Forest Investment Account (FIA) - Forest Science Program
FIA Project Y081243

    Managing northern mixedwood stands to sustainably maximize productivity and minimize costs
Project lead: Hawkins, Chris (University of Northern British Columbia)
Contributing Authors: Hawkins, Chris D.B.; Balliet, Nicole; Man, Cosmin
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Management of this province’s forest resources must include not only social values such as employment, recreation opportunities and cultural integrity, be ecologically grounded to provide a continued supply of timber 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 SFM (sustainable forest management) objectives in all forest regions of this province.
The project’s aim is to determine the density of broadleaf stems (basal area too) that maximizes complex stand productivity, minimizes costs associated with achieving free-growing objectives, models growth and development of complex stands, and ascertains optimal (cost-benefit) treatment regimes to enhance stand productivity. This provides a basis for a more strategic approach to brushing programs: allocating activities to areas where vegetation control is necessary and avoiding treatment of areas where broadleaf densities will not impact conifer growth or where a mixedwood complex stand is an appropriate and desirable condition future forest condition. One significant result of this approach is there will be less herbicide usage at the landscape level. The recent Dawson Creek Timber Supply Review (TSR) of the timber supply area (TSA) (1) identified the need to manage mixedwood stands in order to maintain their attributes on the landscape – to stop “unmixing the mixedwood” forest. It has been suggested that the productivity of mixedwood stands is greater over the long term than single species or conifer regenerated stands (2, 3, 4). It has also been suggested that species mixtures (aspen-spruce, birch-spruce) result in greater wood volumes at harvest than stands with only one of the species. Further some benefits of natural stand dynamics may be realized by managing for complex mixtures. However the current operational ‘default’ of eliminating most or all broadleaf tree species is costly, reduces species and structural diversity, and may not be needed in many instances (5, 6, 7). The cost of carrying out some brushing treatments in order to meet free-growing guidelines in parts of the province may be unwarranted. For example, as part of the Adams Lake Interfor Innovative Forest Practices Agreement (6), studies showed the cost of brushing birch from blocks planted to lodgepole pine may be greater than anticipated increase in crop tree value: a negative investment. Current free-growing guidelines (7) require the removal of deciduous competition despite evidence suggesting that it is not always cost-effective, and does not typically result in higher timber volumes or better wood quality. In fact, wood quality may be compromised: slower crown lift and larger branches. Complex or intimate mixtures are seldom managed for, and when managed, tend to be managed 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 landbase and the allowable annual cut (1).
The absence of management is probably due to a limited understanding of the dynamic processes in complex stands and a lack of available models (growth and yield and successional). There is limited quantitative information available on i) how these stands develop during early seral stages, ii) how early stand composition translates to mid seral stages and future forest condition, and iii) 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 reduced vegetation control on growth and yield and future timber supply are not understood. They need to be quantified and modeled. In 2004 (year 1) this project examined growth responses of young (up to 15 years old) spruce and pine (Mackenzie only) stands to varying densities of residual birch or aspen. 460 plots were sampled in 8 blocks in the Fort Nelson and Fort St. John TSAs in the BWBS zone, and 336 plots were sampled in 8 blocks in the SBS zone in the Mackenzie TSA. Destructive sampling of saplings (construct conifer and deciduous height over age curves) in Fort Nelson and Mackenzie TSAs was completed. This data provided initial species-density (basal area) 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 (year 2), 306 plots were sampled in 8 blocks, 6 of which were re-measurements in Fort Nelson and 194 sampled in 4 blocks, 2 of which were re-measurements in Mackenzie. Modeling was done using tree lists from TSP. Projections suggested that broadleaf densities could be much greater than presently thought: e.g. birch could likely exceed 3000 sph and have no negative effects on spruce growth. Our early data supports model projections. However, there is an age-crop tree-species competitive relationship that we still need to describe. That is, 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 (both crop and competing) at the same density? In 2006 (year 3), more sites were established in the three TSAs, a preliminary paper was presented at an international boreal forest conference, and re-measurements are planned. Even though brief, temporal data suggests the growth model projections are not unreasonable. An experimental manipulation of broadleaf density (basal area) is needed to enhance findings for incorporation into both growth and successional models. During the next three years we plan to add to our temporal data base: effects of broadleaf density (basal area) on conifer growth (re-measurements); establish controlled density plots in each TSA; compare model outputs to temporal data; determine the utility of SORTIE for modeling these complex stands; describe treatment cost-benefit; define the density- species-age-height relationship; and meet with policy makers to discuss the implications and implementation of our early findings.
Related projects:  FSP_Y092243FSP_Y103243


Executive Summary (0.2Mb)
Establishment Report (1.1Mb)
Stand Development Presentation (1.9Mb)

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Updated August 16, 2010 

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