0282-B1

Some Pieces of the Sustainable Forest Management Puzzle in Canada

A. Groot^[1], J.-M. Lussier, A.K. Mitchell and D.A. MacIsaac

Abstract

Innovative forestry practices are being researched, developed and applied to contribute to sustainable forest management across Canada. Examination of innovative practices in three forest types (eastern boreal black spruce, boreal mixed wood and Pacific coastal forests) highlights the central role of residual tree retention during harvesting. Innovative practices can often, though not always, be described using traditional silvicultural terminology. The long-term consequences of more complex practices are not clearly understood. Increased long-term knowledge will allow the integration of such practices into coherent silvicultural systems, facilitating the implementation of sustainable forest management.

Introduction

Sustainable forest management (SFM) has been defined as “management that maintains and enhances the long-term health of forest ecosystems for the benefit of all living things while providing environmental, economic, social and cultural opportunities for present and future generations” (CFS 2002). Time is a key dimension of SFM; management decisions must provide desirable outcomes both in the present and in the future. As a result, there is an increasing need for long-term forecasts of the outcomes of management actions. If future outcomes are poorly understood, then it is not possible to assess whether sustainability will be achieved.

Space is the other key dimension of SFM, and the growing emphasis on landscape management reflects the need to manage for sustainability at the scale of the forest rather than the stand. This need arises because many organisms and ecosystem processes respond to forest characteristics over large areas. Consequently, management activity at one location often has effects at other locations. Furthermore, sustainability is more effectively assessed at larger scales because small-scale temporal variation is averaged out.

The combination of these two dimensions in SFM creates a space-time puzzle: where and when should management actions be carried out, and what should the management actions be? This puzzle can be visualised at the landscape scale as a mosaic of forest stands whose attributes change with time in response to management actions. The goal of SFM is to maintain or enhance forest populations, processes and outputs within this dynamic mosaic.

Although SFM must be planned and assessed at the landscape scale, the implementation of SFM occurs at the stand scale through the application of forestry practices. Clear-cutting is a predominant forestry practice in Canada, but this practice does not always satisfy all SFM objectives. There is strong social pressure, both within and outside Canada, to reduce the use of clearcutting. In some cases, forest management costs can be reduced by carrying out practices alternative to clearcutting. Finally, clearcutting is sometimes inconsistent with ecological objectives, especially the maintenance of biodiversity. These factors have prompted research, development and application of innovative forestry practices.

Innovative forestry practices are frequently motivated by immediate issues, but in order to contribute effectively to SFM, the long-term effects of these practices also must be predictable. It is not possible to solve the SFM puzzle without knowledge of both the immediate and the long-term effects of forestry practices. Knowledge of the long-term effects of forest practices on stand structure, composition and growth defines the pieces of the SFM puzzle.

Understanding of the long-term effects of forestry practices has traditionally been embodied in the specifics of silvicultural systems. Silvicultural systems have their roots in European forestry, and were developed during a period when timber management was the dominant goal, often in forests with relatively simple stand structure and composition. As a result, it has been argued that traditional silvicultural systems may have little relevance for the SFM of more variable Canadian forests (Weetman 1996). While we agree that the particulars of traditional silvicultural systems are often not directly transferable to Canadian situations, we adhere to the view of Smith et al. (1997) that the “principles of silviculture are independent of geography”. A silvicultural systems perspective helps to ensure that both the current and future effects of forestry practices on stand structure and composition are understood. This perspective is particularly important when management objectives include the maintenance of forest structure at the stand level and/or the maintenance of mixed-species stands, because the integration of silvicultural treatments through time and space to achieve these objectives can become complex.

A silvicultural systems perspective also can improve communication about forestry practices by providing a standard terminology. Traditional silvicultural systems, although typically focused on timber production, comprise a wide range of practices, and it is often feasible to describe innovative practices in traditional terms.

The objectives of this paper are (i) to describe, from a silvicultural systems perspective, innovative forestry practices in several Canadian forest types, and (ii) to assess the degree to which the long-term aspects of these practices have been explored.

Shaping the puzzle pieces - innovative forest practices

Practices for eastern boreal black spruce forests

In the eastern Canadian boreal forest, older natural stands of black spruce (Picea mariana) frequently contain abundant advance regeneration of that species. Such two-storied stands are common on a range of sites in Québec, but further west are increasingly restricted to peatland sites. In yet older stands, breakup of the overstory and development of the understory advance regeneration results in stands with irregular size structures.

Advances in logging equipment and techniques have made it feasible to protect advance regeneration during harvest, and practices that aim to protect advance regeneration are termed “Careful Logging Around Advance Growth” (CLAAG) in Ontario, and “Coupe avec Protection de la Régénération et du Sols” (CPRS) in Québec.

Although the height of advance regeneration is variable, most stems are less than 2 m tall, and CLAAG/CPRS results in even-sized or regular stands. This is analogous to the shelterwood silvicultural system in managed stands, and it has been suggested that the use of advance regeneration in natural stands be termed a “one-cut shelterwood system” (Smith et al. 1997) or a “natural shelterwood system” (Weetman 1996).

The natural shelterwood system is widely applied in eastern Canada, because of the prevalence of overmature stands that have had an opportunity to accumulate advance regeneration. The system has been rapidly adopted primarily because it offers low-cost, reliable regeneration. Stand structure and development will likely parallel that of natural even-aged stands. Because the regeneration can be 1 to 2 m tall at the time of harvest, there may be a reduction in the rotation length compared with regeneration by seeding or planting.

The first silvicultural treatment in the natural shelterwood system is also the last. In general, the regenerated stand will be managed by another silvicultural system, because it is unlikely that sufficient regeneration will establish spontaneously within the length of a usual forest rotation to allow a repetition of this system.

Little vertical structure is retained with the natural shelterwood system when most stems are less than 2 m tall, but greater retention is possible in more irregular stands. Operations that retain taller, but not merchantable, stems are termed Coupe avec Protection de la Régénération Hautes et du Sols (CPHRS) in Québec. Those that retain merchantable stems (> 10-12 cm DBH) are termed Coupe avec Protection des Petites Tiges Marchandes (CPPTM) in Québec, and, somewhat inexplicably, Harvest with Regeneration Protection (HARP) in Ontario

The greater structural retention of CPHRS and CPPTM/HARP goes further in satisfying ecological objectives, but usually smaller stems far outnumber larger stems. The regenerated stand is still effectively even-sized, albeit with a range of stem heights, and subsequent management must be even-aged to address this dominant stand component.

In some cases, CPPTM/HARP results in a substantial number of larger residual stems, but this circumstance has not yet been integrated into a well-defined silvicultural system. Depending on the post-harvest structure, such a treatment could be considered a selection thinning (sensu Smith et al. 1997), implying subsequent even-aged management, or the first of a regular series of partial harvests constituting uneven-aged management (e.g. MacDonell and Groot 1996).

As forestry practices in black spruce evolve toward greater retention of larger residual stems, the lack of knowledge about subsequent stand development becomes more acute. For example, information about appropriate cutting cycles and intensity in uneven-aged management is virtually non-existent.

Practices for boreal mixedwood forests

Mesic upland sites in the Canadian boreal forest comprise a mosaic of coniferous and deciduous species, occurring as pure stands and as mixtures. The unifying species on these sites across the boreal forest are trembling aspen (Populus tremuloides) and white spruce (Picea glauca); balsam poplar (Populus balsamifera), white birch (Betula papyrifera), balsam fir (Abies balsamea), black spruce and jack pine (Pinus banksiana) also are components in proportions that vary both regionally and locally. Stand development often leads to an overstory dominated by trembling aspen and a well-stocked coniferous understory (white spruce in the western boreal forest and balsam fir in the east).

Lieffers et al. (1996) summarized a range of silvicultural systems that can be applied to western boreal mixedwood stands, with treatments taking advantage of initial stand conditions to achieve long-term desired outcomes. Many of these systems result in even-aged stands using clearcutting, coppice, and shelterwood silvicultural systems, but opportunities for single-tree selection were also identified.

Among these systems, the natural shelterwood system, carried out in vertically-stratified trembling aspen/white spruce stands, has received the greatest attention in research, development and application. Brace and Bella (1988) proposed a “stand tending and harvest scenario” for stands with this structure, which was implemented experimentally in Alberta as a “two stage harvesting and tending model” by Navratil et al (1994). In this model, the aspen overstory and mature conifers are harvested, while protecting the white spruce understory. Windthrow is a serious threat to understory white spruce after overstory removal and a number of treatment variations have been devised to minimize wind damage (Navratil et al. 1994; MacIsaac et al. 1999)

In addition to releasing the spruce advance regeneration, the overstory harvest stimulates trembling aspen suckers, resulting in a mixed hardwood/conifer stand. Brace and Bella (1998) used an individual tree growth model to project development of such stands, and concluded that this system would achieve substantial yields of white spruce. These projections used simplifying assumptions, however, and the timing of treatments and the implications for growth and yield and long-term stand composition and structure require further elaboration (MacIsaac and Sauder 2001).

In trembling aspen stands lacking white spruce advance regeneration, it is possible to create good conditions for planted white spruce in small openings (e.g., Groot et al. 1997). A system to manage the resultant species mosaic through time has yet to be developed, however.

Practices for Pacific coastal forests

Pacific coastal forests are dominated by conifers, primarily Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla) and red cedar (Thuja plicata) at low elevations, and true firs (Abies spp.), mountain hemlock (Tsuga mertensiana) and yellow cypress (Chamaecyparis nootkatensis) at elevations over 800m. As a result of the mountainous character of coastal B.C. and Vancouver Island, considerable longitudinal differentiation is found and forest cover varies from wet westerly aspects dominated by hemlock to dry easterly aspects dominated by Douglas-fir.

Many approaches have been taken to diversify silvicultural systems in Pacific coastal forests, including both even-aged and uneven-aged stand management and a variety of retention silviculture systems such as group- and single-tree-selection, shelterwood, and seed tree systems (Arnott and Beese 1997). However in coastal British Columbia, issues surrounding the harvesting of virgin forests have resulted in a move toward silvicultural systems that retain forest structure (large living and dead trees, coarse woody debris and heterogeneity of tree size)
in perpetuity (Mitchell and Beese 2002).

Silviculture systems that retain forest structure over the long-term have been collectively called “variable retention” systems (Mitchell and Beese 2002). Retention systems in which less than 10% of the canopy is retained are comparable to traditional even-aged management using clearcut, seed tree and shelterwood systems. Those in which more than 70% of the canopy is retained are comparable to traditional uneven-aged management selection systems. Unlike “traditional" systems, in retention systems, forest structure representative of the pre-harvest stand is retained for very long time frames (hundreds of years) and biodiversity or aesthetic considerations may supersede timber production as the primary objective.

At the stand level, dispersed and aggregated retention are two recognised spatial models for variable retention. Each has its advantages depending on operational and ecological objectives. However, additional benefits can be derived from the combination of the two approaches. In a sense, retained aggregates (larger than 0.25 ha) represent islands of structurally diverse, climatologically moderated habitat and dispersed retention (individual trees) provides stepping stones between those islands. In some jurisdictions, aggregate patches may be the only way to safely conserve structural elements such as snags, elements that could only be reproduced over very long time frames. As it has been implemented on the coast, retention levels are on the order of 10% to 20% with a mixture of aggregates and dispersed trees.

In order that a silviculture system be called variable retention more than 50% of the cutblock area must be under forest influence, defined as the biophysical effects of retained aggregates or single trees on the surrounding land (Mitchell and Beese 2002). However, the influence of retained trees being on the order of one or two tree lengths has been based primarily on climatic data from studies of transects across stand edges and few studies have addressed the extent of forest influence on biotic communities or ecological processes (e.g. nutrient cycling).

The long-term implications of retention systems are unknown. Since one of the prime objectives of those systems is the conservation of old-growth attributes, uncertainty surrounds the longevity of those attributes because the likelihood of windthrow, fire and insect and disease attacks in the retained elements is unknown. Similarly, the persistence of forest influence is in question. At the landscape level, retention systems should reduce the fragmentation of forests that results from cutting small patches over a large area to meet timber supply goals because of the relaxation of limits on opening size that are imposed on clearcut systems.

Discussion

Ecological, social and economic pressures have created a demand for innovative forestry practices in Canada. A feature common to these practices is greater retention of residual trees during timber harvests. Retention of residuals can be effective in addressing immediate ecological, social and economic concerns.

This examination of innovative forestry practices in three Canadian forest types indicates that these practices can often, though not always, be described using traditional silvicultural terminology. The silvicultural systems perspective makes it clear that some practices, such as the natural shelterwood system in black spruce and boreal mixedwoods, can be considered functioning silvicultural systems. The forest practices that most obviously consistent with traditional silvicultural systems are relatively simple, however, and are in most respects similar to even-aged management based on clear-cutting. Other more complex practices, such as Pacific Coast retention harvesting, are potential components of yet-to-be articulated silvicultural systems. Integration of such practices into silvicultural systems is vital to the implementation of SFM.

Integration of more complex practices into silvicultural systems is hindered by lack of knowledge. The amount of knowledge about the long-term effects of forestry practices on stand growth, structure and composition generally decreases as the degree of residual retention increases. This is because much of the knowledge of about the development of forest stands in Canada comes from observations of monospecific, even-aged stands that originated from natural disturbances such as fire or insect attack or from even-aged silvicultural systems. There is much less experience with mixed-species and structurally irregular stands.

This lack of long-term knowledge about the effects of innovative forestry practices creates a problem in SFM planning, because uncertainty about the dynamics of individual pieces makes it impossible to solve the SFM puzzle as a whole. Knowledge about the long-term effects of forestry practices in Canada is being obtained from a variety of sources, including: (i) long-term forestry practices experiments (e.g., Mitchell and Vyse 1999), (ii) chronosequence studies in natural irregular stands (e.g., Hedberg and Blackwell 1998), (iii) examination of historical analogues to current innovative practices (e.g., Groot and Horton 1994), and (iv) empirical (e.g., Brace and Bella 1988) and process-based stand dynamics models (e.g., Bartelink 2000).

The increasing use of innovative forestry practices, along with expanding knowledge about the long-term effects of these practices, is making a strong contribution to solving the SFM puzzle across Canada.

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