Pacific Northwest Research Station

Silviculture and Ecology of Southeast Alaska Team

2008 Science Accomplishments

Scientists quantify carbon fluxes in southeast Alaska

Coastal temperate rain forests sequester large amounts of carbon because cool, wet conditions inhibit decomposition. They are also sources of carbon. The Tongass National Forest exports as much dissolved organic carbon per year in water as would be removed through harvesting 1.6 million board feet of timber-enough to frame 100,000 homes. Much of this carbon is transferred to aquatic systems where it likely plays a key role supporting production of species such as salmon, shrimp, crab, and others. What isn't incorporated into aquatic food webs enters long-term storage within the marine system.

As the climate warms, the rate at which carbon is released from the soils of coastal temperate rain forests could increase. Station scientists continue to measure rates and controls of major fluxes to better understand the carbon cycle and the interplay between terrestrial and aquatic systems. This information will be used to develop forest carbon management strategies and be applied to regional and national carbon sequestration goals.

Partners: University of Alaska Southeast, U.S. Cooperative State Research, Education, and
Extension Service

To learn more, contact David D'Amore at ddamore@fs.fed.us.

Glacier-fed watersheds differ from those without glaciers and have climate change implications

Watersheds in southeast Alaska will be significantly altered as the climate warms. Currently, 86 percent of the water discharged from the Tongass National Forest comes from large continental watersheds containing glaciers and permanent snowfields. The seasonality of discharge, chemistry, and temperature of glacial rivers is very different from nonglacial rivers in the Tongass. As warming continues, the loss of glacial inputs and changes in the timing of runoff related to changes in snowpack and snow-to-rain ratios will dramatically affect stream habitats and the annual pattern of carbon and nutrient inputs to the marine system.
Watersheds that do not contain glaciers exhibit two peaks annually, a spring snowmelt peak and a fall peak. As the snow line rises, discharge will begin to track precipitation, as is observed in the lowest watersheds, and the spring melt peak will disappear. These changes in annual hydrology will interact with nutrient cycles to change the shape and productivity of river habitats.
This research is leading to better modeling of present and changing hydrology of Alaska's streams. Improved models of future runoff will help managers design stream restoration and fish enhancement projects and be used to model potential fish distribution under various climate scenarios.
Partners: University of Alaska Southeast, U.S. Cooperative State Research, Education,
and Extension Service

To learn more, contact David D'Amore at ddamore@fs.fed.us.

New technique identifies sources of soil and stream productivity

A wetland in southeast Alaska. Credit: Rick Edwards

Scientists have identified a type of dissolved organic material that is easily digested by stream micro-organisms by using a novel modeling technique known as parallel factor analysis (PARAFAC). This "labile" organic matter is exported from wetlands and carried downstream. It is generally accepted that soils provide important ecosystem services in the maintenance of terrestrial and aquatic biological systems, but it is difficult to identify the source of this easily degraded material that sustains primary production in soils and streams. The PARAFAC analysis can be used to determine if the type of organic material in watersheds is usable by stream microorganisms, an indicator of proper ecosystem function. Until now, it has been difficult to evaluate management impacts on terrestrial and aquatic systems at this fundamental level. The development of this technique is an important advance, enabling scientists to evaluate soil quality and wetland functions in the coastal temperate rain forest of southeast Alaska.

Partners: University of Alaska-Fairbanks, University of Alaska-Southeast

To learn more, contact David D'Amore at ddamore@fs.fed.us.

Western hemlock and Sitka spruce respond well to thinning

The primary objective of the Cooperative Stand-Density Study, a long-term silviculture experiment located on the Tongass National Forest, is to understand how western hemlock Sitka spruce stands of different ages and site productivities respond to a range of thinning intensities. This study was initiated in the 1970s. After 20 years, data were analyzed from 128 permanent study plots distributed over 250 miles. Scientists found that thinning well stocked, even-aged, mixed-species stands of western hemlock and Sitka spruce in southeast Alaska significantly increased growth in thinned stands relative to that of unthinned stands, the effect being greater for younger stands or stands growing on more productive sites.

The models developed in this analysis will help land managers predict how western hemlock-Sitka spruce stands of different ages and site productivities respond to different thinning intensities in terms of diameter growth during the first 20 years after treatment.

Partner: USDA Forest Service Tongass National Forest

To learn more, contact Michael McClellan at mmcclellan@fs.fed.us.