In Oregon’s 2020 fires, highly managed forests burned the most
Daniel Gavin is a professor of geography, specializing in forest ecosystems and environmental change, at the University of Oregon
This record-breaking fire season has re-ignited discussions about causes of severe fires. One long-standing narrative is that fire suppression has resulted in ‘overgrown’ forests that fuel larger and more intense fires than occur under more intense management (the “fuels narrative”). This narrative, promoted by timber interests and the president, among others, is irrelevant within the context of Oregon’s major western Cascades fires.
Figure 1. Burned area in Oregon from 1985 to 2020. The map highlights forested (light green) and the Western Cascade Lowland ecoregion (dark green). The largest five fires of the 2020 firestorm overlap largely with the Western Cascade Lowlands. The Tillamook fires in the northern Coast Range of the 1930s are also mapped for comparison. Map by Joanna Merson, InfoGraphics Lab, University of Oregon. Data Source: National Interagency Fire Center, edited by Daniel Gavin.
Figure 2. 2020 broke records for the greatest amount of forested area burned in the last 35 years (and likely the last century). The 2020 firestorm was unique also for the amount burned in the western Cascades. Previous large fire years are in 2002 (Biscuit Fire) and 2012 (Long Draw Fire and other rangeland fires in southeast Oregon).
These fires blew up during a record-breaking “east wind” event, when pressure systems coordinated to push dry warm air over the mountain crest. Within the first four hours, the fires were west of the national forests, well into Bureau of Land Management lands and corporate timberland. Although not contained for over a week, the fires grew little after winds decreased two days later. The majority, over 70%, of the burned areas were in lands managed with clearcut rotation forestry. This landscape’s makeup is prescribed by the Oregon Forest Practices Act: 120-acre clearcuts are spaced 300 feet apart with tree buffers along streams, roadsides, and for wildlife; trees are replanted within two years at high densities; broadleaf shrubs and trees are routinely killed by herbicides.
The Holiday Farm Fire along the McKenzie River reached close to its maximum size within the first 48 hours, and fire intensity was much greater on plantation forests than on BLM lands or the Willamette National Forest. Red line shows the near-final fire perimeter.
Top: Land ownership data summarized from Lane County. Beige areas in the north are private lands in Linn County. Middle: Forest-change data showing forest loss from 2001 to 2019 (Hansen et al. 2013) overlayed on aerial imagery.
Bottom: Fire radiative power at eight time slices summarized from the VIIRS (Visible Infrared Imaging Radiometer Suite) 375-m near real time active fire data. Data points were spatially smoothed at a 750-m radius. Some values of fire radiative power exceeded 1000 MW but color ramps saturate at 500 MW.
Note that these are time-slices of fire activity, and fire intensity at places and times in between these data captures is unknown. In addition, fire radiative power may be partly obscured by dense smoke or dense tree canopies. Climate data shows the maximum hourly gust speed and humidity from the Pebble RAWS station east of McKenzie Bridge. Arrows indicate mean hourly wind direction. Times of satellite acquisition shown by colored arrows. A duplicate analysis using MODIS active fire data (not shown) revealed the same pattern.
To make a forest-management argument about the causes of such fires, we must address the management of these timberlands. It is true that relative to the national forests and wildernesses, which occupy the high terrain and receive the bulk of lightning strikes, there have been fewer fires on industrial timberlands; these lands also are gated against human ignition sources and well-roaded to aid fire suppression. Also, because high-intensity logging removes fuels it is seen as serving the same role of natural small-scale wildfire, fostering the common belief that clearcut-rotation forestry fire-proofs the landscape.
However, studies demonstrate that in checkerboards of young, private plantation forests and older federal forests, fires in the timber plantations burn hotter and consume more soil. My analysis of satellite data of burn intensity during the fire (see figures) confirms this finding. Satellite data shows that 40% of the burned corporate land in the Holiday Farm Fire had been harvested within the last 19 years.
(A) Sentinel 2 Satellite imagery of the Holiday Farm Fire obtained at 1:12 PM on September 9th shown as a false-color short-wave infrared composite image. Red represents short-wave infrared which is sensitive to emitted heat >300°C, green represents near infrared which is strongly reflected by green vegetation, and blue represents visible red light which is reflected by bare ground and scattered by smoke.
(B) Enlargement of the active fire front in an area of timberland, draped onto 3D topography. This view shows high temperatures over a broad swath (several miles wide) and little green vegetation within the fire scar, indicating broad areas of high severity.
(C) A perspective view of mature forest on Simmonds Creek, north of Blue River, burned the previous day under extreme conditions. Green areas indicate moderate fire severity. Also note the narrower fire lines to the right compared to the broad areas of intense heat in (B).
Images produced from the Sentinel EO Browser at https://apps.sentinel-hub.com
The young plantations’ flammability is unsurprising given first principles of fire behavior. The available fuel is small in diameter and easily dried by winds and preheated by approaching fire. Plantations are loaded with such fuel of small wind- and sun-exposed trees. This results in fire spread rates on the order of three feet per second, precluding firefighting. While loggers reduce flammable debris after harvest, there is no avoiding the flammability of young trees in a strong wind. This was seen in some long runs in managed land on the second day of the fires.
Management on federal lands is distinctly different. Here, there is no longer clearcutting, and where crowded second-growth forests exist, restoration treatments of thinning and prescribed fire are improving diversity and habitat and reduce fire severity near communities. Indeed, a recent effort among fire scientists noted benefits of thinning and under-burning, especially in drier east-side pine forests. In the west-side forests that recently burned, such treatments have been little tested with recent fire.
In contrast to federal lands, corporate timberlands are often ignored in public calls for forest management changes. Perhaps people accept that working forests must be run to provide jobs and maximize timber production. However, these forests occupy spaces between national forests and major population centers. It is now abundantly clear that these lands can carry fire into our communities. One more day of strong east winds would have pushed several fires into cities, where hundreds of thousands were poised to evacuate.
To move forward, we need a paradigm shift in fire-prevention planning across the entire landscape. Climate change is loading the dice, and sources of ignition near communities, such as powerlines, are increasingly common and need serious attention. However, demands for more thinning and prescribed fires on public lands are insufficient since clearcut rotation forestry surrounds our communities. These fires should put a spotlight on the effect of this landscape on our risk to wildfire.
References:
FIRMS Active Fire Data, accessed online 15 Sept 2020. https://firms.modaps.eosdis.nasa.gov/download/
Hansen, M. C., P. V. Potapov, R. Moore, M. Hancher, S. A. Turubanova, A. Tyukavina, D. Thau, S. V. Stehman, S. J. Goetz, T. R. Loveland, A. Kommareddy, A. Egorov, L. Chini, C. O. Justice, and J. R. G. Townshend. 2013. High-resolution global maps of 21st-century forest cover change. Science 342:850–853.
Li, F., X. Zhang, S. Kondragunta, and I. Csiszar. 2018. Comparison of fire radiative power estimates from VIIRS and MODIS observations. Journal of Geophysical Research: Atmospheres 123:4545–4563.
Moritz, M. A., C. Topik, C. D. Allen, P. F. Hessburg, P. Morgan, D. C. Odion, and T. T. Veblen. 2018. A Statement of Common Ground Regarding the Role of Wildfire in Forested Landscapes of the Western United States. Fire Research Consensus Working Group Final Report, SNAPP Science for Nature and People Partnership. 52 Pages.
Perry, D. A., P. F. Hessburg, C. N. Skinner, T. A. Spies, S. L. Stephens, A. H. Taylor, J. F. Franklin, B. McComb, and G. Riegel. 2011. The ecology of mixed severity fire regimes in Washington, Oregon, and Northern California. Forest Ecology and Management 262:703–717.
Zald, H. S. J., and C. J. Dunn. 2018. Severe fire weather and intensive forest management increase fire severity in a multi-ownership landscape. Ecological Applications 28:1068–1080.