The lodgepole pine (Pinus contorta Dougl. Ex Loud. var. latifolia Engelm.) forests of British Columbia (BC) are currently experiencing the largest mountain pine beetle (Dendroctonus ponderosae Hopkins) (MPB) outbreak since the arrival of European settlers (Eng et al. 2005). It is predicted that by the end of the epidemic 80% of the susceptible (mature, >80 years old) pine will have been killed. Timber supply analysis conducted by the British Columbia Ministry of Forests and Range (MFR) predicts that the mid-term timber supply in the Prince George timber supply area (TSA) will have fallen from a pre MPB AAC (allowable annual cut) of 9.1 million m3 to about 6.9 million m3 35 years from today (Eng et al. 2005, Pousette and Hawkins 2006, Pousette 2006). The post MPB epidemic AAC is based on several timber supply modeling assumptions 1) oldest attacked stands are harvested first, 2) mature stands have attack rates of about 80 % while transitional aged stands (61-80 years old) will have attack rates of about 50 %, 3) there is no attack in immature stands (=60 years old), 4) there is a regeneration delay of 15 years in areas not logged, and 5) product shelf life is 15 years with 5 years for saw logs (Eng et al. 2004, 2005).
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immature pine leading stands (=60 years old) are also being attacked at significant levels (MacLauchlan 2006, Hawkins unpublished data). MPB 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 TSA (Eng et al. 2005, Pousette and Hawkins 2006). The current cut level is expected to be reduced within 5 years and will continue to be reduced until the projected mid-term 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 immature age classes and unlogged mature age classes has the potential to contribute to the mid-term timber supply and reduce the effect of the mid-term timber supply fall down (Rakochy 2005).
MPB mortality emulates a thinning from above. 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 582 million m3 of MPB affected wood (post 2006 flight) 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. Through the use of dendroecological reconstruction, Alfaro et al. (2004) were able to show that in a period of 120 years 3 release events occurred in response to MPB attack, and these averaged 13.8 years in duration with 42.3 years in frequency between outbreak events. Response to release was similar for both pine and non pine spe ...
Hawkins, Chris D.B., Balliet, Nicole; Runzer, Kyle. 2009. The release of secondary stand structure in immature and mature pine stands following MPB attack. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2009MR315
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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