As I walk my solemn journey, I become immersed in the mystical landscape unfolding before me. Towering oaks and sycamore trees look as if ablaze with jagged, fiery red and orange foliage cast against the immaculate azure sky. The brightly-hued shapes spiral down to carpet the surrounding ground. Others are carried off to their fate by an anxious and persistent stream carving its way through the mountain valley. A waterfall up ahead spills quietly down the rock face and splashes into a jade green pool. A cacophony of bird and insect songs meld and echo off the surrounding mountains. In the air there lingers the musty smell of wet, dead leaves and the faint aroma a Mormon Tea. Is this a scene from somewhere in Vermont? Colorado? The Great Smoky Mountains?
The scene just described is actually of Seven Springs, a secluded and lush ecosystem in the middle of the central Arizona deserts. Desert riparian areas are selfsustaining and delicate areas rich with life. As global warming threatens to shift entire belts of wetlands and other vegetation zones, these vulnerable riparian habitats may very well be among the first to disappear. This would be of significant impact to us because several species would be lost, thus weakening the overall stability of the planet as an ecosystem.
Desert riparian areas are a major source of biodiversity, even though they comprise only a small portion of the total land area. These are extremely wellregulated microclimates and contain unique species not found in the surrounding terrain. Deciduous trees such as oak, sycamore and cottonwood are common to these areas as well as tall reeds and grasses. These species are referred to as hydrophylic, (water-loving) and only grow in the proximity of abundant fresh water. The canopy cover created by these large trees helps to maintain cooler temperatures, with riparian zones being about 100 cooler than the surrounding desert. Several species of birds and a variety of mammals make their home to these areas. Several species of fish, including the nearly-extinct Desert Pupfish are also found in riparian streams and pools.
The primary life-giving source in a desert riparian area is water. The source is usually from springs created by high water tables. Streams and pools are formed where the ground is at a lower elevation than the aquifer. The result is a year-round flow of fresh water at or near the surface. Additional runoff from surrounding hills and mountains contribute to the water level as well. This is the case at Seven Springs, where runoff from the surrounding mountains and high water tables create streams and pools.
There is a direct correlation between the flow rate of water in a riparian area and the amount of biodiversity and species abundance. During times of higher flow, the amount of foliage in the immediate area increases proportionally. This in turn provides greater reserves of food for various mammal populations. The result is an increased richness in species. These areas are adapted to thrive within certain water flow parameters. It has been documented that during very dry years, species richness and abundance is significantly decreased. The same holds true for extremely wet years. During floods, there is a decline in biodiversity as well. Tree species richness as related to flow rate can be represented in a bell curve, with moderate flow, producing the greatest species richness. The Seven Springs area is slightly under moderate flow, with a fair amount of tree species. One can find Cottonwood, Willow, Sycamore and Oak trees here, to name a few.
Another parameter directly correlated with species diversity and number is the temperature of the water itself. The types of organisms adapted to live in riparian zones are very sensitive to aquatic temperature shifts. Though there are fluctuations from season to season and from year to year, extreme increases in water temperature can adversely affect the delicate eco logy. Increases in water temperature can increase metabolic rates of aquatic creatures which can cause higher stress on natural food reserves. Disease is also more prevalent when the water temperature is increased. Invertebrate creatures that live in streams are also adversely affected by increased water temperature. Since these invertebrates are at the base of the food chain in this ecosystem, populations of other mammals may decrease. Increased water temperatures have also been shown to alter incubation times of fishes and slows growth in juvenile stages.
The primary mechanism for warming the water in a riparian area is direct solar radiation. The vegetation of the riparian ecosystem is suited to live in water temperatures between 40-600F. If streams were to be heated constantly for a lengthy period of time, the amount of vegetation decreases. Higher water temperature would also cause algal blooms which would deprive the riparian trees and aquatic species of oxygen. This would also result in a general loss of biodiversity.
The areas surrounding the banks of the streams are known as riparian forests. These forests only occur within a belt along streams which ranges from 50-500m in length. The microorganisms that live in the ground in these forests contribute to the nutrients available to vegetation and are adapted to this moist ecotone. An increase in temperature would heat the ground and change the metabolism of the microbes which would in turn affect the amount of vegetation in the area. The many mammals which take refuge in riparian forests would also seek shelter and food elsewhere as food supplies dwindle and water decreases.
What exactly are the implications for riparian areas if a global temperature rise does occur? Imagine a bland desert overrun by sagebrush where there was once that beautiful grove of oaks leaning over leaf-littered pools. Where there were there were once various flowering plants and colorful birds hovering around them, there is only dry and yellow grass.
Seven Springs has already seen some changes over the last decade due to an increase in average temperatures. Flow rates have been reduced to almost zero during the summers, a phenomenon only seen previously during droughts. It is already evident that the growth rates and life expectancies of trees there have been reduced. Also at risk is the extremely rare Gila Monster Lizard. This the only area where it resides in the world. If trends continue, the world will lose yet another irreplaceable and magnificent creature forever.
The global temperature is predicted to rise by 2-30C in the next 50 years. This temperature increase threatens to shift climatic zones. Riparian areas are regulated by fairly constant water and ground temperatures and would not have enough time to adapt to such an abrupt change in climate. These extremely sensitive ecosystems are high at risk if global warming continues to occur. They should be a reminder of the fragility of wetlands and our entire planet as an ecosystem.
REFERENCES CITED:
1.) McReary, Edward L., Interactions Between Small Riparian Animal Communities, National Ecology Science, Inc., New York, 1989.
2.) McReary, Edward L., Interactions Between Small Riparian Plant Communities National Ecology Science, Inc., New York, 1989.
3.) Newton, David E., Global Warming: A Reference Handbook ABC-Clio, Denver, Co., 1993.
4.) Gates, David Murray, Climate Change and its Biological Consequences, millstones Inc., Sunderland, MA., 1993.
5.) Temple, Stanley A., "Easing the Travails for Migratory Birds," Environment Jan. 1998, pp. 3-5.
6.) Metzger, J.P., "Diversity in Riparian Forest Fragments," Plant Ecology, Vol. 133, Dec. 1997, pp. 135-137.
7.) H. Saiko, "Effects of Natural Disturbance on Regeneration of Riparian Forests," Plant Ecology, vol. 132, Oct. 1997.
8.) Flanagan, Lawrence B., "Ecosystem-Atmosphere C02 Exchange," Ecology and Evolution Jan. 1998, vol. 13, pp. 10-20.
9.) Condit, Richard, "Forest Turnover, Diversity and C02," Ecology and Evolution, July 1997, vol. 12, no. 7, pp. 249-254.