Processing of leaf litter in a northern jarrah forest stream,Western Australia: I. Seasonal differences

Seasonal differences in the processing of jarrah (Eucalyptus marginata) leaves were examined in a small forest stream of the Darling Range, Western Australia. Processing rates in both summer and winter were very low, placing this species in the slow category (k < 0.005) of Petersen & Cummins (1974).Macroinvertebrates did not contribute to the processing of jarrah leaves during summer and autumn, coincident with the period of peak litter fall. The low quality of detritus entering the streams, and possibly some adverse interactions with the physical and chemical environment, inhibits processing during the summer months. As a consequence, a significant proportion of the coarse-particle detritus entering these streams may be exported unprocessed at the onset of high winter flows.In contrast with previous studies, jarrah leaves were processed at a faster rate during winter than summer. This seasonal difference can, in part, be attributed to the increased density and proportion of shredders at this time. Despite this, the processing of jarrah leaves during winter was very slow and must reflect the poor quality of this detritus as food for invertebrate consumers.     

Spatial and temporal variation in the macroinvertebrate fauna of streams of the northern jarrah forest, Western Australia: community structure

SUMMARY. 1. Streams of the northern jarrah forest, Western Australia, were sampled at twelve sites from December 1981 to December 1982 to examine spatial and temporal changes in the structure of the macroinvertebrate community.
2. The climate of this region is quite predictable by Australian standards and each year a hot, dry summer is followed by a mild, wet winter. Highest stream discharge occurs during winter (June-November) reducing to negligible flow over late summer and autumn (January-May). The low flows in summer were associated with warm water, lower dissolved oxygen, increased concentrations of cations and, in many cases, lower pH.
3. Temporal changes in abundance, diversity and evenness indicated that the invertebrate fauna became dominated by a few taxa during the summer months. Major spatial and temporal changes in the composition of the fauna were detected by classification and ordination. Summer and winter faunas were identified at most sites and were clearly associated with the seasonal changes in the physical and chemical environment. This seasonality is not typical of stream systems previously studied in Australia. Large spatial differences also occurred over small distances among sites in two similar-sized forested catchments.
4. Multiple discriminant analysis and stepwise multiple regression analysis showed that velocity and depth were highly associated with the observed temporal changes in the fauna, though other variables, including concentrations of cations and water temperature, were also important. Spatial differences were correlated with concentrations of cations which may simply reflect differences in the geologies of the catchments.     

Spatial and temporal variation in the macroinvertebrate fauna of streams of the northern jarrah forest, Western Australia: functional organization

SUMMARY. 1. Spatial and temporal changes in functional organization of the invertebrate community of streams of the northern jarrah forest, Western Australia, were examined in the light of predictions of the river continuum concept (Vannote et al. , 1980).
2. The composition of the fauna was largely as predicted for forested headwater streams with detritivores, principally collectors, dominating the fauna. Although shredders are generally considered to be codominant in such streams, they were not abundant in the riffle areas sampled in this study.
3. Some of the observed temporal changes in the composition of functional feeding groups were in agreement with those predicted by the generalized model. The abundance and richness of collectors were higher during the summer than winter, whereas the converse was true for filterers. This corresponded to the presumed availability of deposit and suspended fine-particulate organic matter during summer and winter respectively. Scrapers and predators showed no consistent temporal pattern among sites. However, the density of the latter was highly correlated with the density of other invertebrates, particularly collectors.
4. Temporal changes in the abundance and richness of shredders were not synchronized with the marked summer input of coarseparticulate organic matter. The possible reasons for this, and the role of shredders in Australian stream systems, are discussed.     

Litter decomposition in a temperate and a tropical stream: the effects of species mixing,litter quality and shredders

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