Agriculture Reference
In-Depth Information
almost certain that even if humans were here during that early period they were
not a dominant presence on these landscapes.
Approximately 13 000 BP represents the age at which there is nearly complete
agreement on human occupation and rapid expansion throughout North and South
America. Between 13.5 and 13 cal kBP (thousands of calendar/calibrated years before
present), 17 or more genera of North American megafauna (animals
100 kg)
became extinct (Martin & Klein
1984
). The timing of this event was coeval with
Paleoindian expansion, implicating human involvement, but the extinctions also
coincided with significant climatic changes, making it difficult to parse out the
relative importance of each. However, this megafauna survived previous Pleistocene
interglacial episodes of sharp climatic warming; thus the arrival of humans would
seem to be an important factor driving their extinction.
It is hypothesized that this period of time marked a change in fire regimes in
California and other parts of the western USA, driven by novel anthropogenic
sources of ignitions, altered fuel structure related to megaherbivore decline, and
warming climates (Pinter
et al.
2011). On coastal and foothill landscapes the
arrival of human ignitions resulted in an immediate increase in fire frequency
and subsequent changes in vegetation such as localized replacement of chaparral
with herbaceous vegetation. In the higher interior mountains where Native Ameri-
can populations were scarce, and there were abundant natural ignition sources
from lightning, forest structure was probably little affected by humans.
This model contradicts the climate-only model of Marlon
et al.
(
2009
) because it
infers a multifactorial explanation in which humans, herbivores, climate and fire
sort out along landscape gradients. It is consistent with Marlon
et al.
's data
because that study sampled largely from high-elevation landscapes where natural
lightning ignitions were not limiting, and human settlements were absent. How-
ever, for those landscapes such as the lower elevations in California where natural
ignitions were limiting, humans had the potential for greater impact on fire
regimes, both from increased ignitions and from altered landscape fuel patterns
due to the demise of megaherbivores.
The mid Holocene marks a change in food economy of the California Indians
with increased emphasis on natural seed crops as the main dietary staple, and
populations increased throughout all regions within the California Floristic Pro-
vince (Erlandson & Glassow
1997
). Although agriculture had already begun to
flourish in parts of the Americas, it was basically absent in California. Nonethe-
less, Native Americans did manage the California landscape, often very intensely
through the use of fire (Timbrook
et al.
1982
; Keeley
2002b
). As was the case over
much of the globe, the primary management goal was to displace less useful
woody vegetation with high seed output annual forbs and grasses, and fire was
a reliable means of doing this. The primary focus of burning was to break up dense
shrublands into mosaics of herbaceous and woody species (Cooper
1922
; Bauer
1930
). Many of the typical postfire species in these shrublands are high seed
producers and were heavily exploited by Indians as food sources. Fire was used
for other purposes, for example for herding animals during hunting or killing
