Site Index Curves for Common Alder and Grey Alder Growing on Different Types of Forest Soil in Sweden

Growth data were collected from 32 stands of common alder and 26 stands of grey alder growing on forest land in Sweden. The stands ranged in latitude from 56 to 60° N and from 58 to 63° N. The mean age of common and grey alder stands was 48 yrs (range 21-91) and 40 yrs (range 21-66), respectively, the mean stand density 1174 stems ha^-1 (range 440-2994) and 2140 stems ha–¹ (range 591-5120), and the mean diameter at breast height (on bark) 21 cm (range 13-27 cm) and 17 cm (range 9-25 cm). Site index curves were constructed for total age. Curves for H₄₀ (dominant height at 40 yrs total age) were constructed using data from all stands investigated. Curves fitted for H₄₀ total age of common alder were found to have the same shape as curves developed for German conditions. Site index curves for grey alder show higher growth for middle-aged trees compared with curves from Norwegian stands. Older Finnish site index curves for grey alder were found to have the same shape as curves constructed in the present study. Soil types in the common alder stands were divided into four groups: moorland peat/light clay (n=5), moorland peat/sand (5), cambisol/sand (4) and fine sand (4). For grey alder stands the soils were divided into three groups: silt (4), sandy till (3) and cambisol/light clay (3). Soil types represented by only one or two stands were not included in the analysis. No statistically significant differences in site index were found between the four soil-type groups in common alder stands or between the three soil-type groups in grey alder stands. Some recommendations for the management of common and grey alder stands are given.