Radial growth of residual overstory trees and understory saplings after mountain pine beetle attack in central British Columbia

Abstract

There is uncertainty regarding the timing and rate of radial growth of understory saplings and overstory trees in unsalvaged mountain pine beetle (MPB) attacked lodgepole pine stands following one of the largest MPB epidemics in British Columbia (BC). This study was designed to quantify the radial growth response of understory saplings and residual live overstory trees before and after MPB attack. This information is important to assess management options and future timber supply. In total 91 stands were sampled from different age classes and biogeoclimatic sub-zones of central BC. Radial growth was quantified based on five years of tree ring widths immediately preceding the MPB outbreak and five years after attack. Finally, the ratio of area growth was calculated for each tree to describe the change in tree growth following MPB attack. After the death of larger pine trees, healthy vigorous understory species exhibited increased radial growth (percent mean growth increment: MGI) compared to healthy overstory trees. Generally shade tolerant species demonstrated the greatest radial growth among understory species; whereas shade intolerant species had the best growth response among residual live overstory trees. In understory species, the degree of radial growth increased with increased pine mortality while overstory species were not affected by level of MPB attack. This study indicates that radial growth in residual tree species showed a positive response after MPB caused mortality. This may have implications for initiating management strategies and accurate mid-term timber supply projections for MPB killed stands in central BC.