Early weed control can increase long-term growth, yield and carbon sequestration of Sitka spruce stands in Britain

Abstract

Six experiments, initially established to investigate the effects ofweed control on establishment of Sitka spruce (Picea sitchensis (Bong)Carr.)were revisited 15-25years after planting, and6-22years afterweed control ceased. At three of the six experimentsweed control resulted in initial benefits to growth and in some cases survival at Age 3,while no effectwas evident at the other three sites. Atmid-rotation, 15-25 years after planting, although therewere no persistenteffectsofweedcontrolonheightor diametergrowth,at threeof theexperiments therewasapositiveeffecton survival. Projectionof thesemid-rotationsurvival effects tofull rotationusingagrowthandyieldmodel indicatedthat weed controlmay have the potential to increase final yield and carbon storage at some of these sites in the longer term. The existence and magnitude of benefits from weed control were highly site dependent. This study demonstrates that there is clear potential for early weed control to increase the cost-effective carbon storage and hence the climate change mitigation potential of some British Sitka spruce forests, particularly on nutrient rich sites and with stands that are subsequently thinned. The development ofdedicated long-termweeding trials in theUK, including thinned stands where cumulative volume removed in thinning is recorded, is required to confirmthis. © 2014 © Institute of Chartered Foresters, 2014. All rights reserved.