DIFFERENCE IN THE ECOLOGICAL STRATEGIES OF CONIFEROUS TREE SPECIES IN EUROPEAN AND CANADIAN BOREAL FORESTS: A MODELING ANALYSIS

Abstract

The role of net primary productivity (NPP) allocation to tree organs as a parameter reflecting the ecological strategy of trees is discussed. The application of an individual-based spatially explicit simulation model of the tree-soil system (EFIMOD) to European and North American boreal forests reveales significant differences in ecological parameters (silvics) between North American jack pine (Pinus banksiana Lamb.)and black spruce (Picea mariana Mill.) of Canadian boreal forests and European Scots pine (Pinus sylvestris L.) and Norway spruce (Piceaabies L. [Karst.]). A significant difference between these species was found in NPP allocation between the needles and fine roots. In the North American coniferous species, the proportion of annual biomass increment, as reflected by NPP, which is allocated to fine root production is higher than in the European ones. A simulation experiment was performed to investigate the influence of NPP allocation on the components of carbon balance and wood productivity. Additionally, a parameter „turnover capacity“ (TC) as the sum of NPP and soil respiration was used. North American and European conifers were compared in two sets of modeling runs. In the first set, the model was run upon changes in NPP allocation in tree species ‘growing’ under their native conditions (Canada or Russia). In the second set, the Canadian conifers were simulated under Russian climate and soil conditions, whereas the European ones, under respective Canadian conditions. The results showed considerable dissimilarities of tree growth rate, soil development and parameters of carbon balance depending of NPP allocation patterns.The trees with relatively higher NPP proportions allocated to fine root production demonstrated lower growth rate even at a high carbon turnover capacity corresponding to the milder climate of European Russia. On the other hand, trees with the European, more uniform, NPP allocation pattern showed higher growth rates compared with the Canadian trees even under the colder continental conditions of Central Canada. The results suggest that wood productivity levels may be significantly different at similar NPP and turnover capacity if trees have different NPP allocation patterns. This difference reflects the adaptation of the North American coniferous species to harsh soil and climatic conditions, which are very cold in the northern and very dry in the southern part of Central Canadian boreal forests. NPP allocation index (NPP partitioning between leaves and fine roots) is proposed as a measure of tree stress tolerance, adaptation to severe climatic conditions, and ecological strategy.