A CENTURY OF CHANGE IN THE STATEN-ISLAND FLORA - ECOLOGICAL CORRELATES OF SPECIES LOSSES AND INVASIONS

We analyzed three consecutive floristic censuses of Staten Island, New York, to determine (1) the general pattern of vascular plant species gains and losses over 112 years (1879-1991), (2) the extent of increas es in non-native species, and (3) ecological features that characteriz e those species that were lost. Over forty per cent of the original na tive species (53% of regionally rare and endangered species) are prese ntly missing. Most of the losses have occurred during an accelerating period of suburbanization over the last 60 yr. At the same time, the p roportion of non-native species has increased from 19% to > 33% of the flora, while average abundances of most native species apparently dec lined. Species from different habitats were lost in similar proportion s, indicating that broad-scale habitat alteration has been the main fa ctor in the flora's decline. Only two ecological features examined wer e statistically correlated with the missing species: (1) herbaceous sp ecies were more vulnerable than woody plants; (2) species reported to be uncommon in a previous census were more likely to be absent in the next. Unless conservation measures are improved, further degradation o f this historically rich and varied flora can be anticipated.