A first approximation of the historical and extant vascular flora of New York City: Implications for native plant species conservation1

Journal of the Torrey Botanical Society, Jul-Sep 2004 by DeCandido, Robert, Muir, Adrianna A, Gargiullo, Margaret B

There are many natural areas in New York City for which no comprehensive published flora is available (Table 1). These natural areas include parks as well as land owned by the private sector or agencies other than the City of New York Department of Parks and Recreation. Obtaining information for extant occurrence of many herbaceous species was difficult for these natural areas that are primarily concentrated in Brooklyn, Queens and Manhattan. Similarly for plant species that we (and the other sources that were consulted) consider to be extirpated, there exists a degree of uncertainty (see Palmer 1995). A few species that we consider extirpated may be re-discovered, especially on Staten Island where extensive research is now being conducted. However, we believe that the pattern of plant extirpations in New York City we outline in this paper will not change significantly.

For data analysis in this paper, if more than one subspecies or variety of a particular species has been extirpated in New York City, but another variety or subspecies still exists, then that species is considered to be extant. We used chisquare tests with one degree of freedom to compare the proportion extirpated of native herbaceous versus native woody species compared to the proportion (herbaceous vs. woody) still remaining in New York City. We also compare the proportion extirpated of native vs. non-native species ever known from New York City.

All nomenclature follows Mitchell and Tucker (1997) with minor revisions found in Mitchell (2000) including designation as a native, nonnative (alien) or introduced species. Alien species are defined here as not native to the northeastern United States, not planted (uncultivated) and reproducing to a significant degree. Introduced species have escaped from cultivation and are not reproducing to any significant degree in New York City. Designation of a species to woody or herbaceous status follows Gleason and Cronquist (1991). Most of the species from the historical period were collected beginning in the 1870s, though some were collected prior to this time. The complete list of species can be found in DeCandido (2001).

Results. In New York City, the historical and extant flora includes a total of 161 plant families with 779 genera and 2177 native and alien species, collected from the mid-19th century to 2000 (DeCandido 2001). The City retains 57.4% of its native plant species diversity with 779 extant native species compared to 1357 ever recorded or collected (Tables 2 and 3). New York City has also lost 409 (of 820) alien species in this same time period. However, native plant species have been significantly more likely to become extirpated than non-native species (χ^sup 2^ = 10.9, P

Seven plant families in New York City with the greatest number of species contain 41.2% of the total known flora of New York City (Table 4). The largest of these families are Asteraceae (226 species, 136 native), Poaceae (199 species, 123 native) and Cyperaceae (184 species, 177 native). Most of the extant diversity of these seven families is due to high numbers of native species, except in Brassicaceae in which 68.0% of the extant species are non-native. Overall 24 (14.9%) of the 161 families ever found in New York City contain only non-native species (DeCandido 2001).