Research Highlights

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:

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: