Sep 27, 2016
Science Tuesday: Rainforest or Fireforest?
Picture a quintessential old-growth redwood forest: damp and dark, with prehistoric sword ferns taller than you, huckleberry and rhododendron thickets as far as the eye can see, and the sweet, musty smell of mosses and rotting logs wafting through the misty air. A rainforest, unchanged for thousands of years.
But what if I told you that this picture is wrong—that our collective image of redwood rainforests is in truth a snapshot of a highly departed forest? That these rainforests are actually fireforests?
Two weeks ago, my colleagues with University of California hosted the Coast Redwood Science Symposium here on the North Coast of California. There were three days of great presentations and field tours, but I have to say—my favorite talks were the fire ones (big surprise!).
At the end of the last day, Morgan Varner (formerly with Humboldt State University and now with the USDA Forest Service Pacific Northwest Research Station) gave a provocative presentation on what he called the “enigmatic” fire regime of redwoods. In his talk, Morgan blew our minds by asking us to see redwoods not as the static rainforests that we’ve all come to know and love, but as victims of fire exclusion—frequent fire forests that are suffering the same fate as ponderosa pine and longleaf and other textbook “fireforests” (he also coined this term, which I love!). He asked us to question the sword fern, the rotting logs, and the mosses, and look deeper to the fire scars, bark char and fire-caused cat faces that are ubiquitous in redwood forests. He told us that these forests haven’t always been damp and dark and rife with crazy deep duff and ferns and shrubs that are virtually impassable; rather, they were more open, heterogenous and dynamic. Redwoods evolved with fire, and they have the traits to prove it: they have incredibly flammable leaf litter, and they’re one of the only conifers that can resprout after fire.
Now we’ve all heard that redwoods are fire adapted, but during this presentation, mouths were agape. How had we—a room full of redwood region biologists, managers, industry representatives, foresters and academics—never collectively recognized the pivotal role of fire in redwood forests, or identified it as a real priority in our restoration and management?
Even though his presentation was provocative and novel in many ways, the concepts that Morgan shared are actually well documented in the fire science literature. Earlier in the symposium, Jeff Kane from Humboldt State University did a nice job synthesizing the fire history studies that have been conducted over the years throughout the range of coast redwood, and he also used previously collected fire history data to analyze relationships between fire frequency and topographic and climatic gradients.
There are many nuances to this work, but there is one strong message that I want to highlight: fire was historically quite frequent in these forests. Jeff and his collaborators found an average fire return interval of 17.6 years across the fourteen studies that they looked at, with a range of 7.1 to 30.6 years. Fires were a result of both lightning and human ignitions, though the relative importance of those ignition types is not well known. And since 1940, redwood forests have seen little fire aside from the rare wildfire that isn’t fully suppressed. From a fire perspective, the redwood forests we see now are not the forests of the past, even though the trees themselves may have been there for millennia.
Like most people in my region, I’ve spent a lot of time in redwood forests. I’ve spent whole field seasons hiking off trail in redwood, climbing over massive logs and crawling under huckleberry to get to my field sites, and I’ve noted signs of fire in every redwood forest I’ve ever been in. But I think I, like many people listening to Morgan that day, had never really added it all up: the enigma of the redwood fire regime, and how absent it’s been from our perceptions of what redwood forests should look like and how we should be managing them. We’ve preferred the charm and comfort of the rainforest over the dynamism and uncertainty of the fireforest, even when that static perspective threatens the very values we hold dear.
For me, it was so refreshing to have a kick in the pants that day during the symposium—to question my assumptions, and to better align my knowledge with my feelings. And I know I wasn’t alone, because at the end of the symposium, the room was abuzz with plans to get more fire back into the redwoods!
For More Information:
Kane, J., Carroll, A., Engber, E., and Sillett, S. Assessing climate-fire history relationships in coast redwood forests. Presentation at the 2016 Coast Redwood Science Symposium. (Paper in preparation.)
Baxter, W.T. and Brown, P.M. 2003. Fire history in coast redwood forests of the Mendocino Coast, California. Northwest Science. 77(2): 147-158.
Stephens, S.L. and Fry, D.L. 2005. Fire history in coast redwood stands in the northeastern Santa Cruz Mountains, California. Fire Ecology, 1(1), pp.2-19. http://www.elkhornsloughctp.org/uploads/files/1235506472Steophens%26Fry_2005.pdf
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