Patterns of Leaf Mass, Area and Nitrogen in Young Northern Hardwood Forests

Abstract

Patterns of leaf mass per unit area (LMA) and area-based foliar N concentration (N area) through the canopy were examined for seven tree species growing in reference and fertilized plots of two early successional northern hardwood stands in New Hampshire. Increases in LMA with height in the canopy were significantly related to increasing average daily photosynthetically active radiation (PAR). As expected, the slopes of regressions between LMA and PAR (i.e., plasticity) were higher for shade tolerant than intolerant species in both stands. Fertilization increased leaf area index in both stands. For the shade intolerant species (Prunus pensylvanica, Betula papyrifera), average canopy LMA increased in response to fertilization but no response was observed in the more tolerant species (Acer spp., Fagus grandifolia, Betula allegheniensis). The slopes of regressions between N area and PAR were highly significant, with higher plasticity of N area for shade tolerant than intolerant species. Average canopy N area increased in response to fertilization, and the response was particularly large for the intolerant species. The increase in N-area for these species was associated with the significant response of shaded foliage, as sun exposed foliage showed no response to fertilization.