Orchards have undergone significant changes due to the widespread usage of dwarfing rootstocks. Older blocks of 250 trees per hectare have been replaced by plantings of 600 to 2,500 trees per hectare. Ultra-high-density systems, with more than 5,000 trees per hectare, also are under test in some regions. The transition to high-density, or intensive, orchard systems is a systemic change that encompasses far more than simply an increase in tree density, however. It requires a reevaluation of all orchard practices and operations, and higher managerial skills. The failure to assess a high-density orchard from a total systems approach can lead to erroneous decisions and a failure of the enterprise.
The primary reasons for the adoption of high-density orchard systems have been earlier cropping and higher yields, which translate to higher production efficiency, better utilization of land, and a higher return on investment. Trees in high-density orchards may be freestanding, staked, or supported by a trellis. This is a function of the training system, the tree species, the rootstock and cultivar selected, and the goals of the enterprise. Intensive orchards require a greater outlay of capital, labor, and managerial skills, especially during establishment. The need for greater investment is a function of the larger number of trees and tree supports and will be especially significant if a wire-supported training system is proposed.
134 CONCISE ENCYCLOPEDIA OF TEMPERATE TREE FRUIT LIGHT ENVIRONMENT
One of the primary advantages of a high-density system is increased light interception by the tree canopy. Light distribution within the canopy is a determining factor in flower bud development and vigor. Portions of the canopy that receive less than a third of the ambient levels have a significant reduction in flower bud formation, spur vigor, and spurs that produce flowers. Furthermore, given the influence of light on fruit quality, the few fruit present in the shaded interior of the canopy of standard trees have poor color and lower marketability. High-density systems with smaller tree canopies and better light interception overcome the limitations encountered with standard-size trees.
Light interception in intensive orchards is influenced by both the training system and the foliage density. Most trellised systems have canopies in an almost two-dimensional configuration, and those with vertical or inclined orientations have better exposure to light than training systems with more globular tree forms.
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