Kohler uses several kinds of evidence to show that human effects, not solely climatic factors, were important factors in the abandonment of settlements. One key indicator of change in the environment surrounding these prehistoric settlements is the wood that was used there. Archaeological study of wood charcoal found in hearths dating to the various episodes of occupation indicated that the species use changed in a patterned way. Over time there was a decline in the use of juniper and pinon (native, slow-growing species of trees) and an increase in woody shrubs and fast-growing cottonwood. The species of wood used in the construction of buildings also changed. Fewer pinon were being used, and those that were used seem to be from increasingly old trees, while juniper continued to be from young trees. The implication is that the forest that did remain was changing to relatively more junipers, a tree that is more fire resistant, better able to reproduce in open settings, and less desirable for construction than pinon. Kohler argues that pinon was disappearing from the locale of settlements and that this put an additional nutritional strain on the population, which used nuts from the tree as well as its wood. [■]The relative proportion of different species of animals hunted by people in the region also changed progressively. [■] A final source of evidence was the seeds found in the archaeological deposits, which had blown or been brought to the settlement. [■]As time went on, there was a substantial increase in seeds from pioneer plants, attesting both to agricultural intensification and to an increasingly disturbed local environment. [■]Earlier, they had pursued animals native to woodlands such as deer and rabbit and later, those more at home in open or disturbed environments such as antelope and jackrabbit..
