The More the Merrier or the Fewer the Better Fare? Effects of Stand Density on Tree Growth and Climatic Response in a Scots Pine Plantation

In forests, the growth and productivity of individual trees and stands as a whole are regulated by stand density among other factors, because access to vital resources is limited by competition between trees. On 18 experimental plots of Scots pine (Pinus sylvestris L.) planted with a density of 500-128,000 trees/ha in the south taiga (Middle Siberia), interactions between stand density, tree- and stand-scale productivity, and tree-ring parameters were investigated. Tree-scale productivity variables, tree-ring width, and latewood width had stable negative allometric relationships with stand density (R-2 > 0.75), except for tree height (insignificant for inventory surveys at ages of 20 and 25 years; R-2 > 0.4 at the age of 35 years), while positive allometry was registered for stand productivity variables (R-2 > 0.7) and the all-time average latewood ratio (R-2 = 0.5 with planting density). Tree-ring parameters aside from the age trends correlate (p < 0.05) between the plots and demonstrate common responses to moderate moisture deficit. Although, its seasonality apparently depends on the resource base and intensity changes with stand density. February-June precipitation is more important for pine growth in dense stands, July-August conditions affect the latewood ratio stronger in sparse stands, and medium-density stands are more resistant to winter frosts.