Xinzeng Wei

Contrasting relationships between species diversity and genetic diversity in natural and disturbed forest tree communities

• This study aimed to reveal species-genetic diversity correlations (SGDCs) and their underlying mechanisms in natural and disturbed forests. • A community survey and molecular analyses were carried out to compare species diversity (SD), the genetic diversity of the dominant tree species Euptelea pleiospermum (GD), the altitudinal patterns of SD and GD, SGDC, genetic differentiation (F(ST) ), community divergence (F(ST) -C), effective population size (N(e) ), and recent migration rate between mountain riparian forests along the Yandu (natural) and Nan (disturbed) rivers. • In natural forests, both SD and GD showed a unimodal altitudinal pattern and GD was positively correlated with SD, whereas a unimodal pattern and positive SGDC were not found in the disturbed forests. SD and F(ST) at the natural sites were higher than those at the disturbed sites. However, there were no significant differences in GD, F(ST) -C, N(e) or recent migration rate between the natural and disturbed sites. • A correlation between the patterns of SD and GD along a geographical gradient (e.g. altitude) is an important driver of positive SGDC. The absence of positive SGDC in the disturbed forests may result from reduced SD but unaffected GD, indicating nonparallel changes in SD and GD. This study furthermore cautions against generalizations about changes in SD and GD following disturbance.

Landscape Genetic Structure of a Streamside Tree Species Euptelea pleiospermum (Eupteleaceae): Contrasting Roles of River Valley and Mountain Ridge

We used landscape genetics and statistical models to test how landscape features influence connectivity or create barriers to dispersal for a mountain riparian tree species, Euptelea pleiospermum. Young leaves from 1078 individuals belonging to 36 populations at elevations of 900–2000 m along upper reaches of four rivers were genotyped using eight nuclear microsatellite markers. We found no evidence for the unidirectional dispersal hypothesis in E. pleiospermum within each river. The linear dispersal pattern along each river valley is mostly consistent with the “classical metapopulaton” model. Mountain ridges separating rivers were genetic barriers for this wind-pollinated tree species with anemochorous seeds, whereas river valleys provided important corridors for dispersal. Gene flow among populations along elevational gradients within each river prevails over gene flow among populations at similar elevations but from different rivers. This pattern of gene flow is likely to promote elevational range shifts of plant populations and to hinder local adaptation along elevational gradients. This study provides a paradigm to determine which of the two strategies (migration or adaptation) will be adopted by mountain riparian plants under climate warming.

Community Composition and Structure of Badagongshan (BDGS) Forest Dynamic Plot in a Mid-subtropical Mountain Evergreen and Deciduous Broad-leaved Mixed Forest, Central China

Mountain evergreen and deciduous broadleaved mixed forests in China are mainly distributed in the mid-subtropical mid-mountain zones.Mount Badagongshan(BDGS) is located on the northern end of the Wuling Mountains at the north rim of the mid-subtropical zone,and has a typical mountain evergreen and deciduous broadleaved mixed forest.To investigate dynamics of this forest,biodiversity origin and maintenance mechanisms in East Sichuan and West Hubei in 2010-2011,the Wuhan Botanical Garden,Chinese Academy of Sciences established one 25 hm2(500 m× 500 m) forest dynamic plot of subtropical mountain evergreen and deciduous broadleaved mixed forest in the Badagongshan(BDGS) National Nature Reserve according to the standards of the Center for Tropical Forest Science(CTFS).Here,we present the flora,community composition,structure,size class and spatial distribution based data collected from all woody(bamboo and liana not included) plants with DBH≥1 cm.Our results demonstrated that BDGS was a typical mountain evergreen and deciduous broadleaved mixed forest,dominated by pantropic distribution families(24.50%) and northern temperate distribution genera(24.56%).There were nine rare and endangered wood plants.We classified 186556 individuals into 53 families,114 genera and 238 species(94 evergreen and 144 deciduous).Dominant species were from the families of Fagaceae,Ericaceae,Lauraceae and Theaceae.There were 38 species with 1000 individuals(63.16% evergreen).In total,103 rare species( 25 individuals) accounted for 43.28% of all the woody plants.The forest strata was divided into a canopy layer dominated by Cyclobalanopsis multinervis and Fagus lucida,an understory layer dominated by Rhododendron stamineum and Litsea elongata,and a shrub layer dominated by Eurya brevistyla and Symplocos anomala.Abundant(1000 individuals) and rare species were mainly from the shrub layer.Limited by growth form,the plot had a fairly small mean DBH(5.41 cm) and was dominated by small sized individuals(68.40%).The size class of five dominant trees was reverse J.

Limited genetic impacts of habitat fragmentation in an “old rare” relict tree, Euptelea pleiospermum (Eupteleaceae)

Euptelea pleiospermum is an “old rare” tree species distributed along the high-elevation streamsides in Burma, China, and India. Deforestation and construction of roads for timber transport have highly fragmented the natural habitats of this species in the Shennongjia Forestry District. In this study, we used this fragmentation to test the hypothesis that “old rare” tree species are insusceptible to the genetic consequences of habitat fragmentation. Using eight microsatellite loci, we estimated allelic richness (AR), observed heterozygosity (HO), expected heterozygosity (HE), Wright’s inbreeding coefficient (FIS), and genetic differentiation (FST and DEST) between pre- and post-fragmentation cohorts. We found no significant differences in either genetic diversity or genetic differentiation between the two cohorts. The limited genetic effects of fragmentation may result from too few fragmented generations, because the time between the start of fragmentation (year 1970) and our study (year 2008) was less than one generation of this tree species. It should be mentioned that clonal reproduction by sprouting, a common phenomenon in many “old rare” tree species, can help E. pleiospermum buffer the genetic impacts of fragmentation by delaying the time between generations. Therefore, we conclude that this “old rare” tree species show limited genetic impacts from recent habitat fragmentation. However, the elimination of rare alleles and increase of inbreeding coefficient in the post-fragmentation cohort are early warnings of deleterious genetic consequences of fragmentation. Our results provide valuable information to formulate conservation and restoration guidelines for E. pleiospermum.

Gene flow and genetic structure of a mountain riparian tree species, Euptelea pleiospermum (Eupteleaceae): how important is the stream dendritic network?

Riparian landscapes are dendritic in nature. However, much attention on genetic structure of riparian plants has been paid to linear models of connectivity while studies that investigate the influence of dendritic landscape are scarce. In this study, we used nuclear microsatellite markers to investigate genetic diversity, gene flow, and genetic structure of a streamside tree species (Euptelea pleiospermum) in a natural stream dendritic network in the Shennongjia Mountains, central China. We tested the following hypotheses: (1) genetic diversity is higher at confluence than that at headwater populations and (2) genetic structure within the stream dendritic network was determined by in-stream dispersal or out-of-stream dispersal. Contrary to our prediction, we found that both genetic diversity and effective population size are congruent at headwater and confluence populations. We found symmetrical gene flow in most (four out of six) headwater–confluence pairs and asymmetrically downstream gene flow in the other two headwater–confluence pairs. Analysis of molecular variance (AMOVA) detected significant differentiation at two scales (among streams within catchments, among populations within stream) and did not reveal significant structure among catchments. STRUCTURE analysis clustered individuals from different catchments into the same genetically homogeneous group. There was no significant isolation by distance (IBD) with Euclidean, stream, or overland distance. Our results suggest that E. pleiospermum populations within the stream dendritic network did not present a hierarchical genetic structure probably because of extensive out-of-stream dispersal.

A dendroclimatic investigation of radial growth–climate relationships for the riparian species Cercidiphyllum japonicum in the Shennongjia area, central China

Cercidiphyllum japonicum is a rare endemic species of East Asia flora and a common component in riparian forests. Dendrochronological techniques were employed to trace radial growth of C. japonicum in the Shennongjia area of central China and examine its relationships with local climate. Effects of precipitation on width of C. japonicum annual rings were negligible except for some temporary negative impacts in prior winter. The variables most strongly controlling radial growth were temperatures in the previous December and during the current summer. Relationships for most pairs of ring-width and monthly/seasonal climate variables were temporally unstable but occasionally significant. Radial growth–climate relationships for C. japonicum were likely shaped by riparian site characteristics, root habits, and regional climatic regimes.