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Growth and distribution of the vegetation of a southern Fraser delta marsh Moody, Anne Irene


The foreshore marshes of the Fraser River estuary are of great importance to migrating and resident waterfowl and shorebirds, transient juvenile salmonids, and to the many other components of the intricate estuarine food web. Urban residential, agricultural and ' industrial developments have encroached, and continue to encroach, upon these valuable foreshore marshes. This study was initiated to obtain information on the factors controlling, and characteristics of, the primary productivity, decomposition and spatial and temporal distributions of the emergent vegetation of Brunswick Point marsh. Sampling locations were selected to cover elevational and salinity gradients in this brackish tidal marsh. Periodic harvesting of the aerial vegetation components was undertaken to estimate net primary productivity. In addition, shoot density, reproductive shoot numbers, and nitrogen content, among other vegetation characteristics were related to such environmental variables as salinity, temperature and elevation. Standing crops for Scirpus mavitirms and Carecc lyngbyei showed a positive association with elevation; peak standing crops were 565 g/m² and 909 g/m² respectively. Shoot densities, reproduction shoot numbers and nitrogen content all showed relationships with elevation. The growth rate of Carex lyngbyei,, the most productive species, was very high, on the order of 20 g/m²/day in-May and June. During litter bag field trials, Triglochin mavitima and Salicovnia vivginiaa decomposed much more rapidly than did S. mavitimus and C. lyngbyei. In vitro decomposition studies reflected a similar pattern for these species. Transplant studies of the species used in the decomposition investigations showed that S. mavitimus tolerated the varied conditions at the four transplant sites best of all. The role of S. mavitimus as .a. pioneer species in marsh succession at Brunswick Point was further supported by field observations and historical information. A simple succession pattern occurs in the Brunswick Point marsh where S. mavitimus and S. ameviaanus colonize the barren mud and sand flats and are succeeded by C. lyngbyei. The emergent marshes of the Fraser River estuary have experienced major modifications during the past century and these may continue. Extensive dyking of high marsh areas has reduced the areal extent of foreshore marshes: The remaining marsh areas are an important source of detrital material which forms the basis of extensive estuarine food webs.

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