To explore whether leaf traits and trait relationships varied during progressive succession within the understory and canopy layers, specific leaf area (SLA), leaf nitrogen (N) and phosphorus (P) concentrations (mass- and area-based), and photosynthetic capacity (A: mass- and area-based) of tropical woody vegetation were measured in 2 layers in 3 successional stages of tropical forests. For understory plants, 4 out of 7 leaf traits varied significantly along the successional stages. The slopes of the Nmass—SLA and Pmass—SLA relationships were steeper in early than in intermediate and old-growth forests. The slopes of the Nmass—Amass, PmasS—Amass' and SLA—Amass relationships did not differ among the 3 successional stages, but the y-intercepts were higher in early than in intermediate and old-growth forests. The slope of the Nmass—Pmass relationship changed little along the successional gradient, but the y-intercepts were higher in old-growth forest than in early and intermediate successional forests. For canopy trees, 3 out of 7 leaf traits changed significantly, but the slopes of 6 bivariate relationships remained invariant over the successional chronosequence. However, the y-intercepts of the Nmass—Amass and SLA—Amass relationships were higher in early and intermediate forests than in old growth forest, and the y-intercept of the Nmass—Pmass relationship was higher in early than in intermediate and old-growth forests. These results show that understory plants adjusted their SLA to adapt to environmental conditions more readily in intermediate and old-growth forests than in early successional forest. Resource allocation strategies did not differ within the canopy layers during the successional progress, and variations in photosynthetic nitrogen and phosphorus use efficiency (PNUE/PPUE) and N:P ratios were unrelated to resource allocation strategies, but likely responded to environmental pressures.
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Vol. 19 • No. 3