Rigdon Fire History: Fire in Old-Growth Douglas-fir Stands

Guest Blogger: James Johnston

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Any time you can be in the woods hiking around and calling it work it’s fun, but reconstructing historical fire in old-growth Douglas-fir forests is…. less fun than in other areas.  For starters, the slopes tend to be really steep and the trees are really big and hauling around gas and giant wood samples gets old. 

Finding fire scarred trees in stands with oak and ponderosa pine is relatively easy.  Ponderosa pine typically has a cat face like this one which allows you to easily see evidence of historical fire.  You saw out a partial cross section and use the unique pattern of wide and narrow rings to cross date that sample, and assign to each of those fire scars a calendar year. 

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In old-growth Douglas-fir/western hemlock forests you can rarely see visual evidence of historical fire and so I’ve been using a chainsaw to basically excavate these large stumps left over from logging operations. 

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If you crack open enough of these stumps, you can find fire scars buried in these giant chunks of wood.  They look like this:  

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Most scientists assume that these old-growth Douglas-fir/western hemlock forests go hundreds of years without fire, and when they do burn, it’s generally stand replacing fire. But when we crack open these big stumps, we are seeing far more evidence of historical fire than predicted by theory. 

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JAMES JOHNSTON IS A RESEARCH ASSOCIATE (POST-DOCTORAL) AT OREGON STATE UNIVERSITY FOR THE FOREST ENGINEERING AND RESOURCE & MANAGEMENT DEPARTMENTS. HIS RESEARCH INTERESTS INCLUDE FIRE ECOLOGY, DENDROECOLOGY, RESTORATION FORESTRY, ENVIRONMENTAL LAW AND POLICY, AND COLLABORATIVE GOVERNANCE.

Rigdon Fire History: Fire in Oak Stands

Guest Blogger: James Johnston

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Hunting for fire scars is a ton of fun.  My favorite spots within the Youngs Rock-Rigdon planning area are those areas with oaks. 

Oregon white oak (Quercus garryanna) is an amazing tree.  It is relatively slow growing and usually can’t compete with Douglas-fir.  It is extremely fire resistant because it has thick, protective bark and adventitious buds—buds that can quickly resprout following fire damage.  Oak savannahs and woodlands are archetypal fire-dependent ecosystems.  Historically, they burned very frequently which promoted dominance by oaks and excluded conifers that were not quite as well adapted to very frequent fire. 

Many oak stands up the Middle Fork are kind of sad because younger Douglas-fir has over-topped the oak and killed it.  Douglas-fir competes with the oak for water and light.  White oak needs an enormous amount of light—usually light from all directions—in order to survive and grow new leaves every year.   These oaks (right) died just within the last year or two.  

Right next to these dead oaks was a ponderosa pine stump (at 43 29.576, -122 23.091) that was an incredible source of data.  It had rings from when it was cut down in 1956 to the year 1344 (in that same year, at the Siege of Algeciras in Spain, a European army used gunpowder for the first time).  And it recorded fires in 1849, 1842, 1839, 1833, 1829, 1826, 1822, 1818, 1815, 1805, 1792, 1790, 1788, 1783, 1781, 1779, 1775, 1768, 1763, 1754, 1744, 1739, and 1728.  As far as I know, this site experienced more frequent historical fire than any site where fire has been reconstructed in the Pacific Northwest.   

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JAMES JOHNSTON IS A RESEARCH ASSOCIATE (POST-DOCTORAL) AT OREGON STATE UNIVERSITY FOR THE FOREST ENGINEERING AND RESOURCE & MANAGEMENT DEPARTMENTS. HIS RESEARCH INTERESTS INCLUDE FIRE ECOLOGY, DENDROECOLOGY, RESTORATION FORESTRY, ENVIRONMENTAL LAW AND POLICY, AND COLLABORATIVE GOVERNANCE.

Rigdon Fire History: Fire History Research

Guest Blogger: James Johnston

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Dendroecology is the application of tree-ring analysis to ecological questions.  North American conifers tend to live for a long time and they lay down annual growth rings that can be used to learn all sorts of interesting things about the past. 

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One of the oldest and most interesting uses of dendroecology is fire history reconstruction.  We often only have several decades of reliable direct observation of fire in many landscapes.  Tree-ring based fire reconstructions allow us to gain knowledge about fire occurrence over hundreds of years.  Disturbance processes have often been significantly altered by management practices over the last 100 years, and so tree-ring fire histories allow us to determine what the natural range of variability—or natural fire regime—is like for different forests. 

Our tree ring lab at OSU is currently working to reconstruct fires along the upper Middle Fork Willamette River in the vicinity of the Forest Service’s Youngs Rock-Rigdon project area.  Information about the natural range of variability in fire disturbance should be useful in designing silviculture treatments that will restore historical structure and composition. 

Tree ring-based fire history reconstructions are painstaking and time consuming.  The first part of the process is the most fun—searching an area of interest for fire-scarred trees.  When we find a stump or old log that shows evidence of past fire, we saw out a few cross sections with a chainsaw. 

We’re looking for wood that has scars where a past fire killed the cambium—the living tissue of the tree—and the tree survived to lay down wood over the scar.  The arrow in the photo points to a fire scar.  We sand these samples to a fine polish so they look like this:

Trees are hydro-climatically sensitive, meaning that their annual growth varies as a function of climate.  Trees lay down narrow rings in years that are warm and dry and wide rings in years that are cool and wet.  The pattern of wide and narrow rings during different time periods is as distinctive and unique as human fingerprints.  These unique patterns allow us to cross date—or assign to each ring a calendar year.  Calculating the average length between the years where fires scarred the tree provides information about fire frequency in a given area. 

All of the wood we collect in the field eventually finds its way to our tree ring lab at Oregon State University.  Here’s the lab:

We have a really cool machine in the lab that we use to measure each individual tree ring to the nearest hundredth of a millimeter.  We use a variety of algorithms to match the tree ring measurements to a master chronology of tree ring widths to determine in which year each ring was laid down.  The big machine: 

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James Johnston is a Research Associate (post-doctoral) at Oregon State University for the Forest Engineering and Resource & Management departments. His research interests include fire ecology, dendroecology, restoration forestry, environmental law and policy, and collaborative governance.

Save the Date: Fire History & Special Habitats - Rigdon Learning Session

Save the date for a Rigdon Learning Session: Thursday, May 2nd, 9:00 - 12:00, at Greenwaters Park in Oakridge. OSU research scientists James Johnston will present a research update from the Rigdon fire history study followed by a Walama Restoration presentation about 2018 monarch survey results and upcoming field work. 

Fire History Study - James Johnston

Managers and stakeholder groups need information about variation in fire disturbance over long time periods in order to craft restoration strategies that create resilient forests and provide for essential ecosystem services. Oregon State University College of Forestry is using tree ring evidence to reconstruct detailed fire histories of different forest types in the Rigdon landscape, ranging from pine savannah to moist old-growth Douglas-fir/western hemlock.  Research results will inform the efforts of the Southern Willamette Forest Collaborative (SWFC) and the Forest Service to develop strategies to restore diverse forests stands that are resilient to future change.  

Special Habitats - Maya Goklany

Walama Restoration Project conducted 2018 milkweed and monarch butterfly surveys last summer in the Rigdon area.  Maya will present survey findings and possible future restoration opportunities. Following the learning session, Walama Restoration is offering a field training for those who are interested in volunteering for 2019 surveys (see description below and attachment for additional dates).