Modelling the responses of crown profiles to competition in terms of different tree classes and directions in two coniferous tree species in northeastern China

Using branch data from 63 L.kaempferi and 36 L.gmelinii sampled trees in northeastern China, the responses of crown profiles with different tree classes (dominant, intermediate and suppressed trees) and aspects (north, east, south and west) to competition were studied. Crown displacement, defined as the distance between the centre of gravity of the crown and the stem base, was calculated for all the sampled trees to estimate the crown plasticity. The horizontal crown overlapping area (COA H ) between sampled trees and the closest neighbouring trees was calculated to estimate the neighbour competition. A crown profile model that includes COA H as the explanatory variable was developed, and the effect of COA H on the crown profile of two tree species was analysed. The results showed that more than half of the trees had the largest crown radius and upper crown surface area on the north and east sides for L.kaempferi and on the north and south sides for L.gmelinii . The crown displacement of L.kaempferi was greater on the north and east sides, and that of L.gmelinii was greater on the south and east sides. COA H had a significant effect on the crown profile model for both species. The mean square error reduction (MSER) for the crown profile model including COA H relative to the model without COA H was 1.68% and 2.10% for L.kaempferi and L.gmelinii , respectively. The COA H had a greater impact on the crown profile of L.gmelinii than that of L.kaempferi . The inflexion point of the dominant and intermediate trees for both species was sensitive to COA H and gradually moved towards the crown base as the neighbour competition intensified, while the inflexion point of the suppressed tree showed a weak response to COA H . The crown profile in the four directions was closely related to the current radial stem growth.