Mixtures with spruce species can be more productive than monocultures: evidence from the Gisburn experiment in Britain

• Published in: Forestry (London) Vol. 87; no. 2; pp. 209 - 217
• Main Authors: Mason, W. L, Connolly, T
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01-04-2014
• Subjects: Alnus glutinosa; basal area; forests; issues and policy; Picea abies; Picea sitchensis; Pinus sylvestris; planting; Quercus petraea; England
• ISSN: 0015-752X; 1464-3626
• DOI: 10.1093/forestry/cpt042

In 1955, an experiment was established at Gisburn forest in northern England to compare the performance of pure and mixed plots of four species: Norway spruce (Picea abies), Scots pine (Pinus sylvestris), sessile oak (Quercus petraea) and common alder (Alnus glutinosa). At the end of the first rotation, there was enhanced growth in all mixtures with Scots pine while there was a negative interaction in the Norway spruce/sessile oak mixture. The experiment was felled in 1989 after windblow and replanted in 1991, when Sitka spruce (Picea sitchensis) was added to the species trialled. After 20 years of the second rotation, patterns of individual species growth were generally similar to those in the first rotation, except that height and diameter growth of Norway spruce and Scots pine was significantly greater (P < 0.01) in mixed plots. Basal area growth of three combinations (Sitka spruce/Scots pine; Norway spruce/Scots pine; Norway spruce/common alder) was about 40 per cent greater than (and significantly different from) that predicted from performance in pure plots of the same species, evidence of transgressive overyielding. These results indicate that facilitation effects through improved nutrient status can lead to better productivity in mixed-species stands in planted forests. The implications of these findings for policies seeking to diversify single species planted forests are considered.