Optimum pruning intensity for reducing crop suppression in a Gmelina –maize smallholder agroforestry system in Claveria, Philippines

On-farm trials were conducted to assess the effects of four branch pruning levels on maize grain yield, tree growth and stem shape. The experimental plots consisted of Gmelina ( Gmelina arborea R.Br.) trees planted at 1 × 10 m with maize intercropped in the 10 m-wide alleys between lines of trees. Pruning levels consisted of retaining a live crown ratio of 60–70% ( T 1 ), 40–50% ( T 2 ); 30–40% ( T 3 ) and of 20–30% ( T 4 ). At the end of the experiment, the total maize grain yield was highest under the high pruning intensity ( T 4 ) (18.06 t ha −1 ) and lowest under T 1 (14.48 t ha −1 ). Maize grain yield under the pruning regime T 2 and T 3 were 16.08 and 17.21 t ha −1 , respectively. Mean annual increment (MAI) in tree diameter was greater (5.0 cm year −1 ) under T 1 than those at T 4 (4.1 cm year −1 ). Pruning regimes T 2 and T 3 resulted in a MAI of 4.7 and 4.5 cm year −1 , respectively. Financial analysis showed that maize-tree systems under T 4 were more profitable than under T 1 as long as the reduction of the average dbh at harvest were not greater than 1 cm. Pruning trees intensively also generated greater returns from labour than moderate pruning, as the greater maize grain yields under T 4 compensated for the cost of pruning and the lower timber yield. In the context of resource-poor farmers, intensive branch pruning was a practice that prolonged the period of profitable intercropping and was compatible with commercial timber production.