7 Dec 2009, 1:32pm
Forestry education
by admin

A Brief History of the Post-Cretaceous Forests of SW Oregon, Part II

Part II. The Forests of the Anthropocene


A discussion of fire ecology in Southwest Oregon that recently came to my attention contained another statement that troubled me:

A natural fire regime is a general classification of the role fire would play across a landscape in the absence of modern human mechanical intervention, but including the influence of aboriginal burning (Agee 1993, Brown 1995).

Why do USFS ecologists conflate natural fire with anthropogenic fire when the differences are enormous?

Historically speaking, in SW Oregon over the last 12,000 years or so, the incidence of anthropogenic fire has been thousands of times more prevalent than natural (lightning) fire. Furthermore, lighting fires are random in time and space whereas human-set fires are deliberate actions (planned, timed, executed) by intelligent people with intent (informed by successful experience) to alter the landscape.

As a consequence, anthropogenic fire has had a much more profound and dominant effect on SW Oregon during the Anthropocene than lightning fire. Human fires have shaped the vegetation for millennia. The “natural fire regime” touted by USFS ecologists is a pernicious myth, or more simply, crappy science.

What’s the Anthropocene? It’s a cute name bestowed on the latter stages of the Holocene by the Nobel Prize winning atmospheric chemist Paul Crutzen, who considers the influence of humans on the environment in recent centuries so significant as to constitute a new geological era [here].

But human influences on the environment have been significant for more than a few centuries. For thousands of years, indeed the entire Holocene/Anthropocene (and much longer), people have been impacting the planet by setting fires. Anthropogenic fire regimes have dominated while “natural” fire regimes all but disappeared thousands (possibly hundreds of thousands) of years ago.

To grasp the enormity of this concept, we must first examine the onset of the Holocene/Anthropocene in greater detail.

The Great Warming

The Wisconsin Glaciation was the latest in a series of 100,000-year-long glacial stadials that have chilled the Earth for the last 1.8 million years. Approximately 15 kya (thousand years ago) the cold dipped to its lowest point during what is called the Oldest Dryas period. Not only was the planet a good 15°C colder than now (in the Arctic, less so in the Tropics), it was colder than any time during the last 250 million years.

[Note: you may put an exclamation point on that sentence. The Ice Ages have been a terrible shock to Life Itself. It has almost always been warmer, much warmer, than now on Planet Earth. Cold is bad for living things; warm is good. Please repeat the following over and over until our (clueless) leaders have got the message: warmer is better, warmer is better, warmer is better...]

Then 14.67 ky BP (14,670 years ago, before present) a sharp temperature rise occurred. The exact mechanism is not well-understood, but the driver was increasing summer insolation (radiation from the Sun striking the Earth) due to Milankovitch Cycles (eccentricities in the earth’s orbit).

During glacial stadials summer is not warm enough to melt the previous winter’s snow. The snow becomes ice and builds up, and during the Oldest Dryas the ice sheets reached their maximum extent. The Cordilleran Ice Sheet reached the Columbia River near Portland, and tundra/steppe conditions blanketed Southwest Oregon.

Those conditions flipped 14.67 ky BP, and the Bølling-Allerød interstadials commenced. The warm period ran from c. 14.7 to 12.7 ky BP. A Giant Melting occurred. Huge lakes formed from the melting ice sheets, including Glacial Lake Bonneville and Glacial Lake Missoula. These lakes were more like inland seas. G.L. Bonneville was more than 984 feet above the present level of the Great Salt Lake today and covered an area of more than 19,691 square miles [here].

As the warming continued the glacial lakes broke through ice dams and sent huge floods called jokulhlaups across Eastern Washington and down the Columbia River to the sea, backwashing up the Willamette Valley 100 miles or more [here].

In the Pacific Northwest a cold period known as the Older Dryas occurred in the middle of the Bølling-Allerød interstadial. The Bølling oscillation peaked around 14,500 BP, and the Allerød oscillation peaked closer to 13,000 BP.

Then the erratic warming stopped altogether and temperatures plunged again during what is called the Younger Dryas [here]:

The Younger Dryas saw a rapid return to glacial conditions in the higher latitudes of the Northern Hemisphere between 12,900–11,500 years before present (BP)[5] in sharp contrast to the warming of the preceding interstadial deglaciation. The transitions each occurred over a period of a decade or so.[6] but the onset may have been faster.[7] Thermally fractionated nitrogen and argon isotope data from Greenland ice core GISP2 indicate that the summit of Greenland was ~15°C colder during the Younger Dryas[6] than today.

For another 1,400 years Ice Age cold gripped SW Oregon (and much of the rest of North America). Then the increasing Milankovitch Cycle insolation overwhelmed the cold and temperatures warmed rapidly:

Measurements of oxygen isotopes from the GISP2 ice core suggest the ending of the Younger Dryas took place over just 40 – 50 years in three discrete steps, each lasting five years. Other proxy data, such as dust concentration, and snow accumulation, suggest an even more rapid transition, requiring a ~7 °C warming in just a few years;[5][6][15][16] the total warming was 10°±4°C.[17]

Trees Moved In

When the Younger Dryas finally broke, the Holocene began. The tundra and steppe of SW Oregon were invaded by trees, but not rapidly. It took thousands of years for all the species of today to arrive from coastal refugia and occupy the landscape. Even under the best conditions (warm summers, bare ground to invade), conifers spread at a rate of ~10 miles per century.

The first tree species to appear were spruces, jack pine, birch, and alder. All are boreal species adapted to extreme cold. Then around 11.5 kya Douglas-fir arrived. Fifteen hundred years later oaks showed up. Ponderosa pine appeared around 9 kya, sugar pine and western red cedar a few thousand years after that.

Those dates are approximate; SW Oregon is a big place, local conditions vary, and few palynological (fossil pollen) studies have been done. But accumulating evidence suggests that it took thousands of years of Holocene warmth for the full plant assemblage of modern SW Oregon to invade.

The trees were not alone. Something else had invaded as the ice melted, and probably even before the Holocene began. Super-smart and capable hominids bearing Neolithic technology came into SW Oregon, before most of the tree species extant today.

Homo “Pyro” Sapiens

Our species has always been masters of fire. So were the Neanderthals for that matter, and Homo erectus. Swartkrans Cave, in the Sterkfontein valley about 30 miles NW of Johannesburg, is the single richest hominid site in Africa. Remains of cooking fires there date back 1.8 million years [here]. Homo sapiens (us) are thought to have evolved ~200 kya.

We inherited the mastery of fire from our pre-human ancestors. Fire is as much a part of our makeup as opposable thumbs.

Homo sapiens brought fire with us when we left Africa. By 40,000 years ago we were setting fire on a regular basis to most of Australia. And Asia, too — the trans-Siberian Beringian migration could not have happened without plenty of fire.

There is ample controversy about when we first arrived in North America. The anthropology and archaeology battles over the issue are very well-documented and explored in First Peoples In a New World: Colonizing Ice Age America by David J. Meltzer [here]. Suggestive evidence exists hinting that people arrived here as much as 30 kya, but conclusive evidence indicates that we have been here for at least 12,500 years.

In other words, humans arrived in NA no later than the the Bølling-Allerød interstadials, and suffered 1,000 years of the Younger Dryas stadial. That re-glaciation probably helped wiped out many NA fauna and the Clovis Culture as well, but by 11.5 kya humans had spread across North and South America.

The First Residents were smart, successful survivors. At Monte Verde, an archaeological site in southern Chile, an entire village dating from 11.8 to 13.6 kya was unearthed from an ancient mudslide that had preserved it. Besides house planks, wooden artifacts, stone tools, animals hides, twine, the remains of meals that included bones, tusks, teeth and ribs of mastodon, paleo llama bones, fish bones, shellfish, and birds, the researchers found charred plants:

About a third of the plants [some 75 species] at Monte Verde were charred from cooking; a quarter were exotic, imported to the site from the Pacific coast some 30 kilometers distant (including seaweed, the residue of which adhered to many tools, from high Andean settings, or from arid grasslands up to 600 kilometers away. Coincidence or not, more than half the the plants are still used by the native Mapuche as food, drink, medicine, or materials. The archaeological list includes charred skins of wild potato, along with burned and unburned juncus (rushes) and scirpus (sedges) seeds were found mashed into the cracks of wooden basins. Among the most unusual of the MVII plant remains a half-dozen plugs of chewed bolo leaves mixed with seaweed, forming a medicinal tea still used by the Mapuche to relieve stomach ills, colds, and congestion. — from First Peoples In a New World: Colonizing Ice Age America by David J. Meltzer

The First Residents had to be clever and adaptive to survive first the Younger Dryas and then the sudden climatic change to the Holocene. The tool of choice: fire and lots of it.

Why? People used fire to cook and keep warm, but also to alter the landscape to promote the growth of nuts, berries, root crops, craft fibers, browse for game, and myriad other reasons. Hunters used fire to drive game. Broadcast burning in dense stands of young trees created dry, easy to collect firewood. The clearing of underbrush by fire opened vistas and reduced the chances that enemies could sneak up and attack villages. Etc.

Potential aboriginal ignition rates were 270–35,000 times greater than known lightning ignition rates . — from “Are Lightning Fires Unnatural? A Comparison of Aboriginal and Lightning Ignition Rates in the United States” by Charles E. Kay [here].

Pyro-dendrochronology studies around the country suggest that the high frequency of fires in sequoia-mixed conifer forests of the Sierra Nevada, the oak-hickory forests of eastern North America, and the lodgepole pine forests of the Rocky Mountains could not be explained by the contemporary ignition rate from lightning alone but only in conjunction with indigenous burning (Abrams 1992; Barrett and Arno 1982; Barret 1981; Kilgore and Taylor 1979). Stephen Pyne, the acknowledged authority on the history of fire, and Thomas Bonnicksen, a renowned expert on fire and restoration ecology, have both presented major studies that emphasize the importance of understanding indigenous peoples’ uses of fire (Bonnicksen 2000; Pyne 1982, 1991, 1997). — from “Introduction to Omer Stewart’s Forgotten Fires” by Henry T. Lewis [here].

See also:

Before The Wilderness: Environmental Management by Native Californians, Thomas C. Blackburn and M. Kat Anderson, eds [here]

Indians, Fire, and the Land in the Pacific Northwest, Robert Boyd, ed [here]

“References on the American Indian Use of Fire in Ecosystems” by Gerald W. Williams [here]

America’s Ancient Forests–From the Ice Age to the Age of Discovery by Thomas M. Bonnicksen [here]

Tending the Wild: Native American Knowledge and the Management of California’s Natural Resources by M. Kat Anderson [here]

and all the other references found in the W.I.S.E. Colloquium: History of Western Landscapes [here]

Anthropogenic fire has scorched the Americas (everywhere that will burn) for 12,500 years at least. That very ancient yet continuous practice has had a profound effect on landscapes and vegetation across the continent, including SW Oregon. By deliberate intent of the long-time human residents, continuous burning created open, park-like forests, prairies, and savannas arranged across landscapes in anthropogenic mosaics (human-induced vegetation patterns).

Somehow I have rattled on and on in this section and failed to describe the titular Anthopocene forests. But we’re getting there…

Next: Part III: Anthropogenic Mosaics

7 Dec 2009, 4:04pm
by Tim B.

I’ve always been intrigued with the temperature graphs I have seen from multiple sources (though these days one has to wonder about their accuracy) showing a striking stabilization of average world temperatures right about at the commencement of the Holocene, as compared to the wild swings that supposedly happened during prior geologic epochs. Curious that this stabilized temperature more or less coincides with the development of agriculture.

Or maybe it could have been from a critical mass of fire users (and I am sure the old folks who figured out annual agriculture probably first cleared their fields-to-be with fire), affecting temperature by particulate production or changes in surface albedo (I doubt from CO2 as biomass burning couldn’t possibly compare to volcanic sources in that regard). Or may both activities in combination.

Whatever, it seems pretty obvious from a number of perspectives that humans have had a large effect on things ever since we learned how to use fire.

7 Dec 2009, 11:46pm
by Bob Zybach


You are making a very important point of which the large majority of climate modelers are either unaware (ignorant) or do not fully comprehend its significance.

In 1991 I gave an EPA-sponsored paper to an international group of forest and climate scientists regarding carbon sequestration in temperate forest regions of the world. At that time I cited a 1976 source (so newer information may be currently available) that approximately 1/3 of the world’s forests had been removed for grazing and farming purposes between 5,000 and 7,000 years ago.

Newer numbers are possibly more refined, but I suspect the basic facts remain the same. As you point out, this process of deforestation could only have been accomplished via fire.

Imagine the smoke. The clouds of CO2. The dramatic change in evapotranspiration across the landscape, and the resulting effects on creeks, rivers, and cloud formations. Seasonal covers of vast expanses of snow. Massive increases in grazing animal populations. And so on.

This vast deforestation was followed by the warmest period in human history, so far as we can tell. Was this a cause-and-effect relationship, or just a coincidence?

This information, plus the stated opinion that the predictive models being used at the time by James Hansen and others were incapable of making accurate predictions, were enough to eliminate my funding and marginalize my contributions.

Above all else, climate science seems to need consensus. Ignoring contrary research and opinions and eliminating funding are two ways in which to achieve that result.

8 Dec 2009, 9:25am
by bear bait

The obvious, then, would be to buy into global climate change as a man-made activity, all the while denying anthropogenic landscape management by fire over millennia. That has to be disingenuous at the least. At the worst, it would be bad science.

But, as a former logger and timberland manager (my every move being driven by bad science expressing itself as work-a-day regulation by “concerned” citizen purveyors of urban popular but provocatively bad science) is how things seem to work in the real world. If we expect anything different out of Copenhagen other than an addictive buzz, we will be sorely disappointed. The lemmings are on the march.

8 Dec 2009, 10:00am
by Mike

Yup, bear, it’s a pip.

They spout wild-ass theories about anthropogenic global warming — as if humanity controlled the global climate — and yet deny the plain fact that human beings have been in active residence on this continent for thousands of years.

Some view the cognitive dissonance expressed by the power elite as racist, or fascist, or braying stupidity. But it is really just common, ordinary fraud, collusional scams, 3-card-monte with the entire nation (and world) as easy marks.



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