林窗对岷江冷杉幼苗种群优势度增长与周期性波动的影响

在川西亚高山岷江冷杉原始林中布设样带,开展林窗和林下更新幼苗生长状况调查,采用Logistic模型和谱分析进行种群优势度增长和周期性波动分析。结果表明：Logistic模型能较好地反映出岷江冷杉幼苗种群优势度增长规律,基于基面积和总生物量拟合的种群优势度最大环境容量分别为11.34 mm²/m²和4.64 g/m²,内禀增长率为0.60和0.62,基面积和生物量均能很好地表示岷江冷杉幼苗种群大小。基于基面积拟合和计算的林窗种群的最大环境容纳量、内禀增长率和最大增长速率约为林下种群的4.2倍、1.4倍和5.8倍,最大增长速率出现时间较林下种群早2龄级。谱分析发现岷江冷杉幼苗种群的波动性是多个周期的叠加,大周期内存在着小周期,均以基波振幅最大,林窗种群基波振幅约为林下种群的3倍,谐波对林窗种群影响较林下种群早2龄级。林窗干扰提高了岷江冷杉幼苗种群优势度的环境容纳量和内禀增长率、增强了基波对种群周期性波动的控制,使幼苗种群具有更强的增长优势和相对稳定的生长环境。因此,在岷江冷杉原始林的管理过程中应充分重视林窗的作用。

Effects of Canopy Gap on the Growth Dynamics of Dominance and Periodic Fluctuation of Abies faxoniana Seedlings in a Subalpine Coniferous Forest

Abies faxoniana coniferous forests play important roles such as conserving water and soil and maintaining habitat stability for the giant panda in the eastern Tibetan Plateau and the upper reaches of the Yangtze River. Canopy gap disturbance drives successional dynamics of forest communities and shapes forest structure, dynamics and biodiversity in the A. faxoniana forests. The objective of this study was to elucidate the growth dynamics of dominance and periodic fluctuation of seedling population and evaluate the effects of canopy gaps on A. faxoniana regeneration. There strip transects (300 m×2 m), including forest canopy(FC) and canopy gaps (CG), were established in a subalpine coniferous forest in the Wanglang National Nature Reserves, Pingwu County, western Sichuan Province. We investigated the diameter, height and biomass of A. faxoniana seedling (H≤100 cm) and used the Logistic model and spectra analysis for data analysis. The results showed that the Logistic model fitted well with the dynamic adjustment process of the growth dynamic of dominance of A. faxoniana seedling population. The habitat carrying capacity based on basal area and total biomass were 11.34 mm²·m^-2, 4.64 g·m^-2, respectively, and the intrinsic rate of increase were 0.60 and 0.62, respectively. The ratios of the habitat carrying capacity and the intrinsic rate of increase of CG and FC seedling populations were 4.2:1 and 1.4:1 , and the biggest absolute growth rate of CG seedling population was two age classes in advance of FC seedling population. The spectra analysis showed that the fundamental wave regulated the periodic fluctuation of A. faxoniana seedling population and the harmonic wave affected the fluctuation. The fundamental wave of CG population had higher amplitude than the fundamental wave of FC population, and the ratio amplitude was 3:1. The harmonic wave effects on CG population appeared earlier. CG are an important impetus for growth dynamics of dominance, e.g., they improve habitat carrying capacity and intrinsic rate of increase, and advance the appearance of the biggest growth rate. CG can also affect the periodic fluctuation of seedling population, which enhance the regulation of the fundamental wave, and advance the time of the harmonic effect. After the beginning of the highest absolute growth rate, the A. faxoniana seeding population growth was inhibited by intraspecific competition in CG and environmental resource constraints. The influence of CG seeding population on the growth dynamics of dominance and fluctuation of global seeding population was not strong, so we should pay attention to the role of the forest gap in the process of A. faxoniana forest ecosystem management.