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Foliar responses of subalpine r [Abies lasiocarpa (Hook.) Nutt.] to thinning were studied in a 35-yr-old mixed stand of paper birch (Betula papyrifera Marsh.) and conifers. The stand regenerated naturally after a wild re with a canopy dominated by paper birch (average height 9.8 m) and an understorey dominated by subalpine r (average height 1.6 m). The stand was thinned to four densities of birch: 0, 600 and 1200 stems ha ¼ 1 and control (unthinned at 2300-6400 stems ha ¼ 1 ) in the autumn of 1995. The understorey conifers, mainly subalpine r, were thinned to 1200 stems ha ¼ 1 . The study used a completely randomized split-plot design. Three sample trees were systematically selected from each treatment replicate and each tree stratum (upper, intermediate and lower understorey). One-year-old and older age class needles were collected from one south-facing branch within the fth whorl from the tree top. Thinning of paper birch signi cantly (pB 0.001) increased leaf area and dry weight per 100 needles for intermediate and short trees except in the 0 birch treatment. Understorey subalpine r trees in 600 stems ha ¼1 birch (T3) had the largest leaf area and leaf dry weight per 100 1-yr-old needles. Speci c leaf area (SLA) decreased from unthinned (T1) to 0 birch (T4). Lower understorey trees had the largest SLA. One-year-old needles had signi cantly higher N, P and K concentrations in all the thinning treatments. These responses are consistent with the shade tolerance of subalpine r. The results suggest that when managing a paper birch -conifers mixed-wood forest it may be of bene t to understorey conifers to leave a birch canopy as a nursing crop.

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