Investigating the human impact on the Bay environment Presenter: Kent LIghtfoot
Today it is my pleasure to discuss the issue of human-environment relations
in the San Francisco Bay from a long-term perspective. The study of the
diachronic relationship between humans and their environments is known
as historical ecology. It is important to examine the historical
ecology of the San Francisco Bay Area, as it may alter some of our ideas
about the San Francisco Bay.
If asked when humans began to impact the local area, most people would respond
that human impact is fairly recent, perhaps in the late 19th and
20th centuries. During that time, we see evidence of:
- agricultural activities
- diking of the bay shore
- hydraulic mining debris from the Sierra Nevada Mtns
- land reclamation and urbanism
- disposal of pesticides, domestic and industrial wastes
Prior to 1850, before Anglo-American colonization, it
is not uncommon for people to imagine the San Francisco Bay as a pristine wilderness.
The primary purpose of my talk is to have you rethink
this, and begin to consider the Bay as a very old anthropogenic landscape.
The ecology of the Bay has been shaped by humans for many centuries. We cannot
consider the ecology of the bay since its very formation without taking account
of humans. I argue that there never has been a truly natural or pristine San
Francisco Bay.
Today I will make four basic points about the Historical
Ecology of the Bay, from early prehistoric times through the early colonial
period when Spanish, Mexican, and Russian peoples colonized the area.
I. Local native peoples were here during the creation of the San Francisco
Bay system.
As discussed earlier this morning, the greater SF Bay
was created only in the last 11,000 to 10,000 years as a consequence of the
post-Pleistocene sea level rise.
- Archaeological research in the region shows evidence of human occupation,
for example:
- Up on the Sonoma County coast – Duncans Landing site
- Los Vaqueros area in Alameda County
- Sites in Santa Clara County
These sites provide ample evidence that local hunter-gatherer
peoples, native Californians, occupied the area when the Golden Gate was first
inundated by rising sea waters about 10,000 years ago.
This is rather significant when you think about it. Native peoples witnessed
the creation and expansion of the San Francisco Bay system! I think about the
stories told over countless nights around campfires, in oral traditions handed
down from one generation to another, that may have described the growth of the
great bay.
So people were here from the very first.
II. Once the rate of sea level began to decline and
the current bay shore began to emerge, human habitations began to dot the landscape.
Most estimates of sea level rise suggest rapid expansion
of the Bay system from 10,000 to 6,000 years ago. About 6000 years ago, sea
level rise began declining, and expansion of the bay took place at slower rate.
At this time, the current configuration of San Francisco Bay, San Pablo Bay,
and Suisun Bay began to emerge. Thousands of acres of intertidal mud flats and
salt and brackish tidal marshes were beginning to take root and thrive during
the period of 6000 to 2000 before the present. The chronology of archaeological
sites tends to follow the establishment of tidal wetlands around the Bay. The
earliest Bayshore sites date to about 5000 to 4000 years ago.
The kinds of archaeological sites that were created are rather unique. They’re
known as shell mound sites. Many of our observations of these
impressive sites are from early UC Berkeley archaeologists (Max Uhle,
Nels Nelson and others) beginning with excavations in 1902.
Below are mages of a shell mound in Emeryville, CA, excavated by Max
Uhle. Click to zoom in on each image.
There are several characteristics of shell mound sites.
A. MOUNDED SPACE
- The mounds are built up from tons and tons of rock, soil, ash, and shell.
- They vary greatly in size: the largest ones cover two football fields
laid end-to-end, and are 30 feet high.
B. BURIALS
- Human remains have been exposed in all cases where large mounds have been
excavated.
- The remains are often deep in the core of the mound.
- Many mounds contained several thousands of graves, a key observation.
C. ARCHITECTURAL FEATURES AND ARTIFACTS
- In large mounds that have been extensively excavated, we find house floors,
hearths, roasting pits and other “domestic” features.
- The houses have circular floor plans, are often saucer shaped – 3 to 5.5
meters in diameter, and are of hard packed clay – 7 - 10 cm thick
D. DIVERSE CONTENT
- The mounds contained a diverse range of lithic, shell and bone artifacts.
Archaeologists have proposed various interpretations for shell mounds. Early
UC Berkeley archaeologists proposed the interpretation of “kitchen middens”
or “rubbish dumps”. Later archaeologists have added two other possible
interpretations: Specialized cemeteries, where mortuary ceremonies and
feasting rituals took place, or mounded villages, with ancestors buried
below, and people living on top of mounds.
No matter how you interpret mounds, it is clear that these were not just ephemeral
campsites. They were very sizeable mounded structures.
III. It is clear that prehistoric native peoples had some kind of impact
on environment of the greater SF Bay.
The large size and number of shell mounds suggest a fairly large population
of Native Californians. Initial survey work by Nels Nelson recorded 425 large
mounds dispersed around the bay. He did not locate all of them, because
unfortunately urban expansion destroyed many of them. Furthermore, a regional
settlement pattern characterized by mound clusters shows that where freshwater
empties into the Bay, we find not just one or two mounds but often a cluster
of between 4 to 6 mounds.
It is difficult to estimate population density very precisely at this time.
On one hand, not all of these mounds were probably occupied at the same time.
But on the other hand, many appear to have been used over multiple centuries.
There were overlapping occupation spans. Certainly when early Spanish explorers
entered the Bay Area between 1769-1775, they described very dense population,
with smoke rising from many villages around the Bay.
What is clear is that a diverse range of resources were being exploited by
Bay Shore peoples. This is borne out by archaeological studies of faunal or
animal remains in the shell mounds. These remains include:
- Lots of shellfish: Bay Mussels (Mytilus trossulus /edulis), Pacific Oyster
(Ostrea lurida), Bent-nose clam (Macoma nasuta).
- Terrestrial mammals, including elk, black-tailed deer, and pronghorn; these
would have been hunted with darts or bow and arrow. We also see wolf, fox,
bear, skunk, and raccoon.
- A diverse range of fish remains, including bat rays, green and white sturgeons,
king and silver salmon, sharks, surf perches, jack smelt. Fishing was a major
activity. They probably used a hook and line, nets (dip nets, seine nets
with weights), and tule balsas (on display at Coyote Hills Regional Park).
Tule balsas were built of tule bundles wrapped together; they would hold 1,
2, or 3 people and use double bladed paddles—they were not for ocean voyages.
- Sea mammals, such as sea otters, harbor seals, fur seals, and sea lions.
They would have been hunted with spears, darts, nets, clubs.
- Birds, in very high numbers, especially water fowl such as ducks, geese,
cormorants, loons, and grebes. They were probably captured with nets, using
tule decoys.
In considering the overall impact that Native Californians
had on SF Bay ecology, there are two schools of thought.
A. RESOURCE MANAGERS
This perspective questions the old idea of California Indians as passive
hunter-gatherers who simply collected the fruits of a “wild” and “pristine”
land. Kat Anderson, Thomas Blackburn, Lowell Bean and others view California
Indians as nurturing land managers who constructed a “cultivated” landscape
through deliberate human intervention over many centuries.
They proposed that native peoples created and maintained various kinds of
productive habitats through techniques including fire management (burning),
tillage, pruning, broadcasting of seeds, weeding, and conservation practices.
Highly skilled in enhancing wild resource production, they created grasslands
and open oak parklands through manipulation of the environment.
B. RESOURCE INTENSIFICATION
Proponents of this theory present a darker, more complicated story of prehistoric
hunter-gatherers. It was first suggested by early Berkeley archaeologists,
who noted that shell mounds contained large numbers of mollusk remains, which
must have had an impact on local shellfish beds.
Their point comes into sharper focus when you consider that one mound, such
as Ellis Landing, is estimated to contain more than 17 million mollusk
shells (Nelson 1909:346). That’s quite a few clam bakes!
Early Berkeley archaeologists noted a pattern in shellfish frequencies in
excavations: bay mussels and oysters tend to be found at lowest levels, while
clams are found in younger or upper levels. But there is considerable variation,
reflecting local changes in estuarine habitats. They argued that the change
from mussel and oyster to clam may have been caused by various factors, including
changes in the tastes of Indians and changes in the environment (silting of
the bay would be ideal for burrowing clams). But it could also suggest the
idea that overexploitation of shellfish beds forced them to shift to different
kinds of mollusks as favorite food sources disappear from some bay habitats.
The major advocates for this position, Jack Broughton and Dwight Simons,
have examined faunal remains from various shell mounds. Their research results
show a shift over time (in Late Holocene), from large prime animals to smaller
game. Lower (earliest) strata contain large numbers of big “fat” artiodactyls
(deer, elk, pronghorn) and large fish (such as white and green sturgeon),
while these decrease in frequency in upper (later) strata. They are replaced
by increasing numbers of smaller game, such as sea otters and small species
of fish.
Their interpretation is that when large terrestrial game and sturgeons (optimal
prey because they are big food packages) were hunted or fished out, people
were forced to turn to smaller, less optimal food packages including sea otters
and small fish. At these times they also observe more emphasis on acorns
and birds.
While many factors may account for these changes in faunal remains, most
archaeologists who advocate resource intensification argue that the primary
reason was population growth, which created resource stress and forced people
to go after secondary resources.
I feel that these two perspectives (Resource Managers and Resource Intensification)
are NOT mutually exclusive. There were probably elements of both taking place
through space and time. The critical point is that these perspectives
do not view the prehistoric San Francisco Bay area as pristine wilderness.
It has long been very much a human altered landscape and seascape. Both viewpoints
support the idea of natives creating an anthropogenic landscape.
IV. The environment of the Bay Area underwent significant
shift in its anthropogenic landscape with the early colonization by Spanish
and Russian settlers.
The Spanish colonization of the Bay Area began in 1776, when Spanish soldiers
and Franciscans began to build presidio and missions. They implemented a program
of missionization among native peoples, and developed extensive agricultural
ranches and farms.
What one sees with the coming of the Spanish and later Mexican settlers is
the transformation of one anthropogenic environment to another. The Native Peoples
(Ohlones, Coast and Bay Miwok) were aggregated into the missions. The Spanish
no longer allowed them to burn grasslands, so they were no longer maintaining
native grasslands and open oak woodlands. The Indian manipulated landscape
was replaced by an agrarian one.
The late 1700s and early 1800s unleashed a plethora of Old World animals and
plants into the environment. Thousands of cattle, sheep, and horses grazed
around the Bay, and thousands of acres of wheat and barley fields, orchards
and vegetable gardens were cultivated.
The most devastating aspects of the new introductions were that various pests,
such as pigs and rats, were unleashed into the environment. Alien weeds thrived
in the new environment, especially with intensive grazing. Archaeological research
on pollen and macrobotanical remains from archaeological contexts, especially
in the adobe bricks of missions, shows rapid colonization of weeds (various
types of thistles, curly dock, cheeseweed, and wild oat). These
began to out-compete indigenous grasses.
It is not clear how this initial Spanish colonization effected Bay Area waters,
though there is some evidence of increased sedimentation in coastal estuaries
during Spanish times, which appears to be related to over-grazing and run-off.
It is interesting to note that Russian colonization did have an impact on the
Bay. Russians colonized Fort Ross from 1812-1841 in a trade outpost. It generated
significant economic activity from sea mammal hunting, specifically sea otter.
They used Native Alaskans (baidarkas, “wolf packs”). They began hunting along
the Sonoma and Marin coasts, portaging along Point Bonito on the Marin Headlands
to the SF Bay. The SF Bay contained thousands of sea otters, which represented
a rich hunting area for the Russians. They began their hunting illegally,
sneaking into Spanish waters.
The Russians increased their harvest when Mexico took over administration
of California in 1821. They negotiated a contract allowing the Russians
to hunt sea otters. They exterminated the population, along with other
sea mammals such as harbor seals and sea lions. This had a potentially
major impact on the Bay, as sea otters are a “keystone” predator with
voracious appetites. They consume 25% of their body weight each day, and
their preferred foods are sea urchins, crabs, clams, and abalones.
Studies of sea otters in Alaska show that when otters disappear, it affects
marine productivity. Sea urchins and other herbivorous invertebrate populations
increase, and they in turn consume kelp forests that support fisheries. Thus
the decrease in sea otter population results in the degradation of kelp forests
and local fisheries.
It is not clear what happened in the SF Bay, but when the SF Bay sea otter
population was wiped out by the 1830s and 1840s, it must have had a real impact
on clam and crab populations, causing a major growth spurt. It is even possible
that prehistoric hunting of sea otters may have decreased population enough
to allow the clam population to grow unchecked, which could explain why we see
a preponderance of clam in late prehistoric shell mounds.
The point to keep in mind is that human impact on one
component of the ecology of the Bay can have significant effects on others,
which we need to think about.
V. The critical point of my talk is that the San Francisco Bay is an excellent
setting in which to view the symbiotic relationship of humans and the environment
over the last 11,000 years or so.
If we think about it in terms of the creation of anthropogenic landscapes,
the San Francisco Bay has been undergoing transformations for many centuries.
What we see today in the SF Bay is part of a long-term process, in which
human modification to the local environment is accelerating at an unprecedented
pace.
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