What to connect: defining the linkage analysis area

Defining wildland blocks

Every corridor or linkage design must connect blocks of habitat for species. We will call these habitat blocks wildland blocks. Between wildland blocks is a mosaic of wildlands and developed lands in which the wildland blocks are imbedded; we call these lands the matrix. The linkage design typically recommends that portions of the matrix be managed for connectivity.

Besides being composed of potential habitat for focal species, an important characteristic of wildland blocks is that they should be likely to remain wild for at least several decades. Conserving a linkage is an expensive endeavor, and there is no point designing a linkage that connects to a wildland that will soon be converted to urban uses. Although the US Congress may occasionally fund a “bridge to nowhere,” conservationists should not emulate this practice.

The stakeholders and the analyst should agree on how the wildland blocks are defined, because the decision will affect the map of the modeled linkage. Wildland blocks may be restricted to lands with the strongest conservation mandate, such as designated wilderness areas or strict nature reserves. But some wildland blocks have no areas in such status, and consist entirely of multiple use natural lands. Stakeholders must judge whether the conservation mandate of Forest Service, BLM, military lands, tribal lands, state trust lands or private conservation easements justify including these lands in wildland blocks, or whether they should be part of the matrix for which conservation recommendations will be made. As long as the areas to be connected are likely to remain wild, these blocks can be delineated on the basis of what conservation investors have an interest in conserving.

Wildland blocks aren't always the starting and ending points for a corridor

Within a wildland block, habitat for each focal species may be limited in quality and amount, an issue we return to in Modeling habitat patches. GIS procedures will require the analyst to specify a start-end point within each habitat block. A terminus is usually not the same as the entire wildland block. We discuss this in Corridor end points.

How much of the wildland blocks to include?

The analysis area for a linkage design is typically a rectangle that includes

• The wildland blocks to be linked. For a very large wildland block, it may make sense to exclude the “back end” of the block (that is, the end farthest from the facing edges), so that maps can be displayed at a reasonable scale.
• The matrix between the blocks.
• Enough additional matrix to allow the model to identify looping corridors. Constraining the analytical window too much may exclude potential source patches, stepping-stone patches, or other facilitating elements outside the core habitat blocks and intervening matrix. These facilitating elements may be part of an optimal solution.