CLIMATIC AND HYDROLOGIC EFFECTS ON THE REGENERATION OF POPULUS-ANGUSTIFOLIA JAMES ALONG THE ANIMAS RIVER, COLORADO

Investigated dates of origin of riparian forests dominated by Populus angustifolia, and recent interannual fluctuation in P. angustifolia seedling abundance on a relatively undisturbed 6-mile reach of the Animas River. Empirical models related seedling abundance and stand-origin events to climatic and hydrologic fluctuations. Seedlings were most abundant in years with cool winters, wet springs, and cool, wet falls. Both good seedling years and stand-origin years were associated with winter blocking in the North Pacific and a persistent late-summer Arizona Monsoon. Extant stands originated in 10-13 discrete periods between 1848-1976, in years with both high spring and fall peak discharges. Expected seedling abundance and stand-origin dates since 1914 were reconstructed using climate data, and were extended to 1556 using tree-ring chronologies. Model results suggest good seedling years occurred more frequently (about ever 3.4 yr) than stand-origin years (every 10-15 yr). Good seedling years were 2-3 times, and stand-origin years were 5 times more common from 1848-1985 than from 1556-1848. Recent expansion of P. angustifolia may have been favoured by more frequent cool, wet years since 1848. -from Author