2. What are the ecological consequences of the different forms of extensive subsistence land use?

Question

2. What are the ecological consequences of the different forms of extensive subsistence land use?

Answer 1

Hunting and Gathering - highly variable. Some cultures in prehistoric times practiced burn-overs to replenish soil nutrients and to produce open fields to attract game animals and facilitate hunting.  Many people who do not undrstand ecology would consider this a negative or adverse impact, but, in fact, since human beings are a part of their ecosystems, the value judgment doesn't really make sense.

Pastoralism - has had a very limited distribution in both prehistoric and historic times, and its importance has probably been overstated as a result of cultural evolutionary emphasis on cultures in what we now call the Middle East. Very little environmental effect.

Horticulture  - usually couple with hunting and gathering. Some denutrification of soil when crops are planted in the same field with no fallow period after several years.  However, it is very difficult to imagine that this happened often because most hunting and gathering cultures had at least a vague notion of how easy it is to damage soil long before they adopted horticulture.

Agriculture - Generally very damaging if not practiced carefully.  The agircultural system of the Mediterranean - highly influenced by very early Islamic agronomic science and the diversity of edible plants in the area, is a fairly eco-friendly system and very highly efficient.  However, it doesn't necessarily work well in every soil type or climate.  Native American prehistoric agricultural systems were often highly destructive. These usually involved clearing massive areas - even on hill slopes - through slash and burn techniques.  this complete denudation of a landscape, coupled with slope and high rainfall, results in massive, catastrophic soil erosion. Australia, in historic times, has had similar problems with the transplantation of European agricultural systems into its eco-system.  

Agri-business:  The environmental problems associated with fully modern agro-systems can not even be simplistically summarized in anything short of a doctoral dissertation.  Pesticides, chemical fertilizers, erosion, clear-cutting, denutrification.  It's all there. Governments make attempts to regulate teh damage, but more often thannot, the laws have no teeth and nothign can be enforced.  Lots of reading ahead of you if you have to discuss this.

Answer 2

Depletion of resources, which causes war fare and famine.  It also has consequences for other animals, plant life that her dependent on the same plants and animals.

It is what happened to the Mayans and what caused the Anasazi to be cliff dwellers.

Answer 3

"When settlers first came onto the North American prairies, the topsoil depth averaged ten inches, built up over the centuries and held in place by deep grass roots. In the hundred years since the prairie sod was broken by the steel plow and the land was converted to farming, on average about half the topsoil has been eroded away. The creation of the breadbasket of America from the virgin prairies has come at great cost in topsoil."

http://www.kerrcenter.com/HTML/green_exc...

There's a passage from "Caravans" where they are in an area of ruins. Asked why the area was abandoned the reply was "salt." That irrigation left salt behind and it eventually killed the land. See:

http://www.geology.ucdavis.edu/~cowen/~G...

As can be seen, soil depletion results in a loss of productivity and eventually the ability to farm anything. The Great Dust Bowl was a result of poor farming practices and resulted in a huge loss of topsoil. The Mississippi Delta has hundreds of feet of topsoil. So much that the land sinks from the weight.

Any use of land for growing crops requires careful soil conservation.