Physiological Considerations for Growing Temperate-Zone Fruit Crops in Warm Climates

Abstract

Temperate fruit trees evolved in climates prevalent between the 34th and 48th northern parallels. Various species of fruit trees are native to China, Kazakhstan, the Caucasus, and Europe. Temperate-zone fruit trees are adapted to a winter — summer climate where the typical winter is relatively cold and the summer is moderately mild. Evolution forced them to produce their crop, form flower primordia during the summer and fall and complete flower development just before bloom during next spring, store a certain amount of reserves to survive the winter and support the early spring activities from reserves before the leaves are old enough to produce photosynthates again. At the beginning of this century, trees started to be planted in large quantities in milder than traditional climates. This introduced new considerations. The trees did not receive enough cold in southern California (Chandler 1925) or in southern Georgia (Weinberger 1950), but also did not need the reserves for the harsh winters. The high summer heat encountered in the new areas also caused new problems especially in the southeastern United States where high night temperatures increased respiratory losses and this limited productivity. Beginning in the 1940s trees were planted in even more tropical climates. This magnified both types of difficulties: those caused by the lack of winter and those created by high summer heat. Problems related to lack of winter cold are discussed in the various chapters of this book. This chapter is limited to a discussion of those problems of tree physiology that are related to the high temperatures of the subtropical areas.

Deceased June 1998