Foliar morphology and spatial distribution in five-year-old plantations of Betula alnoides

Foliage spatial distribution and morphological variation within crowns reflect the adjustment of a tree to acclimatise to different microenvironments within crowns and stands. They play important roles in the light use efficiency, carbon assimilation and photosynthesis capacity of the whole tree. In this study, leaf quantity and size at the tree and crown layer levels, and leaf morphology across crown layers, sectors and zones, from 18 trees were investigated in five-year-old Betula alnoides plantations with six planting densities. The results showed that the vertical distributions of leaf number, leaf area index, cumulative branch cross sectional area and leaf area and their ratios were skewed towards the upper crown layers, especially for high planting densities. There was a tendency for leaf size (leaf length, width, perimeter and area) and leaf dry mass to increase from lower to upper crown layer and also from the inner to outer crown zones. The leaf shape factor was larger, and the ratio of leaf length to width and specific leaf area were much smaller, for leaves in the outer and upper crown positions. Leaves in the southern and eastern sectors were smaller than those in the northern and western sectors, but leaf length to width ratio, leaf shape factor and specific leaf area did not differ significantly among four crown sectors. In addition, planting density had no significant effect on leaf related traits at the individual tree and crown layer levels, and leaf morphology also did not vary regularly with planting density, but the specific leaf area was significantly negatively correlated with planting density. However, the interactions between planting density and crown layer, crown sector and crown zone, and among planting density, crown layer and crown zone, were significant. The findings confirmed the acclimation of leaf distribution and morphology to different microenvironments, and provided baseline information for plantation management of B. alnoides and other valuable hardwood species in southern China and other regions with similar climate conditions.