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Criterion 1 Indicator 5
Rationale
   
When a forest is fragmented into small pieces, ecological processes can be disrupted and habitat areas reduced or unavailable to wildlife. Fragmented areas may be too small to maintain viable breeding populations of some species. The distances between forest fragments can interfere with pollination, seed dispersal, wildlife movement, and breeding. Although some wildlife species decline as forests become more fragmented, other species can benefit, especially those species that prefer forest edges. Ultimately, excessive fragmentation can contribute to the loss of plant and animal species that are unable to re-colonize forests after an area is disturbed. In areas converted to agricultural purposes, remnant forest fragments will provide refuges for many, although not all, components of the original, diverse forest communities (USDA Forest Service, 1997).
 
Once the positive and negative effects of fragmentation are identified, it is important to know the historical context, what changes have occurred, and what current conditions are. This information provides a base from which management decisions can be made.

Can This Indicator Be Quantified
 
Before modern forest management, Pacific Northwest forests were naturally fragmented due to fires, windstorms, landslides, and other disturbances. In order to understand the effects of modern forest management, it is necessary to first understand the historical landscape. The significance of modern activities can only be understood when viewed in this context.
 
In eastern and midwestern forests, fragmentation has usually resulted when forests are converted to other uses, such as urban development or agriculture, and forests are lost permanently. In the Pacific Northwest, forest fragmentation has usually been the result of disturbances such as wildfire or timber harvest. Because each part of the landscape has its own disturbance history, there are many different fragmentation patterns in Oregon’s forests.
 
Although large-scale data is not available on forest fragmentation, small-scale studies have been done on fragmentation’s effects on vertebrate populations in Oregon. Currently, attempts are being made to develop useful metrics to describe and model forest fragmentation. These metrics measure such things as the area of patch type and the frequency distributions of patch sizes, patch density, richness, fractal dimensions, and edge density. These measures may be used in modeling programs to predict interactions among landscape patterns, landforms, living organisms, and landscape processes such as disturbances, biomass trends, and nutrient cycling (Diaz, 1996). An example of such a program is FRAGSTATS (McGarigal and Marks, 1995).

Trends
 
 
Historically, Pacific Northwest forests were fragmented by natural disturbances such as fire and disease. Fire effects differed considerably in terms of frequency and severity from one forest region to another. These variations produced a diverse landscape in which some forests were dominated by small habitat patches while others were characterized by larger forest patches (Agee, 1998).
 
Since the late 1800s, timber harvest and fire suppression have replaced natural disturbances as the primary forces shaping forest landscapes. Perhaps the most important consequence of timber harvest has been the significant reduction in amounts of old growth forest on private land and the high degree to which old-growth forests are fragmented on federal land. Over the last several decades, fire suppression has also changed natural disturbance patterns, and has "de-fragmented" some Pacific Northwest forests (Sallabanks et. al., 1998).
 

Data Source and Availability
  Large-scale data is currently not available on historical forest fragmentation patterns, changes in patterns, and current forest fragmentation conditions in Oregon.

Reliability of Data
  Not Applicable.

Scale
  Not Applicable.

Recommended Action for Data Collection
  Satellite imagery should be taken to determine the current level of forest fragmentation in Oregon. Useful metrics and modeling systems will be necessary to properly use any GIS data obtained for management purposes.

Definitions
  Fragmentation — Fragmentation is a landscape-level process in which a specific habitat is progressively sub-divided into smaller, geometrically more complex, and more isolated fragments as a result of both natural and human activities. It involves changes in landscape composition, structure, and function at many scales and occurs on a backdrop of a natural patch mosaic created by changing landforms and natural disturbances (McGarigal and McComb, 1998).
 
Patch — A unit of homogeneous vegetation.
 
Matrix — The matrix is the most "connected" or continuous part of the landscape, also often the largest in area.
 
Corridor — A narrow, elongated patch that serves as a route for the movement of organisms.
 
Edge — The zone of transition between dissimilar patches. An edge may have features of both adjacent types.
 
Core area — The portion of a patch that is free from edge effects. Also known as the interior habitat (Forman and Godron, 1986).

Selected References
  Agee, J. K. 1998. Disturbance effects on landscape fragmentation in interior West forests.
 
Bunnel, Fred L. What habitat is an island? University of British Columbia, Vancouver, BC.
 
Diaz, Nancy M. 1996. Landscape metrics: a new tool for forest ecologists.
 
Franklin, Jerry F., and Richard T. T. Forman. 1987. Creating landscape patterns by forest cutting: ecological consequences and principles. Journal of Landscape Ecology, Volume 1, no. 1, pp. 5-18. SPB Academic Publishing, The Hague.
 
McGarigal and McComb. 1998. Forest fragmentation effects on breeding bird communities in the Oregon Coast Range.
 
Rochelle, James A., and Jerry P. McIlwain, editors. 1998. Conference summary statement. Conference on forest fragmentation: wildlife and management implications. Portland, OR. November 18-19, 1998.
 
Sallabanks, R., and J. B. Haufler, W. Wall, B. A. Gilbert, P. Heglund, K. S. Warner. 1997. Understanding relationships between landscape composition and nest success of forest songbirds: a study design and preliminary data from the Intermountain Northwest.
 
USDA Forest Service. 1997. First approximation report for sustainable forest management.