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School of Geography

Simon Lewis Dr Simon Lewis

Contact details

School of Geography
University of Leeds
University Road
Leeds LS2 9JT   UK


+44 (0) 113 34 33337

Student hours:
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Work in progress

Current Projects

2004-2009 Evaluating Functional and Biodiversity Changes Across Tropical Forests.

Funded of the Royal Society. The text below is reprinted from Royal Society "Lay Summary" of project


Both climate change and tropical deforestation have regularly been in the news for years. We know they are important issues, but they are often dealt with in isolation. This is largely true both in the wider media and within the scientific community. For example, remaining 'virgin' tropical forests are thought by many to be pristine environments. However, we now know that human impacts on the environment, such as rising air temperatures, affect even remote areas. Moreover, the 21st century will see these global environmental changes reach unprecedented levels: air temperatures will continue to rise, and atmospheric carbon dioxide concentrations will reach levels unprecedented over the past 20 million years. Alone, these global changes will change tropical forests, while in concert with other human impacts the implications are likely to be staggering: deforestation alone is predicted to cause the sixth mass extinction in evolutionary history. Indeed, scientists have called this period the Anthropocene: we are living through truly epoch-making times.

My research focuses on the impacts and interactions of multiple anthropogenic global change phenomena and tropical forests. A number of strands of recent research show that apparently undisturbed tropical forests have altered dramatically over recent decades: (1) they have become a net carbon sink, absorbing carbon and buffering the rate of climate change, (2) their tree populations have become much more dynamic, and I have recently shown (3) that these two trends have occurred simultaneously within the same forest stands, as forest productivity has increased. So far however, studies of long-term changes in tropical forests have investigated only stand-level properties: only the behaviour of all the trees together has been studied. These stand-level changes beg several questions: (1) are some tree species becoming more abundant at the expense of others? (2) What do these changes mean for critical ecosystem functions, such as how much carbon these forests store and hence their contribution to either slowing or accelerating the rate of climate change? (3) What drivers are causing such changes? Thus, the aims of this fellowship are to understand the recent, current, and likely future functional trajectory of the tropical forest biome, by conducting the first comprehensive investigation into changes in forest composition and function across the tropics.

Research Methods

I will tackle this ambitious agenda by: (1) using a unique resource of >200 long-term forest monitoring plots from across the tropics where each tree is identified and tracked over time by periodic re-measurement, which I have helped develop, and (2) by collecting and collating currently disparate data on individual species' effects on ecosystem functions, such as carbon storage. Firstly, I will assess where, when and by how much different taxa (species and higher groupings) have altered. Secondly, by assigning each stem in the plot monitoring database with a value for a functional trait, such as the amount of carbon that a species typically holds in its wood, and then assessing the spatial and temporal trends in these traits, I will be able to quantify the impacts of these changes on ecosystem functions, and the likely factor(s) driving these trends. The key barriers to this work have been the lack of plot data, poor understanding of species' ecological behaviour, and inconsistencies in tree nomenclature across the tropics. My recent work has already assembled the plot data needed, while collaborations with other experts (most of whom I already work with) will allow functional trait data to be collated. Finally, the nomenclature problems across space and time for >200,000 tree records, and >5,000 species in the plot database can be practically resolved for the first time, as new Internet tools available this year will allow complex searches across key herbaria worldwide. Hence the discovery of long-term compositional trends, using a variety of statistical techniques, will now be possible for the first time.

Wider Implications

The results from this research will be of great societal importance for two reasons. Firstly, will surviving tropical forests remain a carbon sink - currently equivalent to the fossil fuel emissions of entire European Union - or will rising temperatures and other changes cause them to become a source? Secondly, as tropical forests house more than half the world's species, the interactive balance of millions of plant and animal species is bound to change, even within the largest areas of forest. What does this mean for global biodiversity conservation? On the ground monitoring of forests, as this project proposes, to understand how, when and where changes in composition and carbon balance of tropical forests are occurring will provide essential information, possibly including early warnings of more radical changes. This will assist policy makers and wider civil society to make better-informed choices about the kind of future world we want to live in.

Previous Projects

  • 2000-2003 'Changing Tropical Forest Dynamics: a critical evaluation of physical, chemical and biological drivers'.
    NERC funded (with O. Phillips & Y. Malhi).