Seasonal Rain Forest Research Articles

Converting tropical rainforest to native rubber plantations alters soil bacterial and fungal communities

Driven by soil biochemistry and plant community composition, soil microbial communities reflect land management and environmental conditions. To evaluate the effects of land-use change on soil microbial diversity, we used denaturing gradient gel electrophoresis (DGGE) combined with sequencing to compare bacterial and fungal community profiles between rubber plantation (RP) and nearby seasonal rainforests (SR). Rainforest soil generally had higher soil total C and microbial biomass C concentration, smaller soil aggregate proportions, and a soil pH below rubber plantation soil. The bacterial and fungal richness and diversity were similar after converting primary forests to rubber plantations. However, the composition of bacterial and fungal communities has significantly changed in rubber plantations. Basidiomycota, the predominant group of fungi, was significantly different between primary forests and rubber plantations. However, Basidiomycota showed higher heterogenetic distribution in the rainforest under rubber plantations. In conclusion, land-use changes mainly affect soil microbial community composition and heterogeneity distribution patterns, especially for saprotrophic fungi, which consist of changes in litter inputs and soil C conditions.

Structuring Interaction Networks Between Epiphytic Bryophytes and Their Hosts in Yunnan, SW China

Ecological networks are commonly applied to depict general patterns of biotic interactions, which provide tools to understand the mechanism of community assembly. Commensal interactions between epiphytes and their hosts are a major component of species interactions in forest canopies; however, few studies have investigated species assemblage patterns and network structures of epiphyte–host interactions, particularly non-vascular epiphytes in different types of forest. To analyze the characteristics of network structures between epiphytes and their hosts, composition and distribution of epiphytic bryophytes were investigated from 138 host individuals using canopy cranes in a tropical lowland seasonal rain forest (TRF) and a subtropical montane moist evergreen broad-leaved forest (STF), in Southwest China. We structured binary networks between epiphytic bryophytes and their hosts in these two forests, which presented 329 interactions in the TRF and 545 interactions in the STF. Compared to TRF, the bryophyte–host plant networks were more nested but less modular in the STF. However, both forests generally exhibited a significantly nested structure with low levels of specialization and modularity. The relatively high nestedness may stabilize the ecological networks between epiphytic bryophytes and their hosts. Nevertheless, the low modularity in epiphyte–host networks could be attributed to the lack of co-evolutionary processes, and the low degree of specialization suggests that epiphytes are less likely to colonize specific host species. Vertical distribution of the bryophyte species showed structured modules in the tree basal and crown zones, probably attributing to the adaptation to microclimates within a host individual. This study highlights the nested structure of commensal interaction between epiphytic bryophytes and host trees, and provides a scientific basis to identify key host tree species for conservation and management of biodiversity in forest ecosystems.

Adaptive genetic diversity of dominant species contributes to species co-existence and community assembly

The synthesis of evolutionary biology and community ecology aims to understand how genetic variation within one species can shape community properties and how the ecological properties of a community can drive the evolution of a species. A rarely explored aspect is whether the interaction of genetic variation and community properties depends on the species' ecological role. Here we investigated the interactions among environmental factors, species diversity, and the within-species genetic diversity of species with different ecological roles. Using high-throughput DNA sequencing, we genotyped a canopy-dominant tree species, Parashorea chinensis, and an understory-abundant species, Pittosporopsis kerrii, from fifteen plots in Xishuangbanna tropical seasonal rainforest and estimated their adaptive, neutral and total genetic diversity; we also surveyed species diversity and assayed key soil nutrients. Structural equation modelling revealed that soil nitrogen availability created an opposing effect in species diversity and adaptive genetic diversity of the canopy-dominant Pa. chinensis. The increased adaptive genetic diversity of Pa. chinensis led to greater species diversity by promoting co-existence. Increased species diversity reduced the adaptive genetic diversity of the dominant understory species, Pi. kerrii, which was promoted by the adaptive genetic diversity of the canopy-dominant Pa. chinensis. However, such relationships were absent when neutral genetic diversity or total genetic diversity were used in the model. Our results demonstrated the important ecological interaction between adaptive genetic diversity and species diversity, but the pattern of the interaction depends on the identity of the species. Our results highlight the significant ecological role of dominant species in competitive interactions and regulation of community structure.

Miocene pinhole borer ambrosia beetles: new species of Diapus (Coleoptera: Curculionidae: Platypodinae)

New fossil species of the genus Diapus (Coleoptera: Curculionidae: Platypodinae) are described in Miocene amber from Ethiopia and Zhangpu, China, based on male and female specimens. We report 24 male and 6 female specimens in Zhangpu amber and one male from Ethiopian amber. However, the number of specimens in Ethiopian amber will probably increase when more material is available for study. The large amount of Diapus specimens supports the paleoenvironmental reconstruction of the Zhangpu amber forest as a megathermal seasonal rainforest. The new species highlight that Platypodinae diversification likely associated with angiosperms may have started in the Cretaceous with an increase of diversity in the Miocene. The specimens described here are the first record of Diapus preserved in amber.

Intra-annual radial growth of Garuga floribunda in tropical seasonal rain forest and its response to environmental factors in Xishuangbanna, Southwest China

We examined the seasonal growth dynamics of a deciduous tree species Garuga floribunda in the tropical seasonal rain forest in Xishuangbanna and monitored the stem radial growth with both high resolution dendrometer and microcoring methods. Combining with the monitoring of non-structural carbohydrates (NSCs) in stem and environmental factors, we analyzed the eco-physiological drivers underlying the seasonal cambial activity and radial growth dynamics. The results of high reso-lution dendrometer method showed that the growth of G. floribunda began at the end of May (day of year, DOY: 149.3±7.2) and ended at the end of August (DOY: 241.0±14.7) in 2020, the annual total radial growth was 3.12 mm, and the maximum growth rate was 0.04 mm·d-1. Based on the microcoring methods, we found that xylem cell enlarging started from March 9th (69.2±6.2) and cell wall thickening ended on September 19th (DOY: 262.8±2.8). The cumulative xylem radial growth was 1.76 mm, and the maximum growth rate was 0.009 mm·d-1. The daily radial growth rate of G. floribunda was significantly and positively correlated with precipitation, relative humidity, daily minimum air temperature, soil moisture and temperature at the depth of 20 cm, and was negatively correlated with daily maximum air temperature, vapor pressure deficit, maximum wind speed, and water vapor pressure. The starch and soluble sugar contents in the sapwood of G. floribunda were relatively higher before the growing season. The starch content was lowest in the end of March, while the content of soluble sugars was lowest in middle of May. At the end of the growing season, the contents of starch and soluble sugar in G. floribunda peaked in the middle of October and the end of December, respectively.

Litter and microclimate controls on soil heterotrophic respiration after converting seasonal rainforests to rubber plantations in tropical China

Land-use changes can alter carbon cycling. Soil carbon loss resulting from the conversion of natural forests to rubber plantations (RP) may occur due to changes in litter inputs or in biotic and abiotic environmental conditions. In this study, we conducted a reciprocal soil and litter translocation mesocosm experiment for 15 months in a seasonal rainforest (SR) and RP to elucidate the effect of litter, soil and site conditions on heterotrophic respiration and its temperature sensitivity after land-use conversion. We found that rate of soil heterotrophic respiration (Rh) was higher at RP site than at SR site or for SR litter than RP litter with significant interactions between forest site and litter type, and did not differ between SR and RP soils. The Q10 values of Rh did not differ between forest sites, soils, or litter types but were substantially lower when litter was absent and substantially higher when RP soil was incubated in SR site and vice versa. Removal of surface litters led to a reduction of Rh by 27-45%. Soil labile organic C pool and microbial biomass were not influenced by litter type or forest site, but were influenced by soil origin, with higher values for SR soil than RP soil. Soil temperature and moisture were not influenced by litter type and soil but differed between forest sites with higher moisture at RP site than SR site. Our results suggested that changes in physical environmental conditions, rather than changes in litter input or soil biochemical properties, attributed to the elevated soil heterotrophic respiration in RP, resulting in soil carbon loss following the tropical land-use changes.

Higher water and nutrient use efficiencies in savanna than in rainforest lianas result in no difference in photosynthesis.

Differences in traits between lianas and trees in tropical forests have been studied extensively; however, few have compared the ecological strategies of lianas from different habitats. Here, we measured 25 leaf and stem traits concerning leaf anatomy, morphology, physiology and stem hydraulics for 17 liana species from a tropical seasonal rainforest and for 19 liana species from a valley savanna in south-west China. We found that savanna lianas had higher vessel density, wood density and lower hydraulically weighted vessel diameter and theoretical hydraulic conductivity than tropical seasonal rainforest lianas. Compared with tropical seasonal rainforest lianas, savanna lianas also showed higher leaf dry matter content, carbon isotope composition (δ13C), photosynthetic water use efficiency, ratio of nitrogen to phosphorus, photosynthetic phosphorus use efficiency and lower leaf size, stomatal conductance and nitrogen, phosphorus and potassium concentrations. Interestingly, no differences in light-saturated photosynthetic rate were found between savanna and tropical seasonal rainforest lianas either on mass or area basis. This is probably due to the higher water and nutrient use efficiencies of savanna lianas. A principal component analysis revealed that savanna and tropical seasonal rainforest lianas were significantly separated along the first axis, which was strongly associated with acquisitive or conservative resource use strategy. Leaf and stem functional traits were coordinated across lianas, but the coordination or trade-off was stronger in the savanna than in the tropical seasonal rainforest. In conclusion, a relatively conservative (slow) strategy concerning water and nutrient use may benefit the savanna lianas, while higher nutrient and water use efficiencies allow them to maintain similar photosynthesis as tropical seasonal rainforest species. Our results clearly showed divergences in functional traits between lianas from savanna and tropical seasonal rainforest, suggesting that enhanced water and nutrient use efficiencies might contribute to the distribution of lianas in savanna ecosystems.

Traits, strategies, and niches of liana species in a tropical seasonal rainforest

Plant functional traits and strategies hold the promise to explain species distribution, but few studies have linked multiple traits to multiple niche dimensions (i.e., light, water, and nutrients). Here, we analyzed for 29 liana species in a Chinese tropical seasonal rainforest how: (1) trait associations and trade-offs lead to different plant strategies; and (2) how these traits shape species’ niche dimensions. Eighteen functional traits related to light, water, and nutrient use were measured and species niche dimensions were quantified using species distribution in a 20-ha plot combined with data on canopy gaps, topographic water availability, and soil nutrients. We found a tissue toughness spectrum ranging from soft to hard tissues along which species also varied from acquisitive to conservative water use, and a resource acquisition spectrum ranging from low to high light capture and nutrient use. Intriguingly, each spectrum partly reflected the conservative–acquisitive paradigm, but at the same time, the tissue toughness and the resource acquisition spectrum were uncoupled. Resource niche dimensions were better predicted by individual traits than by multivariate plant strategies. This suggests that trait components that underlie multivariate strategy axes, rather than the plant strategies themselves determine species distributions. Different traits were important for different niche dimensions. In conclusion, plant functional traits and strategies can indeed explain species distributions, but not in a simple and straight forward way. Although the identification of global plant strategies has significantly advanced the field, this research shows that global, multivariate generalizations are difficult to translate to local conditions, as different components of these strategies are important under different local conditions.

Long-term variation characteristics of radiation in the tropical seasonal rainforest in Xishuangbanna, southwestern China

Long-term variation characteristics of radiation in the tropical seasonal rainforest in Xishuangbanna, southwestern China

Seed dormancy profiles for forest dynamics plot data: focusing on a tropical seasonal rainforest in Xishuangbanna, southwest China.

Long-term forest dynamics monitoring plots provide information on number of individual species in the plot, allowing us for the first time to construct seed dormancy profiles at the species and individual levels for a specific site. Focusing on the Xishuangbanna tropical season rainforest plot (XTRDP), we used data from nine forest dynamics plots (two for tropical, four for subtropical and three for temperate) and information on kind of seed dormancy to generate seed dormancy profiles for communities across tropical to temperate latitudes at the species and individual levels. Seed dormancy information was collected from previous publications, and some data were provided by two germplasm banks that test seed germination of wild plants in China. In XTRDP, 35% of the species and 58% of individuals have non-dormant seeds; the dominant species have non-dormant seeds. In all plots, the most common kind of dormancy among species and individuals with dormant seeds was physiological dormancy. At the species level, the profile for tropical, subtropical and temperate plots was similar to profiles for each of these vegetation regions. In all plots, except one subtropical plot, the percentage of species versus individuals with dormant seeds differed. All temperate plots had a higher percentage of individuals than species with dormant seeds, but this pattern was not consistent for tropical or subtropical plots. We show that dormancy increases with latitude at both the species and individual levels. Dormancy profiles at the individual tree level provide new insight into seed dormancy relationships within plant communities.

Identification of Varied Soil Hydraulic Properties in a Seasonal Tropical Rainforest

Identification of Varied Soil Hydraulic Properties in a Seasonal Tropical Rainforest

Soil nutrients, canopy gaps and topography affect liana distribution in a tropical seasonal rain forest in southwestern China

AbstractQuestionsLianas are a conspicuous element of tropical forests but have largely been ignored in species‐level vegetation surveys. As a result, there is limited understanding of how environmental factors structure liana communities.LocationA 20‐ha forest dynamics plot in Xishuangbanna National Nature Reserve, southwestern China.MethodsWe evaluated the distribution of the 50 most abundant liana species, comprising >18,000 individuals, in the 20‐ha forest plot. Ordination analysis and generalized linear mixed models were used to evaluate how species distribution and abundance are associated with soil pH, soil phosphorus (P), soil nitrogen (N), and soil potassium (K), canopy gaps and topography. We calculated the average weighted distribution as a proxy for the optimum resource condition for each species.ResultsThe first two axes of a canonical correspondence analysis explained 65% of the variation in liana species composition, with pH and P being the strongest drivers and highly correlated with each other. We modelled the responses of liana species to soil nutrients, and found a negative, unimodal or positive response of liana abundance with increasing soil nutrient concentrations. Forty‐six of the 50 species occurred under significantly higher or lower soil nutrient conditions than expected at random. Lianas mainly separated along the P gradient, whereas for N and K most liana species tended to occupy locations with high nutrient concentrations.ConclusionsAlthough lianas are thought to be notoriously light‐demanding, soil conditions were stronger drivers of liana species distribution than gaps. Species differences in distributions were mainly driven by soil gradients in pH and P, highlighting the importance of soil nutrient status for liana niche partitioning in wet tropical forests on highly weathered soils. Most liana species had high resource requirements for N, K and light, which come along with their fast growth and acquisitive resource use strategy. Hence, below‐ground resource availability plays an important role in shaping the assembly of liana communities.

Multivariate relationships between litter productivity and its drivers in a tropical karst seasonal rainforest

Litter is a vital component of ecosystem functionality, which is inherently linked to net primary productivity and global biogeochemical cycles. To better understand the drivers that modify net primary productivity, we need to disentangle the processes that underly changes in the generation of litter. We employed structural equation models (SEMs) to test for the direct and indirect effects of biodiversity, the stand structural attributes, and abiotic drivers on annual litter production in a tropical karst seasonal rainforest. For this study, annual litter production was evaluated over a five-year period in 90 permanent sample litter traps in a dynamic 15-ha long-term forest plot in Southern China. For each circular plot stand (with central litter traps) we quantified biodiversity, structural variations, basal area, and growth rate, which are important for net primary productivity. The four best-fit SEMs with different metrics of biodiversity for the paths between biodiversity, structural attributes, abiotic drivers, and annual litter production had a similar goodness of fit to the data. They accounted for 42.7–47.8% of the variation in annual litter production, 4.7–16.8% of the variation in stand-level growth rate, 29.3% of the variation in stand-level basal area, 8.2–13.2% of the variation in stand structural variation, and 4.4–6.5% of the variation in biodiversity. Although biodiversity had a positive effect on annual litter production through direct or indirect effects via the stand-level growth rate, abiotic drivers had the strongest impacts on annual litter production. We also found that the structural attributes of the stands had positive effects on the annual litter production; however, only the stand-level growth rate had significant consistently positive effects on annual litter production in the four best-fit SEMs. These results implied that annual litter production is most strongly driven by abiotic factors, followed by stand structural attributes and biodiversity. Theoretically, our study supports that niche differentiation and facilitation might enhance productivity; however, this enhanced capacity is primarily contingent on how abiotic variations are controlled in the sampling of natural karst forest systems. Biodiversity and the conservation of specific habitats should therefore be a key component in the management of forest resources, forest conservation, and sustainability.

Conspecific and heterospecific crowding facilitate tree survival in a tropical karst seasonal rainforest

Tree mortality plays a vital role in forest dynamics and contributes to species coexistence and community assembly. However, the mechanisms that control tree mortality are poorly understood, particularly in species-rich tropical forests. Size-dependent abiotic constraints and biotic interactions act simultaneously to cause tree mortality in natural forests. However, these drivers are often studied independently, which can limit our understanding of how they interact to affect tree mortality in natural forests. We employed a hierarchical Bayesian logistic regression modeling approach to quantify the simultaneous effects of tree size, topography, neighborhoods, and their interactions on tree mortality in a 15-ha fully mapped tropical karst seasonal rainforest in Southern China. Of the variables tested, tree size exhibited the most consistent and strongest negative effect on tree mortality, while topography and neighborhood competition were of secondary importance. Neighbors, particularly heterospecific neighbors, had a facilitative effect on lowering mortality, while only several species showed conspecific negative density dependent on mortality. The topographical wetness index had a significant positive effect on tree mortality. Size-dependent and neighborhood competition-induced tree mortality was stronger for shade-intolerant than for shade-tolerant species, and the size-dependent mortality was the strongest for shrub species among the three growth forms. Our results indicated that the size-dependent effect was the dominant cause of tree mortality; however, neighbors, particularly heterospecific neighbors, had a facilitative effect on lowering tree mortality. Furthermore, the relative importance of these mechanisms for tree mortality differed within life-history strategies guilds. Our study highlighted the value of simultaneously considering the individual and interactive effects of multiple mechanisms toward understanding the dynamics and coexistence of highly diverse metacommunities in harsh environments.

Size dependent associations between tree diameter growth rates and functional traits in an Asian tropical seasonal rainforest.

Many studies focus on the relationships between plant functional traits and tree growth performances. However, little is known about the ontogenetic shifts of the relationships between functional traits and tree growth. This study examined associations between stem and leaf functional traits and growth rates and their ontogenetic shifts across 20 tropical tree species in a tropical seasonal rainforest in Xishuangbanna, south-west China. For each species, physiological active branches of individual trees belonged to three size classes (i.e. small, diameter at breast height (DBH) 5-10 cm; middle, DBH 10-20 cm; big, DBH >20 cm) were sampled respectively. We measured 18 morphological and structural traits, which characterised plant hydraulic properties or leaf economic spectrum. Associations between diameter growth rates and functional traits were analysed across three size classes. Our results revealed that diameter growth rates of big-sized trees were mainly related to traits related to plant hydraulic efficiency (i.e. theoretical hydraulic conductivity (Ktheo) and leaf vein density (Dvein)), which suggests that the growth of large trees is limited mainly by their xylem water transport capacity. For middle-sized trees, growth rates were significantly related to traits representing leaf economic spectrum (i.e. specific leaf area (SLA), individual leaf mass (ILM), palisade thickness (PT) and spongy thickness (SP)). Diameter growth rates of small-sized trees were not correlated with hydraulic or leaf economic traits. Thus, the associations between tree growth rates and functional traits are size dependent. Our results suggest ontogenetic shift of functional traits which could potential contribute to different growth response to climate change.

Detecting Growth Phase Shifts Based on Leaf Trait Variation of a Canopy Dipterocarp Tree Species (Parashorea chinensis)

Canopy species need to shift their adaptive strategy to acclimate to very different light environments as they grow from seedlings in the understory to adult trees in the canopy. However, research on how to quantitively detect ecological strategy shifts in plant ontogeny is scarce. In this study, we hypothesize that changes in light and tree height levels induce transitions in ecological strategies, and growth phases representing different adaptive strategies can be classified by leaf trait variation. We examined variations in leaf morphological and physiological traits across a vertical ambient light (represented by the transmittance of diffuse light, %TRANS) and tree height gradient in Parashorea chinensis, a large canopy tree species in tropical seasonal rainforest in Southwestern China. Multivariate regression trees (MRTs) were used to detect the split points in light and height gradients and classify ontogenetic phases. Linear piecewise regression and quadratic regression were used to detect the transition point in leaf trait responses to environmental variation and explain the shifts in growth phases and adaptive strategies. Five growth phases of P. chinensis were identified based on MRT results: (i) the vulnerable phase, with tree height at less than 8.3 m; (ii) the suppressed phase, with tree height between 8.3 and 14.9 m; (iii) the growth release phase, with tree height between 14.9 and 24.3 m; (iv) the canopy phase, with tree height between 24.3 and 60.9 m; and (v) the emergent phase, with tree height above 60.9 m. The suppressed phase and canopy phase represent “stress-tolerant” and “competitive” strategies, respectively. Light conditions drive the shift from the “stress-tolerant” to the “competitive” strategy. These findings help us to better understand the regeneration mechanisms of canopy species in forests.

Species composition and community classification of the 20-ha tropical seasonal rainforest dynamics monitoring plot in the Naban River, Yunnan

Species composition and community classification of the 20-ha tropical seasonal rainforest dynamics monitoring plot in the Naban River, Yunnan

Precipitation influences on the net primary productivity of a tropical seasonal rainforest in Southwest China: A 9-year case study

The net primary productivity (NPP) of tropical forests is a key part of the global carbon cycle. Numerous studies have estimated tropical forest NPP, yet most of them focus on how annual NPP dynamics vary over several years. Little is known about how NPP responds to long-term climatic variation at the monthly or seasonal scales. We estimated NPP at three-month intervals from 2009 to 2017 for a tropical seasonal rainforest in Xishuangbanna, Southwest China using data from >2000 dendrometer bands and litter fall traps within a 20-ha permanent forest dynamics plot. We asked which climatic factor has the greatest effect on forest NPP at the sub annual scale, and how the relationships vary with seasonality. Calculations showed that NPP ranged from 12 to 20 t ha−1 yr−1, and that forest productivity showed a slight, but insignificant increase from 2009 to 2017. NPP was significantly higher in the wet season than that in the dry season and was significantly related to precipitation only when all data were concerned. During the dry season, precipitation had a significant positive influence on NPP, but no effect during the wet season. We further identified that there was a threshold effect of precipitation on NPP. Specifically, productivity increased more rapidly when monthly precipitation below 229 mm. In summary, we conclude that periods of low rainfall strongly regulate the productivity in this tropical seasonal rainforest which could guide the management design of water use efficiency in tree based land-use system, like agroforestry ecosystems.

Linking ectomycorrhizal mushroom species richness and composition with dominant trees in a tropical seasonal rainforest

Linking ectomycorrhizal mushroom species richness and composition with dominant trees in a tropical seasonal rainforest

Partial mutual exclusion of ectomycorrhizal and saprobic fungi in a tropical seasonal rainforest

Partial mutual exclusion of ectomycorrhizal and saprobic fungi in a tropical seasonal rainforest