Effect of intra-specific competition on tree architecture and aboveground dry matter allocation in Scots pine

摘要

The study was carried out in a 25 year old Scots pine spacing trial, established with grafted clones at four different spacings. The oven-dry weight of the different aboveground parts of the tree (i.e. stem, large and small branches, needles and cones) was assessed separately. With closer spacing, the relative proportion of cones and of large branches per tree decreased, while the dry matter increment allocated to stemwood increased gradually from 11.7 to 28.5 percent. Without competition, the dry matter allocated to cones was nearly similar to that of current stemwood increment. On a unit area basis, the dry matter weight allocated to cones did not change significantly at different density levels and remained between 0.6 and 1.0 tonnes per ha. The highest total biomass per unit area was measured at maximum stand density (98.2 t/ha), where stem number is regulated by natural mortality (self-thinning). A slightly positive effect of competition on height growth was detectable only when the trees were young. The results show the plasticity of Scots pine architecture in relation to spacing in the early phases of stand development.