Tree species diversity and their carbon sequestration potential on cultivated farms in Agago District

Abstract

On-farm tree species retention usually results in maintenance or increase of tree diversity and carbon sequestration. This study evaluated the contribution of trees integrated on-farm to tree species diversity and carbon sequestration potential in Agago District. The specific objectives were to: assess on-farm tree species diversity, examine factors influencing retention of on-farm tree species and determine amount and variation of carbon sequestered by trees on-farms. Multistage sampling procedure based on administrative structure was used to select the respondents from which 60 cultivated farms with tree species retained in them were randomly selected. Each of the sampled cultivated farms was measured and then divided diagonally into approximately four equal sub-units. In each sub-unit a 10 x 10 m plot was demarcated by placing pegs at each corner. Semi structured questionnaires were used in household (HH) surveys while checklists were used during Focus Group Discussions (FGDs) and Key Informant Interviews (KIIs). Transect walks with counts of on-farm trees were then carried out to ascertain diversity of trees on each farm. During on-farm tree species inventory, tree diameter at breast height, height and crown diameter were measured on each encountered tree. HH survey data were analyzed using SPSS statistical packages. On-farm tree species inventory was conducted and total number of trees and each tree species encountered were recorded and used to determine on-farm tree species abundance and diversity in MS Excel Spread Sheet. Shannon Wiener Index was used to compute on-farm tree species diversity. Descriptive statistics were then summarized into frequencies and One-way ANOVA conducted to examine variations. Majority of on-farm trees were derived from retention during farm establishment and protection to allow natural regeneration after farm establishment. On-farm tree species diversity was relatively high (2.836) with up to 26 trees species documented. Factors which influenced retention of on-farm tree species were need for biomass energy, food security, household income generation, farm boundary markings/land tenure security and wind breaks. While Vitellaria paradoxa ssp. nilotica was the main multipurpose tree species retained for provision of food/household income, Combretum collinum and Piliostigma thonningii were retained for biomass energy. Potential on-farm tree species carbon sequestration was between 6.50tCO2/ha for Piliostigma thonningii to 183 tCO2/ha for Ficus ovata. There was a significant variation in the amount of carbon sequestered by different individual on-farm tree species (P≤0.05). Potential carbon sequestration varied significantly in different tree species by Dbh categories (P≤0.05). Results of such a study would be useful in designing and developing sustainable on-farm tree-based technologies like retention of trees in crop fields and on-farm boundaries as a way of maximizing carbon sequestration by trees resilient to environmental changes and attaining more sustainable socio-economic and ecological benefits of on-farm trees. Farmers should also be trained on Forestry Business Development skills to promote marketing of on-farm fruits and associated products as opposed to other non-fruit tree species products (Fuel wood and construction materials). This should be done by farmers being undertaken through a process of forming forestry business organisations and provision of forestry business management advisory services at local levels.