecific competition via thinning is a frequently discussed option investigated in the second, eight-year-long study. In a 26-year old Norway spruce monoculture, three thinning intensities, i.e. unchanged (control), moderate thinning (MT with reduced basal area by 43%) and heavy thinning (HT, reduced basal area by 67%) were applied, potentially mitigating drought by reducing intraspecific competition and increasing soil water availability. Indeed, in both thinning intensities the duration of drought stress for the trees (soil water content below critical value) was reduced compared to controls for up to 5-7 years following the event. However, increased radiation and higher growth rates of the individual trees accompanied by the fast establishment of a vital ground vegetation diminished the difference in stand transpiration between MT and HT within two years. Moreover, belowground competition with the understorey vegetation suppressed fine root recovery under HT compared to MT in contradiction to increased leaf area on HT on tree-level and therefore increased transpirational demand.

The presented studies suggest admixing of broadleaved beech into monocultures of Norway spruce to be a promising management measure in the long-term. In juvenile monocultures of Norway spruce frequent and intense thinning interventions while preventing the establishment of a vital understorey vegetation appears to be a promising forest measure, mitigating drought without losing sight of economic needs.

How to cite: Gebhardt, T., Hesse, B. D., Grams, T. E. E., Ammer, C., and Häberle, K.-H.: Mitigation of drought stress in forest stands - insights from a throughfall-exclusion and a thinning experiment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10592, https://doi.org/10.5194/egusphere-egu2020-10592, 2020.

Wind disturbance to forests extends across spatial and temporal scales and encompasses direct and indirect wind effects on the dynamics of forest ecosystems. It is detrimental to the provision of ecosystem services and reduces forest resistance and resilience to future natural disturbances. Historically, in the ecological and land-use scientific communities, forecasting the extent and probability of wind disturbance to forests has represented a serious challenge, with most studies electing to adopt qualitative or statistical approaches. The low degree of portability of statistical assessments of vulnerability to wind has limited their applicability and use, but it is recognised that they have a role in building hypotheses of the processes involved in wind damage that can be subsequently tested under experimental conditions. Results from tree stability experiments have contributed, in the last two decades, to the development of a mechanistic model of wind damage - ForestGALES. This is a process-based wind risk model that was originally created to inform the management of commercial forest plantations in the UK. Built on principles of forest science, physics, and ecology, ForestGALES requires a simple set of inputs and it has now been expanded to cover more than 20 common conifer species from across three continents, and multiple broadleaved species (e.g. Oak, Beech, Birch, and Eucalypts). Two methods of assessing vulnerability to wind damage are available in ForestGALES, one designed for application at stand level, and a novel approach that estimates vulnerability to wind at the individual tree within a stand – the latter allowing for use in complex forest stands, and for the effect of competition between trees in a stand. Until recently, ForestGALES was only available as desktop software and as an online tool as part of forest decision support systems (only for selected countries and species). These formats can be limiting for research and academic projects that aim to model and understanding wind disturbance dynamics across diverse landscapes, and that require a bespoke approach with a high degree of flexibility. To accommodate these broader requirements, ForestGALES has recently been redeveloped and released as a FOSS R package (“fgr”) that is fully customisable and easily integrated in R and modelling workflows and FOSS GIS frameworks. With this poster we present two exemplar studies of assessing wind damage risk to forested landscapes, one for each ForestGALES method (stand- and individual trees level), to showcase the capabilities and flexibility of the model in working with e.g. climate projection data, with other process-based models (e.g. 3PG) within an R modelling framework, and with LiDAR data, at the individual tree level.

How to cite: Locatelli, T., Hale, S., Nicoll, B., and Gardiner, B.: Flexible open-source software for modelling wind disturbance and damage to trees and forests, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10829, https://doi.org/10.5194/egusphere-egu2020-10829, 2020.

Mangrove ecosystems play an important role in carbon sequestration of coastal wetlands through litterfall and soil carbon accumulation. Maximum canopy height (H_max) is a key variable in assessing above-ground carbon stocks and productivity, and it is relatively easy obtained from forest inventories or satellite remote sensing products. However, the drivers that regulate canopy height in these ecosystems are still poorly understood. It is a common assumption that climatic drivers, such as precipitation and air temperature, account for most of the mangrove height variability. Nevertheless, local productivity and carbon allocation are known to be largely controlled by salinity, which represents one of the dominant sources of abiotic stress in tidal environments. Yet, the control of salinity on canopy height has received scarce attention in the literature.

In this study, we present a global analysis of H_max as a function of seawater salinity, species richness, and air temperature. Our results identify both salinity and air temperature as major abiotic co-factors in control species richness and H_max. For example, the largest number of species is observed in Southeast Asia (> 25), where high temperature co-occurs with low salinity. In contrast, low temperatures in subtropical zones and high salinity in arid regions strongly limit diversity. Such low diversity is generally associated with mangrove ecosystems with short canopy. The multivariate analysis of both global and regional patterns reveals that salinity is the main limiting factor for H_max, while the air temperature is mostly unrelated to H_max. The effects of salt-stress are particularly evident in ecosystems with low species richness (number of species ≤10), while it does not have a detectable effect on H_max in species‐rich communities (number of species >10).

We hypothesize that high stress induced by salinity reduces the niche breadth and decreases competition for above-ground resources, limiting diversity and H_max. On the other hand, more tolerable salinity conditions might promote species coexistence, competition for light, therefore increasing canopy height and mangrove productivity through complementary resource utilizations.

How to cite: Perri, S., Detto, M., and Molini, A.: Salinity and species richness determine mangrove canopy height, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16742, https://doi.org/10.5194/egusphere-egu2020-16742, 2020.

Forest dynamics triggered by natural disturbances occurred in the Aosta Valley region were spatially mapped over time using long-term trends derived from Landsat time series spanning over 35 years, from 1985 to 2019. Among biotic and abiotic disturbance agents, the following were selected: wildfires, windthrows, snow avalanches, landslides and insect outbreaks. Landsat TM, ETM+ and OLI images acquired during the vegetative season (from June to September) with less than 80% cloud cover were employed to create synthetic images at one-year interval using the geometric median approach at the pixel-level. Forest dynamics due to disturbance occurrence and the following vegetation recovery were explored through inter-annual time series of different spectral indices such as normalized vegetation indices (Normalized Burn Ratio, Normalized Moisture Index) and the tasseled cap band transformations (wetness, angle). Changes in the linear trends of the spectral indices time series caused by disturbance occurrence were detected using a novel bottom-up approach in which a wavelet basis is adaptively constructed by merging neighbouring segments of the data. This method doesn’t require a priori knowledge of the time series parameters making it fully automated. Prior to perform the trend analysis, vegetation indices time series were filtered to remove residual invalid pixels and fill gaps of one-year length. Considering abrupt disturbances, this method highlighted sensitivity toward both high and low magnitude events and was able to accurately detect different severity degrees within the perimeter of the affected forest area. Historical wildfire perimeters and crown fires patches provided by the forest fire fighting corps of the Aosta Valley were used to perform preliminary severity maps validation. Considering two severity classes, ‘low to moderate’ and ‘moderate to high’, maps produced using the Normalized Burn Ratio achieved an overall accuracy of 83%. Future work is aimed to validate all the selected natural disturbance agents using historical field data available at the regional scale. Moreover, a rigorous and wide scale-based assessment of the capabilities of the algorithm in tracking post-fire forest recovery will be performed by integrating forest structure data from filed surveys and airborne LiDAR measurements.

How to cite: Marzano, R., Morresi, D., Lingua, E., Motta, R., and Garbarino, M.: Mapping forest natural disturbances dynamics in the Aosta Valley (Italy) through long-term trends derived from Landsat time series and innovative statistical approaches, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19901, https://doi.org/10.5194/egusphere-egu2020-19901, 2020.

Regional ecological security diagnosis is the most basic prerequisite for environmental management and restoration. However, the traditional single method is greatly affected by human and difficult to quickly identify. Thus, This paper combined principal component analysis and unsupervised k-means clustering algorithm to provide a fast and efficient method for  safety evaluation of environmental management. Basing on this method, the clustering result was defined as five different levels of ecological safety zone combining with the principle of place name + landform + danger degree. The results showed that there were more than half of the study area were unsafe (56.3%), what was even more surprising was that there were many high-value of NDVI and NPP in these areas. The partition result was finally verified in order to ensure the accuracy of the partition, and it had been proved that the ecological environment is not necessarily safe where in the areas with good vegetation coverage. This article provided a new technical reference for the evaluation of ecological areas.

How to cite: Bai, X. and Chen, H.: Ecological security assessment for environmental restoration and management in SW China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21067, https://doi.org/10.5194/egusphere-egu2020-21067, 2020.

In recent years, due to climate and environmental change, most forest areas suffer from land degradation, mainly caused by the bark beetle disturbance which damaged many tree species. The complex multiple interactions between climate and influence factors have highlighted the need for an efficiency integrated model based on decision support system, determining important implications and support for forest management planning. Based on expert perceptions, the Bayesian Belief Networks (BBN) approach provides a more consistent method of handling uncertainties, aiming to facilitate the interpretation of interdependencies between factors considered against risk. In this research, we have developed a BBN algorithm and program to estimate the potential risk in national scale, this technique was compared to the fuzzy logic model. Both models propose rapid solution for solving complex decision problems, they could be reused in other worldwide similar study areas.

How to cite: Tahri, M., Kašpar, J., Vacik, H., and Marušák, R.: Predict potential risk of bark beetle disturbance applying Bayesian Belief Networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21348, https://doi.org/10.5194/egusphere-egu2020-21348, 2020.