Many conservation practitioners operate with a common assumption that all ecosystem restoration is good no mater the size of the project area. A new study in the Journal of Applied Ecology contradicts this notion by showing that when it comes to tropical reforestation and the effect on birds, bigger is better and too small may be bad.
The work by Emily Morrison and fellow researchers is groundbreaking not just because it shows the importance of patch size in restoration but because it looks at animal behavior to reach its conclusions. Most studies evaluate restoration success with birds by looking at metrics like species diversity.
This study though looked at just four birds - cherrie’s tanagers, rufous-capped warbler, common tody-flycatcher and plain wren - and compared their insect foraging behavior across restored forest patches of different sizes.
They found that in the smaller patches the birds attacked insects at a lower rate (i.e fewer attacks per minute) and exerted more effort while foraging (i.e more jumping around). They also found that arthropod density was nearly twice as great in larger reforestations (greater than 3500 square meters) than smaller ones (less than 350 square meters).
Together these results indicate that birds in the smaller patches are having a more difficult time foraging for food which may have negative consequences for their fitness. This in turn may impede restoration success given that birds in the tropics play an important role in a number of ecosystem processes such as pollination and seed dispersal. Interestingly, a more conventional assessment looking at just species diversity likely would not have picked up on this problem.
These results have practical applicability because conservationists - whether in the tropics or elsewhere - are constantly weighing restoration size against project cost. Obviously, much more research is needed to determine how widely these results translate to other settings. In the case of tropical forests the authors recommend,
"Thus, forest restoration efforts using a patch-based planting scheme should consider patch size as an important factor that is likely to affect the quality of the patches as habitat for birds that use woody habitat. We recommend that small patches be avoided and that patches of at least a few thousand square metres be planted when resources are available."
--Reviewed by Rob Goldstein
Morrison, E., Lindell, C., Holl, K., & Zahawi, R. (2009). Patch size effects on avian foraging behaviour: implications for tropical forest restoration design Journal of Applied Ecology
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