Fig. 3. Rates of photosynthesis near to the northern limit of trees at Värriö, northern Finland (67°46′N, 29°35′E, 390 m a.s.l.) in contrasting years: 1999 (closed circles) and 2001 (open circles). Graphs show daily totals of photosynthesis, measured with in situ branch chambers (A), annual patterns of temperature (B) and cumulative photosynthesis over the first half of the growing season (C). Data kindly provided by Professor P. Hari.