Climatic and Hydrologic Effects on the Regeneration of Populus angustifolia James Along the Animas River, Colorado

I investigated the dates of origin of riparian for- summer Arizona Monsoon. Extant stands originated in ten ests dominated by Populus angustifolia James, and recent to thirteen discrete periods between 1848 and 1976, in years interannual fluctuation in P. angustifolia seedling with both high spring and fall peak discharges. Expected abundance on a relatively undisturbed 6-mile reach of the seedling abundance and stand-origin dates since 1914 were Animas River in southwestern Colorado. The goal was to reconstructed using climate data, and were extended to 1556 develop plausible hypotheses about the roles of floods and using tree-ring chronologies. Model results suggest good interannual climatic fluctuation in structuring these forests. seedling years occurred more frequently (about every 3.4 I determined the year of origin of 242 recently-established years) than stand-origin years (about every 10-15 years). seedlings and fifty-seven forest stands, and then developed Good seedling years were 2-3 times, and stand-origin years empirical models relating seedling abundance and stand- were 5 times more common from 1848 to 1985 than from origin events to climatic and hydrologic fluctuations. Seed- 1556 to 1848. Recent expansion of P. angustifolia may have lings were most abundant in years with cool winters, wet been favoured by more frequent cool, wet years since 1848. springs, and cool, wet falls (R2adj=0.98). Both good seed-