半干旱黄土区不同自然恢复时期坡面植被组成与分布特征

Composition and distribution characteristics of vegetation in different natural restoration periods in semi-arid loess region

为研究半干旱黄土区长期封禁条件下植被自然恢复过程的动态特征,选取黄土丘陵沟壑区梁峁坡为研究区,基于2009和2016年样方调查数据,应用地统计方法,分析封禁25~32年之间坡面草本植物群落物种组成、结构和空间分布的变化特征。结果表明:1)2009年到2016年物种新增16种,坡面优势种由菊科、禾本科加豆科变为菊科、禾本科、豆科和莎草科。2)坡面生物量的平均值由2009年的98.57 g/m2增加到2016年的141.27 g/m2,坡下部的生物量明显增加,生境差异对生物量的影响减弱,群落更加稳定。3)Margalef指数、Shannon-Wiener指数和Pielou指数的均值都明显增加,坡面总体上物种更为丰富,群落稳定性增大;半阳坡坡下物种基本达到稳定状态;其他立地类型物种多样性明显增加。4)与2009年相比,2016年植被盖度、高度、生物量和干鲜质量比的空间自相关性均减弱;2009—2016年Margalef指数空间自相关性由弱变强,自相关距离约为60 m;Shannon-Wiener指数空间自相关性持续微弱,Pielou指数由空间正相关变为负相关。总体上梁峁坡面植物物种更加丰富,空间分布更加均匀,群落稳定性增强。经过32年的封禁,在半干旱黄土梁峁坡面,植物生活型依然以多年生草本植物为主,半灌木的优势度明显增加,群落正在向更稳定的方向演替;但植被演替过程缓慢,为了加速植被恢复,适当的人工干预是必要途径。

[Background] After decades of returning farmland to forests and grasslands,vegetation in semi-arid loess region has been significantly restored. Investigating the dynamics of plant community during natural restoration process could be helpful in managing the ecosystem and further promoting the restoration rate. [Methods]A hill top of 8. 89 hm2 enclosed around 25-32 years was taken as the study area and geostatistical analysis was applied to explore the changes of species composition and structure and spatial heterogeneity of the plant community based on 31 plants quadrats of 1 m × 0. 5 m in 2009 and2016 respectively. [Results]1） From 2009 to 2016,16 new species were found while the life form was still mainly concentrated in perennial herbaceous plants in whole slope. With the dominated species changed from Artemisia sacrorum,Artemisia leucophylla,Stipa capillata,Lespedeza bicolor and Artemisiafrigida to Artemisia sacrorum,Carex tristachya,Cleistogenes chinensis,Lespedeza bicolor and Artemisia frigida. The dominance of subshrub increased significantly. 2） The average biomass of the quadrats in2009（ 98. 57 g/m2） was significantly different that in 2016（ 141. 27 g/m2） in the level of 0. 01. The differences of biomass on lower slopes and upper slopes became smaller in 2016 indicating that environmental factors had less impact on vegetation growth. 3） The species diversity index increased significantly. The average values of Margalef index,Shannon-Wiener index and Pielou index increased from 1. 361,1. 510 and 0. 764 in 2009 to 1. 831,1. 716 and 0. 841 in 2016,indicating that the community became more stable. Compared to other site types with the species diversity increased remarkably,the species diversity index in lower-semi-sunny slope had little change indicating that the community had almost reached a steady state. 4） Compared to 2009,spatial autocorrelation of plant coverage,height,biomass and ratio of dry to fresh became weak in 2016. The spatial autocorrelation of Margalef index changed from strong to weak and the autocorrelation distance was about 60 m. ShannonWiener index did not show significant spatial autocorrelation both in 2009 and 2016. The spatial autocorrelation of Pielou index changed from positive correlation to negative. It indicates that the spatial variability of plant richness increased while the spatial variability of plant homogeneity decreased.Overall,plant species were richer,the spatial distribution was more uniform and community stability was enhanced on the investigated slope. [Conclusions] From 2009 to 2016,the number of species in the study area increased and the species diversity index showed an increasing trend. The plant life-form of perennial herbaceous plants still dominated in the study area. Results indicated that the community on the hill top became more stable but not reached to a steady state after 32 years of natural restoration and human intervention is necessary to accelerate the natural restoration rate.