Based on the framework of attribute diversity (a generalization of Hill numbers of order q), we develop a class of functional diversity measures sensitive not only to species abundances but also to ...trait-based species-pairwise functional distances. The new method refines and improves on the conventional species-equivalent approach in three areas: (1) the conventional method often gives similar values (close to unity) to assemblages with contrasting levels of functional diversity; (2) when a distance metric is unbounded, the conventional functional diversity depends on the presence/absence of other assemblages in the study; (3) in partitioning functional gamma diversity into alpha and beta components, the conventional gamma is sometimes less than alpha. To resolve these issues, we add to the attribute-diversity framework a novel concept: τ, the threshold of functional distinctiveness between any two species; here, τ can be chosen to be any positive value. Any two species with functional distance ≥ τ are treated as functionally equally distinct. Our functional diversity quantifies the effective number of functionally equally distinct species (or "virtual functional groups") with all pairwise distances at least s for different species pairs. We advocate the use of two complementary diversity profiles (τ profile and q profile), which depict functional diversity with varying levels of τ and q, respectively. Both the conventional species-equivalent method (i.e., τ is the maximum of species-pairwise distances) and classic taxonomic diversity (i.e., τ is the minimum of non-zero species-pairwise distances) are incorporated into our proposed τ profile for an assemblage. For any type of species-pairwise distance matrices, our attribute-diversity approach allows proper diversity partitioning, with the desired property gamma ≥ alpha and thus avoids all the restrictions that apply to the conventional diversity decomposition. Our functional alpha and gamma are interpreted as the effective numbers of functionally equally distinct species, respectively, in an assemblage and in the pooled assemblage, while beta is the effective number of equally large assemblages with no shared species and all species in the assemblages being equally distinct. The resulting beta diversity can be transformed to obtain abundance-sensitive Sørensen-and Jaccard-type functional (dis)similarity profiles. Hypothetical and real examples are used to illustrate the framework. Online software and R codes are available to facilitate computations.
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.
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.
Theory predicts that higher biodiversity in the tropics is maintained by specialized interactions among plants and their natural enemies that result in conspecific negative density dependence (CNDD). ...By using more than 3000 species and nearly 2.4 million trees across 24 forest plots worldwide, we show that global patterns in tree species diversity reflect not only stronger CNDD at tropical versus temperate latitudes but also a latitudinal shift in the relationship between CNDD and species abundance. CNDD was stronger for rare species at tropical versus temperate latitudes, potentially causing the persistence of greater numbers of rare species in the tropics. Our study reveals fundamental differences in the nature of local-scale biotic interactions that contribute to the maintenance of species diversity across temperate and tropical communities.
Canopy‐opening disturbance such as thinning has immediate and substantive effects on understory microclimate and therefore the establishment and growth of understory plants. A large number of studies ...have reported the effects of thinning on tree growth, but few studies have examined long‐term effects of thinning on understory light environments and species and functional diversity of understory plants. Even less is known whether the change in understory plant community structure observed following canopy disturbance is short‐lived and would diminish as the canopy closes or a long lasting due to legacy effects. We examined the effects of an experimental removal of 25% and 50% of the woody vegetation on understory light availability and variability on understory plant community structure in a subtropical Cryptomeria japonica plantation nine years after the treatment. Differences in availability of understory light among treatments diminished nine years after the experimental vegetation removal (thinning), but variability of understory light was still two times higher in the thinned treatments than the un‐thinned control. Species diversity of dominant and common understory plants was lower in the control than in the two thinning treatments, which were not different from each other. Community species and functional composition were also different between the un‐thinned control and the two thinning treatments. The thinned plots had proportionally more individuals of grasses and forbs and fewer individuals of ferns. Our results indicate that the effects of thinning on understory light variability last longer than on light availability representing an important and long‐lasting alteration of resource heterogeneity. At both species and functional group levels, greater diversity and unique composition in the thinned treatments compared to undisturbed control suggest a link between resource heterogeneity and biodiversity in the forest understory or legacy effects associated with the thinning‐induced changes in understory plant community.
•Landscape patterns effectively estimate major ion exports with 200 m riparian buffer width.•Landscape-level configuration metrics (PD, CONTAG, and IJI) account for most of the variations in cation ...discharges.•Class-level configuration metrics (EDBUD, PDBAR, and IJIAGR) primarily explain the variations in anion discharges.•No significant disparities in regression model performance are observed between wet and dry seasons.
The impacts of landscape pattern on water quality of streams are intricate and influenced by spatiotemporal scales. Untangling the interactions between landscapes and water, and identifying the pivotal indicators that drive spatial and temporal changes in nutrient dynamics, are essential steps towards facilitating sustainable water resource management. This study explored the relationship between landscape patterns and annual and seasonal (wet and dry seasons) exports of major cations (Na+, K+, Ca2+, and Mg2+) and anions (Cl-, SO42-, NO3-N, and PO4-P) in 43 watersheds across subtropical mountainous regions of Taiwan during the 2015–2016 period. Multiple stepwise regression models were constructed to elucidate the crucial landscape variables influencing variations in stream ion exports across different time scales, and spatial extent, ranging from watershed to various riparian buffer widths (100, 200, 500, 1000, 1500, and 2000 m). The findings indicated that the buffer width of 200 m emerged as the optimal scale for illustrating the connections between landscape patterns and water chemistry, outperforming larger scales. Nevertheless, there were minor deviations in the optimal scale for Na+ and Cl- (ranging from 100 to 500 m). Landscape-level configuration metrics (PD patch density, CONTAG Contagion, and IJI Interspersion and Juxtaposition) played a significant role in explaining the majority of data variations in cations. This suggest that overall landscape fragmentation tends to enhance cations exports, regardless of land cover types. On the contrary, class-level configuration metrics (EDBUD edge density of buildup, PDBAR patch density of bareland, and IJIAGR Interspersion and Juxtaposition of agriculture) played a primary role in interpreting data variations of anions. This indicated that the configurations of specific land cover types, such as buildup, agriculture and bareland, are the primary factors influencing anion exports. Furthermore, the regression models exhibited robust performance during both wet and dry seasons, implying their consistent efficacy in estimating ion exports. This synthesis illustrated the benefits of utilizing this cost-effective approach to assess landscape-water connections in challenging mountainous regions, assisting water resources management.
•Nitrate and phosphate exports in subtropical mountainous Taiwan are among the highest worldwide.•Landscape patterns within 200 m riparian buffer can effectively predict NO3-N and PO4-P exports.•The ...class-level metrics have the best predictive capacity on nutrient fluxes compared to landscape-level metrics.•The IJIAGR and EDBUD are most imortant indices to characterize the behaviors of NO3-N and PO4-P exports.
Landscape composition and configuration, which runoff flows through, have substantial effects on nutrient export of humid mountainous watersheds. The relationships between landscape metrics and annual and seasonal NO3-N and PO4-P fluxes are developed for 43 watersheds distributed island-wide in Taiwan during 2015–2016. The results show that the watersheds with higher concentrations of NO3-N and PO4-P mainly distributed on western Taiwan whereas watersheds with lower concentrations of NO3-N and PO4-P scattered across mountain regions and eastern Taiwan. Multiple stepwise regression models are used to realize the effects of landscape pattern on NO3-N and PO4-P exports at watershed level and riparian buffers of various width (100 m, 200 m, 500 m, 1000 m, 1500 m, and 2000 m). Our findings show that the average annual exports of NO3-N and PO4-P across various watersheds are 3.8–50.8 and 0.04–7.7 kg ha−1 yr−1, respectively, much higher than reported values worldwide. The class-level metrics IJI (interspersion and juxtaposition) of agricultural land and LPI (largest patch index) of buildup area obtained from 200 m buffer explain 85% of variation of NO3-N flux, and ED (edge of density) of buildup area and LPI of water body or percentage of water body at 200 m buffer combined contribute 90% of variation in PO4-P exports. The highly mixed development of urban and agriculture distributed along with the limited extent of riparian buffers within watersheds in Taiwan make the watershed susceptible to loss of a large quantity of nutrients and sediments into streams. Management practices such as diminishing fragmented agriculture and buildup area are recommended as they should help to reduce water pollution, and better designs of developed area and water body can further improve water quality.
QUESTIONS: How do frequent disturbances of varying intensity affect heterogeneity of canopy openness and resulting regenerating tree diversity in subtropical rain forests? How does canopy gap pattern ...and regeneration time of a forest experiencing frequent but unpredictable typhoon disturbance vary over 17 yr? How is the understorey light environment influenced by canopy gaps in a forest experiencing frequent defoliation? Compared to non‐gap areas, do gaps provide unique niches reflected in different seedling communities? LOCATION: Natural evergreen hardwood forest, northeastern Taiwan. METHODS: We examined gap characteristics, light availability and variability, and seedling diversity in both gaps and non‐gaps in a subtropical forest with frequent typhoon disturbance, and compared the results to a survey at the same site conducted in 1995 following six typhoons in 1994. RESULTS: Gaps were smaller and covered a much smaller proportion of the forest in the 2012 survey (mean gap size 10 m², 3.3% of the forest) than the 1995 survey (33 m²and 10%). Canopy regeneration times estimated from the 2012 survey (200–400 yr) were much longer than those based on the 1995 survey (50–175 yr). Neither light availability nor variability differed between gaps and non‐gaps, so gaps ostensibly did not provide a unique niche space. There were no seedling species occurring exclusively in gaps, and very high plant community similarity (>90%) between gaps and non‐gaps. CONCLUSIONS: In ecosystems with small canopy gaps resulting from frequent disturbance, gaps play a neutral role in understorey light environment and thus provide no unique niches and play a neutral role in plant diversity. Our study also suggests that measures of gap area, occurrence and forest turnover should be taken multiple times, during years with varying background disturbance rates.
•Meteorological and hydrological droughts in LHC are becoming prominent after 2001.•High spring rainfall lead to earlier SOS and longer LOS.•Earlier SOS and longer LOS result in higher P-Q deficit ...(precipitation minus runoff)•Summer rainfall contributes only on water budget.
Upstream forested watersheds supply critical ecosystem services through providing clean freshwater and maintaining stable hydrological conditions. Responses of vegetation phenology to climatic variations have vital implications for hydrological regimes that are region-specific, but the associations of climate-phenology-hydrology have rarely been examined especially in tropical/subtropical regions. In this study, we utilized 46-year (1975–2020) hydroclimate records in forested watershed at central Taiwan, and showed that precipitation and streamflow anomalies and incidences of meteorological and hydrological droughts are becoming prominent after 2001. We further investigated the effects of monthly temperature and precipitation on vegetation growth using monthly EVI (enhanced vegetation index) of a watershed derived from MODIS (Moderate Resolution Imaging Spectroradiometer), and explored the effects of seasonal precipitation on the variations of vegetation phenological and subsequent watershed streamflow between 2001 and 2020. The EVI and temperature showed a linear relationship without time-lag effect (R2 = 0.50, p < 0.001), whereas EVI and precipitation exhibited a log-linear relationship with 2-month lag (R2 = 0.40, p < 0.001), indicating the accumulation of rainfall during relatively dry period was crucial for vegetation growth. Structural equation modeling revealed that earlier start of growing season (SOS) caused by relatively high spring rainfall (February-March) led to longer growing season (LOS) and higher P-Q deficit (precipitation minus runoff) during the growing season. Nevertheless, the large amount of precipitation during growing season has no effect on the end of growing season (EOS), LOS and P-Q deficit. Neither EOS has influence on LOS and P-Q deficit. Understanding the vegetation responses to climatic variations is required for future hydrologic regime projections, especially under changing climate.
PDF
