Tuesday, April 21, 2015

To fence or not to fence, that is the question*

The stereotypical view of African drylands is often of a parade of elephants marching steadily across endless expanse of savannah grassland –free to roam. Another staple image, especially of African savannah documentaries, is the massive wildebeest migration where thousands of individual animals moving as an aggregation navigating the hazards of the landscape.

Majestic African animal migrations. Main image: "Wildebeest-during-Great-Migration" by Bjørn Christian Tørrissen - Own work by uploader, http://bjornfree.com/galleries.html. Licensed under CC BY-SA 3.0 via Wikimedia Commons. Inset: By Amoghavarsha amoghavarsha.com (Own work) CC BY-SA 3.0 via Wikimedia Commons

In both of these examples, animals are moving with purpose for food and water, because this is how an animal survives in a place where rainfall and vegetation are seasonably variable. These migrations are vital to the survival of many dryland species. But even at smaller scales, and much less dramatically than a massive migration, animals need to move through a landscape to access food, water and mates.

Yet, as human populations spread their influence by altering ecosystems, they increasingly come in contact with wildlife, and often compete with them for space, water and agricultural crops. To reduce these human-wildlife conflicts, people often erect fences to exclude species and steer them elsewhere. Farmers and ranchers, concerned with their livelihood, need to exclude grazers from crops and predators from domesticated animal herds.

Example of a dryland fence barrier. From: Photo by William I. Boarman, USGS, From press release: USGS Report Finds Too Few Studies Assess the Success of Desert Tortoise Recovery Actions, Aug. 10, 2006. http://online.wr.usgs.gov/ocw/g_agassizii/barrier_fence.jpg

While fencing might offer some protection to human interests, fences can also have broad long-term consequences for animal populations. However, it is also increasingly appreciated that fencing can be used as a conservation measure to protect animals from these conflicts and from illegal hunting. In a thoughtful paper on dryland fencing policy, Durant and colleagues argue that current fencing policies are often based on limited information, with an under appreciation of the large-scale, long-term consequences of fencing nature.

Durant and colleagues argue that fencing can result in multiple costs and benefits. They cite an important example –fencing to protect lions. Fences constructed as a lion conservation tool may result in higher lion population sizes –which seems to valid fencing as a conservation tool; but yet analyses showed that when carrying capacities are accounted for, fences may not provide better protection, and further may not be worth the economic and ecological costs.

Lions of the Masai Mara –do they benefit from fences? Photo by Benh LIEU SONG (Own work) CC BY-SA 3.0 via Wikimedia Commons    
 The authors recommend that fencing policy needs to driven by evidence, and not a reaction to human-wildlife conflict alone. The critical factors that they suggest are: 1) Economic sustainability of erecting and maintaining fences, and that the benefits justify the costs; 2) The permeability of the barrier, because not all species will equally perceive the fence as a hard edge, and so a fence may not be a well justified as a universal management tool; 3) Using fencing within a landscape context –fences may complicate how animals deal with natural features, such as cutting off a natural river crossing; 4) Connectivity is critical for both the maintenance of genetic variability within populations and allowing animals to access variable and ephemeral resources; 5) Ensuring that fences do not interfere with or reduce the delivery of ecosystem services; and finally 6) Safeguarding the wellbeing of human communities, especially marginalized and vulnerable groups that might depend on resources from natural areas.

By creating international policy and regulations based on these six criteria, Durant and colleagues argue that sensible fencing policy can be developed, which ensures that fences are used to maximally benefit humans, animals and natural processes.

 *Note -this post was originally written for the Applied Ecologist's Blog.