Studies On Plant Species Diversity And Productivity In Forests Planted For Ecosystem Restoration

Over the past several decades, people have witnessed that the natural ecosystems of the worlds have been increasingly degraded, which has attracted the intense attention from the government and academia. Thus, the restoration and reconstruction of these degraded ecosystems has been an emergent and hot topic in ecology. Biodiversity and ecosystem functioning are among the most important parameters in evaluating the restoration and reconstruction. The increase of the biodiversity and the improvement of ecosystem functioning due to the increasing of biodiversity have been the critical points which people concern. For a given ecosystem, biodiversity and ecosystem functioning are linked closely, and most scientists believe that the ecosystem functioning improves with the increase of the biodiversity at low intensity and saturates at high intensity due to complementarities and sampling effect. So far, the previous achievements have been conspicuous, but the research about the relationship between the biodiversity and ecosystem functioning in forests planted for ecosystem restoration (FPER) is rare. Using observational and investigative methods, we studied herbaceous, shrub, and tree species diversity and productivity, tree seedling diversity in different restoration stages, restoration types, and the management of Liupanshan FPER which had a long history of human disturbance. We also analyzed the effects of restoration time, type and management on the relationship between plant diversity and productivity. The results indicated that:1) After more than30years restorations, the biodiversity has been increased, the ecosystem functioning completed step-by-step, and the ecological environment significantly improved in Liupanshan National Natural Reserve FPER. There were higher plant diversity and productity in deciduous broadleaf forests and mixed forest. The herbaceous species diversity and productivity (y) declined with time(t), and described as a quadratic function. y=at2-bt+c; the shrub species diversity, productivity and tree species diversity ascended, also described as a quadratic function, y=-at2+bt+c:the tree productivity increased with time, and the productivity-time relationship could be best described as a linear function, y=at+b.2) In FPERs. with the amelioration of the light conditions, the increase of slope gradients, and the decrease of elevation, the plant species number increased. The studies also showed that both plant diversity and productivity benefited from higher soil Mg2+and pH. Plant diversity increased with shallow soil Na+, but plant productivity increased with shallow soil available phosphorus.3) There were different relationships between biodiversity and ecosystem functioning in different restored time FPER. In FPER less than20years, the relationships between herbaceous plant diversity (x) and productivity (y) were best described as an exponential growth function,y=axb; the ones for shrub plant diversity (x) and productivity (y) were best described as quadratic growth function. y=ax2-bx+c. In PFER between20-40years, the relationships between herbaceous and shrub plant diversity (x), productivity (y) were best described as an exponential growth function. y=axb; then in PFER more than40years, the relationships between tree, shrub and herbaceous plant diversity (x) and productivity (y) were best described as an exponential growth function, y=axb, by using the Curve Estimation. Moreover, the results showed that such effect of biodiversity on ecosystem functioning was decreasing with restoration times.4) The results from different forest restoration types revealed that the relationship between biodiversity and ecosystem functioning was best described as an exponential growth function, y=axb. in conifer and mixed forests, and the changes of plant diversity have more magnitude effect on ecosystem process in conifer forests than in mixed forests. Such relationships disappeared in the broadleaved forest.5) Tree-thinning affected the relationship between understory herb species diversity and productivity.'Both biodiversity and biomass of understory herb plants were higher in tree-thinned FPER than that in undisturbed FPER, and there was a negative correlation between richness and productivity in the thinning treated communities, whereas a positive correlation was found in undisturbed communities. Structural equation modeling (SEM) suggests that both the community composition and abiotic condition, directly or indirectly changed by tree-thinning, influenced the biodiversity-productivity relationship.6) Our studies also showed that tree seedling density, seedling diversity and Shannon-Wiener richness index were highest in broadleaved forest, and then in P. labulaeformis forest, P. armandii forest, and lowest in L. Principis-rupprechtii forest. The results from investigated tree species seedlings showed that the more popular species were Quercus wuiaishanica, Acer letramerum var. Betulifolium, Tilia paucicostata, Populus davidiana, Betula albo-sinensis, and B. platyphylla; the fewer species were Pinus tabulaeformis, and P. armandii, and there was no L. Principis-rupprechtii seedlings found in every type restoration forest indicating this species failed to regenerated itself in Liupanshan region. The broadleaved seedling density and growth status were better in sunny slope than in shady slope; however, the conifer seedlings were more likely discovered in shady regions.7) In broadleaved forests, tree species seedling density and diversity index were decreasing with time. However, in conifer restoration forests, tree species seedling density, species richness, and Shannon-Wiener index were peaked at the intermediate basal type forests (30～35m2/ha), and then decreased with increasing of the basal area of the predominant species.