Spatial dynamics of soil moisture and temperature in a black spruce boreal chronosequence

This study analyzed the spatial dependencies of soil moisture and temperature in a six-stand chronosequence of boreal black spruce (Picea mariana (Mill.) BSP) stands. Spatial variability of soil temperature (T-SOIL) was evaluated twice during the growing season using four transects in each stand, employing a cyclic sampling design with measurements spaced 2-92 m apart. Soil moisture (theta(g)) was measured on one occasion. A spherical model was used to analyze the geostatistical correlation structure; theta(g) and T-SOIL at the 7- and 21-year-old stands did not exhibit stable ranges or sills. The fits with stable ranges and sills modeled the spatial patterns in the older stands reasonably well, although unexplained variability was high. Calculated ranges varied from 3 to 150 m for these stands, lengths probably related to structural characteristics influential in local-scale energy transfer. Transect-to-transect variability was significant and typically 5%-15% of the mean for T-SOIL and 10%-70% for theta(g). T-SOIL and theta(g) were negatively correlated for most stands and depths, with T-SOIL dropping 0.5-0.9 degrees C for every 1% rise in theta(g). The results reported here provide initial data to assess the spatial variability of T-SOIL and theta(g) in a variety of boreal forest stand ages.