Position: graduated M.Sc. 2000
Project: Forest Harvesting and Food Limitation in BC’s Interior Streams
Stream systems are very dynamic and disturbance events (e.g. spates) can occur relatively frequently depending on the geomorphology and hydrologic regimes of the system (Resh et al. 1988). Most of the stream research to date in British Columbia is from coastal streams where the timing of the high quality autumnal detrital input results in low retention and high export of organic material due to the discharge regime of these streams (Richardson 1994). Interior streams are characterized with a more stable discharge regime in the winter, which may result in greater retention of detritus (Richardson 1994). Snow cover reduces winter litter inputs, but this results in a pulse of litter with spring snow melt (Fisher and Likens 1973). This may influence detritivore productivity and the timing of emergence (Richardson 1994). Discharge regimes exert important controls on the dominance of primary production in streams and spates may prevent the establishment of filamentous green algae (Cummins 1974). Therefore, th e factors that influence macroinvertebrate community structure in BC interior streams may differ from the coast in terms of relative importance and timing of disturbance.
The present management guidelines for riparian areas in the interior of British Columbia were based on fish/forestry interaction research conducted in coastal areas. Although the riparian area management guidelines for streams in the interior of the province are different from the coast, there is little scientific research to confirm the effectiveness of these guidelines. Streams in the dry, interior of BC may react differently from those on the coast as a result of differing climate, soil types, forest cover and a snowmelt dominated runoff regime (Heise 1997). This, coupled with the lack of riparian protection for small, fishless streams, results in a need for research on small, interior streams to give information of the effects of riparian-harvesting in these areas. This research examines whether algae and benthic macroinvertebrates are resource limited in small, forested BC interior streams. Both terrestrial organic inputs and primary productivity energy sources have been examined and the relative importance of each food resource to community composition is addressed. Finally, how riparian forest harvest affects stream food resources and the composition of stream macroinvertebrates is being investigated.
This research is comprised of two parts: both a field study and an experiment. All fieldwork was performed in the Interior Douglas Fir and the Sub-boreal Spruce biogeoclimatic zones in the Cariboo Forest Region near the town of Horsefly, British Columbia. The field study consisted of five streams sampled in two upstream-forested areas and a downstream harvested area. Many physical and biotic factors were sampled at each stream section in the summer and the fall of 1997. The data from these streams are presently being analyzed. The experimental study, conducted in the autumn of 1997, consisted of artificial stream channels set-up next to a creek with both stream energy sources, i.e. leaf litter and algae, manipulated in a 2×2 factorial design (a high and low level of both leaf litter and algae). This experiment was meant to mimic the conditions found in both forested and harvested stream sections with respect to stream food resources. Specific taxa from the macroinvertebrate groups, the shredders and th e gatherers, showed a response to the leaf litter addition suggesting that they were food limited. If the field study shows a similar result in the riparian-harvested stream sections, it would suggest that some macroinvertebrates are food limited due to the decrease in leaf litter input. The lack of a response from the algal community may have been due to the time of year, as the summer is the time of highest algal production, not the fall. As it is believed that stream macroinvertebrates track their food resources, it is not surprising that I did not find a response from those taxa that feed on algae. Perhaps the results from the summer field samples will shed some light on the effects of forest harvest on algal food resources. Stay Tuned….