Δ13C trends of one “standard” (CCHF), “survivors” (CCHF) and untreated trees (C) respectively. Sample size was three at both the CCHF site and the C site. Increasing Δ13C trends were observed soon after the year the coppice was cut (approximately done in 1958–1960 y) and the year it was thinned (1995). Error bars indicate the standard error of the means. The dashed lines indicate the date the coppice was cut and the year it was thinned.