Long-Term Effects of Lodgepole Pine Terminal Weevil and Other Pests on Tree Form and Stand Structure in a Young Lodgepole Pine Stand in Southern British Columbia

Abstract

This study describes the impacts of 25 damaging agents recorded on young lodgepole pine trees over a 30-year period in a study plot in southern British Columbia. During the study, density fluctuated due to infill and mortality. Of the 1,295 stems per hectare present at the outset of the study, 37% of lodgepole pine died and only 24% of the trees remained pest-free by the final assessment. Pest-free trees were predominantly small and suppressed infill, leaving just over 1,000 stems per hectare of crop trees. Lodgepole pine terminal weevil affected over 38% of pine, with up to six attacks per tree. Fifty percent of lodgepole pine in the study was infected or killed by one or more hard pine stem rusts, with comandra blister rust and western gall rust being the predominant diseases, affecting 32% and 19% of the pine, respectively. Until age 20, 70% of weevil attacks caused major defects. From age 20–40 years, 50% of attacks caused major defects, often forks or multiple tops (stagheads). Defects were more severe when trees were attacked early in stand development. There was a strong correlation between the number of weevil attacks per tree and tree form, and the number of pests recorded per tree and tree form. Two or more pests per tree caused tree form to shift from good to moderate or poor.

Cumulative Impact of Biotic and Abiotic Damage Agents on Lodgepole Pine Tree Form and Stand Structure in Southern British Columbia

“…(Coleoptera: Curculionidae; Scolytinae) (IBM) (Safranyik & Carroll 2006, 1 This study summarizes the results of monitoring insect, disease, animal, and abiotic damage on individual trees within 14 plots in two biogeoclimatic zones in the southern portion of the Thompson Okanagan Region of British Columbia for up to three decades, and describes and interprets their cumulative effect on tree development over time. This broader analysis expands on the detailed analysis of pest impact reported in the case study by Maclauchlan and Brooks (2020).…”

“…The impacts of climate change on trees (young and old), landscapes, insects, and diseases are accelerating (Woods et al 2000, Allen 2009, Pojar 2010, Woods et al 2010, Ramsfield et al 2016, Maclauchlan & Buxton 2019, Maclauchlan & Brooks 2020. We anticipate that they will become more pronounced and damaging as we experience unseasonable or extreme weather events (Woods 2011, Woods et al 2005, van Mantgem et al 2009, Haughian et al 2012, whether by new pest occurrences or existing site-resident pests, until these stands reach their harvest age.…”

“…These plots were established in two biogeoclimatic zones in south central British Columbia to investigate the incidence and impact of lodgepole pine terminal weevil attack and other damage agents on individual trees over time. One of these original plots, not included in this report, was summarized in Maclauchlan and Brooks (2020) as a case study to lay the foundation for the analysis and interpretation of this plot network. Six of the 14 plots included within this study were originally established as part of a Ph.D. research project (Maclauchlan 1992).…”

“…This enabled us to determine if defects caused by weevil attacks remained unchanged from the first record of attack or increased or decreased in severity over time as the tree developed. Four categories of stem defect were used to describe each attack by lodgepole pine terminal weevil (crease, crook, fork, staghead) (Maher 1981, Alfaro 1989, Maclauchlan & Borden 1996, Maclauchlan & Brooks 2020.…”

“…The final plot assessment was conducted in 2020. At this time, we visually evaluated tree form and rated the tree as having good, moderate, or poor form (Maclauchlan & Brooks 2020). We measured the height of the lowest occurring (first) stem gall caused…”