Competition trials of Pinus banksiana and Populus tremuloides under a range of proportions and densities

Abstract

This study was the -first study designed specifically to analyse the competitive effects of density and species mixture for both Pinus banksiana and Populus tremuloides seedlings during the initial stages of growth and development. To this end, replacement series experiments with jack pine and trembling aspen seedlings were used in both a greenhouse and field study. In a 12~week greenhouse pot study species ratios of 100/0, 75/25, 50/50, 25/75, and 0/100 were planted at densities of 729, 2,344, and 10,000 pi ants/m In a. field study, similar mixes were planted at densities of 17, 83, 204, 494, and 2,500 plants/m[superscript]2. This field test will be continued for a period of three to four growing seasons. In the greenhouse study, jack pine assumed a dominant role at the highest density (10,000 plants/m[superscript]2). As the density was lowered, trembling aspen gained dominance over the pine in the mixtures. This relationship was reflected in relative crowding coefficients, as well as in replacement series diagrams for relattive yield. Also, it was determined that an adjustment in allocation of biomass with respect to the dominant competitor occurred. Trembling aspen increased its percentage biomass allocated to leaf weight, when jack pine was the dominant competitor. However, the aspen seedlings allocated a greater percentage to stem weight in response to aspen assuming the dominant role, A final observation included the lowering of aspen survival as the percentage of aspen in mixture increased. Increased density further accentuated this relationship , Jack pine survival was consistently high across the range of treatments.. From the preliminary measurements carried out on the field trial, it was found that both aspen height growth and crown development were affected by species composition. In general, as the percentage of aspen decreased at a given density, both height and crown volume increased. Furthermore, both height growth and crown volume for jack pine decreased, as density decreased. The cause for this response to density was related to the influence of environmental factors.