Forest In Southwest China Research Articles

Small Roots of Parashorea chinensis Wang Hsie Decompose Slower than Twigs

Plants produce above- and below-ground biomass. However, our understanding of both production and decomposition of below-ground biomass is poor, largely because of the difficulties of accessing roots. Below-ground organic matter decomposition studies are scant and especially rare in the tropics. In this study, we used a litter bag experiment to quantify the mass loss and nutrient dynamics of decomposing twigs and small roots from an arbuscular mycorrhizal fungal associated tree, Parashorea chinensis Wang Hsie, in a tropical rain forest in Southwest China. Overall, twig litter decomposed 1.9 times faster than small roots (decay rate (k) twig = 0.255, root = 0.134). The difference in decomposition rates can be explained by a difference in phosphorus (P) concentration, availability, and use by decomposers or carbon quality. Twigs and small roots showed an increase in nitrogen concentration, with final concentrations still higher than initial levels. This suggests nitrogen transfer from the surrounding environment into decomposing twigs and small roots. Both carbon and nitrogen dynamics were significantly predicted by mass loss and showed a negative and positive relationship, respectively. Our study results imply that small roots carbon and nitrogen increase the resident time in the soil. Therefore, a better understanding of the carbon cycle requires a better understanding of the mechanisms governing below-ground biomass decomposition.

Contrasting responses of soil fungal communities and soil respiration to the above‐ and below‐ground plant C inputs in a subtropical forest

The roles of soil fungal diversity and community composition in regulating soil respiration when above‐ and below‐ground plant carbon (C) inputs are excluded remain unclear. In the present study, we aimed to examine the following. (a) How does the exclusion of above‐ and below‐ground plant C inputs affect soil respiration and soil fungi singly and in combination? (b) Are changes in soil fungal diversity aligned with changes in soil respiration? A field experiment with manipulation of plant C inputs was established in a subtropical forest in southwest China in 2004 with litter removal and tree stem‐girdling to exclude inputs of the above‐ and below‐ground plant C, respectively. In 2009, we measured the rates of soil respiration with an infrared gas analyser and soil fungal community structure using Illumina sequencing. We found that the rates of soil respiration were reduced significantly by litter removal and girdling, by similar magnitudes. However, they were not decreased further by the combination of these two treatments compared to either treatment alone. In contrast, litter removal increased the diversity of soil fungal communities, whereas girdling decreased the abundance of symbiotrophic fungi but increased the abundance of saptrotrophic and pathotrophic fungi. These changes in soil fungal community might initiate CO2 emission from soil C decomposition, offsetting further decline in soil respiration when plant C inputs are excluded. These results revealed that the exclusion of the above‐ and below‐ground plant C inputs led to contrasting soil fungal communities but similar soil function. Our findings suggest that both above‐ and below‐ground plant C are important in regulating soil respiration in subtropical forests, by limiting substrates for soil fungal growth and altering the diversity and composition of the soil fungal community.Highlights Litter removal and girdling decreased soil respiration by similar magnitudes The combination of litter removal and girdling did not further decrease soil respiration Litter removal significantly increased species richness of soil fungal communities Girdling changed the abundance of functional guilds of soil fungal communities

The contrasting leaf functional traits between a karst forest and a nearby non-karst forest in south-west China.

Karst and non-karst forests occur in the same region in south-west China, but the soil water and mineral nutrients availability are different between the forests. Our hypothesis was that the leaves of karst trees would be better adapted to dry, nutrient-poor conditions than those of trees in a nearby non-karst forest. We compared the gas exchange, anatomical characteristics and mineral nutrient concentrations in leaves from 21 tree species in a tropical karst forest and 19 species in a nearby non-karst forest in south-west China. We found that the leaves of karst trees had higher P concentrations, photosynthetic capacity and water use efficiency, and greater adaxial and abaxial epidermis thickness than leaves of non-karst forest trees. Evergreen and deciduous trees differed more significantly in leaf functional traits in the karst forest than in the non-karst forest. The leaf palisade:spongy mesophyll thickness ratio was positively correlated with stomatal conductance and negatively correlated with photosynthetic water use efficiency in the karst forest but not in the non-karst forest. Our findings indicate that karst forest trees are more conservative in water use, whereas soil P deficiency could be a major limiting factor for the growth of non-karst forest trees.

Obligate to facultative shift of two epiphytic Lepisorus species during subtropical forest degradation: Insights from functional traits

Epiphytic ferns are an important group of plants strongly affected by sudden changes in forest community composition and structure. However, a key gap persists in our understanding of their responses to forest degradation, specifically concerning the changes in species distributions and functional traits and their underlying mechanisms. Here, we investigated the vertical distribution of two Lepisorus species of a subtropical primary forest and its two-stage degraded forests in Southwest China, and measured 18 plant functional traits of individuals growing in terrestrial (i.e., on the ground) and 0.5–2.5 m epiphytic forest habitats. We found that the relative abundance of both species peaked at heights of approximately 8–16 m in the canopy of primary forest but at heights of 0–4 m on tree trunks in two degraded forests. Terrestrial individuals occurred only in secondary forests, and the relative abundance of these two species on lower tree trunk and forest ground increased with canopy openness within degraded forests. Principal component analysis of the epiphytes’ functional traits and plasticity provided evidence for two suites of traits related to light acclimation and nutrient strategies. Furthermore, variation in both species’ morphological and physiological traits revealed resource use trade-offs in response to forest degradation. Epiphytic individuals in primary forest had higher capacity for light capture while those in secondary forests had a higher photosynthetic capacity and resource-use efficiency. Within the same secondary forest, terrestrial individuals tended to acclimate to a low-light understory and were more efficient in their nutrient use than epiphytic conspecifics. Together, these results showed a shift of two obligate epiphytic ferns to be facultative in secondary forests, and underwent a downward shift in their microhabitat occupancy to lower tree trunks and understory soils in response to forest degradation. They could achieve this shift by adjusting their functional traits at an intraspecific level, which promoted rhizome extensions to find optimal habitats for persistence.

Non-dominant trees significantly enhance species richness of epiphytic lichens in subtropical forests of southwest China

Abstract Host species has an important influence on the distribution of epiphytic lichens in forests. However, the importance of non-dominant trees in shaping lichen communities has been poorly studied owing to the relative rarity of individuals. The importance of dominant and non-dominant trees for distribution of epiphytic lichens was determined in eight subtropical forests in southwestern China. Dominant trees supported more abundant total and exclusive lichen species only in secondary forests. The occurrence of non-dominant trees promoted lichen diversity within forest types and influenced lichen communities on both tree groups. The effects of total tree species on lichen distribution largely resulted from the presence of non-dominant trees. Dominant and non-dominant trees supported distinct lichen assemblages within forest types, and ordination analyses showed a clear separation. Our study, therefore, reinforces the importance of non-dominant trees for conserving epiphytic lichens, and highlights that lichen assemblages are shaped by both dominant and non-dominant trees.

Evidence of forest restoration success and the conservation value of community-owned forests in Southwest China using dung beetles as indicators.

Protection of the world’s remaining forests and biodiversity is a matter of global concern. Yunnan, China is home to China’s only mainland tropical rainforests, and 20% of China’s total biodiversity. Despite restoration measures and establishment of new protected areas, this region is still experiencing biodiversity loss due to inadequate management and monitoring. We evaluate restoration success of China’s tropical forests in Xishuangbanna National Nature Reserve (XSBN-NNR), Yunnan, China using dung beetles as an indicator taxon. We sampled across a land-use gradient of human alteration: protected forest, restored forest, community owned forest, and rubber plantation. We collected 3,748 dung beetles from 21 species over a 3 month period. Multivariate analyses revealed unique assemblages in each land-use category, but with restored forest most similar to protected areas, suggesting restoration success in this region. Community forests were more diverse than plantations, suggesting that community forests may be a valuable and practical conservation tool in this region. Most species were generalists, although some had dietary and habitat preferences. Furthermore, dietary niche breadths were, on average, higher in disturbed areas, suggesting that disturbance may result in dietary changes. We show that restoration of tropical forests appears to be successful for a key ecological and biological indicator group- dung beetles. Furthermore, community-owned forests appear to be valuable and practical method of maintaining ecosystem health and biodiversity in the region. Future management in this region would likely benefit from encouragement to maintain community-owned forests, economic incentives for restoring farmland to forest, and increased environmental monitoring across the land-use gradient.

Nitrogen deposition increases N2O emission from an N-saturated subtropical forest in southwest China

Nitrous oxide (N2O) is a major greenhouse gas, with elevated emission being reported from subtropical forests that receive high nitrogen (N) deposition. After 10 years of monthly addition of ammonium nitrate (NH4NO3) or sodium nitrate (NaNO3) to a Mason pine forest at Tieshanping, near Chongqing city in Southwest China, the simulated N deposition was stopped in October 2014. The results of soil N2O emissions monitoring in different seasons during the nitrogen application period showed that nitrogen addition significantly increased soil N2O emission. In general, the N2O emission fluxes were positively correlated to nitrate (NO3−) concentrations in soil solution, supporting the important role of denitrification in N2O production, which was also modified by environmental factors such as soil temperature and moisture. After stopping the application of nitrogen, the soil N2O emissions from the treatment plots were no longer significantly higher than those from the reference plots, implying that a decrease in nitrogen deposition in the future would cause a decrease in N2O emission. Although the major forms of N deposition, NH4+ and NO3−, had not shown significantly different effects on soil N2O emission, the reduction in NH4+ deposition may decrease the NO3− concentrations in soil solution faster than the reduction in NO3− deposition, and thus be more effective in reducing N2O emission from N-saturated forest soil in the future.

Disentangling Climate and LAI Effects on Seasonal Variability in Water Use Efficiency Across Terrestrial Ecosystems in China

AbstractWater use efficiency (WUE), the ratio of gross primary productivity (GPP) over evapotranspiration (ET), is a critical ecosystem function. However, it is difficult to distinguish the individual effects of climatic variables and leaf area index (LAI) on WUE, mainly due to the high collinearity among these factors. Here we proposed a partial least squares regression‐based sensitivity algorithm to confront the issue, which was first verified at seven ChinaFlux sites and then applied across China. The results showed that across all biomes in China, monthly GPP (0.42–0.65), ET (0.33–0.56), and WUE (0.01–0.31) showed positive sensitivities to air temperature, particularly in croplands in northeast China and forests in southwest China. Radiation exerted stronger effects on ET (0.55–0.78) than GPP (0.19–0.65), resulting in negative responses (−0.44 to 0.04) of WUE to increased radiation among most biomes. Increasing precipitation stimulated both GPP (0.06–0.17) and ET (0.05–0.12) at the biome level, but spatially negative effects of excessive precipitation were also found in some grasslands. Both monthly GPP (−0.01 to 0.29) and ET (0.02–0.12) showed weak or moderate responses to vapor pressure deficit among biomes, resulting in weak response of monthly WUE to vapor pressure deficit (−0.04 to 0.08). LAI showed positive effects on GPP (0.18–0.60), ET (0–0.23), and WUE (0.13–0.42) across biomes, particularly on WUE in grasslands (0.42 ± 0.30). Our results highlighted the importance of LAI in influencing WUE against climatic variables. Furthermore, the sensitivity algorithm can be used to inform the design of manipulative experiments and compare with factorial simulations for discerning effects of various variables on ecosystem functions.

Deposition and Fate of Mercury in Litterfall, Litter, and Soil in Coniferous and Broad‐Leaved Forests

AbstractMercury dynamics in the process of litter decomposition is crucial to understanding the atmospheric mercury deposition to soils in the forest catchments. This work aimed to quantify mercury internal biogeochemical cycling and the fractionation process in a coniferous forest and a broad‐leaved forest in southwest China. Annual deposition fluxes of total mercury (THg) and methylmercury (MeHg) via litterfall were 40.5 and 0.10 μg/m2 in the coniferous forest and were 90.9 and 0.34 μg/m2 in the broad‐leaved forest, respectively. The litterfall biomass was the most influential factor resulting in the higher mercury input in the broad‐leaved forest. During the one‐year incubation, THg and MeHg mass in the decomposing litter increased 49 and 444% in the coniferous forest compared to those in the broad‐leaved forest, respectively. Methylation has increased the risk of MeHg mobilization to aquatic and soil ecosystems during litter decomposition. Additionally, higher mercury deposition flux but lower accumulation in the broad‐leaved forest resulted in similar mercury content in the coniferous forest soils. Six mercury fractions were determined by sequential extraction for the decomposing litter, while MeHg concentrations were statistically significantly correlated to water soluble and salt soluble fractions. The residual mercury fraction accounted for over 90% of the THg and increased with litter decomposition. During the last half of the litter decomposition, the ratio of residual fraction significantly increased, while the sum of the other ratios reduced, which indicated that litter dynamics in the internal forests stabilized the mercury in organic soils during litter decomposition.

Spatial Patterns and Drivers of Microbial Taxa in a Karst Broadleaf Forest.

Spatial patterns and drivers of soil microbial communities have not yet been well documented. Here, we used geostatistical modeling and Illumina sequencing of 16S rRNA genes to explore how the main microbial taxa at the phyla level are spatially distributed in a 25-ha karst broadleaf forest in southwest China. Proteobacteria, dominated by Alpha- and Deltaproteobacteria, was the most abundant phylum (34.51%) in the karst forest soils. Other dominating phyla were Actinobacteria (30.73%), and Acidobacteria (12.24%). Soil microbial taxa showed spatial dependence with an autocorrelation range of 44.4–883.0 m, most of them within the scope of the study plots (500 m). An increasing trend was observed for Alphaproteobacteria, Deltaproteobacteria, and Chloroflexi from north to south in the study area, but an opposite trend for Actinobacteria, Acidobacteira, and Firmicutes was observed. Thaumarchaeota, Bacteroidetes, Gemmatimonadetes, and Verrucomicrobia had patchy patterns, Nitrospirae had a unimodal pattern, and Latescibacteria had an intermittent pattern with low and high value strips. Location, soil total phosphorus, elevation, and plant density were significantly correlated with main soil bacterial taxa in the karst forest. Moreover, the total variation in soil microbial communities better explained by spatial factors than environmental variables. Furthermore, a large part of variation (76.8%) was unexplained in the study. Therefore, our results suggested that dispersal limitation was the primary driver of spatial pattern of soil microbial taxa in broadleaved forest in karst areas, and other environmental variables (i.e., soil porosity and temperature) should be taken into consideration.

Reducing Uncertainties in Applying Remotely Sensed Land Use and Land Cover Maps in Land-Atmosphere Interaction: Identifying Change in Space and Time

Land use and land cover (LULC) data are a central component of most land-atmosphere interaction studies, but there are two common and highly problematic scale mismatches between LULC and climate data. First, in the spatial domain, researchers rarely consider the impact of scaling up fine-scale LULC data to match coarse-scale climate datasets. Second, in the temporal domain, climate data typically have sub-daily, daily, monthly, or annual resolution, but LULC datasets often have much coarser (e.g., decadal) resolution. We first explored the effect of three spatial scaling methods on correlations among LULC data and a land surface climatic variable, latent heat flux in China. Scaling by a fractional method preserved significant correlations among LULC data and latent heat flux at all three studied scales (0.5°, 1.0°, and 2.5°), whereas nearest-neighbor and majority-aggregation methods caused these correlations to diminish and even become statistically non-significant at coarser spatial scales (i.e., 2.5°). In the temporal domain, we identified fractional changes in croplands, forests, and grasslands in China using a recently developed and annually resolved time series of LULC maps from 1982 to 2012. Relative to common LULC change (LULCC) analyses conducted over two-time steps or several time periods, this annually resolved, 31-year time series of LULC maps enables robust interpretation of LULCC. Specifically, the annual resolution of these data enabled us to more precisely observe three key and statistically significant LULCC trends and transitions that could have consequential effects on land-atmosphere interaction: (1) decreasing grasslands to increasing croplands in the Northeast China plain and the Yellow river basin, (2) decreasing croplands to increasing forests in the Yangtze river basin, and (3) decreasing grasslands to increasing forests in Southwest China. Our study not only demonstrates the importance of using a fractional spatial rescaling method, but also illustrates the value of annually resolved LULC time series for detecting significant trends and transitions in LULCC, thus potentially facilitating a more robust use of remotely sensed data in land-atmosphere interaction studies.

Environmental and spatial contributions to seedling and adult tree assembly across tropical, subtropical and subalpine elevational gradients

Aims: Quantifying the relative importance of the mechanisms that drive community assembly in forests is a crucial issue in community ecology. The present study aims to understand the ways in which niche-based and spatially based processes influence community assembly in areas in different climatic conditions and how these processes change during the transition from seedling to adult. Methods: In this study, we investigated how taxonomic and phylogenetic beta diversity in seedling and adult stages of forest trees change across three elevational transects in tropical, subtropical and subalpine forests in Southwest China, and the relationships of these changes to the environment and inter-site distances. We quantified the relative contribution of environmental conditions and spatial distribution to taxonomic and phylogenetic beta diversity of both seedling and adult life stages along each elevational transect. We also quantified the taxonomic and phylogenetic similarity between seedlings and adult trees along elevations. Important Findings: Taxonomic and phylogenetic beta diversity of both seedlings and adult trees increased with an increase in both environmental distance and spatial distance in all three transects. On both taxonomic and phylogenetic levels, the effects of environmental filtering and spatial disposition varied between life stages and among forest types. Phylogenetic similarity between seedlings and adult trees increased with elevation, although the taxonomic similarity did not show clear elevational patterns. Our results suggest that the relative contribution of niche-based and space-based processes to taxonomic and phylogenetic assemblages varies across major plant life stages and among forest types. Our findings also highlight the importance of ontogenetic stages for fully understanding community assembly of long-lived tree species.

Spatial distribution of tree species in evergreen-deciduous broadleaf karst forests in southwest China

Understanding the spatial distribution of tree species in subtropical evergreen-deciduous broadleaf karst forest is fundamental to studying species coexistence and karst species diversity. Here, complete spatial randomness and heterogeneous Poisson process models were used to analyze the spatial distribution patterns of 146 species with at least one individual per ha in a 25-ha plot in southwest China. We used canonical correspondence analysis (CCA) and the torus-translation test (TTT) to explain the distributions of observed species. Our results show that an aggregated distribution was the dominant pattern in Mulun karst forests; the percentage and intensity of aggregated decreased with increasing spatial scale, abundance, mean diameter at breast height (DBH), and maximum DBH. Rare species were more aggregated than intermediately abundant and abundant species. However, functional traits (e.g., growth form and phenological guild) had no significant effects on the distributions of species. The CCA revealed that the four analyzed topographic variables (elevation, slope, aspect, and convexity) had significant influences on species distributions. The TTT showed that not all species have habitat preferences and that 68.5% (100 out of 146 species) show a strongly positive or negative association with at least one habitat. Most species were inclined to grow on slopes and hilltops.

Snow damage strongly reduces the strength of the carbon sink in a primary subtropical evergreen broadleaved forest

A primary subtropical evergreen broadleaved forest in southwest China experienced a particularly extreme snowfall event during January 2015. The 2015 event enabled the quantification of the impact of the extreme meteorological event on the forest carbon balance. We analyzed five years of continuous measurements of CO2 exchange across the biosphere/atmosphere interface in the forest using an eddy covariance technique. We quantified how exposure to an extreme meteorological event affected ecosystem processes that determine gross primary productivity (GPP) and ecosystem respiration (Reco), and thus annual net carbon (C) sequestration. The forest canopy was severely damaged by the heavy snow, and the leaf area index (LAI) decreased significantly from January to July 2015. GPP, net ecosystem exchange (NEE), and Reco all sharply decreased in 2015 after the heavy snow. On average, a strong decrease of 544 g C m−2 year−1 in annual NEE in 2015 was associated with a decrease of 829 g C m−2 year−1 in annual GPP and a decrease of 285 g C m−2 year−1 in annual Reco. Overall, annual net C uptake in 2015 was reduced by 76% compared to the mean C uptake of the previous four years. A sharp increase in carbon uptake was also observed in 2016, indicating that long-term, continuous measurements should be carried out to evaluate the overall response to the disturbance.

Canopy temperature variability in a tropical rainforest, subtropical evergreen forest, and savanna forest in Southwest China

Canopy temperature (Tc) measurements with infrared thermometry have been widely used to assess plant water status. Here, we evaluated Tc and its controlling factors in a primary tropical rainforest (TRF), subtropical evergreen broad-leaved forest (STF) and valley savanna forest (SAF) in southwestern China. We found differences between Tc and air temperature (Ta) of as much as 2.2 °C between the dry and wet seasons in the TRF. However, the canopy-to-air temperature difference (Tc-Ta) was only 0.3 °C between the dry and wet seasons in the STF. Solar radiation (SR) was the dominant factor in Tc-Ta variations during the dry and wet seasons at the three sites. The increased heating in the canopy leaves was likely the result of low stomatal conductance leading to low transpiration cooling. Changes in Tc-Ta in the TRF were highly sensitive to the degree of stomatal closure. The change in Tc-Ta was controlled by the climate, but inherent plant traits, such as stomatal conductance, also played an important controlling role.

Successional leaf traits of monsoon evergreen broad-leaved forest, Southwest China

Understanding the variation of functional traits of plant species along forest successional gradients may provides useful insights into community assemblages. However, species performance during forest succession is controversial. We explored the variation of leaf traits along a forest succession by examining ten leaf traits in four successional stages in a monsoon evergreen broad-leaved forest in Southwest China. Results showed significant differences in all leaf traits except leaf area and leaf carbon content among the successional stages. Five leaf traits were highly correlated to successional stage, while the first principal component showed no correlation with successional stage. The first principal component accounted for 56.1% of the total variation in all ten leaf traits. Almost 50% of the relationships between leaf traits differed along the examined successional gradient, indicating that leaf traits were affected by the successional stage.

Temporal variability of ammonia emission potentials for six plant species in an evergreen subtropical forest in southwest China.

The temporal variability of leaf ammonia (NH3) emission potentials (the ratio of leaf tissue ammonium to proton concentration) and nitrogen (N) pools of six dominant plant species were investigated at the Tieshanping (TSP) forested catchment, southwest China. The results showed that the NH3 emission potentials and N pools presented small variations among seasons, which were mainly controlled by plant species and the leaf age. Also, high emission potential in one species did not correspond to high tissue N content. Specifically, the Chinese fir (Cunninghamia lanceolata) had higher NH3 emission potential (mean: 46.2) but lower N content (mean: 1.6% of Dw). The leaf privet (Ligustrum quihoui Carr.) was with the moderate emission potential (15) and the highest N content (2.7% of Dw) on average, which for the Masson pine (Pinus massoniana) were both low. Overall, the emission potentials of the six species were too low (<200) to build up a sufficiently high NH3 partial pressure in the leaves. Therefore, the Masson pine dominant subtropical forest at TSP acts as a sink for the atmospheric NH3, indicating that using the N flux in throughfall only may significantly underestimate the N income of the ecosystem. The results are informative for future modeling of plant-atmosphere NH3 exchange and estimating N budget in local or regional scales.

Evapotranspiration from a primary subtropical evergreen forest in Southwest China

AbstractEvapotranspiration (ET) was observed over a 5‐year period at a primary subtropical evergreen forest in southwest China. The study used the eddy covariance method and quantified the precipitation, throughfall, stemflow, soil evaporation, and routine meteorological parameters to analyze the contributions of stand‐level transpiration and canopy interception loss to the total ET. The annual ET ranged between 785 and 901 mm. The average ratios ET–potential evapotranspiration were 0.45 and 0.87 during the dry and wet seasons, respectively. The relative contributions of soil evaporation, stand‐level transpiration, and canopy interception loss to ET were quantified in order to understand their roles in today's climate and in a potential future climate. Solar radiation was a driver for ET, although the occurrence of drought limited the tree transpiration and thus ET. Specifically, deep soil moisture was an important driver of ET during the dry season. During the wet season, the vapor pressure deficit became one of the main drivers. Although the current study did not collect specific data for the effect of fog on ET, fog likely plays an important role in the ecohydrologic system and deserves further investigation. Although the hydrological system is currently stable, it is anticipated that the groundwater recharge from the ecosystem may be largely reduced in the future, likely through climate change and an associated positive temperature–ET feedback loop.

Water use efficiency in a primary subtropical evergreen forest in Southwest China

We calculated water use efficiency (WUE) using measures of gross primary production (GPP) and evapotranspiration (ET) from five years of continuous eddy covariance measurements (2009–2013) obtained over a primary subtropical evergreen broadleaved forest in southwestern China. Annual mean WUE exhibited a decreasing trend from 2009 to 2013, varying from ~2.28 to 2.68 g C kg H2O−1. The multiyear average WUE was 2.48 ± 0.17 (mean ± standard deviation) g C kg H2O−1. WUE increased greatly in the driest year (2009), due to a larger decline in ET than in GPP. At the diurnal scale, WUE in the wet season reached 5.1 g C kg H2O−1 in the early morning and 4.6 g C kg H2O−1 in the evening. WUE in the dry season reached 3.1 g C kg H2O−1 in the early morning and 2.7 g C kg H2O−1 in the evening. During the leaf emergence stage, the variation of WUE could be suitably explained by water-related variables (relative humidity (RH), soil water content at 100 cm (SWC_100)), solar radiation and the green index (Sgreen). These results revealed large variation in WUE at different time scales, highlighting the importance of individual site characteristics.

Effect of habitat fragmentation on ranging behavior of white-headed langurs in limestone forests in Southwest China.

The critically endangered white-headed langur (Trachypithecus leucocephalus) is confined to fragmented karst forests of southwest Guangxi Province, China. A lack of information on the influence of habitat fragmentation on langur behavior has prevented a comprehensive understanding of their ranging behavior and the development of effective langur conservation strategies. We collected comparative data on time budgets, daily path lengths, home range and diets of four langur groups inhabiting the lightly fragmented Fusui forest (G1, G2) and the more heavily fragmented Chongzuo forest (G3, G4). The aim was to explore the effect of this fragmentation on langur ranging behavior. Our results showed that the Fusui groups spent more time on moving and less time on feeding and playing than the Chongzuo groups. Daily path lengths were 472.4-536.1m for the Fusui groups and 449.6-480.7m for the Chongzuo groups, indicating no marked inter-site variation. The Fusui groups occupied much larger home ranges (23.8-33.8ha) than the Chongzuo groups (14.5-15.8ha). However, all groups had similar monthly home ranges. Diets significantly differed among langur groups. The Fusui groups consumed more young leaves and had much lower diet diversity compared with the Chongzuo groups. Our findings indicate that habitat fragmentation is one of the crucial determinants of white-headed langur ranging behavior because fragmentation reduces and restricts the home range. Langurs in fragmented habitat adopt an energy conservation strategy characterized by devoting more time to feeding and less time to moving, with a smaller home range and consumption of more plant species. We argue that linking fragmented forests with corridors should be considered a priority in a wider and comprehensive longer term langur population conservation and habitat management strategy.