The scale that you work at is pretty important in some of these things. One kilometer square for the unit of analysis kind of dampened the effects of small scale edge effects. One problem originally with the Grizzly Bear cumulative effects model was it was on such a fine scale that mines and clear cuts that provided a lot of edge came out as real good bear habitat. But with our familiarity with the environment in this region, we feel this map or cost surface is a fairly realistic picture of what is good bear habitat and what isn't.

Vegetation...

We used these two indices--vegetation type and amount of edge--to determine habitat quality in terms of just what was out there for bears. But then we subtracted an index of human disturbance. We derived this index of human disturbance from road data. Roads have been shown to displace Grizzly Bears up to 500 meters or even more. So, we calculated the average road density in each square kilometer pixel. Several studies have shown that road densities of greater than one mile of road per square mile of habitat (0.625 kilometer per square kilometer) is avoided by Grizzly Bears.

So we calculated the road density in each pixel and we gave a fairly subjective weighting to the roads. But this weighting is also somewhat borne out by the literature. Interstate highways had a value of three times as much as gravel roads and two-lane paved roads had twice the value. In this case, low road density areas are dark. We essentially subtracted the road density index from the sum of the two habitat values and we ended up with a cell value that represented its value to Grizzly Bears as best as we could approximate it. This resulted in what we call the Habitat Effectiveness.

When you take into account the humans, you find that bears will avoid even really good habitat if there are humans nearby. They'll often try to get by on marginal habitat as long as it's remote from people. Of course, every bear is different. Some bears learn to tolerate people; some bears learn to even get food from people. And the data indicate that once bears start to become habituated to humans, at least in the Rocky Mountains, they're almost always killed. So trying to provide areas where bears don't learn that or don't have to be forced into areas with humans is fairly important in preserving bears.

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