The temporal development of old-growth structural attributes in second-growth stands: a chronosequence study in the Coastal Western Hemlock zone in British Columbia

One of the key issues facing forest resource planners is the conservation and recruitment of old-growth characteristics in managed forests. The paucity of long-term data sets in many regions has limited our ability to project the temporal patterns of structural development in second-growth forests. Age-based thresholds have been employed in some jurisdictions, but these lack flexibility and are arbitrary in nature. Here we conduct a chronosequence study consisting of second-growth and old-growth stands in the coastal forests of Vancouver Island, British Columbia, to identify structural attributes that are suitable for quantifying and monitoring the progressive development of old-growth characteristics. The following structural attributes were identified and evaluated in the chronosequence analysis: volume and density of large live stems, standard deviation of stem DBH, density of large-diameter snags, volume of woody debris, and understory vegetation cover. The rate at which old-growth structural characteristics developed in second-growth stands varied considerably, with the earliest reaching levels observed in old-growth stands within 112 years, while most requiring 200 to greater than 250 years. The use of quantifiable measures of old-growth structure will help forest managers plan for the continued protection and recruitment of old-growth structure within managed forest landscapes.