Carbon stock of beech trees at canopy gaps in temperate Hyrcanian forest (Case study: Alandan forest,Mazandaran)

Diverse gap sizes have formed in temperate Hyrcanian forests as a result of different silvicultural operations. Understanding the consequences of these practices on forest stand dynamics can help in deciding the choice of silvicultural methods. Therefore, the purpose of this study was to investigate the effect of canopy gaps on the carbon stock of beech trees and compare it with the adjacent stand and also the interaction between tree attributes and their carbon stock.

The created gaps from single-tree cutting were classified in three classes of small, medium and large area with five replicates for each. Trees were also identified in the adjacent forest to each gap at a distance of 20 m from four directions of them. Tree height, DBH, surface area, volume, length, diameter of crown and carbon stock of trees were measured. One-way analysis of variance was used to compare the average carbon stock index of beech trees in canopy gaps and in different situations as well as for large diameter trees. Independent t-test was applied to compare the average carbon storage in the height classes of the trees and also between the adjacent forest stands with the canopy edges. Pearson correlation coefficient was used to determine the correlation between the index of carbon stock amount with some structural features of beech trees in the edge of the canopy gaps and the adjacent forest stand.

The findings revealed that the carbon stock of beech trees along the gaps' edges differed significantly (p≤0.05). No significant difference in carbon stock was observed for beech trees among different directions at the edge of the gaps (p≤0.05). There was no significant difference between the mean value carbon storage of trees at the edge of the gaps and the adjacent forest (p≤0.05). The highest mean of carbon was observed in the large-sized trees (3725.28 ± 584.49) at the large gaps. The results of correlation showed that with increasing DBH, height, length and diameter of the crown and the volume of the crown, the amount of carbon storage of trees increased at the edge of the gaps and also in the adjacent forest (p≤0.01). 

Findings indicate the effect of canopy gap area resulting from the implementation of single-tree selection method in beech forest. The correlation between the structural characteristics of beech trees such as DBH, height and crown area with carbon stock shows that when applying silvicultural methods (tending and logging) in Hyrcanian forests, structural characteristics Beech trees, especially the abundance of large-sized trees, should be considered with more carbon stocks in them.