Spatial and temporal variability of soil moisture and temperature in response to fire in a montane ponderosa pine forest

Wildfires greatly impact ecosystems in the western US, where dry summertime conditions are ideal for forest fire ignition and expansion. The Hi Meadow fire of June 2000 was a high intensity burn that destroyed more than 5,000 ha of ponderosa pine dominated forest near Bailey, Colorado. This research addresses the impacts of the Hi Meadow fire upon the forest microclimate, focusing on changes in soil temperature and moisture. Microclimate characteristics were measured in both a burned and unburned area of the forest in order to determine the impacts of the fire. The objectives of the research were to compare the variability of soil characteristics between and within each of the two sites and to determine the major factors contributing to variability between the sites. To test the temporal variability, soil moisture and temperature were recorded continuously at two adjacent plots within each of the sites with a CR10X datalogger. Partway through the growing season, the litter-duff layer was removed from one of the plots in the unburned area and placed on a plot in the burned area. This provided an indication of the role of the litter layer on soil moisture and temperature in each of the two areas. To examine how soil characteristics varied spatially, a 100 by 100-m grid, divided into 36 points 20-m apart, was constructed in each site. Soil moisture and temperature, and snow depth were measured at each of the points on a weekly basis from October 6, 2002 until present. In addition, canopy cover at each of the points was measured using an LAI-2000. Litter depth was measured at each of the points within the unburned site. The litter layer was completely combusted at the burned site, so depth at each of the points was zero. Marked differences exist between the soil characteristics at each of the sites, suggesting that the Hi Meadow fire did have an impact on the soil characteristics. The differences in soil characteristics were attributed to fire-induced differences in the burned area such as loss of canopy cover, loss of litter layer and changes to soil texture. Results from this study can be used to predict impacts of wildfire in similar environments, allowing for better management of forests after a fire. Additionally, the results can be used to assess the contribution of wildfire to energy changes on local, regional and global scales.