Harvest traffic monitoring and soil physical response in a pine plantation
Mechanized forest harvest operations induce changes in soil physical properties, which have the potential to impact soil sustainability and forest productivity. The assessment of soil compaction and its spatial variability has been determined previously through the identification and tabulation of visual soil disturbance classes and soil physical changes associated with each disturbance class. This is a time consuming and inaccurate process. The utilization of the GPS provided a means to monitor harvest traffic and transform that information into a detailed map of trafficking. Knowledge of the number of passes (intensity) and their location within the harvest landscape permitted the measurement of soil physical changes in response to the number of machine passes and their spatial structure. Soil bulk density and cone index increased in response to trafficking but the peak values achieved by each varied by sampling time. Soil samples collected immediately after harvest indicated slight response to trafficking but soil samples collected within one year of harvest indicated a greater response, especially in cone index. This was presumably due to differences in soil moisture content at the time of sampling. Spatial structure was evident in the portion of the harvest tract which had less soil moisture. Regardless of temporal differences, bulk density exhibited directional dependence while cone index was isotropic.