Permanent Forest Plots Research Articles

Live biomass carbon density is related with species demographics in eastern Qinghai-Tibet Plateau forests

Previous assessments of forest carbon sequestration mainly emphasized expanding forests and monitoring their growth over time. However, limited research has tackled enhancing carbon sequestration efficiency in existing forests, particularly by altering tree species demographics. Identifying species with significant contributions to carbon storage through growth and recruitment, as well as pinpointing regions and species with higher mortality rates (MRs), is essential for guiding forest restoration initiatives. This study utilized 1,248 permanent forest plots and 103,773 individual trees to examine the spatiotemporal demographic patterns of 20 dominant tree species from 1979 to 2017 in the Eastern Qinghai-Tibet Plateau and their impacts on forest live biomass carbon density. The findings indicate significant differences in the demographic rates of the 20 dominant tree species. The trees species composition and distribution in the study area were changed with the expansion and reduction of individual numbers of different trees species. For example, the expansion of Alnus cremastogyne, the shrink of Pinus yunnanensis and Pinus armandii populations. The growth rates (GRs) and recruitment rates (RRs) of Abies fabri, Acer miyabei, Betula albosinensis, Picea asperata, Juniperus squamata, Quercus semecarpifolia, and Salix takasagoalpina significantly increased live biomass carbon density. Conversely, increased MRs of Abies fabri, Cupressus funebris, Larix gmelinii, Picea asperata, Pinus armandii, Pinus densata, Pinus yunnanensis, and Salix takasagoalpina reduced forest live biomass carbon density. GRs and RRs offset MRs, resulting in an increase in carbon storage. Competition, which was estimated by the basal area per plot (BAplot), constrained the growth and recruitment and increased mortality of Pinaceae (Pinus armandii, Tsuga chinensis, Pinus yunnanensis, Pinus densata, Larix gmelinii, Picea likiangensis), particularly at low elevations and in the south of the study area. Interspecific variations in GRs, RRs, and MRs suggest selecting optimal species associations with high GRs and RRs, while thinning forests containing species with high MRs in suitable locations. The study enhances insights into the demographic rates of different species, establishes links between population dynamics and forest carbon sequestration, and further demonstrates the importance of adaptive scientific afforestation planning and forest management.

Spatiotemporal variation in the negative effect of neighbourhood crowding on stem growth

Abstract Neighbourhood interactions drive tree growth and forest ecosystem functioning. The strength of interactions depends on the climate. However, it remains unclear how plant–plant interactions are modified by environmental conditions operating both spatially and temporally, which is crucial for predicting forest dynamics under climate change and for effective forest management. In this study, we used annual growth data for 4139 stems from 2010 to 2021 across 50 permanent forest plots located at six sites in eastern China. We quantified the effect of neighbourhood crowding on the annual basal area increment. We explored how interactions among neighbouring trees vary with water availability and temperature gradients in the spatial (across sites) and temporal (across time within sites) dimensions. Our findings revealed a negative impact of neighbourhood crowding on stem basal area growth, which is size‐ and trait‐dependent at some sites. The negative effects of light competition tended to be more intense at warmer sites, supporting the stress‐gradient hypothesis (SGH) in a spatial dimension. However, the patterns of crowding effects along interannual climate anomalies are inconsistent across sites, making it difficult to predict crowding effects under the SGH framework in a temporal dimension. Synthesis: Our study demonstrated that tree interactions depend on the climate context. The climate dependence of interactions may be inconsistent between the spatial and temporal dimensions. Light competition across sites supported the SGH in the spatial dimension but not in the temporal dimension. These results further highlight the complexity of biotic interactions and the need for caution when extrapolating findings from the spatial to the temporal dimension.

Latitudinal richness patterns in a temperate forest region: disentangling the effects of evenness, density and aggregation

It is well known that species diversity declines with increasing latitude. However, the underlying causes and mechanisms remain ambiguous due to effects of scale, the shape of the species abundance distributions (SAD), the total number of individuals (N) and the spatial aggregation of individuals (AGG). In this study, we examine how SAD, N and AGG contribute to the latitudinal richness gradient. Our study is based on a dataset that includes tree, shrub, and herbaceous plants collected from 445 permanent forest plots scattered across an expansive temperate forest region, covering latitudes from 39.71°N to 53.37°N. We compared multiple diversity patterns along the latitude between three life forms (trees, shrubs and herbs) and analyzed the effects of SAD, N and AGG on the latitudinal richness gradient. Our results reveal a general decline in most diversity measures along the latitudinal gradient, with the exception of herbaceous plants. Furthermore, we observed consistent effects of AGG and SAD on the latitudinal richness gradient across all three life forms. Specifically, a decreasing species evenness with increasing latitude led to a reduction in richness, while the simultaneous decrease in spatial aggregation, along with the effects of total number of individuals, collectively contributed to the decline in species richness with increasing latitude. However, the effect of total abundance varies among life forms, with a negligible effect on tree richness, a negative effect on shrub richness, and a significantly positive effect on herbaceous richness. These findings highlight the dependency of the “more-individuals hypothesis” on specific life forms. Our study shows that decomposing species richness into community structure components provides an opportunity for linking specific processes to latitudinal diversity gradients.

Ecological preferences of the Swiss pine (Pinus cembra L.) forests in the Gorgany Nature Reserve

Swiss pine (Pinus cembra L.) is a montane Carpathian (Alpine-Carpathian) species. The modern distribution of the Swiss pine is disjunct, the two isolated areas are located in western and central Europe (Alps) and the middle and high mountains of the Carpathians. The largest areas of Swiss pine in Ukraine are preserved in the Gorgany region at the altitude of 1250‒1450 m above sea level, where it forms the upper forest line. In the Gorgany Nature Reserve, P. cembra grows in the altitude range from 1070 to 1475 m ASL. The lower boundary, in the form of individual trees, descends to 1000 m ASL, and the upper boundary rises to 1585 m ASL. To define the ecological preferences of the Swiss pine, a series of route surveys were conducted and research sites (permanent forest monitoring plots, stationary research profiles, and stationary areas for the counting of natural forest regeneration) were established. The study of the plant communities with P. cembra on the southwestern slopes of the Dzhurdzhi tract showed the dependence of the forest species composition on the altitude above sea level. The forest stands quantitative composition and productivity are also significantly influenced by slope exposure. The proportion of P. cembra in the forests on steep slopes (30‒55°) of west and north-west exposure is relatively high (from 17.1% to 49.0%). Under other conditions, the proportion of P. cembra in the stand composition gradually decreases. Swiss pine is almost completely absent on the slopes of eastern and northern exposures except for rare single trees in Pinus mugo Turra scrub on northern slopes. The forests with P. cembra are typical of sunny slopes where the available sum of active temperatures ranges between 1000° and 1400° and the average ambient temperatures from -12.2°С to +16°С. The optimal environmental conditions for the relict species P. cembra in the Dovbushanski Gorgany region are on the western slopes with a steepness of 17‒55° and southwestern and northwestern slopes with a steepness of 35°‒42°. In terms of soil fertility, oligotrophic edaphotopes with moderate moisture are optimal for the growth of Swiss pine.

FORMS: Forest Multiple Source height, wood volume, and biomass maps in France at 10 to 30 m resolution based on Sentinel-1, Sentinel-2, and Global Ecosystem Dynamics Investigation (GEDI) data with a deep learning approach

Abstract. The contribution of forests to carbon storage and biodiversity conservation highlights the need for accurate forest height and biomass mapping and monitoring. In France, forests are managed mainly by private owners and divided into small stands, requiring 10 to 50 m spatial resolution data to be correctly separated. Further, 35 % of the French forest territory is covered by mountains and Mediterranean forests which are managed very extensively. In this work, we used a deep-learning model based on multi-stream remote-sensing measurements (NASA's Global Ecosystem Dynamics Investigation (GEDI) lidar mission and ESA's Copernicus Sentinel-1 and Sentinel-2 satellites) to create a 10 m resolution canopy height map of France for 2020 (FORMS-H). In a second step, with allometric equations fitted to the French National Forest Inventory (NFI) plot data, we created a 30 m resolution above-ground biomass density (AGBD) map (Mg ha−1) of France (FORMS-B). Extensive validation was conducted. First, independent datasets from airborne laser scanning (ALS) and NFI data from thousands of plots reveal a mean absolute error (MAE) of 2.94 m for FORMS-H, which outperforms existing canopy height models. Second, FORMS-B was validated using two independent forest inventory datasets from the Renecofor permanent forest plot network and from the GLORIE forest inventory with MAE of 59.6 and 19.6 Mg ha−1, respectively, providing greater performance than other AGBD products sampled over France. Finally, we compared FORMS-V (for volume) with wood volume estimations at the ecological region scale and obtained an R2 of 0.63 with an MAE of 30 m3 ha−1. These results highlight the importance of coupling remote-sensing technologies with recent advances in computer science to bring material insights to climate-efficient forest management policies. Additionally, our approach is based on open-access data having global coverage and a high spatial and temporal resolution, making the maps reproducible and easily scalable. FORMS products can be accessed from https://doi.org/10.5281/zenodo.7840108 (Schwartz et al., 2023).

Biotic and Abiotic Factors Controlling Spatial Variation of Mean Carbon Turnover Time in Forest Soil

AbstractSoil carbon persistence in forests plays a pivotal role in regulating terrestrial feedback to climate change. However, the relative contributions of biotic and abiotic factors in controlling geographic variation of forest soil carbon turnover time (τsoc) remains unclear. Here, we first sampled soils from 12 permanent forest plots across eastern China and detected higher radiocarbon‐derived mean turnover time of soil organic carbon in the deep (30–100 cm; 2,087 ± 246 years) than the surface (0–30 cm; 249 ± 80 years) layer. Further analyses based on the partial Mantel test and structural equation model illustrated that the interactions of climate, vegetation, and soil factors are more complex in deep than surface soils. Then, we established a global database of radiocarbon‐derived τsoc from 1897 forest soil samples. On the global scale, τsoc was significantly higher in the deep (3,081 ± 398 years) than the surface (332 ± 56 years) layer. Soil depth alone explained 11.7% of the spatial variation in τsoc, and the interactions between climate, stand age, and soil depth account for 68.6% of the variation. These findings highlight the joint control of climate, vegetation, and soil depth in the spatial variation of soil carbon persistence in global forests.

Sample coverage estimation, rarefaction, and extrapolation based on sample-based abundance data.

Sample coverage, the proportion of individuals that belong to observed species in a sample, is a metric used to measure the completeness of a sample. Rather than using equal sample sizes, equal sample coverage has become a widely accepted standard for comparing diversity across multiple assemblages, resulting in a more accurate representation of the true relationship between the richness of the assemblages. In practice, sample-based abundance data are the most frequently used data type for evaluating species diversity. In sample-based abundance data, the sampling unit (e.g., a plot, net, trap, or transect) is randomly selected from the target area, and the number of individuals for each species observed in the sampled unit is recorded. In this case, the individuals in the sample are no longer randomly and independently sampled, and the Good-Turing estimators of abundance-based sample coverage in reference, rarefied, and extrapolated samples may be severely biased when individuals present a highly spatially aggregated pattern. Here, I derive a novel estimator of abundance-based sample coverage based on the Good-Turing frequency formula. Additionally, a new analytical approach is introduced for enabling smooth coverage-based rarefaction and extrapolation to compare richness among assemblages. The near unbiasedness of the proposed estimator and a less biased richness ratio achieved using the newly developed coverage-based standardizing approach are demonstrated by analyzing three ForestGEO permanent forest plot data sets.

A species richness estimator for sample‐based incidence data sampled without replacement

Abstract The accurate estimation of species richness in a target region is still a statistical challenge, especially in a highly heterogeneous community. Most richness estimators have been developed based on the assumption that data are randomly sampled with replacement or that data are sampled from an infinite population. However, in reality, most sampling schemes in the field are implemented as sampling without replacement (SWOR). As such, estimators derived based on sampling with replacement may cause overestimation as the sampling fraction increases and not converge to the true richness as the sampling fraction approaches one. Sample‐based incidence data, in which the sampling unit is a plot, and only the presence or absence of a species in each chosen plot is recorded, is one of the most commonly used data types for assessing species diversity in ecological studies. In this manuscript, according to sample‐based incidence data collected through SWOR, a new richness estimator is proposed using a truncated beta‐binomial mixture model. The new estimator was obtained through the moment approach, which avoids using iterative numerical algorithms for parameter estimation and presents a closed‐form estimator as an alternative to the maximum likelihood method. Although the newly proposed method is a parametric‐based richness estimator, similar to nonparametric estimators, only the rare species in the sample (i.e. the frequencies of uniques and duplicates) are required to estimate undetected richness. Based on the hypothetical models, the statistical performances of the proposed estimator are evaluated under varying degrees of heterogeneity and different mean species detection rates. Compared to other widely used nonparametric and parametric estimators, the simulation results indicate that the proposed estimator has a smaller bias and lower root mean square error when the sampling fraction is greater than 10%, particularly in highly heterogeneous communities. In addition, one ForestGEO permanent forest plot dataset is used to evaluate and compare the proposed approach with other estimators discussed in the study. The results demonstrate that the proposed estimator, in comparison to other widely used estimators, produces less biased estimate of true richness, along with more accurate 95% confidence interval.

Climate change drives substantial decline of understorey species richness and abundance in Norway spruce forests during 32 years of vegetation monitoring

AbstractQuestionsObservations in permanent forest vegetation plots in Norway and elsewhere indicate that complex changes have taken place over the period 1988–2020. These observations are summarised in the “climate‐induced understorey change (CIUC)” hypothesis, i.e. that the understorey vegetation of old‐growth boreal forests in Norway undergoes significant long‐term changes and that these changes are consistent with the ongoing climate change as an important driver. Seven testable predictions were derived from the CIUC hypothesis.LocationNorway.MethodsVegetation has been monitored in a total of 458 permanently marked plots, each 1 m2, in nine old‐growth forest sites dominated by Picea abies at intervals of 5–8 years over the 32‐year study period. For each of the 52 combinations of site and year, we obtained response variables for the abundance of single species, abundance and species density of taxonomic–ecological species groups and two size classes of cryptogams, and site species richness. All of these variables were subjected to linear regression modelling with site and year as predictors.ResultsMean annual temperature, growing‐season length and the number of days with precipitation were higher in the study period than in the preceding ca. 30‐year period, resulting in increasingly favourable conditions for bryophyte growth. Site species richness decreased by 13% over the 32‐year study period. On average, group abundance of vascular plants decreased by 24% (decrease in forbs: 38%). Patterns of group abundance change differed among cryptogam groups: although peat‐moss abundance increased by 39%, the abundance of mosses, hepatics and lichens decreased by 13%, 49% and 67%, respectively. Group abundance of small cryptogams decreased by 61%, whereas a 13% increase was found for large cryptogams. Of 61 single species tested for abundance change, a significant decrease was found for 43 species, whereas a significant increase was found only for 6 species.ConclusionsThe major patterns of change in species richness, group species density and group abundance observed over the 32‐year study period accord with most predictions from the CIUC hypothesis and are interpreted as direct and indirect responses to climate change, partly mediated through changes in the population dynamics of microtine rodents. The more favourable climate for bryophyte growth explains the observed increase for a few large bryophyte species, whereas the decrease observed for small mosses and hepatics is interpreted as an indirect amensalistic effect, brought about by shading and burial in mats of larger species and accelerated by reduced fine‐scale disturbance by microtine rodents. Indirect effects of a thicker moss mat most likely drive the vascular plant decline although long‐term effects of tree‐stand dynamics and former logging cannot be completely ruled out. Our results suggest that the ongoing climate change has extensive, cascading effects on boreal forest ecosystems. The importance of long time‐series of permanent vegetation plots for detecting and understanding the effects of climate change on boreal forests is emphasised.

Impacts of forest management on stand and landscape-level microclimate heterogeneity of European beech forests

ContextForest microclimate influences biodiversity and plays a crucial role in regulating forest ecosystem functions. It is modified by forest management as a result of changes in forest structure due to tree harvesting and thinning.ObjectivesHere, we investigate the impacts of even-aged and uneven-aged forest management on stand- and landscape-level heterogeneity of forest microclimates, in comparison with unmanaged, old-growth European beech forest.MethodsWe combined stand structural and topographical indices derived from airborne laser scanning with climate observations from 23 meteorological stations at permanent forest plots within the Hainich region, Germany. Based on a multiple linear regression model, we spatially interpolated the diurnal temperature range (DTR) as an indicator of forest microclimate across a 4338 ha section of the forest with 50 m spatial resolution. Microclimate heterogeneity was measured as α-, β-, and γ-diversity of thermal niches (i.e. DTR classes).ResultsEven-aged forests showed a higher γ-diversity of microclimates than uneven-aged and unmanaged forests. This was mainly due to a higher β-diversity resulting from the spatial coexistence of different forest developmental stages within the landscape. The greater structural complexity at the stand-level in uneven-aged stands did not increase α-diversity of microclimates. Predicted DTR was significantly lower and spatially more homogenous in unmanaged forest compared to both types of managed forest.ConclusionIf forest management aims at creating a wide range of habitats with different microclimates within a landscape, spatially co-existing types of differently managed and unmanaged forests should be considered, instead of focusing on a specific type of management, or setting aside forest reserves only.

The impact of abiotic and biotic factors on growth, mortality and net tree C stock in mountain forest ecosystems in southwest China

Mountain forest ecosystems play an important role in global carbon sequestration and may respond differently to variations in climate. The timely and accurate assessment of the factors (abiotic and biotic) that affect forest types will improve our understanding of the ecological mechanisms underlying forest carbon stock and dynamics. Here, we used linear mixed effect models to assess the impact of abiotic and biotic factors on the rate of net tree C accumulation, growth, and mortality, over nearly four decades in 1248 permanent forest plots, in different forest types along an elevational gradient on the eastern Qinghai-Tibet Plateau in China. We found that the annual rise in net tree C stock ranged from 0.13 to 0.23 Mg C ha−1 yr−1, as forest growth increased from 1979 to 2017. The highest rates of growth and mortality were in coniferous broad-leaved mixed forest (CBMF), followed by deciduous broad-leaved forests (BDF), evergreen, deciduous broad-leaved mixed forest (EDBMF), and coniferous forest (CF). Mortality increased in EDBMF and CF during the study period. The most important biotic factors were tree richness and tree density, especially in BDF and CBMF. The most important abiotic factors driving these biological responses were a significant rise in monthly mean temperature (MMT) and a decline in precipitation in the growing season. The decrease in precipitation was negatively correlated with net tree C in CBMF and CF. The increase of MMT was positively correlated with growth and mortality of each forest type, and generally more important than richness and density, and overall had a positive effect on net tree C in CBMF and CF. Overall, we suggest that tree carbon stocks will continue to increase in CBMF and CF in the coming decades due to the warming.

An exploration of sustainability versus productivity and ecological stability in planted and natural forests in Sichuan, China

AbstractImplementation of the Natural Forest Protection Project and Grain‐for‐Green Program in China has promoted forest restoration, increased productivity, and enhanced carbon stocks. However, few studies have characterized temporal and spatial variation in productivity and ecological stability in planted and natural forests and evaluated the factors driving such variation. In this study, we used 1399 permanent forest plots to identify change patterns in the productivity and temporal stability of above‐ground biomass (AGB), and evaluate the factors driving these changes in planted and natural forests in Sichuan Province, China. The mean temporal stability of AGB was higher for natural forests than for planted forests from 1979 to 2017; While the productivity of planted forests was higher. The stability decreased at a rate of −0.013 yr−1 in entire natural forests and −0.011 yr−1 in planted forests, and the productivity of natural forests decreased significantly over time, with a slope of −0.0065 Mg ha−1 yr−1. Altitude, latitude, annual precipitation, and stand age dominated variability in the productivity and AGB stability of natural forests. Richness, tree density, and stand age were the determinants of productivity and stability in the planted forest. Our results suggest that selective thinning, enriching species richness, and forest stand age can effectively balance the productivity and biomass temporal stability of planted forests. Due to climate change, older natural forests should be strictly protected.

The presence of peat and variation in tree species composition are under different hydrological controls in Amazonian wetland forests

AbstractThe peat‐forming wetland forests of Amazonia are characterized by high below‐carbon stocks and supply fruit, fibres and timber to local communities. Predicting the future of these ecosystem services requires understanding how hydrological conditions are related to tree species composition and the presence, or absence, of peat. Here, we use continuous measurements of water table depth over 2.5 years and manual measurements of pore‐water pH and electrical conductivity to understand the ecohydrological controls of these variables across the large peatland complex in northern Peruvian Amazonia. Measurements were taken in permanent forest plots in four palm swamps, four seasonally flooded forests and four peatland pole forests. All trees ≥10 cm diameter were also measured and identified in the plots to assess floristic composition. Peat occurs in eight of these twelve sites; three seasonally flooded forests and one palm swamp are not associated with peat. Variation in tree species composition among forest types was linked to high flood levels (maximum flooding height) and pH: seasonally flooded forests experience high flood levels (up to 3.66 m from the ground surface) and have high pH values (6–7), palm swamps have intermediate flood levels (up to 1.34 m) and peatland pole forests experience shallow flooding (up to 0.28 m) and have low pH (4). In contrast, the presence of peat was linked to variation in maximum water table depth (i.e. the depth to which the water table drops below the ground surface). Surface peat is found in all forest types where maximum water table depth does not fall >0.55 m below the ground surface at any time. Peat formation and variation in tree species composition therefore have different ecohydrological controls. Predicted increases in the frequency and strength of flooding events may alter patterns of tree species composition, whereas increases in drought severity and declines in minimum river levels may pose a greater risk to the belowground carbon stores of these peatland ecosystems.

Low-Severity Wildfire Shifts Mixed Conifer Forests toward Historical Stand Structure in Guadalupe Mountains National Park, Texas, USA

Wildfire is an important natural disturbance agent, shaping mixed conifer forest structure throughout the Southwestern United States. Yet, fire exclusion caused by late 19th century livestock grazing followed by human fire suppression has altered forest structure by increasing forest density, basal area, and canopy cover in recent decades. Changes in the abundance and vertical and horizontal continuity of fuels have increased the potential for high-severity fire, which construes a major regional forest management concern. In May 2016, the Coyote Fire burned through a network of permanent forest monitoring plots in Guadalupe Mountains National Park. This study employed a repeated-measures sampling design to quantify the effects of low- to moderate-severity wildfire on forest stand structure, species composition, fuels, and tree mortality using hierarchical cluster analysis, non-metric multidimensional scaling (nMDS), and paired t-tests. The 2016 Coyote Fire reduced live tree density in small-diameter size classes, but produced minimal changes in canopy stand structure and fuel loadings, despite nearly a century of fire exclusion and pre-fire tree densities that were four-times higher they were prior to last major wildfire in the early 1900s. Small-diameter surface fuel loadings (1 h and 10 h fuels) did not significantly change after fire, although 1000 h fuels increased significantly (p < 0.05), likely from the addition of new fuel from fire-caused tree mortality. While the wildfire reduced live tree density, the nMDS analysis indicated that the wildfire did not trigger major shifts in tree species composition. However, the wildfire triggered significant decreases in seedlings and small-diameter trees (<30 cm DBH) (p < 0.05). Although the fire thinned the forest, the persistence of fuels and increases in dead small-diameter trees heighten the need for additional fuel reduction treatments to mitigate the risk of future high-severity fire under extreme fire weather. Management of low-severity fire in this forest type may provide opportunities to reduce fuels and restore more desirable stand structure to enhance forest resilience to landscape fire.

Size‐dependent intraspecific variation in wood traits has little impact on aboveground carbon estimates in a tropical forest landscape

Abstract There is increasing evidence that intraspecific trait variation plays a role in governing rates of ecosystem functioning. While wood traits such as wood specific gravity (WSG) and wood carbon concentration (WCC) are key drivers of forest aboveground carbon (AGC) stocks, the sources of intraspecific variation in these wood traits and the consequences of this variation on AGC are poorly known, especially in the tropics. Here, we investigated intraspecific variation in wood specific gravity (WSG) and wood carbon concentration (WCC) from 556 individual trees belonging to 15 species that well characterize different successional stages of seasonal evergreen forests in Southeast Asia. Specifically, we tested the contribution of individual or species characteristics (tree size, growth rate and regeneration guilds) and local environmental conditions (topographic wetness index and successional stages) to intraspecific variation in WSG and WCC, and assessed the consequences of intraspecific variation in these wood traits on AGC estimates in 14 permanent forest plots established along a successional gradient in Khao Yai National park, Thailand. We found that tree size was the main driver of intraspecific variation in WSG and WCC as tree sizes increased from 10–100 cm in diameter, WSG increased by 7.3%, while WCC increased by 2.4% in heartwood, 1.6% and 2.7% in sapwood without and with volatile carbon included. There was no effect of the topographic wetness and other local environment condition in wood traits led to a slight overestimation of AGC in young secondary forests (+0.09% to +1.29%) and a small underestimation in older forests (−0.86% to −2.87%), but overall AGC estimates (13 of 14 forest plots) remained within error margins (the 95% interval). Our study provides evidence that tree size variation translates into intraspecific variability in wood traits, whereas local environmental conditions related to topography successional stages had no effect on wood trait variability. While size‐dependent variation in WSG and WCC have largely been undocumented and thus ignored in forest carbon assessment approaches, we highlight that it has a limited impact on AGC estimates, indicating that it does not invalidate current forest carbon stock estimation approaches. Read the free Plain Language Summary for this article on the Journal blog.

Disentangling the effects of biotic neighbors and habitat heterogeneity on seedling survival in a deciduous broad-leaved forest

In forest ecosystems, seedling dynamics play a critical role in understanding species coexistence and community assembly. Exploring the effects of key factors on seedling survival can therefore offer key insights into how they interact to affect seedling mortality in natural forests. Based on 5 years of woody seedling census data and tree census data from a 25-ha permanent forest plot in the subtropical-temperate transitional region in the Qinling Mountains of north-central China, we examined the effects of biotic neighborhood processes and habitat heterogeneity as well as their interactions on seedling mortality using survival data of 11,408 seedlings of 69 species (i.e., 30 tree species and 39 shrub species). The results showed that negative density-dependence (NDD) had significant effects on seedling dynamics and survival at community level. Both biotic and abiotic factors affected seedlingsurvival at different ages, but the influence of negative density-dependence was much more significant, especially on the tree seedlings ≥ 5 years old. For the shrub seedlings, however, biotic factors had a larger effect on their survival than abiotic factors. Thus, we concluded that both habitat heterogeneity and negative density-dependent mortality shaped species coexistence at the seedling stage in the deciduous broad-leaved forest.

Tree diversity depending on environmental gradients promotes biomass stability via species asynchrony in China’s forest ecosystems

There is mounting evidence that biodiversity promotes ecological stability in changing environments. However, understanding diversity–stability relationships and their underlying mechanisms across large-scale tree diversity and natural environmental gradients are still controversial and largely lacking. We used thirty-nine 0.12 ha long-term permanent forest plots spanning China’s various forest types to test the effects of multiple abiotic (climate, soil, age and topography) and biotic factors (taxonomic and structural diversity, functional diversity and community-mean traits, and species asynchrony) on biomass stability and its components (mean biomass and biomass variability) over time. We used multiple analytical methods to identify the best explanatory variables and complicated causal relationships for community biomass stability. Our results showed that species richness increased biomass stability by promoting species asynchrony. Structural and functional diversity had a weaker effect on biomass stability. Forest age and structural diversity increased mean biomass and biomass variability significantly and simultaneously. Communities dominated by tree species with high wood density had high biomass stability. Soil nitrogen enhanced biomass stability directly and indirectly through its effects on mean biomass. Soil nitrogen to phosphorus ratio increased biomass stability via increasing species asynchrony. Precipitation indirectly increased biomass stability by affecting tree diversity. Moreover, the direct and indirect effects of soil nutrients on biomass stability were greater than that of climate variables. Our results suggest that species asynchrony is the main mechanism proposed to explain the stabilizing effect of diversity on community biomass, supporting two mechanisms, namely, the biodiversity insurance hypothesis and complementary dynamics. Soil and climate factors also play an important role in shaping diversity–stability relationships. Our results provide a new insight into how tree diversity affects ecosystem stability across diverse community types and large-scale environmental gradients.

Red Argentina de Parcelas Permanentes de Bosques Nativos para promover colaboraciones científicas en estudios de largo plazo

Permanent forest plots are sampling areas where tree identity, abundance and size are recorded periodically, in order to study how forests change with climate, natural disturbances, uses and management. So far, patterns of change observed with permanent plots in Argentina have been local or regional. To promote scientific collaborations between different research groups within and among regions of Argentina, we created the Network of Permanent Plots of Native Argentinian Forests (RAPP), which includes the regions of Bosques Andino-Patagónicos, Chaco Seco, Chaco Húmedo, Monte de Sierras y Bolsones, Monte de Llanuras y Mesetas, Selva Paranaense and Yungas. Here we synthesize and characterize the information of 317 permanent plots (328.9 ha) included in the RAPP, describing their geographic distribution, objectives, main methodological aspects, and characteristics of the forests where they are established (e.g., disturbance, land tenure, structure, species richness), and after that, discuss the complementarity between the RAPP and the national inventories of native forests. Permanent plots are established over a wide range of latitude (22.02-54.89° S) and elevation (19 a 2304 m a. s. l.), but they are mainly concentrated in Subtropics (Chaco Seco, Chaco Húmedo, Selva Paranaense, and Yungas) and in Bosques Andino-Patagónicos. In all plots, trees are taxonomically identified and different dasometric variables are remeasured, which are the basis for potential collaborations to answer ecological questions at a larger scale. We hope to continue incorporating working groups in the RAPP and encouraging the establishment of plots, mainly in regions with a low number of permanent plots such as Monte, Espinal, and Delta e Islas del Paraná. The goal is that the RAPP advances in the long-term study of all native forests in Argentina, achieving a greater national cover and more interactions among research teams.

Biomass and demographic dynamics of the Brazil nut family (Lecythidaceae) in a mature Central Amazon rain forest

In this study, we analyze the demographic rates and biomass dynamics of Lecythidaceae in a 100-ha permanent forest plot in the Central Amazon. We characterize habitats in the plot, analyze the effect of habitat on tree density, species richness, and biomass and demographic dynamics, and quantify significant species habitat associations. The plot experienced a 13.2 % net loss of Lecythidaceae individuals (n = 1023) but aboveground biomass (AGB; Mg ha−1) did not differ between the two censuses. Growth rates averaged 1.2 mm year−1 with high intraspecific variation and differed significantly among species height classes. Stem density and species richness decreased in all six terra firme habitats and were significantly lower in both years in the flood disturbed habitat. Only the flood disturbed areas experienced a significant loss in AGB, along with the highest annual mortality, recruitment, and growth rates across the plot. The lower-lying habitats experienced higher mortality rates than the slopes and plateaus, suggesting too much moisture is a higher risk to Lecythidaceae individuals than drought in this plot. There were no overlapping habitat associations among sister species, or among the seven most abundant species, which suggests that terra firme habitat association provides a niche partitioning mechanism for closely related Lecythidaceae species. As intended with its establishment, this plot continues to provide integral baseline data for one of the most ecologically dominant and culturally significant tree families in the Amazon region.

Effects of neighborhood interaction on tree growth in a temperate forest following selection harvesting

Selection harvesting is a common silvicultural practice in uneven-aged natural forests. Understanding the complex response of individual trees to forest harvesting is of great importance to clearly assess how forest ecosystems respond to future management. While tree growth dynamics following forest harvesting have been well documented at the stand level, at the individual level, how neighborhood interaction affects tree growth after forest harvesting has received little attention. Based on the data from four1-ha permanent forest plots with mapped trees and different harvesting intensities in Northeastern China, the effects of neighborhood interaction on tree growth of 1,108 focal trees were analyzed four years after forest harvesting. Neighborhood interaction was quantified by several indices, considering both crowding and biological dissimilarity (based on taxonomy, phylogeny, and functional traits) between neighboring trees. Additionally, we tested whether the effects of the neighborhood interaction on tree growth might differ across harvesting intensities. Our results found that selection harvesting significantly increased tree growth and biological dissimilarity but decreased crowding at the individual tree level. Focal tree growth decreased by 12.9%, 9.7%, and 7.9% as a result of neighborhood interaction based on taxonomic, phylogenetic, and multi-trait dissimilarity, respectively. Neighborhood interaction based on maximum height appeared to be the most important determinant of tree growth among the four traits examined (i.e., leaf dry mass per area; leaf nitrogen concentration; wood density; and maximum height), and its effect was much stronger than that of the multi-trait dissimilarity index. Moreover, among the neighborhood interaction indices, increasing neighborhood crowding reduced tree growth and there was a significant negative crowding effect at medium to high harvesting intensities (40%∼60% basal area removed) on tree growth. Our study expands our understanding of the relationship between neighborhood interaction and tree growth by identifying crowding and biological dissimilarity as important neighborhood indices for post-harvest tree growth.