Almost any location may experience a rainless period of a few days or longer which puts water stress on trees. Therefore is selecting trees for landscaping purposes where drought is a risk, it is useful to know their drought tolerance. Drought tolerance refers to the ability of trees and other plants to survive a period with an inadequate supply of water, and to recover from it with little or no lasting damage to growth, and leaf, flower or fruit production.
In cases of periods of drought, some plants which are normally evergreen, may become deciduous in response to water stress; this is referred to as a plant being facultatively deciduous. As well, during the period of water stress the rate of growth may slow or nearly stop, and flowering and fruiting diminished or suppressed altogether. These responses reduce a plant’s water demands and allow it to continue to survive for a longer period than if it were functioning normally. Drought tolerance is a genetic trait generally acquired by trees in their native area as an evolutionary attribute. Molecular biology studies of drought tolerance have revealed that it is complex genetic trait, governed by multiple genes working in combination; this factor makes plant breeding for drought resistance a huge challenge. Treeworld has gathered information on the reported drought tolerance of trees and shrubs in their inventory and listed it in the species descriptions as low, medium or high, with some trees designated as low to medium and others as medium to high. In certain instances drought tolerance of a tree is simply not known. Over 100 trees in the Treeworld inventory are considered to have high drought tolerance. Among them are the Acacia spp.; the Geigers (Cordia spp.); the Stoppers (Eugenia spp.); Crepe Myrtles (Lagerstroemia spp.) and the Tabebuia spp. Another 60 Treeworld trees possess moderate drought tolerance. Examples are the Pink Cassia and others (Cassia spp.); the Lignum Vitaes (Guaiacum spp.); the Privets (Ligustrum spp.) and Bay Trees (Pimenta spp)