Characterization of Western Spruce Budworm Outbreak Regions in the British Columbia Interior
Total Page:16
File Type:pdf, Size:1020Kb
Canadian Journal of Forest Research Characterization of Western Spruce Budworm Outbreak Regions in the British Columbia Interior Journal: Canadian Journal of Forest Research Manuscript ID cjfr-2017-0278.R1 Manuscript Type: Article Date Submitted by the Author: 13-Mar-2018 Complete List of Authors: Maclauchlan, Lorraine; BC Ministry of Forests, Lands and Natural Resources, Forest Health Daniels, Lori; University of British Columbia, Geography Hodge, Janice;Draft Contractor Brooks, Julie; Contractor western spruce budworm, dendrochronology, defoliation, aerial surveys, Keyword: ecosystems Is the invited manuscript for consideration in a Special N/A Issue? : https://mc06.manuscriptcentral.com/cjfr-pubs Page 1 of 60 Canadian Journal of Forest Research 1 Characterization of Western Spruce Budworm Outbreak Regions in the British Columbia 2 Interior 3 4 5 Lorraine E. Maclauchlana, Lori D. Danielsb, Janice C. Hodgec and Julie E. Brooksd 6 7 8 a Ministry of Forests, Lands and Natural Resource Operations and Rural Development, 9 Thompson Okanagan Region, Draft441 Columbia Street, Kamloops, B.C. V2C 2T3 10 b University of British Columbia, Faculty of Forestry, Department of Forest and Conservation 11 Sciences, Forest Sciences Centre 3030, 2424 Main Mall, Vancouver, B.C. V6T 1Z4 12 c JCH Forest Pest Management, 7700 DeJong Drive, Coldstream, B.C. V1B 1P3 13 d Forest Health Management, 466 Central Avenue, Gibsons, B.C. V0N 1V1 14 1 https://mc06.manuscriptcentral.com/cjfr-pubs Canadian Journal of Forest Research Page 2 of 60 1 Abstract 2 3 The western spruce budworm (Choristoneura freemani Razowski; WSB) shapes Douglas-fir 4 (Pseudotsuga menziesii) (Mirb.) Franco forests throughout western North America with periodic, 5 severe landscape-level defoliation events. The largest and most continuous recorded defoliation 6 occurred in the 2000s, largely centered in the Williams Lake and 100 Mile House WSB Outbreak 7 Regions, peaking in 2007 at 847,000 hectares defoliated in B.C. Unique WSB Outbreak Regions 8 in south central B.C. are described using biogeoclimatic ecosystem classification, geography, 9 106 years of documented defoliation, and 46 stand-level Douglas-fir host tree-ring chronologies. 10 Since the 1980s, recorded defoliation in B.C. has shifted from coastal ecosystems and become a 11 dominant disturbance in drier, colder, InteriorDraft Douglas-fir ecosystems. Defoliation records 12 demarcate four outbreaks from 1950-2012 and up to three growth suppression events from 1937- 13 2012. Outbreak duration was shorter in the north and far south of B.C. with recovery periods (no 14 trees showing growth suppression) shorter over all WSB Outbreak Regions in the 2000s, 15 suggesting trees may be increasingly susceptible to each successive defoliation event. Knowing 16 the regional outbreak periodicity may facilitate early detection of incipient WSB populations, 17 which is critical for management as many of our low elevation Douglas-fir forests become more 18 stressed with changing and unpredictable climate regimes. 19 20 21 Key Words: western spruce budworm, B.C. outbreak history, aerial overview records, 22 dendrochronology, Douglas-fir 23 2 https://mc06.manuscriptcentral.com/cjfr-pubs Page 3 of 60 Canadian Journal of Forest Research 1 Introduction 2 The western spruce budworm, Choristoneura freemani Razowski, formerly Choristoneura 3 occidentalis Freeman (Lepidoptera: Tortricidae) (WSB), is a native defoliator that periodically 4 experiences often long lasting, landscape level population outbreaks throughout its range in 5 western North America (Fellin and Dewey 1982; Maclauchlan et al. 2006; Volney and Fleming 6 2007). WSB primarily feeds on both coastal (P. menziesii var. glauca (Beissn.) Franco and 7 interior Douglas-fir (Pseudotsugae menziesii var. menziesii (Mirb.) Franco), but also feeds on 8 true firs (Abies spp.), Engelmann spruce (Picea engelmannii Parry ex Engelm.), and western 9 larch (Larix occidentalis Nutt.) (Furniss and Carolin 1977; Fellin and Dewey 1982; Fellin 1985). 10 Cumulatively since 1909, approximatelyDraft 3.5 million hectares of interior Douglas-fir forest have 11 been defoliated (Table 1) one or more times by WSB in British Columbia (B.C.) (Parfett et al. 12 1994; FLNR 1996-2016; Maclauchlan et al. 2006). WSB is an early season defoliator that 13 totally or partially consumes new buds and flushing foliage. This feeding pattern results in 14 uneaten foliage, which dries and turns a characteristic reddish brown that is easily detected from 15 the air and the ground. WSB survival, population growth, and subsequent impacts to the tree are 16 closely tied to its synchrony with budflush and depend upon the tree’s age, position in the 17 canopy, and geographic location (elevation, latitude) (Swetnam and Lynch 1993; Maclauchlan 18 and Brooks 2009; Nealis 2012). Outbreaks are a result of several influences and processes, 19 including climate (Thomson et al. 1984; Campbell et al. 2006), reproduction, host availability, 20 mortality factors and dispersal (Régnière 1982; Royama 1984; Régnière and Nealis 2007). 21 Climate can promote more synchronized budflush and larval emergence, leading to an increase 22 in reproduction and insect survival (Thomson 1979; Alfaro et al. 2014). This insect-host 23 synchrony results in more complete bud destruction and defoliation by larvae. When viewed 3 https://mc06.manuscriptcentral.com/cjfr-pubs Canadian Journal of Forest Research Page 4 of 60 1 from a broad geographic scale, WSB exhibits expansive, sustained outbreaks; however, at a 2 smaller geographic landscape scale, WSB may display rather fast-cycling, eruptive outbreaks 3 (Campbell et al. 2005). 4 WSB can have devastating effects on Douglas-fir forests, by reducing overall growth and yield, 5 increasing susceptibility to other insect pests and diseases, and limiting forest management 6 options. Partial or selective harvesting may be compromised because WSB feeding will: reduce 7 available seed source on affected sites; damage or kill understory trees that are relied upon as the 8 next crop; and will increase the number of years until harvest cycle due to reduced radial growth 9 (Alfaro and Maclauchlan 1992; Day 1996; Maclauchlan and Brooks 2009). Due to WSB’s 10 preferential feeding on the current year buds and foliage, height growth is severely reduced or 11 eliminated during years of substantive defoliation.Draft Feeding by this insect also causes stem 12 defects, top-kill and tree mortality (Alfaro et al. 1982, 1985; Alfaro and Maclauchlan 1992) and 13 is particularly damaging to understory and suppressed trees in multi-layered stands (Maclauchlan 14 and Brooks 2009). The understory and suppressed component of stands have proportionally less 15 new foliage and therefore fewer WSB larvae are needed to cause severe defoliation 16 (Maclauchlan and Brooks 2009). The larger, overstory canopy trees can support much higher 17 WSB densities (Magnussen et al. 2005) before defoliation causes significant top-kill or mortality 18 (Alfaro et al. 1984; Alfaro 1986), or is even visible in aerial surveys. Defoliation also impedes 19 the radial growth of trees by destroying photosynthetic tissue, thereby reducing the supply of 20 carbohydrates needed for growth (Kramer and Kozlowski 1979). The width of annual rings 21 produced during infestation years is reduced in response to the phenological synchrony of buds 22 and larvae and the amount of larval feeding on foliage. This is characterized in the tree-rings as a 23 cause–effect relationship that usually has a lag of one or more years (Alfaro et al. 1985; Alfaro 4 https://mc06.manuscriptcentral.com/cjfr-pubs Page 5 of 60 Canadian Journal of Forest Research 1 and Maclauchlan 1992). After the infestation collapses, defoliated trees take several years to 2 regain their full foliage compliment; during this period, radial-growth rates slowly recover. 3 Duration and periodicity of outbreaks may be changing in some geographic areas (Maclauchlan 4 et al. 2006) as a response to global climate trends (Dale et al. 2001; Logan et al. 2003; Volney 5 and Hirsch 2005; Battisti 2008), regional topography, host species composition, latitude, canopy 6 structure and natural mortality factors. The most recent (1987-2015) WSB outbreak in B.C. 7 extended north along the Fraser River to immediately south of Quesnel (Fig. 1), well beyond the 8 previously recorded historical outbreak range (Maclauchlan et al. 2011). Early indications are 9 that the impact in these more northern stands is more severe than in stands to the south (L. 10 Maclauchlan, pers. observations). StandDraft composition and structure has changed dramatically 11 over recent decades in more northerly stands located in the Cariboo-Chilcotin Plateau due to 12 increased fire suppression and selective harvesting of larger, mature trees (Harvey et al. 2017). 13 These practices have led to many stands developing dense, overstocked understory layers that are 14 conducive to supporting high WSB populations (Maclauchlan and Brooks 2009). Also, in 15 mixed-conifer stands, the mountain pine beetle (Dendroctonus ponderosae Hopkins) has 16 removed most of the lodgepole pine (Pinus contorta Dougl.) component (Westfall and Ebata 17 2008; Safranyik et al. 2010), leaving Douglas-fir- or spruce-dominated stands that offer a more 18 susceptible resource for WSB. Interior Douglas-fir forests have seen a dramatic change in stand 19 structure and composition over the last century, largely due to human interventions (Swetnam 20 and Lynch 1993; Maclauchlan and Brooks 2009;