Soil temperatures vary with topography and vegetation type in taiga ecosystems. At the Bonanza Creek Experimental Forest Long Term Ecological Research (BNZ-LTER) site we are monitoring a number of climate parameters, including soil temperatures and seasonal thaw at 6 locations on the Tanana River floodplain and 3 sites in the uplands on a year-round basis. These 9 environmental stations are located within successional forest stands following fire in the upland and silt-bar deposition on the floodplain. On the floodplain they are located in the following succesional stages: 1) a young willow stage, 2) a young balsam poplar stage, 3) a mixed white spruce-balsam poplar stage,204) a mature white spruce stand, 5) a black= spruce stand without permafrost and 6) a black spruce stand with permafrost. In the upland the sites are located in: 1) a herbaceous-shrub stage following the 1983 Rosie Creek Fire, 2) a mixed paper birch-aspen- white spruce stand that originated following a fire in about 1920, and 3) a mature old white spruce stand that originated following a fire in about 1780.20 In this paper we show differences in soil temperature and seasonal rate and depth of thaw that have developed as result of the successional change in the vegetation. We also compare upland soil temperature and moisture profiles with those under the influence of river level changes on the Tanana River floodplain. One factor of importance in determining the soil temperature profile is organic layer thickness. We show how soil temperature and rate of seasonal thaw vary with organic layer thickness on alluvial terraces on the Tanana River floodplain.

Phyllis C. Adams
Institute of Northern Forestry
308 Tanana Drive
Fairbanks Alaska 99775-5500
Phone: (907) 474-3310
Fax: (907) 474-3350
e-mail: padams@spruce.lter.alaska.edu

Leslie A. Viereck, PhD
Principal Plant Ecologist (retired)
Institute of Northern Forestry
308 Tanana Drive
Fairbanks Alaska 99775-5500
Phone: (907) 474-3324
e-mail: lviereck@spruce.lter.alaska.edu