The original abandoned elevated High Line was a commercial railroad paralleling 10th Avenue between 13th and 34th Streets. Built in the 1930s as an elevated commercial rail line to carry congested rail traffic above New York City streets, the High Line was part of the “West Side Improvement Project,” which ran 13 miles (20.92 km) from Spuyten Duyvil at its northern terminus to Spring Street in lower Manhattan. The birth of the Interstate Highway System in the 1950s propelled the trucking industry to dominance, resulting in a precipitous decline in rail freight on the High Line. A train carrying three carloads of frozen turkeys made a final journey on the High Line in 1980 (Stalter 2004).

When initially studied in 2002, the High Line consisted of a 7.5 by 2,330-m strip that traversed 20 city blocks. It was exposed to full sun except in the area of 29th Street, which was partially shaded by tall buildings. Occasional human visitors to the abandoned High Line probably transported seeds to the site, one potential source of vascular plant species. Additional site conditions included a shallow soil profile that induced drought stress in dry weather, low soil fertility, human trampling and cutting vegetation, and the smothering of plants by debris such as tires, bottles, and additional refuse. The aforementioned variables created a multiplicity of habitats on the old High Line that could account for its species diversity (Stalter 2004).

In the time since it was initially studied, the High Line has been transformed into a highly visited urban park. A remnant of the old High Line between 30th and 33rd Streets and 12th Avenue was preserved when the High Line Park was created in 2009 (Fig. 1). The vascular plants, lichens, and mosses of this preserved remnant were the subject of a subsequent study in 2019 that is the focus of this contribution. The High Line remnant is fenced, and access is limited by High Line Park. The lichens, mosses, and vascular plant species at this site were similar to those present on the old High Line sampled by the first author in 2002. Several taxa, notably Lunaria annua L., Celtis occidentalis L., Ulmus americana L., and Pyrus calleriana Decne. have invaded the old High Line remnant, most likely from plantings at High Line Park. The preserved remnant also contains mosses and vascular plant species observed by Stalter (2004) when he conducted his original flora study of the High Line in 2002.

Fig. 1.

Flora on the old High Line, July 2019.

The abandoned High Line provided habitat for primary succession taxa, including lichens and mosses. Almost as an afterthought, Stalter (2004) collected lichens and mosses, early colonizers at the site. Lichens and mosses were sent to Bill Buck at The New York Botanical Garden for identification. In the present study during the growing season of 2019, mosses were collected in April and May and sent to Buck for identification. The lichens on the old three-block High Line remnant were collected by R. S. in May, and with The New York Botanical Garden lichenologist J. L. in June, who identified all lichens collected in the present study. The old High Line remnant located adjacent to High Line Park lies between 30th and 33rd Streets and 12th Avenue.

High Line Park, the site of the old abandoned High Line, was created in 2009. The park contains more than 110,000 plants within 500 vascular plant species (Eric Rodriguez, personal communication). Taxa at the park were chosen for their hardiness, sustainability, and ever-changing textures and colors for all seasons. Most of the park's planted taxa can only exist on the multiplicity of special habitats that have been created at the park. Among the selected taxa are Typha latifolia L., Symplocarpus foetidus (L.) Salisb. ex W.P.C. Barton, Ilex glabra (L.) A. Gray, and Magnolia macrophylla Michx. that thrive in the artificial habitats. Tall-grass prairie species Andropogon gerardi Vitman, Panicum virgatum L., and Sorghastrum nutans (L.) Nash are conspicuous members of High Line Park's created flora. Diligent, continuous weeding by park horticulturists have eliminated most invasive taxa. However, invasive Poa annua L., Chenopodium album L., and Trifolium repens L. were collected by Stalter at High Line Park in 2019.

The primary objective of this study was to compare the lichens, bryophytes, and vascular plants present at the High Line in 2002 with those present in 2019.

Methods.

Results and Discussion.

The vascular flora collected at the High Line in 2002 consisted of 155 species in 125 genera in 47 families. The largest families in the flora were the Asteraceae (31 species), Poaceae (22 species), and Rosaceae (12 species). All together, these families, totaling 65 species, composed 42.2% of the flora. The largest genera were Solidago and Potentilla, each with four species. Eighty-eight invasive species (56.8%) composed more than half of the flora. No New York State endangered or threatened species occurred there (Young and Weldy 2004).

Four lichen species were identified in the original 2002 study, whereas 10 were found in 2019 (Table 1). One of the species, Endocarpon petrolepideum (Nyl.) Nyl., a common squamulose species of calcareous rocks (Lendemer 2007), appears to be a new record for New York State (Harris 2004). All of the lichens found in 2019 were saxicolous (rock-dwelling) or terricolous (soil-dwelling); none were corticolous (bark-dwelling). Unfortunately, only one lichen voucher from the original study could be located at NY, and it was thus not possible to reexamine all the original specimens. Nonetheless, none of the species found in 2002 were relocated in 2019. Three of the lichens found in 2002 were foliose macrolichens (Cladonia sp. reported as C. mateocyatha Robb. by Stalter in 2002, Phaeophyscia insignis (Mereschk.) Moberg., and Xanthoria parietina (L.) Th. Fr.), and one was a crustose microlichen (Lecanora sp.). Specimens of Lecanora collected by Stalter in 2002 and deposited at The New York Botanical Garden were not located by Lendemer in 2019, so Lecorna could not be identified to species. Rinodia glauca was not correctly identified in 2002, because this lichen does not occur in New York State, although it could represent a species of Rinodia. In contrast, 6 of the 10 lichens collected in 2019 were crustose microlichens and four were foliose or fruticose macrolichens. None of the species found in 2002 were relocated in 2019, and likewise it appears as though none of the species found in 2019 were present in 2002.

Table 1.

Summary of lichens, bryophytes, and vascular flora of the High Line, New York City, NY in 2002 and 2019. Those from 2019 are in parentheses. Total values are for vascular plants.

Some of the taxa found in 2019 could have been overlooked in the original study due to their inconspicuous appearance (e.g., Bacidina egenula (Nyl.) Zahlbr., Psorotichia schaereri (A. Massal.) Arnold, Verrucaria sp.). However, it is unlikely that the fruticose Cladonia with mature podetia found in 2019 and that were readily identifiable to species would have been overlooked in 2002. The same is true of Caloplaca feracissima H. Magn. and Candelariella aurella (Hoffm.) Zahlbr., both of which have conspicuous bright orange or yellow apothecia. It seems likely that the majority of the lichens found in 2019 became established on the High Line after the original study in 2002. All of the lichens found on the High Line, both in 2002 and 2019, are typical of early successional or urban habitats (Allen 2020). Nonetheless, their discovery in a remnant section of elevated rail line in Manhattan, nearly two decades after a search of the same area failed to locate them, is noteworthy.

Six species of bryophytes were found in 2002 and 2019, although only two, Tortella humilis (Hedw.) Jenn. and Weissia controversa Hedw., were detected in both studies. Brachythecium campestre (C.M.) BSG., Bryum pseudotriquestum (Hedw.) Brid., Atrichum angustatum BSG., and Ceratodon purpureus (Hedw.) Brid., were found exclusively in 2002, and Hygroamblystegium varium (Hedw.) Monkemeyer, Leptodictyum riparium (Hedw.) Warnst., Bryum argenteum Hedw., and B. lisae De Not. var. cuspitadum were present in 2019. The increase in the number of lichens found in 2019 (six taxa), and four new mosses are best explained by the author's primary objective in the 2002 study that focused on vascular plant species. Crustose lichens were overlooked by Stalter in the 2002 study, because mosses and lichens are usually not included in vascular plant floras. No rare mosses occurred at this site.

The vascular plant species collected in 2019 consisted of 32 families, 68 genera, and 79 species. Nonnative taxa, 48 species, compose 60.8% of the flora. The High Line remnant shared 55 taxa with the original High Line, including 45 dicots and 10 monocots. Twenty-three taxa were new to the High Line: 21 dicots and 2 monocots. The Asteraceae, 15 species, and Poaceae, 9 species, were the largest families in the flora in 2019, as they were in 2002 when they were composed of 32 and 18 taxa, respectively. No genus was represented by more than two species in 2019.

Thirty-four woody taxa were identified in 2002, 22% of the flora and 155 species. These included 18 species of trees, 10 species of shrubs, and 6 lianas. Fourteen woody taxa were identified in 2019, including nine species of trees, three species of shrubs, and two lianas (17.7% of the flora). Seventeen invasive woody taxa were identified in 2002 (50% of the total), whereas nine invasive woody taxa were identified in 2019 (53% of the total).

The most conspicuous species of the spring flora were species of Potentilla spp., along with the rosettes of Eupatorium, Symphyotrichum, and Solidago. These genera were also the most conspicuous herbaceous components of the summer and early fall flora, when the goldenrods, beginning with S. juncea Ait., flowered. By late September, the flowering goldenrods and asters were the prominent members of the flora. Eupatorium hyssopifolium L., another common member of the Asteraceae, flowered in mid-October, along with wiregrass, Aristida dichotoma Michx. From mid-October to mid-November the aforementioned taxa were the most common components of the fall flora.

Abundant woody species in 2002 were the nonnative Celastrus orbiculatus Thunb., Rosa multiflora Thunb., and Ailanthus altissima (Mill.) Swingle. Ailanthus reached its best development on the partially shaded portion of the rail line around 29th Street in 2002. Species associated with Ailanthus at 29th Street in 2002, but nowhere else, included Quercus palustris Münchh, Ageratina altissima (L.) R.M. King & H. Rob. (Eupatorium rugosum Houtt.), Acer platanoides L., and Trichostema dichotomum L.

Shrubs and low-growing trees grew in small clumps or individually; they were components of both the forb/grassland and Ailanthus-dominated thicket communities in 2002 described above. Notable woody taxa included the shrubby Rosa multiflora and lianas Celastrus orbiculatus, Parthenocissus quinquefolia (L.) Planch., and Ampelopsis glandulosa (Wall.) Momiy. Low-growing individual trees scattered about the High Line included Prunus serotina Ehrh., Ulmus pumila L., Malus pumila Mill. (Pyrus malus L.), and Populus spp.

Common woody taxa in 2019 were Rhus copallinum L., R. typhina L., Rosa multiflora, Morus alba L., Prunus serotina Ehrh., Pyrus calleryana Decne., and Populus spp.

The number of taxa identified in 2019 (79) was slightly more than half the taxa identified in 2002 (155). The lower number of taxa was expected, because the 2019 site, a three-block remnant of the old High Line, is approximately 10% the size of the original High Line. This small remnant is exposed to bright sun throughout the day, whereas the original High Line experienced both shade and bright sun.

The old High Line was not easily accessible. R. S.'s original entry was through an adjacent artist's loft to the roof of an adjoining building. There, a ladder and rope provided a “bridge” to the plant community on the High Line in 2002. No other person was observed on the High Line while R. S. was plant collecting during the growing season of 2002. The preserved, fenced old High Line remnant borders a three-block portion of the north side of High Line Park, where hundreds of thousands visit the park each year. These visitors are a potential source of new seeds, especially those of invasive taxa. Nearly fifty-six percent (55.8%) of the flora of the original High Line in 2002 was composed of nonnative taxa, compared to 60.8% in 2019 (Table 2). The percent invasive taxa in 2019 was similar to that reported at Liberty Island, NY (65%; Stalter and Tang 2002), and Ellis Island, NY (60.3%; Stalter and Scotto 1999). Two islands in New York Harbor that were part of the Ellis Island immigration complex, Hoffman and Swinburne, also had a high percent of invasive taxa, 63% (Stalter and Munir 2002). That visitation contributed to invasive taxa was predictable, because Lamont and Stalter (1991) found 47% of the flora at the accessed eastern portion of Orient Beach State Park, NY, was populated by nonnative taxa, whereas the rarely visited western portion of the park's flora was 19% alien. When Orient Park was sampled by Latham (1934), few people visited the site; 19 alien taxa were observed by him (8% of the 227 species he identified).

Table 2.

Frequencies of native versus nonnative plants at High Line, NY 2002; High Line, NY 2019; Hoffman and Swinburne Islands, NY (Stalter and Munir 2002); Liberty National Monument, NY (Stalter and Tang 2002); Ellis Island, NY (Stalter and Scotto 1999); and sidewalk plots, Brooklyn and Queens, NY (Stalter and Rachlin 2018).

The percent of nonnative taxa on the old High Line in 2019 was almost as high as the percent of invasive taxa found on sidewalk plots in Queens and Brooklyn reported in a 5-yr study by Stalter and Rachlin (2018), 70.2%. Stalter and Rachlin (2018) found 121 taxa on 100 sidewalk plots, but 31, 25.5% of the total, were only reported once in 5 yr. They concluded that many vascular plant species colonized the sidewalk plots briefly and disappeared. Predictably, sites that are visited by thousands of people generally have significantly more alien taxa than those with few visitors (Table 2). We predict that thousands of visitors to High Line Park can bring seeds of invasive taxa to the preserved old High Line and that the flora there will experience constant change.

The preserved old High Line serves as a refuge for lichens, mosses, and vascular plant species occupying a unique habitat within New York City. Data in the present study and by Stalter in 2002 will enable future lichenologists, bryophyte specialists, and vascular plant enthusiasts to conduct comparative studies at the old preserved High Line in the future.