Light Thresholds for Apple Tree Canopy Growth and Development

Abstract

Understanding canopy development of fruit trees is important to their management. The tree canopy physically supports the fruit crop. The leaf canopy intercepts light and produces carbohydrates used in growth and metabolic activity, Light distribution within the canopy affects fruit color and quality, and the rate and timing of canopy development affects pest infestation and control. Ultimately, then, canopy development relates to crop quantity and quality and, thus, economic yield of an orchard. The challenge to horticulturists is to manipulate and manage the tree canopy to maximize economic production. Light is an important aspect of canopy studies because of its role in photosynthesis, its function in developmental morphology of leaves and shoots, its role in flower initiation and fruit set, and its importance to fruit development and quality. Because effects of light can be influenced by the tree training system, pruning, or other mechanical means, such as shading, the question arises, How much light is needed to maximize orchard performance? The purpose of this paper is to review some of the relationships of light to apple tree physiology and performance. Two aspects of light and tree canopy development must be considered. First, interception of available light by the total orchard canopy is correlated to total biomass production of the crop system (Monteith, 1977). Second, penetration and/or distribution of light within a single tree canopy must be optimized for maximum tree performance and crop development.