The Impacts Of A Logging Road On The Soil Microbial Communities, And Carbon And Nitrogen Components In A Northern Zone Costa Rican Forest

Logging road development is considered as potentially more damaging to a tropical forest than the felling of the actual trees. However, little work has been conducted to determine how logging road development impacts the soil microbial communities and associated C and N cycle activities in tropical forests. This study was conducted within an upland tropical forest in the Northern Zone of Costa Rica that had a 2-year abandoned logging road system (used for harvesting trees felled during a tornado) to determine how development of logging roads affected soil C and N cycle activities, efficiency of organic C use, and bacterial and fungal community compositions. Soil samples from a set of logging roads, the road edges, and adjacent primary forests were analyzed for C, N metrics, the Microbial Quotients, and DNA-based microbial taxonomic community compositions; which were tested for differences using multivariate statistical analyses. The logging road soils had significantly greater bulk density and clay, and lower levels of sand, TN, NO3-, NO3-/NH4+, TOC, C Biomass, and Microbial Quotients compared to the road edge and forest soils. The composition of the total bacterial genera of the road edge and forest soils were similar to one another and different from that of the logging road soils, and the composition of the total fungal genera was unique within each of the three areas sampled. The relative abundance of DNA sequences of N-cycle bacteria were greater, and lignin degrading bacteria and wood rot/lignin degrading fungi were less in the logging roads compared to the edge and forest soils. These results suggest that the rate of recovery of both the C and N cycle activities and associated microbial groups in the soils from the road edges is occurring more rapidly than in the abandoned logging road soils. Thus, we suggest that a new tropical forest management practice should include the movement of the slash and debris from the road edge regions onto the logging roads after abandonment, as it would enhance the rate of recovery of both the C and N cycle activities in the soils, and perhaps begin to address the concern that logging roads add an additional 10-15 years to tropical forest recovery following deforestation.