Out of the shadows: ecology of open ecosystems

摘要

Biomes of the world have long been assumed to be determined by climate. Major disparities, where open low biomass systems occurred in the same climate zone as closed forests have been dismissed as products of deforestation. Many of these open ecosystems of the world, have been shown to be of ancient origins, stable alternatives to forests, and typically maintained by disturbance regimes. Open ecosystems include some of the most biodiverse regions in the world. They are often consumer-controlled by large mammal herbivores or fire. Mosaics of closed forest and open ecosystems have been interpreted as alternative stable states with each state maintained by positive feedbacks to environmental conditions that maintain that state. For example, flammable grasses maintain fires which consume woody plants, while closed forests exclude flammable grasses by shading them out. Understanding open ecosystems may therefore require some radical revision of familiar ecological concepts, starting with the hypothesis that climate largely determines world vegetation patterns. Open ecosystems function differently from forests in an earth system context affecting the hydrological cycle, rates of rock weathering, and presenting a different planetary surface to solar radiation reaching the earth's land surface. Open ecosystems require explicit attention in conservation policy and management.