Historical Ecology - Human-mediated Disturbance

Human-mediated Disturbance

Homo sapiens have interacted with the environment throughout history, generating a long-lasting influence on landscapes worldwide. Humans sometimes actively change their landscapes, while at other times their actions alter landscapes through secondary effects. These changes are called human-mediated disturbances, and are effected through various mechanisms. These mechanisms vary; they may be detrimental in some cases, but advantageous in others.

Both destructive and at times constructive, anthropogenic fire is the most immediately visible human-mediated disturbance, and without it, many landscapes would become denatured. Humans have practiced controlled burns of forests globally for thousands of years, shaping landscapes in order to better fit their needs. They burned vegetation and forests to create space for crops, sometimes resulting in higher levels of species diversity. Today, in the absence of indigenous populations who once practiced controlled burns (most notably in North America and Australia), naturally ignited wildfires have increased. In addition, there has been destabilization of "ecosystem after ecosystem, and there is good documentation to suggest fire exclusion by Europeans has led to floral and faunal extinctions."

Biological invasions and the spread of pathogens and diseases are two mechanisms that spread both inadvertently and purposefully. Biological invasions begin with introductions of foreign species or biota into an already existing environment. They can be spread by stowaways on ships or even as weapons in warfare. In some cases a new species may wreak havoc on a landscape, causing the loss of native species and destruction of the landscape. In other cases, the new species may fill a previously empty niche, and play a positive role. The spread of new pathogens, viruses, and diseases rarely have any positive effects; new pathogens and viruses sometimes destroy populations lacking immunities to those diseases. Some pathogens have the ability to transfer from one species to another, and may be spread as a secondary effect of a biological invasion.

Other mechanisms of human-mediated disturbances include water management and soil management. In Mediterranean Europe, these have been recognized as ways of landscape alteration since the Roman Empire. Cicero noted that through fertilization, irrigation, and other activities, humans had essentially created a second world. At present, fertilization yields larger, more productive harvests of crops, but also has had adverse effects on many landscapes, such as decreasing the diversity of plant species and adding pollutants to soils.