Anne Thomas and Richard Gill, Brigham Young University
Life Sciences
Providing water for expanding urban communities in the western United States is a growing concern for city planners and governmental agencies. Landscaping can claim up to 50% of the urban water budget but also has the most potential for water conservation. Landscape water use is highly variable, however, because of species-specific differences in tree water use and because of decision-making by city planners and residents in maintaining trees. The objective of this study is to improve our ability to predict urban forest water use by identifying differences in tree basal area and diversity between neighborhoods that have arisen at different periods of development in Heber Valley, Utah. We classified neighborhoods as established, exurban (rural housing), commercial, or new tract based on age, location, and lot size. We performed a stratified random survey with twenty lots in each category and collected diameter and species data for each tree in the lot. Some of the patterns we observed were easily anticipated, such as higher basal area per hectare in the older, established neighborhoods relative to newer tract housing. Surprisingly, the number of individual trees per hectare in tract and established neighborhoods is very similar. Perhaps of more interest is the low species richness of tract housing compared to exurban communities. Because exurban communities are being replaced by tract housing there is evidence that tree diversity will be lost. Another important aspect of community structure in urban forests is the ratio of conifers to broadleaf trees because of fundamental differences in water use patterns. Conifers comprised twenty-five percent of the basal area in exurban and thirty-five percent in established neighborhoods, as opposed to five percent in tract. Our data suggest that tree diversity is likely to decrease while water demand is likely to increase with changes in urban forests in the coming decade.