半干旱沙丘缀块生境植被格局过程对尺度和环境的响应

Investigations of spatial patterns have been used to gain understanding about the interactions between ecological processes and natural physical elements. Especially, many ecological studies have addressed issues of vegetation spatial patterns in attempts to understanding the scale-dependent mechanisms and the responses of vegetation processes to environmental conditions. In this project, our study is conducted at the semi-arid sand dune patchiness combination, located at the western of Horqin Sandy Land, northeastern China. The patchiness combination includes active sand dunes, fixed sand dunes and inter-dune lowlands. We select a census plot of 100 ha between dune patches, and two census plots of 1ha in each type dune patches. The large-scale quadrat census in every 1m×1m quadrat is conducted to survey the vegetation and monitor the environments at each census plot. Using the methods and techniques of ecological models, geographic information systems and geostatistics, we frame the multi-scale point quadrat charts of vegetation pattern based on the superposition of survey data from every 1m×1m quadrat. We discuss spatial patterns and ecological processes of vegetation, such as biodiversity, species association and coexistence along the multi-scale. Then, we determine the critical threshold and the characteristics scale in the dynamics of vegetation processes, and distinguish the control weights of natural physical elements on vegetation pattern-processes in multi-scale, based on the mechanisms analysis of vegetation patterns and ecological processes affected by habitat fragmentation and heterogeneity. Our study would not only compensate for the lack of studies on multi-scale vegetation patterns, but also deepen the understanding the vegetation succession mechanism of sand dune ecosystems, which could provide a scientific basis for the hot issues of biodiversity conservation and vegetation restoration ecology in semi-arid regions.

植被格局是生态过程和自然物理要素间互馈作用的结果，特别是植被格局过程对尺度的依赖及对环境因素的响应机制是植物生态学家面临的重要挑战之一。本研究以科尔沁沙地西部沙丘缀块镶嵌体(流动沙丘-固定沙丘-丘间地)为对象，在缀块间(100ha)和缀块内(1ha)进行植被调查和环境要素定位监测。利用每1m×1m样方内调查数据的叠加获得多尺度植被点格局信息，综合生态学模型及地理信息系统和地统计学等方法与技术，深入探讨多尺度下植被格局特征、植物多样性变化趋势、种间关系和共存机制等生态过程，分析沙丘生境破碎化和自然要素异质性对植被格局过程的影响机制，确定作用于植被格局过程的临界阈值及特征尺度，区分自然物理要素在不同尺度上对植被格局过程的控制权重。本研究不仅可弥补内陆沙丘生态系统多尺度点格局研究的欠缺，而且可加深对沙丘植被演替机理的理解，为半干旱区植物多样性保护和植被恢复等生态学热点问题提供科学依据.

科尔沁沙地西部的沙丘生态系统具有很强的缀块性，固定沙丘、流动沙区及丘间低地等缀块呈不规则形状镶嵌。生境破碎化导致的自然物理要素异质性可能在不同空间和尺度上影响植被组成和分布格局。本研究分别在沙丘生态系统缀块间大尺度 (1000m×1000m) 、缀块内中尺度(100m×100m) 以及种群微小尺度((3m×3m) 进行网格状样方(1m×1m) 植被调查和土壤取样。目标是探讨物种多样性、种间关系和共存机制等生态过程的格局与特征尺度，深入解析植被格局与环境要素的关系。.研究结果表明沙丘生态系统共有25科79种植物。缀块间样地大尺度上物种多样性空间均质性随尺度下降而增强。物种多样性组成中草甸植物、杂草植物和一年生植物特征尺度较大，而其他植物类型特征尺度均较小。缀块内1ha样地植物多样性在中尺度上空间均质性较高，但空间异质性随尺度下降而增强。流动沙丘物种丰富度空间异质性特征尺度约为14m，固定沙丘物种丰富和香浓多样性指数空间异质性特征尺度约为11.9m，而丘间低地物种丰度空间异质性特征尺度为29.3m，物种多度和香浓指数的特征尺度则为7m。缀块内中尺度上多物种以聚集分布格局为主，一年生草本植物与灌木半灌木植物呈显著正相关，而与多年生草本植物具有一定的竞争关系。在种群内微小尺度上，物种大多呈现由种子扩散导致的聚集分布格局；流动沙丘物种间相关性不显著，而固定沙丘优势物种的竞争或互利关系在特定尺度内有所变化，而丘间低地大部分优势物种间呈显著的负相关关系。大尺度上植被空间异质性主要由地形地貌等环境因素制约；中尺度上植被空间异质性主要由土壤养分等环境要素和种间关系等生物要素共同作用；微小尺度上植物分布格局主要取决于种子扩散等生物因素..本项目基本构建了我国半干旱内陆沙地中具有典型沙丘缀块破碎化生境的物种分布特征、格局和尺度以及环境因素的网格状数据，同时通过二者之间的协同或归一化分析，阐明了不同物种分布格局以及选择不同描述植物变化的指数随尺度变化的特征，确定了不同特征尺度阈值，为后续研究提供基本取样标准的重要科学依据。