Stand dynamics and carbon stock in a sal (Shorea robusta C.F. Gaertn) dominated forest in Southern Nepal

Abstract: There is a lack of knowledge about the stand dynamics and carbon storage in forests dominated by Shorea robusta C.F. Gaertn (fam. Dipterocarpaceae) in southern Nepal, especially in forests managed by local communities. Since S. robusta is a major tree species and REDD+ is of growing importance in Nepal, it is necessary to know about these characteristics. This study aimed to explore these stand characteristics, by analysing field data from a 700-hectare big community forest. The data was collected at four occasions, 2005, 2010, 2013, 2015 and consisted of 68 randomly positioned and 500 m² big plots, where measurements of diameter at breast height for more than 4000 trees were done, including 10 % of which also had their height measured. Height models were developed through regression analyses for all major species and existing volume equations were used to calculate the volume for all trees. Biomass was estimated by using existing algometric functions. Carbon stock was assumed to be 52 wt.% of the biomass. An additional analysis was done on single tree development of S. robusta. The standing volume was found to have increased from 99 to 161 m³ha⁻¹ over the years studied. Thus, the periodic annual increment (PAI) was 5.6 m³ha⁻¹1year⁻¹. In 2015, S. robusta accounted for 74 % of the volume and a PAI of 4.1 m³ha⁻¹year⁻¹. Recruitment showed a sudden decrease from 43 to 18 trees ha⁻¹year⁻¹. The above ground carbon stock of trees increased from 48 tonnes ha⁻¹ to 80 tonnes ha⁻¹ resulting in a PAI of 2.9 tonnes ha⁻¹year⁻¹. Standing volume, carbon stock, volume PAI and carbon stock PAI were at the highest in the diameter range between 10 and 30 cm. The strongest correlations with single tree growth of S. robusta were tree volume, tree basal area PAI and current and previous tree basal area. As expected, S. robusta dominated many of the processes in the forest. The carbon stock estimation showed that this type of S. robusta dominated forest under management of a local community, could be a carbon sink to count with.