Partial harvest to reduce occurrence of American beech affected by beech bark disease: 10 year results

Abstract

Beech bark disease stunts American beech (Fagus grandifolia Ehrh.) to unmerchantable size, and promotes heavy sprouting that outcompetes more desirable sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britt.). We investigated whether selection harvest targeting removal of large beech can promote maple and birch regeneration while limiting beech competition. Forty plots were established in 2003 in north-western New Brunswick, Canada, with 26 plots harvested and 14 control plots. Harvested plots were re-measured the year after harvest and both harvested and control plots were re-measured 10 years later. Residual tree diameter increment doubled from 0.24 to 0.51 cm/year for maple, and 0.29 to 0.69 cm/year for birch. Harvest did not alter species composition of regeneration, with seedlings comprised of 88 per cent sugar maple in both treatments, 6 per cent beech in harvested plots vs 3 per cent in control plots, and other species ranging from 1 to 5 per cent. There were four times more beech seedlings/ha in control than in harvested plots, but beech still comprised ~60 per cent of the over 2000 stems/ha of saplings in harvested plots. Rapid growth from beech sprouts provided a strong competitive advantage. Residual tree mortality was negligible. Downed deadwood was 58 per cent greater and standing deadwood basal area 71 per cent lower in harvested plots. The harvest maintained strong overstory growth and survival, and did not benefit beech; however, beech remained a dominant species among the larger regenerating cohort. Our results suggest that similar treatments applied to stands with diseased beech can secure adequate regeneration of maple and birch, but will not control profuse regeneration of beech.