Size Matters

One of the crowning achievements for wildlife protection in the United States was the establishment of the National Wildlife Refuge system in the 1930s, when the populations of waterfowl were perilously low. The various refuges provided breeding and migratory habitat that has allowed a remarkable recovery of many species of ducks and geese.

Now, the National Wildlife Refuge system is under periodic Congressional attack, with attempts to remove lands from protection to foster land development and with measures to prohibit the addition of new lands to the system, even when they become available adjacent to existing refuges. Writing in the Wall Street Journal of April 24, Shawn Regan urges the National Park Service to stop acquiring new lands and to sell unneeded lands to fund its existing maintenance deficit. These recommendations should be thwarted.  For both National Parks and National Wildlife Refugees, size matters.

A rich scientific literature of ecology shows that the preservation of species is greatest when large, contiguous areas of land are protected.  Species are lost, especially predators with large home range, when preservation focuses only on small fragments of habitat.  One study in Thailand found that nearly half of the species of small mammals disappeared from small fragments of preserved habitat within 14 years of isolation.  Similar rates of loss were observed for birds in newly-created small fragments of Amazonian rainforest.

Small protected areas are often most vulnerable to invasions of exotic species and to human encroachment along their borders, behooving us to increase the size of refuges to minimize their ratio of perimeter to area.  In one area of the Amazon, rainforests lost 36 percent of their plant biomass within 100 meters of the border within a couple of decades of isolation.  Minimizing the length of border while maximizing area has a lot of advantages.

In the U.S., most decisions for land preservation were made after the majority of the land was already fragmented by roads, agriculture and urban areas. But when we see pristine areas such as rainforest fragmented, the lessons learned still apply to us.  Indeed, the most efficient way to preserve biodiversity in North America will be to insure the preservation of large tracts of habitat and to add peripheral tracts of land to existing refuges whenever feasible. Not all park lands need regular maintenance, trails, kiosks, and interpretive signs. Nature does pretty well on her own.  And for many lands, we have only one chance to act.



Ferraz, G., G.J. Russell, P.C. Stouffer, R.O. Bierregaard, S.L. Pimm, and T.E. Lovejoy. 2003. Rates of species loss from Amazonian forest fragments.  Proceedings of the National Academy of Science 100: 14069-14073

Gibson, L., A.J. Lynam, C.J.A. Bradshaw, F. He, D.P. Bickford, D.S. Woodruff, S. Bumrungri, and W.F. Laurance.  2013.  Near-complete extinction of native small mammal fauna 25 years after forest fragmentation.  Science 341: 1508-1510.

Laurance, W.F., S.G. Laurance, L.V. Ferreira, J.M. Rankin-de-Merona, C. Gascon and T.E. Lovejoy.  1997.  Biomass collapse in Amazonia forest fragments.  Science 278: 1117-1118.

Terborgh, J., L. Lopez, P. Nunez, M. Rao, G. Shahabuddin, G. Orihuela, M. Riveros, R. Ascanio, G.H. Adler, T.D. Lambert and L. Balbas. 2001.  Ecological meltdown in predator-free forest fragments.  Science 294: 1923-1926.

Woodroffe, R. and J.R. Ginsberg. 1998.  Edge effects and the extinction of populations inside protected areas.  Science 280: 2126-2128.

3 thoughts on “Size Matters

  1. In the PNW US, mortality is higher along edges of clearcuts, and the microclimate is altered 4-6 times tree height into the forest (Chen et al. 1992, 1999). Larger areas and connectivity between them are essential. See the following link on imagery analysis of land-use change that has occurred in the West:
    “Every 2.5 minutes, the American West loses a football field worth of natural area to human development…”

  2. I whole heartedly support this concept and action. Thank you for your important work.
    Gerard Peer

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