Here Today or Here to Stay?

ForWarn monitors seasonal duration of forest disturbance impacts

by Stephanie Worley Firley
A traditional weekly ForWarn map image (left) shows the magnitude of damage from the 2015 gypsy moth outbreak in Pennsylvania based on percent changes in vegetation greenness. A 12-week Seasonal Duration map (right) shows duration of the disturbance based on the number of weekly monitoring periods in which a loss of vegetation greenness exceeded 3% during the 2015 growing season. Both maps compare vegetation greenness to that of the previous year.

A traditional weekly ForWarn map image (left) shows the magnitude of damage from the 2015 gypsy moth outbreak in Pennsylvania based on percent changes in vegetation greenness. A 12-week Seasonal Duration map (right) shows duration of the disturbance based on the number of weekly monitoring periods in which a loss of vegetation greenness exceeded 3% during the 2015 growing season. Both maps compare vegetation greenness to that of the previous year.

Some disturbances come and go, leaving forests no worse for the wear.

Hailstorms, insect defoliations, and light prescribed fires, for example, commonly occur early in the growing season, but, because of the timing and nature of these disturbances, trees and other vegetation may quickly regrow leaves after the damage is done. In such cases, even the most extreme damage diminishes by mid-summer.

Other times, disturbance damage causes longer lasting effects on forests when dieback or mortality results.

When viewed from above with coarse resolution remote sensing, such as with satellite imagery or aerial surveys, canopy impacts can appear similar whether disturbance damage is fleeting or more enduring. How can managers gauge the true impacts of forest disturbance on forest growth and productivity?

U.S. Forest Service Eastern Forest Environmental Threat Assessment Center researchers behind the satellite-based ForWarn tool have developed new Seasonal Duration map products that distinguish short-lived disturbances from lasting disturbances.

While traditional ForWarn maps are generated each week year-round to show how much vegetation greenness may have changed compared to expected conditions for a given location and day of year, seasonal disturbance impacts and recovery cannot be judged by one snapshot in space and time.

Seasonal Duration maps are generated every six weeks during the growing season and can complement weekly ForWarn maps to provide a more complete picture of the extent of the growing season impacted by disturbance.

ForWarn‘s Seasonal Duration products record the count of weekly monitoring periods that fell below a three percent drop in vegetation greenness compared to the prior year,” explains Bill Hargrove, Eastern Threat Center research ecologist and lead ForWarn researcher. “These maps provide a simple way to identify areas that have experienced long lasting change that are easily overlooked due to the low magnitude of the disturbance or persistent cloud cover during the growing season.”

Though the Seasonal Duration maps are a new innovation developed this year, they are now available for each growing season going back to 2006. ForWarn researchers plan to produce Seasonal Duration maps three times during each growing season, a frequency that can assist users with annual reporting activities.

The Seasonal Duration map products have recently been particularly useful for tracking the duration of gypsy moth damage in the northeastern Unites States — disturbance that has captured the attention of land managers, homeowners, outdoor enthusiasts, and plenty of media. Efforts to assess the impacts of the 2015 gypsy moth defoliation event spanning parts of Pennsylvania, New Jersey, and New York and the 2016 event that affected Massachusetts and nearly the entire state of Rhode Island are summarized on the ForWarn website.

“Based on the lasting duration of declines in canopy greenness across a large part of the state, 2016’s gypsy moth defoliation event in southern New England was particularly severe,” says Eastern Threat Center research ecologist and ForWarn researcher Steve Norman.

The next ForWarn Seasonal Duration map will be available shortly after the last day of summer (September 21) as the 2016 growing season winds down across much of the eastern United States, and researchers look forward to the insight these new map products can provide in the future.

“For some critical measures, such as annual growth or productivity, the magnitude of change in vegetation greenness for a given day or period may not be particularly telling. Changes in forest health are best contextualized by a multi-period or seasonal perspective. ForWarn’s calculation of seasonal duration of disturbance impacts can provide that context and serve as a unique new measure for forest monitoring,” says Norman.

For more information, email Steve Norman at stevenorman@fs.fed.us.

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Forest Health Research and Education Center Shares $3 Million NSF Grant

U.S. Forest Service part of effort to improve cyberinfrastructure for tree resources

by Zoё Hoyle, SRS Science Communications
View from the Blue Ridge Parkway just south of Asheville, NC. Photo by Fran Trudeau, courtesy of Wikimedia Commons.

View from the Blue Ridge Parkway just south of Asheville, NC. Photo by Fran Trudeau, courtesy of Wikimedia Commons.

The Forest Health Research and Education Center (Forest Health Center), a collaborative project among the Forest Service Southern Research Station (SRS), the University of Kentucky, and the Kentucky Division of Forestry, will share a $3 million grant from the National Science Foundation with researchers from Washington State University (serving as lead), the University of Tennessee, and the University of Connecticut.

The funded project will establish a network and cyberinfrastructure for sharing comprehensive tree health and genetic data among scientists and the public. The grant will help researchers continue work on a user-friendly web-based interface using Tripal, a flexible program that scientists, tree breeders, and the public can use to more easily access information about trees, tree genetics, sequences of tree genomes, and other information that’s archived in specialized tree breeding and research databases.

The grant also supports promoting education and outreach programs towards conservation efforts and involving the public in monitoring forest health. The Forest Health Center will play a primary role in this aspect, presenting workshops for woodland owners, private industry, and state agencies.

“It’s more and more important to involve the public in monitoring our forests for insects, diseases, and invasive species,” says Dana Nelson, SRS research geneticist and Forest Health Center co-director. “This not only helps us to identify and track problems but provides people with new reasons and ways to learn about the forests around them.”

This fits well with the mission of the Lexington, Kentucky-based Forest Health Center to advance the conservation of forested ecosystems by integrating genetics-based biological research with social science and education on the factors that affect tree health and forest restoration.

“Part of our education and outreach efforts at the Forest Health Center are focused on promoting the understanding of forest health threats in relation to the genetics of resistance and the use of new genetic tools for improving resistance,” says Nelson. “The grant will help us better convey our findings to those who can use them to help improve forest health using genetics-based tools and knowledge.”

For more information, email Dana Nelson at dananelson@fs.fed.us.

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Scientists Find Evidence of Regime Shift in Forest Watershed Cut in the 1970s

Long-term data shows nitrogen still elevated

by Sarah Farmer, SRS Science Communications
At the Coweeta Hydrological Laboratory, 16 operational weirs measure streamflow. Streams in watershed 7 have elevated nitrogen concentration from a clearcut almost 40 years ago. Photo by U.S. Forest Service.

At the Coweeta Hydrological Laboratory, 16 operational weirs measure streamflow. Streams in watershed 7 still have elevated nitrogen concentration from a clearcut almost 40 years ago. Photo by U.S. Forest Service.

After disturbances, healthy ecosystems are usually resilient enough to return to a pre-disturbance state. However, some disturbances are extreme enough to permanently shift an ecosystem, a phenomenon known as a regime shift.

“Ecosystem regime shifts have been well documented in lakes, streams, and oceans,” says Forest Service Southern Research Station (SRS) scientist Jennifer Knoepp. “We identified a functional regime shift in a forested watershed that had been clearcut in the 1970s.” The study was led by Jackson Webster, a professor emeritus at Virginia Tech, and published in the journal Ecosystems.

The scientists paired the clearcut watershed with an adjacent watershed that was similar, except for the fact that it had not been clearcut. Both watersheds are located at the SRS Coweeta Hydrologic Laboratory, where Forest Service research has been conducted since 1934. Knoepp and her colleagues used a 36-year dataset to compare the two watersheds.

“We found surprising effects on water chemistry, effects that persist almost 40 years later,” says Knoepp, a research soil scientist. In the clearcut watershed, dissolved nitrogen was higher, and the seasonal spike in nitrogen concentration had shifted from summer to winter.

“In many ways, the recovery of the clearcut watershed was rapid,” says SRS project leader and study coauthor Chelcy Miniat. “Within 10 years, tree cover had returned and within 30 years the total amount of aboveground biomass was about the same as before logging.” The amount and speed of water flowing through the streambeds increased immediately after the clearcut, but within 7 years, returned to predicted levels.

The scientists expected that the stream nitrogen concentration would also decline. However, about 10 years after the clearcut, it actually increased. Almost 40 years after the clearcut, it remains elevated.

Nitrogen is an important plant nutrient, but when it reaches the water – especially in the form of nitrate and ammonia – it can affect water quality. Nitrogen enters the forest via several pathways, and in the studied watershed, one of the most important sources was black locust.

Black locust trees dominated the clearcut watershed for the first 10 years after the cut. The species, which is native to the southern Appalachians, has nitrogen-fixing bacteria in its roots. The bacteria can convert atmospheric nitrogen to a form that plants can use for growth.

Black locust has declined on the study site, which is now dominated by tulip poplar and oak. However, the amount of nitrogen in streams remains elevated. Studies on black locust have found that as it decomposes, it contributes large amounts of relatively inert nitrogen to the soil and may have accumulated in the deeper levels of the soil, as well as areas next to the streams.

“It is very difficult to distinguish a regime shift from a very slow recovery,” says Knoepp. “If we had stopped measuring the amount of dissolved nitrogen in streams after 10 years, we probably would have thought the ecosystem was recovering to its original state.”

Whether stream nitrogen levels in the watershed will eventually return to pre-disturbance levels is unknown, and whether the change represents a regime shift or simply a very slow recovery is unclear. Although the nitrogen concentration is much higher than in other nearby watersheds, it is low in comparison to streams that flow through agricultural lands or cities, and is not a water quality issue.

“However, the long-lasting effects suggest the need for forward-looking management,” says Knoepp. “Management should aim to increase the resilience of forests and create or maintain desired nutrient cycling regimes.”

Read the full text of the article.

For more information, email Jennifer Knoepp at jknoepp@fs.fed.us or Chelcy Miniat at cminiat@fs.fed.us

 

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