Forest Investment Account (FIA) - Forest Science Program
FIA Project M075046

    Stand and forest dynamics following MPB: how spatial patterns of salvage harvesting affect Warren root collar weevil pressure in regenerating stands
 
Project lead: Aukema, Brian
Contributing Authors: Aukema, Brian H.; Klingenberg, Matthew D.
Imprint: Prince George, BC : Canadian Forest Service, 2007
Subject: Forest Investment Account (FIA), Dendroctonus Ponderosae, British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
The outbreak of mountain pine beetle in BC currently covers 7 million ha, although the majority of the outbreak in the northern interior of the province has run its course (Aukema et al. 2006a). Salvage operations will continue at unprecedented rates throughout the next decade, transforming the landscape into a mosaic of numerous patches of regenerating stands adjacent to killed timber. Despite widespread salvage operations, little is known about how the spatial patterns of salvage logging will affect recruitment and success of both planted and naturally regenerating stands. Large-scale disturbance events such as insect outbreaks frequently affect plant and animal species assemblages in successional communities (Matsuoka et al. 2001). In the current context of mountain pine beetle disturbance, a significant threat to regeneration is the Warren root collar weevil (Hylobius warreni) both concentrating in and migrating from residual stands. The Warren root collar weevil is prevalent in lodgepole pine and mixed lodgepole pine/spruce stands throughout BC. Larvae develop and feed subcortically on the root collars of trees. Large diameter trees typically tolerate feeding, although the feeding wounds may predispose surviving trees to root pathogens. Larvae frequently girdle and kill small diameter trees, and cumulative mortality in past studies has ranged as high as 16% (Schroff et al. 2005). Adults may live up to five years, and females lay 25-30 eggs per year. Of these, approximately 25% typically survive to the damaging larval stages (Cerezke 1994). Several site conditions favour Warren weevil development, and many of these may be created by timber salvage operations following MPB. First, an increased duff layer, such as from logging slash, may create conditions favourable for weevil proliferation. For example, a study by Czereke (1994) noted that the number of weevils per tree increased up to 5 after a pre-commercial thinning treatment, and the proportion of trees sustaining injury doubled from 25% to 50%. Second, open site conditions, such as within a clearcut, allow increased soil temperatures amenable to larval development. Third, planted lodgepole pine often has significant root deformation (Robert and Lindgren 2005), and such trees may suffer increased mortality due to weevil attack (Robert 2004). Finally, weevils are most abundant on moist to wet sites, which may become more prevalent as water tables rise due to extensive lodgepole pine mortality (Cerezke 1994). Salvage logging of MPB-killed stands might act to decrease endemic resident weevil populations, but in fact, the opposite may be true. MPB-caused mortality would essentially remove dead trees from the host pool, and weevils would typically concentrate on the remaining live stems. After salvage harvesting, larvae will continue to develop in residual stumps (Cerezke 1973), while adults may migrate to nearby regenerating stands, such as within clearcuts, although the extent of the latter activity is unclear. Aerial surveys in the Nadina Forest District by Ken White and Carolyn Stevens (Project Partners with the BC Ministry of Forests and Range) indicate mortality of up to 40% in regeneration openings, frequently within 100m of MPB-killed stands. Quantifying this migration and subsequent mortality to subsequent regeneration in relation to spatial arrangement of MPB-killed stands is the focus of this proposal. This project will lead to an understanding of the spatial pattern of attack/mortality of Warren root collar weevil in regenerating stands adjacent to MPB-killed stands. Characterizing these patterns as either homogenous (such as random) or inhomogeneous (such as a clear gradient from stand edge implying migration, or clustering) will allow us to infer processes driving Warren root collar weevil populations. For example, a random distribution might imply localized eruptions within the regenerating clearcut. A detectable gradient of attack and mortality may imply significant migration from the edge of the MPB-killed stand. A pattern of clustering could be associated with ingress into naturally planted stands, or be related to other stand edge or site characteristics. Hypothetically, it is possible that migration could be mistaken for localized eruptions if the insects were to migrate quickly into a clearcut, saturate the area, and assume a random or regular distribution. However, we do not anticipate such problems since (1) this insect is flightless and (2) team member Niklas Björklund will be studying short-term adult weevil movement in live vs. MPB-killed lodgepole pine stands on a separate NSERC-funded project, using harmonic radar. Given our sample design and analyses (detailed below), we will be able to separate endemic weevil pressure from migration, and gain inference on site factors that may influence Warren weevil attack and mortality to regeneration. Understanding process may inform future management strategies, such as non-host species selection for harvesting on high-risk sites, deployment of potential chemical or visual attractants and traps, or creation of buffer-habitat unsuitable for migration.
Contact: Aukema, Brian H., (250) 960-5924, baukema@nrcan.gc.ca

    Deliverables:

Executive Summary (0.1Mb)

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Updated August 16, 2010 

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