Effect Of Size Inequality On Above-ground Biomass And Species Diversity Of Plant Communities

Size inequality is ubiquitous in plant populations, mainly due to various biological factors and ecological factors’differences. A large number of studies show that individual size inequality had certain influence on their own and adjacent individuals forest regeneration and growth. The individual size not only affected the growth of diameter at breast height and height of the adjacent plants, but also was related to the species diversity. Studying its influence on community productivity and species diversity was significant for natural secondary forest management. Improving the ecosystem service value of forests was one of the most important aims of forest management.We selected 7 plots, which were located in typical subtropical secondary forest communities in the Lishui Forest Farm, Jiangsu Province. We studied the relationship between the coefficient of variation (CV) of height, diameter at breast height (DBH) variation coefficient, above-ground biomass and species diversity index (Shannon-Wiener index). Then we used the FORET model to simulate forest dynamics of these communities under the natural state and artificial management. By comparing the changes before and after the implementation of management measures in total biomass of the stand, the stand leaf area and species importance value, we evaluated the effects of different forest management measures. The results showed that,1. There were horizontal differentiations in biomass among several plots. The spatial distribution of biomass was different in different communities. The biomass of deciduous broad-leaved forest was relatively small and the distribution was more uniform, while the biomass of coniferous broad-leaved forest was relatively large.2. In the broad-leaved mixed forest (with a low canopy cover) dominated by Pinus massoniana, community biomass was positively correlated with individual size inequality, while a negative correlation was found in the deciduous broad-leaved forest and in the broad-leaved mixed forest dominated by Cunninghamia lanceolata (with a higher canopy cover). There was a downward trend in the promoting effect of size inequality on community biomass overall increased competition intensity. It may due to excessive competition would led to smaller individual deaths, and then community biomass accumulation rate would decrease. But in higher canopy cover forest community, the individual size relatively consistent was benefit to community productivity.3. Species diversity was positively correlated with size inequality, but the relationship was related to the canopy density. Such as the deciduous broad-leaved forest and the broad-leaved mixed forest dominated by Cunninghamia lanceolata (with a higher canopy cover), the correlation between species diversity index and size inequality was higher. While in the broad-leaved mixed forest dominated by Pinus massoniana, whose canopy cover was lower, the significant level of correlation was also lower.4. For the Quercus acutissima—Quercus variabilis community, there was no obvious difference in the changes of the forest community composition and the structure between under tending measures and in natural development. This suggested that such community, which was close to the zonal vegetation, didn’t need any intense artificial management. While for the Quercus acutissima—Pinus massoniana community, Ilex chinensis—Pinus massoniana community and Cunninghamia lanceolata—Vernicia fordii community, which were at relatively early succession stages, comprehensive measures should be taken, including intermediate cutting, replanting, tree pruning and etc. Implementing these different measures at the same time can speed up the community succession, and promote the accumulation of stand biomass and leaf areas.In summary, individual size inequality was beneficial to increasing species diversity, and had a positive effect on aboveground biomass of low cover communities. The results also suggested that the forest gap model had a potential application value in the decision-making of forest management, and it may be a useful tool for quantitative assessment of forest management effect. The result indicated the effect of size inequality on above-ground biomass and species diversity of plant communities, could provide a reference for natural secondary forest ecological tending.