The vegetation immediately surrounding water bodies (i.e. riparian or floodplain vegetation)
is particularly important to freshwater ecosystem health, as it shades water bodies
(regulating water temperatures and providing thermal refugia) and supplies organic
material such as falling leaves, insects, and woody debris to freshwater systems. The deforestation
of Amazonian floodplains is considered to be one of the major forces behind
208 WORLD WILDLIFE FUND
the decline of Amazonian fisheries, as deforestation in these seasonally flooded areas
has led to massive erosion, increased sediment load, and a decrease in large, woody debris
in the river (Goulding et al., 1996). Although its function has not been studied extensively
in tropical rivers, large, woody debris has been shown to play numerous important
roles in temperate river systems, including altering flow to create habitat
heterogeneity (i.e. stepped channels and deep pools) and helping to determine river
channel form and stability. Woody debris also has a long residence time in most water
bodies, and provides substrate, food, and shelter for a wide range of plants and animals
(Bilby and Bisson, 1998; Petts, 2000).