火烧迹地柽柳灌丛资源岛特征及植被的自然恢复

干旱半干旱地区灌丛资源岛特征及形成机制多有报道,但资源岛土壤对群落稳定性与火烧迹地植被的自然恢复作用尚不明确。以酒泉盐碱地柽柳灌丛地火烧3年后,自然恢复的柽柳(Tamarix ramosissima)及其冠下草本群落为研究对象,构建柽柳枯立株体量指数(SSI,Shrub Size Index)和恢复力综合指数,探讨了资源岛特征与植被恢复、冠下草本群落多样性的关系,量化不同大小柽柳灌丛的恢复力稳定性。结果表明:(1)在不同SSI的柽柳枯立株下土壤有机质和含水率明均显高于灌丛间地,形成了明显的资源岛特征。土壤有机质最大值出现在0—10 cm土层,中灌丛的肥力积聚效果最明显。(2)土壤主要以中性盐为主,在0—40 cm土层,灌丛区域土壤可溶性盐低于冠外,呈明显的盐谷特征,中灌丛的盐谷分布最为明显。(3)随着枯立株SSI的增大,柽柳新生枝条的数量及其高度均有所增大,冠下植物的高度、盖度、密度和地上植物量也明显高于灌丛间地,且灌丛越大恢复效果越明显。(4)灌下植物Simpson指数、Shannon?Wiener指数、Margalef指数和Pielou指数随着枯立株SSI的增大均先降后升,多样性指数低,群落结构简单。(5)恢复力综合指数随着枯立株SSI的增大呈先升后降的趋势,当SSI=52.17时灌丛群落的稳定性最强。柽柳较小时主要是冠下草本植物的恢复维持群落稳定性,随着灌丛的增大逐渐以柽柳灌木的恢复来维持群落稳定性。柽柳灌丛形成的高养低盐的土壤环境对植物群落稳定性的维持和植被的恢复有促进作用,对荒漠生态系统火烧迹地植被恢复和生态保护具有重要意义。

Features of resource islands under Tamarix ramosissima shrubs and natural recovery of vegetation on the burned area in Jiuquan, Gansu Province, China

The characteristics and formation mechanism of resource islands in arid and semi-arid regions were widely reported. However, the effect of resource islands on community stability and vegetation natural restoration on burned area was still unclear. We investigated restoration of Tamarix ramosissima and vegetation under the shrub canopies on burned area. The shrub size index (SSI) and composite resilience index were established to study relationships between resource islands, vegetation restoration, and diversity of vegetation under the canopies. We quantified resilience stability of shrubs with different SSI. The results indicated that:(1) soil organic matter and soil moisture content were obviously higher under and at the edge of canopies than those outside the canopies, which formed resource island. The maximum value of soil organic matter was found in 0-10 cm soil layer. The phenomenon of fertilizer accumulation was the most obvious in middle T. ramosissima. (2) Soil salinity was mainly composed of neutral salt. The soluble salt in the soil layer of 0-40 cm under canopies was significantly lower than that outside the canopies. It showed obvious characteristics of salt valley in soil under shrubs. It was easy to observe this phenomenon for the middle shrubs. (3) With the increase of SSI of dead standing T. ramosissima, the number and height of branches increased, and the height, coverage, density, and biomass of vegetation under the shrubs were significantly higher than those outside the shrubs. The larger shrubs were, the better effect of the natural recovery was. (4) With the increase of SSI, Simpson index, Shannons-Wiener index, Margalef index, and Pielou index of vegetation under the canopies decreased firstly and then rose, with low diversity index and the simple community structure. (5) Composite resilience index showed a trend of firstly ascending and then descending with the increase of SSI. The value of community stability of T. ramosissima shrub was the highest when SSI was equal to 52.17. Community stability was mainly maintained by the restoration of herbaceous plants when shrubs were small on burned area. With the increase of SSI, community stability was maintained by the restoration of shrubs. The soil environment with high nutrient and low salt was formed from shrubs, which contributed to the restoration of vegetation. Resource island also played a positive role in maintaining the diversity and stability of plant communities. It was of great significance to vegetation recovery on burned area and ecological protection of desert ecosystem.