Inter-and intra-specific mode of competition of Scots pine in pure and mixed stands along an environmental gradient in Europe

Abstract

Mixed forests are considered more productive and resilient to perturbations than monospecific stands. Mechanisms explaining this outperformance are usually related to complementary use of resources over time through reduced competition. The amount of secondary growth allocated can be (i) constant through tree size, reflecting complete symmetric competition; (ii) proportional to the tree size (symmetric competition), (iii) more than proportional, where the observed growth of large trees is higher than proportional (asymmetric competition) or (iv) inversely proportional, where small trees growth proportionally more than larger trees (inversely size-asymmetric competition). These modes of competition can vary with changes in nutrient and climatic conditions. We hypothesize that the response is also modulated by the species at contest. Data from three transect of triplets across Europe were used to test if Scots pine mode of competition change in pure stands or mixed with European Beech, Norway Spruce and Oak. A triplet is a set of three plots representing two pure stands and one mixed stand of the corresponding species. We use a size-growth relationship to test the existence of mixing effects across environmental gradients and time. We started testing if symmetric competition is dominant in dry years and if mixing effects can modulate the response. Previous results indicated that the mode of competition is site specific with divergent mixing effects across Europe.