XVI International Botanical Congess

We examined mycorrhizal colonization dynamics on seedling roots following the clearing of two 1-ha areas in a mixed-conifer forest. We planted seedlings of Pinus ponderosa and Pseudotsuga menziesii along transects that began within the intact forest and extended to the center of the clearing. We measured seedling survival and growth together with mycorrhizal colonization and diversity. After two seasons, growth of P. menziesii was not related to position on the transect, yet the percent of roots colonized by mycorrhizae significantly declined with distance away from the intact forest. In contrast, P. ponderosa grew significantly better farther into the clearing, but colonization of its roots showed no relationship with proximity to the forest. These results suggest that the importance of mycorrhizal colonization to regenerating trees may vary by species and resource supply.