Document Details
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Title |
The release of secondary stand structure in immature and mature pine stands following MPB attack | ||||||||||
Author |
Hawkins, Chris D.B. | ||||||||||
Date |
2010 | ||||||||||
Abstract |
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 | ||||||||||
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