“The Ribbon of Green: Change in Riparian Vegetation in the Southwestern United States” is a big book with a big message. Within its 462 pages, authors Robert H. Webb, Stanley A. Leake and Raymond M. Turner use maps and matched, high-resolution photographs to challenge the conventional history of our riparian plant communities.
This offering by the University of Arizona Press examines the condition of Arizona’s streamsides through time. Modeled after “The Changing Mile Revisited,” by Raymond M. Turner, Jan Bowers and Rod Hastings, this book will stimulate plenty of discussion and controversy.
Except for chapters on Utah’s Virgin River and the Mojave River in southeast California, most of the book features Arizona drainages. The conclusions are not what we have come to expect. Gleaned from a repeat photography study of 2,724 photos, we learn that woody vegetation has increased in density and biomass in 73 percent of the matches and showed no change in 15 percent. The remaining views are mostly of stream beds inundated by reservoirs or dewatered by water diversions and groundwater pumping.
The photos make the case that cattle and floods are not long-term enemies of riparian vegetation; the condition of streamside communities is a function of flooding and hydrology. Spring flooding is actually essential to the regeneration of riparian trees. These gallery forests now benefit from narrower stream channels due to arroyo cutting and channelization. Although livestock and beavers impact riparian vegetation, their presence is more effect than cause.
Not all of the before-and-after photo matches are comforting. Although cottonwoods, willows and other riparian trees have increased more than 50 percent, the exotic tamarisk shows an 88 percent increase — mostly downstream from reservoirs.
Some views, including those along major rivers such as the Gila, Salt and Santa Cruz, are downright depressing. The tributaries (including the San Pedro River, Aravaipa Creek, Virgin River, Hassayampa River and Oak Creek) are a different case. Most support as many or more riparian trees than they did 100 years ago.
The authors know their subject. Webb and Leake are research hydrologists with the U. S. Geological Survey; Turner, a retired botanist, is an expert on repeat photography. Enlightening and thoughtful, this book will challenge how we view riparian habitats.
–David E. Brown
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