until it is time to harvest them, which requires more
human labor.
Agriculture requires work of a much different sort
from that required of hunting and gathering. People
alter the local ecology to redirect a significantly
greater portion of the sun’s energy to themselves.
This alteration or perturbation of the ecosystem, the
conversion of a natural ecosystem to one containing
only selected, harvestable species, forms the essence of
agriculture.
The Neotropics are the place of origin for:- Maize (corn), sometime between 9,000 and 8,000
B.P. (years before present). - Pumpkin and related squash, about 10,000 B.P.
- Potato, about 7,000 B.P.
- Peanut, about 8,500 B.P
- Manioc, about 8,000 B.P.
- Chile pepper, about 6,000 B.P.
- Other important crops include cacao, tobacco, peach
palm, and rubber.
In order to support agriculture a plot of land must be
cleared of all competing species. Desired species must
be planted and continuously protected as they grow.
This requires human labor. People are concentrated
around relatively small agricultural plots, tending
crops (plate 17- 4).
Because land can be farmed repeatedly, and because
agricultural labor requires constant human effort,
permanent or semipermanent villages form. Traditional
agriculture supports somewhere between 10 and 100
persons per square mile, a one to two order- of- magnitude
increase from that of hunter- gatherer societies.
Crop ecosystems are ecologically unstable, open to
invasion by both competitors and herbivores. Thus
energy input from human labor is fundamental to
preserve the stability of crop ecosystems. What this
means, of course, is that humans must reinvest some
of the energy (in the form of human labor) they derive
from the present growing season’s crops to ensure
the success of crops in the forthcoming season. They
must also devote some of the productivity of the crops
to sustaining domestic animals. Work provided by
animals includes not only pulling objects such as plows
but also supplying essential fertilizer. Animals are also
used as food.Slash- and- Burn Agriculture
Tropical peoples face a challenge in attempting to
farm in rain forest, because the soils are nutrient- and
mineral- poor. Most of the minerals and nutrients are
not in the soil but in the biomass: the trees, lianas, and
epiphytes. To clear an area for farming, it is obviously
necessary to remove that mass of vegetation. But to do
so seems to doom the farming effort, because the poor
soil will not sustain very much in the way of crops. The
way out of this dilemma is fire, applied in a practice
that has come to be termed slash- and- burn agriculture.
Slash- and- burn agriculture follows a typical pattern:
A small plot of land (usually between 0.4 and 0.6
ha/1– 1.5 ac) is chosen, and machetes and axes are used
to cut down all of the vegetation. Trees too large to
be cut are girdled, which kills them. The tangled pile
of vegetation is then set on fire rather than removed.Plate 17- 4. This plot of cleared land, planted mostly with corn,
is a milpa. It is typical of rotational agriculture in southern
Belize (in this case) as well as much of the rest of the tropics.
Photo by John Kricher.Plate 17- 5. The charred remains of trees are readily visible
among the bananas growing in this agricultural plot on
Trinidad cleared by slash and burn. Photo by John Kricher.chapter 17 human ecology in the tropics 369