| Planted Pinus nigra is reproducing and spreading in Saugatuck Dunes State Park Natural Area, significantly altering natural dune conditions and impacting native species. Ten randomly located sites were selected in each of the four main dune habitats for estimating the rates and patterns of P. nigra spread and for comparing the selected parameters of the regeneration niches of P. nigra and native P. banksiana. The spatial occurrence of threatened Cirsium pitcheri and populations most threatened by the spread of P. nigra were also documented using GPS and GIS techniques. Currently stands of P. nigra are spreading to the north in the foredunes and northeast in the inland blowouts, attributed to prevailing southwesterly winds. Foredune stands have increased on average by 37% in area since original plantings in 1963, while inland blowout stands have increased 25% since 1966. The average rates of spread per plant ranged from 0.04 m yr-1 to 0.20 m yr-1, but were as high as 15 m yr-1 . The wetpannes were considered the most threatened dune habitat, due to high densities of P. nigra progeny and the presence of unique dune flora and fauna. The measured parameters of regeneration niches of P. nigra and P. banksiana co-occurring in the vicinity of planted P. nigra were similar, and no habitat partitioning was apparent. Eleven populations and 29 individuals of C. pitcheri were documented in the foredunes and inland blowouts, including five critical areas that contained both P. nigra progeny and C. pitcheri. |
