The Globalization of Ecology by Humans
Humans have had a profound impact on our planet, wherever they have lived. Since the industrial age, man’s impact on the environment has even extended beyond where he lives, as atmospheric changes impact remote places such as the polar regions. Humans are a particularly restless species of animal, forever fleeing whatever conditions threaten existence or seeking a better life ahead. Because we are an adaptable species with the capacity to alter conditions, we have a wider range of movement than other animals.
Wherever humans have gone, they have taken with them the seeds of plants, at first unwittingly and then purposefully after the advent of agriculture. Edward Salisbury, a 19th Century British horticulturalist, reported raising 300 plants of 80 different species from the debris in his trouser cuffs, despite wearing spats.(1)
The impact of Native Americans on the landscape
Native Americans arrived in North America about 13,000 years ago and slowly migrated to South America. The megafauna that Native Americans found when they arrived disappeared soon after they arrived. Although not all scientists agree, there is strong evidence that the megafauna, such as enormous buffalo and mastodons were hunted to extinction by the first human inhabitants of the New World. The loss of these huge herbivores was a factor in the development of grasslands that were not adapted to heavy grazing.(2)
The most profound alteration of the ecology of the New World by Native Americans was their use of fire to assist their hunting and gathering activities. Burning grassland to the ground encourages the growth of new sprouts that improve grazing and attract the animals the Native Americans hunted. And burning grassland funneled the animals into the hunt. These frequent burns prevented the succession of grassland to shrubs and forest, maintaining prairies that were essentially manmade.
The arrival of Europeans in the New World
This process of transplanting plants around the globe was greatly accelerated by the age of exploration which began in earnest in the 15th century. When Columbus arrived in the New World in 1492, he found a land that had already been radically altered by Native Americans, though he had no way of knowing that.
The Europeans that eventually settled the New World were ignorant of the impact of Native Americans on their new home until the advent of archaeology in the 20th century. Their ignorance was based on their mistaken perception that the Native American population was small.(3)
In fact, the population of Native Americans was decimated by the time the Europeans settled the New World nearly 200 years after the early explorers arrived at the end of the 15th century. The early explorers introduced European diseases to which they were immune, but the Native Americans were not. From just a few localized contacts with Europeans these diseases–such as measles, smallpox, and syphilis–spread quickly through Native American communities, sometimes reducing the population by as much as 90%. These deadly epidemics were largely unwitnessed by the tiny population of early explorers.
Alfred Crosby speculates in Ecological Imperialism, that Native Americans were particularly vulnerable to these diseases because they had virtually no domesticated animals. He gives us a fascinating explanation of how Europeans developed their immunities by living in close proximity with animals for centuries.
The history of Native Americans was initially recorded by the European settlers who arrived in numbers nearly 200 years after initial contact in the 15th century. Their perception that they found a pristine wilderness, largely untouched by human hands, has persisted to this day in the public’s mind. It is that perception that has led native plant advocates to the conclusion that the pre-European landscape should be the goal of restorations.
The impact of Europeans on the landscape
As much impact as Native Americans had on our landscape, it pales in comparison to that of Europeans. The importation of domesticated animals—such as cattle, pigs, horses, and sheep—changed the ecology of the New World quickly. Because the population of early settlers was small and the grazing resources vast, these animals quickly became huge herds of feral animals, roaming places such as the pampas of Argentina and the prairies of the mid-west of North America. The native grasses were quickly replaced by the non-native grasses spread by these wandering herds. (4)
Likewise, the agricultural practices of European settlers have introduced virtually everything we eat today in North America. Nearly all of our fruits, vegetables, and cereals are not native to North America. If non-native food were to be banished from California, we would be reduced to a diet of game, acorn mush and a few species of nuts and berries. The diet of Europeans would be equally impoverished if they lost the potatoes, corn, tomatoes, etc. that came to them from the New World.
The Anthropocene: The geologic age of humans
The Earth’s ecology is in a constant state of change. Humans are not the source of much of that change. The continents shift. The climate oscillates. Plants are moved by the wind and tide. Animals move without the assistance of humans, often taking plants with them. But change has been accelerated by the restless movements and activities of humans.
Scientists have recently begun to advocate for the naming of a new geologic era, the Anthropocene. The Anthropocene would officially acknowledge that the environment has been altered by humans. Although the beginning of this era is still being debated by scientists, Erle Ellis (University of Maryland, Baltimore) believes that an appropriate beginning would be about 6,000 years ago, when humans domesticated animals.
Why are we suddenly afraid of change?
Changes in the ecology of North America resulting from the movement of humans have been going on for thousands of years and have greatly accelerated in the last 500 years. Until very recently, these changes were broadly perceived as improvements. We enjoy a more varied diet than our ancestors and we are shielded from famine by our access to food from anywhere in the world. We find the products of the New World useful in other ways, such as the rubber that is essential to transportation.
Suddenly, for little apparent reason, we are afraid of everything new in our environment. The media is full of panic-stricken reports of alien “invasions.” Most of these panic attacks eventually prove to be baseless. The newcomers are eventually absorbed into the landscape or they disappear without a trace. Or scientists eventually explain that the newcomers are better adapted than their predecessors to the climate, water, and soil conditions created by the activities of man.
We asked a scientist who advises us occasionally this question: Since new species of plants and animals have been introduced to our landscape for hundreds, if not thousands of years, why the sudden panic? His reply was: “It’s trendy. It’s ‘cutting edge.’ It’s ‘hot.’ It’s…fundable.”
In the service of a scientific fad that has spread into the popular culture, introduced species of plants and animals are being needlessly destroyed. Many of these new species are better adapted to present conditions than their predecessors. Many are essential to our way of life and the animals with which we share the planet.
(1) Richard Mabey, Weeds: In Defense of Nature’s Most Unloved Plants, Harper-Collins, 2011
(2) Alfred Crosby, Ecological Imperialism. Cambridge University Press, 2004
(3) Charles Mann, 1491, Random House, 2005