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Haddad, Nick M., David R. Browne, Alan Cunningham, Brent J. Danielson, Douglas J. Levy, Sarah Sargent, and Tim Spira. 2003. Corridor Use by Diverse Taxa. Ecology, 84(3): 609-615.

RELEVANT TO: HABITAT LINKAGES

SPECIES

DESCRIPTION OF DOCUMENT

This document reviews one of the most popular approaches for maintaining populations and conserving biodiversity in fragmented landscapes: retaining or creating corridors that connect otherwise isolated habitat patches. Through large-scale, landscape experiments, the authors found that corridors do in fact direct movements of different types of species, including butterflies, small mammals, and bird-dispersed plants, causing higher movement between connected than between unconnected patches. The authors incorporate new and previously published data to address two specific questions: 1) For which taxa do corridors direct movement? and, 2) What are the magnitudes of the effects of corridors on movement across various types of species (taxa)? The authors also examine a third question: For what taxa do corridors increase emigration? Their results indicate that corridors have the potential to be valuable tools for landscape-scale conservation of diverse taxa and the biological processes that they direct.

MAJOR FINDINGS

1. Corridors are long, thin strips of habitat that connect otherwise isolated habitat patches. They are thought to reduce local extinction by "rescuing" isolated populations (Brown and Kodric-Brown 1977) and by promoting gene flow.
2. Recent studies have demonstrated that corridors can increase animal movement between patches (Haas 1995, etc.), increase population sizes (Fahrig and Merriam 1985, etc.), increase gene flow (Aars and Ims 1999, etc.), and maintain biodiversity (Gonzalez et al. 1998). Other studies have found no corridor effects (Arnold et al 1991, etc.). However, one recent review (Beier and Noss 1998) found that although many studies were inconclusive due to flaws in study design, 10 or 12 well-designed studies demonstrated positive effects of corridors.
3. The authors studied 10 species including 2 butterflies, 2 mammals, 4 plants, one plant pollen, and one bee. Of these 10 species, 5 moved significantly more often between connected than between unconnected patches, and all species showed movement associated with corridors.
4. Results demonstrate that corridors in the experimental landscapes consistently direct the movement of diverse taxa. These results include the first demonstration that corridors affect interact movement of plants.
5. The effects of corridors on movement direction were uniformly large. For all 10 species, at least 68% more individuals moved to connected than to unconnected patches. The low probability that 10 species would show the same positive responses to corridors by chance along led the authors to conclude that the corridor effect is generally significant.
6. For which taxa do corridors increase emigration? The authors cite previously published results from their experiments: corridors did not influence the number of emigrants of any species for which this response was measured, including butterflies and small mammals. The authors' results suggest that emigration of the study species is not determined by landscape pattern.
7. In total, including results from this and previous studies in the experimental landscapes there were only two species of 13 for which corridors did not direct movement. All of the species in this study showed a positive effect of corridors on movement, and none showed a negative response to corridors.

8. Results suggest that corridors may have broader, community-wide impacts. This possibility is typically overlooked by studies of single species. Taken together, the authors' results suggest that corridors have the potential to be valuable tools for landscape-scale conservation of diverse taxa and the biological processes that they direct.

QUESTIONS THIS RAISES FOR THE THREE FORESTS

• Have the Three Forests reviewed potential isolation of sensitive populations because of fragmented habitat?
• Have the Three Forests surveyed or documented use of corridors by specific wildlife? Have the Three Forests completed any work to date that identifies and maps important corridors on the given Forest?
• How might specific corridor identification be included in the Forest Plan revisions? How can the Forests ensure the protection of identified corridors?
• What implications do the results of this study (that corridors are important) have on management of the Three Forests for diverse and robust populations of various taxa?

FOREST MANAGEMENT SIGNIFICANCE

• The Three Forests must identify and map (using GIS) important corridors (if this has not been completed to date) on each Forest as part of the Forest Plan revision process. Wherever possible, the Forests should coordinate with UDWR, adjacent land management agencies and willing private landowners for corridor identification and support.

2. Corridor identification can be completed via developed models (i.e. least cost path) as well as expert opinions of biologists familiar with each forest. This information should be gathered at a landscape level (e.g. the forest or larger) rather than project by project.

1. Identified corridors should be managed so that important ecological process can proceed unimpeded.