Above- and below-ground biomass and nutrient distribution of a paper birch and subalpine fir mixed-species stand in the Sub-Boreal Spruce zone of British Columbia

Abstract

Stand structure, height and diameter growth, above- and below-ground biomass, and nutrient concentrations and content were determined for a 35-year-old fire-origin paper birch ( Betula papyrifera) and subalpine fir ( Abies lasiocarpa) mixed-species stand in the Sub-Boreal Spruce (SBS) zone of British Columbia. Paper birch, which formed the dominant overstory following the 1961 fire, had normal distributions of height and diameter classes. Subalpine fir, which dominated the understory, had the reverse J-shaped height and diameter distributions that are expected of a shade tolerant, climax species. Paper birch grew more than three times the height of subalpine fir. Growing in the summer shade of the birch, subalpine fir had slow but steady height growth during the first 10–15 years, after which height growth declined somewhat. Allometric equations, relating dry weight of foliage, branches, stemwood, stembark, roots, and total biomass to diameter at breast height (DBH), were developed to estimate above- and below-ground biomass. Total biomass of paper birch reached 83.2 t ha −1, while subalpine fir biomass was 26.7 t ha −1. Subalpine fir allocated more biomass to foliage and branches compared to paper birch. Foliage of paper birch had higher nutrient concentrations of N, P, K, Ca, and Mg than subalpine fir foliage. Branches and stembark of subalpine fir had higher P, and Ca concentrations than paper birch. Subalpine fir branches contained more of all examined nutrients than paper birch branches. This is a significant component in nutrient cycling of the mixed-species forest.