0596-B1

Developing Silvicultural Systems for Sustainable Forestry in Canada

A.K. Mitchell^[1], D. Burgess, D. Maynard, A. Groot, J.-M. Lussier, H. Ottens, and B. Titus

Abstract

The development of silvicultural systems for sustainable forestry in Canada involves providing science-based options to manage forests for multiple values. Currently, the focus of forest management is shifting toward partial cutting and retention systems, based on the assumption that forest structure, habitat, biodiversity and healthy ecosystem processes form links in a sustainability chain. However, the links in the chain have seldom, if ever, been tested. This defines a vital role for undertaking silvicultural research that is closely linked with forestry operations and can be applied to rationalize the apparent dilemma of managing for both timber and forest values. Long-term silviculture experiments supported by the Canadian Forest Service and its partners form an integral part of the development of silvicultural systems for sustainable forest management in Canada. In this paper, case studies are used to illustrate how the issues of (1) managing old-growth forests, (2) emulating natural disturbance, and (3) promoting the regeneration of natural forests through partial cutting are being addressed through scientific research. By providing information for comparing the ecological impacts of silvicultural alternatives, science-based systems can be developed to manage forests for diverse products and services. These systems need to be flexible enough that adaptive strategies can be used to address changing societal issues and values.

Introduction

The need to focus scientific research in support of developing new and modifying present, silvicultural systems has been driven by changes in what society wants from Canada's forests and by the advancement of our knowledge about forests. The development of silvicultural systems, which encompasses the methods used for harvesting, regenerating, and tending forests (Smith et al. 1997), is a key component in sustainable forestry. By applying silvicultural alternatives, foresters will be able to manage for a variety of economic, ecological, and social values (Forestry Canada 2000).

Forest-management practices have become increasingly complex in order to optimize the balance between timber production and long-term site productivity, and between forest diversity and ecological function. Developing silvicultural systems for sustainable forestry involves assembling the components of a silvicultural prescription such that the prescription will successfully maintain a range of ecosystem attributes (values). Those components include a suite of harvesting, regeneration, and tending methods. The patterns resulting from natural (historical) disturbances could also be used as components of a template for establishing guidelines for partial cutting and retention systems, particularly in the boreal forest. Considering regional variations in tree and forest structures at the stand- and landscape-levels, both in time and space, would lead to more ecologically sound prescriptions than if only arbitrary limits are used.

To achieve this, a long-term interdisciplinary approach to silvicultural research has been taken by the Canadian Forest Service (CFS) and its partners with the aim of measuring progress toward sustainability through a system of key ecological indicators. In this way, scientific information and knowledge of the differing effects of alternative silvicultural techniques can be applied to the development, testing, and implementation of initiatives such as the Criteria and Indicators for sustainable forest management (Canadian Council of Forest Ministers 2000) and Forest Certification (Staddon et al. 1999).

Using examples from silvicultural research projects conducted by CFS scientists and their partners across Canada-and considering the diversity of Canadian forests, and the tensions inherent in making forest-management decisions when scientific certainty is lacking-this paper briefly illustrates why long-term research is required to address the sustainability of forests in Canada.

Silvicultural Systems and Sustainability

The development and use of a variety of silvicultural systems can provide ways to achieve sustainable forest management through the retention of forest structure in old-growth ecosystems and the diversification of forest structure in managed forests. The idea that forest structure is the key to sustainable forest management can be described as a sustainability chain (Figure 1) (Burgess et al. 2001). By using silviculture to diversify forest structure, diverse habitats are created. These diverse habitats then support a variety of biota that underpin healthy ecosystem processes. In turn, the existence of healthy ecosystem processes provides a basis for concluding that forest-management practices are ecologically sound and sustainable.

The effects of forestry practices on the links in the sustainability chain have seldom, if ever, been tested (Spence 2001). For example, although the bark of a single tree in a large opening retains the structure required to support a community of microarthropods, the habitat may not be suitable as a result of extremes in temperature and moisture, and the community would perish. In that instance, forest structure would not beget habitat and the sustainability chain would be broken. Similarly, the link between biodiversity and ecosystem processes is poorly understood. This is partly because of the long temporal and large spatial scales that must be considered. In addition, quantitative data about how species diversity and abundance are affected by different silvicultural systems are rarely available. This clearly defines a role for using research that is linked closely with forestry operations in finding the route toward the goal of sustainability through science-based forest management.

The issue of managing forests for multiple values can place timber harvesting and managing forests for other uses in conflict. Timber values tend to increase with the level of harvesting while forest values (non-timber values) tend to decrease with increasing levels of cutting (Figure 2). This has led to the perception that the trade-off between timber and forests is an all-or-nothing proposition. However, for particular values, the picture may not be so simple. For example, trade-offs between wildlife (forest) and financial (timber) values were shown to have a classical convex production possibility curve (Calkin et al. 2002). Similarly, aesthetic (forest) values may reach near-maximum when less than 100% of the basal area is retained. In a test of alternative silvicultural systems (Arnott and Beese 1997), the retention of 25% of the basal area led viewers to conclude that they were not looking at an aesthetically unacceptable (clearcut) harvesting treatment. By considering how the balance of various values such as biodiversity, wildlife, and water would be described along a continuum of harvesting intensity, perhaps the balance between timber and forest values can be more clearly rationalized.

Delivering Silvicultural Research

The CFS is positioned to provide links between research on operational aspects of forestry practices and basic aspects of the biological functions of forest organisms. Strong partnerships are in place, and more are needed, to deliver scientific information about the development and modification of silvicultural systems to forest practitioners. Agreements with 29 government agencies, 25 forestry companies, and 24 academic institutions across Canada (Table 1) are evidence of the demand for CFS silvicultural research. Both operational and basic process-oriented studies are under way to develop sound criteria for science-based forest management.

Research Directions

The forests of Canada are diverse and most have originated from natural disturbances. They cover a wide range of climate, elevation, forest vegetation communities, and soil types. This geographic and biological complexity has resulted in the need to design a variety of silvicultural research approaches to address different issues across Canada. Although most harvesting in Canada is done with the clearcutting system in natural (previously uncut) forests, the trend is toward a greater application of other silvicultural approaches involving partial cutting. These systems include patch and shelterwood cutting, selection systems, and retention systems (Burgess et al. 2001).

Following are three examples that illustrate how research on the development of silvicultural systems for sustainable forestry is addressing: (1) management of old-growth forests, (2) emulation of natural disturbance, and (3) regeneration of natural forests through partial cutting. All three projects focus on managing forest structure.

The Montane Alternative Silviculture Systems (MASS) project addresses the issue of developing alternative silvicultural systems for managing multiple values in old-growth coastal montane forests in British Columbia. It is a research and operations partnership with representatives from government, industry, and universities that tests and compares four harvesting treatments that vary in the extent and pattern of tree removal (patch cut, shelterwood, green tree retention, and clearcut). The objectives of the MASS Project were to test whether systems that retain overstory trees are operationally feasible, economically viable, and ecologically sound (Arnott and Beese 1997).

The Ecosystem Management by Emulating Natural Disturbance (EMEND) project addresses the issue of developing silvicultural systems for emulating natural disturbance regimes in northern boreal mixedwood forests. It is a large-scale, collaborative study involving the CFS, University of Alberta, industry, and other research institutions. It tests silvicultural practices that best maintain biotic communities, spatial patterns of forest structure, and functional ecosystem integrity for comparison with mixedwood landscapes that have originated through wildfire and other inherent natural disturbances (Volney et al. 1999).

The Meridian Road Silvicultural project addresses the issue of developing silvicultural systems involving partial cutting for the regeneration and management of natural stands of eastern white pine. It is an interdisciplinary study with linkages to government, industry, and universities. It is examining the impacts of partial cutting, site preparation, and underplanting on forest ecosystem dynamics, and particularly on the regeneration of pine (Burgess and Wetzel 2000).

Benefits of Long-Term Silvicultural Research

The CFS has invested in long-term, stand-level research across Canada (Mitchell and Lee 1999). These field sites enable the integration of operational, economic, and ecological aspects of developing and testing a variety of silvicultural alternatives. One of the most important benefits of long-term research is the demonstration that decisions based on short-term data could be erroneous in view of long-term results. For example, positive effects on the growth of regeneration observed three years after harvesting disturbances were completely reversed after 15 years (Figure 3).

Benefits from silviculture research are also in providing options to deal with uncertainties surrounding ecological change, economic stability, and social acceptability. For example, benefits come from new knowledge characterizing whether silvicultural interventions can change ecosystems beyond the limits of historical (natural) variability from which they may never recover. Both timber and non-timber products can benefit from the characterization of conditions that favourably influence growth rates, wood quality, and fibre properties, or that promote non-timber species such as mushrooms and medicinals. Social benefits of silviculture research can be both functional and aesthetic. Enhanced visual quality and recreation potential are examples of social benefits that can result from applying silvicultural systems research.

Conclusion

Uncertainty must be recognised and addressed in predicting the appropriate levels of sustainable development for Canadian forests. While there is a general understanding that we should strive to achieve sustainability to meet an acceptable balance of environmental, social, and economic needs now and in future, the concepts of sustainable forestry or sustainable forest development continue to evolve. Many silvicultural systems need further testing and modification, and this takes time. More care in the planning and supervision of forestry practices, and better assessment techniques, are needed. Presently, the most significant knowledge gaps are in understanding the ecological impacts of using the various silviculture systems that involve partial cutting. Through forest science, new technologies, approaches, and ideas can be developed to fill these gaps.

Unfortunately, scientific data do not yet support a consensus on what is meant by forest sustainability. Through research on the development and testing of silvicultural alternatives, a foundation is being built for facilitating science-based decision making in forest management. The development of the Criteria and Indicators policy is an attempt to set standards for maintaining and monitoring sustainable forestry practices. Altogether, the Criteria and Indicators policy provides an implicit definition of sustainable forest management. The issue of forest certification can also provide a strong justification for forestry practices research, particularly as it relates to measuring and assessing the processes that underpin productive, healthy forest ecosystems. Through partnerships, silvicultural systems can be developed that: (1) provide a means to manage forests for diverse products and services, and (2) are flexible enough to enable adaptive strategies to address changing societal issues and values.

Acknowledgements

The authors thank Mr. E. Wass and Mr. J.P. Senyk (Pacific Forestry Centre) for data used in Figure 3. We also thank Dr. P. Puttonen (Helsinki University) and Mr. R. Whitehead (Pacific Forestry Centre) for assistance in developing the figures, and Mr. S. Glover (Pacific Forestry Centre) and Ms. K.A. Hagan for scientific editing of the manuscript.

References

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Table 1: CFS forestry practices research partners (1997-2002).^[2]

Abbreviations: FP, Forest Products; FERIC, Forest Engineering Research Institute of Canada; SCBC, Science Council of BC; USDA FS, United States Department of Agriculture-Forest Service; Env, Environment; MF, Model Forest; NCE SFMN, National Centres of Excellence Sustainable Forest Management Network; MNR, Ministry of Natural Resources; DFO, Canada Department of Fisheries and Oceans.

Figure 1: The sustainability chain. (Modified from Burgess et al. 2001)

Figure 2: Balancing timber and forest values. A simple theoretical model for visualizing trade-offs in forest management. Retention = percent of basal area retained. (Modified from Burgess et al. 2001)

Figure 3: The importance of long-term research as illustrated by the changing effects of soil disturbance on seedling volume after 3, 10, and 15 years. Results are expressed on the basis of percent of volume growth on undisturbed soils. Soil disturbance treatments: R, stumped and raked; S, stumped and scalped; U/T, undisturbed and tracked; R/T; stumped, raked, and tracked; S/T, stumped, scalped, and tracked. (Modified from Wass and Senyk 1999)