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Average growth in 17 control and OTC plots, each between 1999 and 2010 near Ny-Ålesund. Arrows designate the start of the artificial warming in 2004. Error bars indicate the s.e.m. Annual shoot length (A), total leaf length (B), number of leaves (C) and average leaf length (D) were assessed for at least one shoot per plot (n = 18). Significant growth differences are marked by an asterisk (one-way ANOVA, P < 0·05).
