Landscape Level Characteristics

 For BFL to be successful, we need participants to describe the 2,500-acre block of landscape surrounding their study site. In particular, knowing what percentage of the surrounding area is forested and the amount of edge present will help us to understand the relationship between forest birds and forest fragmentation on a landscape scale.

  We realize that, because these measurements are best taken from aerial photographs or up-to-date topographic maps, it may be difficult for you to provide this information. For assistance, refer to “How to get help: Working with site coordinators” in this section or contact the BFL staff.

  If possible, clearly mark your study sites on a copy (or photocopy) of the aerial photos or maps you used to make your landscape calculations and send this to us. If obtaining the landscape information is causing you to delay sending us your data, please do not hesitate to call a site coordinator or the BFL staff for assistance.

  • Patch Edge—Check all habitat/land-use types that are adjacent to your patch. You may need to answer this question in the field as well as at home while looking at your topographic maps. For habitat types such as secondary growth or natural shrub, you may need to drive or walk around the area surrounding your patch to actually see what habitat types ajoin your patch. Topographic maps will probably show land uses such as residential and industrial/commercial.

  • Forest Patch size—Record the size of the forest patch. (See Appendix B for information on how to measure patch size). Also mark whether you determined the size by measuring (using a grid, pacing, GIS, etc.) or estimating. If you ask the landowners for patch size, try to find out if they measured or estimated it. In situations where one or more forest stands are connected by corridors, try to determine the total size of contiguous (connected) forest.

Making your calculations using the BFL grid

Begin by outlining a 2,500-acre (1,000-hectare) block on the map or photo with the survey point at the center. Use the transparent grid provided or Table 2 to find the dimensions of the block. Within this block, estimate the percentage of land that is forested and the total length of forest/nonforest edge.

  • Percentage of forest—Estimate the percentage of forested land within the 2,500-acre (1,000-hectare) block surrounding your survey point. You can do this in several ways:

• If you are using a 1:24,000- or 1:25,000-scale map or aerial photograph (7.5 minute), you can use the transparent grid overlay provided in this kit to measure percentages.
• If you are using other map/photo scales, you will use a similar method, but with a different grid. You can create your own grid (with 100 or 1,000 squares) using the dimensions in Table 2. If your map scale is not listed in Table 2, you will have to calculate the dimension yourself. If you need help, contact a site coordinator or the BFL staff.
• A site coordinator or professional land manager may be able to help you measure landscape characteristics.

  • Linear distance of edge—Estimate the total linear distance of edge (the boundary between forest and nonforest habitats) within the 2,500-acre (1,000-hectare) block. Measure along the perimeter of all isolated forest patches as well as the boundary of any continuous forest. If several forest patches are located within the same 2,500-acre (1,000-hectare) block, calculate linear distance of edge as a total for all patches within the block (see Figure 1).

  If the boundary between forest and nonforest is fairly simple (straight and not very long) you can use a ruler to measure it, and then convert the measurement to linear feet or meters using the map or photo scale (Table 2). If your scale is not listed and you need help, contact the BFL staff.

  If the edge that you are measuring is convoluted, you can use either a map wheel or the “string method” to measure inches or centimeters on your map, then convert the measurement to linear feet or meters of edge.

• Map wheel—This device is available for in-office use at most land management offices and some engineering or architectural firms. Trace the edge boundary with the wheel to measure edge length, then convert the measurement to feet or meters using the scale of your map or photo (Table 2).
• String method—Lay a piece of string on your map or photo along the habitat edge boundary. Mark the string to indicate the length of the edge, then straighten it and measure the distance between the marks with a ruler. Convert to feet or meters using the scale of your map or photo (Table 2). Waxed dental floss works well because it is tacky and sticks to the photo or map.

 

Isolation measurements

Patch isolation is a measure of the distance from your forest patch to other forest patches. This measurement gives us another way of describing how your forest patch fits into the landscape, and how the arrangement of patches in the landscape might affect forest bird distribution and breeding.

  If your patch is 1,000 acres (400 hectares) or more, you do not need to complete this part of the form. If your patch is less than 1,000 acres, please measure the distance from the edge of your patch to the nearest patch of 100 acres (40 hectares) or more and to the nearest patch of 500 acres (200 hectares) or more. Depending on the type of fragmentation surrounding your patch, you may be able to use the same photo or map you used to measure the percentage of forest and linear edge, or you may need a larger map.

  To measure isolation, find the edge of your patch and look for the nearest neighboring forest patch of 100 acres (40 hectares) or more. Measure the distance on the map or photo from the edge of your patch to the edge of this neighboring patch and convert the measurement to either feet, miles, meters, or kilometers using the map scale (see Table 2). Mark this distance on your form under the category “100 acres (40 hectares) or more” (located on the right under “Isolation measurements”) and indicate whether it was measured in feet, miles, meters, or kilometers.

  Now look for the nearest patch of forest that is 500 acres (200 hectares) or more. Again, measure the distance from the edge of your patch that is closest to the edge of this larger neighboring patch and convert this measurement to feet, miles, meters, or kilometers. Mark this distance on your form under the category “500 acres (200 hectares) or more” and indicate the units. Note that if the first neighboring patch of 100 acres (40 hectares) or more also happens to be 500 acres (200 hectares) or more, you should use the same distance for both measurements.

  If your patch is very isolated (miles from the nearest patch of 100 or 500 acres or 40 or 200 hectares), you may estimate the distance to the neighboring patches. Be sure to mark “mi” or “km” to indicate “miles” or “kilometers.”