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Evaluation of the impact of N fertilization on mountain pine beetle success in mature lodgepole pine stands at the leading edge of an infestation
McLean, John
Nitrogen is one of the key limiting factors for life systems (White 2005) and the lodgepole pine forests of British Columbia are generally deficient in this nutrient (Brockley 2000). Waring and Pitman (1985) reported that improved nitrogen nutrition hastened lodgepole pine tree recovery from attack by the mountain pine beetle (MPB), Dendroctonus ponderosae (Coleoptera:Curculionidae [Scolytinae] but did not prevent attacks by beetles until growth efficiencies exceeded 100g of wood production per square metre of foliage. The major line of defense for lodgepole pine trees is the dynamic wound reaction (DWR) rather than oleoresin flow alone (Raffa and Berryman, 1982). Excessive N fertilization might render the lodgepole more suitable as a food source for attacking beetles which would be a counterproductive result but one that would need to be allowed for (Herms, 2002). Recent literature reports near isometric scaling of whole- plant respiration, N content and plant mass (Reich et al. 2006) suggesting that additional N would enhance respiration which we will in turn evaluate by the enhancement of the dynamic wound response capabilities of the trees. Experience in the Cascade Forest District in the Southern Interior Forest Region during the summers of 2004 and 2005 showed that 140 year old lodgepole pine responded significantly to a single fertilizer treatment of 200 KgN/ha with longer needle growth and an apparent improved capability to pitch out attacks by the mountain pine beetle. Several trees in the two fertilized stands attacked in 2004 maintained green foliage in 2005, had no additional attacks by the mountain pine beetle and few emergence holes from the 2004 attacks (Coggins and McLean 2005). This project seeks to verify these observations in a fully randomized experiment in a leading edge infestation of mountain pine beetle in a ~120 year old lodgepole pine forest.
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