间伐对生态公益林冠层结构及土壤养分的影响

Effects of thinning on canopy structure and soil nutrient in ecological plantation

为定量分析上海城郊生态公益林间伐后林分冠层结构变化及对林下环境的影响,2009年7月采用TRAC植物冠层分析仪研究了香樟(Cinnamomum camphora)、杜英(Elaeocarpus sylvestris)和栾树(Koelreuteria paniculata)3种生态公益林间伐2年后林分冠层结构参数,设置临时样方调查各林分林下植物分布及生物量,测定了土壤N、P、K和有机质的变化。结果表明:间伐后3种林分的LAI、丛生指数和平均接触次数均降低,而间隙分数增大。间伐增加了林分间隙和LAI的空间异质性,间伐后3个树种LAI变异系数增加了19%～45%。轻度间伐后香樟、杜英和栾树林下PPFD(Photosynthetic Photon Flux Density)分别是未间伐林分的1.6、7和2.1倍,重度间伐香樟林内PPFD增大了8.9倍。间伐后林下植物种类、总盖度和干生物量随林下PPFD增加呈增大趋势。除全P和全K含量没有变化外,林地土壤全N、速效K、速效P和有机质含量均比未间伐林地有不同程度降低,但轻度间伐杜英林地速效养分消耗显著高于香樟和栾树林分。因此,研究区生态公益林结构调控需根据树种特性和林下环境变化,确定适宜的发展模式,提高公益林的综合效益。

For quantitative analysis of canopy structure change in Shanghai suburb ecological forest after thinning and which impact on understory environment.In July 2009,using TRAC to analyze canopy structure parameters of Cinnamomum camphora,Elaeocarpus sylvestris and Koelreuteria paniculata stands after thinning two years,temporary quadrat were setted in each stands to investigate the understory plant distribution and biomass,the soil N,P,K and organic matter of each stands was also determined.The results showed that LAI,clumping index and mean contact number all decreased for 3 stands,while the gap fraction increased.Thinning improved the gap fraction and LAI spatial variation,CV of LAI for 3 stands increased 19%～45%.Understory average PPFD（Photosynthetic Photon Flux Density）of C.camphora,E.sylvestris and K.paniculata stands after slight thinning increased 1.6,7 and 2.1 times than control,respectively,the number was 8.9 times in heavy thinning C.camphora stands.Understory plant species,total coverage and dry biomass in 3 stands after thinning increased with PPFD.In addition to total P and total K content in soil has not changed after thinning,total N,available K,available P and soil organic matter content reduced to varying degrees.Therefore,the ecological forest structure control in study area need to consider understory environment changes after thinning,then determined the suitable development model,and promoted forest comprehensive benefit.