Growth of understorey Scots pine (Pinus sylvestris L.) saplings in response to light in mixed temperate forest

Predicting growth and mortality of trees growing in the understorey requires estimates of their light requirements but would provide valuable help for the management of irregular forest stands, especially for light-demanding species like Scots pine (Pinus sylvestris L.). Sixty-five pine saplings from 0.4 to 6 m high and aged from 2 to 58 years were sampled in different light conditions in the understorey of mixed sessile oak-Scots pine stands in a temperate forest in central France. Each pine sapling was described by its height, diameter and age and by the light reaching its apex. Pine sapling height and diameter were positively correlated with light and age. The results highlighted that Scots pine, a tree species usually described as shade-intolerant, is able to grow, although slowly, in shaded conditions (less than 10 per cent of full sunlight). However, the results also showed that a more shaded growing environment leads to lower maximal pine sapling height whatever its age. Together with results from studies on other species, these results provide further evidence of a critical sapling size at a given light level beyond which the pine sapling is likely to die and suggest that this critical size increases with light availability.