Exploring the relationship between stand growth, structure and growth dominance in Eucalyptus monoclonal plantations across a continent-wide environmental gradient in Brazil

Abstract

Stand structure can have a considerable influence on forest growth and productivity. A stand’s response to factors like temperature, precipitation, vapor pressure deficit and different soil characteristics may result not only from the mean change in tree responses (e.g. growth decrease or increase), but may also depend on how individual tree responses vary in relation to their size and how they cope with competition. There may be a large growth imbalance among trees as a function of their size, which is referred to as growth dominance. That is, a change in a factor may have different impacts on stand growth depending on stand structure and how growth is distributed. Thus, using an experimental platform spanning tropical Brazil, we explored the relationship between growth dominance and stand growth, and whether this relationship changes across a wide climatic gradient, represented by soil water deficit. We found a predominance of negative growth dominance during the early phase of stand development which increased until dominance became positive, after about 30 months, and kept increasing afterwards. Increasing soil water deficit slowed the increase in growth dominance throughout time. The intensification of growth dominance (either positive or negative) was associated with decreasing stand growth. Increasing soil water deficit decreased the negative effect of growth dominance on increment in absolute terms, but we showed that, at the end of a 5-year rotation, increasing growth dominance at a site with more intense water deficit led to a greater growth loss in relative terms than at a site with milder water deficit. For example, the estimated difference in increment between a stand with a low growth dominance of 0.05 and a stand with a high growth dominance of 0.20 at the end of a 60–month rotation at a site with an accumulated water deficit of −200 mm was about 28 m3 ha−1 year−1, which is equivalent to a 39% decrease in relative terms. This same GDC difference under a water stress of −4000 mm resulted in a decrease in increment of approximately 18 m3 ha−1 year−1, or 48% in relative terms.