PLANT COLONIZATION OF BARE PEAT SURFACE - RELATIVE IMPORTANCE OF SEED AVAILABILITY AND SOIL

A field survey on two former peat harvesting sites of similar successional age revealed a marked difference in species composition and a 30-fold difference in biomass of the established vegetation. Based on this observation, a field experiment in which the substrate was changed between sites was conducted to examine whether the differences in revegetation were mainly a consequence of differences in seed supply or in substrate quality. After three growing seasons, a many hundred-fold difference in plant biomass existed between the transplanted and control plots with the same substrate, but only a small difference between the plots with a different substrate within the site. Biological activity in the substrate of the slowly revegetating site (site 1) increased when transported to the more rapidly revegetating site (site 2), while the opposite was true when substrate from site 2 was transported to site 1. The sites differed in the rate of N mineralization, and particularly in nitrification. Despite the differences in substrate quality between the two sites, seed supply appeared to be the major factor controlling colonization. The impact of the soil factors on plant establishment was, however, considered to be large enough to act as an additional controlling factor.