Light response curves of fully current-year Pinus cembra needles at 2 180 m a.s.l. (krummholz belt; top), 2 100 m a.s.l (tree line; middle), and 1 950 m a.s.l. (forest limit; bottom) assessed in fall (open symbols) and in summer (closed symbols). Measurements were made in situ at ambient CO₂, 15 °C, and 70% of relative humidity.