ABSTRACT
Thousands of plants have adapted to life in water or wetlands, with a significant proportion of them occurring only in wetlands and shallow water. Many wetlands are readily identified by vegetation and traditional methods relied on plants for wetland identification and delineation (Chapter 6). Plants also serve as a basis for wetland classification (Chapter 8). Yet, despite the value of using plants for these purposes, all wetlands are not simply recognized by vegetation alone. Identifying the point on the gradient at which wetland begins and upland (dryland) ends can be straightforward in areas of high relief or extremely difficult in relatively flat terrain. In the former situations, plants may be used as boundary delineators, but in the latter, soil properties tend to be more indicative of prolonged saturation at or near the surface (Chapter 5). As wetland hydrologic conditions vary from permanent wetness (inundation and/or soil saturation) to periodic or seasonal waterlogging and soil wetness decreases, plant composition changes from a more typical and predictable wetland community to a transitional (ecotonal) community where wetland species intermix with mesic species, making wetland identification challenging and, by plants alone, most difficult and somewhat arbitrary. A multitude of hydrologic regimes associated with wetlands create a diverse set of environmental conditions that requires different degrees of adaptation or tolerance of wetness by colonizing plants. This chapter reviews environmental conditions induced by prolonged wetness, describes plant adaptations for living in wetlands (focusing on morphological properties that are important for wetland recognition) and the concept of a hydrophyte, and discusses how plants can be used to identify wetlands and as indicators of associated environmental conditions. Hundreds of articles and several books have been written about plant response to wetness because many plants experiencing flooding and soil saturation are economically important (e.g., rice, pines, and Atlantic white cedar). Some of the classic texts on the subject include works by Kramer (1949), Hook and Crawford (1978), Kozlowski (1984c), and Crawford (1987, 1989), while Mancuso and Shabala (2010) offer a more recent treatment. Special issues of two journals address recent research on responses of plants to flooding stress: Volume 96 of Annals of Botany (Jackson and Colmer, 2005), and Volume 190 of New Phytologist (Perata et al., 2011). Kozlowski (2002) provides a summary of physiological and ecological impacts of flooding on riparian forests. Readers are encouraged to consult these and other sources for more detailed discussions, especially regarding physiological adaptations.
