取样方式对喀斯特和非喀斯特混合分布区森林种—面积关系的影响

Sample effects on species-area relationships of typical forests in karst and non-karst mixing distribution areas

关键词:  种—面积关系  起测胸径  最小取样单元  喀斯特季节性雨林  非喀斯特森林

Key words:  species-area relationship  minimum measured DBH  base sample unit  karst seasonal rain forest  non-karst forest

摘要:

种—面积关系是生态学研究中的基本格局之一,是生物多样性保护实践和生物地理学研究的重要工具之一。不同区域最优种—面积关系模型的选择和取样调查方式对种—面积关系的影响目前仍未十分明确。广西北热带是喀斯特和非喀斯特混合分布的区域,生物多样性丰富,其中保护较好的有喀斯特区的弄岗国家级自然保护区和非喀斯特区的十万大山国家级自然保护区。依据典型性和代表性的原则,分别在两个保护区中建立典型群落的调查样地,对所有胸径大于2 cm的木本植物进行取样调查。为了明确该区域典型森林的优选模型,探讨取样方式对种—面积关系的影响,采用组合样方法建立对数模型、逻辑斯蒂克模型和幂函数模型,用赤池信息准则(AIC)检验模型的拟合优度,并用秩相关分析检验最小取样单元和起测胸径对不同模型的影响。结果表明:逻辑斯蒂克模型在两种区域均为优选模型,最小取样单元和起测胸径对种—面积关系的模型均有影响,但不同模型对取样方式变化的敏感性不一致; 逻辑斯蒂克模型是一种较为稳健的模型,可用于描述广西北热带喀斯特区和非喀斯特区森林树种种—面积关系; 在种—面积关系研究和模型的应用时,需要特别注意取样方式的影响。

Abstract:

The species-area relationship(SARs)is a fundamental pattern in ecological research. It is also a common tool in predicting species extinction and assessing species diversity. The species-area relationships curves describe the increase of species number with increasing scales. Various factors affect the shape of species-area curves at different scales. However,it is still not clear in selecting the best SARs model for a certain area and insufficient attention has been paid to the effects of sample methods and standards on SARs. The region in north tropics of Guangxi,where the karst area and non-karst area are mixing distributed,supports very high level of biodiversity. In this region,the Nonggang National Natural Reserve is located in the typical tropical karst terrain where forests are less disturbed and conserve hyper diverse endemic species. The forests in the Nonggang National Natural Reserve are typical karst forests which are shaped by the distinctive geological environments. In contrast,the terrain in the Shiwandashan National Natural Reserve is non-karst forests where are mainly shaped by climatic conditions. A contrastive study of species-area relationships between the karst forests and non-karst forests in the same climatic zone and elucidate the difference of species diversity may provide insight into the conservation of biodiversity in the karst area and non-karst area mixing distributed region. In this study,we established 14 plots of 400-600  in Nonggang and 15 plots in Shiwandashan. These plots contain representative forests communities in the study area,for example,including Excentrodendron tonkinense,Cephalomappa sinensis,Deutzianthus tonkinensis, Litsea dilleniifolia in Nonggang and Eberhardtia aurata,Madhuca pasquieri,Lithocarpus pseudovestitus,Hopea chinensis in Shiwandashan. All individuals of tree species with DBH(Diameter at breast height)greater than 2 cm were recorded and identified to species. Based on the sample data of 10 m×10 m subplots,species number was counted by a series continuous sample area. In order to determine the optimal SARs models and sample effects on SARs models,we constructed three SARs models(Logarithm model,Logistic model,and power model)from noncontiguous grid combinations design based on survey data of typical forest communities. To assess the effects of minimum measured DBH on SARs,species numbers of individuals with DBH≥2 cm,DBH≥4 cm,DBH≥6 cm,DBH≥8 cm,DBH≥10 cm were counted separately. We used least square method and Gauss-Newton method to estimate the parameters of SARs models. Akaike Information Criterion(AIC)was used to compare the goodness-of-fit of each model. Spearman rank correlation was used to assess the effect of base sample unit and minimum measured DBH on SARs. The results showed that logistic model was the best among the three SARs models both in karst area and non-karst area. Base sample unit and minimum measured DBH both had significant effects on SARs,but the effect varied among the SARs models. We argue that logistic model is a robust model to describe SARs of tree species in karst and non-karst forests in north tropics Guangxi. The results also suggest that special attention must be paid to the influence of sample methods as applying SARs models to protection practices.