Out of the shadows: ecology of open ecosystems

ABSTRACT

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.

KEYWORDS:

• Alternative stable state
• fire ecology
• grassy biomes
• mammal herbivory
• shrubland
• trophic control
• Grubb Review

Acknowledgements

Many people have helped me develop the concept of open ecosystems over the years. I am particularly grateful to those who hosted me on field trips in different parts of the world. Seeing ecosystems at first hand is always first prize, especially when interpreting widely used words such as ‘forest’. For laying the foundations, I am most grateful to Guy Midgley, Ian Woodward, Sally Archibald and Carla Staver. In recent years, Juli Pausas, Nikki Stevens and Caroline Lehmann have helped stimulate and refine ideas or come up with the data to test them. I thank William Gosling for inviting me to write this review and the editors and reviewers for their critical contributions. It is a personal pleasure to write a review honouring Peter Grubb as a thank you to him for memorable field trips and stimulating conversations.

Disclosure statement

No potential conflict of interest was reported by the author(s).