Growth, yield and carbon density of bagras (Eucalyptus deglupta Blume) in smallholder tree-based agroforestry systems in Northern Mindanao, Philippines
2012
Palma, R.A.
Agroforestry systems using Eucalyptus deglupta Blume for timber and biomass production are essential options for smallholder agroforestry farms in Northern Mindanao, Philippines for the reason that they amalgamate timber and food production. Matching tree species to appropriate site conditions and stand management is vital for sound agroforestry timber production. In this study, the multiple linear regression analysis was used to develop an appropriate prediction models for estimating height, yield and biomass expansion factor (BEF) from soil chemical properties (i.e. pH, OM, P, K), physiographic characteristics (i.e. elevation, slope, aspect), stand attributes (i.e. age, site index, spacing, basal area, provenance), rainfall temperature, biomass inventoried volume (BV) of bagras planted in alley cropping, boundary planting and woodlot or block planting. Data were purposively taken from established agroforestry systems in Northern Mindanao, Philippines were sampling extended over the entire range of tree sizes and environmental conditions. Results showed strong association of independent variables with the dependent variable based on the output of multiple regression analysis in all site index, yield prediction and biomass expansion factor models. It was found about 68%, 86.10% and 95.4% of the total variance of height for alley cropping, boundary planting and woodlot, respectively can be explained by age, pH, OM, P, K, elevation, slope and aspect. Likewise, it was observed that about 96.20%, 86.6%, 88.70% proportion of variance of yield can be predicted from site index, age, spacing, basal area, provenance, temperature and rainfall. Comparison of yield and aboveground biomass accumulated by bagras from alley cropping, boundary planting and woodlot relative to the abovementioned equations was in order woodlot greater than boundary planting greater than alley cropping. Future climate scenario had positive and negative effects on the yield of bagras depending on the type of agroforestry system. Decreasing rainfall was predicted to diminish yield of bagras planted in alley cropping (decrease with decreasing rainfall). On the other hand, the predicted increase in seasonal mean temperature will have positive impact on the yield of bagras establish in boundary planting. Predicted yield of bagras will increase with decreasing seasonal mean rainfall in woodlot. Finally, models for three smallholder tree-based agroforestry systems in Northern Mindanao were validated using an independent data set from the same provinces. Validation showed that there were no significant differences between the predicted and observed height and yield for bagras at 5% level.
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