Stand density effects on tree growth and climatic response in Picea obovata Ledeb. plantations

Stand density critically affects the growth and productivity of trees in various forest ecosystems, and thus their ability to provide goods and services. However, a better understanding of tree growth and forest stand structure interrelationships are critically lacking, which hinders our ability to develop sustainable management plans for climate resilient forests growth and development. The present study was carried out on Siberian spruce (Picea obovata Ledeb.) in southern taiga of Central Siberia in experimental plantations created in 1982. The initial planting densities DENS0 at 18 plots ranged from 500 to 128 000 trees ha-1. Further stand density dynamics due to self-thinning was defined mainly by tree age; log-linear regression models explained 80-99% of its variation. The average tree diameter demonstrated allometric negative dependence on stand density persistently for inventory surveys at ages of 20, 25, and 35 years, while tree height became significantly dependent on stand density only to age of 35 years. Tree-level productivity (trunk volume and basal area) was negatively affected by stand density, while stand productivity was positively linked with it. Mean tree-ring width and latewood width both decreased persistently with rising stand density, and their responses to temperature and precipitation shifted to earlier calendar dates, e.g., from June-July to May-June. At the same time, behavior of latewood ratio chronologies (their synchronicity and climatic response) divided all plots in two groups: sparse (planting density of 500-6 000 trees ha-1) and dense stands (8 000-128 000 trees ha- 1).Besides shift of positive response to precipitation from August to July, for trees in dense stands latewood ratio is negatively affected by winter snow.