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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graphic depiction of our research focus through time

Below is a series of wordles based on the abstracts of papers published by KJ Feeley  and colleagues during each of the last 5 years (2010-2014).  Each wordle word cloud contains 150 words and the size of the words is relative to its prominence in the source text (i.e., the article abstracts from that year). I was actually surprised how consistent the wordles appear from 2010-2013 (we really like “species”!) followed by a very abrupt shift in 2014 (driven by the rash of papers of on the effects of meat consumption).

2010:

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2011:

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2012:

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2013:

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2014:

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Bahamians Eat Meat. A Lot of It.

Originally posted by Dr. Craig Laymen on the Abaco Scientist Blog

Abaco Scientist friend Ken Feeley has been doing a lot of research recently on the remarkable environmental impacts that stem from a single human activity – eating meat.  For instance, here is one short letter he wrote on the issue – read the whole thing. Ken was looking at Abaco Scientist, and it got him thinking about how The Bahamas compares with other areas on per capita meat consumption.  With so many seafood options, it was striking to see meat consumption numbers for the country (as compared with the global average, data from http://faostat3.fao.org/).

This relates back to Ken’s letter because of the vanishingly small proportion of meat and pork demand that is met by internal production. In other words, demand for meat in The Bahamas results in a net export of environmental damage to other countries.   We think so much about environmental challenges within the country, yet this case is an interesting example of how activities in The Bahamas results in damaging environmental effects in other parts of the globe.

Global warming is doing more than melting ice

On last Friday’s (05/16/2014) Science Friday segment on “Antarctic Ice Sheet Slipping Into the Sea“, host Ira Flatow started off by stating that “It’s well known that global warming is having its greatest impacts at the poles”.  I disagree.  I strongly contend that while it is widely believed that global warming is having its greatest impacts at the poles, the greatest impacts are actually in the tropics – at least in terms of impacts to biota and the living world.  The belief that impacts are strongest at the poles comes from the fact that the absolute rate of warming are indeed fastest at high latitudes and the impacts of this warming are very visible is the form of melting ice.  In the tropics, the absolute rate of warming is lower but the relative rate of warming is much higher than anywhere else.  This is because the climate of the tropics are naturally very stable and thus any change in climate, even very small changes, takes the climate outside of the envelope of normal variation, rapidly creating novel climates that we have never seen on earth before and that no species are adapted to.  Similarly,as a consequence of the normally stable climates, tropical species have narrow thermal tolerances and small geographic ranges (ranges which are rapidly shrinking to due loss of natural habitats due to deforestation and land conversion) and consequently they are unable to persist in the face of even minor changes.

Making matter worse, tropical species have less options for migrating to stay at equilibrium with changing climate due to the absence of any latitudinal temperature gradient between 24 and -24 degrees latitude (meaning that while temperate and boreal species can shift their ranges to high elevations or higher elevations to escape rising temperatures, tropical species can only shift their ranges to higher elevations).  The ability of tropical species to migrate is further impeded by the rapid rates of deforestation and habitat loss which is creating thousands of new hectares of inhospitable terrain every day.

We also simply have many more species in the tropics than in the temperate, boreal, or polar realms.  So even a loss of just a small percentage of species will correspond to the extinction of thousands and thousands of species.  Finally, we have a lot more people who directly depend on tropical systems for their livelihoods than we have people that depend on on polar systems.  The loss of ecosystems services resulting from climate change in the tropics will directly impacts billions of people, many of whom are living in poorly developed countries with poorly developed support systems.

Global warming is doing more than melting ice – it is driving the extinction of thousands of tropical species and endangering the lives of billions of people.

Does driving a hybrid vehicle really help you become green?

Unless you live in one of the major US cities with sufficient public transport (New York, Chicago, LA), living in the United States unfortunately comes with the requirement of owning a car. When the day comes to buy a new car, I want to make the most environmentally informed purchase on which car I purchase. Certainly more eco-friendly cars such as hybrids and electric vehicles will be in the mix.

Hybrid and electric vehicles are all the rage these days due to the ‘greener’ image they portray. These cars are marketed as eco-vehicles but do they really reduce emissions compared to more conventional vehicles? The short answer is yes.

Does driving this really make me green?

Does driving this really make me green? photo from hybridcars.com

Critics (coming largely from the US auto industry) of eco-friendly vehicles argue that the energy used in the advanced technologies required to make a hybrid or electric vehicle end up harming the environment relative to conventional automobiles. Critics are partially correct in pointing out that the manufacturing process and materials used to make advanced batteries in eco-friendly cars drive up the energetic cost of production. However, the energy used to make a car accounts for anywhere between 5-20% of the total energy of an automobile from cradle to grave. That means between 80-95% of the energy used by a car over its lifetime comes from fossil fuels burned while driving the vehicle. More fuel-efficient vehicles more than compensate for the increased manufacturing energy costs through reduced energy consumption during day-to-day driving.

That said, owning an eco-friendly car doesn’t necessarily make you ‘green’. At the end of the day hybrids still run on fossil fuels and emit harmful greenhouse gases. Driving patterns such as urban vs. highway driving or driving aggressively as opposed to defensively can greatly reduce the efficiency of hybrid cars. In addition, driving a hybrid still uses much higher amounts of fuel and releases more emissions than public transport (excluding airplanes) or walking/biking.

Pure electric vehicles do not directly emit greenhouse gases but do so indirectly because they are running on electricity produced from a fossil fuel based power plant somewhere (assuming that the household is not run exclusively on solar or wind derived energy sources). In the US, much of the electricity delivered to households is generated by coal burning power plants. If an electric vehicle is charged with only electricity derived from coal-burning sources, the emissions cost of operating the electric vehicle is on par with a conventional automobile, or in some cases even worse

Where does the electricity come from to power your electric 'green' car? Photo from bbc.co.uk

Where does the electricity come from to power your electric ‘green’ car? Photo from bbc.co.uk

How often you replace your car can also greatly offset any eco-efficiency advantages of driving a hybrid or electric vehicle. One study based on European Union countries recommends changing cars only at 20-year intervals in order to justify the amount of energy used to manufacture a new hybrid vehicle. Some of this cost is obviously offset if you are einstein-bikepurchasing a used car but the cost of manufacturing a car cannot be ignored.

The moral of the story for me is that when I buy my next car I should look at hybrids and
choose a car I can drive for the next few decades. Or I could simply move to a place that doesn’t require a car and be more like this guy.

The ability of species to migrate depends on the species

Evan Rehm of the upwithclimate team has published a letter in the Proceeding of the National Academy of Sciences (PNAS) responding to a recent article by Freeman and Freeman. Evan’s letter is copied below.  You can access the Freeman and Freeman’s original article and their reply to Evan here and here.

 

Rates of upslope shifts for tropical species depend on life history and dispersal mode

The recent paper by Freeman and Class Freeman (1) adds to a growing body of literature documenting the upslope distributional shifts of tropical montane species in response to climate change. Armed with just a handful of studies from the tropics, the authors compare upslope shift rates between tropical and nontropical species and conclude that tropical species are, on average, shifting their distributions faster than temperate species. On the basis of this broad comparison, the authors contend that tropical montane species are more sensitive to temperature changes than are temperate species. Although this is a laudable first attempt to synthesize basic patterns of range shifts in tropical species, I believe that the authors drew spurious conclusions because they overlooked some basic ecological differences between taxa.

Following the example of Freeman and Class Freeman, and incorporating an additional publication on tropical trees in Costa Rica (2), I compared the upslope shifts of temperate and tropical species, but now separating plants from animals. This morenuanced analysis shows that shift rates (observed/expected shift rate) in tropical plants are similar to those of temperate plants (tropical plants: 0.63 ± 0.33, n = 3; temperate plants: 0.51 ± 0.33, n = 6; t4.1 = −0.53, P = 0.625), contradicting the contention that tropical species are in general more sensitive to climate change. For animals, the shift rates for temperate species do lag behind those of tropical species (tropical animals: 1.07 ± 0.62, n = 5; temperate animals: 0.28 ± 0.26, n = 22; t4.3 = −2.74, P = 0.047), but the difference is only marginally significant.

Dispersal ability can play a leading role in determining current and future species’ ranges, especially for plants (3). Animals have the ability to move to new areas when their current locations become climatically unsuitable. Conversely, upslope shifts of plants largely depend on seed dispersal and successful recruitment into new habitats, with large range shifts occurring over several generations (4).

It is not surprising that plants, whether tropical or temperate, are lagging well behind climate shifts, whereas tropical animals in general appear to be keeping pace. If tropical plant species are indeed more sensitive to temperature changes than temperate species, the lagged migration response shown here could mean that tropical plant species will have elevated extinction risks because they cannot adapt to changing temperature conditions in situ, and their migration rates are occurring much slower than what is required to keep pace with climate change.

I caution that making generalizations of how tropical species will shift upslope with increasing global temperatures is not possible at this time. The reality is that our knowledge of species-specific responses remains extremely limited, especially in the hyperdiverse but understudied tropics. For example, we are only now beginning to appreciate the important role that microclimate refugia may play in moderating the effects of climate change, particularly in topographically complex areas such as mountains (5). By acknowledging the differences between taxonomic groups, we see that tropical plants are not shifting their ranges faster than temperate species and are not keeping pace with climate change.

 vs. 

Rehm, EM. 2014. Rates of upslope shifts for tropical species depend on life history and dispersal mode. PNAS 2014 111 (17) E1676; published ahead of print March 21, 2014, doi:10.1073/pnas.1403417111