Open Collections

Abstract

Retention silvicultural systems, defined by leaving mature trees in patches (group retention) or dispersed arrangements (dispersed retention), are used in ~30% of harvested area in coastal British Columbia (BC) to balance timber and ecological objectives. Silvicultural systems (objective-driven pathways of harvesting, regeneration and tending activities in a stand) affect forest pathogens, which creates complex decisions where foresters match associated impacts (positive and negative) of pathogens and silvicultural systems to management objectives. This study measured infection patterns of hemlock dwarf mistletoe (HDM; Arceuthobium tsugense (Rosend.) G.N. Jones subsp. tsugense), a native hemi-parasitic plant on hemlock (Tsuga heterophylla (Raf.) Sarg.), to infer additional infection from mature tree patches in group retention relative to clearcut systems. Infection patterns were measured at 11 sites in coastal BC along 55 m edges separating mature forest harbouring HDM from a regenerating clearcut (23–45 years old). HDM infection was assessed with a six-class rating (DMR) that ranged from 0 (uninfected)–6 (>50% branches infected). Mature forests (infection source) had high incidence (95%) and variable average DMR (range = 1.4–5.7) and infected basal area (range = 18–106 m²/ha). Spread into regenerating forests was variable across infection boundary (3–32 m from edge), incidence (range, trees ≤15 m from edge = 0–100%) and average DMR (range, trees ≤15 m from edge = 0–3.0). Model predictions for a median site indicated light and moderate infection severities were most probable