Changes in land use and housing on resource lands in Washington state, 1976–2006

Changes in human land use patterns have wide-ranging social, economic and ecological implications. How urban and residential areas develop to accommodate population increase can have varying effects on forest and agricultural production from resource lands. Estimates of the amount and type of land use change differ substantially with definitions and analytical methods used. The purpose of this study was to apply a robust manual image classification method to assess changes in land use and housing density across Washington state for a 30-year period. Digital imagery from 1976, 1994, and 2006 was classified to land use, classifications were assigned to a systematic-random grid of 44,554 photointerpretation points on nonfederal lands, and houses were identified within 80-ac circles around each nonurban point. Population in the state increased by 2.5 million people (66 percent) over the 30-year period, during which time 1.16 million acres were converted from forest and agriculture land use classes to residential and urban land uses. The greatest changes were in western Washington, where forest lands declined at a rate of 0.2 percent per year and intensive agricultural lands declined at a rate of 0.7 percent per year. Twenty percent of nonfederal land in western Washington was in developed land uses in 2006. The density of housing structures on lands that remained in forest and agricultural land uses also increased over the period of interest, particularly in areas close to developed land uses. The rate of housing increase on resource lands was greater from 1994 to 2006 than from 1976 to 1994 in eastern Washington, but declined in western Washington. This method of assessing land use change compared favorably with other approaches, and had the advantage that it could be applied consistently to a longer period of time and allowed detailed assessment of patterns at local scales.