The question of what was the driving force in post-Columbian ecological change is a complex one. However, it is often boiled down to the question of whether the changes came about because of imperialistic greed or ignorance of environmental consequences. This, in my opinion, is a false choice, as both had a major impact on the development of post-Columbian ecological collapse. However, each played a unique role; Imperialistic greed lead the Spanish conquerors to make decisions, while their ignorance provided good odds that their choices would be the wrong ones. To use a pop-cultural analogy, greed was the Gallagher to ignorance's Sledge-o-matic, with the environment winding up as useful as a squashed watermelon. Thus, the ultimate cause is the greed, but it would not have happened as it did without the ignorance.

The Conquistadors, and the English, Dutch, and French who followed them, had many powerful weapons in their arsenal, not the least of which was disease. Long centuries of living with their animals had exposed the Europeans to a wide variety of diseases, and gave them the ability to resist them. The Native Americans, however, had no such resistances, and so many European diseases ravaged their population, killing many and disabling most of those who did not die in so-called "virgin soil epidemics". This removed much of the Native Americans' benefit of numbers, and allowed the conquerors advantage in technology to be much more telling. In addition, these diseases spread far in front of the conquerors, making the path of later explorers less populated.

Behind disease came the Europeans themselves, mounted, often as not, on horses and with cattle, pigs, and other domesticated creatures in tow. Domesticated animals live in much denser concentrations than their wild counterparts, and therefore have a much heavier impact upon the local environment. Whereas a herd of deer might be 20 strong, and graze in a rotational pattern through many separate meadows, a herd of cattle is likely to be 200 strong and growing, and graze on only one or two of those meadows. This gives the flora less time to recover, and packs the earth tightly under the hooves of many more beasts, making it still harder for the land to recover. These factors led to a loss of ground cover, which made erosion more common. Erosion silted up rivers, furthering a vicious cycle that served only to make the land unsuitable for any enterprise save dust farming.

In addition to disease and animals, though, the very mindset of the European invaders led to problems. First of all, the primary mindset of the Spanish is reflected in their name; they were not colonists, but conquistadors. As such, the lands were spoils of war, to be exploited as the conquerors saw fit. In addition, the size of the continent encouraged all of the Europeans who came to America to see it as nigh infinite. With the thought that they could never exhaust natural resources in mind, they set to work with characteristic efficiency exploiting those resources. This lead to deforestation, the near-extinction of many species of plants and animals, and the destruction of topsoil by irresponsible land use.

Elinor Melville gives a powerful example of this in her book Plague of Sheep, in "el Valle del Mezquital", or "The Valley of Mesquite". Pre-conquest, the valley was a large patchwork of horticulture, open meadows, and woodlands. The valley was densely populated by pre-Columbian standards and well watered by springs and rivers. The tree cover on the mountainsides helped to capture water from the rains, keeping the subterranean aquifers recharged, so they could keep the springs flowing. The springs fed rivers, which provided water for the gardens that supplied many of the vegetable needs of the populace, while the meat needs were often met by the wildlife that lived in the wooded hillsides. The rivers fed from springs provided enough evaporation for a healthy level of precipitation, which in turn watered the hillsides and the gardens below. The Native Americans took advantage of this cycle, choosing which plants to grow in profusion and removing those that they did not want from their gardens. While their way of life altered the landscape from what it would have been without humans, they were essentially part of their environment, rather than its would-be masters.

The Spanish, however, did not continue this profitable system. The initial wave of disease swept through the valley, killing many people and leaving their lands vacant. The Spanish moved into these areas, turning many of them into stations for pastoral herders. Other areas they turned away from relatively low-impact horticulture into much higher impact agriculture. Simultaneously, they deforested and mined the hillsides, which had a negative impact on the hydrologic cycle in the area.

Some of the impact of domesticated animals has already been discussed, but there were several more points that the Valley of Mesquite brought to the fore. First of all, the Native Americans were not used to having to fence their plots; the animals they found grazing on their crops were scared of humans, and would make a nice addition to the stewpot if they didn't run fast enough. However, domesticated animals were not scared of humans, and were thus unlikely to run just because one approached them. Rather, they would continue to eat and trample the crops of the native farmer. Since Spaniards usually owned the animals, the native rarely had much in the way of legal recourse to get rid of the animal, and herdsmen would violently protect their charges. Thus, the ecological decline was continued because Spanish greed allowed their ignorance of ecology to come into play.

In agriculture, the Spanish greed and misconceptions further damaged the ecology. They would turn varied horticultural plots, grown in the native style, into agricultural farms. Often, they would grow plants less-suited for the area than the native plants, and increasingly encourage monocultural plots, increasing the vulnerability of small holders to famine due to a single plant disease destroying their entire crop. These farmers would then face starvation or destitution, meaning they would be forced to join in the logging or mining efforts, furthering the impact those activities had upon the environment.

To the Spaniards, the hills that surrounded the Valley of Mesquite were great treasures, possessing a limitless wealth of wood and minerals. As such, they encouraged the deforestation and mining of the hills. Without trees holding the soil in place, however, heavy rains would wash away the topsoil, causing massive erosion, covering the fields below in mud, and silting up the rivers. Also, the trees had ensured that much more water re-entered the aquifers. With them removed from the hillsides, springs and rivers slowly began to go dry, and the rains came less frequently. Thus, farmers were forced to irrigate more and more from smaller and smaller rivers, which were simultaneously being polluted with the effluent from mining operations in the hills, which consumed a massive amount of water in and of themselves.

Despite the rampant evidence for ignorance of the consequences being a major cause of environmental problems in the Valley of Mesquite, it must be remembered that all of this was driven by greed. The Spaniards deforested the hillsides because the lumber was valuable, not only for the building of houses and ships, but also as supports for the mines that produced even more valuable minerals. They pressured farmers into accepting monocultural agriculture because that will produce more profit than multicultural horticulture, and ignored the problems of livestock foraging on the crops of farmers because livestock were more valuable still. Thus, without the impetus of greed to drive them, the Spanish conquerors would have had a much lighter impact upon the ecology because they would have had no reason to do many of the things that led to environmental collapse. Without the environmental collapse they brought about, however, one can only wonder what our continent would be like today.

Melville, Elinor G. K. A Plague of Sheep: Environmental Consequences of the Conquest of Mexico. Cambridge University Press, 194/1997