Central Park's Woodlands
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Central Park’s Woodlands: Forest Community Changes after a Decade of Management Nyssa sylvatica in four seasons, at Tupelo Meadow in the Ramble. Alex Hodges Submitted in partial fulfillment of the Master of Natural Resources degree Oregon State University Fall 2020 1 ABSTRACT The management of the natural landscapes of New York City’s Central Park has varied over the years, but recently the Central Park Conservancy has begun to make a concerted effort to consolidate these naturalistic landscapes within one cohesive management unit. Much of the management of the plant community involves systematic removal of invasive species, planting and seeding of native species, and encouragement of native plant population regeneration and diversity in order to improve various aesthetic, cultural, community, and ecological values. The resulting Natural Areas management section currently includes the Hallett Sanctuary (a small ~4 acre ‘island’ of woodland in the southern end of the park), the Ramble (a ~36 acre woodland near the center of the park), the North Woods (a ~ 38 acre woodland in the far north section of the park) and the Dene Slope native meadow (the only non-woodland ‘natural area’, converted from lawn in 2016). Ongoing management and capital projects, which includes path/trail improvements as well as plantings and invasive species removal, currently utilizes 13 full-time employees as well as seasonal interns and weekly volunteer groups. The potential addition in the near future of another area, the Great Hill (which is adjacent to the North Woods) could expand the Natural Areas further. There are few studies which quantify the species composition of these woodlands. One such study, by Dr. Regina Alvarez nearly a decade ago (Alvarez 2012), produced valuable baseline diversity data and pointed out which woody species, both native and non-native, are most prolific in different size classes. Species such as oaks (Quercus spp.) were found to be well represented in higher size classes but not in lower size classes, and non-native species such as Ailanthus altisimma, Acer platanoides and Acer pseudoplatanus were heavily represented in lower size classes. Species such as Phellodendron amurense and Styphnolobium japonicum were also identified as showing increased recruitment, with their continual monitoring for invasive qualities suggested as well. This study aims to measure changes in the species composition of these woodlands’ woody plants greater than 1cm diameter at breast height (DBH) over the last decade, as well as determine the efficacy of management efforts over that period by applying the same point-centered quarter survey method utilized in the Alvarez study. This comprehensive survey spanned each of the three designated woodlands in the park, as well as the Great Hill. Data was collected from 1480 woody plants in the designated woodlands, with 119 species from 67 genera identified. This is compared to 1272 individuals sampled from the Alvarez study, which yielded 82 species from 50 genera. In addition to the observed increase in richness, shifts in the dominant species of the entire sample population were also noted. The primacy of Prunus serotina remains but is less pronounced, and when grouped by genus, Quercus jumped ahead of Prunus in comparison to the last survey when comparing Importance Values. In the lower quartile size range (roughly between 1cm and 2.4cm DBH, depending on the specific woodland), significantly less invasive species were found, though certain non-native and/or invasive species had increased in this size class since the last survey. From the Great Hill, 384 woody plants were tallied which included 44 species from 30 genera. While the dominant species (as measured by Importance Value) were largely native, there was a noticeably higher component of invasive species than in the other 3 woodlands. The difference in the lower quartile size range was also significant in comparison to the other landscapes, with a much larger component of invasive species, as well as noticeably lower regeneration from some dominant canopy species. Overall, these results reflect a decade of successful active management, for which the intention/need was outlined in the Alvarez study. The structure of the woody species community in these woodlands has changed, largely along the intended trajectory: increased overall diversity, increased regeneration of oaks, and decreased presence of specific invasives in particular size classes, among other insights. Another major aspect of this study is the application of this sampling method to the woodland landscapes of the Great Hill, which establishes a baseline of data describing this landscape’s structure from which to measure future management actions. The insights from the second survey of the Ramble, North Woods and Hallett also provide a measure of the efficacy of the Natural Areas team’s efforts, which creates a reasonable expectation for potential management goals at the Great Hill. 2 Table of Contents Abstract…………...………………………………………………………………………………………………………………………………………………..…….....2 Table of Contents ……………………………………………………………………………………………………………………………………………….……....…3 Acknowledgements ….…………………………………………………………………………………………………………………………………….....….……..…5 Introduction ………..………………………………………………………………………………………………………………………………………...…………….6 Research Intent……………………………………………………………………………………………………………………………………...…….….7 Background ……………………………….………………………………………………………….......................................................…………………….…………..8 Historical Context……………………………………………………………………………………………….……………...………………….…………8 Geographic Context….…………………………………………………………………………………………….…………………………………...…...10 Site Locations ……………………………………………………………………………..…………………..…………………..……………10 Climate……………………………………....……………………………………………………………………………………….…………10 Topography/Hydrology/Soils……………………………………………………………………………………………………………...……10 Vegetation……………………...….……………………………………………………………...…………………………………….………12 Social Context ………………………...…………………………………………………………………………...………………………………………...13 Management Philosophy and Goals …….…………………………………………………………………………..……………………………………..15 Methods ……………………..………………………………………………………………………………………………………….…………………………………18 Concerning Species Nomenclature ………...………………………………………………………………………..……………………………………..24 Data Analysis …………………...………………………………………………………………………………………………………………………………………..26 Importance Value Calculation ...…………………………………...………………………………………………………………………………………26 Diversity Indices …………………………………………………………………………………………………………………………………………….29 Points per Area ……………...…………………………………………………………………………………...…………………………………………29 Results ………………………………...…………………………………………………………………………………………..………………………………………31 Diversity ……………………………………………………………………………………………………………………………………………………..31 Natives vs Exotics …………………………………………………………………………………………………………………………………………...34 Importance Values ………………………………………………………………………………………………………………………………………….35 Total Woodlands ………………………………………………………………………………………………….………………………………………...35 Invasive Species Changes …….……………………………………………………………………..…………………………………..……..36 Native Species Changes …..…………………………………………………………………………….……………………..……………….37 By Genus …...……………………………………………………………………………………………..…………………….……………...38 Lower Quartile Range………...……………………………………………………………………...…………………………...…………….38 Map of areas sampled ………………………..……………………………………………………………………………………..………….40 Importance Value rankings by species …………….…...………………………………………………………………………………………41 Descriptive statistics …..……………….…………………………………………………………………………………………..…..……….44 Importance Value rankings by Genus …………….…………….……………………………………………………………………………...47 Lower quartile range Importance Value rankings by species ………………………………………………………………………………….49 The Ramble ..……………..…………………………………………………………………………………………………………………………………51 Invasive Species Changes ….…………………………………………………………………………………………………………………..51 Native Species Changes ………………………………………………………………………………………………………………………..52 By Genus ……...………………………………………………………………………………………………………………………………..53 Lower Quartile Range ..…………………………………………………………………………………………………………......….………53 Ramble sample unit locations ……………………………………………………………………………………..……………......………….55 3 Importance Value rankings by species ………………………………………………………………………………………………………....56 Descriptive statistics …...………………………………………………….......................................................………………………………..59 Importance Value ranking by genus .…………………………………………………………….……………...…………………..…………62 Lower quartile range Importance Value rankings by species …………………………………….……………………...………………….....64 The North Woods ………...……………………………………………………………………………..…………………………………..………………66 Invasive Species Changes ….……………....…………………………………………………………………………………..………………66 Native Species Changes …….………………………………………………………………………………………………………….………67 By Genus .……………………...….……………………………………………………………...……………………………………….……68 Lower Quartile Range ....…………………………………………………………………………...…………………………………...……...69 North Woods sample unit locations …….……………………………………………………………..………………………………...……..71 Importance Value rankings by species ...………………………………………………………………….……………………………………72 Descriptive statistics …………..………………………………………………………………………..………………………………..……..74 Importance Value ranking by genus ……………………………………………………………………………………………………….…..76 Lower quartile range Importance Value rankings by species …..……………………………………………………………………...………78 The Hallett Sanctuary ………..…………………………………………………………………………………………………………………………….79 Invasive Species Changes ……...……………………………………………………………………………………………………..………..80 Native Species Changes .…………………………………………………………………………...………………………………………..…81 By Genus …..…………………………………………………………………………………………..………………………………….……82