| Plant functional traits are the features(morphological, physiological, phenological) that represent ecological strategies and determine how plants respond to environmental factors,affect other trophic levels and influence ecosystem properties.The functional structure of a community is defined as the distribution of species and their abundances in the functional space. Functional community structure analysis based on functional traits has been proven to be a new research field in modern community ecology that connects the basic characteristics of vegetation and the regional ecosystem services. The subtropical evergreen broad-leaved forest is the most representative zonal vegetation type in the subtropical region of China.It has the most complex structure and highest biodiversity in the subtropical region of China. The subtropical evergreen broad-leaved forest plays a very important role in maintaining regional ecological environment and global carbon balance. With the increasing of altitude and the decreasing of temperature, the subtropical evergreen broad-leaved forest is gradually replaced by the subtropical evergreen-deciduous broadleaved mixed forest. Few information exists on the stand features and ecosystem services of this forest type, meanwhile, the study of its functional community structure and dynamics has never been carried out. In this thesis, on basis of our established permanent forest dynamics plots of the subtropical evergreen-deciduous mixed broadleaved forest in southwest Hubei Province, the stand structural and diversity features were systematically analyzed. Recovery series in stands of different stages(20-year-old second growth, 35-year-old second growth and old growth) was constructed in the Mulinzi National Nature Reserve. Major plant functional traits were sampled and measured, and the functional community structures and their dynamics were explored.Community level functional trait and functional diversity were used to quantitatively analyze the functional community structures and their recovery dynamics. The key environmental factors in controlling functional community structure and dynamics were determined. The mainfindings of this study will provide a scientific basis for regional forest vegetation conservation and the restoration of ecosystem services. The main results are as follows:(1) On basis of field investigation, community types were classified by using two-way indicator species analysis(TWINSPAN) and detrended correspondence analysis(DCA). The results showed that the subtropical evergreen-deciduous broadleaved mixed forest in the southwest of Hubei could be classified into 5 community types. The relationship between environmental factors and species distribution was examined by permutation-based multiple regression on distance matrices(MRM). The elevation, aspect, soil total nitrogen content, soil total phosphorus content, soil available nitrogen content and soil available phosphorus content were the major factors affecting evergreen and deciduous species distribution across the five community types. Anthropoginic disturbances also affected the change of the community types.The distribution of deciduous species in the subtropical evergreen-deciduous broadleaved mixed forest in our study area was mainly caused by the low temperature stress with the increasing of elevation.(2) The species richness, abundance and basal area of evergreen and deciduous species in each community type were different. Disturbance could increase the proportion of deciduous species in the community, while evergreen species were more related to soil nutrients. The species richness, abundance and basal area of evergreen species in most community types were higher than those of the deciduous species in the small size classes(1 cm ≤DBH< 5 cm).Meanwhile, the species richness, abundance and basal area of deciduous species in majority of the community types were higher than those of the evergreen species in large size classes(DBH≥ 10 cm).(3) We established 42 forest dynamics plots in satnds of three recovery stages(20-year-old second growth, 35-year-old second growth and old growth,14 plots in each of the recovery stage respectively) and explored the changes in evergreen and deciduous species diversity and the abiotic factors after clear-cutting in the subtropical evergreen-deciduous broadleaved mixed forest in southwest Hubei of central China. The results showed that total species richness and species diversity were highest at the intermediate recovery stage. The species richness, speciesdiversity and stem abundance of evergreen species increased, while total and deciduous species stem abundance decreased with forest recovery. The basal area of both total and evergreen species increased, while that of the deciduous species showed a unimodal pattern. The abiotic conditions varied with the recovery process, generally, soil water content(SWC) and all the soil nutrients(soil organic matter(SOM), total nitrogen(TN), total phosphorus(TP), available nitrogen(AN), available phosphorus(AP) and available potassium(AK)) initially decreased and then increased with recovery. The canopy openness(CO) decreased with recovery and was lowest in old growth forests. Soil pH value did not show any significant change during the recovery. Changes in species compositions were generally correlated with different environmental factors. Soil pH, TP and CO were the significant factors affecting species composition in 20-year-old second growth. Evergreen species in 20-year-old second growth were only significantly affected by soil pH, while deciduous species were affected by soil pH and CO. Soil AK, TP, and CO were the factors significantly affecting species composition in35-year-old second growth. Distributions of the evergreen and deciduous species in 35-year-old second growth were significantly correlated with soil AK. The distributions of all species and evergreen species in old growth were significantly affected by soil pH, AN, and TP. Deciduous species distribution was also affected by soil AK.(4) We examined the changes of functional community structure along the recovery chronosequence following clear cutting in the subtropical evergreen-deciduous broadleaved mixed forest in southwest Hubei of of central China. 5 functional traits for the 151 woody plants in the chronosequence were measured. With the progress of natural recovery, three patterns emerged in the changes of community level plant functional traits, i.e. unimodal convex(specific leaf area(SLA)), gradual increasing(stem tissue mass density(STD), leaf thickness(LT)) and gradual decreasing(leaf nitrogen concentration per mass(LNC), leaf phosphorus concentration per mass(LPC)). The assemblages with high CWM_ SLA CWM_LNC and CWM_ LPC but low CWM_ LT and CWM_ STD in early recovery stages were progressively replaced by those with low CWM_ SLA, CWM_ LNC and CWM_ LPC but high CWM_ LT CWM_ STD. Evergreen and deciduous species were significantly different in allthe mean values of the 5 measured functional traits in each stage of recovery. The major abiotic factors significantly associated with the functional community structure of different recovery stages were: CO and soil phosphorus in the 20-year-old second growth and 35 year second growth, and CO, TN, AN, TP and AP in the old growth respectively. Our study suggested that with the progress of natural recovery, the functional composition of plant assemblages were in accordance with the changing abiotic conditions, furthermore, the subtropical evergreen-deciduous broadleaved mixed forest was shifting from a resource acquisitive to a resource conservative assemblage, in which evergreen species will become functionally more and more important than deciduous species.(5) We examined the changes of functional diversity along the recovery chronosequence.With the progress of natural recovery, functional richness, functional evenness and functional dispersion showed a unimodal pattern. Functional divergence increased with the process of recovery, but the difference was not significant between each recovery stage. Species richness and functional diversity showed a positive correlation. The major abiotic factors significantly associated with the functional diversity of different recovery stages were: CO, SOM and TN in the 20-year-old second growth, CO and TP in the 35-year-old second growth, and TP and AN in the old growth respectively.(6) The phylogenetic structure(NRI and NTI) decreased first and then increased along the recovery stage. Phylogenetic structure changed from clustering to overdispersion with the increasing of recovery time. Phylogenetic diversity showed a unimodal pattern with the recovery process. Phylogenetic diversity and phylogenetic structure in the early recovery stages were clustered,which reflected the great influence of abiotic filtering.However, phylogenetic diversity and phylogenetic structure of later recovery stages tened to be overdispersed,which reflected the increase of biotic interactions and decrease of abiotic filtering. |
