Long-Term Effects of Tree Density and Tree Shape On Apple Orchard Performance

A replicated field trial planted in 1997 compared 8 tree densities (range 598-5382 trees/ha) and two tree shapes (conic and V) with 4 apple cultivars ('Gala', 'McIntosh', 'Empire' and 'Fuji') for 13 years. At the lowest density (598 trees/ha), trees were planted on M.7 rootstock and at the second lowest density (840 trees/ha) trees were planted on M.26 rootstock. At all the 6 higher densities, trees were planted on M.9 rootstock. After 13 years, there was a strong negative effect of tree planting density on trunk cross-sectional area. Among M.9 treatments, the highest planting density produced trees about 1/2 the size of the lowest planting density. Tree density was negatively related to cumulative yield per tree, but was positively related to yield per hectare. The cumulative yield per hectare of the highest tree density was 2 times greater than the lowest density. However, tree shape interacted with tree density. At the highest densities the conic shaped trees had the highest cumulative yield while at the lower densities the V shaped trees had the highest yield. Tree density was positively related to canopy light interception from year 2 through 12. The highest tree density achieved 70% canopy light interception by year 7. Cumulative yield was a function of light intercepted. However, there was a significant interaction with tree shape. The V shape intercepted more light, but at high tree densities it had lower yield than the conic shaped trees. Tree density was negatively related to yield efficiency based on light interception or trunk cross-sectional area. Fruit color was negatively related to tree density. However, cumulative crop value based on both yield, fruit size and fruit color was positively related to tree density for both the conic and the V shapes.