Stand volume growth varies with age, site index, and stand density - Comments on Stokland (2021)

Stand volume growth varies with age, site index, and stand density. Analyses of changes in volume growth across stand ages need to consider the non-linear effects of all independent variables and their interactions, as is typically done in forest growth models. This is particularly important for unbalanced data, like the national forest inventory data. Stokland's (2021) analysis did not use this approach, limiting any insights about age effects on volume growth of old stands. Other details of the national forest inventory data in Norway will need special attention in the analysis of age trends in old stands: a lack of fully stocked stands, different management regimes and sites for older and younger stands, and rough estimates of stand ages for old stands.