Dynamics of gaps and large openings in a secondary forest of Northeast China over 50 years

Abstract

The gap dynamics in the studied secondary forest were comparable to those of other temperate forests; large openings were filled within 30 years by afforestation; large and medium gaps closed 30–40 years after they formed. Gaps have important roles in forest regeneration and plant succession. However, it is difficult to determine gap dynamics over long time periods at regional scales. We studied how the dynamics of gaps and large openings (oversized “gaps”) changed in a secondary temperate forest over 50 years. We computed the dynamic indices of gaps (16–3257 m2) and large openings (>3257 m2) using remote sensing techniques applied to six satellite images that were taken approximately every 10 years. Additionally, number-based gap closure ratios were calculated at each interval. Gap dynamics were comparable in magnitude to those calculated for other temperate forests, and 60% and 53% of the large and medium gaps had closed within 30–40 and 20–30 years, respectively. The small gaps closed within 10 years, based on ground-level surveys, and 79.2% of large openings that existed in 1964 were covered by artificial forests in 1994. Gaps of different sizes closed within 40 years due to natural regeneration. Large openings had closed within 30 years via afforestation. These findings can be used for evaluating recovery status and for predicting succession times in secondary forest structures driven by gap formation.