CLIMATE OF THE TANANA RIVER FLOODPLAIN NEAR FAIRBANKS, ALASKA

This paper describes the general environmental conditions on the Tanana River floodplain in the vicinity of the Bonanza Creek Experimental Forest. 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 spruce stand) and compares these measurements with those taken in adjacent artificial clearings. The impact of vegetation-mediated changes on soil temperatures, ground surface evaporation, and precipitation regimes is substantial, but the magnitude of these changes declines with advancing succession. Removing vegetation in the three successional stages resulted in warming of the mineral soil and increased surface evaporation, 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 can be correlated with fluctuations in the river level. Both fluvial and biotic controls interact to influence the course of vegetation and environmental changes in the successional sequence on the floodplain.