Epilogue

Abstract

A primary goal of this book has been to examine the structure and function of North American desert vegetation using a growth form perspective. We have noted the apparent paradox that desert plants are confronted with a myriad of environmental stresses to which they must adapt, yet North American desert vegetation exhibits high biological diversity in many regions. This implies that there are multiple survival options available to desert plants and that the relatively high topographic and climatic diversity of North American deserts provides a wide array of microenvironments to which different growth forms may be optimally suited. For example, on a given site, plants that are rooted in the near-surface soil would be exposed to an episodic but high quality resource base (i.e., water content in the near-surface soil would rapidly fluctuate between field capacity and air dry), which in turn should favor mesophytes that employ either poikilohydry or the annual habit. Deeper-rooted plants would be exposed to a less variable, but lower quality resource base, which should favor xerophytes with lower resource requirements. At the landscape level, washes represent resource-rich habitats in the desert, but they can also be characterized as habitats in which density-independent mortality factors, such as flash floods, prevail in shaping community structure. As a result, these communities are dominated by life forms with short life cycles and/or relatively high resource requirements and growth rates.