Drought-induced tree mortality in the Anthropocene has increased at an unprecedented rate and is expected to increase even more sharply in the next few decades due to anthropogenic climate change. Fennoscandian boreal forests are particularly at risk of drought-related mortality because they are less adapted to drought conditions compared with lower latitude forests. Currently, tree mortality research is inhibited by a lack of data on tree deaths, but we can still anticipate mortality events by monitoring forest health. In this study we determine indicators of forest ‘hydraulic health’ which we define as the ability of a forest to withstand and recover from drought events. Ultimately, this may help to predict and prevent drought-induced tree deaths under future climatic shifts.  

 To describe the hydraulic health of Fennoscandian forests we examine vegetation water content at both short (sub-daily) and intermediate (weekly) timescales using remotely sensed vegetation optical depth (VOD) measurements. Whilst short-timescale VOD is more tightly linked to water stress, intermediate-timescale VOD can demonstrate forest resilience and recovery to drought events. Here, we use a multivariate time series model to integrate VOD measurements at different timescales, presenting a novel opportunity to disentangle the drivers and responses of forests to drought. 

 The method introduced here is a first step towards quantifying abiotic hazards for forests. By focusing on smaller time steps of VOD data we can minimise the noise attributed to biomass changes over time and can better detect changes in vegetation water content. We hope that by quantifying hydraulic health indicators, they can serve as an early warning system for drought-induced mortality or help in predicting other hazards such as wildfire. Although we focus on Fennoscandian forests, in principle, these methods could be applied to other biomes.  

How to cite: O'Sullivan, H. and Junttila, S.: Quantifying the Hydraulic Health of Fennoscandian Boreal Forests in a Changing Climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10975, https://doi.org/10.5194/egusphere-egu24-10975, 2024.

Excess tree mortality in the wake of climate extremes has been observed globally. However, we still lack precise data on mortality at global scale to understand respective drivers and spatiotemporal dynamics. The Sentinel-2 satellite fleet, equipped with the MultiSpectral Instrument (MSI), covers the entire earth on average every five days at spatial resolutions ranging from 10 m to 60 m. Mapping tree mortality from Sentinel-2 globally in diverse ecosystems requires equally diverse reference data. Using globally distributed high-resolution aerial orthoimagery reference data and artificial intelligence methods, we can translate spectral signatures of remote sensing into deadwood. Specifically, in this study we show how to predict the share of standing deadwood for a 10 m pixel in a specific year. The method takes into account temporal patterns, spatial context, as well as all Sentinel-2 spectral bands. This will enable us to map tree mortality globally at a new level of precision.

How to cite: Mosig, C. and the co-authors: Mapping Tree Mortality at Global Scale Using Sentinel-2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18230, https://doi.org/10.5194/egusphere-egu24-18230, 2024.

The effects of climate extremes on the vulnerability to forest dieback of widely distributed Mediterranean pine species are poorly understood but important for forecasting their responses to climate change. As air temperature increases, evaporative demand will also rise, exceeding the drought tolerance of tree species to pervasive droughts. Using a spatially comprehensive network of six pine species with > 800 tree-ring chronologies, > 500 plots from the the ICP-forest network (defoliation, moratlity, etc) and drought-induced mortality database combined with NDVI (Normalized Difference Vegetation Index) encompassing the wide ecological and climatic gradients across Mediterranean Basin. We show that an increase of climate water deficit produced legacy post-drought effects on growth with strong variation in growth across its distributional range, but common patterns were found within each provenance. Vulnerability to legacy effects of extreme droughts were most prevalent in dry provenances and western, in contrast to limited legacy effects after drought observed in wet provenances and high-elevation sites. Post‐drought legacies decreased with latitude and wetter conditions but decreased with spring precipitation in western mediterranean. Trees from dry, rear-edges sites in the Mediterranean Basin were more vulnerable to recurrent droughts than trees from wet. The increase in summer temperature and evapotranspiration favour hotter droughts that can increase defoliation, decrease tree growth and productity casusing drought-induced forest dieback in drier regions over the next decades.

How to cite: Sanchez-Salguero, R., Gazol, A., Vicente-Serrano, S., Battipaglia, G., Ripullone, F., Hevia, A., and Camarero, J. J.: Global change effects on Mediterranean pine forests: hotspots of dieback, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19939, https://doi.org/10.5194/egusphere-egu24-19939, 2024.

Stomatal conductance is the principal mechanism of plants to regulate transpiration rates in response to environmental conditions. However, disturbances directly affecting leaves, such as outbreaks of defoliating insects, can impact the ability of trees to control canopy water loss, leading to significant shifts in plant water relations and forest water budget dynamics. One such example is the pine processionary moth (Thaumetopoea pityocampa; PPM), the main defoliating insect of pines and cedars in the Mediterranean Basin, that could have a significant effect on forest ecohydrology and tree vulnerability to drought. However, despite its potential relevance, PPM effects on tree water use patterns remain largely unexplored. Our study aimed to assess the effects of PPM defoliation on tree hydraulic patterns over time, and on tree stomatal sensitivity to soil water limitations during and after defoliation periods. We conducted a 12-month study of two stands in a Pinus nigra forest affected by PPM in Spain by combining measurements of stem sap flux, soil water content, and micrometeorology. The selection of the study site was based on the high presence of PPM nests during October and November, marking the onset of the defoliation period. In each stand, we installed 15 sap flux sensors on trees with contrasting abundance of PPM nests. These devices recorded sap flux density (Js), air temperature and air relative humidity at an hourly resolution. Ten TMS-4 dataloggers were also placed in each stand to measure soil temperature and soil water content (SWC) to a depth of 14 cm. The percentage of defoliation was visually assessed both at the beginning and at the end of the defoliation period, in November and next season May. Sensitivity in tree water use to changes in soil moisture was determined using stepwise regression models to estimate the breakpoint at the tree level between SWC and Js, representing the point at which constraints on water use shifts from SWC to atmospheric vapor pressure deficit (VPD). We hypothesized that defoliation would initially increase tree water use in relation to VPD due to damage to the leaf cuticle and/or reductions in stomatal sensitivity to aridity as the leaves are consumed by PPM. Results indicate a transitory increase in sap flux density with defoliation, with differences between the trees that tend to be reduced over time. By offering novel insights into the importance of defoliation in water use patterns and its regulation in relation to environmental conditions, our study contributes to enhanced decision-making for water conservation efforts.

How to cite: Houdas, H., Hernández-Alonso, H., Olano, J. M., Hultine, K., Bush, S., Guo, J., de la Encarnación Coca, M., and Sangüesa-Barreda, G.: Impacts of pine processionary moth defoliation on tree water use patterns, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22250, https://doi.org/10.5194/egusphere-egu24-22250, 2024.

The Mediterranean basin is exposed to a growing risk of forest fires due to recent climate changes, which are increasing their frequency and intensity. Forest fires can profoundly alter the ecological functions of Mediterranean forests, affecting hydrological regulation, resource supply, soil stability and biodiversity conservation. They also cause physiological dysfunction and tree mortality, significantly reducing the ability of forests to absorb CO₂ and mitigate climate change. The study of fire effects is therefore essential for planning effective post-fire management practices and strategies for future fire regimes. Current technological advances allow the integration of ground surveys with satellite analysis, providing a comprehensive approach to fire studies and accurate assessments of ecological effects and post-fire dynamics.

In this context, our research focused on analysing the impacts of a forest fire that occurred in July 2017 in a Pinus nigra Arnold forest on Mt. Cairo in central Italy. We integrated satellite analysis to identify fire-affected areas with forest surveys and tree-ring analysis to assess impacts on tree growth, water use efficiency and post-fire CO₂ uptake.

Our results highlight the importance of using remote sensing to accurately identify fire-affected areas and accurately plan ground-based activities. While remote sensing is key to providing an overview of fire size and distribution, it is equally important to integrate this data with detailed field surveys. In particular, the use of dendrochronology and stable isotopes in tree rings allowed us to assess post-fire tree growth and changes in water use. Our analyses showed that defoliated trees experienced a significant reduction in growth and change in water use due to severe canopy damage. We also found a significant reduction in the ability of damaged trees to absorb CO₂ from the atmosphere, highlighting serious implications for the ecosystem service of carbon sequestration.

In conclusion, our study shows that the combination of satellite and ground analysis provides a comprehensive understanding of the effects of forest fires, which can significantly contribute to the recovery and restoration goals of fire-affected areas.

How to cite: Niccoli, F., Altieri, S., Kabala, J. P., and Battipaglia, G.: Integration of satellite and ground-based analyses in the assessment of Pinus nigra Arnold forest fires, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5225, https://doi.org/10.5194/egusphere-egu24-5225, 2024.

El Niño’s impact on tropical forests is critical, as reduced rainfall and severe drought induced by this phenomenon affect species diversity and tree dynamics. As seedling is a crucial stage for forest regeneration to maintain population and species diversity in the forest, it is important to understand how El Niño-induced drought affects seedling dynamics. We monitored the seedling dynamics at monthly intervals for 7 years in a seasonally dry tropical forest (SDTF). We analyzed the differences in seedling recruitment and mortality during the El Niño and non-El Niño periods and compared two forest types in an SDTF: a deciduous dipterocarp forest (DDF) dominated by deciduous species, and an adjacent lower montane forest (LMF) with more evergreen species. The long-term data on seedling dynamics revealed that El Niño-induced drought triggered immense seedling mortality in both forest types. This effect was stronger in evergreen species, leading to higher mortality in the LMF during El Niño. However, El Niño increased seedling recruitment only in the DDF, mainly because of the massive recruitment of the deciduous oak, Quercus brandisiana (Fagaceae), which counterbalanced the seedling mortality in the DDF. Consequently, El Niño increased seedling density in the DDF while decreasing it in the LMF. Our findings showed that the El Niño-induced drought effects on seedling dynamics varied by forest type and leaf habit, suggesting that future changes in drought regimes may alter the species composition and spatial distribution of Asian seasonally dry tropical forests through differences in the response of seedlings to drought.

How to cite: Nutiprapun, P., Hermhuk, S., Marod, D., Kanzaki, M., Nanami, S., and Itoh, A.: Seedling dynamics under the pressure of El Niño drought in a seasonally dry tropical forest in Northern Thailand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4395, https://doi.org/10.5194/egusphere-egu24-4395, 2024.

Droughts are becoming more frequent in the Mediterranean forests due to warmer climate and longer periods without precipitation. In the Mediterranean region, cambial activity is mostly determined by water availability and it occurs during favorite seasons. However, a few studies have focused on the seasonal patterns of wood formation (xylogenesis) response to ongoing climatic conditions in pure stand oak forests. To investigate tree growth response under predicted climate change scenarios, xylogenesis was assessed in Quercus ilex L. trees growing at a site located in the Vesuvio National Park, southern Italy. Sample were taken every two weeks for two consecutive years, and quantitative wood anatomy was used to study the progressive production of cambium, wood and phloem cells. The primary xylogenesis phases (cambium cell formation, occurrence of post-cambial cells, cell-wall thickening, and maturity) were linked to the climate data over 5 to 15 days’ time periods. In helm oak, cambial activity onset in early April, with the development of wood and secondary phloem simultaneously and stopped in early August. Early June was a favorable season for both late wood and late phloem production. Cell wall thickening increased in June to July and August to September as the temperature rose, and vapor pressure decreased in these months. In conclusion, warm climatic conditions and high evaporation rate during spring and summer enhanced plant growth. Herein, earlier growth peaks in helm oak and maximum responsiveness to spring-summer season allowed mediterranean species to mitigate the impact of summer drought.

How to cite: Liyaqat, I., Balzano, A., Niccoli, F., and Battipaglia, G.: Xylogenesis responses to drought stress in Quercus ilex L. at Mediterranean site, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5493, https://doi.org/10.5194/egusphere-egu24-5493, 2024.

Street trees are exposed to various stresses, thus the detection and management of stresses is significant for street tree vitality. Hyperspectral imaging is one of the non-destructive techniques to detect stress responses and vitality of trees. The spectral reflectance of leaves could change as the method for hyperspectral image measurement. We aimed to research the effect of distance and angle between the hyperspectral camera and leaves to recognize the factors for the optical method at the leaf scale. The target is tree seedlings for three major street tree species (Ginkgo biloba L., Chionanthus retusus Lindl. & Paxton and Prunus × yedoensis Matsum.). The hyperspectral images were collected at various distances (30cm and 80cm) and angles (90° (top), 60°, 30°) between the camera and leaves. When measuring, the halogen light was located at the same height as the camera and maintained a 45° angle with leaves. Also, hyperspectral images were collected at various light intensities (low, medium, high) with an 80cm distance and 90° angle between the camera and leaves. We analyze the change in reflectance in the spectral range of 400nm~1000nm as the various measurement methods. For all species, the effects of measurement methods on spectral reflectance were similar. The reflectance near infrared region increased at 30cm distance compared to 80cm distance. Also, the difference in spectral reflectance between 30cm and 80cm distance was continuously increased at over 800nm. However, there were no changes in the spectral response pattern among the light intensities. It means that the reflectance changes due to the distance between the camera and leaves might result from the physical distance, not the light intensity that can increase as the distance gets closer. Meanwhile, the reflectance value could change slightly, but the spectral response patterns were similar among angles between the camera and leaves. The wavelength in which the reflectance value changed differed for species. Therefore, the distance between the camera and leaves might be the major factor in setting the method. We select the distance between the camera and leaves as 80cm to measure the whole seedling crown. Then, we treated the salt stress (three times of 5% CaCl2 500ml with 2-3 days intervals) for G. biloba L. and C. retusus Lindl. & Paxton seedlings. The hyperspectral images were measured before and 7 days after salt treatment with an 80cm distance and 90° angle between the camera and leaves. The changes in the spectral index (R900/800) by the treatment compared between control and salt treatment. The stress responses were detected with the set measurement method; the spectral index increased higher in salt treatment than in the control.

How to cite: Chang, H., Jeong, S. G., and Je, S. M.: Research on the major factor of hyperspectral image measurement method for tree leaves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7313, https://doi.org/10.5194/egusphere-egu24-7313, 2024.

Drought can affect mature and young trees differently, and many studies suggested that large trees might be more prone to drought-related damage and mortality than conspecific smaller individuals. A higher drought vulnerability for tall trees is generally assigned to increasing constraints to water transport with tree height, but a multitude of other biotic and abiotic factors can additionally contribute and modulate their drought resistance. The interrelation of these factors and its consequences for the different drought vulnerabilities between small and dominant trees is so far not well understood and awanting exploration.

Within our study, we took advantage of the Swiss Canopy Crane II (SCC II) site to simultaneously measure critical physiological parameters related to drought stress, namely, pre-dawn and mid-day leaf water potentials (LWP) and stomatal conductance, of mature, ca. 30 m tall individuals and small saplings of 9 common temperate European tree species. These measurements took place throughout the growing season 2023 that was characterized by high temperatures and extended dry periods in late summer and early autumn. Independent of tree size, the increasingly drier conditions caused pre-dawn and mid-day LWP to decrease significantly along the season, with mature trees of some species showing values close or at the species-specific P50 threshold (i.e. the LWP where 50 % loss of xylem conductivity is expected). Our results show that mature trees experienced overall more negative LWP than saplings. Most of these differences could be explained by increasing hydrostatic constraints with increasing tree height. However, even after accounting for this hydrostatic effects (-0.01 MPa per meter tree height), there remained significant differences in pre-dawn and mid-day LWP between mature trees and sapling in some of the investigated species, that were likely caused by either 1) microclimatic effects (especially VPD differences between the upper canopy and the understory), 2) different abilities to refill tree-internal water stores during the night, or 3) differences in soil water access due to rooting differences. Following this first assessment, we are planning to expand our investigations in the next years to better disentangle these different factors that significantly contribute to differences in drought vulnerability with tree size in different tree species, with important implications for the future state and population dynamics of temperate forests.

How to cite: Hoch, G., Dups, R., Peters, R., Steger, D., Zhorzel, T., and Kahmen, A.: Drought stress vulnerability for mature versus young trees in a mixed temperate forest stand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15274, https://doi.org/10.5194/egusphere-egu24-15274, 2024.

We have observed tree die-offs in a variety of regions in the world. Understanding the diverse causes of tree mortality requires exact information about which trees are dying and where. With the increased user-friendliness of drones and the availability of airborne imagery, high-resolution imagery of forests is becoming widely available. Delineating standing deadwood in such aerial imagery has become a classic segmentation task and several models with varying accuracy have been developed. However, these machine-learning based models are not generic and limited to specific image resolutions, sensor characteristics, geographic regions, and forest ecosystems. The reason for this lack of generality is that previous models have been trained using only datasets representative of specific regions and obtained from a single source. In this study, we obtain a diverse dataset spanning more than a dozen countries across continents and implement a single convolutional neural network (CNN) model that is able to cope with most forest ecosystems, varying image quality, and spatial resolutions. 

How to cite: Möhring, J. and the co-authors: Delineating Standing Deadwood in High-Resolution RGB Drone Imagery, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19025, https://doi.org/10.5194/egusphere-egu24-19025, 2024.

Secondary sexual dimorphism plays an important role in shaping the response of plants to different environmental constraints, particularly in relation to energy requirements. Dioecious plants exhibit intricate sex-specific differences that influence stress tolerance mechanisms. In Mediterranean ecosystems, the challenges to stress tolerance are exacerbated by climate change-induced changes in temperature, precipitation patterns and frequency of extreme weather events. Understanding how male and female dioecious plants cope with stress is essential for the development of effective conservation strategies.

This study focuses on the investigation of secondary sexual dimorphism in the wood and leaf anatomy of a Mediterranean shrub Rhamnus alaternus L., to identify potential sex-specific responses to environmental stressors. We conducted a comprehensive analysis of wood and leaf anatomy in male and female individuals at a southern Italian Mediterranean site. Microscopy and subsequent image analysis allowed the quantification of anatomical features related to water-use efficiency, safety against embolism and photosynthetic efficiency. Parameters measured included stem vessel size and distribution, reaction wood formation, stomata characteristics, leaf tissue thickness and mesophyll density.

Our results show a coordinated sex-specific adaptation in anatomical traits that influence either the efficiency or safety of water flow and the regulation of gas-exchange. This knowledge is crucial for improving the resilience and diversity of these plant populations in the face of climate change impacts. The knowledge gained from this study will contribute to the development of targeted conservation strategies for dioecious species in Mediterranean ecosystems.

How to cite: Balzano, A., Amitrano, C., Merela, M., Motti, R., and De Micco, V.: Exploring sex-specific anatomical adaptations in Rhamnus alaternus L. a Mediterranean dioecious shrub: implications for resilience to climate change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20354, https://doi.org/10.5194/egusphere-egu24-20354, 2024.

Evolutionary processes such as phenotypic plasticity and genetic adaptation are key mechanisms that have enabled tree species to cope with major changes in their environments and to colonize new areas over millennia. Forest populations are currently experiencing extremely rapid environmental changes due to anthropogenic climate change, challenging their adaptation and resilience over the coming decades. Tree ecophysiological traits do not vary independently but are rather coordinated; however, our understanding of whether these functional traits are governed by the same evolutionary processes is far from complete. In this study, we assessed the evolutionary drivers of functional traits of two major European tree species: sessile oak (Quercus petraea (Matt.) Liebl.) and European beech (Fagus sylvatica L.). We used multiple common garden experiments (four per species) established in the 1990s within the distribution area of these two species, each comprising 9 to 11 provenances. We measured the following traits: i) tree growth including diameter at breast height, height and basal area increments; ii) specific leaf area; iii) long-term responses to climate including the correlation between annual tree growth and climate; and iv) short-term responses to extreme drought. Individual traits were modelled as a response of environment (sites), genetic identity (provenance) and genetically based plasticity (its interaction). To explore the potential influence of climate conditions at seed origin, both, genetic identity and genetically based plasticity, were correlated with the 19 bioclimatic variables from the seed origin (1961–1990) using Pearson correlations. Associations between the climate of origin and multi-trait genetic effects and genetically based plasticity, as well as associations between the climate of the site and multi-trait plasticity were also explored for both species.

Our results indicate that range-wide variation in the studied traits of oak and beech is markedly driven by phenotypic plasticity. At the individual trait level, sessile oak showed evidence for both genetic and plastic causes of trait variation. In contrast, the variability of traits of European beech seemed to have been mostly shaped by environmentally driven responses with no clear signs of genetic effects and small genetically based phenotypic plasticity. The results of the integral multi-trait phenotypes, however, suggested genetically driven differences along a resource-use gradient governed by temperature conditions in both species. The plasticity of coordinated traits also reflects the ability of all provenances to adjust to new environmental conditions by optimizing the integrated phenotype along a resource-use gradient. Our results suggest that mitigation strategies for climate change could be directed towards seeking provenances that are more plastic in their integral phenotype across the resource-use gradient, rather than typically searching for populations adapted to the current or future conditions at the target site.

How to cite: Martínez-Sancho, E., Rellstab, C., Fonti, P., Benito Garzón, M., Bigler, C., Grossiord, C., Miranda, J. C., project partners, C.-R., and Vitasse, Y.: Evolutionary drivers of phenotypic traits in two European tree species – evidence from common garden networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15860, https://doi.org/10.5194/egusphere-egu24-15860, 2024.

The Mediterranean basin is a well-known drought-prone region, making forest ecosystems potentially vulnerable to drought episodes, heat waves and dry spells. In the last two decades, extreme weather events affected different regions of Europe including mediterranean áreas. This led to significant impacts on forest ecosystems, with extensive mortality events, episodes of crown dieback, and identified reduced tree growth at local level. The predictive abilities to depict early warning signals of negative extreme-induced impacts, well before that the mortality event might occur, are pivotal for monitoring Mediterranean forests. The 3D-CMCC-FEM model, a detailed ecophysiological process-based model, is here applied at gridded level over the Basilicata region, in southern Italy. The model is run on a regular 1x1 km grid for the period 2005-2019 to simulate, among others, gross primary productivity, carbon allocation and tree growth, processes which are controlled by abiotic, e.g. meteorological conditions, and biotic factors, e.g. trees reserve pools, in a mechanistic manner. This modeling approach allows discriminating the degree of decoupling of  carbon assimilation, and tree growth , e.gcarbon woody accumulation. As a result of such interaction between processes and factors, the model  highlighted different emerging patterns of the system under investigation. In particular, results show pronounced differences between European beech dominated areas and oaks dominate areas of the region. Generally, despite a significant drop of summer GPP in beech forests and an overall negative GPP trend, in accordance with remote-sensing based data, the tree growth rate is still positive. Oppositely, the oaks dominated forests show contrasting patterns, with areas where positive trends in GPP can be accompanied by positive but even negative trends in tree growth. The 3D-CMCC-FEM is shown to identify areas which might be prone to statistically significant negative trends in tree growth and, thus, likely to be prone to higher mortality risk in the near future. Indeed, these negative growth trends can not be explained only in terms of forest aging, but also in terms of abiotic factors. Our results show how the diverse degree of coupling between assimilation and growth between different species might be predicted by the model and leading to increase our capability to detect early signals of declining growth, which might already occur in spite of an apparent full recovery after a drought event at canopy level.

How to cite: Dalmonech, D., Vangi, E., and Collalti, A.: Biotic and abiotic  heterogeneity show contrasting GPP and growth trends in mediterranean forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16915, https://doi.org/10.5194/egusphere-egu24-16915, 2024.

Native forest landscapes globally face unprecedented challenges due to land use changes and climate changes, impacting terrestrial biodiversity conservation. Despite efforts to control forest loss, fragmentation, and degradation, uncertainty persists regarding the effects of climate change on forest dynamics, including shifts in productivity, species composition, and disturbance patterns. This study focuses on the Mediterranean ecosystems in Central Chile, known for their resilience to stressors like drought and wildfires. However, changing disturbance regimes in recent decades have tested their adaptive mechanisms. Understanding the effects of new disturbance regimes and their interactions on forest recovery is crucial, particularly in poorly studied ecosystems like the Mediterranean region in South America. Using remote sensing-based vegetation indices, we analyzed short-term (5-year) vegetation recovery after wildfires in Central Chile during the Mega Drought period (2010-2022) and compared it with two preceding decades (1992-2009). Normalized Difference Vegetation Indices (NDVI) were employed, and environmental variables, including climate, topography, and burn severity, were considered to model post-fire recovery from Random Forest models. Drought duration emerged as the most influential factor negatively affecting post-fire vegetation recovery, particularly in hillside areas. Fire severity showed a complex relationship with recovery, positively correlated in humid years but negatively in dried years. Our findings emphasize the critical role of drought in shaping post-fire vegetation recovery in Mediterranean forests. With the ongoing Mega Drought in Central Chile, understanding these dynamics becomes paramount for adaptive management. The study underscores the importance of comprehensive remote sensing monitoring to assess ecological processes, model ecosystem vulnerability, and study climate and disturbance regime interactions. These insights are essential for developing effective strategies to protect and manage forest ecosystems in the face of changing environmental conditions.

How to cite: Hernandez-Duarte, A. and Saavedra Pimentel, F.: Insights into Post-Fire Dynamics: Evaluating Short-Term Vegetation Recovery During Mega Drought in Central Chilean Mediterranean Forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13580, https://doi.org/10.5194/egusphere-egu24-13580, 2024.

Temperatures are expected to rise 1.5ºC for 2100 due to climate change caused by anthropogenic emissions. These risen of temperatures are causing an increase in frequency and intensity of drought events that are expected to get even more frequent and more extreme in the following decades. Most predictions suggests that drought stress will cause a large-scale tree mortality, species distribution range contractions and a general productivity loss throughout this century. Defoliation represents an early stage of dieback, at which some silvicultural practices can be done to reduce competence or to improve water retention. Therefore, identifying and mapping these areas is of crucial importance to forest managers in the context of global change. 

The aim of this study is to develop a classification model to differentiate die-off and healthy Scots Pine plots using field data and Landsat time series and to extrapolate the model results to other areas of the species’ distribution. 

We have 51 plots (17 m ~ Landsat pixel) in four sites with healthy (<30% defoliated) and die-off (>= 30% defoliated) areas for which we collected dasometric information along with defoliation and mortality. We downloaded, decomposed, and modelled Landsat time series (1985-2023) of Tasseled Cap components and fitted linear models since the last severe drought (2017) that affected Pinus sylvestris populations. A set of candidate explanatory variables were built including the slope of the linear model between 2017 and 2024, mean trend values from 2022 and mean amplitude from 2022.  

Field data were randomly divided in two independent groups (train and test plots). This process was repeated 100 times and a support vector machines (SVM) model was calibrated for every possible combination of explanatory variables. The best candidate model was chosen according to the model performance metrics of the 100 calibrated models. 

The best model had an AUC > 96.97%, an OAA>88.23% and a die-off prediction rate over 83.3% for the 75 out of 100 repetitions. Applying model ensemble to all the plots an AUC = 97.5%, a die-off prediction rate of 95% was obtained. With this work we conclude that Landsat info from 2017 can successfully classify plots into healthy and non-healthy ones. The results of the model are good enough to extrapolate to areas of similar conditions to our study plots and will be, hence, applicable to most of the Pinus sylvestris distribution. 

How to cite: Rodes, M., Seidl, R., Ruiz Benito, P., Ángel Zavala, M., Aguado, I., Samblás Vives, E., Fernández de Blas, C., Rebollo, P., Tjerín, J., and Mariano, G.: Classification of defoliation of Scots Pine using SVM algorithm and Landsat imagery, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22173, https://doi.org/10.5194/egusphere-egu24-22173, 2024.