南宁老虎岭林区多种外来植物入侵程度与影响因子模型解释

了解森林环境中多种外来植物对多种环境因子的互作效应,可以更有针对性地应对外来入侵威胁。在南宁老虎岭林区分6个区进行样方调查,以样方所有外来植物的相对百分比作为外来植物入侵程度,利用以分区为随机截距的混合效应模型和一般线性模型来分析有关因素对入侵的影响,用R-effects包的互作效应图形化和数据提取来解释互作效应的复杂变化。多因素混合效应模型分析表明,路边对入侵的主效应为正且极显著(P=0.000),林冠郁蔽度和优势最大株高对入侵的主效应为负(P=0.000),土著物种丰富度对入侵的主效应不显著,但土著物种丰富度与路边的互作对入侵的效应极显著(P=0.007);路边的土著物种丰富度明显提升入侵抵抗性,但林内的土著物种丰富度只能微弱增加入侵抵抗性;林冠郁蔽度和优势最大株高的互作对入侵的效应极显著(P=0.004),但两个因素对入侵的限制作用非可加。一般线性模型分析表明,林龄和抚育时间对外来植物入侵的影响趋势不明显;未发现引进树种造林与乡土树种造林的林下外来植物入侵程度有差异;相对于林道的样方位置高低影响入侵程度,林道下方的样方较易被入侵。在监测或防控林业外来植物时,重点应放在低于林道的森林。

Modeling Association among Multispecies Plant Invasion and Impact Factors in Laohuling Forest,Nanning

A deep understanding of the interactions between multispecies invasions and impact factors facilitates more pertinent control of invasions. Plot survey was carried out in Laohuling Forest, Nanning, and the vegetations were recorded in six districts; and relative cover of all alien plants in a plot, the alien ratio, was used as invasion index. R-lme4 mixed effect model with random district intercept and SPSS GLM-GEN were used to calculate impacts of environmental on invasions, and R-effects package to visualize the complex interaction effects. Multivariate mixed effect model showed that roadside had positive main effect on invasion(P=0.000), canopy cover and dominant plant height both had negative main effect on invasion(P=0.000); native richness' main effect on invasion was not significant, but its interaction with roadside had significant effect on invasion(P=0.007); on roadside, native richness strongly raised resistance to invasion; while within forest, native richness weakly increased resistance to invasion; canopy cover and dominant plant height's interaction effect on invasion was significant(P=0.004), but their filter effects were non-additive. GLM-GEN results indicated that forest age and tending times did not influence invasion; and we did not find significant difference between introduced and native species plantations in impacts on invasions; furthermore, plot locations relative to forest lanes influenced alien invasions, and plots below forest lanes were more vulnerable to invasions. In future works of monitoring and controlling alien plants in forest, emphasis should be focused on stands those below forest lanes.