Inter-tree competitive processes occurring over 24 years in a mixed-species Nelder trial

Development of symmetric and asymmetric inter-tree competitive processes was assessed to 24 years of age in a Nelder wheel experiment in Queensland, Australia. It contained a mixture of hoop pine ( Araucaria cunninghamii Aiton ex D.Don) and Queensland maple ( Flindersia brayleyana F.Muell.). The levels of these processes were assessed through the changes with age of the growth dominance statistic at different stocking densities at planting; this statistic is based on the relative contributions of larger and smaller trees to total stand growth. After 6 −11 years of age, asymmetric competition, probably for light, developed in hoop pine but had barely developed in maple by 24 years. As stocking density increased, hoop pine suffered progressively more intensive competition, but this did not occur in maple. Earlier work had examined tree stem growth rates and found that maple exerted more intense competition on hoop pine than on other maple trees. Hoop pine had much lower inter- and intra-specific competitive effects than maple. It is suggested these effects might be explained through architectural differences between the crown structures of the two species allowing maple to compete asymmetrically for light with hoop pine but not with itself nor hoop pine with maple.