Some riparian habitats are subject to routine fluctuations between inundation and drought and taxa adapted to these sites must exhibit a degree of resilience to extremes of soil-moisture gradients (
Devall and Parresol, 1998;
Konings and Gentine, 2017). Indeed, a high degree of resiliency and plasticity to both drought and waterlogging is not the case for most bottomland-dwelling angiosperm species (
Niinemets and Valladares, 2006a, 2006b). However, some examples of documented outliers include
Alnus maritima (Marshall) Muhl. ex Nutt. (
Schrader et al., 2005),
Pinkneya bracteata (W. Bartram) Raf. (formerly
Pinkneya pubens) (
Stewart et al., 2007),
Taxodium distichum (L.) Rich., and
Magnolia virginiana L. (
Nash and Graves, 1993). In their evaluation of drought tolerance of seven
Magnolia L. species, Sjöman et al. (2018b) corroborated the ability of
M. virginiana to tolerate drought better than its congeners. In the wild,
M. virginiana is found almost exclusively in bottomland habitats (
Preston, 1989) and the related taxa involved in their study are usually found inhabiting mesic sites, yet multiple reports have corroborated the ability of
M. virginiana to surpass its congeners in drought tolerance.
Species that belong to the genus
Carya exhibit strong taproots that persist beyond their juvenile development stages (
Thompson and Grauke, 1991). Although in this study we have reported drought tolerance predictions, other studies recommend the potential for some
Carya species to use drought avoidance strategies.
Sparks (2002) suggests that
C. illinoinensis, with its strong taproot, is phreatophytic, and will grow to the water table and that this taxon cannot be grown on dry sites (
Sparks, 2005). Although all hickories are noted for the development of a taproot, it is unclear if all
Carya species are accurately classified as phreatophytes. In their study of a population of oaks and hickory in central Missouri,
Parker et al. (1982) provide evidence that
C. tomentosa, a species common on mesic sites, may use drought avoidance strategies. Our study is focused on predicting drought tolerance in a few select species. We recognize that some species in this genus, such as
C. tomentosa, may be better classified as drought avoiders. However, given the evidence we have provided for
C. illinoinensis, we question if some species may be better classified as opportunistic, rooting into deep soil horizons when capable or enduring drought via seasonal osmotic adjustment when necessary. We also question whether generalizations of
C. illinoinensis were made through the lens of prolific nut production rather than simple growth and survival.