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Design of riparian zones: temporal response of secondary productivity to stream geomorphology and classification.
Pearsall, Isobel A.
One of the premises of EBM is to ensure maintenance of primary & secondary productivity, where primary productivity is defined as the rate at which biomass is produced per unit area by plants, & secondary productivity is defined as the rate at which biomass is produced per unit area by heterotrophic organisms (Begon et al. 1981). One method of trying to attain this is to ensure that there is representation of all ecosystem types (represented by the site series surrogate model for the Central Coast EBM). Another method would be to retain representative habitat (through a structural analysis). The availability of habitat (in which ecosystem classification may or may not be representative) is agreeably one of the primary factors that influences distribution & abundance of species. However, not all ?habitat? is created equal, & it is widely recognized that riparian areas facilitate a much higher density of species. If riparian areas provide a disproportional representation of habitat use (& types) & populations are generally not proportional to habitat area, & then a 1:1 ratio is not appropriate. If we are to accept this logic, then it should also be correct to assume that secondary productivity is not consistent among all riparian areas. Giving consistent steam size, one of the variables may be the geomorphic characteristics of the stream (alluvial vs. semi-alluvial vs. non-alluvial). The objectives of riparian management include protecting aquatic habitats, water quality, & riparian habitat. Current management approaches in British Columbia include delineation of management zones in which timber harvest is not allowed (riparian reserve zone) or where harvest is allowed with limitations of equipment use or levels of tree removal (riparian management zone). Widths of reserves depend on stream size, presence of fish, & the downstream use of water for domestic supply (BC FPC 1995, FPPR 2004). Streams lacking fish & not used for drinking water, & very small streams with fish (<1.5 m bankfull width) have no required reserve. However these streams do get a management zone intended to keep heavy machinery out & away from the streambank during harvest operations. Fish-bearing streams > 1.5 m get a reserve width that increases from 20 to 30 & then to 50 m based on increasing channel widths. A 50 m reserve is intended to serve more than the immediate objectives of LWD supply, & the large alluvial rivers with this reserve size may have more riparian dependent wildlife species than smaller streams. One of the major questions is how wide should a buffer strip be? Clearly, fixed buffer sizes are simple to administer & to implement. However, variable width buffer strips have the potential to improve stream protection based on individual stream reach characteristics. Washington & California currently implement variable width buffer strips under their respective forest practice act regulations. Use of variable widths would allow buffer strip layout to more closely mimic natural ecosystem disturbance, in keeping with "new forestry" concepts. However, very few studies appear to have been carried out to determine the advantages or disadvantages of variable width over minimum fixed width buffers. Interfor (& some other licensees) has an alternate riparian strategy where they can vary widths based on site level information. Prescribing foresters need to make a decision based on an ?ecological rationale that is supported by riparian factors?. Riparian factors include the need to buffer the system from deleterious materials that affect water quality & fish habitat, channel & bank integrity, as well as the role of trees & understory vegetation in conserving water quality, fish habitat, wildlife habitat & biodiversity. Interfor takes into consideration the stream bank (slope, soil type, stability), wind firmness (current stand & future rotations), channel type (e.g. less sensitive entrenched to least sensitive seasonally confined) & the
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Geomorphology Final Report
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