Tropical forests in the Anthropocene - new review published

We have a new review paper out in Annual Reviews of Environment and Resources, entitled "Tropical forests in the Anthropocene". This paper reviews and explores the multiple drivers of change in tropical forests, ranging from the Pleistocene through to the 21st century and beyond.

I wrote this paper with colleagues in the US, Sweden and Poland, in one of the most enjoyable and stimulating paper-writing processes I have ever engaged in. We never met in person in the entire process, but ideas and critiques whirled and swirled back and forth in a way that was immensely creative and educational for us all. In addition, we sent it out for informal review to several senior tropical forests scientists, who all provided constructive informal reviews and pointed out areas we had missed or where we had over-reached in interpretation.

We were keen to ensure that this paper did not become a gloomy catalogue of impending tragedies, and to look for realistic and pragmatic paths forward for tropical forests. Quoting from the paper:

While there are many reasons to be concerned about tropical forests in the Anthropocene, we intend this review to be neither a gloomy catalogue of threats, nor a paean of resilience optimism. Instead, our approach is to (i) recognize and describe the reality of the Anthropocene for tropical forests and of the altered tropical forest ecosystems that are emerging, and (ii) drawing on this review, identify the major challenges, unknowns and opportunities that can assist in navigating the tropical forest biomes through the challenges of the early Anthropocene.

The paper is available here:

Malhi Y. , Gardner T.A., Goldsmith G.R., Silman M.R., Zelazowski P. Tropical forests in the Anthropocene, Annual Review of Environment and Resources, Vol. 39: 125-159. DOI: 10.1146/annurev-environ-030713-155141

The figures in this paper are particularly rich in information, and I describe them below. They are all freely available (with underlying data) on Figshare.

Facets of Anthropocene change in tropical forests

Figure 1 Facets of Anthropocene change in tropical forests.


(a) Presents the extent of evergreen tropical forests and other dense broadleaf forests within the tropics. Gray shading represents the extent of forest in the 1700s before the onset of the Anthropocene. Green shading represents current extent; dark green represents the least disturbed areas, which consist almost entirely of evergreen forests (95%). Red shading represents the most intense clearance over the period 2000--2012 (≥10% per 10 km2), using Landsat data. Inset plots summarize data (area shown in km2) for the tropical Americas, Africa, and Southeast Asia with Australasia (“Asia”) and also employ a more conservative definition of undisturbed forests (black outline), using a 5-km buffer from any high-intensity human influence , which is assumed to give a more reliable representation of areas with robust faunal assemblages.


(b) Human population density (within forest mask only) and fire intensity as two proxies for the overall anthropogenic pressures on tropical forests. Fire intensity in seasonal forests includes both natural fire dynamics as well as anthropogenic pressure.


(c) Potential future impacts of climate change and enhanced CO2 concentration at 4°C global warming on humid tropical forests. Dark gray areas mark the climatological niche of these forests derived from the current climatological conditions (water stress and annual precipitation) and are predicted to remain in such a niche by all climate models assessed in this analysis. The gray-red-black scale indicates the risk of climate change--induced dieback, the number of climate models reviewed that predict humid rainforests would no longer be viable under a global warming of 4°C. Isoclines represent the average local warming in degrees Celsius for a mean global warming of 4°C. Light gray areas show the current extent of seasonal forests. 

A high-resolution version of the figure and underlying data are available at http://dx.doi.org/10.6084/m9.figshare.1018766.

The early Anthropocene bottleneck and the future of tropical forests 

Figure 2 The early Anthropocene bottleneck and the future of tropical forests. The composition, condition, and dynamics of future tropical forest landscapes will be largely determined by the size of the bottleneck that forests are experiencing. The severity and duration of this bottleneck, influenced by the current state and heterogeneity of tropical forests and ongoing pressures and management responses, will lay the groundwork for how viable and effective future management actions are likely to be in restoring and conserving native biota and ecological interactions, and hence will influence the likely trajectories of environmental change in tropical forests around the world. Pressures (red belts) include both interacting land- and forest-use-related drivers (including forest clearance and fragmentation, overexploitation of natural resources, and fire), exacerbated by the effects of biotic mixing and cascading species interactions, coupled with atmosphere- and climate-related drivers (including increasing temperatures, CO2 concentrations, and changes in precipitation patterns). These are offset by management interventions (blue hooks) that act to avoid and mitigate ongoing pressures (e.g., through reduced deforestation, responsible forest management, global climate change mitigation) and to rehabilitate degraded areas (e.g., through restoration and enrichment plantings, landscape connectivity, invasive species eradication) to maximize the biological and functional diversity, and therefore long-term ecological resilience, of human-modified landscapes. Our ability to maintain the resilience and diversity of tropical forests around the world depends critically on our ability to foster multiple transitions in the way in which these forests are exploited, managed, and restored---thus avoiding severe bottlenecks, turning around positive feedback cycles of environmental degradation, and facilitating the recovery of elements that have already been depleted. 

A high-resolution version of the figure is available at http://dx.doi.org/10.6084/m9.figshare.1018765.

The location and focus of recent research in tropical forests 

Figure 3 The location and focus of recent research in tropical forests. 

(a,b) A map of recent (2009--2013) field studies in the tropics reveals the dominance of research from the Americas (~65% of the studies) relative to Africa (~13%), Asia-Australia (~16%), and small tropical islands (~6%). Mesoamerica (~33%) is subject to considerably more study relative to its land area than other regions, with the 15 km2 Barro Colorado Island in Panama accounting for ~10% of all field studies.

 (c) From a thematic perspective, most recent studies (~58%) do not possess topic words indicating a focus on key drivers of environmental change in the Anthropocene. Where they do, this research focuses largely on either structural disturbance to the forest (e.g., deforestation, logging, fragmentation; ~49%) or atmospheric change (e.g., CO2, temperature, precipitation; ~29%). Fire, biotic mixing, and defaunation together account for ~22% of the studies. 

Underlying data is available at http://dx.doi.org/10.6084/m9.figshare.1018762. 
A high-resolution version of the figure is available at http://dx.doi.org/10.6084/m9.figshare.1017333.