Haddad and colleagues have published another useful assessment of the current state of affairs in the corridor world, this time focusing on the possible negative effects of corridors. Their paper includes a well-defined literature review with supportive meta-analyses, and they tackle this tangled subject by parsing out the negative effects into 5 main categories. The punchline is that, when one looks at the evidence thus far, these potential negative effects do not outweigh the potential positive impacts.
To me, this paper rests on the premise of “innocent until proven guilty” which almost runs counter to the idea of the precautionary principle (where the burden of proof of no-harm falls upon the people taking an action). But is there enough research to get us to consensus yet? The authors acknowledge the paucity of empirical research on the 5 effects, especially regarding disturbance and invasive species spread. By saying that they “found no overarching support for concerns that construction and maintenance of habitat corridors may result in unintended negative consequences,” the authors imply that concerns should be either abated or laid to rest. Are we really at that point? If not, then is the solution more research or a different approach to corridor planning? (Or both, of course!)
One next step to resolving this repeated concern might involve the sort of approach that Gregory and Beier (2014) take in their evaluation of response variables around corridor effectiveness. Those response variables are evaluated with respect to 3 criteria (conservation goals, lag time, and cost). Just like positive effects, potential negative effects of corridors can only really be understood if they are related to overarching aims. For example, the spread of invasive plants through corridors (a subject near and dear to this researcher’s heart) may only be a problem if habitat quality for other species is negatively impacted. A mountain lion moving through the corridor may be unresponsive to the presence of plant invaders, but the butterflies drifting along that same corridor may not reach the next habitat patch due to lack of their native food resources. Thus goals around reducing possible negative impacts and how those interact with positive ones should always be part of the process when planning and managing corridors.
Overall, I think this paper functions as a great (first!) status update on this topic, moves us to an area of scientific consensus, serves as a guide to articulating main categories of negative impacts, and pinpoints specific types of studies that should follow this review.
Haddad, N. M., L. A. Brudvig, E. I. Damschen, D. M. Evans, B. L. Johnson, D. J. Levey, J. L. Orrock, J. Resasco, L. L. Sullivan, J. J. Tewksbury, S. A. Wagner, and A. J. Weldon. 2014. Potential negative ecological effects of corridors. Conservation Biology 28(5): 1178-1187.
Gregory, A. J. and P. Beier. 2014. Response variables for evaluation of the effectiveness of conservation corridors. Conservation Biology 28(3): 689-695.