Document: JEN-3-53-12

Effects of landscape structure on avian community compostion and probability of occurrence in fire-dominated Mediterranean ecosystems.

RECHEL, J.L.*, D.M.FREEMAN and D.A.LARSON

USDA Forest Service, Riverside, CA 92507-6099 USA ¹

Abstract:
Some populations of migratory and resident birds in the Mediterranean ecosystem in southern California have declined due to many factors including urban developments, habitat conversions, and alteration of the 'natural' fire regime. Indeed, because of fire suppression, the absence of fire may be an important factor that contributes to habitat changes and subsequent population declines. Habitat requirements of birds are often inferred by correlating bird abundance and occurrence with features of occupied habitats. Such correlations might not appropriately weight habitat features. Habitat associations and probability of occurrence were modeled using logistic regression in conjunction with a geographic information system (GIS). The model used topography, vegetation type, structure and diversity of canopy, shrub, and herbaceous layers, fire disturbance, precipitation, temperature, presence or absence of water, and landscape structure. Surveys were conducted on the San Dimas Experimental Forest and the San Jacinto Ranger District for four years (1997 - 2000) to determine which habitat features are important to occurrence and distribution of birds. Data were collected during the spring and early summer (March - June) on 191 fixed circular point plots. Birds were assigned to migrant, partial migrant, and resident categories. Model accuracy was good and ranged from 79.8% to 88%. Important habitat features for migrants and partial migrants were presence of water or high structural diversity and composition of vegetation patches, while for residents were < 30 percent canopy cover, > 70 percent shrub cover, homogenous patches of old growth ( > 40 years) chaparral stands, and adjacency of these stands to mixed oak woodland and riparian areas. This suggests that old growth stands of chaparral are ecologically important to many species of birds and that the more typical fire interval of 50 to 70 years for mixed chaparral is likely beneficial. By calculating probabilities of occurrence and distribution using logistic regression, and using them to derive maps, results more accurately reflect the use of spatial features. These probability maps may be useful to design and implement habitat conservation policies and changes in fire suppression and prescribed fire programs.

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This abstract is being presented at: 2:00 PM in session:
Oral Session #14: Disturbance Effects on Bird Populations.