ACT Reading Jun. 2017 74C - Passage IV

The ecology of the city is defined not only by the

cultivated plants that require maintenance and the pro-

tected remnants of natural landscapes, but also by the

spontaneous vegetation that dominates. the neglected
₅ interstices. Greenery fills the vacant spaces between

our roads, homes, and businesses; lines ditches and

chain-link fences; sprouts in sidewalk cracks and atop

neglected rooftops. Some of those plants, such as box

elder, quaking aspen, and riverside grape, are native
₁₀ species present before humans drastically altered the

land. Others, including chicory, Japanese knotweed,

and Norway maple, were brought in intentionally or,

unintentionally by people. And still others - among

them common ragweed, path rush (Juncus tenuis), and
₁₅ tufted lovegrass (Eragrostis pectinacea) - arrived on

their own, dispersed by wind, water, or wild animals.

Such species grow and reproduce in many American

cities without being planted or cared for. They can pro-

vide important ecological services at very little cost to
₂₀ taxpayers, and if left undisturbed long enough they may

even develop into mature woodlands.

There is no denying that most people consider

many such plants to be "weeds". From a utilitarian per-

spective, a weed is any plant that grows on its own
₂₅ where people do not want it to grow. From the biologi-

cal perspective, weeds are opportunistic plants that are

adapted to disturbance in all its myriad forms, from

bulldozers to acid rain. Their pervasiveness in the urban

environment is simply a reflection of the continual dis-
₃₀ ruption that. characterizes that habitat-they are not its

cause. In an agricultural context, the competition of

weeds with economic crops is the primary reason for

controlling them. In an urban area, a weed is any plant

growing where people are trying to cultivate something
₃₅ else, or keep clear of vegetation altogether. The com-

plaints of city dwellers are usually based on aesthetics

(the plants are perceived as ugly, or as signs of blight

and neglect) or on security concerns (they shield human

activity or provide habitat for vermin).

₄₀ From a plant's perspective, it is not the density of

the human population that defines the urban environ-

ment, but the abundance of paving (affecting access to

soil and moisture) and prevalence of disturbance. In

other words, a sidewalk crack is a sidewalk crack
₄₅ whether it is in a city or a suburb. Urbanization is a

process, not a place-a process that tends to leave the

soil in a compacted, impoverished, and often contami-

nated state.

The plants that grow and survive in derelict urban
₅₀ wastelands are famous (or infamous) for their ability to

grow under extremely harsh conditions. Through a

quirk of evolutionary fate, they developed traits in their

native habitats that seem to have "preadapted" them to

flourish in cities. One study, by biologist Jeremy T.
₅₅ Lundholm of St. Mary's University in Halifax, Nova

Scotia, and his then student Ashley Marlin, concluded

that many successful urban plants are native to exposed

cliffs, disturbed rock outcrops, or dry grasslands, all of

which are characterized by soils with a relatively high
₆₀ pH. Cities, with their tall, granite-faced buildings and

concrete foundations, are in a sense the equivalent of

the natural limestone cliff habitats where those species

originated. Similarly, as the British ecologist and

"lichen hunter" Oliver L. Gilbert noted in his classic
₆₅ book The Ecology of Urban Habitats, the increased use

of deicing salts on our roads and highways has resulted

in the development of microhabitats along their margins

that are typically colonized by calcium-loving grass-

land species adapted to limestone soils or by salt-loving
₇₀ plants from coastal habitats.

In general, the successful urban plant neeqs to be

flexible in all aspects of its life history, from seed ger-

mination through flowering and fruiting; opportunistic

in its ability to take advantage of locally abundant
₇₅ resources that may l:!e available for only a short time;

and tolerant of the stressful growing conditions caused

by an abundance of pavement and a paucity of soil. The

plants that grow in our cities managed to survive the

transition from one land use to another as cities devel-
₈₀ oped. The sequence starts with native species adapted

to ecological conditions before the city was built. Those

are followed, more or less in order, by species

preadapted to agriculture and pasturage, to pavement

and compacted soil, to lawns and landscaping, to infra-
₈₅ structure edges and environmental pollution-and ulti-

mately to vacant lots and rubble.