Philip J. Burton. (2002). Effects of clearcut edges on trees in the sub-boreal spruce zone of Northwest-Central British Columbia. Silva Fennica vol. 36 no. 1 article id 566. https://doi.org/10.14214/sf.566

Keywords: tree growth; windthrow; canopy influence; clearcut logging; edge effects; edge orientation; opening influence

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Clearcut-forest boundaries were evaluated for their effects on mature and regenerating trees in the northern interior of British Columbia, Canada. Two hundred and eighteen rectangular plots measuring 200 m2 each were arrayed in transects across 12 cutblock edges created 9 to 21 years earlier, with the wall of standing timber facing either north or south. The density of canopy trees on the inner edge was found to be reduced by 19% (on north-facing edges) to 46% (on south-facing edges) from average densities found in forest interiors. This reduction was primarily due to windthrow after logging, which was elevated by 27% (over interior background levels) at north-facing edges, and by 216% at south-facing edges. Of the trees situated within 10 m of south-facing cutblock edges, 11% of the Pinus contorta, 18% of the Abies lasiocarpa, and 42% of the Picea engelmannii x glauca trees have apparently collapsed, primarily those having height-to-dbh ratios greater than 71:1. As a result, irradiance in the forest understory was elevated (over interior levels) at south-facing edges to distances of approximately 65 to 70 m into the forest. Increased irradiance from adjacent cutblocks enhanced the understory growth of Picea for approximately 60 m into the inner edge of forests, 75 m for Abies. Mature Pinus trees on south-facing edges showed an unexplained 48% decrease in radial growth compared to average growth rates in forest interiors, an effect that was detectable up to 45 m into the forest. Elevated densities of conifer seedlings were evident for up to approximately 70 m into clearcuts from north-facing forest edges. Seedling growth in clearcuts was largely unaffected by shade from stand edges. Though the extent of edge effects varies considerably with the statistical techniques used to detect them, it appears that opening effects on trees can extend between 40 and 120 m into this forest type, while canopy effects reach shorter distances into clearcuts.

Burton, Symbios Research and Restoration, P.O. Box 3398, 3868 13th Avenue, Smithers, British Columbia, Canada V0J 2N0 E-mail: symbios@bulkley.net

Category : Review article

article id 74, category Review article

Philip J. Burton, S. Ellen Macdonald. (2011). The restorative imperative: challenges, objectives and approaches to restoring naturalness in forests. Silva Fennica vol. 45 no. 5 article id 74. https://doi.org/10.14214/sf.74

Keywords: afforestation; disturbance regime; ecological restoration; forest rehabilitation; native species; reclamation

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Many of the world’s forests are not primeval; forest restoration aims to reverse alterations caused by human use. Forest restoration (including reforestation and forest rehabilitation) is widely researched and practiced around the globe. A review of recent literature reveals some common themes concerning forest restoration motivations and methods. In some parts of the world, forest restoration aims mainly to re-establish trees required for timber or fuelwood; such work emphasizes the propagation, establishment and growth of trees, and equates with the traditional discipline of silviculture. Elsewhere, a recent focus on biocentric values adopts the goal of supporting full complements of indigenous trees and other species. Such ecosystem-based restoration approaches consider natural templates and a wide array of attributes and processes, but there remains an emphasis on trees and plant species composition. Efforts to restore natural processes such as nutrient cycling, succession, and natural disturbances seem limited, except for the use of fire, which has seen widespread adoption in some regions. The inherent challenges in restoring “naturalness” include high temporal and spatial heterogeneity in forest conditions and natural disturbances, the long history of human influence on forests in many regions of the world, and uncertainty about future climate and disturbance regimes. Although fixed templates may be inappropriate, we still have a reasonably clear idea of the incremental steps required to make forests more natural. Because most locations can support many alternative configurations of natural vegetation, the restoration of forest naturalness necessarily involves the setting of priorities and strategic directions in the context of human values and objectives, as informed by our best understanding of ecosystem structure and function now and in the future.

Burton, Canadian Forest Service, Natural Resources Canada, 3333 University Way, Prince George, British Columbia, Canada V2N 4Z9 E-mail: Phil.Burton@NRCan-RNCan.gc.ca
Macdonald, Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada E-mail: sem@nn.ca

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