Charles H. Racine

Climate change. Increasing shrub abundance in the Arctic.

The warming of the Alaskan Arctic during the past 150 years has accelerated over the last three decades and is expected to increase vegetation productivity in tundra if shrubs become more abundant; indeed, this transition may already be under way according to local plot studies and remote sensing. Here we present evidence for a widespread increase in shrub abundance over more than 320 km of Arctic landscape during the past 50 years, based on a comparison of historic and modern aerial photographs. This expansion will alter the partitioning of energy in summer and the trapping and distribution of snow in winter, as well as increasing the amount of carbon stored in a region that is believed to be a net source of carbon dioxide.

PERMAFROST DEGRADATION AND ECOLOGICAL CHANGES ASSOCIATED WITH A WARMING CLIMATE IN CENTRAL ALASKA

Studies from 1994–1998 on the TananaFlats in central Alaska reveal that permafrostdegradation is widespread and rapid, causing largeshifts in ecosystems from birch forests to fens andbogs. Fine-grained soils under the birch forest areice-rich and thaw settlement typically is 1–2.5 mafter the permafrost thaws. The collapsed areas arerapidly colonized by aquatic herbaceous plants,leading to the development of a thick, floatingorganic mat. Based on field sampling of soils,permafrost and vegetation, and the construction of aGIS database, we estimate that 17% of the study area(263,964 ha) is unfrozen with no previous permafrost,48% has stable permafrost, 31% is partiallydegraded, and 4% has totally degraded. For thatportion that currently has, or recently had,permafrost (83% of area), ∼42% has been affected bythermokarst development. Based on airphoto analysis,birch forests have decreased 35% and fens haveincreased 29% from 1949 to 1995. Overall, the areawith totally degraded permafrost (collapse-scar fensand bogs) has increased from 39 to 47% in 46 y. Based on rates of change from airphoto analysis andradiocarbon dating, we estimate 83% of thedegradation occurred before 1949. Evidence indicatesthis permafrost degradation began in the mid-1700s andis associated with periods of relatively warm climateduring the mid-late 1700s and 1900s. If currentconditions persist, the remaining lowland birchforests will be eliminated by the end of the nextcentury.

Snow–Shrub Interactions in Arctic Tundra: A Hypothesis with Climatic Implications

In the Arctic, where wind transport of snow is common, the depth and insulative properties of the snow cover can be determined as much by the wind as by spatial variations in precipitation. Where shrubs are more abundant and larger, greater amounts of drifting snow are trapped and suffer less loss due to sublimation. The snow in shrub patches is both thicker and a better thermal insulator per unit thickness than the snow outside of shrub patches. As a consequence, winter soil surface temperatures are substantially higher, a condition that can promote greater winter decomposition and nutrient release, thereby providing a positive feedback that could enhance shrub growth. If the abundance, size, and coverage of arctic shrubs increases in response to climate warming, as is expected, snow‐shrub interactions could cause a widespread increase (estimated 10%‐25%) in the winter snow depth. This would increase spring runoff, winter soil temperatures, and probably winter CO 2 emissions. The balance between these winter effects and changes in the summer energy balance associated with the increase in shrubs probably depends on shrub density, with the threshold for winter snow trapping occurring at lower densities than the threshold for summer effects such as shading. It is suggested that snow‐shrub interactions warrant further investigation as a possible factor contributing to the transition of the arctic land surface from moist graminoid tundra to shrub tundra in response to climatic warming.

Five Stages of the Alaskan Arctic Cold Season with Ecosystem Implications

Abstract We divide the Alaskan Arctic cold season into five stages based on transitions in climatological and thermophysical conditions in the atmosphere, snowpack, and soil active layer. Each of these stages has distinct characteristics which drive ecosystem processes. During the two autumnal stages (Early Snow and Early Cold) soils remain warm, unfrozen water is present, and the highest rates of cold-season soil respiration occur. The next two stages (Deep Cold and Late Cold) are characterized by a frozen active layer with decreasing temperature. Thaw is critical in determining the length of the growing season and the resumption of biological processes. Deep Cold and Late Cold result from a radiation deficit, show little interannual variation, and will be resistant to change under almost any reasonable climate change scenario. These are also the stages with the least amount of biological activity and have the least impact on the ecosystem. However, Early Snow, Early Cold and Thaw stages vary significantly from year to year, have more ecosystem implications, and are also the most likely to undergo significant change in timing and character as the arctic climate changes. This 5-fold subdivision is useful for framing discussions of biophysical interactions during the arctic winter and for focusing attention on critical cold-season periods.

Tundra Fire and Vegetation Change along a Hillslope on the Seward Peninsula, Alaska, U.S.A.

Abstract A 1977 tundra fire burned a hillslope where prefire soils and vegetation ranged from poorly drained moist tussock-shrub tundra on the lower slopes to well-drained dwarf shrub tundra on the back slope and very poorly drained wet sedge meadow on the flat crest. We sampled the vegetation on this slope before the fire and at 8 sites following the fire at irregular intervals from 1 yr to 25 yr. During the first decade after the fire, short-term recovery was dominated by bryophytes, sedges, and grasses from both regrowing sedge tussocks and seedlings. However, during the second and third decade, and by 24 yr after the fire, evergreen (Ledum palustre) and deciduous shrubs (mainly Salix pulchra willow) expanded dramatically so that shrub cover was generally higher than before the fire. Labrador tea has increased by vegetative means on the poorly drained lowest 3 tussock-shrub tundra sites. Upslope on the better-drained and more severely burned tussock-shrub and dwarf shrub tundra sites, willows became established from seed mainly during the first 10 yr after the fire and, based on their relatively large size (0.5–1 m tall) and cover, have grown rapidly during the past 15 to 20 yr. There has been very little or no recovery of Sphagnum moss and fruticose lichens after 24 yr at any site, except for Sphagnum moss in the wet meadow site. The permafrost active layer thickness has diminished to prefire levels at the lower slope tussock-shrub tundra sites but is much greater or degraded completely on the steeper slope, corresponding with the distribution of willow shrub colonization. These changes in tundra vegetation and permafrost following fire suggest that such fires could accelerate the predicted effects of climate warming on ecosystems in the Arctic.

Slow Recovery of Lichen on Burned Caribou Winter Range in Alaska Tundra: Potential Influences of Climate Warming and Other Disturbance Factors

ABSTRACT Lichen regeneration timelines are needed to establish sound fire management guidelines for caribou (Rangifer tarandus) winter range. Paired burned and unburned permanent vegetative cover transects were established after 1981, 1977, and 1972 tundra fires in northwestern Alaska to document regrowth of tundra vegetation including caribou forage lichens in the wintering range of Alaskas largest caribou herd. Following fire, lichen had recovered very little compared to unburned transects (1% cover vs.15% cover) after 14 years. After 24 or 25 years, lichen cover in the burns remained low (3–4%), whether or not caribou were present during the recovery period. In addition, lichen cover on unburned transects at one study site had decreased from 14% to 6%. Shrub cover was higher on the burned plots than the unburned plots. Cover of cottongrass (Eriophorum vaginatum) initially increased following the fire and tussocks quickly became more vigorous than on paired unburned transects, remaining so for more than 14 years. Persistent changes in vegetation following fire likely reflect the cumulative impacts of seasonal caribou use and favorable growing conditions (warmer soils, longer growing season) for rooted vascular species during the recovery period. The actual recovery of forage lichens after fire on our study sites is slower than predictions based on ideal growth potential.

White Phosphorus Poisoning of Waterfowl in an Alaskan Salt Marsh

The cause of the yearly death of an estimated 1,000 to 2,000 migrating dabbling ducks (Anas spp.) and 10 to 50 swans (Cygnus buccinator and C. columbianus) has remained a mystery for the last ten years in Eagle River Flats (ERF), a 1,000 ha estuarine salt marsh near Anchorage, Alaska, used for artillery training by the U.S. Army. We have gathered evidence that the cause of this mortality is the highly toxic, incendiary munition white phosphorus (P4). The symptoms of poisoning we observed in wild ducks included lethargy, repeated drinking, and head shaking and rolling. Death was preceded by convulsions. Farm-reared mallards dosed with white phosphorus showed nearly identical behavioral symptoms to those of wild ducks that became sick in ERF. White phosphorus does not occur in nature but was found in both the sediments where dabbling ducks and swans feed and in the gizzards of all carcasses collected in ERF. We hypothesize that feeding waterfowl are ingesting small particles of the highly toxic, incendiary munition P4 stored in the bottom anoxic sediments of shallow salt marsh ponds.

Groundwater-Discharge Fens in the Tanana Lowlands, Interior Alaska, U.S.A.

Large expanses of herbaceous floating mat wetlands (FMW) bordered by slightly higher uplands with forest or scrub occur in the northwest corner of the Tanana Flats between the Alaska Range and the Tanana River. Five major FMW systems, together with other outliers and extensions, are linear in shape and cover over 20 km2. Nutrient-rich and circumneutral water flows slowly through these areas toward the northwest and through outlets to the Tanana River. The floating mat vegetation consists of tall emergent macrophytes; mosses, in particular Sphagnum spp., are conspicuously absent and shrubs are infrequent. Although species dominance shifts over short distances on the mat, four community types can be recognized: (1) Menyanthes trifoliata, (2) Carex aquatilis, (3) Typha latifolia, and (4) Calla palustris. Below the water surface, the mat extends to a depth of 0.5 to 1.0 m and consists of rhizomes and roots in a matrix of well-decomposed peat and water. The mat then either directly overlies unfrozen gray silts at a depth of 1 m, or more commonly, floats on a clear-water or loose peat zone above more consolidated peat lying on unfrozen silt at a depth of 1.5 to 2.5 m. No permafrost or frozen ground was detected in late August or late winter below these floating mats but it is ubiquitous on the bordering uplands, 0.5 to 2 m above the FMW. The topographic location, apparent absence of permafrost, water chemistry, and vegetation composition suggest that these areas are fens fed by groundwater sources flowing out of the Alaska Range. Permafrost degradation and lateral expansion of these FMW is indicated by slumped blocks of forest peat, dead trees, and open water moats along the upland margin. Although floating mats are frequently described in the literature as occupying the edge of northern ponds and lakes, the FMW described here do not and they appear to be unique because of their large extent, absence of mosses, physiographic position, and presumed origin.

Use of off-road vehicles and mitigation of effects in Alaska permafrost environments : a review

Use of off-road vehicles (ORVs) in permafrost-affected terrain of Alaska has increased sharply over the past two decades. Until the early 1960s, most ORV use was by industry or government, which employed heavy vehicles such as industrial tractors and tracked carriers. Smaller, commercial ORVs became available in the 1960s, with the variety and number in use rapidly increasing. Wheeled and tracked ORVs, many used exclusively for recreation or subsistence harvesting by individuals, are now ubiquitous in Alaska. This increased use has led to concern over the cumulative effects of such vehicles on vegetation, soils, and environmental variables including off-site values.Factors affecting impact and subsequent restoration include specific environmental setting; vegetation; presence and ice content of permafrost; microtopography; vehicle design, weight, and ground pressure; traffic frequency; season of traffic; and individual operator practices. Approaches for mitigating adverse effects of ORVs include regulation and zoning, terrain analysis and sensitivity mapping, route selection, surface protection, and operator training.

White Phosphorus Contamination of an Active Army Training Range

Detonations of military ordnance will leave various amounts of chemical residue on training ranges. Significant adverse ecological effects from these residues have not been documented except for ordnance containing white phosphorus. At a military training range in Alaska, USA, the deaths of thousands of waterfowl due to poisoning from white phosphorus ordnance prompted a two-decade-long investigation of the extent of the contamination, remediation technologies, and methods to assess and monitor the effectiveness of the remediation. This paper gives an overview of these investigations and provides the outcome of the remediation efforts.