Site index curves for Norway spruce (Picea abies (L.) karst.) planted on abandoned farm land

Abstract

Growth data were collected from 157 Norway spruce (Picea abies (L.) Karst.) stands planted on farm land in Sweden from 55 to 66° N. The mean age of the stands was 41 years (range, 25–91), the mean stand density 1 640 stems ha⁻¹ (range, 400–3 722), and the mean diameter at breast height (outside bark) 25 cm (range, 12–48). The height growth was measured in 56 stands during the initial five years after plantation and followed systematically until the stands were 30 years old. Early height growth for spruces growing on clay soils was lower than for trees growing on sand, till and peat soils. The height increment for 5-year-old spruces predicted the height increment for mature spruces (30–50 years old).

Site index curves were constructed for total age. Curves for H₄₀ (dominant height at 40 years total age) were made for both northern (50 stands, 61–66° N) and southern (107 stands, 55–61° N) Sweden. Site index curves for H₅₀ at total age are presented for Sweden as a whole (Lat. 55–66° N) and southern Sweden only. Curves based on breast height age were also constructed for H₄₀ and H₅₀. Curves fitted for H₄₀ at breast height were well in accordance with the curves presented in the past for spruce on forest lands by Nordic studies. The curves from the present study have slower growth for young spruces than curves for forest land. For 40–90-year-old spruce stands, curves from the present study indicate taller heights than from forest land curves.