Historical Colonization of South Puget Sound Prairies by Douglas-Fir at Joint Base Lewis-McChord, Washington

Abstract

Abstract Native Americans used fire to maintain prairies in western Washington, but few prairies remain due to land-use conversion and forest encroachment. We describe the process of forest encroachment on former western Washington prairies. We used 1853–1871 General Land Office Survey data to describe the historical prairie and associated timbered area conditions at six Joint Base Lewis-McChord sites (JBLM). We described modern stands growing in these same areas with stem density, Reineke stand density index (Reineke 1933), and site index. After harvesting selected trees we measured decadal tree-ring increments and analyzed trauma rings on 242 Douglas-fir stumps to reconstruct stand development. We plotted individual tree stem diameter growth curves to illustrate patterns of establishment. Douglas-fir density increased in waves from 1878–1938 associated with low-intensity fires with fire return intervals of 10 to 91 years. Historical tree density, which ranged from < 1 to 49 trees ha-1 has increased to 1...