Simulations on impacts of different management strategies on long-term site productivity in lodgepole pine forests of the central interior of British Columbia

doi:10.1016/S0378-1127(99)00234-0

Forest Ecology and Management

Volume 133, Issue 3, 15 August 2000, Pages 217-229

https://doi.org/10.1016/S0378-1127(99)00234-0 Get rights and content

Abstract

Impacts of different management strategies on long-term site productivity over a period of 240 years were simulated using the ecosystem Model FORECAST for lodgepole pine forests of the central interior of British Columbia (BC). Results suggested that the sustainable management strategies for maintaining long-term site productivity in lodgepole pine forests would be 80–120-year rotation lengths, with either stem-only or whole-tree harvesting. However, because of more nutrient conservation stem-only harvesting can achieve higher productivity (3.5–8.5%) than whole-tree harvesting does. The thinning strategy (from 4000 to 1000 stems/ha) would not increase total productivity over a period of 240-year simulation. Thinning, however, can increase the habitat value for Caribou. The best thinning strategies await further simulations on effects of various stocking levels in a broader context. The simulations also showed that organic matter and below-ground woody debris are critical for maintaining long-term site productivity in lodgepole pine forests in the study area, and a significant removal of such material may cause yield decline.

Introduction

The environmental impact of timber harvesting on the forest ecosystems has long been the subject of considerable study and debate. This issue has gained renewed interest in British Columbia (BC) with the introduction of the Forest Practice Code in 1995, along with a recent emphasis on habitat protection and planning issues within the forest industry. In the Cariboo Forest Region, one concern has focused on potential negative impacts of timber harvesting on Caribou habitat in lodgepole pine forests. Clear-cutting removes the arboreal lichen and damages terrestrial lichen through physical disturbance and changes in microclimate (Miège et al., 1999), which has detrimental effects on the suitability of Caribou habitat. Concern has also been expressed that, due to large nutrient removal and depletion, intensive timber harvesting such as whole-tree harvesting may have negative impacts on long-term site productivity in lodgepole pine forests (Dr. J.P. Kimmins, Department of Forest Science, University of British Columbia, pers. commun.). For these reasons, alternative management strategies must be investigated for their effectiveness in minimizing those negative impacts. In 1996, Cariboo Forest Region, Ministry of Forests, initiated a comprehensive project to evaluate ecological impacts of various silvicultural systems on Caribou habitat in the very dry, very cold montane spruce and very dry, cold sub-boreal pine spruce biogeoclimatic subzones in the Chilcotin plateau. As part of the project, this study focused on evaluation of impacts of various management strategies on long-term site productivity.

There are four main approaches that could potentially be used to evaluate the consequences of timber harvesting on site productivity over multi-rotation time-scales: long-term field trials or experiments, chronosequence studies, retrospective studies, and ecosystem simulation. The strengths and weakness of these approaches have been reviewed by Dyck and Cole (1994). Most field studies of the effects of timber harvesting have been limited to time scales of a few years or decades (Dewar and McMurtrie, 1996), and several studies have reported a significant difference between short-term and long-term results (e.g., Dyck and Skinner, 1990). In the absence of multi-rotation experience or field trials, chronosequence studies can be helpful, but there are frequent difficulties in locating valid chronosequence study sites (Dyck and Cole, 1990), and rarely can chronosequences address multiple rotation effects. Retrospective studies often suffer from incomplete knowledge of pre-harvesting conditions and inadequate descriptions of the harvesting. Of the four methods, ecosystem simulation may be the most feasible way of comparing the impact of management or natural disturbance scenarios over long-time scales and large spatial scales (Korzukhin et al., 1996). While simulation modeling is, like the other methods, subject to a variety of shortcomings, including the difficulty of validating the predictions (Dyck and Cole, 1994) (true of all but the long-term field trial method), it may be the only way of undertaking such evaluations.

The ecosystem model FORECAST, or its forerunner FORCYTE, has been used as a management evaluation tool in several types of forest ecosystems (Sachs and Sollins, 1986, Kellomaki and Seppala, 1987, Wei and Kimmins, 1995, Wang et al., 1995, Morris et al., 1997). The model was specifically designed to examine the impacts of different management strategies or natural disturbance regimes on long-term site productivity. A description of the FORECAST model approach will be presented in the next section; additional details can be found in Kimmins (1993) and Kimmins, 1988.

The objectives of this study were to: (1) evaluate some differences in nitrogen budgets between various management strategies and the implications of these differences for long-term site productivity of lodgepole pine forests on zonal sites in the central interior of BC; and (2) quantify these differences between whole-tree and stem-only harvesting; and (3) identify management strategies that can maintain the long-term productivity of these forests.

Section snippets

Study area

Lodgepole pine (Pinus contorta ssp. latifolia Engelm. ex S. Wats.) plays an important role in the forest industry and environment in BC. It is abundant in the montane spruce (MS), sub-boreal pine spruce (SBPS) and sub-boreal spruce (SBS) biogeoclimatic zones in central BC (Pojar, 1985) where it dominates forests that have been subject to high frequencies of wildfire in the past. This study covers both the MSxv and SBPSxc subzones west of Williams Lake in the central interior of BC. These two

Effect of different utilization levels

As expected, the total stem-wood biomass harvested over a 240-year simulation on the SOH sites was higher than on the WTH sites (Table 1 and Fig. 1). This is mainly due to greater amount of decomposing litter (Table 1 and Fig. 2) and coarse woody debris (Table 1 and Fig. 3) left after SOH, and consequently more soil nitrogen available for pine growth (Table 1 and Fig. 4). This suggests that higher productivity can be achieved with nutrient-conservative SOH in the study area. However, the

Conclusions

Our simulations strongly demonstrated that the lodgepole pine is, from a nutrient perspective, an adaptive and resilient species. This may be related to its long-term evolution under harsh environment such as frequent wildfire disturbance, poor and dry site quality. Although application of nutrient-conservative strategies such as longer rotation lengths (120 years) and stem-only harvesting enhance productivity, a range of management strategies including 80–120-year rotation lengths and

Acknowledgements

We thank Bill Chapman, Kim Scoullar, Don Sachs and Hamish Kimmins for valuable input and comments. Funding for this study was provided by FRBC through Ministry of Forests, Williams Lake, BC.

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Simulations on impacts of different management strategies on long-term site productivity in lodgepole pine forests of the central interior of British Columbia

Abstract

Introduction

Section snippets

Study area

Effect of different utilization levels

Conclusions

Acknowledgements

Adv. Ecol. Res.

For. Ecol. Manage.

For. Ecol. Manage.

For. Ecol. Manage.

The concept of nitrogen productivity in forest growth modeling

Mitt. Forstl. Bundes-versuchsant.

Effects of thinning and nitrogen fertilization on the growth rate of Douglas-fir: relative contribution of foliage quantity and efficiency

Can. J. For. Res.

Above and below-ground biomass and production of lodgepole pine on sites with differing soil moisture regimes

Can. J. For. Res.

Sustainable stemwood yield in relation to the nitrogen balance of forest plantations: a model analysis

Tree Physiol.

Nutrient dynamics of above ground detritus in lodgepole pine (Pinus contorta ssp. latifolia) ecosystems, southeastern Wyoming

Ecol. Monogr.