Oak natural regeneration and conversion processes in mixed Scots pine stands

Abstract

Summary The main task of the study was to fi nd out if spontaneous oak regeneration can play an important role in conversion processes of mixed Scots pine stands to native broadleaved forests. The paper examines the amount and structure of oak natural regeneration under different gap sizes and defi nes the optimal gap size for initiation, growth and development of oak regeneration. The investigation was conducted in managed forests in the Garwolin Forest District in the central part of Poland. All gaps, defi ned as openings in the canopy ≥ 20 m 2 in area, intersected by a transect were measured. All seedlings and saplings were counted in circular plots (5 m 2 ) evenly spaced along the long axis of each gap to assess the regeneration in 91 gaps. Data on stand structure and regeneration under the stand canopy were collected in four circular plots established in the stands. It was found that oak regenerated in all gap sizes and under stand canopy. The number of oak seedlings and saplings signifi cantly depended on the gap size. The highest frequency of oak seedlings less than 0.10 m in height was found in gaps of 100 – 150 m 2 and 151 – 300 m 2 ( P 300 m 2 ). The amount of oak regeneration within the gap depended on the number of oak trees surrounding the gap. The most striking feature of the studied stand was the lack of Scots pine regeneration. Pine seedlings up to 7 years old were found in all gaps; however, their quantity decreased with the increase in gap size. The results suggest that the amount of oak regeneration in gaps is suffi cient for the conversion of the old-growth mixed pine stand into a broadleaved tree stand. The results of this study demonstrate the utility of gap-based approach for understanding ecosystem responses to tree cutting. They can be used for the improvement of silvicultural practices in pine stands.