THE HOLOCENE RECORD OF HUMANS AND ENVIRONMENT IN THE SOUTHWEST
Winter-Spring Journal Club, Stanford Univ., May 13, 2002. http://www.geo.arizona.edu/palynology/socalif/stanford.html

Owen K. Davis (University of Arizona, Tucson, Arizona) *

In this web-based presentation, I will rely on palynological research to provide examples of past influences of climate on human affairs, and of the influence humans have had on their environment. I will begin with some examples leading up to the Holocene, follow up with some examples from the Holocene of the Southwest, and then conclude with some on-going studies of coastal southern California.

But, first a brief introduction to palynology: the branch of science dealing with microscopic, decay-resistant remains of certain plants and animals. These include not only pollen, but also spores and other microfossils of similar chemical composition. The word "palynology" was coined to encompass this diversity. These fossils are in every kind of deposit from the sediments of lakes, to glacier ice and the dung of extinct animals.

Pre-Holocene

The most pronounced climate change of the last 100,000 years was the dramatic transition from the last ice age to the present interglacial. Just prior to the transition, people arguably entered the New World for the first time, while sea levels were depressed. Charcoal preserved in palynological preparations has been one clue to the presence of humans in the New World as well as Australia, Japan, Madagascar, and the Caribbean. In Australia 1, elevated charcoal percentages during the preceding interglaciation were though to signal a very early arrival of humans; however, those claims have been attributed to natural fires during the interglacial. In Death Valley a similar sequence is seen.

After humans arrived on islands and in the New World the environment was transformed. The coincidence of human arrival and mammalian extinction is a topic of ongoing investigation. Palynology has played a role in tracing the timing of extinction through the study the dung fungi. The dung fungus Sporormiella shows increased abundance after the historic introduction of cattle and other grazers in the historic period and also prior to 11,000 yr B.P. when Mammoths, Mastodons, and groundsloths still roamed. Idaho California Colorado

The origins of agriculture followed the end of the last glaciation, and it has been traced in the old world through the earliest pollen of cultivated wheat in the Near East, 10,000 years ago. Remarkably, the domestication of plants in the New World began not much later, first with Squash in Central America.2 The earliest dates for corn 3 - about 7000 years ago - are based on pollen in coastal Mesoamerican settings.

Human Impacts in The Southwest

The northward migration of corn (Zea mays) is likewise detected earliest through pollen. Of the various cultivated plants of the Southwest4, corn is the most abundant. Interestingly, the earliest Southwestern corn pollen is much smaller than modern grains, just as the corn ears of primitive corn were very small. The history of domestication is traced 5, palynologically, through the development of weeds. Irrigation along desert rivers transformed that vegetation beginning 4000 years ago. From 1000 - 500 years ago, populations generally peaked, and resources declined, locally.

Returning to the topic of fire, the wetlands of the Southwest probably were at least partly managed for corn-growing. Corn pollen is abundant in Southwestern cienegas (wetlands) at about the same time it is first recorded in archeological sites in Tucson and Albuquerque. Following the Spanish conquest, the fire frequency in the southern Arizona plummeted, and woody vegetation invaded the grasslands and wetlands.

Humans and Climate in California - last 12,000 years

The environmental history of California is different from that of the Southwest east of the Sierra Crest. During the early Holocene, the Sierra Nevada was covered with pine forest, and Sequoiadendron was widespread6. [Exchequer Meadow] The Central Valley, at least from Fresno southward, was filled with Great-Basin-like vegetation. [Tulare Lake] Oak woodland did not begin to form until after 9000 years ago7. [ODP 389] Charcoal percentages increase dramatically at that time8, and the role of human-caused fires in the development of the California grassland and oak woodland is a topic for future investigation.

There is no archeological or palynological evidence for the cultivation of corn by western Californian Indians prior to Spanish Colonization. In addition to acorns, the coastal peoples relied heavily on estuarine shellfish for food. Ongoing palynological investigations have focused on the history of coastal wetlands, from Lompoc south to Oceanside.

The estuaries were best developed during the early Holocene, after raising sea-level flooded coastal river valleys. [sea-level curve] In the early Holocene, tidally-influenced salt marshes intruded far inland. As the estuaries filled with sediment, the estuarine shell-fish resources dwindled. [San Joaquin Marsh II] *. 9 At the same time, coastal populations increased. Inland droughts may to have forced migrations to the coast. The effects of over-population and droughts appear to have been most severe in the millennium prior to the beginning of the Little Ice Age. [San Francisco]10


Trends in Coastal California Palynology

Ongoing Research



References

10 Byrne, R., Ingram, L., Starratt, S., Malamud-Roam, F. 2001.
Carbon-isotope, diatom, and pollen evidence for late Holocene salinity change in a brackish marsh in the San Francisco estuary. Quaternary Research 55: 66-76.

9 Davis, O.K. 1992.
Rapid climatic change in coastal southern California inferred from Pollen Analysis of San Joaquin Marsh. Quaternary Research. 37:89-100.

6 Davis, O.K. and Moratto, M.J. 1988.
Evidence for a warm-dry early Holocene in the western Sierra: pollen and plant macrofossil analysis of Dinkey and Exchequer Meadows. Madroņo 35:128-145.

8 Davis, O.K. 1999.
Pollen Analysis of Tulare Lake, California: Great Basin - Like Vegetation in Central California. Review of Palaeobotany and Palynology 107: 249-257.

5 Davis, O.K. 2002.
Aspects of prehistoric irrigation canals in Arizona. Arizona-Nevada Acad. Sciences 46th Annual Meeting, April 6, Glenndale, AZ. http://www.geo.arizona.edu/anas/annualmeetings/geology02/odavis.html

4 Gish, J.W. 1994
Large fraction pollen scanning and its application to archaeology. AASP Contributions Series 29: 93-100.

7 Heusser, L. 2000.
Rapid oscillations in western North America vegetation and climate during oxygen isotope stage 5 inferred from pollen data from Santa Barbara Basin (Hole 893A). Palaeogeography, Palaeoclimatology, Palaeoecology. 161: 407-421.

3 Pope, K.O., Pohl MED, Jones JG, Lentz, DL, von Nagy, C, Vega FJ, Quitmyer, IR. 2001.
Origin and environmental setting of ancient agriculture in the lowlands of Mesoamerica. Science 292 1370-1373.

1 Singh, G. & E.A. Geissler. 1985.
Late Cainozoic history of vegetation, fire, lake levels and climate, at Lake George, New South Wales, Australia. Philosophical Transactions of the Royal Society of London B 311: 379-477.

2 Smith, B.D. 1997.   The initial domestication of Cucurbita pepo in Mexico 10,000 years ago. Science 276: 932-934.