Ecological effects of the non-native Pinus nigra on sand dune communities

Owing to their successional nature, sand dunes provide an opportunity to examine the effects of non-native species introduced into multiple habitats. We investigated the biotic and abiotic effects of non-native Pinus nigra in four habitats on the dunes of the eastern shore of Lake Michigan. The 26 000 pines were planted in foredunes, forest edges, wetpannes, and inland blowouts as a stabilization measure in 1956-1972, and in 1995 the surviving trees ranged in stand density from 274-1176 trees per hectare. Pinus nigra stands were associated with reduced cover of dune vegetation except in forest edges, and with depressed species richness only in wetpanne sites. Higher densities of woody stems occurred in P. nigra stands at the edge of native forest than in sites lacking P. nigra, suggesting that pines accelerate succession to a woody community. Pinus nigra stands were associated with lower light levels than native stands of comparable or greater stand densities (Pinus banksiana in wetpannes and Populus deltoides in foredunes). In addition, P. nigra sites were drier than P. banksiana sites in wetpannes. The non-native pines may have modified the four dune habitats and appear to be functionally different from stands of native trees.