PHOTOPERIODIC ECOTYPES OF TREES

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Abstract
Seedlings of Pinus sylvestris L. and Alnus incana (L.) Moench. from two widely different latitudes were grown under two different photoperiods, but otherwise under optimum conditions. Under continuous light the seedlings from a far northern latitude grew better than those from a more southern latitude. This situation was reversed under short photoperiods. Since the days of the growing season at the northern latitude are extremely long and those at the southern latitude relatively short, the difference in growth of the seedlings is explained as being the result of heritable adaptation of the trees. The experimental results thus support the theory that within tree species there are "photoperiodic ecotypes" which during evolution have adapted themselves to the photoclimate of their environment.