Forest Investment Account (FIA) - Forest Science Program
FIA Project Y091155

    Design of riparian zones: temporal response of secondary productivity to stream geomorphology and classification.
Project lead: Warttig, Warren (International Forest Products Ltd.)
Author: Pearsall, Isobel A.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
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 steam type. Currently Interfor is using the guidelines to vary Riparian Reserve Zone (RRZ) width based primarily upon the relative sensitivity of streams (alluvial, semi-alluvial, non alluvial, with the latter being the least sensitive). The general interpretation is that RRZ will be less than Forest Practices & Planning Regulation (FPPR) s.47 defaults on non-sensitive stream sections (e.g. confined, low energy, non-alluvial, moderately sloping banks) & greater than FPPR widths on sensitive sections (e.g. frequently confined, moderate energy, semi or fully alluvial, steep banks, high wildlife usage areas), but we are aware of no studies that justify these decisions for the management of secondary productivity. By using insects as an indicator of secondary productivity we could develop a better understanding of where Interfor should be adding RRZ, & where they have leeway to reduce RRZ.

Previous work done in coastal B.C. by I. Pearsall since 2001 has clearly identified that carabid beetles are a highly sensitive indicator, with significantly different communities in clearcut, immature & mature forests. Our work has shown that the responses by carabids are sensitive at small enough spatial & temporal scales such that they may be used to examine edge-responses, & to assess how quickly sites recover & re-establish typical old-growth communities.

Carabid beetles have been used as an indicator of soil diversity after disturbance caused by forest fire (Holliday 1991a, b), clear cutting (Sustek 1981, 1984, Lenski 1982, Jennings et al. 1986, Langor et al. 1991), scarification (Parry & Rodger 1986), pollutants (Stubbe & Tietze 1982, Kolbe 1988), land reclamation (Day & Carthy 1988), management of primeval or old growth forests (Niemela et al. 1988, Terrel-Nield 1990) & climate change (Elias 1991). As primary & secondary predators, carabids integrate a substantial amount of ecological information about the biological communities to which they belong (Day & Carthy 1988). Also, they make up a large fraction of the soil arthropod biomass, forming the basis of the food chain for higher level predators such as gastropods, birds, small mammals, & bears. They are also efficient natural pest control agents (Edwards et al. 1979, Jennings et al. 1986, Sustek 1981, Weseloh 1985).

This project will compare carabid biodiversity & biomass in riparian buffers on replicated alluvial, semi-alluvial & non-alluvial streams for S3 streams with matched stream characteristics for recently logged, immature, & mature 2nd growth systems. We will examine buffers on S3 streams during 2008: future studies aim to extend this to S1 & S2 streams so that we can compare the impacts of buffer size. We wish to determine whether wildlife value (secondary productivity), as assessed by carabid biodiversity & biomass, is greater in alluvial than in semi-alluvial or non-alluvial systems. We propose to examine the response of carabids at the stream edge, within the buffer zone, & extending out into the adjoining forest so that we can determine whether riparian protection results in source populations of carabids that are able to repopulate the adjoining harvested areas, how this is affected by geomorphology, & how this varies over time.

Evaluation of these data will assist managers in determining the most appropriate strategies for varying RRZ width to conserve biodiversity, & possibly challenge or support some of the assumptions used within the Clayoquot Sound Scientific Panel Recommendations (2005) & the South Central Coast Government Order (2007) for the determination of extensive reserve widths. The results from this study will be made available to forest managers of both Interfor & Western Forest Products. This study will also make a significant contribution to a growing body of literature that examines invertebrate responses to forest fragmentation (Newbold 1980, Davies & Margules 1998), & how these responses can affect ecosystem processes (Klein 1989).


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Updated August 16, 2010 

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