Forest Investment Account (FIA) - Forest Science Program
FIA Project Y103243

    Managing Northern Mixedwood Stands to Sustainably Maximize Productivity and Minimize Costs
Project lead: Chris Hawkins (University of Northern British Columbia)
Contributing Authors: Hawkins, Chris D.B.; Carlson, Michael R.; Baker, Cindy
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Management of BC’s forest resources must include not only social values (employment, recreational opportunities and cultural integrity, be ecologically grounded to provide a continued supply of timber and services without compromising important qualities such as high levels of biodiversity), but also be economically feasible. New policy initiatives require rigorous scientific knowledge to demonstrate they will meet sustainable forest management (SFM) objectives in all forest regions of BC.

The project’s objectives are to 1) determine the density of broadleaf stems (basal area) that maximizes complex stand productivity, 2) minimize costs associated with achieving free-growing objectives, 3) model growth and development of complex stands, and 4) ascertain optimal (cost-benefit) treatment regimes to enhance stand productivity and species and structural diversity. This provides a basis for a more strategic approach to vegetation management programs, allocating activities to areas where vegetation control is necessary and avoiding treatment of areas where current broadleaf densities will not impact conifer growth or where a mixedwood complex stand is an appropriate and desirable future forest condition. One significant result of this approach is that there will be less herbicide usage at the landscape level.

The latest Dawson Creek TSA Timber Supply Review (TSR) (MFR 2002) identified the need to manage mixedwood stands to maintain their attributes on the landscape – to stop “unmixing the mixedwood” forest. Lieffers et al. (2007) acknowledged this need. It has been suggested that the productivity of mixedwood stands is greater over the long-term than single species or conifer regenerated stands (Man and Lieffers 1999, Wang et al. 1995, MacPherson et al. 2001, Kelty 2006). That is, species mixtures (aspen-spruce, birch-spruce) result in greater merchantable wood volumes than stands with only one species and some benefits of natural stand dynamics may be realized by managing for complex mixtures (Kelty 2006). However, the current operational ‘default’ of eliminating most or all broadleaf tree species is costly, reduces species and structural diversity, and in many instances may not be needed (Comeau et al. 2005, Pitt and Bell 2005, Comeau et al. 1993).

The cost of carrying out brushing treatments to meet free-growing guidelines in much of BC may be unwarranted when treatment benefits are measured. As part of the Adams Lake Interfor Innovative Forest Practices Agreement (Pitt and Bell 2005), studies showed the cost of brushing birch from blocks planted to lodgepole pine may be greater than the anticipated increase in crop tree value (incremental growth): a negative investment. Early results from our study suggest that three year spruce radial growth is not impacted by competing birch until the number of stems per hectare (sph) exceeds 3000 (Figure 1). Current free-growing guidelines (Comeau et al. 1993) require the removal of deciduous competition despite evidence suggesting this is not cost-effective and does not typically result in greater timber volumes or better wood quality. For birch, sph in excess of 1000 must be removed. In fact, wood quality may be compromised due to slower crown lift and larger branches when the birch is removed.

Complex or intimate mixtures are seldom managed for and, when managed, tend to be done poorly. The 2002 Dawson Creek TSR identified a gap in management of northern complex stands, and the Chief Forester stated that, if these stands were not managed, they would be removed from the timber harvesting land base and hence the allowable annual cut would be reduced (MFR 2002). The lack of management is probably due to a limited understanding of dynamic processes in complex stands and a lack of models (growth and yield and successional). There is limited quantitative information on how complex stands develop during early seral stages and how early stand composition translates to future forest condition, and what the short to long-term growth and yield implications may be.

A better definition of how biological values and economic considerations interact will lead to reduced brushing costs (manual or chemical treatments), and an increase in stand-level and landscape-level species and structural diversity. However, the impacts of less brushing on growth and yield and future timber supply are not understood, and must be modeled, quantified and verified.

In 2004, this project examined growth responses of young (up to 15 years old) spruce and pine stands (Mackenzie only) to varying densities of residual birch or aspen. 460 plots were sampled in eight blocks in the Fort Nelson and Peace districts in the BWBS biogeoclimatic zone. 336 plots were sampled in eight blocks in the SBS biogeoclimatic zone in the Mackenzie District. Destructive sampling of saplings (conifer and deciduous height over age curves) in the Fort Nelson and Mackenzie districts was completed. These data provided initial species-density thresholds found in these complex stands. Modeling (including growth and yield, and successional) of early stand development and linking (projecting) it to desired future forest conditions and longer-term yield predictions will be done when sufficient temporal data is acquired.

In 2005, 306 plots were sampled in eight blocks (two new; six re-measurements) in the Fort Nelson district, and 194 plots were sampled in four blocks (two new; two re-measurements) in the Mackenzie District. Modeling was done using tree lists from the temporary sample plots (TSP). Projections suggested that broadleaf densities could be much greater than presently thought, e.g. birch stocking could likely exceed 3000 sph with no negative effects on spruce growth (Figure 1). However, there is an age (size)-crop tree-species competitive relationship that we still need to describe. For example, how different is the growth response of an eight-year-old spruce-aspen mix with 3000 sph from an older spruce-aspen mix with larger trees but with aspen at the same stocking density of 3000 sph?

In 2006, more sites were established in the three forest districts, a preliminary paper was presented at a boreal forest conference, and re-measurements were completed. Even though brief, temporal data suggests the model projections are not unreasonable. An experimental manipulation of broadleaf density is needed to enhance findings for incorporation into growth and yield and successional models.

In 2007, more sites (both TSP and controlled density or PSP – permanent sample plots) were established in the Fort Nelson and Peace districts. Previously established TSPs were re-measured in both forest districts as well. SORTIE-ND model projections were made and a paper was presented at the IUFRO conference in Sault Ste. Marie, ON. Invited presentations based on this project were made at a Growth and Value Workshop at the Bulkley Valley Research Centre and at SISCO in Penticton, BC.

In 2008, new TSPs were established in all three forest districts and controlled density experiments were established in the Peace and Mackenzie districts. TSPs were re-measured in the Fort Nelson and Mackenzie districts. With the data collected, mixedwood management scenarios will be modeled with SORTIE-ND and economic cost-benefit analyses will be carried out based on these scenarios. SORTIE-ND and TWIGS will be used to project short and long-term growth. When TASS 3 becomes available, it will also be used to project stand growth.

During the next year we plan to add to our temporal data base: effects of broadleaf density on conifer growth (TSP and PSP re-measurements); establish a second controlled density experiment and more TSPs in the Peace district; compare model outputs to temporal data; determine the utility of SORTIE-ND for modeling these complex stands; describe treatment(s) cost-benefit; define the density-species-age-height relationship; and meet with policy makers to discuss the implications of our early findings.
Related projects:  FSP_Y081243FSP_Y092243


Final technical report (0.3Mb)
Presentation: Spring bud phenology in 18 populations of paper birch grown in three common gardens (5.3Mb)

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Updated August 19, 2010 

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