The relative influence of riparian vegetation and geomorphology on trophic
structure was examined at three streams in adjacent catchments of the Frenc
h Massif Central mountains. The study sites differed mainly by the degree o
f anthropogenic alteration of riparian and watershed vegetation, and by val
ley geomorphology. Fishes, benthic macroinvertebrates (grouped into functio
nal feeding groups: FFG), macrophytes and periphyton were sampled seasonall
y between July 1991 and April 1992. At the riffle-pool (10(0) m) scale, ins
tream morphological units appear to control the spatial partitioning of tro
phic resources and their consumers. For example, depositional zones support
ed a specialized trophic structure based on coarse organic matter consumpti
on, whereas in erosional zones (subdivided into lotic and lentic units) per
iphyton and fine organic matter were the main food source. At the reach-seg
ment scale (10(1) to 10(2) m), valley morphology was the primary factor con
trolling the stream ecosystem, but anthropogenic alteration of riparian veg
etation seems to override geomorphological controls on the trophic structur
e. For example, the open-canopied Triouzoune Creek (gentle plateau valley),
characterized by scrapers (>60% by density) and a greater epilithic algal
biomass, had a autotrophic-based structure. At this site, 20% of total fish
biomass was represented by brown trout (Salmo trutta) dominated by fish <1
year old. The other two sites (Vianon and Ozange creeks), with closed cano
pies but different valley geomorphologies (V-shaped moderately incised vall
ey versus a gently sloping plateau valley), were characterized by detrital
organic matter consumers (>50% by density) and fish communities dominated b
y brown trout with high densities of age 1+ individuals. Overall. the resul
ts emphasize the importance of riparian vegetation on the trophic structure
of streams, especially when anthropogenic alteration of riparian vegetatio
n is severe. We conclude that there is a need to better integrate riparian
vegetation into European stream management practices in order to maintain t
he vitality of these systems over the long-term.