Corridors are for connecting

A recent paper in Nature Climate Change by Jantz et al. mapped out potential corridor routes that can be used to connect tropical parks while simultaneously protecting large amounts of carbon.  We (Feeley and Rehm) wrote a response this article highlighting some of the potential problems with this approach (this was subsequently followed by a reply by the Jantz et al.).  The discussion about how to prioritize conservation corridors was also featured in a recent National Geographic News Story available HERE. Our response published in Nature Climate Change is included below:

Priorities for conservation corridors
by Kenneth J. Feeley & Evan M. Rehm

 

To the Editor —

image from mongabay.com: http://news.mongabay.com/2011/0926-hance_tcs_ethanol_atlanticforest.html

The motivation for establishing corridors should be first and foremost to facilitate the moment of individuals and species between otherwise disconnected habitats. image from http://news.mongabay.com/2011/0926-hance_tcs_ethanol_atlanticforest.html

Jantz et al. take advantage of new, high-resolution estimates of biomass and vegetation carbon storage (VCS) to map areas throughout the tropics that, if protected, could simultaneously connect existing protected areas while also retaining large carbon stores. This study highlights how the growing wealth of remotely-sensed data can be used to intelligently and purposely design protected areas. Given the recent emphasis on carbon sequestration in establishing and funding protected areas, it is understandable that the authors took a largely carbon-centric approach when identifying their proposed conservation corridors. We argue, however, that there are more important factors that should be considered when evaluating and prioritizing potential corridors.

The principle motivation for establishing corridors is not to protect VCS but to allow individuals and even entire species to move between otherwise disconnected habitats. Corridors should ideally be set up to connect similar habitats and cross through habitats similar to those being connected. Jantzet al. did not consider the habitat type or the species composition of the areas that they were connecting. Likewise, they did not consider the type of habitats contained within the proposed corridors in relation to the connected protected areas. Instead, the authors proposed corridors that would contain the greatest possible density of carbon and the greatest possible diversity of mammal species. Following these guidelines, high-priority corridors could theoretically be placed through high-biomass, high-diversity areas to connect different low-biomass habitats with distinct species compositions (for example, a corridor of rainforest connecting a savannah park to a dry forest park). In several places, such as in the southeastern Amazon, Jantz et al. suggest corridors through areas that are already heavily-modified and under intense human cultivation.

When prioritizing potential corridors for conservation, it is also important to consider climate-driven species migrations. Climate-driven species migrations are different from the more traditional movements of individuals and species in that they are directional, with species migrating from climatically unsuitable areas to more suitable ones. For example, warming in the tropics will drive species migrations from the lowlands to the colder highlands. By combining species distribution models with general circulation models, it is possible to predict where species are now and where they will need to be in the future, thereby helping to guide where conservation corridors should be established.

Even accepting a carbon-centric viewpoint, Jantz et al. have probably overestimated the long-term VCS in their proposed corridors. By definition, habitat corridors are long and skinny (on average, the proposed corridors are 41–55 km long and 2–3 km wide) and thus a large fraction of the total corridor area will suffer from edge effects. These edge effects can include, for example, biomass/carbon collapse due to the increased mortality of large trees at distances of up to 100 metres from the forest edge and increased susceptibility to fire at distances of up to several kilometres from the edge. The habitat within corridors will inevitably degrade due to pervasive edge effects, causing VCS to decrease over time. In contrast, protecting large, contiguous blocks of natural habitat will result in more stable carbon dynamics as a larger proportion of the protected areas will be core habitat. To protect biodiversity in a changing world, we need an extensive network of large, well-connected protected areas. The corridors that allow for these connections should be designed with species movements, not carbon storage, as the priority.

Feeley, KJ & Rehm, EM. 2014. Priorities for conservation corridors. Nature Climate Change. 4(6): 405-406. http://dx.doi.org/10.1038/nclimate2207

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