Positive feedback between wind-eroded patch size, plant recruitment failure and desertification in semi-arid sandlands

Global climate changes and intensified land use have made desertification one of the most pressing threats to vegetation integrity and associated ecosystem services worldwide. Wind-eroded desertified patches (WEDP) in sandland vegetation communities threaten semi-arid sandland ecosystems. Although the soil seed bank can be replenished by surrounding vegetation, the self-renewal of vegetation within WEDP remains severely constrained by low soil nutrient availability, high maximum day-time soil surface temperatures, frequent aeolian sand dynamics activity and fast soil desiccation. We hypothesized that a positive feedback of environmental harshness inside such patches leads to growing patch size with impoverished current regeneration by seedlings and future potential regeneration from the seed bank. To test this hypothesis, we chose WEDPs of different sizes as representatives of different retrogressive succession stages in sandlands in northern China, and investigated the effects of environmental changes among these successive stages on the densities and composition of soil seed banks and seedling regeneration. We found that WEDPs had unique internal environmental conditions, different from their surrounding area, which caused failed establishment of seedlings even where a substantial soil seed bank existed. Seed bank and seedling densities and composition in WEDPs were strongly influenced by patch size, surrounding vegetation and the prevailing strong wind. Because of the positive feedback between patch size and environmental degradation with retrogressive succession, human intervention is needed to promote future vegetation regeneration in WEDPs. Based on our findings, we propose a combination of the following interventions: (1) building sand barriers or planting native, drought-tolerant shrubs, (2) adding seeds of key local species to enrich the soil seed bank and increase the possibility of successful vegetation regeneration, (3) improving soil stabilization, moisture retention and fertility by covering the soil with local plant litter.