Canopy characteristics in gaps and its relationship with seedlings and saplings in a spruce-fir forest in the Changbai Mountain area of northeastern China

  Objective  The formation of gaps plays an important role in the forest renewal cycle. The relationship between structure and light factors of canopy in the gap and its relationship with the number and growth indicators of seedlings and saplings were analyzed. In order to explore the impact of characteristics of the gap canopy on seedlings and saplings, the measures to promote the natural renewal of spruce-fir forests were put forward to provide scientific basis for the sustainable management and sustainable use of spruce-fir forests.

  Method  This study investigated the canopy structure, light factors, seedlings and saplings of 48 gaps in the spruce-fir heterogeneous mixed forest of Changbai Mountain in Jingouling Forest Farm, Jilin Province of northeastern China in August 2019. Pearson correlation analysis was used to analyze the canopy structure and light factors in gaps of different sizes and their relationship with seedlings and saplings.

  Result  (1) The main distribution intervals of canopy openness (CO), leaf area index (LAI) and trans total radiation (Tot) were 12%−20%, 2−3 and 11%−21%, respectively. (2) CO, LAI and light factors were significantly different in gaps of different sizes (P < 0.05), CO and trans diffuse radiation (TDF) increased with the increase of forest gap, Tot and trans direct radiation (TDR) first decreased and then increased with the increase of gap. (3) The number of seedlings and saplings of each tree species increased first and then decreased with the increase of CO and Tot. The most suitable CO and Tot for the survival of seedlings and saplings were 12%−20% and 11%−21%, respectively. (4) The gap less than 120 m² was most suitable for the growth of fir seedlings and saplings; while the gap less than 90 m² was the most suitable for the growth of Acer seedlings and saplings; spruce seedlings and saplings grew best in gaps less than 30 m² and 60−90 m²; the most suitable gap area for the growth of Korean pine seedlings and saplings was 60−90 m².

  Conclusion  The main canopy distribution interval of the forest is more suitable for the growth of seedlings and saplings of the four tree species, but when the CO and Tot exceed a certain range, the number of seedlings and saplings decreases. Therefore, the number of seedlings and saplings in the gap can be reduced according to the needs of forest management, or the area of gap can be appropriately adjusted to release growth space for the target tree species and promote its regeneration.