Population Ecology Of Alchornea Davidii In Karst Areas Of Chongqing

The rocky desertification is a big ecological problem in karsts areas, southwest China. With obvious habitat heterogeneity and heavy human disturbance, vegetation degradation occurs seriously in karst areas. Interference and water resource constraints are the two major problems which impeding the vegetation restoration in karst regions. In these harsh environments, there are many drought hypercalcium-tolerant and higher sprouting capacity plant species which formed special calcicolous vegetation.The special plant species and vegetation have important ecological values for the controlling of rocky desertification and vegetation restoration in karst areas.Alchornea davidii is an adaptive species and benefit to water and soil conservation in karst areas. The present studies selected A. davidii as the study material to explore the main environmental factors by the principal component analysis and analyzed the correlation between environmental factors and population characteristics to find the main environmental factors affecting the population. Then, we elucidated the effects of human disturbance on A. davidii species through the selection of populations under different disturbance intensities and analysis the difference of population statistics. Finally, we explored the effects of water changing in the Karst habitat on the phenology, growth morphology and reproduction of the suitable species by setting the field sample plots under different water treatments. The main results were as follows:1. The principal component analysis of environmental factors showed that human disturbance, biological factors and terrain factors were the main environmental factors affecting the population growth. Through the analysis of the correlation between environmental factors and population characteristics, we found that Human disturbance contributed to A. davidii population development because of sprout promotion. And the higher the species diversity of shrub layer, the greater competition populations faced, therefore species diversity was unfavorable for the population development. Terrain factors like slope, rocky desertification degree and so on was beneficial for A. davidii population by restricting the light, temperature, moisture to limit other vegetation distribution.2. Through analysis the impact of human disturbance on A. davidii species, we found that:(1) under high strength interference environments(II, III and IV), the population age structure showed an upward pyramid type, and the populations kept growth.(2) Population survival curve trended to a stable Deevey II curve in low strength interference environments(I and II), but a Deevey III curve in high interference conditions(III and IV).(3) Populations under low strength interference environments had higher survival rate and life expectancy, their survival rate and cumulative mortality rate had smaller fluctuation than those under high strength interference environments. The populations under high strength interference environment suffered a severe environmental screening from the first age class to the second age class.(4) The values of dynamic quantitative index Vpi and V’pi in high strength interference environments were higher than those in low disturbance environments, which indicated that the populations had higher growing ability in frequent disturbed environment.(5) All populations showed an obviously clumped distribution at 0~10 m scale, but the peak of clumped degree appeared larger scales in high strength interference environments, which suggested that the populations were expanding. The disturbance promoted the population’s renewal and development.3. The results of study on population growth and reproduction of A. davidii population in different water treatment showed that, plant began to delay the flowering period because of reduction of water treatment, but the flowering process, the number of inflorescence and the development of leaf phenology were not significantly changed under different water treatments. It meant that the flowering and leaf phenology of A. davidii were largely determined by its genetic factors; The number and length of new shoots and the number of new leaves under water reduced treatment were less than others, but the change of water content had little effect on the morphology of plant leaves and the biomass of various organs at flowering stage, which suggested that the growth and reproduction strategies of A. davidii were controlled by genetic factors in a great degree.In a word, research results above told us that, A. davidii population has strong adaptability to special habitat in Karst. After the disturbance, the population can be recovered and increased in a short time.Therefore A. davidii is suitable for the vegetation restoration in the early stage of the secondary succession in Karst areas. It can improve the habitat vegetation cover in a relatively short time and be better at keeping water and soil.