A new study, published in Nature Climate Change in July 2019, investigates the interaction between deforestation and climate change in the tropics. The research was led by Dr Rebecca Senior and Dr David Edwards from the University of Sheffield’s Department of Animal and Plant Sciences, in collaboration with Dr Jane Hill from the University of York’s Department of Biology. The topic is crucial to our ability to predict the overall effect of climate change and thoroughly explores the multiplier effects of both issues working in tandem. 

Image: NASA Earth Observatory

The tropics contain most of the biodiversity hotspots of the world. These hotspots have been identified by the International Union for the Conservation of Nature and are characterised by having a high number of species that are found nowhere else in the world (known as endemics). For this reason, maintaining and protecting these areas is paramount for species conservation. 
Hotspots are threatened by human activity, land use changes and climate change. As the temperature of our planet increases, tropical species must attempt to either adjust to or avoid the warmer climates. To remain in an appropriate temperature range, animals migrate towards the poles or to higher altitudes. This is called a range shift and is a vital mechanism to prevent individual animals from dying or potentially going extinct due to increasing temperatures. Range shifts are dependent on both the availability of similar climate envelopes in other locations, and the connectivity between the current and future habitats. 
Large areas of deforested land in tropical forests can prevent range shifts and therefore leave species vulnerable within habitats as they become more and more inhospitable. The barren and fragmented land left by deforestation means that animals have limited food and shelter and can’t survive the crossing to higher altitudes. Deforested land can often span many miles which further reduces the chance of successful range shifts. 
The tropics are also vulnerable to entirely novel climates and will experience higher temperatures than anywhere else as global warming continues. Species will be unable to adapt to climates they have never experienced before and will be unequipped to face temperatures exceeding their thermal safety margins, the range of temperatures in which they can survive.
Dr Senior et al assess the potential for species to reach similar climate envelopes in the future, which they call “climate connectivity”. They conclude that, “over 62 per cent of tropical forest area is already incapable of facilitating range shifts”, and over the 12 years of their study, deforestation severed connections for a further 27 per cent of the surviving forest.
“The average tropical forest, for any given realm, is not sufficiently connected along a temperature gradient to enable species to avoid climate change by shifting their distribution,” they add.
Even in regions with large connected areas of land mass, such as the western Amazon, the Congo Basin and New Guinea, the pathway to the projected target climates was thousands of kilometres. Even after this migration, species may still experience a few degrees’ warming. 
Overall the study highlights the vital need to curb global warming and, on a more local scale, change the way we manage forests in the tropics. Connecting forests along climate gradients should be a priority when there is opportunity for protecting and restoring the tropical forests. The availability of ‘green corridors’ may be the saving grace of many species and ensure we preserve the maximum biodiversity possible.  


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