On-Farm Tree Abundance and Biomass Carbon Stocks of Grevillea robusta and Eucalyptus saligna on Farms Around Kakamega Forest

Abstract

The integration of trees on farmlands has recently received attention due to their contribution to liv elihoods improvement and climate change mitigation. They pro vide ecosystem services (ESs) like climate change m itigation, improvement of soil fertility, provision of timber and fuelwood am ong others. The choice of trees to plant depends on the role the farmer intends to put them into and the size of the farm. The trees c an either be indigenous or exotic andare mostly pla nted along farm boundaries, in home gardens, as woodlots orientation among others. This study was conducted in western part of Kenya on farmlands that mostly border the Kakamega Forest. The study soughtto dete rmine abundance, distribution and biomass carbon st ocks of Grevillea robusta and Eucalyptus saligna for enhanced climate change mitigation. A total of (N=3,468) trees were inventoried in 80 farms with a total of 27.5ha. The average size of farms where the surv ey was done was about 1.28±1.01 ha. Eucalyptus saligna had a tree abundance 1133 (33%) of the total trees sampled while Grevillea robusta had 2,335 (67%). Two sites were purposively selecte d (Lubao and Tea zone area). In the Lubao site, Eucalyptus saligna abundance was 627 (29%) while Grevillea robusta abundance was 1565 (71%) of the total trees sampled. In Tea Zone site, Eucalyptus saligna abundance was 506 (40%) while Grevillea robusta tree abundance was 770 (60%). Total biomass estimated in the study are a was 3.86±0.21Mgha -1 (1.96Mg C ha -1 ). This was distributed as aboveground biomass (2.8±0.12Mgha -1 ) and belowground biomass (0.87±0.41Mgha -1 ). There was no significant difference in biomass a mong farms in Lubao (F=43.12; p=0.34) and in Tea zone si tes (F=53.12; p=0.23). Lubao site had an estimated biomass of 1.97±0.023Mgha -1 distributed as above ground biomass (1.31±0.043Mgha -1 ) and below ground biomass (0.67±0.023Mgha -1 ). Tea zone site had an estimated biomass of 1.99±0.38Mgha -1 . This was distributed as above ground biomass (1.5 8±0.023Mgha -1 ) and below ground biomass (0.40±0.18Mgha -1 ). Biomass was significantly different among the ag roforestry practices in Lubao (F=13.1; p=0.002) and in Tea Zone (F=29.12; p=0.001). Hedger ow had the highest biomass among the agroforestry p ractices in Lubao (1.91±0.16Mgha -1 ) and in Tea zone sites (1.7±0.23Mgha -1 ). Alley cropping that was only practiced in Lubao had the least biomass (0.0044±0.009Mgha -1 ). The twotree species provided benefits for househ old use and at the same time for monetarysale. Fire wood and timber were the most mentioned (n=80). This was fol lowed by construction material and fencing material . These functions/uses were most preferred by the Eucalyptus grandis