Research Highlights

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: http://onlinelibrary.wiley.com/doi/10.1002/eco.1790/full

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: http://bit.ly/1U7sBkd.

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 http://bit.ly/1U7tKrT.

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: http://onlinelibrary.wiley.com/doi/10.1002/2015JG003050/full.