Variation of shade tree composition and carbon stock of smallholder coffee agroforestry systems along an elevation gradient in Khun Mae Kuang Forest area, northern Thailand

The coffee (Coffea arabica L.) agroforestry systems (CASs) of smallholder farmers can enhance species diversity and carbon stock by managing the shade tree component. This study investigated the variation in shade tree composition and carbon stock of CASs along an elevation gradient in Khun Mae Kuang Forest, Ching Mai Province. Data were collected from 80 plots (20 m × 20 m each) that were divided into groups of 20 plots at four elevation ranges: lower (LE), middle-lower (MLE), middle-upper (MUE), and upper (UE). Differences in species composition and carbon stock were examined to determine the effect of elevation on both characteristics. The results show that the shade tree compositions within MLE and MUE were significantly different, dividing the shade tree composition of CASs according to location (lower vs. upper zone). Species richness and stem density were highest in the lower zone (LE and MLE) forest trees and in the upper zone (MUE and UE) horticultural trees. The total carbon stock at each elevation range was high (186.32–264.12 Mg C ha^–1), and increased with elevation. The aboveground biomass carbon of forest trees contributed the most to the CAS carbon stock, suggesting that the CAS system plays a significant role in carbon storage by promoting the conservation of natural trees in highland agricultural. These findings will help to improve CAS management in mountainous areas, as well as biodiversity conservation and efforts to mitigate climate change.