Canada: British Columbia: Restoration in Coastal British Columbia Riparian Forests

Project Stage:
Completed

Start Date:
1998-07-20

End Date:
2002-07-20

Primary Causes of Degradation

Degradation Description

Historically, timber harvesting has been carried out in many riparian areas. From a logging standpoint, these areas typically have large timber and are among the most accessible terrain. Many accessible riparian areas around coastal streams have been logged at some point following World War II (or earlier via selection hand logging). More stringent guidelines began to be implemented in the 1980s and onwards. Clear-cut harvesting in coastal riparian areas often results in conversion to deciduous stands on the wetter sites (typically alder, Alnus rubra, but also cottonwood, Populus balsamifera ssp trichocarpa, and bigleaf maple Acer macrophylum). These generally develop a variable and often sparse conifer understorey of western red cedar, Sitka spruce and western hemlock. The drier sites typically form dense stands of conifers, often with western hemlock as a leading species. The successional trajectory of these stands following clear-cut harvesting does not necessarily generate the lower density, structurally diverse stands that often existed pre-harvest, at least not in a timeframe that humans would consider reasonable.

Reference Ecosystem Description

Coastal forests (classified as the Coastal Western Hemlock zone1) probably encompass the greatest diversity and abundance of wildlife habitat of any ecological zone in British Columbia (BC). Riparian forests – those that surround streams and rivers – are disproportionately important, as they are highly biodiverse areas that also provide animal movement corridors and fish habitat. Riparian corridors are the main productive forest areas that (depending on stream type) are reserved from harvesting in BC, both to protect salmon and trout habitat and provide for biodiversity and landscape connectivity. Typical management aims relate to stream integrity (bank stability, water quality, shade) and provision of downed trees (large woody debris) for stream channels. Large woody debris is crucial for healthy salmon and trout habitat, as it creates pools and cover, retains nutrients and stabilizes the stream.

Project Goals

The 12 projects focused on thinning overstocked conifer stands, releasing conifers suppressed by overstorey alder, and replanting with preferred (for the site) coniferous riparian tree species. The achievement of old-forest conditions by creating stands of larger, well-spaced conifer trees was the primary objective of the projects. These treated stands will help maximize current and future habitat value; enhance structural and compositional diversity; and ensure a future source of large woody debris for the adjacent streams.

Monitoring

The project does not have a monitoring plan.

Description of Project Activities:
** Thinning Treatments ** Both alder dominated and conifer dominated sites were thinned. In all of the treatment areas, the most abundant stand type was alder dominated stands with a suppressed, scattered understorey of conifers. Understorey conifer growth was improved by removing all alder within a radius of three to ten metres of each conifer tree. Approximately 80% of the alders in the stand was removed - the minimum necessary to achieve a target of 40% full sunlight to the understorey trees. Post-treatment conditions depended on the site - alder stands with conifer understorey were thinned to 100-300 stems per hectare of overstorey alder. Pockets of pure alder were also thinned, and up to 600 stems per hectare were retained depending on the age and height of the stand. The extent of alder stands with sparse conifer understoreys made it logical (from the perspective of promoting diversity) to thin the smaller number of conifer-dominated sites down to numbers that are still relatively high compared to "˜old forest' conditions (e.g. 450 - 600 stems per hectare). This strategy retains higher stocking levels for later removal, in order to meet long-term goals for large woody debris and recruitment of stand structure, while leaving a wind-firm stand. These sites were thinned with the goal of improving conifer growth and establishment. Both uniform and variable density thinning was used to take advantage of productive growing sites, while allowing natural gaps and clusters of trees to prevail. These sites were typically hemlock-dominated. Where western red cedar and Sitka spruce were present, they were preferentially retained. ** Conifer Planting ** Sitka spruce and western red cedar were re-established in many thinned areas by planting, in order to increase the species and structural diversity of the riparian forests. This planting is typically done in clusters on the best available microsites. This approach also allows for easier and more effective brushing - i.e. understorey removal adjacent to the trees - until the trees become established. Plantings were made in openings created by topping and felling. Other planting sites included nurse-stumps, rotted debris piles and individually disbursed trees. Deer-browse protection was not provided. ** River Structures ** Streams adjacent to harvested stands often develop a deficiency of large woody debris - the fallen trees that provide channel complexity and stability. Large woody debris (LWD) is very important for maintaining quality habitat for the salmon species that use coastal BC streams. Many stream restoration projects have been undertaken to re-introduce LWD in BC. The logs used are typically coniferous species (preferred for their longevity), which are cabled into place to make effective use of scarce resources. The use of surplus trees removed from the stands during thinning in these projects was carried out as an experimental treatment - it was seen as effective and inexpensive, given that crews were already felling trees near the stream edge. Structures were made using surplus conifer and alder trees removed at streamside to release existing site conifers. Alder decays quickly, but its felling at streamside provided opportunity for short-term LWD. Trees were directionally felled to form tight "˜self-locking' log jams of two to 17 trees. Where possible, the structures were anchored by orienting them against natural "pinch points', such as boulders or streamside trees. Introduced ballast, cables and boulders are commonly used to anchor engineered fish-habitat structures, but were not required. ** Biodiversity ** The thinning crew and supervisors added a wide range of biodiversity features to treated stands. This involved damaging or topping trees to introduce heart rot; girdling trees to create standing "˜snags'; creating cavities for small mammals and amphibians; and using "˜flanges' to simulate the loose bark used by roosting bats.

Ecological Outcomes Achieved

Eliminate existing threats to the ecosystem:
Follow-up monitoring has been carried out at four sites: Keogh River, Kootowis Creek, Quatam River and Goodspeed River. Keogh River has a post-treatment history of 4.5 years, Kootowis Creek 2.75 years, Quatam River 3.25 years and Goodspeed River 2.6 years. The early post-treatment responses at these four trial sites provide valuable data regarding restoration options for ecological recovery of riparian stands. ** Thinning ** All thinned stands have a park-like, natural appearance brought on by variable thinning regimes. Uniform thinning at variable densities of 450 - 600 stems per hectare (sph) in western hemlock stands achieved 2.2 - 3.4 mm radial growth per year in stands logged in the 1940s and 1950s. Trees from these stands had decreased in diameter growth to ≤1 mm radial growth per year prior to treatment due to over-crowding and canopy closure. Thirty year-old Sitka spruce averaged 5.5 mm radial growth when an overstocked plantation was thinned to 600 stems per hectare. This growth was close to the average radial growth achieved by the trees in the stand prior to thinning, indicating that thinning allowed the trees to retain close to their best growth rates. At 600 sph, adequate trees are retained for removal in subsequent passes. Leaving these higher densities standing in the first pass also assists in minimizing blow-down, a considerable risk in several areas. Trees downed by wind were absent from all conifer sites. However, at Goodspeed River, two alder stands experienced moderate blow-down after thinning. ** Planting ** The best growth of planted seedlings was achieved in alder-dominated stands where 80-90% of overstorey alder was removed. Canopy removal also favoured the growth of competing brush, creating intense competition for growing space. Cluster planting (trees grouped on the best available microsites) managed brush competition for two years following planting, making it possible for seedlings to become established. However, follow-up control of brush was required for sites planted at Quatam and Goodspeed Rivers. Seedling mortality was high for western red cedars in two trial sites. Many young planted trees were absent, browsed or significantly reduced in number, with few sites retaining more than half of the red cedar trees planted. Sitka spruce survival was high. In western hemlock stands under-planted with Sitka spruce and western red cedar, the new understorey established successfully. Height gains were not large compared to seedlings planted in alder stands where significant overstorey was removed. Leader growth in seedlings at conifer sites was 7 - 20 cm annually, compared to 2 - 2.5 times that in the more open alder sites. Good growth rates were an important objective in this project, but the successful establishment of new seedlings was more important. The height growth of seedlings at conifer sites can be improved with additional canopy removal. This may be implemented when appropriate to add more structure for biodiversity or remove trees for in-stream use. ** River Structures ** Most structures monitored remained very close to their original configuration. Several logs pulled away, but were caught on log jams created further downstream. These structures were intact despite having been in place during a 1 in 50-year return interval flood. ** Biodiversity Treatments ** Those biodiversity features that require decay to meet habitat objectives were still far too young to yield results at the time of monitoring. Some woodpecker activity was observed on one topped western hemlock, but all others were devoid of feeding activity. Trees distressed by cutting slabs of bark and wood from the stem were similarly absent of activity due to lack of time. "Face cuts" (removal of a slab of bark) were weather hardened with no sign of decay. Heal-over tissue along the outer edges obscured the nature of the cuts, making it difficult to distinguish them from naturally wounded trees. Girdled conifers in all stands were defoliated, leaving standing snags with excellent upper structure. All girdled and topped trees were still standing. Bat use of the many slots and flanges cut was not readily apparent. Dens cut in logs and stumps for use by mice, voles and shrews similarly lacked evidence of use. Nesting material was absent and droppings infrequent. Many of the small dens were water logged or filled with stagnant water. However, salamanders took advantage of the vacant dens and made extensive use of them. Occupancy was near 100% by western red back and clouded salamanders.

Socio-Economic & Community Outcomes Achieved

Key Lessons Learned

Early results show speeding restoration through silviculture can yield significant benefits. Through planting, sites devoid of conifers can be restocked, but later brush removal is needed to ensure survival. Overstorey trees that shade out desirable understorey trees can be removed, allowing existing or planted trees to thrive. Wood not needed for stand structure can be added to streams or allowed to lie on the ground to provide nourishment for soil or habitat for wildlife.

Establishing a treatment regime that best suits the wildlife needs of a site can be difficult, however. The removal of too few trees may not allow retained trees to achieve their maximum diameter growth response. Removal of too many trees may yield larger diameter trees, but too few for future use by wildlife, snag recruitment or in-stream debris. Significant effort was expended in adding wildlife habitat features to stands, but little actual use was observed. Some features fell victim to the very wet ecosystems in which they were placed; dens and cavities filled with water, making boxes cut for mice and voles more valuable for salamanders instead.

An unexpected result of the treatments was the very positive impact of girdling. Girdling was incorporated into stand treatments to remove overstorey alder for releasing understorey conifers. It was also used to leave standing structure in conifer stands in order to mitigate tree damage by wind-throw. Girdling exceeded all objectives. In conifer stands, the leafless trees provided large standing structure that gradually opened the site to light, and wind-throw was not observed in stands where girdled trees had been left in place. Girdling produced large standing structure at a fraction of the cost of manually topping trees. Although girdled trees may topple quickly, standing snags in areas where trees were formerly girdled suggest that many will decay and break, leaving natural snags similar to those manually cut by topping but at a fraction of the cost.

Long-Term Management

More follow-up monitoring will be required to understand the long-term effects on the forest and any further treatments required.

Sources and Amounts of Funding

The cost of completing these projects ranged from $2,500 to $3,500 per square hectare, depending upon the treatments used. These costs included thinning, girdling, planting, and modifications for biodiversity and in-stream structures. Funding was provided by a provincial fund allocated for forest renewal.

Other Resources

Biogeoclimatic Zones of British Columbia
http://www.for.gov.bc.ca/hfd/library/documents/treebook/biogeo/biogeo.htm

Vince Poulin, V.A. Poulin and Associates Ltd.
Vancouver, BC, Canada
Phone: (604) 263-0424
Email: vpoulin@shaw.ca

Eric Gagné, Western Forest Products
Port McNeil, BC, Canada
Phone: (250) 956-3393
Email: egagne@westernforest.com

Warren Warttig, International Forest Products
Campbell River, BC, Canada
Phone: (250) 286-4567
Email: warren.warttig@interfor.com

Primary Contact

Organizational Contact