Self-organization and complex dynamics of regenerating vegetation in an arid ecosystem: 82 years of recovery after grazing

Understanding the relative contributions of internal dynamics versus external factors in the process of community assembly is important for establishing guidelines for conservation and restoration of native vegetation. The role of internal dynamics and external factors in the process of community assembly at the local scale is a poorly understood issue in ecology, especially in highly variable environments. We analyse an 82-year spatiotemporal record of vegetation recovering from a history of overgrazing within a semi-arid environment to investigate the relative contribution of internal and external factors on community assembly. Community composition and spatial structure were used as indicators of change over time in four sites within a vegetation reserve, which were subjected to the same environmental constraints, climate and grazing history. The four sites follow remarkably different, asynchronous trajectories characterized by periods of stability interrupted by episodic change. The high variability between sites suggests that initial communities are internally reinforced through random chance events, directing them on different pathways of assembly and self-organization; hence external factors may play a less significant role in long-term community assembly at the local scale than previously believed. These results have important implications for rangeland restoration and conservation in many of the world's semi-arid regions. (c) 2012 Elsevier Ltd. All rights reserved.