Hong-Lin Cao

Scale‐dependent relationships between tree species richness and ecosystem function in forests

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.

Forest dynamics of a subtropical monsoon forest in Dinghushan, China: recruitment, mortality and the pace of community change

Structure and demographics in many tropical forests is changing, but the causes of these changes remain unclear. We studied 5 y (2005-2010) of species turnover, recruitment, mortality and population change data from a 20-hasubtropicalforestplotinDinghushan,China,toidentifytrendsinforestchange,andtotestwhethertreemortality is associated with intraspecific or interspecific competition. We found the Dinghushan forest to be more dynamic than one temperate and two tropical forests in a comparison of large, long-term forest dynamics plots. Within Dinghushan, size-classdistributionswerebell-shapedonlyforthethreemostdominantspeciesandreverseJ-shapedforotherspecies. Bell-shaped population distributions can indicate a population in decline, but our data suggest that these large and long-lived species are not in decline because the pattern is driven by increasing probabilities of transition to larger size class with increasing size and fast growth in saplings. Spatially aggregated tree species distributions were common for surviving and dead individuals. Competitive associations were more frequently intraspecific than interspecific. The competition that induced tree mortality was more associated with intraspecific than interspecific interactions. Intraspecific competitive exclusion and density-dependence appear to play important roles in tree mortality in this subtropical forest.

Unimodal Tree Size Distributions Possibly Result from Relatively Strong Conservatism in Intermediate Size Classes

Tree size distributions have long been of interest to ecologists and foresters because they reflect fundamental demographic processes. Previous studies have assumed that size distributions are often associated with population trends or with the degree of shade tolerance. We tested these associations for 31 tree species in a 20 ha plot in a Dinghushan south subtropical forest in China. These species varied widely in growth form and shade-tolerance. We used 2005 and 2010 census data from that plot. We found that 23 species had reversed J shaped size distributions, and eight species had unimodal size distributions in 2005. On average, modal species had lower recruitment rates than reversed J species, while showing no significant difference in mortality rates, per capita population growth rates or shade-tolerance. We compared the observed size distributions with the equilibrium distributions projected from observed size-dependent growth and mortality. We found that observed distributions generally had the same shape as predicted equilibrium distributions in both unimodal and reversed J species, but there were statistically significant, important quantitative differences between observed and projected equilibrium size distributions in most species, suggesting that these populations are not at equilibrium and that this forest is changing over time. Almost all modal species had U-shaped size-dependent mortality and/or growth functions, with turning points of both mortality and growth at intermediate size classes close to the peak in the size distribution. These results show that modal size distributions do not necessarily indicate either population decline or shade-intolerance. Instead, the modal species in our study were characterized by a life history strategy of relatively strong conservatism in an intermediate size class, leading to very low growth and mortality in that size class, and thus to a peak in the size distribution at intermediate sizes.

Spatial Patterns and Interspecific Associations of Three Canopy Species at Different Life Stages in a Subtropical Forest, China

Spatial patterns of species at different life stages are an important aspect for understanding causal mechanisms that facilitate species co-existence. Using Ripleys univariate L(t) and bivariate L(12)(t) functions, we analyzed the spatial patterns and interspecific associations of three canopy species at different life history stages in a 20-ha subtropical forest plot in Dinghushan Nature Reserve. Based on diameter at breast height (DBH), four life stages were distinguished. Castanopsis chinensis and Schima superba showed a unimodal DBH distribution. Engelhardtia roxburghiana showed a bimodal curve. L(t) function analysis showed significantly aggregated distributions of all three species at later life stages and random distribution at early life stages at some scales. From the analysis of L(12)(t) function, the results showed the positive association was a dominant pattern for most species pairs at most scales but the intensity of association decreases with the increase of life stages. Juveniles of the three species had no negative intra- and interspecific associations with the older life stages. Only premature trees were suppressed by overmature trees at some scales. Considering these results, we found three canopy-dominant species that lacked regeneration. There was no direct competition occurring between understorey individuals. Young trees can grow well under conspecific species with two other species. Longevity and lack of regeneration led to a large number of trees stored in mature and overmature stages, therefore, intra- and inter-competition can be strong at later life stages.

Identification and characterization of EST-SSRs and cpSSRs in endangered Cycas hainanensis

We report on the identification and characterization of six EST-linked simple sequence repeats (EST-SSRs) and chloroplast SSRs (cpSSRs) in endangered Cycas hainanensis. The number of alleles ranged from two to eight for EST-SSRs, two to three for cpSSRs. Observed and expected heterozygosities ranged from 0.042 to 0.417 and 0.042 to 0.811 for EST-SSRs, respectively. Expected heterozygosities ranged from 0.156 to 0.457 for cpSSRs. All these markers gave successful cross-species amplification in C. fairylakea. These markers will allow analyses of the baseline genetic variability and population structure of C. hainanensis to provide strategies for effective conservation and management.

Pollen and seed flow under different predominant winds in wind-pollinated and wind-dispersed species Engelhardia roxburghiana

In most plants, the contributions of pollen and seed flow to their genetic structures are generally difficult to disentangle. For typical wind-pollinated and wind-dispersed species Engelhardia roxburghiana in a 20-ha natural forest plot in lower subtropic China, because the prevailing wind directions change during its pollen release and seed dispersal seasons, we could compare its genetic structures in different directions, which could result primarily from pollen or seed flow. Furthermore, because the plot has undergone from an open to a closed canopy stage historically, we also examined forest canopy effects on gene flow in different generations and different directions. Using 522 E. roxburghiana individuals mapped in the plot, our results revealed that greater pollen flow led to biased gene flow in the pollen dispersal-predominant direction (pollen direction), while greater seed flow generated less spatial genetic structure in the seed dispersal-predominant direction (seed direction). The results predicted from generalized additive models indicated that canopy closure enhanced resistance to gene flow from the old generation to the new generation. Analyses by landscape genetic models for the new generation revealed that gene flow associated with pollen direction was more strongly affected by canopy than with seed direction. Our study is new by proposing an alternative way to separate effects of the pollen and seed flow on spatial variation patterns in E. roxburghiana. To our knowledge, our study is also the first attempt to use landscape genetic models to represent canopy effects for different dispersal vectors in spatial scales only up to a few hundred meters.

Genetic variation of Ardisia crenata in south China revealed by nuclear microsatellite.

Abstract  Ardisia crenata Sims, one of the most widely distributed Ardisia in the world, is an important ornamental and medicinal plant species. Using seven polymorphic nuclear microsatellite loci, we studied the genetic variation of 20 natural populations of A. crenata across its distribution center in south China. Significant deviation from the Hardy–Weinberg equilibrium in all populations and at all loci were detected, and the fixation index was high (FIS= 0.725), indicating that inbreeding may be dominant in the mixed mating system of this self‐compatible species. The average genetic diversity within populations was relatively low (HS= 0.321). There was significant genetic differentiation among populations (FST= 0.583), which may have resulted from a high level of inbreeding and a low level of gene flow. Ardisia crenata in south China can be roughly divided into an eastern group and a western group, consistent with the floristic division of the Sino‐Himalayan forest subkingdom and the Sino‐Japanese forest subkingdom. There may be separated glacial refugia in each region.

Development and characterization of microsatellite markers for the invasive weed Mikania micrantha (Asteraceae)

Mikania micrantha is a successful invasive weed in many parts of the world. Twelve polymorphic microsatellite loci were isolated and characterized from an AC‐enriched genomic library of this species. Twenty‐eight individuals from one population in Dongguan were tested for polymorphism. The average allele number of these microsatellites was three per locus, ranging from two to five. The expected and observed heterozygosities ranged from 0.275 to 0.742, and from 0.250 to 1.000, respectively. These microsatellite markers can be applied to study the population genetics in the native and invasive ranges of this species, and to trace its invasion history.

Isolation and characterization of 36 polymorphic microsatellite markers in Schima superba (Theaceae).

PREMISE OF THE STUDY Our objective was to develop microsatellite markers to investigate the level of genetic diversity within and among populations in a dominant evergreen broad-leaved tree, Schima superba, in southern China. METHODS AND RESULTS Thirty-six microsatellite markers were developed and showed polymorphism in three populations. The number of alleles per locus ranged from six to 34, with an average of 19. The observed and expected heterozygosities ranged from 0.242 to 1.000 and from 0.504 to 0.945, respectively. CONCLUSIONS The developed microsatellites will be useful for studying genetic diversity and population structure in S. superba.

Tree aboveground carbon storage correlates with environmental gradients and functional diversity in a tropical forest

Tropical forests play a disproportionately important role in the global carbon (C) cycle, but it remains unclear how local environments and functional diversity regulate tree aboveground C storage. We examined how three components (environments, functional dominance and diversity) affected C storage in Dinghushan 20-ha plot in China. There was large fine-scale variation in C storage. The three components significantly contributed to regulate C storage, but dominance and diversity of traits were associated with C storage in different directions. Structural equation models (SEMs) of dominance and diversity explained 34% and 32% of variation in C storage. Environments explained 26–44% of variation in dominance and diversity. Similar proportions of variation in C storage were explained by dominance and diversity in regression models, they were improved after adding environments. Diversity of maximum diameter was the best predictor of C storage. Complementarity and selection effects contributed to C storage simultaneously, and had similar importance. The SEMs disengaged the complex relationships among the three components and C storage, and established a framework to show the direct and indirect effects (via dominance and diversity) of local environments on C storage. We concluded that local environments are important for regulating functional diversity and C storage.