SCIENCE AND CULTURE

Painting with invasive pigmentsCarolyn Beans, Science Writer

In the abandoned lots of the Bushwick neighborhoodof Brooklyn, NY, dandelion, black nightshade, anddozens of other weedy plants thrive. Although somesee hotbeds of invasive species, artist and Brooklynlocal Ellie Irons sees a vibrant urban ecosystem. Shealso sees the makings of a unique color palette.

Irons extracts pigments from these weeds—or asshe calls them, “spontaneous urban plants”—andtransforms them into watercolor paints. She then paintsdiagrams and maps out plant species. Through this In-vasive Pigments project, her works detail the spread ofplants on scales ranging from continents to city blocks.In Asiatic Dayflower (C. communis), 2012, for example,a global map shows splashes of blue extracted frompetals marking the plant’s geographic range overlaidwith delicately sketched leaves and stems depicting thespecies’movement from Asia to Europe and eventuallythe United States. In Asiatic Dayflower: Wildflower/Superweed, 2014, she shows the distribution of thesame plant on a single city block.

About one quarter of the weeds in Irons’ color pal-ette are native to the northeastern United States. Therest are introduced, often highly invasive plants—some of which the city is actively working to eradicatefrom forested areas. Such efforts are undertaken forgood reason; invasive species spread can devastatean ecosystem.

But Irons believes urban ecosystems are different.After all, many native plants couldn’t survive the harshconditions. Where native plants fail, hardy weedyplants, she reasons, can step up to provide a wealthof ecosystem services—from stabilizing soil and re-ducing nutrient and stormwater runoff to cooling theair and providing food and habitat for animals.

As researchers grapple with how to view urbaninvasive species, Irons seeks to prompt a new perspectivefrom city dwellers. “Become receptive to spots of colorand splashes of leafy green,” she instructs in her hand-book for painting with weeds. “Bend down, reach up,crouch, investigate. These plants are everywhere, butthey are easy to miss if you’re not anticipating them.”

An Expanding PaletteIrons first experimented with mining pigments fromalgae she found growing in the bottom of a planter inher studio. “It was a beautiful color that I didn’t have in

my paint palette,” she says. Next was pokeweed withits lush green leaves and clusters of poisonous, pur-ple berries. Irons turned the berry juice into paint andquickly went searching for more urban plants. “It justtotally changed my lens for the urban environment,”she says. “Rather than focusing on concrete, trash,and gum, the things you see when you look at thesidewalk, I was looking at the inverse of that, all thegreenery.”

Artist Ellie Irons creates watercolor paints by extracting pigments from weedyurban plants. In Dot Cluster: Wild Plants Common in New York City, 2016, sheuses those paints to describe the community of plants growing across about25 vacant lots in Brooklyn. Image courtesy of Ellie Irons.

Published under the PNAS license.

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As she painted with weedy plant species, Irons alsolearned more about their histories and ecology andwhat it means for a species to be invasive. For regu-latory purposes, the federal andmany state governmentsdesignate a species as invasive if it is nonnative and“causes or is likely to cause economic or environmentalharm, or harm to human, animal, or plant health.” (1) Anonnative plant is not necessarily invasive, and nativeplants, although typically not labeled invasive, cansometimes spread aggressively.

Irons noticed, for example, that the native poke-weed spreads prolifically—an observation that helpedher dispense with notions of native plants as basicallygood and nonnative ones as bad. “If [weedy plants]can survive now in a city where we are already 10 de-grees hotter than the surrounding area because of theheat island effect,” she says, “then we kind of needthem.”

Irons creates paints following a traditional process,dating to late 18th-century Britain, that involvesblending natural pigments, water, honey, and gumarabic, a commercially available tree sap, into portablecakes of paint (2). But where paint makers traditionallydrew from a range of sources, including plants, animals,and minerals, Irons primarily uses weedy plants.Around 40 plants make up her local color palette, in-cluding blue from Asiatic dayflower petals, red-orangefrom ripe berries of bittersweet nightshade, and em-erald green from dandelion leaves.

The search for plant pigments has taken Irons tomultiple locales. While attending an artist-in-residenceprogram at Rocky Mountain Biological Laboratory inGothic, CO, she made paints from the plants in themeadow and created a series of color-grid paintings as anod to the way researchers sample a landscape. There,

she worked with ecologist and conservation biologistPaul CaraDonna of the Chicago Botanic Garden andNorthwestern University as he set up a series of 1-meterby 25-meter transects to capture fine-scale variations inplant community composition and pollinator visits.

“I was really interested to see how Paul and theother scientists were drawing grids onto the meadowsthey were working with to give themselves bound-aries,” says Irons. “I hadn’t thought about how I hadalready been doing that because of the grid-basednature of the city.” She didn’t stick to a scientificsampling regimen—the blocks of each color are placedaccording to aesthetic appeal. But the overall effect is acollection of squares that tells the story of what ameadow is made from.

A Question of PlaceTelling that story for an urban plant community de-pends in part on how one views the weedy inhabitantsthat people helped introduce—and those perspec-tives often have nuance. In the early 2000s, artist andjournalist Patterson Clark began volunteering with theNational Park Service to remove invasive plants fromRock Creek Park in the Washington, DC, area. But hedidn’t like the hostility he felt toward the plants. “I wantedto shift my attitude so that it was more of a positiveapproach rather than eradication,” he says. So hebegan thinking of his weeding as harvesting for hisart, which entails fashioning invasive plants into pa-per, wood cuts, intricate wooden sculptures, andpaints. Clark’s work has appeared in art shows acrossthe country and was recently on display as part of thegroup exhibit “Into the Weeds” at the North DakotaMuseum of Art.

At workshops, Irons shares the tools of her trade and encourages city dwellers to notice and even appreciate weedyurban plants. The species she works with include (top row, left to right) blossoms of Asiatic dayflower; medium-ripeberries of Asiatic bittersweet; blossoms of tall morning-glory; leaves, stems, and blossoms of galinsoga; and underripeberries of black nightshade. Image courtesy of Ellie Irons.

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But more often, cities don’t look kindly on theweedy invaders. In New York City, 15 gardeners workin natural areas across the urban landscape to removeinvasive plants, including many of the species in Irons’color palette. “Stormwater management, reduction ofthe urban heat island effect, air purification—all ofthese standard benefits are the greatest in matureforests,” says Kristen King, the Director of NaturalAreas Restoration &Management at NYC Departmentof Parks & Recreation, who manages the effort. “In-vasive species literally physically threaten that foreststructure.” According to King, oriental bittersweetvines can take down native trees. But she concedesthat a vacant lot in a formerly industrial area such asBushwick may not lend itself to reestablishing nativeplants, with the notable exceptions of hardy nativessuch as willow and poplar trees.

So, do invasive plants in these more urban com-munities provide ecosystems services the same as orbetter than native plants would? “They might,” saysurban ecologist Timon McPhearson, director of theUrban Systems Lab at The New School, and leadauthor of a study analyzing the vegetative land coverof about 1,500 New York City vacant lots. He foundthat urban plants are providing key services, such asstormwater mitigation, air pollution removal, andcarbon sequestration (3). “One reasonable hypothe-sis is that if invasive species can grow faster, re-produce faster, spread faster, they might be criticalfor providing climate adaptation related to ecosys-tem services that we care about like stormwater ab-sorption and cooling the city.”

McPhearson would like to see more research intohow the traits of specific species—whether native ornot—affect ecosystem services in cities. Few researchershave studied, for example, the effect of nonnative spe-cies on carbon dioxide sequestration, air quality, andnutrient cycling in cities, as noted in a recent review (4).

But even if nonnative plants prove to be valuable inurban settings, invasive nonnatives can spread fromcities into more natural areas where they threatenbiodiversity. Noting that some of the species in Irons’artwork were originally introduced into cities, biologistSara Kuebbing, a postdoctoral fellow at the Yale Schoolof Forestry & Environmental Studies, worries aboutthe adverse effects of celebrating such plants. “It’simportant that the public understand why we need todo something about invasive species,” she says.

Irons acknowledges the downside—especially ifinvading plants reduce ecosystem complexity. But shemaintains that, at least in some settings, invasiveplants are innocuous. Her work “takes the common-place, or what might even be considered noxious, andgives it a value,” says Jennifer McGregor of Wave Hill,a public garden and cultural center in the Bronx.McGregor included Irons’ paintings in a 2013 exhibitcalled “Drawn to Nature.”

As Irons works outside in vacant lots, people stopand ask her tough questions. “I get to have these morein-depth conversations about what it means to thinkabout an ecosystem as pristine or not pristine, as madeup of desirable natives versus undesirable invaders,”Irons says. “I am always trying to trouble that binary.”

1 Executive Office of the President (2016) Safeguarding the nation from the impacts of invasive species. Available at https://www.federalregister.gov/documents/2016/12/08/2016-29519/safeguarding-the-nation-from-the-impacts-of-invasive-species. AccessedDecember 1, 2017.

2 Finlay V (2002) Color: A Natural History of the Palette (Random House Trade Paperbacks, New York).3 McPhearson T, Kremer P, Hamstead ZA (2013) Mapping ecosystem services in New York City: Applying a social-ecological approach inurban vacant land. Ecosyst Serv 5:11–26.

4 Potgieter LJ, et al. (2017) Alien plants as mediators of ecosystem services and disservices in urban systems: A global review. BiolInvasions, 10.1007/s10530-017-1589-8.

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