灌木层的叉叶苏铁种内和种间竞争

Intraspecific and interspecific competition of Cycas micholitzii in the shrub layer

通过对广西叉叶苏铁群落中48株对象木及757株竞争木的调查,运用Hegyi单木竞争指数模型计算分析叉叶苏铁种内和种间竞争强度,研究物种竞争关系对叉叶苏铁天然更新的影响。结果表明:叉叶苏铁的种内和种间竞争强度比例分别为3.79%和96.21%,说明竞争主要来自种间。叉叶苏铁的伴生种较多,种内与主要伴生种间的竞争关系为仪花>潺槁木姜子>天仙果>龙眼>灰毛浆果楝>红背山麻杆>叉叶苏铁。竞争强度随对象木高度增大而减小,当对象木高度<0.6 m时,所受到的竞争强度较大;当高度>0.6 m时,竞争强度变化很小。种内竞争与总体竞争强度和对象木高度的关系服从幂函数关系,种内竞争中则服从S曲线方程,所得预测模型能很好地预测叉叶苏铁种内和种间竞争强度。对于株高<0.6 m的叉叶苏铁个体应加强保护,可采取人工抚育措施降低种间竞争压力,提高叉叶苏铁天然更新成功率。

Based on the field investigation data of 48 Cycas micholitzii target trees and 757 competitive trees in Guangxi,this paper analyzed the intraspecific and interspecific competition intensity of Cycas micholitzii.The Hegyi individual competitive indices(IC)model was used to explore the effects of species competition on the natural regeneration of Cycas micholitzii.The results showed that the intraspecific and interspecific competition intensity of Cycas micholitzii accounted for 3.79%and 96.21%of the total competition intensity,respectively,indicating a remarkable effect on the interspecific competition.The value of the main competition intensity was laid out in numerical order,i.e.,Lysidice rhodostegia>Litsea glutinosa>Ficus erecta var.beecheyana>Dimocarpus longan>Cipadessa cinerascens>Alchornea trewioides>Cycas micholitzii.Notably,the competition intensity of Cycas micholitzii decreased inversely to height,which showed a stronger competition at heights<0.6 m and appeared weaker at heights>0.6 m.The relationship between the height of objective trees and the competition intensity and between competitive and objective trees in the whole forest and the Cycas micholitzii population nearly conformed to a power function,while that between other competitive trees and objective Cycas micholitzii trees conformed to an S curve equation.In conclusion,this model could effectively predict the intraspecific and interspecific competition of Cycas micholitzii.Individuals of Cycas micholitzii<0.6 m in height should be protected.Artificial tending measures can be taken to reduce the pressure of interspecific competition in order to increase the natural regeneration success rate of Cycas micholitzii.