4 Sep 2009, 10:00am
Forestry education Saving Forests
by admin

No Natural Fire Regimes in Old-Growth Redwood

In a stunning and gutsy scientific study, it has been revealed that old-growth redwood forests of California were dominated by anthropogenic (human-set) fires for hundreds and probably thousands of years.

Dr. Steven P. Norman (currently of the USDA Forest Service Southern Research Station), working out of the U.S. Forest Service Redwood Sciences Laboratory in Arcata CA, has discovered that the historical fire frequency in old-growth redwood was cultural, not “natural”.

His paper, A 500-Year Record of Fire from a Humid Coast Redwood Forest, is in the form of a report to the Save the Redwoods League [here], the 90-year-old organization dedicated to saving redwoods. Interestingly, the verbiage from the Save the Redwoods League extols “naturalness”:

Since 1918, Save the Redwoods League has saved ancient redwood forests and redwood ecosystems to ensure that current and future generations can feel the awe and peace that these precious natural wonders inspire. We also save redwoods because they are rare — their natural range is only in central and northern California and southern Oregon — and because they are Earth’s tallest and some of the oldest and most massive living beings.

Yet the redwoods have been tended by human beings for millennia. Human burning on a frequent, seasonal basis in an eco-zone with little lightning kept redwoods free from severe fire as well as competition and allowed trees to reach phenomenal ages.

Absent frequent, ground-hugging, anthropogenic fire, infrequent severe, stand-replacing fire would have shortened tree life-spans considerably. Biologically, redwoods do not require long life spans to reproduce. There is no biological imperative for great ages. The long lives of redwood trees are an artifact of human intervention in the ecosystem, without which redwoods may have gone extinct during the Holocene.

We have not been given permission to post Dr. Norman’s paper in toto, but the abstract follows (at present the entire paper may be downloaded from the SRL site [here]):

California’s coast redwood (Sequoia sempervirens) forests have long been associated with moderately frequent to frequent fire, particularly in the southern and interior portions of the species range. The historical importance of fire in northern coast redwood forests is generally thought to be much less because lightning ignitions are rare, and cool coastal temperatures and summer fog ameliorate the fire hazard. Support for this climate-fire gradient hypothesis has been limited because of insufficient fire history data from the northern coast redwood range. Past efforts to test this hypothesis range-wide are made difficult because of methodological differences among studies and problems with scar preservation in redwood. This research revisits the fire history of an area thought to have experienced fire only a few times per millennium in Del Norte Coast Redwoods State Park. I found that fire frequency was substantially more frequent than previously thought. Between 1700 and 1850, mean fire intervals within 0.25 to 1 ha sample areas varied from 11 to 26 years. Fire intervals did not correspond to a latitudinal, coast-interior or a topographically defined moisture gradient. Instead, patterns of fire frequency better fit a cultural burning gradient inferred from the ethnographic and historical record. Areas close to aboriginal villages and camps burned considerably more often than areas that were probably less utilized. Summer season fires, the ones most likely set by the Native Tolowa for resource needs, were 10 years shorter than the mean fire interval of autumn season fires. In the dryer eastern portion of the study area, frequent fire resulted in unimodal or bimodal pulses of Douglas fir (Pseudotsuga menziesii) establishment suggesting moderate to high fire severity. Near a Tolowa village site, a frequent fire regime before the late 1700s initiated a pulse of Douglas fir establishment that dominated the forest canopy for centuries; long after the village was abandoned, possibly due to epidemic disease. While variability in coastal fog-stratus and drought may also influence fire regimes, these relationships provide a weaker explanation than human ignition history. Variable human and climate influence on old-growth redwood fire regimes suggests that old growth redwood forests are not in equilibrium, but are dynamic due to a long history of variable human influence. Remnant old growth forests are likely to continue to evolve in response to human management. Efforts by managers to restore and sustain these remarkable forests can be enhanced by understanding how complex histories give rise to biodiversity. [emphasis added].

Another paper published in this month’s Forest Ecology and Management echoes these remarkable findings:

Craig G. Lorimer, Daniel J. Porter, Mary Ann Madej, John D. Stuart, Stephen D. Veirs Jr., Steven P. Norman, Kevin L. O’Hara and William J. Libby. 2009. Presettlement and modern disturbance regimes in coast redwood forests: Implications for the conservation of old-growth stands. Forest Ecology and Management, Volume 258, Issue 7, 15 September 2009, Pages 1038-1054.

Abstract: Coast redwood (Sequoia sempervirens), a western North American conifer of ancient lineage, has a paradoxical combination of late-successional characteristics and strong adaptations to disturbance. Despite its shade tolerance and heavy dominance of the canopy on many sites, redwood saplings are uncommon in upland old-growth stands. Information needed to ensure the conservation of old-growth redwood forests has been limited. In this review paper, we integrate evidence on redwood biology with data on the historic and modern disturbance regimes to help clarify the degree to which key attributes of redwood forests may have been dependent upon periodic disturbance. Available evidence suggests that episodes of fire, flooding, and slope failure prior to European settlement were frequent but predominantly of low to moderate severity and extent, resulting in broadly uneven-aged forests. The majority of fires prior to European settlement were apparently of human origin. Frequency and severity of the major disturbance agents have been radically changed in modern times. Fires have been largely excluded, and flooding has been altered in ways that have often been detrimental to old-growth redwoods on alluvial terraces. However, because of the apparent anthropogenic origin of most presettlement fires, the long-term evolutionary role of fire for coast redwood is ecologically ambiguous. With fire exclusion, redwood possibly could be displaced to some extent on upland sites by increasing abundance of fire-sensitive competitors. Alternatively, redwood may be able to maintain dominance by vegetative sprouting and new seedling establishment on root-wad mounds, fallen logs, and on soil exposed by slope failure. Future research priorities are suggested that will help resolve some of the current ambiguities. [emphasis added].

To reiterate, the old ecological paradigm held that natural fire regimes dominated western forests. That paradigm has been found to be incorrect and “ecologically ambiguous”. The new thinking, based on empirical studies, is that human beings played a critical role in the historical development pathways of redwood forests.

The recent research cited above follows the work of the late Dr. Henry T. Lewis [here], the late Dr. Omer C. Stewart [here], Dr. M. Kat Anderson [here], Dr. Thomas M. Bonnicksen [here], Dr. Charles E. Kay [here], and many others (see the W.I.S.E. Colloquium: History of Western Landscapes [here]).

The new paradigm in forest science holds that historical human influences on Western ecosystems were profoundly significant. Without a more complete and comprehensive understanding of traditional (pre-Columbian) ecological practices, we cannot replicate historical forest development pathways and cannot protect, maintain, or perpetuate old-growth forests.

Simply abandoning forests to the vagaries of nature will not protect old-growth. Instead, abandonment into to No Touch set-aside tracts will lead to devastating fires that destroy existing old-growth and preclude the development of future old-growth.

Human stewardship is necessary for the preservation of old-growth forests across the West, not just in coastal redwood.

Dr. Norman will be presenting a paper at the upcoming Association for Fire Ecology meeting in Savannah GA in early December. The submitted abstract reads:

Fire regimes as a cultural and climatic artifact—insights from the coast redwood forests of California by Steve Norman*

Dynamic fire regimes, driven by non-cyclical changes in climate, fuels and cultures of fire use can lead to complex vegetation that is difficult to interpret and manage. That is, certain forest elements may be artifacts of past disturbance regimes, not just disturbance events or the inherent properties of landscapes, such as topography. In this paper, I describe fire regimes from seven locations in the northern range of the coast redwoods (Sequoia sempervirens). Prior research suggested that the northern, near-coast portion of the species range burned rarely; from four fires per century to a few fires per millennium. The stump-top tree ring data that supported those interpretations has been criticized due to the subtle way that surface fire scars form on coast redwood and the ready loss of scars to decay. Further, dating tree rings and fire scars has been difficult due to missing or asymmetric rings. Compounding these uncertainties, most fires that burned prior to fire exclusion are thought to have been of human origin, and this raises fundamental questions about variable human influence and the usefulness of static concepts of fire regimes for long term forest management. In this research, I found that the methods used in several prior studies invalidate their results, and that fire was more frequent that thought in most, but not all portions of the northern coast redwood range. Fire-climate relationships reflect drought and coastal gradients, but were often overridden by human fire. Based on multiple lines of evidence—fire scars, fire cavity attributes and age structure—I argue that many old growth coast redwood forests reflect ecologically significant cultural imprints unto dynamic climate gradients. This suggests that Native Americans, early settlers and modern managers have played and are playing defining roles in the development of one of the most spectacular old growth forests known. [emphasis added]

*US Forest Service, Southern Research Station, Eastern Forest Environmental Threat Assessment Center, 200 WT Weaver Blvd, Asheville, NC 28804 USA

It is exciting to watch this sea change in science; the replacement of an old, anomalous paradigm with new, vibrant, and more realistic theories. The new theories are based on actual measurement of actual forests, not mere conjecture. They explain much that has been mysterious about our forests. The new theories incorporate findings from anthropology and historical landscape geography.

And most important, the new theories and findings offer guides to restoring our priceless heritage forests and protecting, maintaining, and perpetuating them for future generations.



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