Plants have evolved many physiological, morphological, The potential for foliar dehydration tolerance and maxanatomical, and phenological characteristics for imum capacity for osmotic adjustment were compared responding to and resisting drought stress. Certain characamong 12 temperate, deciduous tree species, under teristics and responses to drought do not occur at random standardized soil and atmospheric conditions. but appear to coincide, leading to the sometimes loose Dehydration tolerance was operationally defined as but useful categories of perennial plants as drought lethal leaf water potential (y): the y of the last avoiders or drought tolerators (Ludlow et al., 1983). remaining leaves surviving a continuous, lethal soil Drought avoiders have tissues that are very sensitive to drying episode. Nyssa sylvatica Marsh., and dehydration. They tend to have characteristics that allow Liriodendron tulipifera L. were most sensitive to them to avoid tissue water deficits when soil moisture dehydration, having lethal leaf y of −2.04 and limitation occurs: e.g. deep roots to maximize water −2.38 MPa, respectively. Chionanthus virginicus L., uptake and sensitive stomates to minimize leaf water loss. Quercus prinus L., Acer saccharum Marsh., and Drought tolerators have leaves that can tolerate dehydra-Quercus acutissima Carruthers withstood the most tion, and they tend to have poorly developed responses dehydration, with leaves not dying until leaf y dropped for avoiding dehydration. Tolerators rely on osmotic to −5.63 MPa or below. Lethal leaf y (in MPa) of other, adjustment to survive drought (Ludlow et al., 1985). intermediate species were: Quercus rubra L. (−3.34), Ludlow (1989) has profiled the mechanistically linked Oxydendrum arboreum (L.) D.C. (−3.98), Halesia characteristics that classify these two drought resistance carolina L. (−4.11), Acer rubrum L. (−4.43), Quercus strategies. alba L. (−4.60), and Cornus florida L. (−4.88). In the spectrum of responses ranging from extreme Decreasing lethal leaf y was significantly correlated drought avoidance to extreme tolerance, perhaps the with increasing capacity for osmotic adjustment. C. single most important determinant of drought resistance virginicus and Q. acutissima showed the most osmotic strategy is the dehydration tolerance of the species, which adjustment during the lethal soil drying episode, with is a measure of tissue capacity for withstanding desiccaosmotic potential at full turgor declining by 1.73 and tion (Ludlow, 1989). Dehydration tolerance has been 1.44 MPa, respectively. Other species having reducoperationally defined as the water potential (y) or relative tions in osmotic potential at full turgor exceeding water content (RWC) of the last surviving leaves (called 0.50 MPa were (in MPa) Q. prinus (0.89), A. saccharum the lethal value) on a plant subjected to a slow, continuous (0.71), Q. alba (0.68), H. carolina (0.67), Q. rubra (0.60), soil drying episode (Ludlow, 1989). Drought avoidance, and C. florida (0.52). a strategy possessed by both annual...