Impact of habitat quality on forest plant species colonization

The impact of habitat quality and site history on the recolonization potent ial of ancient-forest plant species on abandoned farmland was studied in th e forest of Ename, Flanders, Belgium. With the exception of a network of fr inge relics (linear elements mainly along exploitation roads), our study ar ea was cleared and converted to arable land ca. 1850. From 1869 onward, mos t fields were gradually abandoned, resulting in a progressive, partly spont aneous reforestation. Each of the 42 actual forest parcels (amounting to 62 ha) was surveyed and a total of 466 plant species were inventoried. Twenty seven of these were identified as ancient-forest plant species and catalog ed in a separate subset. Additionally, the spatial distribution of six anci ent-forest plant species (Anemone nemorosa, Corylus avellana, Hyacinthoides non-scripta, Paris quadrifolia, Mercurialis perennis, Vinca minor) was sys tematically surveyed and digitized in a GIS environment. Habitat quality wa s assessed on the parcel level using intrinsic soil variables on the one si de, and historically related variables (length of the agricultural-occupati on period, length of woody fringe relies, and total length of fringe relies s.l.) on the other. Soil texture had a major impact on the duration of agr icultural land use after deforestation. Soil phosphate content and pH are p ositively correlated with the duration of the agricultural land use. The nu mber of ancient-forest plant species was negatively affected by the length of the agricultural-occupation period and soil phosphate content, and posit ively by the total length of the surrounding fringe relies. The same trends are observed studying the systematically surveyed ancient-forest species. We propose that soil phosphate content affected ancient-forest plant specie s distribution, because it stimulates vigorous vegetation development and a s such has a definite effect on evolving competitive plant relationships. U sing raster-G.I.S analysis tools, mean and maximum colonization distances a nd approximate mean and maximum colonization rates per century were calcula ted for each systematically surveyed species. We conclude that not only see d dispersal capabilities, but also site quality variables play an important role in the colonization process of ancient-forest plant species. In the s hort term, afforestation of previously heavily fertilized farmland will not result in floristically diverse and, thus, valuable forest habitats. The r elatively immobile soil phosphate represents a major barrier. (C) 1999 Else vier Science B.V. All rights reserved.