east harlem's appalachian cliff face

anything can be wildlife habitat if wildlife lives there

blunt-lobed cliff fern growing on the metro north train viaduct at 110thm street

there’s no need for an hours-long car ride if you want to experience the majesty of the appalachian mountains. just take the 6 train to 110th street and walk the road shoulder along the metro north viaduct. after all, it’s the same thing… at least, it’s the same thing to certain cliff-dwelling ferns.

amid the smog, graffiti, and garbage, an ecosystem much like one you’d find on an appalachian cliff face has sprouted from the cracks in the bricks. here lives a variety of habitat-restricted ferns and other strange plants as an unintentional consequence of urbanization. and unlike urbanization’s many catastrophic consequences, this one can offer some hope to those praying for a future where humans and nature live in harmony.

a meme i made. cliff pic form jarek tuszyński, tunnels from wikimedia user beyond my ken

i think i first learned about the viaduct from a recap of a guided trip that i couldn’t make led by nyc botanists zihao wang and marielle anzellone. i finally visited last week, walking slowly along the shoulder of park avenue between 106th and 110th street kicking aside trash and photographing plants until a guy shouted “ey! whatdafuckayoudoin!” out of his car window. i took that as my cue to leave.

i got home and loaded my photos onto inaturalist to look over my bounty. at least four of the species i spotted were rock-dwellers, or lithophytes, that were native to the nearby mountains. that included ferns like purple-stemmed cliffbrake (Pellaea atropurpurea), blunt-lobed cliff fern (Woodsia obtusa), and a fern from the genus Cystopteris, plus a nettle called pennsylvania pellitory (Parietaria pensylvanica). these are just the common ones; other plant-likers have found a variety of less-common plants here.

purple-stemmed cliffbrake was the most common fern on the wall

the plants probably arrived the same way that many of our other plants arrived to the city—their spores and seeds traveled here attached to something and sprouted where they found appropriate habitat. in this case, they hitched a ride on the trains traveling above or the cars driving by. and it’s actually pretty incredible if you think about it. here along a main thoroughfare in the country’s densest city, in an area that should be inhostpitable to most wildlife, on a wall meant to support trains, are range-restricted plants from a habitat that’s not especially common.

and that train viaduct isn’t the only nyc surface hosting unexpected rock-dwelling life. in fact, ecologists posit that many of the species thriving in cities worldwide are those adapted to live in rocky habitats—it’s called the urban cliff hypothesis. botanists have found rare lithophytes in cities across the world, according to one recent paper authored by uconn researcher tammo reichgelt, and we’ve recreated the predator-prey relationship of two cliff-dwellers with the peregrine falcon and the rock pigeon. some researchers have even taken this hypothesis to the extreme, suggesting that humans themselves build cities to satiate a primal urge to live in cliffs. that one seems a little over-the-top to me, though.

peregrines and pigeons are both cliff-dwelling birds that have adapted to city life

but the urban cliff hypothesis alone isn’t enough to explain the plant life on the harlem wall. while certain cliff ferns are more likely to occur in our cities, others don’t appear in cities at all, according to reichgelt’s paper. based on his observations, the warm temperatures of the city caused by the urban heat island effect could be responsible for these specific ferns’ success here and other ferns’ lack of success. meanwhile, fast-growing introduced species like mugwort, princess tree, and common reed make an appearance on our rock walls, too. and they tell a much different story—they’re the result of centuries of intentional and unintentional movement of plants around the world, which has broadly changed the face of our forests and other habitats. their presence on the wall is more a testament to their aggressive, perhaps invasive nature than any specific habitat preference.

the urban cliff hypothesis is more like something we could manifest. in east harlem, we leveled what was once fire-dependant savanna and replaced it with roads, apartment buildings, and a train track, none of which provide as much value ecologically. sure, we could simply allow whatever to grow here and get excited when it’s something cool. but we could also embrace these cliff-like surfaces and further design them to support more native lithophytic plantlife, as described in an essay by jeremy lundholm from saint mary’s university in nova scotia.

the plant life can grow pretty dense on the side of the viaduct

there’s a name for this kind of thinking—reconciliation ecology, or designing our built environment to welcome more kinds of wildlife. and it’s beneficial beyond expanding the number of species on my inaturalist life list. more native plant life in our cities could help reduce overall temperatures from the urban heat island effect, increase local biodiversity, and create more habitat for the native wildlife that lives here or that passes through.

so while our native rock ferns feel like a “life, uh, finds a way” kind of thing, their story is much more intertwined with the story of humans. by leveling forests for cities and moving things around, we create new kinds of habitats and new kinds of species interactions. in most cases, we should probably do our best to minimize all of that habitat altering, and ensure that these changes don’t have permanent detrimental impacts across the ecosystem. but if you’re going to go through all that effort to build something that looks like a cliff, why not embrace it and cover it with our native cliff-loving flora and fauna, too?

postscript

we are deep into southbound bird migration, and there have been lots of birds swarming our parks. but my favorite bird i’ve seen this season is this saffron finch found by linda ewing in greenwood cemetery. it’s certainly an escaped pet, but saffron finches are one of the most common birds in the american tropics, and looking at and hearing this bird kinda transported me to vacations past. kind of a sad story but there wasn’t much i could do—i wasn’t going to be catching this bird—so i just appreciated it for what it was.

this saffron finch had me feeling like i was on vacation

and as a reminder, here’s my upcoming programming:

9/26: bird trivia! 7:30 @ the ditty in astoria. free, register here.
10/4: 5pm @ bryant park fountain (free)
10/6: 9am @ pelham bay park, aileen b. ryan recreational complex (free, register here)
10/12: 9am @ marine park salt marsh nature center (free)
10/13: 9:30am @ wave hill in the bronx ($, register here)
11/2: bird walk at shirley chilsholm state park—free but details tbd
11/10: 9:30 @ canarsie park, seaview av + east 88th st (free, register here)
11/16, nighthunters bird trivia and owl prowl, 4:30pm @ wave hill in the bronx ($65, register here)