Plants That Eat Cities


No matter where man builds his structures, plants wage their silent, ceaseless war of reclamation.

Those of us who live in cities, constantly barraged by the sounds of automobiles, buses and construction, take civilization for granted. We are almost unaware that cities are gripped in a never-ending struggle against natural enemies – windstorms, floods, hail, rain – that would reduce them to rubble. Of all these forces plants are the front-line combatants; they are nature’s living demolition squad.

The best places to witness the assault of vegetation are in tropical cities. In San Jose, Costa Rica, for example, invaders from the nearby jungles – mosses, shrubs, trees – squat in odd places: roofs, gutters, bell towers, statues and abandoned cars. Several high-rises constructed only a few years ago sprouting ferns from joints in the facades. Such plants are called “ediphytes” (building-plants).

The most common plant attack is an aerial approach. The air is filled with microscopic spores of mosses and fungi that travel in wind currents to be deposited like parachutists all over the world. Moss spores, for example, can take to the air in New Zealand and land in the Andes. Other plants hitch rides on the plumage of birds, or travel the ground on the fur of animals or the soles of your shoes.

Often the first ediphytes to arrive are blue-green algae. By providing a film of nutrients, they prepare barren surfaces for larger species such as mosses and ferns that, in turn, capture dust and debris in their root masses.

Plants can find footholds on anything from glass to plaster. This “green seizure” beings any place that humanity settles, from the tropics to the Arctic. Fungi and lichens dissolve a surface with their chemicals to obtain nutrients. A plant’s most destructive weapon is its roots. These find their way into microscopic cracks, develop tremendous hydraulic forces that separate bricks and lift concrete and blacktop. Over time, abandoned buildings are toppled and their man-made materials decompose.

Urban settings provide numerous opportunities for plants. Building surfaces have niches for specialized ferns and grasses called “crack flora”. Sidewalks harbor mosses and grasses. Roads and railway beds are under assault by dandelions, thistles and mushrooms that slowly buckle asphalt. Goldenrod and locust seedlings can turn a former factory site into a field in five years.

Maya Pyramids, Tikal, Guatemala

Maya Pyramids, Tikal, Guatemala

Plants have waged their war of reclamation for thousands of year. Prime examples of old battles – “lost” cities – are found in virgin jungles in Southeast Asia and Central and South America. We know that these tropics once supported great civilizations, long buried by all-conquering vegetation.

Today, when it is being predicted that most tropical forest will have virtually disappeared in less than 40 years, such findings reminds us that jungles have been vigorous and resilient. Whether they can withstand the onslaught of modern man and his technology remains to be seen. But for now there is a certain comfort in the fact that cities continue to be populated by all manner of wonderful plant life.

An interesting documentary of what the world would be like when there are no humans left: