Riparian tree associations and storage, transport, and processing of particulate organic matter in a subtropical stream

Riparian tree associations, leaf-litter storage, transport, and in-stream processing were investigated in subtropical north-central Florida. Chemical constituents, cuticle development, and timing of leaf fall were quantified for 31 species and analyzed with hierarchical cluster analysis. Four groups and two outlying species were classified. Pinus elfottii, uncommon in natural riparian systems, but widely planted regionally in plantations, and Sapium sebiferum, an exotic, were statistically associated with other species, but monocultures could deleteriously affect invertebrates that process leaf litter. These associations can be used to better understand vegetative community management and restoration of riparian areas.; Storage and transport of leaf litter were analyzed biweekly over a year in both a stream and floodplain system. Peak leaf fall occurred from September–December with a smaller peak during January-February and were reflected in peaks of both lateral and longitudinal organic matter transport. Longitudinal transport was also correlated to stream discharge. Floodplain storage was highest during winter 2000–2001 during and after the period of peak leaf fall. Variability in floodplain organic matter increased markedly after flooding during July and September 2001. These results suggest that leaf fall is temporally extended and that fresh litter is available for much of the year.; Leaves of five common riparian tree species were compared for in-stream processing rates. Early-abscising deciduous trees were processed twice as rapidly as late-abscising evergreen trees. In contrast to most temperate streams, shredding macroinvertebrates were rarely collected and appear to be of limited importance in leaf processing. This suggests that fungal and bacterial processing is of greater importance in subtropical streams. Macroinvertebrate abundance on leaf packs decreased from December through May, rather than over the course of processing, suggesting that factors other than leaf availability influence macroinvertebrate abundance. The fact that few shredders were present suggests that invertebrates were using leaf packs as habitat and, in the case of scrapers and collector-gatherers, for feeding fungal communities and zone of fine particulate organic matter accumulation, respectively.; This research fills a void in understanding stream ecosystem function along a latitudinal gradient. Subtropical streams, in terms of both timing of leaf fall and a macroinvertebrate community only loosely synchronized to seasonal leaf inputs, behave in a way intermediate between conditions in temperate streams and those of the Southern Hemisphere.