Successional dynamics and seedling regeneration in Amazonian floodplain forests.

摘要

Amazonian floodplain forests are critical ecosystems that sustain the productivity and diversity of the world's largest and most diverse freshwater system as well as the livelihoods of millions of people. To understand how floodplain forests recover from anthropogenic disturbances in the context of severe flood stress, I tested how environmental stressors and disturbance interact to affect forest recovery at multiple scales in Eastern Amazonian floodplains.;First, I review the land-use history of Amazonian floodplains (Chapter 2). Using laboratory experiments, I tested the effects of short-term and prolonged saturation on seed germination of ten flood-tolerant species (Chapter 3). To understand factors mediating the seedlings, I tested how multiple stressors affect growth and mortality in common garden experiments (Chapter 4). To explore patterns in forest succession, I compared changes in the seedling and tree communities across gradients of livestock activity, flooding, and forest age (Chapter 5). Finally, I estimated aboveground woody biomass storage and accumulation by floodplain forests (Chapter 6).;Seeds of flood-tolerant species had diverse strategies for colonizing floodplains. Mechanical damage to planted seedlings reduced growth and survival during a critical growth window in the low-water season. The effects of damage and flooding were independent, showing how species persist under the combined effects of multiple stressors. Light availability enhanced growth and survival of pioneers. Among trees, flood level and forest age were major drivers of dynamics of change in stand structure and species richness. Seedling species richness of seedlings in the forest was mediated by the interaction of light and flood level, showing that shade was an important limiting factor for seedling diversity. I observed no differences in tree mortality or recruitment across livestock density levels. Biomass accumulation averaged ~5 Mg ha-1 y-1 in forests 15-50 y old, and an average of 70% of biomass gained by tree growth and recruitment was lost to mortality. These results suggested that secondary floodplain forests, despite multiple land-uses, retain high rates of biomass accumulation during secondary succession. These results suggest how floodplain forests sustain high productivity and plant diversity, despite many stressors and disturbances.