Determining the immigration potential of plants colonizing disturbed environments: the case of milled peatlands in Quebec

1. As an aid for restoration projects, the relative potential for plants to immigrate to sites after severe disturbance was investigated and an index developed to determine their relative immigration potential. The goal was to establish baseline knowledge for the species pool in severely disturbed sites prior to restoration. The method was based on the identification of potential colonists, inventories of populations in surrounding vegetation and autecological information on their maximum fecundity and dispersal by wind, water or animals. 2. The method was applied to milled peatlands in south-eastern Quebec, Canada, after the cessation of peat extraction activities. Thirty-two species, ranging from mosses to trees, which are common in natural or abandoned milled peatlands in southern Quebec, were selected as potential colonists. 3. Populations of study species differed markedly in edges of milled peatlands in terms of their abundance, presence and presence of fertile plants. An edge effect was apparent where the populations of many species varied as a function of distance from milled surfaces, caused, in part, by drainage. 4. Mosses had relatively high potential to immigrate to milled bogs because of their high fecundity and the wind-dispersal ability of their spores. The scarcity of mosses in abandoned milled bogs did not appear to be a result of the lack of immigrant propagules. Herbs had relatively low immigration potential, due to their rarity in edges, but herbs such as Eriophorum vaginatum were able to recolonize milled bogs in spite of this low potential. Shrub species generally had high immigration potential because of their abundance at edges and the high dispersal ability of propagules by wind, water and animals. Trees had high immigration potential due to their abundance at edges and their wind-dispersal abilities. 5. Synthesis and applications. An index of immigration potential provides information on the probable initial species pool after severe disturbance, against which the effects of local habitat suitability and establishment factors can be added to assess probable successional patterns. Its flexibility and applicability to varied life forms should make it useful for diagnosing recolonization bottlenecks in a wide variety of disturbance and restoration situations. It also allows for an assessment of the relative need for introducing species during the restoration of severely disturbed environments.