The vascular plant species of sidewalk plots in Brooklyn and Queens: New York City's overlooked "island" flora

The vascular flora at 50 small sidewalk plots in Greenpoint, Brooklyn, Kings County, NY, and also bordering St. John's University, Jamaica, Queens County, NY was identified and compared during spring and fall 2007 through the spring and fall 2011 growing seasons. One hundred twenty-one vascular plant species within 94 genera and 37 families have been identified. Eighty-four taxa were identified in Brooklyn while 71 taxa were identified in Queens; many taxa in Brooklyn were also found in Queens as well. Ninety-six taxa were identified at both sites in the spring while 55 taxa were identified in the fall. The Asteraceae (22 species) and Poaceae (15 species) were the largest families in the flora. Eighty-five taxa, 69% of the flora, are not native to the region. Thirty-one taxa were observed only once during the 5-yr study; those observed only once, twice, and three times composed 50% of the flora. A parsimony algorithm was used to evaluate the distribution and co-occurrence of 121 vascular plant species identified at the above sites in Brooklyn and Queens in the fall and spring of 2007 to 2011. A total of 1,000 plots were sampled during the 5-yr study. The hierarchical cluster analysis forms two major clusters representing a Queens section, Queens fall 2007 to Queens fall 2011, and a Brooklyn section from Brooklyn fall 2007 to Brooklyn spring 2009. The data did not have enough resolution to produce a single unambiguous tree. This may be explained by the dynamic nature of these "islands," as many species colonize these "islands" briefly and disappear. The high diversity at the sidewalk plots may be a product of local disturbance.