Linking forest growth with stand structure: Tree size inequality, tree growth or resource partitioning and the asymmetry of competition

Stand structure can strongly influence forest growth and other processes, such as the water balance, carbon partitioning, nutrient cycling and light dynamics. However, individual structural variables can be positively or negatively correlated with growth. This is the case for variables such as size inequality and those that describe resource partitioning, such as the degree of symmetric/asymmetric competition and growth dominance. Several contrasting growth-structure correlations are reviewed and linked to forest processes by considering the different types of tree interactions they are associated with. Contrasting growth-structure correlations appear to converge when they are examined using a simple framework where stand growth is a function of three variables as opposed to any one of the variables alone; stand density, size distributions and tree size-growth relationships. The size distributions quantify how the stand density is distributed between the different sizes while the size growth relationships quantify how growth is partitioned between different sizes. Size inequality may not often be a useful explanatory variable and instead it appears to sometimes correlate with growth because it can be correlated with other variables that influence growth. The spatial and temporal dynamics of the effects of structure on growth have received little attention and a long-term growth and yield data set from central Europe was used to examine how the effects of structure can change along climatic gradients. The simple framework of three variables could be used to separate the effects of structure and functioning when comparing mixed and monospecific forests, as well as to design silvicultural interventions or to determine whether past management interventions have achieved their goals. The implications for selecting which structural variables to use and when scaling up to the stand level, are also discussed.