Leslie A. Viereck

The Alaska vegetation classification.

Viereck, L.A.; Dyrness, C.T.; Batten, A.R.; Wenzlick, K.J. 1992. The Alaska vegetation classification. Gen. Tech. Rep. PNW-GTR-286. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 278 p. The Alaska vegetation classification presented here is a comprehensive, statewide system that has been under development since 1976. The classification is based, as much as possible, on the characteristics of the vegetation itself and is designed to categorize existing vegetation, not potential vegetation. A hierarchical system with five levels of resolution is used for classifying Alaska vegetation. The system, an agglomerative one, starts with 888 known Alaska plant communities, which are listed and referenced. At the broadest level of resolution, the system contains three formations-forest, scrub, and herbaceous vegetation. In addition to the classification, this report contains a key to levels I, II, and III; complete descriptions of all level IV units; and a glossary of terms used.

Element Cycling in Taiga Forests: State-Factor Control

ronment characterized by drastic seasonal fluctuations in day length and temperature, a short growing season, low soil temperatures, and permafrost (Van Cleve and Alexander 1981). The taiga is part of the circumpolar forest region near the latitudinal limit of tree growth. The taiga occupies large areas of Alaska, Canada, Scandinavia, and the Soviet Union (Van Cleve and Alexander 1981). With changing climate, ecological relationships within the taiga could assume global importance, because this region contains 20% of the worlds stored carbon and is a large but unexplored source of methane and carbon dioxide, two gases implicated in causing climate change (Billings 1987, McBeath 1984, Reeburgh 1990). Flux rates of these gases are expected to change An understanding of taiga ecosystem controls is important for predicting global responses to climate change

Forest Succession in Relation to Nutrient Cycling in the Boreal Forest of Alaska

The successional sequences described in this chapter were located in the central part of Alaska, in the general vicinity of Fairbanks, but the general trends and conclusions derived from our studies should have broader application to most of the North American taiga.

Observations of Thermokarst and Its Impact on Boreal Forests in Alaska, U.S.A.

A hinged gate and flexible loading seal for an inclined conveyor, more particularly for an inclined apron conveyor with pushers for carrying loose, bulk material. The pushers, longitudinally spaced either in staggered arrangement across the conveyor surface or each fully traversing the conveyor width, reduce gross downward movement of the material during conveyor ascent. A segmental gate is hinged above the conveyor in the vicinity of transfer from an unloading conveyor, allows upward passage of the pushers and interrupts downward movement of conveyed material. A flexible, resilient seal fixed above the conveyor and positioned downstream of the hinged gate prevents further downward retreat of escaping conveyed material and redeposits same upstream on advancing pushers.

Taiga Ecosystems in Interior Alaska

For several years the University of Alaska and the Institute of Northern Forestry (USDA Forest Service) have conducted a multidisciplinary study of interior-Alaska forest ecosystems, especially the black spruce type. Black spruce forests are widespread in interior Alaska and are the most fire-prone forest type. They are also the most nutrient-limited and least productive forest type, especially in the late stages of succession. Ecosystem differences in productivity and degree of nutrient limitation are controlled mainly by soil and forest-floor temperatures. (Accepted for publication 3 August 1982)

Wildfire in the Taiga of Alaska

Abstract The taiga of Alaska consists of a vegetation mosaic resulting primarily from past wildfires. Today, both lightning- and man-caused wildfires burn an average of 400,000 hectares annually, creating vast areas of successional ecosystems. However, although the number of reported fires is increasing, fire control is becoming more effective in limiting the average size of fires and the total area burned. One of the important influences of fire in the taiga ecosystem is its effect on permafrost and the soil nutrient cycle. Construction of firelines in permafrost areas has a greater effect on soil erosion and siltation than does the fire itself. Some wildlife species, such as moose and snowshoe hare, depend upon fire and its resultant successional plant communities, whereas fire may have deleterious effects on caribou winter range. Fire has both positive and negative effects on esthetic and recreational values. Fire has always been a part of the Alaskan taiga ecosystem; if it is totally excluded from the environment, some major ecological changes will result. Fire-suppression alternatives are discussed and additional research on fire effects suggested.

The effect of changing environmental conditions on microwave signatures of forest ecosystems: preliminary results of the March 1988 Alaskan aircraft SAR experiment

Abstract In preparation for the first European Space Agency (ESA) Remote Sensing(ERS-I) mission,a series of multitemporal, multifrequency, multipolarization aircraft synthetic aperture radar (SAR) data sets were acquired over the Bonanza Creek Experimental Forest near Fairbanks, Alaska in March, 1988. P-, L- and C-band data were acquired with the NASA/JPL Airborne SAR on five differentdays over a period of two weeks. The airborne data were augmented with intensiveground calibration data as well as detailed, simultaneous in situ measurements of the geometric, dielectric and moisture properties of the snow and forest canopy. During the time period over which the SAR data were collected, the environmental conditions changed significantly; temperatures ranged from unseasonably warm (I to 9°C) to well below freezing (-8 to - 15°C), and the moisture content of the snow and trees changed from a liquid to a frozenstate. The SAR data clearly indicate the radar return is sensitive to these changing environmental fa...

Fire in Taiga Communities of Interior Alaska

Most forest communities in interior Alaska have been extensively influenced by recurring fire. To a large extent, the distribution of the dominant tree species has been shaped by fire. First-time visitors are often struck by the small-scale mosaic of forest types (white spruce, aspen, and paper birch) they observe on some sites in interior Alaska. Fire, working in the context of the influence of soil and topography, is most influential in the distribution of these forest types.

Evaluating the type and state of Alaska taiga forests with imaging radar for use in ecosystem models

Changes in the seasonal CO/sub 2/ flux of the boreal forests may result from increased atmospheric CO/sub 2/ concentrations and associated global warming patterns. To monitor this potential change, a combination of information derived from remote sensing data, including forest type and growing season length, and ecophysiological models which predict the CO/sub 2/ flux and its seasonal amplitude based on meteorological data, are required. The authors address the use of synthetic aperture radar (SAR) to map forest type and monitor canopy and soil freeze/thaw, which define the growing season for conifers, and leaf on/off, which defines the growing season for deciduous species. Aircraft SAR (AIRSAR) data collected in March 1988 during a freeze/thaw event are used to generate species maps and to determine the sensitivity of SAR to canopy freeze/thaw transitions. These data are also used to validate a microwave scattering model which is then used to determine the sensitivity of SAR to leaf on/off transitions and soil freeze/thaw. Finally, a CO/sub 2/ flux algorithm is presented which utilizes SAR data and an ecophysiological model to estimate CO/sub 2/ flux. CO/sub 2/ flux maps are generated, from which areal estimates of CO/sub 2/ flux are derived. >

Monitoring of environmental conditions in Taiga forests using ERS-1 SAR

This paper describes the results of monitoring environmental conditions in Alaskan Taiga forests using ERS-1 SAR dara.