Natural recolonization of cultivated land by native prairie plants and its enhancement by removal of Scots Pine, Pinus sylvestris.
A combination of native and introduced plants colonized abandoned cultivated land with adjacent relict prairie and savanna in the Rice Lake region of southern Ontario. After 71 years, the native colonizers included 86 species found in regional prairie relicts, but much of the area was also colonized by introduced Scots Pine, Pinus sylvestris, which apparently spread from an adjacent planting. The pines formed expanding patches of dense growth that excluded other species. Removal of the invasive Scots Pine from a 200 m2 plot within the abandoned land led to colonization 17 years later by 36 native species characteristic of the prairie, savanna and sand barrens of the region. Included in this group of native prairie colonizers were keystone species such as Andropogon gerardii, Carex siccata, Ceanothus americanus, Comptonia peregrina and Quercus velutina. Areas where patches of Scots Pine had been allowed to continue growing were either devoid of vegetation or had a sparse understory of introduced species and Poison Ivy (Rhus radicans). These observations support the concepts of (1) protecting islands of native dry ground flora which can serve as sources for recolonization and (2) protection of old field and particularly recently cultivated land adjacent to protected native grassland to allow natural restoration. The fact that keystone native species were able to colonize the area from which the introduced Scots Pines had been removed suggests that the pines are aggressive competitors that occupy space to the exclusion of the native species. Scots Pine is thus a driver of ecological change in degraded ecosystems. Management including removal of Scots Pine to support native plant biodiversity is strongly supported.