|7.1 Classification of Riparian Species 128|
|7.2 Biogeographical Scope 129|
|7.3 Previous Work 129|
|7.4 Procedures of this Study 130|
|7.5 Results and Discussion 131|
|7.6 Summary 136|
|Appendix 7.1 141|
Most riparian wetlands possess a flora substantially different from that of the surrounding uplands. The distinction is particularly striking in arid and semiarid lands. Because lack of water limits plant growth, wetlands are often the most favorable plant habitats in the Southwest. Soils of wetlands are saturated for all or part of the year, which results in anaerobic conditions that most xerophytes of the adjacent upland habitats cannot tolerate. Moreover, the frequent flooding of wetlands presents insurmountable challenges to slow-growing xerophytes that can persist through long droughts.
Principal riparian habitats in the Southwest include broadleaf gallery forests and marshes or ciénegas along major perennial or near-perennial rivers and streams and mesquite (Prosopis spp.) bosques and giant sacaton (Sporobolus wrightii) flats found on adjacent floodplains. Ciénegas generally are confined to the headwaters of streams in desert grasslands. 1 Gallery forests of major rivers formerly had understory vegetation similar to that of remnant ciénegas. 2-4 Dick-Peddie 5 also considers closed basin, playa and alkali sink vegetation as riparian communities.
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