Research Highlights

The Holiday Farm fire ignited the night of September 7, 2020, south of the Andrews Forest. Fire entered the Andrews Forest on September 12, at the south boundary of Watershed 9, and progressed northward into Watershed 1, then Watershed 2. The fire burned mostly at low severity within the Andrews Forest, moving along the ground. We see small areas of canopy tree death in these watersheds, where fire continues to smolder in large snags, logs and roots, and could overwinter as embers to reignite next spring. 

Our attention turns now to assessing the damage from the fire and the fire suppression activities. Our headquarters facility was spared, and the stream gauging stations in the three burned watersheds suffered minor or no damage.  Fire lines were dug by hand and by bulldozer in Watersheds 1 and 2, along the 1507 and 2633 roads, and around the headquarters. In some places the fire and fire lines impacted permanent vegetation plots that have been studied for 50 years, and went through study plots for soil moisture, hydrology, plant phenology, and forest microclimate. Much of the cost of repairing research infrastructure will be the expense of extensive personnel time to relocate and resurvey the damaged areas and reinstall sensors.

As we have learned from our long-term work in the Andrews Forest, many unplanned disturbances happen over time; Watershed 1, for example, experienced extensive toppling of the young forest by heavy snow in the winter of 2019. With each event comes new opportunity to learn about this dynamic landscape.  Researchers are working quickly to set up monitoring and studies that will help us learn from the fire, and we have decades of pre-fire data to use as the foundation for comparisons.

Read more on our archived Fire Updates page, view fire photos in our photo gallery, or watch videos of the fire at our  Andrews Forest YouTube channel.

Dwarf mistletoe’s quaint name belies its severity. The native parasitic plant commonly infects western hemlock trees in western Oregon and Washington via projectile seeds that land on branches and bore through the tree’s bark, where the plant induces tissue swelling and deformities. The result: a diminished ability to transport water and other physiological effects, which reduce tree growth and increase mortality, especially among heavily-infected trees.

How might a parasitic plant, like dwarf mistletoe, interact with the climatic conditions scientists project? A long-term data set and new study may provide the answer.

David Bell, a research forester based at the Corvallis Forestry Sciences Laboratory, and Oregon State University colleagues Robert Pabst and David Shaw reviewed several decades of data gathered at the Wind River Experimental Forest, a 500-year-old-forest located in Washington State that is part of the Forest Service’s Experimental Forest and Range Network. Wind River, and the 83 other sites located across the country, are maintained as long-term experimental areas and represent the largest and longest-lived ecological research network in the United States. Bell and his colleagues studied five repeated measurements of nearly 1,400 individual hemlock trees from 1991 to 2014, examining how western hemlock tree growth and mortality varied with temperature increases, precipitation decreases, and mistletoe infection rates.                                                                                         

“Although mistletoe infection intensity varied across individual trees over this time frame, our results suggest that warmer, drier conditions amplified the parasitic plant’s effects on western hemlock growth and mortality,” Bell said.

Specifically, tree growth rates decreased and mortality rates increased during warmer‐drier time periods for all trees, regardless of infection status. Growth reductions and mortality increases were also related to mistletoe infection intensity, most notably during the warm and dry measurement intervals.

“Our study, grounded in a rich long-term data set, revealed an unrecognized vulnerability of forests to climate change as a function of common and endemic pests and pathogens, especially in westside forests, which are generally assumed to have low vulnerability,” Bell said. “We expect that other forest pests or pathogens also would amplify the effects of climate change.”

For managers, these findings suggest that native pest and pathogen management may be a key component of preparing for climate change.

--From: the US Forest Service Pacific Northwest Research Station "Science Spotlight"

The full article "Tree growth declines and mortality were associated with a parasitic plant during warm and dry climatic conditions in a temperate coniferous forest ecosystem" was published in "Global Change Biology".

A new research project at the Andrews Forest aims to shed light on how changes in temperature and precipitation affect patterns of biodiversity. The Forests of Oregon Elevation Gradient (FOREG) is a network of large sample plots, established in 2019, within the HJ Andrews Experimental Forest. Field studies and experiments will test the importance of species interactions to changes in density dependence and biodiversity across environmental gradients.The FOREG project was designed to dovetail and connect with the long-running Reference Stand study at the Andrews Forest.  FOREG is also a part of the much broader Smithsonian "Big Plot" program. The FOREG study is run by Joseph LaManna at Marquette University.  A new photo gallery highlights FOREG summer field work. 

Western hemlock dwarf mistletoe (Arceuthobium tsugense subsp. tsugense) is a small, parasitic plant that infects the leaves and branches of its host plant, the western hemlock (Tsuga heterophylla) tree. Within a forest, like the HJ Andrews Experimental Forest, areas of mistletoe infection are patchy. Some areas of the forest have trees that are not infected, while other areas have trees that are heavily infected. Hemlock trees infected with dwarf mistletoe grow dense, multi-branched growths, called witches’ brooms. Researchers believe that mistletoe infections cause changes in the tree’s growth and water use. To understand the effect of mistletoe in the canopy of a tree, and in the broader area of a forest, graduate student Stephen Calkins and postdoc scholar Sky (Yung-Hsiang) Lan are climbing into the canopy of dozens of western hemlock trees to take a closer look. They measure the extent of the mistletoe infection by noting size and location of brooms in each tree crown. They also map each branch in the tree, recording its location and measuring the size. Each tree will also be cored to measure its sapwood. With these data, Stephen and Sky, together with their advisor, Dave Shaw, from Oregon State University, hope to learn more about how dwarf mistletoe may be affecting forest stands across the Pacific Northwest. See a little of the field work, high in the canopy, at

Hermit Warblers are endemic breeders in forests of the Pacific Northwest; they migrate to Central America (Mexico south to Costa Rica) during their non-breeding period. A new study at the Andrews Forest aims to document migration routes, locations, and migratory connectivity of Hermit Warbler populations. For instance, where will birds from the Andrews Forest, southern Washington, and the Sierras of California overwinter? For the Hermit Warbler, changing climate and habitat loss in the breeding grounds seem to drive population losses. The new study will help us understand whether climate and habitat on the wintering grounds have similar influences, and whether habitat quality on the breeding grounds influence migration behavior. Stretching our knowledge across seasons and over borders will help us make sound conservation strategies for the migratory Hermit Warbler. 

A recent publication out of the HJ Andrews Experimental Forest LTER site illustrates the role that summer research experiences can play in contributing to LTER science and in engaging and mentoring students. Oregon State University graduate student Matthew Kaylor is the lead author on a paper about how trout and salamanders respond to drought. Kaylor wrote this paper in collaboration with two undergraduate students. The first student, Brian VerWay, worked with Kaylor to survey trout and salamanders in a set of streams in the Andrews Forest in 2014 and 2015. As it happened, 2015 was a severe spring/summer drought year in the Pacific Northwest region. VerWay wrote his senior undergraduate honors thesis and published a paper on the movement, growth and abundance responses of fish to drought in one tributary stream of the Andrews Forest (VerWey et al 2018). In 2016 and 2017, the second student, Alvaro Cortes, revisited six of the stream sites that Kaylor and VerWay had surveyed. Cortes wrote his senior theses about the recovery of fish and salamander populations from the 2015 drought. The three students worked with their advisor, OSU Assistant Professor Dana Warren, on a paper that pulled together their research into a broader story. The paper, “Drought impacts to trout and salamanders in cool, forested headwater ecosystems in the western Cascade Mountains” was published in Hydrobiologia. Their findings suggest that drought impacts salamanders and trout, but the responses differ. They found fewer adult trout in the drought year. Salamander abundance remained the same, but body condition was lower in the drought year. Both trout and salamander populations seemed to rebound within two years of the drought. The work could not have happened without strong leadership and mentoring by the graduate student, nor without the engagement and interest of the undergraduate student researchers. It was a collaborative exercise that reached across multiple years of data collection and multiple projects at the Andrews Forest LTER site. 

Researchers at the Andrews Forest, and the forest itself, are featured in an Oregon Public Broadcasting EarthFix television show, "Old Growth Could Be Key For Native Songbird Species To Beat Climate-Change Heat."   Get a stunning, bird's-eye view of the forest from above the trees, and through the trees, and find out what scientists are learning about how birds may be using the old-growth forest to beat the heat.

From OSU Press Release

"Streams and rivers could pump carbon dioxide into the air at increasing rates if they continue to warm, potentially compounding the effects of global warming, a new worldwide analysis has shown.

To reach that conclusion, an international research team conducted the first continental-scale study of carbon flows into and out of streams across six major climatic zones. They collected data in watersheds from Puerto Rico and Oregon to Australia and Alaska. In each one, scientists analyzed the balance between photosynthesis — which uses atmospheric CO2 to generate plant material such as roots and leaves — and respiration, which pumps CO2 back into the air.

“This paper is the first to look at the effects of climate change on stream metabolism at the continental scale using field observations,” said Alba Argerich, co-author who monitored McRae Creek and Lookout Creek in the H. J. Andrews Experimental Forest. “This approach takes into consideration the complexity of an ecosystem, as opposed to controlled experiments where you recreate simplified versions of an ecosystem.” 

Argerich and other scientists monitored streams for water temperature, dissolved oxygen and sunlight at the water surface. The researchers also simulated the balance between net primary production (the product of photosynthesis by all organisms in the stream) and respiration under a 1-degree Celsius rise in stream temperature. The net result of the simulations, they reported, was a 24 percent shift toward more respiration and CO2 emissions. 

The shift toward more CO2 emissions appears to be more pronounced in warmer streams, the scientists found, while colder streams might actually see an increase in net primary production. Carbon cycling in streams can also be affected by other factors such as the plants and microbes in the stream ecosystem and nutrients flowing into the water from surrounding lands."

Also see:

Article from Oregon Public Radio's EarthFix program: 

See the full article in Nature Geoscience, "Continental-scale decrease in net primary productivity in streams due to climate warming"

Old forests that contain large trees and a diversity of tree sizes and species may offer refuge to some types of birds facing threats in a warming climate. In a paper published in Diversity and Distributions researchers in the College of Forestry at Oregon State University reported that the more sensitive a bird species is to rising temperatures during the breeding season, the more likely it is to be affected by being near old-growth forest.  See the full article; View the press release; Watch the video.


Clearcuts often create stark boundaries between forest habitats. These ecological “edges” can seriously affect neighboring undisturbed ecosystems for some distance in from the edge, perhaps representing a multi-decadal legacy of has clearcutting. A new study led by David Bell took on the question of how historical timber harvests have affected the structure of neighboring old-growth forests in western Oregon. Bell and his team used a remote-sensing technique called lidar to map tree basal area (a measurement related to tree density and biomass) in lower and middle elevation mature and old-growth forests in the Andrews Forest. They then assessed how harvest edges have influenced tree basal area and how those effects varied with harvest size and age. They found that forests within 75 meters of harvest edges (approximately 20% on the unharvested forests) had 4-6 percent less live tree basal area than forests tucked in the interior away from edges. They were surprised to find that the length of time since harvest had little or no effect: whether the harvest happened 13 years ago or 60 made little difference on the structure of surrounding unharvested forest area. This implies that the edge influence persisted over many decades in spite of forest recovery processes. This study is important in examining the subtle impact of human activity on forest landscapes in western Oregon and showing how widespread and long-lasting the edge influence of past clearcutting has been on neighboring old-growth forest.

The paper, Historical harvests reduce neighboring old-growth basal area across a forest landscape, is published in the journal Ecological Applications:

Adam Ward (Indiana University) was awarded an NSF CAREER Grant of more than $700,000 to implement an integrated program of research and education. Much of the work will occur at the Andrews Forest. Ward's research strongly leverages the Andrews Forest's geologic diversity, existing instrumentation network, and access to a 5th order river basin. The multi-scale work and educational initiatives will take advantage of the long-term data available from the Andrews Forest site and build upon a body of work from the Andrews Forest on streams, hyporheic zones, and valley bottoms.

Ward hopes his work will help inform an accurate framework to predict and manage hydrologic exchange in the river corridor and the associated ecosystem services and functions at the scales of stream reaches and entire networks. To advance our predictive capabilities in the river corridor, this research will achieve three objectives: (1) improve our understanding of dynamic exchange processes in the river corridor; (2) develop methods to scale findings from geomorphic features to the reach and network scales; and (3) improve predictive capacity that can be readily implemented without extensive field characterization of sites of interest.

The river corridor perspective considers the surface stream its hyporheic zone, riparian zone, hillslope, and aquifer as a continuum, exchanging water, solutes, energy and materials across a range of spatial and temporal scales. The need for prediction of river corridor exchange is underscored by the proposed Clean Water Rule, which clarifies that river corridors are to be regulated as part of the Clean Water Act.The primarily controls on river corridor exchange are broadly recognized to fall within two categories: geologic setting and hydrologic forcing. Geologic setting describes the relatively static physical characteristics of a site, such as stream morphology, the hydraulic conductivity field, macro-scale lithology, and geologic parent material. Hydrologic forcing includes both stream discharge and regional hydraulic gradients causing gaining or losing conditions. More recently, dynamic hydrologic forcing (e.g., storm responses, fluctuations due to tides, dam releases, snowmelt runoff, and baseflow recession) has been recognized as an important control on river corridor exchange.

Results of this research will improve our ability to predict the transport and fate of contaminants in river corridors, enabling more effective management of water resources. The integrated education and research plans will inspire a diverse group of K-12 and undergraduate students to pursue careers in STEM fields. Ward will provide specialized training in integration of hydrology, ecology, and informatics and in River Corridor Science and Management, preparing the next generation of resource managers to effectively and sustainably govern the water resources of the U.S.

There is much discussion about how plantation forestry affects streamflow in dry (lowflow) seasons, especially as climate change may exacerbate water scarcity. Analysis of 60‐year records of daily streamflow from eight paired‐basin experiments in the Andrews Forest revealed that the conversion of old‐growth forest to Douglas‐fir plantations had a major effect on summer streamflow. Average daily streamflow in summer (July through September) in basins with 34‐ to 43‐year‐old plantations of Douglas‐fir was 50% lower than streamflow from reference basins with 150‐ to 500‐year‐old forests dominated by Douglas‐fir, western hemlock, and other conifers. The study, by Timothy Perry and Julia Jones, was published in 2016 in the journal Ecohydrology. View the full article online:

Andrews Forest researcher Dana Warren studies how light affects streams. Forest canopies along streams regulate stream light availability, which influences water temperature, in-stream primary productivity, nutrient dynamics, and, thereby, the entire aquatic ecosystem. In one publication, Dana and his team outlined a conceptual framework for understanding change in stream ecosystem processes and communities when disturbance first creates high light. As a young forest develops, stream light decreases; however, later in stand development canopy gaps are created by localized disturbances, such as windthrow, and stream light increases, but in patches. A second publication, reports results of in-stream experiments to explicitly examine how the spatial variability of stream light patches affects primary production and stream nutrient demand. In well-lit sections of the stream periphyton growth was nutrient limited; conversely, light availability was the limiting factor in poorly-lit sites. Ultimately, in the sites with more light patches (i.e., sites with old-growth riparian forests), the stream shifted frequently between light- versus nutrient-limitation.

“Long-term effects of riparian forest harvest on light in Pacific Northwest (USA) streams”

“Characterizing short-term light dynamics in forested headwater streams”

Streams move carbon from land into oceans and the atmosphere. Carbon in streams can come from leaf litter decomposing in the water. How quickly that leaf litter decomposes depends upon the temperature of the water — the higher the temperature of the water, the faster the rate of decomposition. With climate change, stream temperatures are expected to rise. The rise in stream temperature is projected to increase rates of leaf litter decomposition, thereby affecting the carbon cycle. A team of scientists, including Andrews Forest scientist Sherri Johnson, synthesized 1025 records of litter breakdown in streams and rivers to quantify its temperature sensitivity.

The study indicates average breakdown rates may increase 5 percent to 21 percent with a 1 degree to 4-degree Celsius rise in water temperature — half as much as the 10 percent to 45 percent increase predicted by metabolic theory. Mean annual water temperature for some streams and rivers is currently rising at an annual rate of about 0.01 degrees to 0.1 degrees Celsius due to changes in climate and land use. Read more in a University of Utah press release on the article.

The study “Global synthesis of the temperature sensitivity of leaf litter breakdown in streams and rivers” was published February 2016 in Global Change Biology. View the full article.

Research from the Andrews Forest suggests that old-growth forests may provide a buffer against rising air temperature. “To our knowledge, ours is the first broad-scale test of whether subtle changes in forest structure due to differing management practices influence forest temperature regimes,” wrote authors Sarah Frey, Adam Hadley, Sherri Johnson, Mark Schulze, Julia Jones, and Matthew Betts.  Read more about the paper, Spatial models reveal the microclimatic buffering capacity of old-growth forests, published in 2016, in the press release:

The amount of carbon stored in tree trunks, branches, leaves and other biomass — what scientists call “aboveground live carbon” — is determined more by timber harvesting than by any other environmental factor in the forests of the Pacific Northwest, according to a report published by researchers at Oregon State University: "Complex mountain terrain and disturbance history drive variation in forest aboveground live carbon density in the western Oregon Cascades, USA" (doi:10.1016/j.foreco.2016.01.036).

In forests that are about 150 years old or less, live carbon above the ground is associated primarily with the age of a stand — reflecting how long ago it was harvested — rather than with climate, soil, topography or fire. However, as forests mature into “old growth,” the density of carbon is determined largely by factors other than harvesting.

The Pacific Northwest has some of the highest forest-carbon densities in the world. Understanding how much carbon is stored in growing forests is a critical component of international efforts to reduce climate change. 

Researchers found that air temperatures, sun exposure and soils were also important in driving the variation in live carbon across the region. High-elevation forests tend to be cooler and contain lower amounts of carbon than do low-elevation forests. 

Researchers conducted the study at the H.J. Andrews Experimental Forest in the Cascade Range east of Eugene. They combined data from two types of measurements: LiDAR (an aerial mapping technique that uses lasers) and ground-based forest inventories in which scientists measured tree growth at 702 forest plots. The study is one of the few to quantify carbon in living forest biomass in mountainous terrain.

Harold Zald, research associate in the College of Forestry, is lead author of the paper published in the journal Forest Ecology and Management.

“Very few studies have looked at above-ground carbon at a landscape scale with the combination of LiDAR and detailed disturbance history (logging and fire) that we have at the H.J. Andrews Forest,” said Zald. “These findings can be applied to the Douglas-fir dominated forests on the west slope of the Cascades in Oregon and Washington.”

The researchers found that fire was not a significant driver of carbon density in the H.J. Andrews. In the last century, these forests have experienced little severe “stand replacing fire,” but it’s possible that fire played a significant role in shaping the structure of old-growth forests and increasing carbon density over time. “Remnant old-growth trees resulting from non-stand replacing fires likely enhance the recovery of forest C (carbon) density,” they wrote.

The study was conducted by researchers at Oregon State University, the Pacific Northwest Research Station of the U.S. Forest Service and the University of Natural Resources and Life Sciences (BOKU) in Vienna, Austria.

This story is also available at

In a 2016 publication from Andrews Forest, researcher Alba Argerich and colleagues suggest that forested watersheds may not store quite as much carbon as previously thought. Small, headwater streams, such as those found in the Andrews Forest, import a higher than expected amount of carbon. See the press release. The paper, "Comprehensive multi-year carbon budget of a temperate headwater stream," was published in Biogeosciences:

A publication co-authored by a team of Oregon State University, US Forest Service, and US Geological Survey investigators compares quality of interpretation of northern spotted owl habitat based on traditional aerial photographs, Landsat satellite imagery, and recently-available, high-resolution LIDAR data. This team, led by Steve Ackers, head of the Andrews Forest-based spotted owl crew, uses the well-studied Blue River-Andrews Forest area as a test case. Information from these data sources is used in sophisticated species distribution models for the spotted owl, and many other species as well. As one might expect, each information source has its pluses and minuses. Air photo interpretation is rather subjective, hard to reproduce, and time consuming. Landsat has proven an adequate tool for extensive assessment of habitat quality, although it lacks the high precision possible with LiDAR. It is interesting to note that the first Landsat Thematic Mapper satellite was launched in 1972, just as Eric Forsman began studies of the spotted owl in the Andrews Forest and vicinity, and the first report using that imagery in habitat assessment appeared just two years later. The meter-scale LiDAR data describing topography and vegetation structure makes possible a very refined depiction of habitat, but LIDAR data are not available for the whole region, and the high precision is not necessary for many conservation purposes.  See the paper: The evolution of mapping habitat for northern spotted owls (Strix occidentalis caurina): A comparison of photo-interpreted, Landsat-based, and lidar-based habitat maps