Riparian Ecosystems: Conservation of Their Unique Characteristics1

--Riparian ecosystems have two essential characteristics: laterally flowing water that rises and falls at least once within a growing season; and a high degree of connectedness with other ecosystems. Other pulses such as fire and hurricanes may also be important in ecosystem maintenance. Changes in hydroperiod or amplitude of water level fluc~uation produce the most dramatic changes in riparian communities. Changes in neighboring ecosystems, which have high rates of exchange of energy and nutrients with riparian ecosystems, may also have significant effects. INTRODUCTION PULSES IN RIPARIAN ECOSYSTEMS Riparian ecosystems occur in both fresh One characteristic that distinguishes and salt water; not all have distinct channels; riparian ecosystems from other wetland ecosystems and dominant vegetation may vary from low, is the lateral movement of water through the herbaceous growth to tall trees with high basal ecosystem together with water level fluctuation, area (Table 1). Is there, then, a set of comprising a significant pulse in the physical unique characteristics that justifies regarding environment. This pulse may occur daily in riparian wetlands as a distinct class of eco­ coastal ecosystems, annually in temperate or systems? This paper identifies two such seasonal ecosystems, or irregularly within a characteristics and discusses the effects of year. Perhaps the most important feature is human-induced perturbations on the stability of that both high and low extremes occur within a riparian ecosystems. single growing season. A riparian ecosystem at any time therefore has an upstream and a down­ stream end, although the directionality itself Table l.--Examples of Riparian Ecosystems may be reversed. Fresh Water Salt Water Diversity in wetland ecosystems seems to be inversely proportional to the length of time during the growing season that soils are satu-­ Forested River swamps Riverine rated. Crawford (1976) pointed out that species Bottomland hardwoods maI'.groves of trees that are flood-intolerant are unable to Cypress strands detoxify end-products of glycolysis in the roots Bosques because of anoxia. Flood-tolerant species can either decrease glycolytic activity in anoxic Nonforested Some marshes Tidal conditions or detoxify the end-products of Some peatlands marshes glycolysis. Several such species are capable of withstanding a short flooding period, although the longer the hydroperiod, the fewer the number of tolerant species. Wistendahl (1958) observed that slight differences in topography and depth of flooding had a significant effect on vegeta­ 1 Paper presented at the National Symposium tion species composition in a floodplain. Franz on Strategies for Protection and Management of and Bazzaz (1977) documented the narrow range Floodplain Wetlands and. other Riparian Eco­ of elevations within which each tree species in systems, Callaway Gardens, Georgia, December 11a floodplain is found, reflecting small but distinct differences among species not only in 13, 1~78. Assistant Professor, School of Forest tolerance of mature trees to flooding but in Resources and Conservation and Center for Wet­ require~ents for seed germination and seedling lands, University of Florida, Gainesville. survival as well. Among the most flexible species