CLIMATE OF THE TANANA RIVER FLOODPLAIN NEAR FAIRBANKS, ALASKA

This paper describes the general environmental conditions on the Tanan a River floodplain in the vicinity of the Bonanza Creek Experimental F orest. It describes and discusses environmental measurements taken in three successional stages (stage III, an open willow stand; stage V, a closed balsam poplar - alder stand; and stage VIII, a mature white sp ruce stand) and compares these measurements with those taken in adjace nt artificial clearings. The impact of vegetation-mediated changes on soil temperatures, ground surface evaporation, and precipitation regim es is substantial, but the magnitude of these changes declines with ad vancing succession. Removing vegetation in the three successional stag es resulted in warming of the mineral soil and increased surface evapo ration, even though there were only slight changes in air temperature. Vertical soil moisture movement occurs along a tension gradient from the water table for distances of up to 50 cm in the mineral soil and c an be correlated with fluctuations in the river level. Both fluvial an d biotic controls interact to influence the course of vegetation and e nvironmental changes in the successional sequence on the floodplain.