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Joseph Rachlin


biodiversity; floristic survey; invasives; native plants; species-richness; urban ecology


Van Cortlandt Park is New York City's third-largest park at 464 hectares. Despite 300 years of land-use history, this heavily impacted ecosystem shows surprising resiliency, and can act as a proxy for understanding global issues based on climate change, fragmentation, and anthropogenic impact. A park-wide inventory conducted over six years returned three times the amount of taxa observed in any prior survey suggesting the park has been historically undersampled. At 1102 species, the richness of the park supports the hypothesis that urban regions harbor greater species-richness than historically presumed. Approximately 70.6% of park listings comprise herbaceous plants. Non-natives make up 50% of the total floristic sightings, most of Eurasian or East Asian provenance. With 30 NY state-listed plants, the park represents a refugia for endangered taxa for New York State despite frequent burns, vandalism, and exotic invasion.

A parsimony analysis of presence/absence data returns groupings based on species composition responding to environmental factors such as moisture, sun, and forest fragmentation. Partitioning the data set into separate herbaceous versus woody matrices suggests the two components of the flora track different life histories. Findings concur with similar results from non-metric multidimensional (NMS) ordination and unweighted pair group method with arithmetic mean (UPGMA). Parsimony analysis of ecological data has use as a monitoring tool since the read-out produces a list of what taxa can be found at each site.

Quantitative ecological analyses based on woody frequency data from a quadrat survey shows the three most abundant trees in the park are Prunus serotina (black cherry), Acer platanoides (Norway maple), and Quercus rubra (red oak). Importance Value analyses return the same three taxa but place Quercus rubra in first place position based on its greater diameter-at-breast height (DBH). Alpha diversity indices suggest the park is biodiverse from a woody perspective yet not necessarily even; addition of herbaceous data significantly increases diversity even more. Overall the northern end of the park is more diverse than the southern end. Disturbance specialists in the canopy of the southern park depress richness and evenness. Beta diversity analysis comparing a southern species-poor region versus a northern species-rich region shows turn-over in the park with the woody data having a higher turn-over rate than the herbaceous data.

The ecology of a city environment is a suitable proxy for understanding problems putatively predicted for global warming, e.g. the influence of increased temperatures (e.g. city 'urban island' heat effect) and forest fragmentation on diversity. If so, results from VCP suggest richness may increase following climate warming due to non-native recruitment but long term biodiversity may change if areas are not monitored properly.