College of Agriculture and Natural Resources
Center for Land Use Education and Research

What We're Measuring

Core Forest Explained

Class Descriptions | What the Literature Tells Us | A single-pixel sized core?

Class Descriptions

  Class Description
  Core Forest in general Forest pixels that are relatively far from the forest-nonforest boundary. Essentially these are forested areas surrounded by more forested areas.
  Small Core Forest Core forest patches that are less than 250 acres.
  Medium Core Forest Core forest patches that are between 250-500 acres.
  Large Core Forest Core forest patches that are greater than 500 acres.

What the Literature Tells Us

In the forest fragmentation maps, we divide the core forest into 3 categories to indicate the viability of the core patches with respect to the size of the patch. These three categories – small (< 250 acres), medium (250-500 acres), and large (>500 acres) - are based on the guidelines specified in an extensive literature review conducted by Environment Canada (2004).  Again, all areas designated as “core” are greater than our “edge width” of 300 feet away from non-forested areas.

The literature suggests that total forest cover within a landscape has a greater role in maintaining biodiversity than forest patch size (Lee et al. 2002). However, the importance of forest patch size is still clearly significant for certain species (Lee et al. 2002; Mortberg, 2001; Villard et al. 1999; Andren 1996). The Environment Canada report (2004) suggests that 250 acres should be considered the absolute minimum forest patch size needed to support area-sensitive edge-intolerant species. The recommended minimum forest patch size is 500 acres, as this is likely to provide enough suitable habitat to support more diversity of interior forest species.  These two guidelines are reflected in the medium and large core categories in this study.  The smallest core size in this study is smaller than these habitat-based guidelines, based on the fact that these smaller areas are still valuable from forestry and other perspectives.


  • Andren, H. 1996. Population responses to habitat fragmentation: statistical power and the random sample hypothesis. Oikos, Vol. 76, pp. 235-242.
  • Environment Canada. 2004. How Much Habitat is Enough? (Second Edition) A Framework for Guiding Habitat Rehabilitation in the Great Lakes Areas of Concern.
  • Lee, M., L. Fahrig, K. Freemark and D.J. Currie. 2002. Importance of patch scale vs. landscape scale on selected forest birds. Oikos, Vol. 96, No. 1, pp. 110-118.
  • Mortberg, U.M. 2001. Resident bird species in urban forest remnants: landscape and habitat perspectives. Landscape Ecology, Vol. 16, No. 3, pp. 193-203.
  • Villard, M.A., M.K. Trzcinski and G. Merriam. 1999. Fragmentation effects on forest birds: Relative influence of woodland cover configuration on landscape occupancy. Conservation Biology, Vol. 13, No. 4, pp. 774-783

 A single-pixel sized core?

Because of the way the landscape fragmentation model works, it is possible to have a single core forest pixel surrounded by edge forest. Take, for example, a patch of forest in the land cover map that is about 700ft across. Since we are using a 300ft edge width, the pixel at the center of the forest patch is further than 300ft from any non-forest feature. Therefore, it will be identified as a single pixel core forest surrounded by edge forest, although functionally it is unlikely to act as a core forest.  See the Core Forest Explained section to find out more about our core forest categories.

1 pixel core

The grid to the left shows the minimum case in which a pixel can be called core. The center pixel is a solitary core pixel that is surrounded by edge forest (yellow) and non-forest (gray). Notice that each edge is 3 pixels, or 300 ft.

The take-home message: A single core pixel is part of a forest patch of AT LEAST 700ft by 700ft, or 490,000 square feet, or 11.25 acres.