We demonstrated several impacts of disturbance: fewer algae, more runoff, less nitrogen fixation. This chart shows chlorophyll a values in 1997, when this project was winding up. It was our last field season and so we looked at the natural recovery that had occurred in our sites. We found some interesting things.

At Dugway Proving Ground after five years the trampled area actually had higher biomass than the undisturbed area. Now we are unsure why this is so, but I think one of the problems was that just walking around on the crust just one time with heavy boots is not really enough to give the kind of trampling disturbance you get after 15 years of grazing cattle. So I don't think our trampling treatment was severe enough.

And even the burned area, surprisingly, showed recovery. The Great Basin Desert is a moister, cooler desert, and my guess is that when we had quite a bit of moisture in the fourth year of the study, that was enough to stimulate the recovery of these crusts. They recovered in terms of algal biomass at that point. The San Rafael Swell did not recover in the three years following disturbance. At Yuma Proving Ground we never demonstrated much of a difference to begin with, but there wasn't a difference there as well, either in chlorophyll a or in algal numbers as measured with the most probable number method. At Fort Bliss, again recovery hadn't occurred, but it was only three years after the disturbance was applied.

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