An important goal in plant community ecology is to understand how species traits determine demographic performance. Several functional traits have been shown to correlate with growth and mortality ...rates in trees, but less is known about how the relationships between functional traits and demographic rates change with tree size. We examined the associations of functional traits with growth and mortality across 43 tree species in the Fushan 25‐ha subtropical rain forest plot in northern Taiwan. We estimated the 95th percentile maximum stem diameter, wood density and six leaf functional traits (leaf area, specific leaf area, thickness, succulence, and mass‐based nitrogen and phosphorus contents) obtained from leaves on juvenile and adult individuals of each species. To quantify size‐dependent changes in growth and mortality, relative growth rate (RGR) and mortality were estimated as a function of stem diameter using hierarchical Bayesian models. These rate estimates were then correlated with functional traits at a range of stem diameter classes. Relationships between functional traits and demographic rates varied with tree size. Maximum size was positively correlated with RGR across a wide range of tree sizes. Wood density was negatively correlated with RGR and mortality for small‐sized trees. Leaf traits such as leaf area and specific leaf area at juvenile and adult stages were associated more strongly with demographic rates for corresponding sizes than from other sizes. Synthesis. The observed size‐dependent changes in the trait–demography relationships are possibly due to the effects of developmental and environmental changes with increasing tree size. The underlying effects of functional traits on demographic performance vary with tree size, and this should influence dynamics in a tree community.
Aims: With the aim of understanding why some of the world's forests exhibit higher tree beta diversity values than others, we asked: (1) what is the contribution of environmentally related variation ...versus pure spatial and local stochastic variation to tree beta diversity assessed at the forest plot scale; (2) at what resolution are these beta-diversity components more apparent; and (3) what determines the variation in tree beta diversity observed across regions/continents? Location: World-wide. Methods: We compiled an unprecedented data set of 10 large-scale stem-mapping forest plots differing in latitude, tree species richness and topographic variability. We assessed the tree beta diversity found within each forest plot separately. The non-directional variation in tree species composition among cells of the plot was our measure of beta diversity. We compared the beta diversity of each plot with the value expected under a null model. We also apportioned the beta diversity into four components: pure topographic, spatially structured topographic, pure spatial and unexplained. We used linear mixed models to interpret the variation of beta diversity values across the plots. Results: Total tree beta diversity within a forest plot decreased with increasing cell size, and increased with tree species richness and the amount of topographic variability of the plot. The topography-related component of beta diversity was correlated with the amount of topographic variability but was unrelated to its species richness. The unexplained variation was correlated with the beta diversity expected under the null model and with species richness. Main conclusions: Because different components of beta diversity have different determinants, comparisons of tree beta diversity across regions should quantify not only overall variation in species composition but also its components. Global-scale patterns in tree beta diversity are largely coupled with changes in gamma richness due to the relationship between the latter and the variation generated by local stochastic assembly processes.
Understanding the role of biodiversity (B) in maintaining ecosystem function (EF) is a foundational scientific goal with applications for resource management and conservation. Two main hypotheses ...have emerged that address B–EF relationships: niche complementarity (NC) and the mass-ratio (MR) effect. We tested the relative importance of these hypotheses in a subtropical oldgrowth forest on the island nation of Taiwan for two EFs: aboveground biomass (ABG) and coarse woody productivity (CWP). Functional dispersion (FDis) of eight plant functional traits was used to evaluate complementarity of resource use. Under the NC hypothesis, EF will be positively correlated with FDis. Under the MR hypothesis, EF will be negatively correlated with FDis and will be significantly influenced by community-weighted mean (CWM) trait values. We used path analysis to assess how these two processes (NC and MR) directly influence EF and may contribute indirectly to EF via their influence on canopy packing (stem density). Our results indicate that decreasing functional diversity and a significant influence of CWM traits were linked to increasing AGB for all eight traits in this forest supporting the MR hypothesis. Interestingly, CWP was primarily influenced by NC and MR indirectly via their influence on canopy packing. Maximum height explained more of the variation in both AGB and CWP than any of the other plant functional traits. Together, our results suggest that multiple mechanisms operate simultaneously to influence EF, and understanding their relative importance will help to elucidate the role of biodiversity in maintaining ecosystem function.
Questions
Quantifying tree species persistence through recurrent disturbances is of crucial importance for understanding forest dynamics in typhoon‐prone regions. We ask the following: (a) What are ...the major determinants of dominant tree survival in frequently typhoon‐disturbed forests? (b) Are survival determinants different between small and large trees?
Location
A subtropical old‐growth forest located in Fushan, Taiwan (24°45′34″N, 121°33′58″E), with frequent typhoon disturbances.
Methods
Data were from three consecutive censuses of a 25‐ha permanent forest plot that censused trees ≥1 cm in diameter every five years. The survival of three dominant tree species was modeled using generalized additive model and boosted trees with abiotic and biotic predictors. We evaluated model performance using validation data obtained from the two available census intervals.
Results
Model validations showed that multi‐stemming and tree size enhanced the survival of large and small trees, respectively. For the most dominant species, multi‐stemming had a consistently positive effect on survival irrespective of diameter classes. Abiotic factors and conspecific density had little effect on tree survival. Furthermore, evaluating model performance based on the data used in the model construction (i.e., training data) overestimated the predictive ability of survival models.
Conclusions
We showed that the survival determinants for the three most dominant species at Fushan changed from tree size for small trees to multi‐stemming for large trees. The results suggest that the dominant species in this frequently typhoon‐disturbed forest have the stature and architectural traits to persist, and thereby maintain their dominance and shape the forest physiognomy. Our approach illustrates how datasets from different census periods can be used in model validation to better assess model performance.
In a frequently typhoon‐impacted forest in Taiwan, yet with low mortality, we found that the survival determinants for the dominant species changed from tree size for small trees to multi‐stemming for large trees. The results suggested that the dominant species in this forest had the stature and architectural traits to persist, and thereby maintain their dominance and shape the forest physiognomy. (Photography by Hui‐Yi Yu.)
1. Individual performance is a function of an individual's traits and its environment. This function, known as an environmental filter, varies in space and affects community composition. However, ...filters are poorly characterized because dispersal patterns can obscure environmental effects, and few studies utilize longitudinal data linking individual performance to environment. 2. We model the effects of environmental filters on demographic rates of nearly all tree species (99) in a 25-ha subtropical rain forest plot. We develop a hierarchical Bayesian model of environmental filtering, drawing inspiration from classic studies of intraspecific natural selection. We characterize the specific environmental gradients and trait axes most important in filtering of demographic rates across species. 3. We found that stronger filtering along a given trait axis corresponded to less spatial variation in the value of favoured traits. 4. Environmental gradients associated with filtering were different for growth versus survivorship. 5. Species maximum height was under the strongest filtering for growth, with shorter species favoured on convex ridges. Shorter stature species may be favoured on ridges because trees on ridges experience higher wind damage and lower soil moisture. 6. Wood density filtering had the strongest effects on survival. Steep slopes and high available P in the soil favoured species with low-density wood. Such sites may be favourable for fast-growing species that exploit resource-rich environments. 7. Synthesis: We characterized trait-mediated environmental filters that may underlie spatial niche differentiation and life-history trade-offs, which can promote species coexistence. Filtering along trait axes with the strongest effects on local community composition, that is, traits with the strongest filtering, may necessarily have a weaker potential to promote species coexistence across the plot. The weak spatial variation in filters with strong effects on demography may result from long-term processes affecting the species pool that favour habitat generalist strategies.
Long‐term surveys of entire communities of species are needed to measure fluctuations in natural populations and elucidate the mechanisms driving population dynamics and community assembly. We ...analysed changes in abundance of over 4000 tree species in 12 forests across the world over periods of 6–28 years. Abundance fluctuations in all forests are large and consistent with population dynamics models in which temporal environmental variance plays a central role. At some sites we identify clear environmental drivers, such as fire and drought, that could underlie these patterns, but at other sites there is a need for further research to identify drivers. In addition, cross‐site comparisons showed that abundance fluctuations were smaller at species‐rich sites, consistent with the idea that stable environmental conditions promote higher diversity. Much community ecology theory emphasises demographic variance and niche stabilisation; we encourage the development of theory in which temporal environmental variance plays a central role.
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•A facile electrospinning approach of composite nanofibers was presented.•Self-heating conductive conjugated PVA-G composite nanofibers.•G sheets dispersion within the nanofibers were ...proposed.•Characteristics of PVA-G nanofibers in electrical and thermal abilities were discussed.•On-chip device surface for humidity detection was demonstrated.
In this study, we measured the performance of self-heating conductive conjugated polyvinyl alcohol, (PVA)/graphene (G) composite nanofibers in the detection of environmental humidity. PVA-G polymer nanocomposite fibers were electrospun together from suspensions of PVA and varying concentrations of pristine G sheets. The extent of graphene dispersion in the nanocomposite fibers were characterized via Raman and transmission electron microscopy (TEM) analysis. Where the main content of C and O elements in composite nanofibers were obtained from the energy dispersive (EDX) spectra and EDX mapping results. Thermal characteristics and structural morphology were then investigated through thermal gravimetric analysis (TGA), and focused ion beam scanning electron microscopy (FIB-SEM) & laser scanning confocal microscopy (LSCM), respectively. Applied voltages (0−10 V) to the PVA-G polymer nanocomposite fibers under varying conditions of humidity were investigated. With increasing concentration of G, increased sensitivity to relative humidity could be observed through the proportional changes in resistance. In addition, at PVA-G concentrations at 6%, the tested humidity sensor remained highly responsive while operating at low temperatures of 60 °C and with minimal power consumption.
Context
This study examined how human-induced landscape changes affected bird diversity in mountain villages with mixed forests and cultivated fields.
Objectives
We focused on the bird species ...composition (beta diversity) to determine whether species homogenization varied with forest cover differences. This study developed it as a novel metric potentially quantifying homogenization level comparison in species functional groups.
Methods
Bird surveys were conducted at 27 sites with forest cover scattered from 0 to 100%. Bird species were divided into forest birds and nonforest birds. Beta diversity was partitioned into turnover and nestedness-resultant components, and their contribution ratio to Sørensen beta was used to examine the effect of forest cover and pairwise cover difference.
Results
Our results indicated that forest birds exhibited low turnover and low nestedness, whereas nonforest birds exhibited nestedness distribution characteristics. The nestedness-resultant contribution ratio of nonforest birds was higher, driven by forest cover difference (slope = 0.0080, Pseudo
R
2
= 0.35
**
) than that of forest birds (slope = 0.0018, Pseudo
R
2
= 0.02
**
). Thus, we quantify the result of forest cover decreased lead to the dominated by nestedness species in nonforest birds.
Conclusions
These findings highlight the distinct effects of environmental changes on these two bird functional groups. Although the Sørensen beta diversity increases with forest cover decrease, most are contributed by nestedness-resultant nonforest birds and lead to homogenization. Thus, it is recommended that conservation plans should separately address forest and nonforest bird species to avoid the risk of underestimating species homogenization due to anthropogenic land-use and habitat degradation.
1. The relationship between species richness and ecosystem function, as measured by productivity or biomass, is of long-standing theoretical and practical interest in ecology. This is especially true ...for forests, which represent a majority of global biomass, productivity and biodiversity. 2. Here, we conduct an analysis of relationships between tree species richness, biomass and productivity in 25 forest plots of area 8-50 ha from across the world. The data were collected using standardized protocols, obviating the need to correct for methodological differences that plague many studies on this topic. 3. We found that at very small spatial grains (0.04 ha) species richness was generally positively related to productivity and biomass within plots, with a doubling of species richness corresponding to an average 48% increase in productivity and 53% increase in biomass. At larger spatial grains (0.25 ha, 1 ha), results were mixed, with negative relationships becoming more common. The results were qualitatively similar but much weaker when we controlled for stem density: at the 0.04 ha spatial grain, a doubling of species richness corresponded to a 5% increase in productivity and 7% increase in biomass. Productivity and biomass were themselves almost always positively related at all spatial grains. 4. Synthesis. This is the first cross-site study of the effect of tree species richness on forest biomass and productivity that systematically varies spatial grain within a controlled methodology. The scale-dependent results are consistent with theoretical models in which sampling effects and niche complementarity dominate at small scales, while environmental gradients drive patterns at large scales. Our study shows that the relationship of tree species richness with biomass and productivity changes qualitatively when moving from scales typical of forest surveys (0.04 ha) to slightly larger scales (0.25 and 1 ha). This needs to be recognized in forest conservation policy and management.
Aim
The relationship between the proportion of sites occupied by a species and the area of a site occupancy–area relationship (OAR) offers key information for biodiversity management and has long ...fascinated ecologists. We quantified the variation in OAR for 3,157 woody species in 17 forest plots worldwide and tested the relative importance of environment and species traits for explaining this variation and evaluated overall model predictive ability.
Location
Global.
Time period
Early 21st century.
Major taxa studied
Woody plants.
Methods
We used mixed‐effect regression to examine the observed shape of the OAR (its “slope”) against species‐specific and plot‐wide predictors: coarse‐grain occupancy, tree size, plot species richness, energy availability and topographic complexity.
Results
We found large variation in OAR slopes, and the variation was strongest among species within plots. The OAR slopes showed a latitudinal trend and were steeper near the equator. As predicted, coarse‐grain occupancy and tree size negatively affected OAR slopes, whereas species richness had a positive effect and explained most of the variance between plots. Although hypothesized directionalities were broadly confirmed, traits and environment had relatively limited overall predictive power.
Main conclusions
These results document the variation of the OAR for 3,157 species at near‐global extent. We found a latitudinal gradient in OAR slopes and confirmed key hypothesized predictors. But at this global extent and over the large set of species analysed, the remaining unexplained variation in OAR slopes was substantial. Nevertheless, this large‐scale empirical analysis of the OAR offers an initial step towards a more general use of OARs for the fine‐scale prediction of species distributions and abundance.
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