Using lidar to assess impacts of forest harvest landings on vegetation height by harvest season and the potential for recovery over time

Tree regeneration and growth is generally reduced at forest harvest landing areas because of significant soil compaction, but it is commonly believed that harvesting in winter can reduce these impacts and that recovery occurs naturally with time. We used lidar data to assess differences in vegetation height between landing and general harvest areas across 79 sites in northern Minnesota, United States, that had been harvested in either summer/fall or winter and between 2 and 175 months since harvest. Vegetation height was significantly lower at landing areas compared with general harvest areas; however, there was no effect of harvest season on the difference (p = 0.50), indicating that impacts occur during all seasons. There was a significant (p < 0.01) positive relationship between the difference in vegetation height and time, regardless the harvest season, providing evidence that recovery occurs across a wide range of conditions within our time period of assessment. Sites with three landings present had the lowest relative landing area and also had the lowest differences in vegetation height between landing and general harvest areas, demonstrating the potential for optimized landing configurations to minimize impacts to growth. Based on our findings, landing areas should be kept as small as reasonably possible during all seasons of harvest, but the need for active reclamation practices is probably not warranted given that recovery occurs within the first few decades after harvest.