热带不同土地利用方式林下植被多样性和生物量分配特征及其季节动态

Seasonal dynamics of understory vegetation diversity and biomass allocation across different tropical land use types

林下植被在维持生物多样性和生态系统功能以及对森林生物量的贡献等方面发挥着重要作用,而热带地区典型的土地利用方式和季节变化势必会对林下植被多样性和生物量产生影响。以西双版纳地区的常规管理胶林(CR)、自然恢复胶林(NR)、人工恢复胶林(AR)、香蕉林(BP)以及次生林(SF)五种典型土地利用方式的林下植被为研究对象,探究了林下植被物种组成结构、多样性指数及生物量分配对不同土地利用方式及季节的动态响应。结果表明:(1)五种土地利用方式共调查到灌木50种,分属于31科41属;草本88种,分属于45科79属,且多年生草本植物居多,占草本总种数的60%以上。灌木主要以豆科植物为优势类群,草本则以禾本科和菊科植物为主。(2)相比SF和人为干扰较少的NR及AR,人为干扰较大的CR和BP显著改变了旱季和雨季林下植被的物种组成和优势类群的分布,并降低了林下植被群落的平均高度、盖度、多样性及总生物量和地上与地下部分生物量。同时,CR灌木的地下/地上生物量比显著高于SF、NR和AR,而草本的地下/地上生物量比在不同土地利用方式间无显著差异。(3)草本群落结构、多样性及生物量相较于灌木更容易受季节变化的影响。CR草本群落的盖度和高度雨季显著高于旱季,而SF多年生草本的Pielou指数和一年生草本多样性雨季显著低于旱季。此外,所有橡胶林分的林下植被及其草本层的各生物量组分雨季显著高于旱季,而BP则呈相反趋势。灌木和草本的地下/地上生物量比无明显季节变化,但雨季一定程度上提高了草本植物的地下/地上生物量比,这得益于多年生草本的较大贡献。综上所述,热带土地利用方式转变及季节变化对林下植被多样性及生物量分配具有一定影响。研究将为热区人工经济林生物多样性保护和可持续经营管理提供科学依据。

Understory vegetation plays a crucial role in sustaining biodiversity and ecosystem functions,as well as contributing to forest biomass.It is inevitably affected by land use types and seasonal variations in the tropics.This study investigated the understory vegetation of five typical land use types,namely conventional management of rubber plantation(CR),natural restoration of rubber plantation(NR),artificial restoration of rubber plantation(AR),banana plantation(BP)and secondary forest(SF),in Xishuangbanna,southwestern China.The study aimed to examine the response of species composition,diversity and biomass allocation of understory vegetation to different land use types and seasons.The results showed that:1)A total of 50 shrub species belonging to 41 genera and 31 families and 88 grass species belonging to 79 genera and 45 families,with perennial herb accounting for more than 60%of the total grass species,were found under five land use types.The dominant group of shrubs were mainly leguminous,and the majority of grasses were of the Poaceae and Asteraceae families.2)CR and BP,where anthropogenic disturbances were stronger,significantly altered the species composition of understory vegetation and the distribution of dominant groups,as well as decreased the average height,coverage,total biomass,aboveground and belowground biomass of understory vegetation compared to SF,NR and AR,where disturbances were rather weak.Meanwhile,belowground/aboveground biomass ratio of shrub under CR was obviously higher than that of SF,NR and AR,while there was no difference in belowground/aboveground biomass ratio of grass across different land use types.3)The community structure,diversity and biomass of grass exhibited greater susceptibility to seasonal variability than shrub.The average coverage and height of grass under CR were significantly higher in rainy season than in dry season,while the Pielou index of perennial herb and annual herb diversity under SF were significantly lower in rainy season than in dry season.In addition,the biomass of understory vegetation and its herbaceous layer in all rubber stands were obviously higher in rainy season than in dry season,whereas BP showed the opposite trend.There was no significant seasonal variation in belowground/aboveground biomass ratio for shrub and grass,with the rainy season resulting in an increase in belowground/aboveground biomass ratio for grass plants,due in part to a greater contribution from perennial herb.In conclusion,changes in tropical land use and season had distinct effects on understory vegetation diversity and biomass allocation.This study will provide a scientific basis for biodiversity conservation and sustainable management of artificial economic plantations in tropical region.