Forest Gaps Research Articles

Long wings and small eyes help tropical birds traverse gaps in fragmented forests

Long wings and small eyes help tropical birds traverse gaps in fragmented forests

High correlations between plant clonality and ecosystem service functions after management in a chronosequence of evergreen conifer plantations.

Climate change and mono-afforestation or mono-reforestation have continuously caused a decline in biodiversity and ecosystem services on forest plantations. Key plant functional traits in forests or plantations may affect ecosystem functions after forest management practices. Plant clonality, a key functional trait, frequently links to biodiversity and ecosystem functions and affects the biodiversity-ecosystem functioning relationship. However, little is known about how plant clonality affects ecosystem functions and services of plantations after forest management. We conducted a field experiment to discuss the diversity and proportion of clonal plants, plant diversity of the communities, and ecosystem service functions and their relationships under 10 years of close-to-nature (CTN) management, artificial gap management, and control (i.e., without management) in the three stages of C. Lanceolata plantations. Our results showed that CTN and gap management modes significantly facilitated diversity of clonal plants, plant diversity of the communities, and parameters of ecosystem service functions in C. lanceolata plantations. Moreover, CTN management promoted plant community diversity, soil water conservation, and carbon storage the most in the earlier stand stages. Diversity of clonal plants was significantly positively correlated with ecosystem service functions after forest management. Structural equation modeling analysis indicated that forest gap or CTN management indirectly positively affected ecosystem service functions through increasing diversity of clonal woody plants and plant diversity of the communities. Our results indicate a highly positive effect of gap or CTN management on diversity and proportion of clonal plants and on plant diversity of the communities, which link to improvements in ecosystem service functions (i.e., water and soil conservation and carbon storage). The link between forest management, diversity, and ecosystem functions suggests that key functional traits or plant functional groups should be considered to underline the mechanism of traits-ecosystem functioning relationships and the restoration of degraded plantations.

A new approach to derive productivity of tropical forests using radar remote sensing measurements.

Deriving gross & net primary productivity (GPP & NPP) and carbon turnover time of forests from remote sensing remains challenging. This study presents a novel approach to estimate forest productivity by combining radar remote sensing measurements, machine learning and an individual-based forest model. In this study, we analyse the role of different spatial resolutions on predictions in the context of the Radar BIOMASS mission (by ESA). In our analysis, we use the forest gap model FORMIND in combination with a boosted regression tree (BRT) to explore how spatial biomass distributions can be used to predict GPP, NPP and carbon turnover time (τ) at different resolutions. We simulate different spatial biomass resolutions (4 ha, 1 ha and 0.04 ha) in combination with different vertical resolutions (20, 10 and 2 m). Additionally, we analysed the robustness of this approach and applied it to disturbed and mature forests. Disturbed forests have a strong influence on the predictions which leads to high correlations (R2 > 0.8) at the spatial scale of 4 ha and 1 ha. Increased vertical resolution leads generally to better predictions for productivity (GPP & NPP). Increasing spatial resolution leads to better predictions for mature forests and lower correlations for disturbed forests. Our results emphasize the value of the forthcoming BIOMASS satellite mission and highlight the potential of deriving estimates for forest productivity from information on forest structure. If applied to more and larger areas, the approach might ultimately contribute to a better understanding of forest ecosystems.

Forest Gap Extraction Based on Convolutional Neural Networks and Sentinel-2 Images

As a type of small-scale disturbance, forest gap and its accurate extraction are of great significance to monitor forest long-term dynamics, to choose forest recovery mode and to predict forest recovery pace. Currently, airborne LiDAR and high-resolution multi-spectral data are commonly used to accurately classify forest gaps, but they are costly to acquire and have limited time and space availability. In contrast, the Sentinel-2 multi-spectral data with a 10 m spatial resolution overcomes these drawbacks in forest gap extraction. In this work, an integrated framework that combines multi-source remote sensing, machine learning and deep learning to extract forest gap in wide regions was proposed and tested in three sites. First, LiDAR, Sentinel series and random forest (RF) algorithm were synergized to produce a canopy height product in model training site. On this basis, samples for forest canopy, forest gap and non-such were identified from LiDAR-derived canopy height model (CHM) and Sentinel-based canopy height inversion (HI) data to train forest gap extraction models by applying the Deep Forest (DF) and Convolutional Neural Networks (CNN) algorithms, followed by a comparison of the accuracy and the transferability among the four models (DF-CHM, DF-HI, CNN-CHM and CNN-HI). The results indicated that the R2 and RMSE of Sentinel-based canopy height retrievals were estimated at 0.63, and 7.85 m respectively, the difference in the mean height and standard deviation between HI and CHM was 0.03 m and 4.7 m respectively. And there was a spatial agreement of about 98.60% between the HI-identified samples and the CHM-identified samples, with an agreement of 54.89% for the forest gap class. The CNN-HI model had the highest accuracy in both transfer learning test sites, with an overall accuracy (OA) of 0.85 and 0.87, Kappa coefficient at 0.78 and 0.81, respectively, proving that it has good transferability. Conversely, the DF-based models generally gave poorer accuracy and transferability. This study demonstrates that combining Sentinel-2 multi-spectral data and CNN algorithm is feasible and effective in forest gap extraction applications over wide regions.

Effects of Gap Size on Natural Regeneration in Picea asperata Forests of Northern China

Our study aimed to assess the impacts of varying forest gap sizes on the density, growth, and spatial patterns of seedlings and saplings in spruce (Picea asperata) forests in the Saihanba region, Hebei Province, China. Twenty-four forest gaps were surveyed and categorized into six classes based on the gap size. A one-way ANOVA was used to compare differences in the density, height, and ground diameter of seedlings and saplings among six gap classes. Ripley’s K function was used to explore the spatial patterns of regeneration establishment in each class. The findings of our study indicated that the forest gap size did not significantly influence the density of seedlings or the ground diameter growth of saplings, whereas it significantly influenced the height growth of saplings. In smaller gaps, natural regeneration occurred primarily in the gap edges. As the gap size increased, the natural generation began to shift from the edge areas to the gap centers. Large forest gaps had the highest percentages of random distribution patterns across all spatial scales. Aggregated distributions were observed at distances less than 1 m in all gap size classes, whereas uniform distributions tended to occur in the small gaps at distances of 2–4 m. Our findings indicated that larger forest gaps, ranging from 60 to 120 m2, were more conducive to spruce regeneration. The results can inform the development of targeted strategies for understory afforestation and the artificial promotion of natural regeneration in spruce forests.

Effect of Gap Size and Elevation on the Regeneration and Coexistence of Abies, Betula, and Acer Tree Species in a Subalpine Coniferous Forest

Forest gaps play an important role in species regeneration and forest succession. Gap size has a primary influence on tree species coexistence and community assembly along an elevation gradient. In this study, we evaluated the regeneration and coexistence of Abies faxoniana, Betula utilis, and Acer maximowiczii at different life history stages in varied gap sizes along an elevation gradient (between 3000 and 3500 m a.s.l). We found that gap size can positively enlarge the effects of elevation on the regeneration density of the three species. In the process of regeneration from seedling to sapling, Abies had stronger regeneration capability, with regeneration niche breadths of more than 0.6 in different gap sizes. A factor analysis of mixed data indicated that regeneration density, soil nutrient contents, and air humidity were mainly related to gap size, but habitat temperature was largely determined by elevation. The connection between the species regeneration density and habitat conditions was due to differences in their regeneration niches, reflecting the selective preemption of environmental resources of different species in different life stages. Microhabitat heterogeneity, controlled by the characteristics of forest gaps along an elevation, affected the regeneration niche differences of the tree species, which contributed to the species coexistence and community assembly processes.

Fish and aquatic salamander responses to the creation of riparian canopy gaps along forested headwater streams

Many headwaters across temperate North America have uniform mid‐succession riparian forests recovering from historic land clearing. These young riparian stands contrast with late‐succession forests, which have complex structural characteristics including canopy gaps. Canopy gaps provide structural diversity that can be important for terrestrial species, and they are also hypothesized to be important features for aquatic environments. The light patches below gaps create productivity hotspots in streams and therefore create potential for increased stream apex predator abundances through bottom‐up food web drivers. However, increasing light may also affect stream temperature, a consideration for coldwater fish (salmonids). We established an experimental before‐after control‐impact study to explicitly assess how creating canopy gaps in the riparian forest affects the abundance and biomass of coastal cutthroat trout (Oncorhynchus clarkii clarkii) and Pacific giant salamanders (Dicamptodon tenebrosus) in paired reference and treatment reaches at five replicate streams. Gaps were designed to resemble those in old‐growth forests in the treatment reach of each system although wood was explicitly left out of the stream. At four of five sites, we found small and generally consistent positive responses in adult cutthroat trout and total vertebrate biomass to localized increases in light but only 2 years after treatment. Results suggest that opening riparian canopies adjacent to streams via gaps is a viable tool to enhance structural complexity of riparian forests without negatively impacting stream vertebrates; however, a single gap alone had small effects on aquatic vertebrates. More or larger gaps would likely be needed to notably enhance aquatic apex predators.

Effects of Forest Gaps on Forest Floor Microbial Community Composition in Pinus tabulaeformis Forests in a Rocky Mountain Area, Beijing, China

Forest gaps induce environmental heterogeneity, but their effects on the local forest floor microbial communities are not fully understood. This research investigated the impact of forest gap positions on the forest floor microbial community composition to provide baseline information for projects to accelerate nutrient cycling and forest regeneration and enhance ecosystem services. A one-year-old forest gap and an area of 40–50 m2 in Pinus tabulaeformis plantations were selected in the Beijing mountainous area. Forest floor samples were collected from the following positions: gap center, gap border, and adjacent closed canopy. Our study demonstrated that gap positions significantly influenced the forest floor microbial community composition. The Gram-positive bacteria, Gram-negative bacteria, and total bacteria, as well as the fungi, were significantly greater in the forest gap center and gap border compared to those in the closed canopy, and the dissolved organic carbon, readily oxidized organic carbon, ammonia nitrogen, and nitrate nitrogen followed the same trend. Compared with those of the closed canopy, the Gram-positive bacteria, Gram-negative bacteria, total bacteria, and fungi in the gap center were markedly greater by 23%, 25%, 22%, and 24% and by 14%, 14%, 11%, and 16% in the gap border, respectively (p < 0.05). Redundancy analysis demonstrated that shifts in the litter microbial community composition were predominantly predicted by litter moisture and β-1,4-glucosidase. In addition, we discovered that the microbial community composition was greater in the undecomposed forest layer than that in the semi-decomposed layer. In summary, gap positions and forest floor layers have a significant impact on microbial community composition. Nevertheless, additional long-term investigations are needed. Our study provides a reference for the promotion of nutrient cycling to guide future ecological management.

Effects of interaction between forest structure and precipitation event characteristics on fuel moisture conditions

Estimating forest fire danger is of primary concern for the Austrian forest fire management. The fine fuel moisture code (FFMC) of the Canadian Fire Weather Index (CFWI) is used for determining ignition danger. The FFMC is calculated by using the Integrated Nowcasting through Comprehensive Analysis (INCA) system, which provides interpolated weather parameters, available at 1 km2 spatial resolution. Automated fuel sticks were used for measuring microclimate-defined moisture content from 2018 to 2020 in two differently structured sites: closed forest and forest gap. A remotely automated weather station (RAWS) measured the meteorological parameters of the research area. First, the capability of an interpolated large-scale FFMC to capture local moisture conditions was studied. Second, the effects of an interaction between forest structure and precipitation event characteristics on moisture content behaviour were investigated. Bayesian-based techniques in dependence of the three consecutive years were applied. Our results show that the correlations between INCA FFMC and RAWS FFMC are high (0.80–0.95) and INCA FFMC is capable of capturing the local microclimatic variations (0.68–0.78). Correlations ranging from 0.74 to 0.86 were evidenced between the fuel stick FFMC values of the forest and the gap, revealing that INCA FFMC cannot capture the microclimate induced differences between the two forest conditions. We found that: (i) the buffering capability of forest structure slows the absorption rate by 1.8 to 3.4%/h, (ii) absorption rate difference between the forest and the gap was lowest (1.8%/h) in the case of short and heavy rain, (iii) during the desorption phase the moisture content remained similar for both the closed forest and the gap. Overall, the structure induced buffering capability was strongest in the case of short and light rain. Longer and more intensive precipitation events, especially after canopy saturation during throughfall, are likely to lessen the buffering capability of the forest.

ECOLOGICAL FUNCTIONALITY OF FOREST AND STREAM CORRIDORS IN AN AREA OF THE PLAINS PIEDMONT IN CASANARE

Between 2010 and 2020 a study was conducted on the functionality of the ecological corridors within the San José de Matadepantano farm, a property of 811 ha located in plains piedmont, which alternates poorly drained savannas, swamps, and forests, with land uses for agriculture, livestock, and the infrastructure of a rural university campus. To evaluate the functionality of the forest corridors, length, amplitude, coverage area, and continuity metrics within the landscape were estimated using multiannual LANDSAT images; additionally, field visits were made to record possible forest gaps that could affect the flow of fauna through the corridors. In order to determine the functionality of the stream corridors, four sampling points were chosen along caños Tiestal and Güio, where physiographic and bathymetric profiles were modeled using the SURFER 15 software, in addition, spatial heterogeneity was calculated using the Shannon-Wiener index, physiognomy and floristic composition of the streamside vegetation was represented in scale graphic profiles, the percent distribution of aquatic habitats was determined and species diversity of fish communities was calculated. Findings obtained during the last decade allow us to conclude that the ecological corridors maintain their functionality with an active biotic flow in both forest and stream corridors. However, critical points were detected where the forests could lose their connectivity, which would affect the sustainability and transit of regional biodiversity.

Plant Functional Traits of Plants Species Colonizing Forest Gaps

In this research, we analyzed functional plant traits and life forms of plant species growing on five forest gaps in the Dinaric fir–beech forest in Slovenia. The forest gaps were created as a result of natural disturbances. We selected 18 functional plant traits, whose values were obtained from the BiolFlor database. With the help of the JUICE program, we calculated the frequency of occurrence in individual forest gaps for each functional plant trait. Then, we calculated Spearman’s correlation coefficient at p < 0.05 between the occurrence of individual functional plant traits and each forest gap. Individual locations differed statistically in 87 categories of plant functional traits. The forest gap Nad Drago differed statistically from the other forest gaps in 16 functional plant traits. Forest gaps are mainly colonized by perennials and herbaceous perennials and chamaephytes. These are plant species that begin to flower in June and July, bloom for two or three months, and are pollinated by insects, mainly hover flies and wild bees. This colonizing plant species reproduce via seeds or spores and vegetatively. Furthermore, birds and forest mammals are the vectors of fruit and seed dispersal.

The response of seedlings and saplings to canopy structure and light in different gaps in a spruce-fir mixed stand in Changbai Mountains, China

Environmental heterogeneity caused by the formation of forest gaps has important implications for the establishment and growth of forest regeneration, and different tree species with different shade tolerance at various stages of regeneration respond differently to the environment. In this study, we investigated 48 forest gaps and classified them into four classes based on their area, including small (< 20 m2), medium (20 m2 to 50 m2), large (50 m2 to 120 m2), and extra-large (> 120 m2). We conducted an analysis of the differences and variations in canopy structure (canopy openness and leaf area index (LAI)) and light environment (direct light, diffuse light, and total light) for different sizes of gaps and along the north–south axis of the gaps. Additionally, we conducted a preliminary study of how the seedlings and saplings of different tree species (Korean pine (Pinus koraiensis), Ezo spruce (Picea jezoensis), and Khingan fir (Abies nephrolepsis)) respond to environmental factors such as canopy structure and light within gaps. Gap size significantly influenced the direct and total light in northern (N, N1) portion of gaps, while for diffuse light, gap size demonstrated a notable effect along the north–south axis, except for the N. Maximum direct light did not occur at the center of gaps, but rather near the center of the gap and tended to the crown edge. In contrast, the maximum diffuse light occurred at the center of gap. When the forest gap area < 20 m2, the diffuse light dominated the northern part of the gaps. However, when the gap area > 20 m2, the northern part was dominated by direct light. The variation pattern of total light showed a level of consistency with that of direct light. A redundancy analysis (RDA) showed that the density of shade-tolerant fir seedlings and saplings, as well as spruce seedlings, were primarily positively correlated with the LAI, while the density of spruce saplings was negatively correlated with direct light. The density of heliophilous species Korean pine seedlings and saplings was strongly and weakly positively correlated with the direct light, respectively. The mean ground diameter and height of spruce and fir seedlings and saplings positively correlated with diffuse light, whereas the mean ground diameter and mean height of Korean pine seedlings and saplings strongly positively correlated with the canopy openness and direct light, respectively. These findings suggest that the gap size and location within gaps can compensate each other in silvicultural practices based on the creation of gaps. Knowledge of the ecological characteristics of the target species, enables the selection of appropriate relative positions to achieve more suitable light conditions for their growth.

Social but not solitary bee abundance tracks pollen protein accumulation in forest canopy gaps

Abstract Forest restoration projects that create canopy gaps can promote floral diversity and may provide reservoirs for bee–flower interactions. However, periods of bee activity must match availability of floral nutrition for bees to benefit from these effects. We model variation in canopy gap size, floral density, pollen protein and bee and floral traits to test the hypothesis that patterns of floral visitation in bee–flower interactions are predicted by patch structure, variation in bee life histories and floral phenotypes. Canopy gap size did not predict overlap of foraging bee abundances and floral protein, but bee life‐history traits did. Foraging activity of large ground‐nesting bees matched accumulation of protein density, whereas activity of small cavity‐nesting bees and kleptoparasitic species preceded peak protein density. Floral visual traits predicted visitation rates, with more interactions for taller species with large floral displays. Both native and invasive species have high nutritional value for bees in canopy gaps and can support frequent and rich interactions. Landscapes with both weedy and native floral species may have higher phenological diversity and provide more foraging opportunities for early‐season bees. We conclude that canopy gap creation is likely to have similar impacts on bee–flower interactions regardless of gap size, but activity periods of larger bees are more aligned with pollen protein density than activity of small bees, and floral visual displays are decoupled from pollen protein content.

Nitrogen addition changes the canopy biological characteristics of dominant tree species in an evergreen broad-leaved forest

Many studies have focused on the impact of nitrogen deposition on plants, but due to technical limitations, research on the responses of forest canopy to manipulated nitrogen deposition is relatively scarce. Based on a canopy nitrogen addition (CN) platform, this study used laboratory analysis and unmanned aerial vehicle (UAV) observations to assess the impact of CN on the canopy traits of dominant tree species (Engelhardia roxburghiana, Schima superba, and Castanea henryi) in an evergreen broad-leaved forest in China. The results showed that nitrogen application at 25 kg N ha−1 y−1 (CN25) and 50 kg N ha−1 y−1 (CN50) significantly increased the actual net photosynthetic rate (An) of all the three tree species. CN25 significantly increased superoxide dismutase (SOD), catalase (CAT), and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities in C. henryi. CN50 significantly increased the leaf area of all the three tree species and significantly reduced the leaf thickness of C. henryi, and significantly increased the POD and Rubisco activities in S. superba and C. henryi. CN significantly changed the number of forest gaps, but did not significantly change the area of forest gaps within the sample plots. CN25 significantly decreased the vertical projection area but increased the canopy flowering coverage of S. superba in dominant directions. CN25 and CN50 significantly increased the flowering coverage of C. henryi in favorable directions. It is found that under long-term (10-year) nitrogen addition, the balance between carbon fixation and antioxidant defense functions of E. roxburghiana may be broken down, but the carbon assimilation, antioxidant capacity and reproduction potential of S. superba and C. henryi may be well coordinated, which will have a potential impact on the species composition and ecological functions of the evergreen broad-leaved forest. This study may also provide scientific basis for forest management in the context of enhanced atmospheric nitrogen deposition.

Forest gap effects on snow storage in the transitional climate of the Eastern Cascade Range, Washington, United States

Forest thinning and gap creation are being implemented across the western United States of America (USA) to reduce wildfire and forest mortality risk as the climate warms. The Eastern Cascades in Washington, USA, is in a transitional zone between maritime and continental climate conditions and represents a data gap in observations describing the relationship between forest density and snowpack. We collected 3 years of snow observations across a range of forest densities to characterize how forest management efforts in this region may influence the magnitude and duration of snow storage. Observations indicate that peak snow storage magnitude in small gaps ranges from the same to over twice that observed in unburned forest plots in the Eastern Cascades. However, differences in snow duration are generally small. Across all Eastern Cascade sites and years, we observed a median difference of snow storage lasting 7 days longer in gaps as compared to nearby forest plots. A notable exception to this pattern occurred at one north-facing site, where snow lasted 30 days longer in the gap. These observations of similar snow storage duration in the Eastern Cascades are attributed to minimal differences in canopy snow interception processes between forests and gaps at some sites, and to higher ablation rates that counterbalance the higher snow accumulation in the gaps at other sites. At the north-facing site, more snow accumulated in the gap, and ablation rates in the open gap were similar to the shaded forest due to the aspect of the site. Thus, snow storage duration was much longer in the gap. Together, these data suggest that prescriptions to reduce forest density through thinning and creating gaps may increase the overall amount of snow storage by reducing loss due to sublimation and melting of canopy-intercepted snow. However, reducing forest density in the Eastern Cascades is unlikely to buffer climate-induced shortening of snow storage duration, with the possible exception of gap creation in north-facing forests. Lastly, these observations fill a spatial and climatic data gap and can be used to support hydrological modeling at spatial and temporal scales that are relevant to forest management decisions.

A forest gap is not forever: Towards an objective standard to determine when a gap is considered closed in temperate forests

Forest gaps create environmental heterogeneity and drive forest dynamics through gap-phase regeneration. However, it is unclear when a forest gap can be considered closed, limiting a global synthesis of forest succession that integrates gap patterns and dynamics. We created twelve forest gaps (six large gaps, RD/H [ratio of gap diameter to gap border tree height] = 1.3; six small gaps, RD/H = 0.6) and monitored tree regeneration for seventeen years to establish an objective gap-closure standard for regeneration filling in a temperate secondary forest. Our results indicated that a forest gap could be considered closed or entering a gap-closure phase when the dominant gap regeneration layer (i.e., the top 10% gap-fillers) (1) reached the crown base height (8.9 m on average) of canopy trees and (2) entered a period of stability in density, richness, and evenness. Linear mixed-effects models found that these two conditions met each other in the same period (14.5 years) in the large gaps, with a mean density, richness, and evenness of 0.1 (stem m−2), 4.9 (species gap−1), and 0.9, respectively. However, if no repeated gap disturbance occurred, small gaps were closed by lateral extension rather than by height growth. Light-demanding species (e.g., Juglans mandshurica) mainly contributed to the closure of large gaps and played negligible roles in the small gaps, but intermediate or shade-tolerant species (e.g., Acer mono) in the small gaps had potential for successful gap filling following repeated gap disturbance. Our gap-closure standard links gap structure to species composition and provides a reference for large-scale research on gap patterns and dynamics, which helps to understand the ecological process during forest succession. The standard also provides a relatively clear boundary between forest gaps and closed forest stands, which is a premise to develop appropriate forest management and shorten the restoration period of degraded secondary forests.

Roles of pathogens and mycorrhizae in conspecific negative distance dependency and replacement of tree species in a temperate forest

Maintaining and recovering species diversity is one of the main management goals of forest managers. It is thus important to understand the mechanisms that drive species diversity. The mechanism is strongly related to the harsh biological environment surrounding the tree, especially its interaction with natural enemies, and a well-known mechanism is the Janzen-Connell hypothesis. The hypothesis is best understood by evaluating not only conspecific negative distance-dependent (CNDD) seedling mortality but also replacement of conspecific seedlings by heterospecifics. However, it remains unclear how antagonistic pathogens and mutualistic mycorrhizae affect the strength of replacement. A reciprocal seed-sowing experiment was conducted for five tree species with different mycorrhizal types in forest understorey (FU) and gaps (Gap) in a temperate forest. We investigated seedling mass, mortality, mortality agents, and root infection with arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi. In both FU and Gap sites, two AM species were attacked by pathogens causing damping-off and leaf diseases more severely beneath conspecific than heterospecific adults, and more severely among conspecifics than heterospecifics of focal adults, resulting in strong CNDD and replacement, whereas seedling mortality in two EM species due to damping-off pathogens and leaf diseases did not differ among treatments, resulting in weak CNDD and replacement. One AM species showed an intermediate trend between two AM species and two EM species. Thus, CNDD and replacement caused by pathogens were positively correlated in FU but not Gap sites. These traits reveal that replacement closely correlated with CNDD play an important role in maintaining species diversity, especially when gaps are absent. This study also suggest that replacement plays an important role in regulating the spatial distribution of individual trees and subsequent relative abundance of tree species, as well as CNDD effects. Forest managers need to consider differences in the strength of CNDD and replacement between mycorrhizal fungi types when attempting to achieve successful seedling establishment after harvesting without compromising species diversity.

Seedlings of shade-tolerant tree species are more vulnerable to chilling rain under a forest gap

The manner in which tree species differ in their responses to chilling rain in warm and species-rich (sub-)tropical forests is not well understood. Understanding this variation between species is essential for linking the responses of individual plants to chilling rain with ecological consequences at the forest community and ecosystem levels. We hypothesized that chilling rain can induce detrimental effects on leaf photochemical processes, and the negative impacts are more evident for shade-tolerant species than light-demanding species. This trade-off between species' tolerance to shade and chilling rain may depend on the light environment to which plants are exposed. To test these hypotheses, we conducted two sequential experiments with five subtropical tree species, measuring their leaf photochemical processes during the phases of a chilling rain event and assessing their resistance and recovery. We determined species shade tolerance by integrating their functional traits associated with resource acquisition in a shade environment. Our results showed that Fv/Fm, a measure of maximum quantum yield of photosystem II, was co-determined by the plant's exposure to light and chilling rain. Seedlings exposed to a gap before the chilling rain generally had lower Fv/Fm than those exposed to shade before the rain treatment. Chilling rain, relative to ambient rain, significantly reduced Fv/Fm during the cold and sunny phase. However, the effects of chilling rain were only evident for shade-tolerant species with gap-exposure history. The reduction in Fv/Fm induced by chilling rain led to higher resistance of Fv/Fm to chilling rain for light-demanding species than shade-tolerant species, leading to a trade-off between species' tolerances to shade and chilling rain for plants with gap-exposure history, thus supporting the hypotheses. This trade-off was primarily due to variation in functional traits related to light-use strategy, such as specific leaf area, leaf area ratio, leaf thickness, relative volume growth rate, and root-shoot ratio. As light availability and species' tolerance to shade are critical abiotic and biotic factors determining forest community succession, respectively, these findings may improve the scalability of the physiological responses of individual plants to chilling rain to the dynamics of forest communities. Our results suggest that frequent chilling rain events and canopy disturbances may favor light-demanding species and alter the species composition of subtropical forests.

Long-term dynamics of tree of heaven (Ailanthus altissima) in central European forests

Since the 1950s, the tree of heaven (Ailanthus altissima) has progressively invaded forests in southern Switzerland and is becoming a growing concern also north of the Alps. Recent studies have increased the understanding of the species’ ecology, but its role in long-term stand dynamics remains uncertain. Therefore, we simulated the long-term dynamics of unmanaged and managed forest stands in southern and northern Switzerland under current and future climate conditions (RCP8.5) using the forest gap model ForClim. Our results indicate that A. altissima will increase its presence in the short term (< 100 yrs), but does not gain dominance in the long term (> 200 yrs), confirming its pioneer character. Timber harvesting led to an increasing share of A. altissima compared to unmanaged stands. Overall, our findings suggest that in the long run, a competitive displacement of native dominant species by A. altissima appears unlikely, with the exception of drought-prone sites under strong climate change. Furthermore, our findings underline the importance of the frequency and intensity of forest management for the long-term abundance of A. altissima in forest stands.

High-resolution mapping of snow cover in montane meadows and forests using Planet imagery and machine learning

Mountain snowpack provides critical water resources for forest and meadow ecosystems that are experiencing rapid change due to global warming. An accurate characterization of snowpack heterogeneity in these ecosystems requires snow cover observations at high spatial resolutions, yet most existing snow cover datasets have a coarse resolution. To advance our observation capabilities of snow cover in meadows and forests, we developed a machine learning model to generate snow-covered area (SCA) maps from PlanetScope imagery at about 3-m spatial resolution. The model achieves a median F1 score of 0.75 for 103 cloud-free images across four different sites in the Western United States and Switzerland. It is more accurate (F1 score = 0.82) when forest areas are excluded from the evaluation. We further tested the model performance across 7,741 mountain meadows at the two study sites in the Sierra Nevada, California. It achieved a median F1 score of 0.83, with higher accuracy for larger and simpler geometry meadows than for smaller and more complexly shaped meadows. While mapping SCA in regions close to or under forest canopy is still challenging, the model can accurately identify SCA for relatively large forest gaps (i.e., 15m &amp;lt; DCE &amp;lt; 27m), with a median F1 score of 0.87 across the four study sites, and shows promising accuracy for areas very close (&amp;gt;10m) to forest edges. Our study highlights the potential of high-resolution satellite imagery for mapping mountain snow cover in forested areas and meadows, with implications for advancing ecohydrological research in a world expecting significant changes in snow.