基于Hegyi改进模型的毛竹林空间结构和竞争分析

以浙江省天目山国家级自然保护区内少受干扰的毛竹林为研究对象,设置100m×100m的固定标准地,进行连续5a的每竹调查,用全站仪精确测定每竹坐标(X,Y,Z)。提出新的竞争指数——竞争势(CP)。利用CP对2009—2013年毛竹林分竞争动态进行定量分析,并分别研究各年份毛竹林竞争强度与对象竹胸径、年龄之间的动态关系。结果表明:毛竹大小年现象明显,毛竹大年(2010、2012)的林分竞争强度明显大于小年(2009、2011、2013),且大小年之间竞争强度存在显著性差异(P0.01),毛竹大年之间林分竞争强度无显著性差异(P0.05),毛竹小年(2011、2013)之间林分竞争强度无显著性差异(P0.05),2009年毛竹林受雪灾和新竹株数影响,与其它年份林分竞争强度存在显著性差异(P0.01);毛竹林竞争强度随对象竹径阶的增大而减小,且服从幂函数关系;毛竹林竞争强度随对象竹龄级的增大而增大,且服从线性函数关系。CP在Hegyi模型的基础上,增加考虑毛竹生理特性,使对毛竹竞争关系的分析有了进一步拓展,从而更加全面有效地描述毛竹林分的竞争关系,应用CP分析毛竹林竞争动态规律,可为毛竹林经营提供参考依据。

Analysis of the spatial structure and competition with a Phyllostachys edulis standbased on an improved Hegyi model

At present, many individual tree competition indices are used to measure the competitive ability of trees, and they are generally divided into distance-independent indices and distance-dependent indices depending on whether one is considering the space between trees. Distance-dependent indices are commonly used, especially the Hegyi competition index (CH). The CH was used to analyze the spatial structure of a Phyllostachys edulis stand studied by Tang et al., but we found that this CH needs to be improved. P. edulis is a Bambusoideae (Gramineae) species and does not have secondary cambium tissue, resulting in the termination of diameter at breast height (DBH) growth after completion of the stem growth. Unfortunately, there are different competitive intensities associated with the spatial structure of P. edulis stands, even in situations where the same distance exists between object and competition bamboo plants. This means they might have the same DBH, but would be considered to be of a different age. Such distinctions cannot be provided by the existing CH. In fact, competition within a P. edulis stand is affected significantly by intensity of physiological activity, which changes with variation of the metabolic turnover and aging process of an individual, or with its material growth period. Material growth periods are divided into enhancement stages, stationary stages, and declining stages, depending on different intensity of physiological activities. In the light of characteristic of P. edulis, considering its metabolic turnover and aging process, and adding a material growth period factor, a new competition index-competition potential (CP), which is based on CH (the Hegyi model), was proposed to analyze the spatial structure of P. edulis stands. A permanent plot measuring 100 m × 100 m, including a relatively lightly disturbed P. edulis stand, was established in the Tianmu Mountain National Nature Reserve, Zhejiang province. There have been five annual surveys of the plot. Each bamboo tree was tallied and its coordinates (X, Y, Z) were measured using a total station survey device. From 2009 to 2013, we used the new competition index, CP, to quantitatively analyze the dynamic competition within the bamboo stand, as well as to study the dynamic relationship between intensity competition and DBH, and the dynamic relationship between intensity competition and age class. The results showed that the P. edulis stand has clear on-year/off-year cycles and that the competitive intensity of on-years (2010, 2012) is obviously higher than that of off-years (2009, 2011, 2013). The difference in competitive intensity within the P. edulis stand between on-years and off-years was significant (P < 0.01). The difference in competitive intensity within the P. edulis stand between on-years was not significant (P > 0.05), as was the difference in competitive intensity between off-years (2011and 2013; P > 0.05). Because of a snow disaster and the emergence of a number of new shoots, the competitive intensity within the P. edulis stand in 2009 showed significance difference (P < 0.01) from other years. The competitive intensity within the P. edulis stand decreased with increasing objective diameter class, and the results showed that the competition had a powerful relationship with DBH. The competitive intensity within the P. edulis stand increased with increasing age class and also had a significantly linear correlation with DBH.A combination of the growth characteristics and adopted physiological characteristics of P. edulis was used to develop an expanded analysis of competition between individuals of P. edulis. This allowed us to develop a more comprehensive and effective model (CP) to describe competition within a P. edulis stand. The new CP is therefore a feasible and reliable way to analyze competition within P. edulis stands and their dynamic characteristics. For these reasons, it could provide a theoretical basis for management of artificial P. edulis stands.