Residual mature trees and secondary stand structure after mountain pine beetle attack in central British Columbia

Abstract

Lodgepole pine forests in British Columbia (BC) are experiencing the largest mountain pine beetle (MPB) epidemic in recorded history. Now that the peak of the epidemic has passed, information regarding the existing live secondary stand structure (height >4m but DBH <7.5cm), regeneration (⩽4m in height) and residual mature trees (DBH >7.5cm) in the MPB-attacked stands are needed to assess management options and future timber supply. In total, 459 MPB-attacked pine stands were sampled from eight different age classes (13–250yr) in three different ecological subzones (dry, mesic, moist) of central BC. Mean MPB attack was greater than 40% when stand age was ⩾20years. Secondary stand structure and residual mature tree layers offer significant opportunities for mitigating the effects of MPB attack on future commercial wood values and ecological processes. The mean density of secondary stand structure and regeneration varied widely within and among ecological subzones. Depending on stand age, 44–98% of stands still contained sufficient stems after MPB attack to be considered stocked. Species composition varied at the stand level, but most stands had sufficient amounts of BC’s preferred commercial species. Due to MPB caused mortality, most of the stands were moving towards a mixed species and uneven aged condition. A SORTIE-ND model projection suggests that stands which had a minimum of 900 stems/ha of secondary structure >4m in height can reach merchantable volumes within 30years.