Whether the gravitational model can be used to analyze tree competition in forest community is a valuable question. A tree relative vitality circle based on the gravitational model can illustrate the magnitude of competitive tree vitality. A gravitational competition index based on the relative vitality circle of competitive trees can accurately depict the relationship between growth and competition. This study was conducted in the coniferous and broadleaf mixed forest of Tianmu Mountain National Nature Reserve in Zhejiang Province. We carried out correlation analyses between the V_Hegyi competition index and diameter at breast height (DBH), between the gravitational competition index and DBH, and between the two competition indices and the basal area increment. We further analyzed the correlation between the growth rate of DBH and the ratio of the two-phase gravitational competition index, that is, the ratio of the 2021 gravitational competition index to that of 2006. In addition, the correlation analysis was applied between the relative vitality circle diameter and DBH. We also compared the magnitudes of the competition indices between the living standing trees and the dead trees. The results showed that both competition indices were negatively correlated with DBH, and followed a power function relationship. The basal area increment was negatively correlated with each of the two competition indices. However, the gravitational competition index was better than V_Hegyi competition index for indicating the relationship between tree growth and tree competition. Compared with the ratio of the V_Hegyi competition indices, the ratio of the two-phase gravitational competition indices could better demonstrate the relationship between tree growth and tree competition. In the coniferous and broadleaved mixed forests, the correlation coefficient between the growth and competition of broadleaved species was greater than that of coniferous species. The dead trees were significantly influenced by competition. Tree relative vitality circle size was negatively correlated with DBH. The gravitational model was one of the critical models that reflect spatial interactions and could be applied to examine forest competition. The gravitational competition index could be used as a spatially structured indicator to evaluate tree competition and tree vitality, which could better indicate the relationship between tree growth and tree competition than the V_Hegyi competition index.
引力模型是否可以应用于森林群落林木竞争关系分析是值得研究的问题。基于引力模型建立林木相对活力圈能反映竞争木活力大小,基于竞争木的相对活力圈建立引力竞争指数能准确反映林木生长与林木竞争的关系。以浙江省天目山国家级自然保护区针阔混交林为研究对象,将V_Hegyi竞争指数、引力竞争指数分别与胸径进行相关分析,胸高断面积生长量分别与2种竞争指数进行相关分析,胸径生长率与2期引力竞争指数的比值(2021年与2006年的引力竞争指数之比)进行相关分析,此外,对相对活力圈直径与胸径进行相关分析,并比较分析了活立木与枯死木的竞争指数大小。结果表明: 2种竞争指数与胸径均呈显著负相关,且均服从幂函数关系。林木胸高断面积生长量与2种竞争指数均呈显著负相关,但引力竞争指数比V_Hegyi竞争指数更能反映林木生长与林木竞争的关系。相对于V_Hegyi竞争指数的比值,2期引力竞争指数的比值更能说明林木生长与林木竞争的关系。在针阔混交林中,阔叶树种的生长与竞争的相关性>针叶树种生长与竞争的相关性。林木枯损受竞争的显著影响。林木相对活力圈大小与林木胸径大小呈显著负相关。引力模型是反映空间相互作用的重要模型之一,可以应用于林木竞争关系的研究,且基于引力模型建立的引力竞争指数可以作为评价林木竞争和林木活力的一个空间结构指标,比V_Hegyi竞争指数更能反映林木生长与林木竞争的关系。.
Keywords: V_Hegyi competition index; gravitational competition index; tree relative vitality circle.