Forest Investment Account (FIA) - Forest Science Program
FIA Project Y091153

    Analysis of Riparian Restoration techniques on Biodiversity: Use of Invertebrates Indicator species to Determine Appropriate Restoration Options for Ecological Recovery of Riparian stands
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
The values provided by streams & their riparian zones within forested landscapes continue to be of key concern in forest management (Lindenmayer & Franklin, 2002; Carey, 2006). Riparian forests provide a heterogeneous mosaic of habitats, with high levels of biodiversity, high productivity, & distinctive species compositions. They also serve as movement corridors for a number of species, including birds, bears & amphibians. In B.C., coastal forests within the coastal western hemlock zone likely contain the greatest diversity & abundance of wildlife habitat over any other ecological zone in the province.

Riparian forests make up a significant component of the productive forest in B.C. that is protected at some level from harvesting. Objectives of protection include provision of biodiversity & landscape connectivity, as well as protection of salmon & trout habitat. Guidelines with regards to methods for logging riparian sites were not provided until the 1980s, after much of the low density, structurally diverse riparian forest stands had been logged. Post-harvest stand development has often failed to recreate the complexity of the original stands, & thus efforts are sometimes made to employ silvicultural interventions to thin these stands.

It is proposed within Interfor’s Forest Stewardship Plan to commercially thin 2nd growth riparian areas to accelerate old growth characteristics. There has also been discussion on applying similar techniques in non-riparian forests for the same purpose as a recruitment method for old growth representation where a particular site-series-surrogate (Central Coast) is under-represented. Interfor is working collaboratively with Alan Banner in the development of second growth recovery curves, where it is hoped that the habitat contribution of second growth can be measured.

Interfor & Western Forest Products Inc. have been instrumental in the development of riparian restoration techniques designed to introduce old-growth attributes into riparian habitat. Between 1998 & 2002, these companies completed 12 operational riparian restoration field projects, totaling 348 ha of treated area along 70 km of fish habitat. The primary objective of these treatments, which included thinning overstocked conifer stands, releasing conifers suppressed by overstory deciduous trees, & replanting with preferred riparian tree species, was the rapid production of adequate large & coarse woody debris. Use of topping & habitat creation techniques produced 966 specialized biodiversity features such as topped & distressed trees, bat & small mammal, amphibian, & insect habitats. Effectiveness monitoring carried out in r sites in 2004 showed positive response in terms of radial growth, seedling establishment, enhanced fish habitat & reduction of windthrow. However, biodiversity responses were generally not apparent, as the time since treatment & monitoring was deemed too low.

Since a complete census of diversity is not feasible in stands, even those that have a relatively simple structure & composition, “indicators’ or surrogate measures of diversity must be identified. Indicators must not only be ecologically meaningful, but must also be amenable to measurement by non-specialists & have wide applicability if management objectives for biodiversity are to be fulfilled. Epigaeic carabid beetles will be used as an indicator species, together with the associated invertebrate by-catch, to examine the effectiveness of riparian treatments carried out in West Vancouver Island.

The link between structural diversity of forest stands & their associated biodiversity has begun to receive increasing attention for invertebrates. Forest-floor invertebrates are a critical group to consider in riparian studies given their huge abundance & diversity, as well as their importance in forest ecosystem functioning e.g. in nutrient cycling, pollination & defoliation, & as a food base for other vertebrates & invertebrates (Schowalter 2000). In this latter respect, primary & secondary predators such as carabid beetles integrate a substantial amount of ecological information about the biological communities to which they belong (Day & Carthy 1988): they also make up a large fraction of the soil arthropod biomass & form the base of the food chain for higher level predators such as birds, small mammals, reptiles & bears.

Previous work done in coastal B.C. by I. Pearsall since 2001 has shown that the responses by carabid indicator species are sensitive at small enough spatial & temporal scales such that they can be used to assess how quickly sites recover & re-establish typical old-growth communities (Pearsall 2001, 2002, 2003, 2004, 2005, 2006). Strong habitat associations of ground beetles have been shown in many other studies (e.g. Refseth 1980, Niemela et al. 1993 Niemela & Spence 1994, Craig 1995, Lemieux 1998, McDowell 1998), where old- growth forest specialists, forest specialists, forest generalists, or xerophilus (open area preferring) species have been identified. For these reasons, invertebrates are used worldwide as biological indicators in ecological studies that involve inventory & monitoring (e.g. Pearson 1994; Rykken et al. 1997). Characterization of the assemblages in treated versus untreated riparian buffers will identify whether silvicultural treatments are successful in providing old-growth attributes to the riparian forest.

Recent studies have examined the communities of terrestrial invertebrates associated with alternative forest management practices for riparian zones (e.g. Moring & Stewart 1994, Andersen 1997, Labonte 2002, Rykken et al. 2007). Studies focusing on ground beetles include: communities of headwater riparian zones (Rykken et al. 2007), effects of stream sizes on the feeding habits of riparian ground beetles (Hering & Plachter 1997), analysis of terrestrial invertebrates as prey for salmonids (Baxter et al. 2005), effects of terrestrial invertebrate prey on stream food webs (Nakano et al. 1999), analysis of aquatic insect biomass produced under moderate thinning & clearcutting with several different buffer widths along headwater streams (ver Linden, in Moldenke lab), & effects of riparian management (sizes of buffer strips) on invertebrate communities in the Malcolm Knapp Research Forest (Klimuk, in Richardson lab). Such studies have indicated the presence of a distinct riparian invertebrate community. However, little is known about the potential impact of specific riparian restoration techniques on such invertebrate communities. Thus, the work proposed in this project will directly build upon & complement these ongoing studies.

The riparian buffers that we will utilize were originally set up as part of the Kennedy Flats Watershed Restoration Program (KWRP) in Clayoquot Sound (Poulin & Simmons 1999). This watershed is classified as a “target watershed”. Kootowis Creek drains the Kennedy Flats east of Pacific Rim National Park, & exits through the park into Grice Bay. A significant amount of logging took place in the 1960’s & 1970’s with stands of 30-40 year old Douglas fir comprising large contiguous blocks of dense second-growth forest.

This study will compare 6 sites in treated riparian buffers, with 6 sites in untreated buffers of similar stream classification, site series & forest age. We will also work in an old-growth control site. This comparison will focus primarily on the invertebrate communities, assessing biomass & species assemblages of carabid beetles, as well as by-catch. Additionally, we will assess small mammal & salamander usage of artificial dens & cut logs in the treated sites. Understory vegetation will also be assessed.

Results will provide a valuable reference for selecting & integrating restoration options for ecological recovery of riparian stands.


Riparian Final Report (5.1Mb)
Powerpoint overview (0.5Mb)
Technical summary (0.4Mb)

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Updated August 16, 2010 

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