7Marks PL The role ofpin cherry(Prunus pensylanica L. )inthema --intenance of stab ility in northern hardwod ecosystems[M]. Ecol Monogr,1974, 473-88.
8Rein Kalamee R, Zobel M. Soil seed bank composition in different succes--sional stages of a species rich wooded meadow in Laelatu [J], western Estonia. Acta Oeco1,1998,19(2):175-180.