An old-growth index for Douglas-fir stands in portions of the Interior Douglas-fir zone, central British Columbia

Abstract

We describe a quantitative old-growth index for Douglas-fir (Pseudotsuga menziesii var. glauca) stands in two Interior Douglas-fir (IDF) biogeoclimatic variants (dk3 and dk4) in the central interior of British Columbia. The index uses stand structure data including basal area of very large (≥ 57.5 cm DBH) and large (≥ 37.5 cm DBH) trees, density of small (< 27.5 cm DBH) trees, tree size variability, canopy complexity, density of declining and dead trees, and occurrence of canopy gaps. Three forms of the index were developed to accommodate different objectives and levels of data availability. Index values are grouped into four classes (early seral, mid-seral, mature, and old growth). Qualifiers of these classes provide additional descriptions of old-growth structural development as well as guidance for designing management practices to enhance old-growth development. A link is provided to a Microsoft Excel spreadsheet that can be used to calculate old-growth index values using each form of the index.