Effects of Permanent and Temporary Edges on Pinus clausa (sand pine) Architecture and Stand Conditions

Effects of permanent (i.e., maintained) and temporary edges with north- and south-facing exposures were studied in sand pine (Pinus clausa var. clausa) scrub, an open-canopied forest type in Ocala National Forest, Florida. On edges and interiors of four stands of each type, we measured canopy tree architecture in 5 x 100 m plots and stand density and basal area in 5 x 200 m plots. Edge effects were modest but often stronger on south- than north-facing edges and along permanent forest roads than temporary edges of clearcuts that were allowed to regrow. Compared to interior trees, those on edges were typically shorter, retained branches lower on their boles, oriented their first branches more towards the edge, and produced more asymmetrical crowns with the long axis extending into the opening; these trends were greater on south- than north-facing edges and along permanent than temporary edges. Contrary to expectations, there were no edge effects on total basal area, dead tree densities, proportions of sand pine trees with leaning trunks, directions of lean, or angles of lean. Instead of an edge effect, most trees leaned southwesterly, which seems related to the northeastern origin of prevailing winds and wind gusts.

Characterizing Ectomycorrhizal Fungal Community Structure and Function of Two Varieties of Pinus clausa That Differ in Disturbance History

Despite the immense amount of diversity present in the soil biota, the ecological and evolutionary processes that regulate species diversity and abundance of ectomycorrhizal (ECM) fungi across space and time remain elusive. In forest ecosystems, ECM fungal diversity may be maintained by periodic disturbances which operate at different time scales due to their effects on host genetic and phenotypic characteristics and the associated environment. To investigate the degree to which these factors shape ECM fungal community composition and function, I sampled 10 independent sites for a pine species indicative of an endangered ecosystem, the Florida scrub, where disturbance history has driven the divergence of a single species into two genetically distinct varieties (Pinus clausa var. immuginata and var. clausa). A total of 300 ECM fungal species were identified based on rDNA ITS sequences, but each variety harbors different ECM species composition and function. A follow-up greenhouse experiment, in which the seed from each variety was grown in its own soil (“home”) and in the soil of the other variety (“away”), suggests these communities differentially impact the growth of their host seedlings. While var. clausa seedlings had the same total biomass regardless of soil origin, var. immuginata had higher biomass in their own soil compared to var. clausa. This is likely due to an increased number of ECM colonized tips in the home soil compared to in away soil. Taken together, these results may suggest different evolutionary histories where structure host genetic and phenotypic characteristics may be important for structuring their dynamics with ECM fungi.