Arid Lands Initiative Spatial Conservation Priorities in the Columbia Plateau Ecoregion

Priority areas were identified using criteria from a conservation action planning process completed by the Arid Lands Initiative (ALI). The results provide a spatial design of priority areas that best met ALI goals and objectives. Marxan, a landscape conservation planning tool, identified a portfolio of sites that could protect a suite of target habitats and species.

The ALI Priority Core Areas (PCAs) were ranked by their contributions to under-represented targets by the following approach:

1. Protected Areas were defined by 4 options:

   • GAP 1 and 2;

   • GAP 1-3;

   • GAP 1-4 non-tribal;

   • GAP 1-4 including tribal).

2. The percent of target occurrences within the protected areas was calculated*;

3. If the percent of target occurrences within protected areas was less than the medium overall goal level for that target, that target was considered under-represented;

4. The the percent of each under-represented target occurring in each ALI priority core area (PCA) (these are non-contiguous polygons from Marxan solution) was calculated;

5. For each PCA, the percentages of under-represented targets occurring were summed. Then, to normalize by PCA size, that sum was divided by the number of hexes in the PCA. The resulting number is an index of the contribution that the PCA makes to under-represented targets;

6. PCAs were mapped based on this index. A quantile classification was used, meaning that there is an equal number of PCAs in each category. The bottom fifth are "low," the top fifth are "High", etc.

* In step 2, to save considerable time, the protected acreage was calculated using the Marxan hexagon database. For each 500-acre hex, acreages for the various GAP codes and all the targets were known. A hex was considered protected at Gap level 1 if at least half of it (250 acres) had that status. If this was the case, then all the targets with that hex were considered "protected." This introduces some error, because the target and the protected areas were not necessarily overlapping within the hex. In some cases, targets might be considered protected when they actually do not overlap GAP lands; in other cases, they might be counted as unprotected when they actually are. We assumed that the errors work in both directions and there are 42,000 hexes, so not much bias resulted overall.