Early development of planted Norway spruce in recently established stands, growing pure and in admixture

In Fennoscandia, Norway spruce (Picea abies Karst.) in clearcut forestry has traditionally been grown as pure species stands. There is increasing interest in mixed stands of spruce and other species such as Scots pine (Pinus sylvestris L.) and birch (Betula spp.). Mixed stands provide a wider range of ecosystem services, although there were concerns that spruce would suffer from competition and grow more slowly than in pure stands. There is still scarce knowledge of the early growth of mixed stands, especially given recent silvicultural advances. We compared the early development of spruce growing in recently established pure stands and mixed stands, either with pine or birch. For sample spruce trees, we reconstructed the past diameter and height growth through stem analysis. For spruce, we investigated differences across admixtures in terms of (Q1) age–size development, (Q2) recent diameter and height growth, and (Q3) achieved mean size. We did not observe strong negative effects in young spruce (<25 years) development growing in mixed stands compared to pure stands. The only differences were an early slower diameter development over age in the spruce–pine stands (not found in the recent growth or mean size achieved), and a higher achieved mean height in spruce–birch stands.