Forest Investment Account (FIA) - Forest Science Program
FIA Project Y102188

    The release of secondary stand structure in immature and mature pine stands following MPB attack
Project lead: Chris Hawkins (University of Northern British Columbia)
Contributing Authors: Hawkins, Chris D.B.; Runzer, Kyle; Balliet, Nicole
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
The lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) forests of British Columbia are currently experiencing the largest mountain pine beetle (Dendroctonus ponderosae Hopkins) (MPB) outbreak since the arrival of European settlers (Eng et al. 2005). Timber supply analyses undertaken by both government and industry for various forest management units predict a significant mid-term timber supply fall down as a result of the current mountain pine beetle epidemic (Pedersen 2004, Canadian Forest Products 2005). An estimated 710 million m3 of merchantable timber has been killed by the mountain pine beetle (MFR 2008): a volume greater than 15 years of normal harvest for the Province’s central and southern interior.

It appears that 61 – 80 year old stands are being attacked at rates similar to those observed in mature stands (>80 years old) and that immature pine leading stands (=60 years old) are also being attacked at significant levels (MacLauchlan 2006, Runzer et al. 2008a, 2008b). Mountain pine beetle induced mortality in immature and transitional aged stands will cause a significant reduction (2.2 million m3) in the merchantable volume available for the mid-term timber supply in Prince George Timber Supply Area (TSA) (Eng et al. 2005, Pousette and Hawkins 2006, Walton et al. 2008). The current cut level is expected to be reduced within five years and will continue to be reduced until the projected mid-term allowable annual cut (AAC) is reached in approximately 35 years. Given the hypothesized drop in future AAC by timber supply models, regeneration or secondary structure (Coates et al. 2006) in attacked immature age classes and unlogged mature age classes has the potential to contribute to the mid-term timber supply and reduce the impact of the mid-term timber supply fall down (Rakochy 2005).

Forest changes will primarily be related to the MPB induced mortality (Hawkes et al. 2004, Stockdale et al. 2004) and abundance and condition of advanced regeneration or secondary structure (Heath and Alfaro 1990, Dale et al. 1998). As attacked trees die and more light reaches the forest floor, advanced regeneration (Cole and Amman 1980, Waring and Pitman 1985) and understory vegetation (Stone and Wolfe 1996) should display enhanced growth rates. According to Thompson et al. (2007), release which results from sudden death of healthy canopy trees, as seen in the current MPB epidemic, should result in a more rapid and prolonged release response compared to release that occurs following slow death of canopy trees.

It is essential for forest managers to consider the contribution that release of advanced regeneration can make towards meeting the mid-term timber supply in MPB killed stands (Veblen et al. 1991, Archibald and Arnup 1993), especially as it is anticipated that 25 - 40% of the 710 million m3 of MPB affected wood will not be salvage harvested.

There is no reason to believe that post-MPB residual trees and secondary structure in the central BC interior will not release; however, the rates of release and subsequent stand dynamics are poorly understood (Veblen et al. 1991, Stockdale et al. 2004) and not documented. Considering the complexity of species composition, abundance, spacing, health and vigor, as well as other stand level attributes including light intensity and hydraulic cycling, it is not an easy task to predict how advanced regeneration will respond to release (Griesebauer and Green 2006). These factors do suggest that 1) residual stands should be those which have significant levels of healthy secondary stand structure, can be restored economically and will contribute to the mid and long-term timber supply or 2) logged stands should be those that do not have adequate levels of secondary stand structure and will be costly to restore or have low potential to contribute to the mid-term timber supply.

The forest planning and practices regulation amendments to protect secondary structure came into force on July 25, 2008. It applies to eight TSAs in BC’s central interior including the Prince George TSA. Through this regulation the Chief Forester aims to protect stands with adequate secondary structure which will contribute to the mid-term timber supply. Section 43.1 of the regulation requires “targeted pine leading stands, at least five hectares in size, with an adequate stocking density of suitable secondary structure to be excluded from cutblocks or harvested in a manner that protects an adequate stocking density of suitable secondary structure” (Anonymous 2008). An adequate stocking density exists if there are a minimum of 700 suitable secondary structure trees per hectare at least 6m tall or a minimum of 900 suitable secondary structure trees per hectare at least 4 m tall. Trees must be healthy and at least 1.6 m apart (Anonymous 2008).

Since 2004, we have conducted MPB attack surveys in approximately 525 polygons: 235 in immature (age class 1 to 3), 80 in transitional (age class 4), and 210 in mature stands (age class 5 to 8). Polygons are primarily located in the southwest, southeast and west-central portions of the Prince George TSA. Release data was collected in a sub-set of the 525 polygons from July to October 2008. The focus was on age class 2 to 4 (21 to 80 years) stands with less emphasis on age class 5 to 8 stands (81 to 250 years). Stands with moderate to high levels of MPB attack were targeted. When these data are combined with the original survey data, they will allow for the 1) description of MPB attack and stand structure; 2) description of the release of secondary structure and residual mature trees; 3) quantification of regeneration by stand attributes; and 4) development of tree lists for use in stand level growth and yield (G&Y) models such as SORTIE-ND.

This project will consider six forest management questions identified by industry and government. 1) What is the quality and quantity of regeneration in MPB affected stands? 2) What are the growth and yield implications of treating or leaving MPB attacked stands and allowing the secondary stand structure to develop? 3) What is the release potential of these stands? 4) Which trees will release and when? 5) What are the economics of treating or leaving MPB attacked stands with varying amount of secondary stand structure? 6) What are the medium and long-term impacts of residual and secondary structure on timber supply? The answers-outcomes of the project will help to improve harvest scheduling, identify stands most suitable for retaining or restoring, and guide stand activities that positively affect the growth and quality of secondary stand structure.

Stand level G&Y modeling which incorporates the response of secondary structure to MPB attack is required to develop sound MPB mitigation strategies. SORTIE-ND is well suited for modeling post-MPB stand dynamics in the central BC interior. We plan to incorporate the release response of secondary stand structure found from data collected by this project, into the model assumptions in order to reflect “on the ground” post-MPB stand dynamics. This will improve SORTIE-ND simulations, growth and yield projections, and timber supply analyses. Several SORTIE-ND simulations will be conducted for each sampled stand: 1) leave the stand alone or allow stand dynamics to proceed without management; 2) under (fill) plant the attacked stand; 3) remove only the dead pine (essentially a thinning from above); 4) remove the pine and under (fill) plant the residual stand; and 5) clear the stand and plant. Each scenario will also include an economic analysis. The above scenarios will be run for a range of attack levels and combinations of the amount of secondary structure. The scenarios and accompanying economic analyses will be put into a decision matrix to help forest managers choose appropriate stands for harvest or retention, as well as helping to select the most cost effective and ecologically sound management strategies.
Related projects:  FSP_Y091188


Final technical report (0.3Mb)
Forrex webinar series presentation: After the beetle - what's there and will it grow? (13.8Mb)
Presentation: Development of Young Lodgepole Pine Leading Stands after Mountain Pine Beetle Attack in the Central BC Interior (11.1Mb)
Presentation: After the beetle and other musings (13.1Mb)

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Updated August 16, 2010 

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