Effect of Stand Structure and Density on Development of Natural Regeneration in Two Picea abies Stands in Sweden

Abstract

Previous studies have indicated that the effect of overstorey density on height increment and mortality of seedlings and saplings is affected by the vertical structure of the overstorey. To test this, 28 plots, including four control plots, were studied at two sites, in northern and central Sweden. Norway spruce dominated all plots. The overstorey was thinned from "above", i.e. harvesting mainly large-diameter trees and maintaining a multilayered structure, or from "below", i.e. harvesting mainly smaller trees and creating a shelterwood. Three different densities were created for each structure, in the range 20-140 m3 ha-1 at the northern site, and 40-200 m3 ha-1 at the southern site. Seven years after treatment, seedling (0.1 m5 heightB 0.5 m) and sapling (0.5 m5 heightB 2.0 m) height increment tended to decrease with increasing overstorey density at both sites for plots thinned from below, but the effect was not statistically significant. Cutting regime had a significant effect on seedling height increment year 5 after treatment at the northern site, and cutting regimen and overstorey density combined had a significant effect on saplings in years 5 and 6 after treatment at the southern site. Annual mortality rates were 2-7% for seedlings and 0-4% for saplings. Ingrowth past 10 cm in height during the 7 yrs after treatment was less than 20 seedlings per hectare and year at the northern site, and less than three at the southern site.