A harmonized database of European forest simulations under climate change

Process-based forest models combine biological, physical, and chemical process understanding to simulate forest dynamics as an emergent property of the system. As such, they are valuable tools to investigate the effects of climate change on forest ecosystems. Specifically, they allow testing of hypotheses regarding long-term ecosystem dynamics and provide means to assess the impacts of climate scenarios on future forest development. As a consequence, numerous local-scale simulation studies have been conducted over the past decades to assess the impacts of climate change on forests. These studies apply the best available models tailored to local conditions, parameterized and evaluated by local experts. However, this treasure trove of knowledge on climate change responses remains underexplored to date, as a consistent and harmonized dataset of local model simulations is missing. Here, our objectives were (i) to compile existing local simulations on forest development under climate change in Europe in a common database, (ii) to harmonize them to a common suite of output variables, and (iii) to provide a standardized vector of auxiliary environmental variables for each simulated location to aid subsequent investigations. Our dataset of European stand- and landscape-level forest simulations contains over 1.1 million simulation runs representing 135 million simulation years for more than 13,000 unique locations spread across Europe. The data were harmonized to consistently describe forest development in terms of stand structure (dominant height), composition (dominant species, admixed species), and functioning (leaf area index). Auxiliary variables provided include consistent daily climate information (temperature, precipitation, radiation, vapor pressure deficit) as well as information on local site conditions (soil depth, soil physical properties, soil water holding capacity, plant-available nitrogen). The present dataset facilitates analyses across models and locations, with the aim to better harness the valuable information contained in local simulations for large-scale policy support, and for fostering a deeper understanding of the effects of climate change on forest ecosystems in Europe.

"Biodiversity Offsetting" in Uganda's Protected Areas: A Pathway to Restoration of Forest Biodiversity?

With limited national financing for conservation, there is an increasing interest in using biodiversity offset funds to strengthen protected area management. Offsetting measures can potentially be used in the restoration of degraded protected areas. However, there are concerns related to the uncertainty of restoration outcomes and time-lags before the expected benefits can be observed. Using a case of the Gangu Central Forest Reserve in central Uganda, we contribute empirical findings showing the potential and limitations of biodiversity offsetting by means of the restoration of a degraded forest reserve. We use forest cover change analysis and community surveys to determine forest changes after eight years of offset implementation, and forest inventories to analyse the current forest structure and composition to ascertain taxonomic diversity recovery. The results revealed that biodiversity offsetting led to a 21% increase in Tropical High Forest cover, and enhanced restoration of forest species composition and diversity. However, attaining permanence of the restoration benefits requires the regulation of community forest resource access and use. Strengthening forest management capacity to monitor the offset sites and compensating impacted communities for foregone forest resource benefits are crucial for the successful implementation of biodiversity offsets.

Adaptive monitoring in action-what drives arthropod diversity and composition in central European beech forests?

Recent studies suggest that arthropod diversity in German forests is declining. Currently, different national programs are being developed to monitor arthropod trends and to unravel the effects of forest management on biodiversity in forests. To establish effective long-term monitoring programs, a set of drivers of arthropod diversity and composition as well as suitable species groups have to be identified. To aid in answering these questions, we investigated arthropod data collected in four Hessian forest reserves (FR) in the 1990s. To fully utilize this data set, we combined it with results from a retrospective structural sampling design applied at the original trap locations in central European beech (Fagus sylvatica) forests. As expected, the importance of the different forest structural, vegetation, and site attributes differed largely between the investigated arthropod groups: beetles, spiders, Aculeata, and true bugs. Measures related to light availability and temperature such as canopy cover or potential radiation were important to all groups affecting either richness, composition, or both. Spiders and true bugs were affected by the broadest range of explanatory variables, which makes them a good choice for monitoring general trends. For targeted monitoring focused on forestry-related effects on biodiversity, rove and ground beetles seem more suitable. Both groups were driven by a narrower, more management-related set of variables. Most importantly, our study approach shows that it is possible to utilize older biodiversity survey data. Although, in our case, there are strong restrictions due to the long time between species and structural attribute sampling.

Telecoupling between urban expansion and forest ecosystem service loss through cultivated land displacement: A case study of Zhejiang Province, China

Urbanization can either directly occupy forests or indirectly lead to forest loss elsewhere through cultivated land displacement, resulting in further forest fragmentation and ecosystem service (ES) loss. However, the effects of urban expansion on forest area and ESs are unknown, and this is especially true for indirect effects. Taking Zhejiang Province, China, a typical deforested province, as an example, this study quantified the direct and indirect effects of urban expansion on forest area and five ESs (timber yield, water yield, carbon sequestration, soil conservation, and biodiversity) from 2000 to 2020, explored the relationship between forest structure (forest proportion, mean patch area, edge density, and mean euclidean nearest neighbor distance) change and ESs, and revealed the telecoupling of urban expansion and forest loss and cascade effects among urbanization, deforestation, forest structure, and ESs. The results indicated that the indirect forest loss (4.30%-6.15%) caused by cultivated land displacement due to urban expansion was larger than the direct forest loss (2.42%). Urban expansion has a greater negative impact on carbon sequestration (6.40%-8.20%), water yield (6.08%-7.78%), and biodiversity (5.79%-7.44%) than on timber yield (4.77%-6.17%) and soil conservation (4.43%-5.77%). The indirect forest ES loss was approximately 2.83-4.34 times greater than the direct forest ES loss. Most forest ESs showed a nonlinear significant positive correlation with changes in forest proportion and mean patch area and a significant nonlinear negative correlation with changes in edge density and mean Euclidean nearest neighbor distance (p < 0.05). There is telecoupling between urban expansion in one region and forest ES loss in other distant regions. This study contributes to guiding sustainable forest conservation and management globally.

Spatiotemporal patterns of urban forest carbon sequestration capacity: Implications for urban CO2 emission mitigation during China's rapid urbanization

Urban forests provide ecological functions and human well-being. However, spatiotemporal changes in urban forest carbon sequestration (CS) under rapid urbanization remain poorly understood. We established a model to predict the annual CS dynamics in urban forests based on plot-measured CS and Landsat images. Our results showed that the urban forest coverage in Changchun increased from 18.09 % to 24.01 % between 2000 and 2019, especially in the urban suburbs. However, urban forest patches became more fragmented and less connected, particularly in the urban center. The NDVI is better than other vegetation indices for mapping urban forest CS. We observed a gradual increase in urban forest CS capacity from 2000 to 2019, with higher CS capacity found in urban suburbs compared to urban centers. The class distribution of urban forest CS capacity was skewed toward low values (0-2 g·m-2·d-1), but this tendency diminished gradually. In 2000, the urban forest in Changchun offset approximately 2.11 % of carbon emissions but declined to 0.88 % by 2019 due to increased carbon emissions. Rapid urbanization was the main factor affecting CS, with impervious surface area accounting for 48.7 % of the variation. Urban landscape pattern indices also influenced the CS, with higher forest patch connectivity and lower patch density leading to greater CS capacity. Our study helps urban managers develop urban greening strategies for carbon neutrality and low-carbon city.

Drought conditions, aridity and forest structure control the responses of Iberian holm oak woodlands to extreme droughts: A large-scale remote-sensing exploration in eastern Spain

Understanding how Mediterranean forests respond to the increasing frequency of extreme droughts and forest densification is crucial for effective land management in the present context of climate change and land abandonment. We study the responses of Iberian holm oak (Quercus ilex L.) woodlands to recent extreme droughts during 2000-2019 along broad gradients of climate aridity and forest structure. To this purpose, we apply large-scale remote-sensing using MODIS EVI as a primary production proxy in 5274 Q. ilex sites distributed within a 100,000 km2 region in eastern Spain. These woodlands were extensively affected by two extreme drought events in 2005 and 2012. Resistance, assessed as the capacity of the ecosystems to maintain primary production during drought, was significantly lower for semi-arid than for sub-humid and dry-transition conditions. Holm oak woodlands located in semi-arid areas of the region showed also poorer resilience to drought, characterized by low capacity to fully recover to their pre-drought production levels. Further, drought intensity and both pre- and post-drought hydric conditions controlled the variations of resistance, recovery and resilience between the two analyzed extreme drought events. Drought effects were particularly negative for dense Q. ilex stands under semi-arid climate conditions, where strong competition for scarce water resources reduced drought resistance. The observed drought vulnerability of semi-arid holm oak woodlands may affect the long-term stability of these dry forests. Adaptive management strategies, such as selective forest thinning, may be useful for improving drought responses in these more vulnerable semi-arid woodlands. Conversely, natural rewilding may more appropriately guide management actions for more humid areas, where densely developed Q. ilex woodlands show in general a high ability to maintain ecosystem primary production during drought.

Effect of forest management choices on carbon sequestration and biodiversity at national scale

Forest management methods and harvest intensities influence wood production, carbon sequestration and biodiversity. We devised different management scenarios by means of stakeholder analysis and incorporated them in the forest growth simulator PREBAS. To analyse impacts of harvest intensity, we used constraints on total harvest: business as usual, low harvest, intensive harvest and no harvest. We carried out simulations on a wall-to-wall grid in Finland until 2050. Our objectives were to (1) test how the management scenarios differed in their projections, (2) analyse the potential wood production, carbon sequestration and biodiversity under the different harvest levels, and (3) compare different options of allocating the scenarios and protected areas. Harvest level was key to carbon stocks and fluxes regardless of management actions and moderate changes in proportion of strictly protected forest. In contrast, biodiversity was more dependent on other management variables than harvesting levels, and relatively independent of carbon stocks and fluxes.

Responses of plant carbon and nitrogen assimilations to nitrogen addition in a subtropical forest: Canopy addition vs. understory addition

The global atmospheric nitrogen (N) deposition has intensified in recent years, resulting in a complex impact on forest ecosystems. This study investigated the effects of canopy (CAN) and understory additions of N (UAN) on leaf carbon (C) and N assimilations, as well as growth parameters of representative woody plant species in an evergreen broad-leaved forest, i.e. Castanea henryi, Schefflera heptaphylla, Blastus cochinchinensis, and Lasianthus chinensis. The results showed that leaf N assimilation key enzyme nitrate reductase (NR) activities of B. cochinchinensis and S. heptaphylla were significantly decreased by UAN, and were significantly decreased by CAN for C. henryi. CAN significantly decreased the nitrite reductase activity of C. henryi, while significantly increased that of L. chinensis. However, the Amax values of each woody species were not significantly different among control (CK), CAN, and UAN. Community surveys demonstrated that CAN and UAN inhibited the growth (diameter at breast height, height, or crown width) of the representative large tree, C. henryi, while promoting the growths of understory woody species (B. cochinchinensis and L. chinensis). Overall, N addition was found to change the physiological processes of N and C metabolisms of the dominant woody species in an evergreen broad-leaved forest. The community of subtropical evergreen broad-leaved forests may further decline and its C fixation capacity may be detrimentally changed under N deposition in the future.

Coupling Mountain Pine Beetle and Forest Population Dynamics Predicts Transient Outbreaks that are Likely to Increase in Number with Climate Change

Mountain pine beetle (MPB) in Canada have spread well beyond their historical range. Accurate modelling of the long-term dynamics of MPB is critical for assessing the risk of further expansion and informing management strategies, particularly in the context of climate change and variable forest resilience. Most previous models have focused on capturing a single outbreak without tree replacement. While these models are useful for understanding MPB biology and outbreak dynamics, they cannot accurately model long-term forest dynamics. Past models that incorporate forest growth tend to simplify beetle dynamics. We present a new model that couples forest growth to MPB population dynamics and accurately captures key aspects of MPB biology, including a threshold for the number of beetles needed to overcome tree defenses and beetle aggregation that facilitates mass attacks. These mechanisms lead to a demographic Allee effect, which is known to be important in beetle population dynamics. We show that as forest resilience decreases, a fold bifurcation emerges and there is a stable fixed point with a non-zero MPB population. We derive conditions for the existence of this equilibrium. We then simulate biologically relevant scenarios and show that the beetle population approaches this equilibrium with transient boom and bust cycles with period related to the time of forest recovery. As forest resilience decreases, the Allee threshold also decreases. Thus, if host resilience decreases under climate change, for example under increased stress from drought, then the lower Allee threshold makes transient outbreaks more likely to occur in the future.

Big-sized trees and higher species diversity improve water holding capacities of forests in northeast China

High water-holding forests are essential for adapting to drought climates under global warming, and a central issue is which type of forests could conserve more water in the ecosystem. This paper explores how forest structure, plant diversity, and soil physics impact forest water-holding capacities. We investigated 720 sampling plots by measuring water-holding capacities from 1440 soil and litter samples, 8400 leaves, and 1680 branches and surveying 18,054 trees in total (28 species). Water-holding capacities were measured as four soil indices (Maxwc, maximum water-holding capacity; Fcwc, field water-holding capacity; Cpwc, soil capillary water-holding capacity; Ncpwc, non-capillary water-holding capacity), two litter metrics (Maxwcl, maximum water-holding capacity of litters; Ewcl, effective water-holding capacity of litters), and canopy interception (C, the sum of estimated water interception of all branches and leaves of all tree species in the plot). We found that water-holding capacity in the big-sized tree plots was 4-25 % higher in the litters, 54-64 % in the canopy, and 6-37 % in the soils than in the small-sized plots. The higher species richness increased all soil water-holding capacities compared to the lowest richness plot. Higher Simpson and Shannon-Wiener plots had 10-27 % higher Ewcl and C than the lowest plots. Bulk density had the strongest negative relations with Maxwc, Cpwc, and Fcwc, whereas field soil water content positively affected them. Soil physics, forest structure, and plant diversity explained 90.5 %, 5.9 %, and 0.2 % of the water-holding variation, respectively. Tree sizes increased C, Ncpwc, Ewcl directly (p < 0.05), and richness increased Ewcl directly (p < 0.05). However, the direct effects from the uniform angle index (tree distribution evenness) were balanced by their indirect effect from soil physics. Our findings highlighted that the mixed forests with big-sized trees and rich species could effectively improve the water-holding capacities of the ecosystem.

How biotic, abiotic, and functional variables drive belowground soil carbon stocks along stress gradient in the Sundarbans Mangrove Forest?

Mangrove forests, some of the most carbon-dense ecosystems on Earth, play an important role in climate change mitigation through storing carbon in the soil. However, increasing anthropogenic pressures and sea level rise are likely to alter mangrove forest structure and functions, including the major source of carbon in mangrove ecosystems - below-ground soil carbon stocks (BSCS). Although estimating soil carbon stocks has been a popular practice in the mangroves, but poorly understood the (I) the linkage between BSCS and key ecosystem drivers (i.e., biotic, abiotic, and functional) and in (II) determining the pathways of how BSCS and multiple forest variables interact along stress gradients. This lack of understanding limits our ability to predict ecosystem carbon dynamics under future changes in climate. Here, we aimed to understand how abiotic factors (such as salinity, canopy gap fraction, nutrients, and soil pH), biotic factors (e.g., structural parameters, canopy packing, and leaf area index, LAI), and forest functional variables (e.g., growth and aboveground biomass stocks, AGB) affect BSCS (i.e., soil organic carbon, SOC, and root carbon, RC) using spatiotemporal data collected from the Sundarbans Mangrove Forest (SMF) in Bangladesh. We observed that BSCS decreased significantly with increasing salinity (e.g., from 70.6 Mg C ha^-1 in the low-saline zone to 44.6 Mg C ha^-1 in the high-saline zone). In contrast, the availability of several macronutrients (such as nitrogen, phosphorous, and potassium), LAI, species diversity, AGB, and growth showed a significant positive effect on SOC and RC. Stand properties, including tree height, basal area, density, canopy packing, and structural diversity, had a non-significant but positive impact on RC, while tree height and basal area significantly influenced SOC. Pathway analysis showed that salinity affects BSCS variability directly and indirectly by regulating stand structure and restricting nutrients and forest functions, although basal area, nutrients, and LAI directly enhance RC stocks. Our results indicate that an increase in nutrient content, canopy density, species diversity, and leaf area index can enhance BSCS, as they improve forest functions and contribute to a better understanding of the underlying mechanisms.

Scale-dependent and driving relationships between spatial features and carbon storage and sequestration in an urban park, in Zhengzhou, China

Research indicates that urban ecosystems can store large amounts of carbon. However, few studies have examined how the spatial features of park greenspace affect its carbon-carrying capacity, and how those effects vary with the spatial scale. Lidar point clouds and remote sensing images were extracted for the 196 ha green space in the China Green Expo to study carbon storage and sequestration in parks. Full subset regression, stepwise regression, HP analysis, and structural equation modeling were used to examine the scale dependency and the driving relationship between carbon storage and carbon sequestration in parks. The results show that the optimal statistical sample diameters for carbon density and carbon sequestration density in parks are 100 m. Under the influence of impermeable surfaces and water bodies, the statistical values of carbon density were minimized when the sample plot diameter was 700 m. Biodiversity and forest structure are the main drivers of carbon density, with the influence of water bodies being more prominent on a larger scale. Texture characteristics explain more carbon density than the vegetation index, and RVI could better explain the variation of carbon sequestration than NDVI. This study explores scaled changes in carbon density, carbon sequestration density in parks, and their driving relationships, which can aid in developing carbon sequestration strategies based on parks.

Long-term tropical cyclones activity shapes forest structure and reduces tree species diversity of U.S. temperate forests

Increasing tropical cyclone (TC) pressure on temperate forests is inevitable under the recent global increase of the intensity and poleward migration of TCs. However, the long-term effects of TCs on large-scale structure and diversity of temperate forests remain unclear. Here, we aim to ascertain the legacy of TCs on forest structure and tree species richness by using structural equation models that consider several environmental gradients and use an extensive dataset containing >140,000 plots with >3 million trees from natural temperate forests across eastern United States impacted by TCs. We found that high TC activity (a combination of TC frequency and intensity) leads to a decrease in maximum tree sizes (height and diameter), an increase in tree density and basal area, and a decline in the number of tree species and recruits. We identified TC activity as the strongest predictor of forest structure and species richness in xeric (dry) forests, while it had a weaker impact on hydric (wet) forests. We highlight the sensitivity of forest structure and tree species richness to impacts of likely further increase of TC activity in interaction with climate extremes, especially drought. Our results show that increased TC activity leads to the homogenization of forest structure and reduced tree species richness in U.S. temperate forests. These findings suggest that further declines in tree species richness may be expected because of the projected increase of future levels of TC activity.

Streamlining urban forest monitoring based on a large-scale tree survey: a case study of highway vegetation in Hong Kong

Through the analysis of an urban tree inventory with the aid of machine learning, this study brought together different aspects of urban forestry. Urban tree monitoring is essential to successful urban forestry. Transport land use accommodates huge tree stock which requires substantial monitoring efforts. In Hong Kong, more research is needed to take into consideration how monitoring works can be improved in response to variations in tree stand characteristics. This case study aimed to illustrate the usefulness of a large-scale tree survey in mainstreaming future tree monitoring and management in transport land use. A total of 7209 trees were found in a large-scale tree survey conducted in 53 slopes and 52 verges along San Tin Highway in Hong Kong. Dominance by Corymbia citriodora (72%) was observed, especially for the highway verges. Using chi-square tests, significant associations were found between monospecific stands, habitat type, and tree risk rating. A logistic regression model was constructed to predict the occurrence of monoculture. Every metre increase in maximum tree height, the odds of a stand being monospecific would be 1.22 times greater. Stands on verges had 5.26 times greater odds of being monospecific against the slope. The associations and relationships were attributed to the dominance of C. citriodora. By boosting the logistic model, model reliability increased as kappa rose from 0.51 to 0.63, while balanced accuracy improved from 0.72 to 0.85. The occurrence of monospecific stands could be reliably predicted using maximum tree height and habitat type of tree stands. These quantitative findings monitoring can guide urban forest monitoring. Through a better understanding of urban forest structure and composition, future monitoring can aid the mainstreaming of urban forestry in transport planning.

Biodiversity responses to restoration across the Brazilian Atlantic Forest

The UN Decade on Ecosystem Restoration is focussing attention and resources on restoration globally. Nowhere is this more crucial than in tropical forests that harbor immense biodiversity, but have also undergone widespread deforestation over the past few decades. We performed a meta-analysis to investigate how biodiversity features respond to forest restoration across the Brazilian Atlantic Forest (BAF), one of the most threatened biodiversity hotspots in the world. We assembled biodiversity in different metrics of structure and diversity features of three taxonomic groups (vascular plants, soil microorganisms, and invertebrates), generating a dataset with 2370 observations from 76 primary studies. We quantified the incomplete recovery of biodiversity (i.e., the rate of recovery to a pre-disturbance state) occurring during the restoration process, which we called the 'recovery gap'. Our results revealed that forests undergoing restoration in the BAF show a recovery gap of 34% for structure features and 22% for diversity features in comparison to reference reforests, considering all taxonomic groups investigated. For vascular plants, soil microorganisms, and invertebrates the recovery gap ranged between 46 and 47%, 16-26%, and 4-7%, respectively. Overall, the recovery gap was influenced by the interaction of restoration actions (i.e., the past land use, restoration age and restoration approach - active and passive restoration), however, structure features responded more sensitively to the time elapsed since restoration started, while the recovery gap for diversity features depended more on the past land-use. Our study can help guide the prioritization of the aforenamed taxonomic groups in restoration, the regulation of potential biodiversity offsetting policies in the BAF, and understanding how coupled biodiversity features respond to the interaction of environmental conditions and restoration actions in a high fragmented tropical landscape.

Estimation of trees height and vertical structure using SAR interferometry in uneven-aged and mixed forests

Estimation of forest height is an important parameter of stands structure that aids in the determination of forest biomass, successional stage dynamics, and the decision of the type of forest management. In addition, estimating the height of trees especially in uneven-aged, massive, and multi-storied forest stands always faces challenges in kind of inventory and accuracy of the assessment. In this research, the synthetic aperture radar (SAR) interferometry technique was used to estimate the height of trees for determining the vertical structure of forest. For this purpose, we focused on an area at the mixed and uneven-aged forest in Iran and evaluated the potential of Envisat ASAR data to characterize the tree height in the forest patches and the digital surface model (DSM) was produced via SAR interferometry. The height of trees and the vertical structure of the forest stands were estimated using produced DSM and Digital elevation Model (DEM). Furthermore, the accuracy of estimated parameters was evaluated with real ground data (11 × 1 ha (100 × 100 m) sample plots). The results indicated that the estimated height of trees was meanly 7.69 m with a 22 m STDV over the reality. Furthermore, the vertical structure in all the plots was three-storied that they are the same as ground truth, but the percentage of the share of trees in the under and middle story was different from the ground truth. In conclusion, the tree height and vertical structure of forest stands can be determined with acceptable accuracy via SAR interferometry and Envisat ASAR data.

Traditional and TLS-based forest inventories of beech and pine forests located in Sila National Park: A dataset

Vegetation structure is a key determinant of species distribution and diversity. Compared to traditional methods, the use of Terrestrial Laser Scanning (TLS) has allowed massive amounts of point cloud data collected for quantifying three-dimensional habitat properties at increasing spatial and temporal scales. We used TLS to characterize the forest plots across a broad range of forest structural diversity, located in the Sila National Park, South Italy. The dataset reports data collected in 24 15-m-radius circular plots, 12 of which were dominated by beech (Fagus sylvatica L.) and 12, by black pine (Pinus nigra subsp. laricio). In detail, this work provides dataset of i) plot-level attributes calculated from raw data, such as the number of trees, ii) tree-level data, comprising a total of 1709 trees, with information related to field-based forest inventory such as the diameter at breast height (DBH), and iii) plot-level information related to the time for conducting both traditional field- and TLS-based forest inventories. Compared to traditional methods, the use of TLS allows a very high-resolution quantification of the 3D forest structural properties, also reducing the time for conducting forest inventories.

Forest structure dependency analysis of L-band SAR backscatter

Forest structure plays an important role in forest biomass inversion using synthetic aperture radar (SAR) backscatter. Synthetic aperture radar (SAR) sensors with long-wavelength have the potentiality to provide reliable and timely forest biomass inversion for their ability of deep penetration into the forest. L-band SAR backscatter shows useful for forest above-ground biomass (AGB) estimation. However, the way that forest structure mediating the biomass-backscatter affects the improvement of the related biomass estimation accuracy. In this paper, we have investigated L-band SAR backscatter sensitivity to forests with different mean canopy density, mean tree height and mean DBH (diameter at breast height) at the sub-compartment level. The forest species effects on their relationship were also considered in this study. The linear correlation coefficient R, non-linear correlation parameter, Maximal Information Coefficient (MIC), and the determination coefficient R² from linear function, Logarithmic function and Quadratic function were used in this study to analyze forest structural properties effects on L-band SAR backscatter. The HV channel, which is more sensitive than HH to forest structure parameters, was chosen as the representative of SAR backscatter. 6037 sub-compartment were involved in the analysis. Canopy density showed a great influence on L-band backscatter than mean forest height and DBH. All of the R between canopy density and L-band backscatter were greater than 0.7 during the forest growth cycle. The sensitivity of L-band backscatter to mean forest height depends on forest canopy density. When canopy density was lower than 0.4, R values between mean forest height are smaller than 0.5. In contrast, the values of R were greater than 0.8 if canopy density was higher than 0.4. The sensitivity SAR backscatter to DBH fluctuated with canopy density, but it only showed obvious sensitivity when canopy density equals to 0.6, where both the linear and non-liner correlation values are higher than others. However, their effects on L-bang HV backscatter are affected by forest species, the effects on three forest structural parameters depend on tree species.

Factors promoting the natural regeneration of Larix principis-rupprechtii plantation in the Lvliang Mountains of central China

Given their complexity, targeted care and management of different areas and tree species are necessary for enhancing the natural regeneration of forests. Thus, an understanding of changes in the overstory and understory is essential for ensuring successful regeneration. Promoting the natural regeneration of Larix principis-rupprechtii plantations is considered challenging; indeed, regional sustainable development through natural regeneration of many stands has often been considered unattainable. Here, we studied several plots with varying extents of regeneration to identify the most important factors that affect regeneration. The plots were divided into three forest types based on the number of regenerating plants. For each type of plot, we measured various factors that might potentially affect regeneration. Representational difference analysis was used to identify the most important factors >9% contribution). Based on these factors, multiple corrections were made to construct a structural equation model of topography, stand structure, soil properties and litter to identify the most important factors driving variation in regeneration. Positive correlations were detected between regeneration with diameter at breast height (0.21) and litter thickness (0.57). Regeneration was negatively correlated with soil (-0.54) and slope (-0.48). Additionally, the number of regenerating plants and the height of regenerating plants were strongly positively correlated. However, there was no significant relationship between regeneration and litter accumulation, stand density, altitude, average tree height, total P and total N. Overall, our study showed that key factors for promoting natural regeneration include appropriate litter thickness, strong parent trees, a gentle slope and sufficient quantities of soil nutrients. Moreover, our findings provide a reference for the design of effective management and restoration plans.

Spatio-temporal transpiration patterns reflect vegetation structure in complex upland terrain

Topography exerts control on eco-hydrologic processes via alteration of energy inputs due to slope angle and orientation. Further, water availability varies with drainage position in response to topographic water redistribution and the catena effect on soil depth and thus soil water storage capacity. Our understanding of the spatio-temporal dynamics and drivers of transpiration patterns in complex terrain is still limited by lacking knowledge of how systematic interactions of energy and moisture patterns shape ecosystem state and water fluxes and adaptation of the vegetation to these patterns. To untangle the effects of slope orientation and hillslope position on forest structure and transpiration patterns, we measured forest structure, sap flux, soil moisture, throughfall and incoming shortwave radiation along two downslope transects in a forested head water catchment in south-east Australia. Our plot locations controlled for three systematically varying drainage position levels (topographic wetness index: 5.0, 6.5 and 8.0) and two levels of energy input (aridity index: 1.2 and 1.8). Vegetation patterns were generally stronger related to drainage position than slope orientation, whereas sap velocity variations were less pronounced. However, in combination with stand sapwood area, consistent spatio-temporal transpiration patterns emerged in relation to landscape position, where slope orientation was the primary and drainage position the secondary controlling factor. On short temporal scales, radiation and vapor pressure deficit were most important in regulating transpiration rates, whereas soil water limitation only occurred on shallow soils during summer. The importance of stand structural parameters increased on longer time scales, indicating optimization of vegetation in response to the long-term hydro-climatic conditions at a given landscape position. Thus, vegetation patterns can be conceptualized as a 'time-integrated' predictor variable that captures large fractions of other factors contributing to transpiration patterns.

Asymmetric competition, ontogenetic growth and size inequality drive the difference in productivity between two-strata and one-stratum forest stands

Size inequality has been considered a key feature of plant population structure with impacts on ecosystem functions. In forest ecosystems, studies examining the relationship between tree size inequality and stand productivity have produced mixed outcomes. These studies found positive, neutral or negative relationships and discussed how this could be influenced by competition for light between trees (e.g. light interception efficiency), but far less attention has been paid to the role played by tree ontogenetic growth. In this article, we present a simple mathematical model that predicts the basal area growth of a two-strata stand as a function of tree basal areas and asymmetric competition. Comparing the growth of this stand to the growth of a spatially homogeneous one-stratum stand and a spatially heterogeneous one-stratum stand, we show that higher growth of the two-strata stand is achieved for concave shape, increasing functions of ontogenetic growth and for low intensities of absolute size-asymmetric competition. We also demonstrate that the difference in growth between the two-strata stand and the one-stratum stands depends on tree size inequality, mean tree basal area and total basal area in the two-strata stand. We finally found that the relationships between tree size inequality and productivity can vary from positive to negative and even non-monotonous. However, we highlight that negative relationships may be more frequent. As a conclusion, our results indicate that ontogenetic growth can have a major impact on the form and the magnitude of the size inequality-productivity relationship.

Nutrient, metal contents and microbiological properties of litter and soil along a tree age gradient in Mediterranean forest ecosystems

The link among the age of aboveground tree species, litter, soil quality and status in Mediterranean forests is not entirely comprehended (especially in Mediterranean forest sites). This study evaluates whether and by what extent tree stand composition and forest structure modify nutrient depository or alter physical, chemical and microbiological properties of soil and litter in a 120 years old pine forest chronosequence. In general, the enzymatic activity related to the phosphorous, carbon and nitrogen cycles were more developed in litter than in soil surface, while the sulphur enzymatic activity was not significantly different between the two analyzed systems. The higher dehydrogenase content measured in the litter may be an index of a higher extracellular microbial activity, compared to soil. A noticeable effect of forest age and structure on the majority of analyzed elements was detected, with nutrients and metals tending to accumulate in soil rather in the litter. Moreover, the contents of P and some metals and sulphur enzymatic activity in the litter are influenced by forest age and associated forest structure. Finally, since nutrient, metals and enzyme contents in the litter increase with forest age, forest management strategies targeted to increase the stand structure may be advisable in order to achieve higher soil functionality.

Influence of stand density and canopy structure on the germination and growth of Scots pine (Pinus sylvestris L.) seedlings

Since the natural regeneration of Scots pine forests is known to be difficult, the effects of canopy structure and environmental variables such as light on germination, seedling growth, and mortality need to be well understood. The knowledge on the relationships between canopy structure, environmental variables, and seedling growth have been helpful for forest managers to formulate silvicultural prescriptions that enhance seedling recruitment. In this study, the influences of stand basal area (BA) (m² ha^-1), leaf area index (LAI), light transmittance (LT), and height-to-crown base (HCB) on germination and seedling growth were explored in a naturally regenerated Scots pine forest in Kastamonu, Turkey. The number of germinants was observed following germination, and total root-collar diameter (RCD) and height of seedlings were monitored after five growing seasons following germination. BA, LAI, LT, and HCB were also examined to determine which variable has more influence on Scots pine seedlings. All variables (i.e., BA, LAI, LT, and HCB) had significant influence on the total seedling growth over a 5-year period. LT was the most significant predictor for total RCD growth and height growth of Scots pine seedlings. The data support the importance of light transmittance through the canopy, along with vertical canopy structure (i.e., HCB) when considering seedling development under a stand canopy.

Spatial distribution, mobility and bioavailability of arsenic, lead, copper and zinc in low polluted forest ecosystem in North-western Mexico

A geochemical-environmental mapping was carried for a low polluted forest in North-western Mexico (Santiago Papasquiaro mining area), as part of the North American forests accounting for environmental behavior of arsenic (As), lead (Pb), zinc (Zn) and copper (Cu) in soil and tree components (stem wood and aciculums). Spectroscopic and microscopic techniques along with standard protocols were used to determine the mineralogical phases containing these elements, and their corresponding spatial distributions in soil and forests and mobility. In soil, total As, Pb, Zn and Cu ranged from 4.9 to 98.3, 19.6 to 768.6, 19.6 to 407.1, and 1.6 to 63.8 mg kg^-1, respectively. Ultrafine particles (<5-10 μm) of arsenopyrite and sphalerite (and complex Zn-Fe phase) were the main As and Zn-bearing phases determined by SEM-EDS, respectively. Complex Pb-Cu-Fe and Cu-O oxide-like phases were the only ones containing Pb and Cu, respectively. Mobility was low for Pb, Zn and Cu, whereas a significant mobility was assessed for As. Concentrations vs. depth profiles suggested progressive accumulations of As, Pb, Zn and Cu in top soil. Total As, Pb, Zn and Cu in pine stem wood varied from 11.5 to 184.5, 98.9 to 7359.8, 3242.7 to 22197.3, 689.2 to 7179.6 μg kg^-1, respectively. The respective concentrations in the pine needles ranged from 50 to 624.2, 100 to 16353.1, 120 to 46440.9 and 720 to 7200 μg kg^-1, indicating an active bioaccumulation of As, Pb, Zn and Cu. A prospective environmental behavior was discussed for As, Pb, Zn and Cu in the low-polluted forest.

Aerial-hawking bats adjust their use of space to the lunar cycle

BACKGROUND

Animals change their habitat use in response to spatio-temporal fluctuation of resources. Some resources may vary periodically according to the moonphase. Yet it is poorly documented how animals, particularly nocturnal mammals, adjust their use of space in response to the moonphase.Here, we asked if an obligate nocturnal mammal, the aerial-hawking common noctule bat (Nyctalus noctula), adjusts its 3-dimensional flight behaviour and habitat use to the lunar period. Using miniaturized GPS loggers, we recorded 3-dimensional flight tracks of N. noctula and related these to a canopy height model derived from aerial laser scans to investigate whether bats adjust forest strata use to moonlight intensities.

RESULTS

Noctules frequently foraged above the canopy of coniferous forest at low moonlight intensities, but switched to using open grasslands and arable fields in nights with high moonlight intensities. During the few occasions when noctules used the forest during moonlit nights, they mostly restricted their use of space to flying below the canopy level. The median overall flight altitude of N. noctula equalled 13 ± 16 m but reached up to 71 m above ground (97.5% quantile).

CONCLUSIONS

Our findings argue against general lunar phobic behaviour of aerial-hawking bats. We suggest that the preferred use of open fields around full moon may be a strategy of noctules to increase the success of hunting airborne insects at night. Specifically, the adjustment in use of space may allow bats to hunt for insects that emerge and disperse over open fields during bright moonlight.

Tree community structure reflects niche segregation of three parapatric squirrel monkey species (Saimiri spp.)

Integration between ecology and biogeography provides insights into how niche specialization affects the geographical distribution of species. Given that rivers are not effective barriers to dispersal in three parapatric species of squirrel monkeys (Saimiri vanzolinii, S. cassiquiarensis and S. macrodon) inhabiting floodplain forests of Central Amazonia, we tested whether forest structure and tree diversity may explain species differences in niche specialization and spatial segregation. We sampled 6617 trees of 326 species in three habitats (high várzea, low várzea and chavascal) used by three Saimiri species, and estimated tree species richness in each of them. For each tree, we measured variables known to influence habitat use in primates, such as crown area and presence of lianas, epiphytes and hemi-epiphytes. We used ANOVA to compare these variables and performed multivariate analyses (NMDS, ANOSIM and SIMPER) to evaluate dissimilarities in forest structure among each habitat inhabited by the three Saimiri species. We identified differences in the tree species richness, crown area and presence of lianas, epiphytes and hemi-epiphytes between the three habitats for all Saimiri species. NMDS demonstrated that areas of high and low várzeas occupied by S. vanzolinii were clearly separated from the other species. We also found that different plant species contributed to dissimilarity among Saimiri ranges. Our findings support the hypothesis that tree community structure may promote niche specialization and spatial segregation among primates. We discuss how these patterns could have been favored by historical changes in forest flood patterns, the evolutionary history of Saimiri spp., and past competition.

Characteristics of tropical human-modified forests after 20 years of natural regeneration

BACKGROUND

Abandoned human-modified forests are refuges for remnant biodiversity. However, there are very few studies on the biodiversity and regeneration of native species in human-modified forests which are rich in exotic trees. Our research aim is to evaluate the regeneration status and biodiversity of two adjacent human-modified forests. The two forests have distinct overstorey exotic species richness prior to abandonment: one is an exotic tree plantation low in species richness, and the other is an exotic arboretum high in species richness. The original management practices of the two forests have been neglected for more than 20 years. A primary forest was selected as a reference forest to compare their diversity and regeneration status. We asked: (1) Is there a structural difference among the three forests? (2) What are the proportions of native saplings in the human-modified forests? (3) Are the introduced exotic species able to naturalize?

RESULTS

We recorded 1316 individuals from 88 species, belonging to 69 genera and 34 families in the three forests [each sampled 16 quadrats (10 m × 5 m)]. Both human-modified forests were similar in their height structure, diameter structure, and sapling density, but differed in species diversity (characterized by rarefaction curves) and floristic composition (indicated by a quantitative similarity index). In the arboretum, only 50% of the sapling individuals were native. Surprisingly, when sampling efforts were standardized, the arboretum had higher native sapling species richness than the exotic species-poor plantation. Moreover, both human-modified forests had conserved a few rare and endemic species. Nevertheless, some exotic species in the arboretum had escaped to the nearby plantation.

CONCLUSIONS

After 20 years of abandonment, the two human-modified forests had converged in structure, but not in diversity patterns of native saplings. This could be due to that the diversity of exotic overstorey composition can influence the natural regeneration of understorey plants. Our study also raised concerns about conserving native species and managing naturalized exotic species in these human-modified forests.

Evaluation of forest structure, biomass and carbon sequestration in subtropical pristine forests of SW China

Very old natural forests comprising the species of Fagaceae (Lithocarpus xylocarpus, Castanopsis wattii, Lithocarpus hancei) have been prevailing since years in the Ailaoshan Mountain Nature Reserve (AMNR) SW China. Within these forest trees, density is quite variable. We studied the forest structure, stand dynamics and carbon density at two different sites to know the main factors which drives carbon sequestration process in old forests by considering the following questions: How much is the carbon density in these forest trees of different DBH (diameter at breast height)? How much carbon potential possessed by dominant species of these forests? How vegetation carbon is distributed in these forests? Which species shows high carbon sequestration? What are the physiochemical properties of soil in these forests? Five-year (2005-2010) tree growth data from permanently established plots in the AMNR was analysed for species composition, density, stem diameter (DBH), height and carbon (C) density both in aboveground and belowground vegetation biomass. Our study indicated that among two comparative sites, overall 54 species of 16 different families were present. The stem density, height, C density and soil properties varied significantly with time among the sites showing uneven distribution across the forests. Among the dominant species, L. xylocarpus represents 30% of the total carbon on site 1 while C. wattii represents 50% of the total carbon on site 2. The average C density ranged from 176.35 to 243.97 t C ha^-1. The study emphasized that there is generous degree to expand the carbon stocking in this AMNR through scientific management gearing towards conservation of old trees and planting of potentially high carbon sequestering species on good site quality areas.

Rainforests north of the Tropic of Cancer: Physiognomy, floristics and diversity in 'lowland rainforests' of Meghalaya, India

The lowland rainforests of Meghalaya, India represent the westernmost limit of the rainforests north of the Tropic of Cancer. These forests, on the Shillong plateau, are akin to Whitmore's 'tropical lowland evergreen rainforest' formation and exhibit striking similarities and conspicuous differences with the equatorial rainforests in Asia-Pacific as well as tropical seasonal rainforests in southwestern China near the Tropic of Cancer. We found these common attributes of the rainforests in Meghalaya: familial composition with predominance of Euphorbiaceae, Lauraceae, Meliaceae, Moraceae, Myrsiticaceae, Myrtaceae and Rubiaceae; deciduousness in evergreen physiognomy; dominance of mega- and mesophanerophytic life-forms; abundance of species with low frequency of occurrence (rare and aggregated species); low proportional abundance of the abundant species; and truncated lognormal abundance distribution. The levels of stand density and stand basal area were comparable with seasonal rainforests in southwestern China, but were lower than equatorial rainforests. Tropical Asian species predominated flora, commanding 95% of the abundance. The differences include overall low stature (height) of the forest, inconspicuous stratification in canopy, fewer species and individuals of liana, thicker understory, higher proportion of rare species, absence of locally endemic species and relatively greater dominance of Fagaceae and Theaceae. The richness of species per hectare (S) was considerably lower at higher latitudes in Meghalaya than in equatorial rainforests, but was comparable with seasonal rainforests. Shannon's diversity index (H' = 4.40 nats for ≥10 cm gbh and 4.25 nats for ≥30 cm gbh) was lower on higher latitudes in Meghalaya in comparison to species-rich equatorial rainforests, but it was the highest among all lowland rainforests near the Tropic of Cancer.

Influence of forest management systems on natural resource use and provision of ecosystem services in Tanzania

Social, religious and economic facets of rural livelihoods in Sub-Saharan Africa are heavily dependent on natural resources, but improper resource management, drought, and social instability frequently lead to their unsustainable exploitation. In rural Tanzania, natural resources are often governed locally by informal systems of traditional resource management (TRM), defined as cultural practices developed within the context of social and religious institutions over hundreds of years. However, following independence from colonial rule, centralized governments began to exercise jurisdictional control over natural resources. Following decades of mismanagement that resulted in lost ecosystem services, communities demanded change. To improve resource protection and participation in management among stakeholders, the Tanzanian government began to decentralize management programs in the early 2000s. We investigated these two differing management approaches (traditional and decentralized government) in Sonjo communities, to examine local perceptions of resource governance, management influences on forest use, and their consequences for forest and water resources. While 97% of households understood the regulations governing traditionally-managed forests, this was true for only 39% of households for government-managed forests, leading to differences in forest use. Traditional management practices resulted in improved forest condition and surface water quality. This research provides an essential case study demonstrating the importance of TRM in shaping decision frameworks for natural resource planning and management.

Forests of opportunities and mischief: disentangling the interactions between forests, parasites and immune responses

Habitat characteristics determine the presence of individuals through resource availability, but at the same time, such features also influence the occurrence of parasites. We analyzed how birds respond to changes in interior forest structures, to forest management regimes, and to the risk of haemosporidian infections. We captured and took blood samples from blackcaps (Sylvia atricapilla) and chaffinches (Fringilla coelebs) in three different forest types (beech, mixed deciduous, spruce). We measured birds' body asymmetries, detected avian haemosporidians, and counted white blood cells as an immune measure of each individual per forest type. We used, to our knowledge for the first time, continuous forest structural parameters to quantify habitat structure, and found significant effects of habitat structure on parasite prevalence that previously have been undetected. We found three times higher prevalence for blackcaps compared with chaffinches. Parasite intensity varied significantly within host species depending on forest type, being lowest in beech forests for both host species. Structurally complex habitats with a high degree of entropy had a positive effect on the likelihood of acquiring an infection, but the effect on prevalence was negative for forest sections with a south facing aspect. For blackcaps, forest gaps also had a positive effect on prevalence, but canopy height had a negative one. Our results suggest that forest types and variations in forest structure influence the likelihood of acquiring an infection, which subsequently has an influence on host health status and body condition; however, responses to some environmental factors are host-specific.

Differences in the impacts of formal and informal recreational trails on urban forest loss and tree structure

Recreational trails are one of the most common types of infrastructure used for nature-based activities such as hiking and mountain biking worldwide. Depending on their design, location, construction, maintenance and use, these trails differ in their environmental impacts. There are few studies, however, comparing the impacts of different trail types including between formal management-created trails and informal visitor-created trails. Although both types of trails can be found in remote natural areas, dense networks of them often occur in forests close to cities where they experience intense visitor use. To assess the relative impacts of different recreational trails in urban forests, we compared the condition of the trail surface, loss of forest strata and changes in tree structure caused by seven types of trails (total network 46.1 km) traversing 17 remnants of an endangered urban forest in Australia. After mapping and classifying all trails, we assessed their impact on the forest condition at 125 sites (15 sites per trail type, plus 15 control sites within undisturbed forest). On the trail sites, the condition of the trail surface, distance from the trail edge to four forest strata (litter, understory, midstorey and tree cover) and structure of the tree-line were assessed. Informal trails generally had poorer surface conditions and were poorly-designed and located. Per site, formal and informal trails resulted in similar loss of forest strata, with wider trails resulting in greater loss of forest. Because there were more informal trails, however, they accounted for the greatest cumulative forest loss. Structural impacts varied, with the widest informal trails and all formal hardened trails resulting in similar reductions in canopy cover and tree density but an increase in saplings. These structural impacts are likely a function of the unregulated and intense use of large informal trails, and disturbance from the construction and maintenance of formal trails. The results demonstrate that different types of recreational trails vary in the type and range of impacts they cause to forests. They highlight the importance of careful consideration towards management options when dealing with trail networks especially in areas of high conservation value.