Forest regeneration and edge effects : an ecophysiological analysis after gap-cutting

Abstract: As continuous cover forestry is an ongoing topic in todays forest debate, questions are raised about eventual issues connected to the management. It is known that seedling performance can be poor near the edge of harvested areas, and around retained trees. This is a critical issue in transitioning toward continuous cover forestry. In the current thesis, seedling abundance and biomass was quantified as a function of the distance to overstory trees after gap-cutting. The gaps had been either planted, planted and scarified, or left as untreated controls. In each gap, sample plots (2m radius) were laid out at distances -10 m (outside the gap, under canopy), 3 m, 10 m and 20 m. Incoming radiation and soil moisture was also measured in each gap. Seedling foliar nitrogen and isotopic analyses (13C/12C and 15N/14N ratio) were also performed to investigate potential causes of observed patterns. Results showed a clear reduction of growth (94%) at the edge compared to the center of the gaps. Proximity to edge-trees had negative effect on both seedling density and biomass, irrespective of treatment. Nitrogen concentration and 15N/14N was lower along the gap edge, while 13C/12C showed the opposite. No signs of light and soil moisture as limiting factors for seedlings growth could be observed. The results implied that competition for nutrients, mainly N, from retained edge-trees was restraining seedlings. The results also indicated presence of a Nsource accessible for center-seedlings but not edge-seedlings, which could be decomposing mycorrhizal mycelium.