Northwest Alaska Research Articles

Enhancing a community-based water resource tool for assessing environmental change: the arctic water resources vulnerability index revisited

People in the Arctic and sub-Arctic continue to face uncertainty in their livelihoods as they contend with environmental variability and change operating at multiple scales. The arctic water resources vulnerability index (AWRVI) was proposed as a tool that arctic communities could use to assess their susceptibility to both changing biophysical conditions affecting their water resources and socioeconomic conditions measuring their ability to respond to such changes. The application of AWRVI in six communities in Northwest Alaska and one in Southcentral Alaska is explored with a view to enhancing the tool as an adaptive capacity index, and a set of AWRVI indicators and parameters was refined by modifying the suite of biophysical measures and societal capacities to enhance the ability of the tool to gauge community adaptive capacity, and incorporate the use of more diverse datasets. A critical update was the development of an indicator for change in timing of precipitation in response to advice from Alaskan practitioners and scientists. Index scores based on the updated AWRVI are compared with the original AWRVI for the seven communities and show small to modest changes in the adaptive capacity scores. The role of the updated AWRVI is discussed as a tool to assist communities as they attempt to understand, negotiate, and reconcile adaptation measures for environmental change at local scales, potentially providing a guide for communities to target adaptive responses.

First Tropical American Species of the “Relict” GenusLitoleptis,and Relationships in Spaniinae (Diptera: Rhagionidae)

The genus Litoleptis has consisted of nine described species, seven of them Asian and only two in the New World: L. alaskensis Chillcott, known from two specimens from northwest Alaska, and L. chilensis Hennig, known from a male specimen from near Santiago, Chile. A third New World species is described here, Litoleptis tico, n. sp., based on a single female from Costa Rica. The species is unique for the genus in having a vestigial proboscis and lacking spermathecal accessory ducts and glands. Female terminalia are unknown for the other two New World species. A morphologically based, preliminary phylogeny of spaniines is provided, indicating Litoleptis is recently derived among spaniines and thus Rhagionidae; the Early Cretaceous Litoleptis fossilis is a stem group to the living species. A derived position of the genus, its apparently broad distribution, and an abundance in Japan where Litoleptis has been bred from liverworts (Imada and Kato, 2016a), all indicate that these flies are probably not at all relict, simply vastly undersampled because of a reliance on mass-collecting techniques.

Fluted projectile points in a stratified context at the Raven Bluff site document a late arrival of Paleoindian technology in northwest Alaska

AbstractOur understanding of the northern fluted point tradition, a critical early New World lithic assemblage, is constrained by limited data from stratified, datable contexts. Here, we report on the Raven Bluff site in northwest Alaska, where fluted projectile points, microblades, and a well‐preserved faunal assemblage have been recovered from datable sediments. Results show that prehistoric inhabitants occupied a stone‐sorted polygon where retooling, game processing, and raw material procurement occurred mostly between 12,720 and at least 11,340 cal. yr B.P. We argue that once polygon formation ended, the stratigraphic context remained relatively intact. Further studies focused on the site’s lithic and bone assemblages will help shape our understanding of the relationship between fluted point technology, microblades, and caribou hunting in northern Alaska.

Critical trophic links in southern Chukchi Sea lagoons

Arctic lagoons support a variety of fish, bird and marine mammal species, as well as subsistence fisheries that are critical to local food security along the Chukchi and Beaufort sea coasts. In summer 2015, diet samples from seven lagoon fishes were non-lethally collected in three lagoons along the Northwest Alaska coastline. Using these samples, we determined that the key prey species that supported these particular lagoon food webs were mysids, chironomids and Ninespine Stickleback. We identified the relative importance of freshwater/terrestrial and marine prey sources in lagoon fish diets and identified three key functional feeding groups of fishes: microbenthivore/zooplanktivores, macrobenthivore/piscivores, and piscivores. Several key predators were found in the microbenthivore/zooplanktivore group indicating a high degree of redundancy, which was lacking in the other functional feeding groups. This suggests that this group has the greatest resiliency, whereas other groups may be more vulnerable to changes in lagoon habitats. Functional groups with less redundancy, such as the upper trophic levels, may be good indicator species for identifying potential impacts to Arctic lagoons from climate change.

Temporal and spatial variability in coastline response to declining sea-ice in northwest Alaska

Arctic sea-ice is declining in extent, leaving coastlines exposed to more storm-wave events. There is an urgent need to understand how these changes affect geomorphic processes along Arctic coasts. Here we describe spatial and temporal patterns of shoreline changes along two geomorphologically distinct, storm-wave dominated reaches of the Chukchi Sea coastline over the last 64 years. One study area encompasses the west- to southwest-facing, coarse-clastic shoreline and ice-rich bluffs of Cape Krusenstern (CAKR). The other covers the north-facing, sandy shorelines on barrier islands, ice-rich bluffs, and the Cape Espenberg spit in the Bering Land Bridge National Park (BELA). Both study areas lie within the zone of continuous permafrost, which exists both on and offshore and outcrops as ice-rich bluffs along the BELA coast. We mapped changes in coastal geomorphology over three observation periods: 1950–1980, 1980–2003, and 2003–2014 using aerial and satellite imagery. We then compared these geomorphic changes to changes in sea-ice coverage, which declined ~10 days per decade between 1979 and 2016 in the southern Chukchi Sea. Changes in coastal geomorphology in both BELA and CAKR exhibited high spatial variability over the study period. Between 2003 and 2014, shorelines of barrier islands in BELA exhibited the highest mean rates of change, −1.5 m yr−1, while coarse, clastic barrier beaches in CAKR showed only minimal change. Overall, shorelines in both BELA and CAKR became more dynamic (increasing erosion or increasing accumulation) after ca. 2003, with spatial variability in shoreline changes roughly doubling between the first period of observation (1950–1980) and the last (2003–2014). This increase in coastal dynamism may signal a transitional period leading to new state of geomorphic equilibria along these ice-affected coastlines.

Tundra be dammed: Beaver colonization of the Arctic.

Increasing air temperatures are changing the arctic tundra biome. Permafrost is thawing, snow duration is decreasing, shrub vegetation is proliferating, and boreal wildlife is encroaching. Here we present evidence of the recent range expansion of North American beaver (Castor canadensis) into the Arctic, and consider how this ecosystem engineer might reshape the landscape, biodiversity, and ecosystem processes. We developed a remote sensing approach that maps formation and disappearance of ponds associated with beaver activity. Since 1999, 56 new beaver pond complexes were identified, indicating that beavers are colonizing a predominantly tundra region (18,293km2 ) of northwest Alaska. It is unclear how improved tundra stream habitat, population rebound following overtrapping for furs, or other factors are contributing to beaver range expansion. We discuss rates and likely routes of tundra beaver colonization, as well as effects on permafrost, stream ice regimes, and freshwater and riparian habitat. Beaver ponds and associated hydrologic changes are thawing permafrost. Pond formation increases winter water temperatures in the pond and downstream, likely creating new and more varied aquatic habitat, but specific biological implications are unknown. Beavers create dynamic wetlands and are agents of disturbance that may enhance ecosystem responses to warming in the Arctic.

Ethnohistoric documents as analogical tools: A case study from northwest Alaska

Archaeologists endeavour to reconstruct technological, environmental, social, cultural, and even ideological aspects of past groups and individuals using the fragmented material past. Many, if not all, of these analyses rely on analogy. Archaeologists have used the direct historical approach extensively in the Arctic to develop more nuanced understandings of the prehistoric Inuit. In many cases, the direct historical approach is not truly direct; archaeologists often assume that secondary activities, such as those that occur contemporaneously with initial deposition but that are not described in the ethnographic record such as cleaning and post-depositional processes such as weathering, alter the archaeological patterns and inhibit direct comparison to ethnohistoric sources. In this study, I analyse the relationship between the archaeological record and documentary sources to establish which patterns and activities are visible in the archaeofaunal record. I test expectations based on the documentary record, ethnoarchaeological studies, and taphonomic processes against the faunal assemblage from an early Thule Inuit semi-subterranean dwelling at Cape Espenberg, Alaska. Despite expected disturbances from contemporary activities and post-depositional processes, the faunal assemblage closely resembles expectations of primary household activities described in ethnohistoric accounts relating to consumption, preparation, and storage of subsistence resources. Only a few expectations based on secondary activities are supported. Further work is needed to test these results throughout the Arctic and across time. However, these results suggest that archaeologists can use the direct historical approach, and related ethnographic analogies, directly to interpret archaeofaunal patterning in Thule semi-subterranean houses and middens.

Early fall and late winter diets of migratory caribou in northwest Alaska

Lichens are the primary winter forage for large herds of migratory caribou (Rangifer tarandus). Caribou select for lichens more than they are available across the landscape and they generally avoid, during winter, habitat that has been burned by wildfires for decades while lichen abundance recovers. However, the relative importance of lichens in the diet is subject to debate. From 2010-2013, we conducted one of the largest microhistological studies of the early fall (58 samples from 1 site) and late winter (338 samples from 58 sites) diets of barren-ground caribou. Lichens con­stituted ~ 71% of the late winter diets of caribou in northwest Alaska, whereas moss (11%) and shrubs (9%) were the next most common forage items. Early fall diets were very similar to late winter, perhaps because deciduous vegetation is senescent during both periods. Diets of males, non-pregnant females and pregnant females were not significantly different. Pregnancy was not associated with the abundance of any forage type during winter but was associated with higher physiological stress. This result was expected as fall body condition dictates conception, caribou are ‘capital’ breeders, and gestation can be energetically demanding. Caribou that migrated south (i.e., wintered south of 67.1°N) had lower levels of nutritional stress, higher levels of lichen in the diet, and lower levels of moss and shrubs compared to caribou that did not migrate south. Future investigations into the potential connection between lichen abundance in the winter diet and survivorship, as well as linking the late summer diets of individuals to their reproductive success, should be undertaken.

Flow patterns in the Chukchi Sea based on an ocean reanalysis, June through October 1979–2014

The oceanography of the Arctic is changing, with the potential to restructure the function and production of its ecosystems. The physical oceanographic conditions that have occurred on the Chukchi Sea shelf during June through October of the years 1979–2014 were investigated using the ORAS4 ocean reanalysis product. Time series of vertically integrated temperatures (especially during September and October) indicate greater warming in the first half of the 36-year record. This change in the long-term temperature trend may be in part due to trends in the mean currents, which in Herald Canyon and off the coast of Northwest Alaska tended to be slightly less poleward after 2000. A k-means cluster analysis of monthly mean sea surface height anomaly distributions was used to describe five distinct patterns of flow. Two of the five patterns (clusters 2 and 4) relate to the strength of the Alaskan Coastal Current (ACC). Another pair of patterns (clusters 3 and 5) had their strongest expressions in the northwest Chukchi Sea and relate to periods of weak southeastward versus strong northwestward flow in this region associated with the presence or absence of the Siberian Coastal Current. The fifth pattern (cluster 1) was defined by weak southeastward flow anomalies in the western Chukchi and a slightly suppressed ACC relative to the mean in the eastern Chukchi Sea. The composite sea surface height anomaly patterns of the five cluster types correspond closely with the mean sea level pressure anomaly distributions during the months constituting each cluster type. Our findings for the Chukchi Sea region provide a long-term context for previous field observations and may be useful for interpretation of past ecosystem variations.

Application of a weight of evidence approach to evaluating risks associated with subsistence caribou consumption near a lead/zinc mine

Overland transport of ore concentrate from the Red Dog lead/zinc mine in northwest Alaska to its seaport has historically raised concerns among local subsistence users regarding the potential impacts of fugitive dust from the operation, including the potential uptake of metals into caribou meat. Caribou are an integral part of life for northern Alaska Natives for both subsistence and cultural reasons. The Western Arctic caribou herd, whose range includes the Red Dog mine, transportation corridor, and port site, sometimes overwinter in the vicinity of mine operations. A weight of evidence approach using multiple lines of evidence was used to evaluate potential risks associated with subsistence consumption of caribou harvested near the road and mine. Data from a long-term caribou monitoring program indicate a lack of consistent trends for either increasing or decreasing metals concentrations in caribou muscle, liver, and kidney tissue. Lead, cadmium, and zinc from all tissues were within the range of reference concentrations reported for caribou elsewhere in Northern Alaska. In addition, a site use study based on data from satellite-collared caribou from the Western Arctic Herd showed that caribou utilize the area near the road, port, and mine approximately 1/20th to 1/90th of the time assumed in a human health risk assessment conducted for the site, implying that risks were significantly overestimated in the risk assessment. The results from multiple lines of evidence consistently indicate that fugitive dust emissions from Red Dog Operations are not a significant source of metals in caribou, and that caribou remain safe for human consumption.

The 3.6 ka Aniakchak tephra in the Arctic Ocean: a constraint on the Holocene radiocarbon reservoir age in the Chukchi Sea

Abstract. The caldera-forming eruption of the Aniakchak volcano in the Aleutian Range on the Alaskan Peninsula at 3.6 cal kyr BP was one of the largest Holocene eruptions worldwide. The resulting ash is found as a visible sediment layer in several Alaskan sites and as a cryptotephra on Newfoundland and Greenland. This large geographic distribution, combined with the fact that the eruption is relatively well constrained in time using radiocarbon dating of lake sediments and annual layer counts in ice cores, makes it an excellent stratigraphic marker for dating and correlating mid–late Holocene sediment and paleoclimate records. This study presents the outcome of a targeted search for the Aniakchak tephra in a marine sediment core from the Arctic Ocean, namely Core SWERUS-L2-2-PC1 (2PC), raised from 57 m water depth in Herald Canyon, western Chukchi Sea. High concentrations of tephra shards, with a geochemical signature matching that of Aniakchak ash, were observed across a more than 1.5 m long sediment sequence. Since the primary input of volcanic ash is through atmospheric transport, and assuming that bioturbation can account for mixing up to ca. 10 cm of the marine sediment deposited at the coring site, the broad signal is interpreted as sustained reworking at the sediment source input. The isochron is therefore placed at the base of the sudden increase in tephra concentrations rather than at the maximum concentration. This interpretation of major reworking is strengthened by analysis of grain size distribution which points to ice rafting as an important secondary transport mechanism of volcanic ash. Combined with radiocarbon dates on mollusks in the same sediment core, the volcanic marker is used to calculate a marine radiocarbon reservoir age offset ΔR = 477 ± 60 years. This relatively high value may be explained by the major influence of typically carbon-old Pacific waters, and it agrees well with recent estimates of ΔR along the northwest Alaskan coast, possibly indicating stable oceanographic conditions during the second half of the Holocene. Our use of a volcanic absolute age marker to obtain the marine reservoir age offset is the first of its kind in the Arctic Ocean and provides an important framework for improving chronologies and correlating marine sediment archives in this region. Core 2PC has a high sediment accumulation rate averaging 200 cm kyr−1 throughout the last 4000 years, and the chronology presented here provides a solid base for high-resolution reconstructions of late Holocene climate and ocean variability in the Chukchi Sea.

Marine Resource Intensification and the Reorganization of Lithic Technologies during the Middle-Late Holocene in Northwest Alaska

ABSTRACTThis study uses lithic technological organization from two successive Middle–Late Holocene archaeological cultures in northwest Alaska to test hypotheses about marine resource intensification through time. Researchers argue that maritime adaptations in northwest Alaska progressed from supplementary seasonal exploitation towards a highly complex, year-round reliance on marine resources. Robust faunal assemblages and organic technologies necessary to demonstrate this developmental transformation are generally lacking in sites from this time period. Instead, our primary sources of data are site locations, features, and lithic technology. Theorists have shown that technological organization, including lithic components, is greatly influenced by subsistence strategy and residential mobility. In theory, an increased reliance on marine resources should result in increased technological complexity, greater use of local raw materials, and overall less concern with optimizing size and weight of tools. I test these hypotheses using Arctic Small Tool and Norton tradition lithic assemblages from the stratified, multi-component site of Iyatayet, located in northwest Alaska. The results indicate technological organization of the later culture differed in many important ways from the earlier group, supporting interpretations of reduced mobility and a greater reliance on resources from the sea through time.

Promoting Community Conversations About Research to End Suicide: learning and behavioural outcomes of a training-of-trainers model to facilitate grassroots community health education to address Indigenous youth suicide prevention

ABSTRACTAlaska Native (AN) youth suicide remains a substantial and recalcitrant health disparity, especially in rural/remote communities. Promoting Community Conversations About Research to End Suicide (PC CARES) is a community health intervention that responds to the need for culturally responsive and evidence-supported prevention practice, using a grassroots approach to spark multilevel and community-based efforts for suicide prevention. This paper describes theoretical and practical considerations of the approach, and assesses the feasibility and preliminary learning and behavioural outcomes of the training-of-trainers model. It details the training of a first cohort of intervention facilitators in Northwest Alaska (NWA). Thirty-two people from 11 NWA village communities completed the PC CARES facilitator training, preparing them to implement the intervention in their home communities. Facilitator pre-post surveys focused on readiness to facilitate, a group quiz assessed participants’ understanding of relevant research evidence, and practice facilitation exercises demonstrated competency. Curriculum fidelity and accuracy scores were calculated using audio recordings from learning circles conducted by facilitators in their home communities. Facilitator reflections describe the successes of the model and identify several areas for improvement. As of March 2017, 20 of the 32 trained facilitators in 10 of the 11 participating villages have hosted 54 LCs, with a total of 309 unique community members. Coding of these LCs by 2 independent raters indicate acceptable levels of fidelity and accurate dissemination of research evidence by facilitators. Facilitator reflections were positive overall, suggesting PC CARES is feasible, acceptable and potentially impactful as a way to translate research to practice in under-resourced, rural AN communities. PC CARES represents a practical community education and mobilisation approach to Indigenous youth suicide prevention that displays preliminary success in learning and behavioural outcomes of local facilitators.

Where the wild things are [climate change and conservation

Climate change is affecting the natural world. Can technology help conservationists protect animals before it's too late, or are there other more pressing threats for them to deal with. In September 2016, a dead fin whale washed up on a Devon beach. Over the last few months, 30 sperm whales have beached around the British, German, French and Dutch coasts. Early in October, 6,000 Pacific walruses arrived on a beach in north-west Alaska. Around the same time, an Exeter University study concluded that Cornish cod may have trouble reproducing when they move northwards along the British coast, and Manchester University researchers claimed that the natural world might soon face the crisis of species splintering into isolated populations. These are just a few effects that climate change is already having on the natural world. As global and local temperatures rise, land and marine habitats change, affecting the animals reliant on those habitats.

Ten years of measurements and modeling of soil temperature changes and their effects on permafrost in Northwestern Alaska

Multiple studies demonstrate Northwest Alaska and the Alaskan North Slope are warming. Melting permafrost causes surface destabilization and ecological changes. Here, we use thermistors permanently installed in 1996 in a borehole in northwestern Alaska to study past, present, and future ground and subsurface temperature change, and from this, forecast future permafrost degradation in the region. We measure and model Ground Surface Temperature (GST) warming trends for a 10year period using equilibrium Temperature-Depth (TD) measurements from borehole T96-012, located near the Red Dog Mine in northwestern Alaska—part of the Arctic ecosystem where a continuous permafrost layer exists. Temperature measurements from 1996 to 2006 indicate the subsurface has clearly warmed at depths shallower than 70m. Seasonal climate effects are visible in the data to a depth of 30m based on a visible sinusoidal pattern in the TD plots that correlate with season patterns. Using numerical models constrained by thermal conductivity and temperature measurements at the site, we show that steady warming at depths of ~30 to 70m is most likely the direct result of longer term (decadal-scale) surface warming. The analysis indicates the GST in the region is warming at ~0.44±0.05°C/decade, a value consistent with Surface Air Temperature (SAT) warming of ~1.0±0.8°C/decade observed at Red Dog Mine, but with much lower uncertainty. The high annual variability in the SAT signal produces significant uncertainty in SAT trends. The high annual variability is filtered out of the GST signal by the low thermal diffusivity of the subsurface. Comparison of our results to recent permafrost monitoring studies suggests changes in latitude in the polar regions significantly impacts warming rates. North Slope average GST warming is ~0.9±0.5°C/decade, double our observations at RDM, but within error. The RDM warming rate is within the warming variation observed in eastern Alaska, 0.36–0.71°C/decade, which suggests changes in longitude produce a smaller impact but have warming variability likely related to ecosystem, elevation, microclimates, etc. changes. We also forward model future warming by assuming a 1D diffusive heat flow model and incorporating latent heat effects for permafrost melting. Our analysis indicates ~1 to 4m of loss at the upper permafrost boundary, a ~145±100% increase in the active layer thickness by 2055. If warming continues at a constant rate of ~0.44±0.05°C/decade, we estimate the 125m thick zone of permafrost at this site will completely melt by ~2150. Permafrost is expected to melt by ~2200, ~2110, or ~2080, if the rate of warming is altered to 0.25, 0.90, or 2.0°C/decade, respectively, as an array of different climate models suggest. Since our model assumes no advection of heat (a more efficient heat transport mechanism), and no accelerated warming, our current prediction of complete permafrost loss by 2150 may overestimate the residence time of permafrost in this region of Northwest Alaska.

Evidence of Eurasian metal alloys on the Alaskan coast in prehistory

Six metal and composite metal artifacts were excavated from a late prehistoric archaeological context at Cape Espenberg on the northern coast of the Seward Peninsula in Alaska. X-ray fluorescence identified two of these artifacts as smelted industrial alloys with large proportions of tin and lead. The presence of smelted alloys in a prehistoric Inuit context in northwest Alaska is demonstrated here for the first time and indicates the movement of Eurasian metal across the Bering Strait into North America before sustained contact with Europeans.

Genetic stock identification of immature chum salmon (Oncorhynchus keta) in the western Bering Sea, 2004

Genetic stock identification studies have been widely applied to Pacific salmon species to estimate stock composition of complex mixed-stock fisheries. In a September-October 2004 survey, 739 chum salmon (Oncorhynchus keta) specimens were collected from 23 stations in the western Bering Sea. We determined the genetic stock composition of immature chum salmon based on the previous mitochondria DNA baseline. Each regional estimate was computed based on the conditional maximum likelihood method using 1,000 bootstrap resampling and then pooled to the major regional groups: Korea - Japan - Primorie (KJP) / Russia (RU) / Northwest Alaska (NWA) / Alaska Peninsula - Southcentral Alaska - Southeast Alaska - British Columbia - Washington (ONA). The stock composition of immature chum salmon in the western Bering Sea was a mix of 0.424 KJP, 0.421 RU, 0.116 NWA, and 0.039 ONA stocks. During the study period, the contribution of Asian chum salmon stocks gradually changed from RU to KJP stock. In addition, North American populations from NWA and ONA were small but present near the vicinity of the Russian coast and the Commander Islands, suggesting that the study areas in the western Bering Sea were an important migration route for Pacific chum salmon originating both from Asia and North America during the months of September and October. These results make it possible to better understand the chum salmon stock composition of the mixed-stock fisheries in the western Bering Sea and the stock-specific distribution pattern of chum salmon on the high-seas.

A Clay source provenance survey in Northwest Alaska: Late Holocene ceramic production in the Arctic

Ceramic compositional analysis can contribute to the study of late Holocene Arctic hunter-gatherer social interaction through reconstruction of past ceramic distribution patterns. The results of an ethnographically informed clay source survey in Northwest Alaska are presented here. The survey provided contextual data on clay depositional environments, clay variability, and local environmental factors that influenced pre-contact clay availability. Geochemical analysis of clays and tempers clarified the location of ceramic production zones. Concurrence between survey results and ethnographic data highlights the persistence of clay knowledge despite post-contact absence of pottery making. This research demonstrates that ethnographically informed source survey can aid in interpreting ceramic geochemical data and yield important insights into pre-contact ceramic production processes.

Seasonality of suicide behavior in Northwest Alaska: 1990–2009

ObjectivesSuicide is a leading cause of death worldwide, and disproportionately affects Indigenous populations. Seasonal suicide patterns are variable in the literature, and could offer novel approaches to the timing and focus of prevention efforts if better understood. With a suicide surveillance system in place since 1989, this study offers an unprecedented opportunity to explore seasonal variations in both fatal and non-fatal suicide behavior in an Indigenous Arctic region. Study designCross-sectional. MethodsIn this descriptive study, we analyzed data collected from 1990 to 2009 in the rural northwest region of Alaska, both graphically and using the chi-squared test for multinomials. ResultsWe found a significant monthly variation for suicide attempts, with a peak in suicide behavior observed between April and August (P = 0.0002). Monthly variation was more pronounced among individuals ≤29 years of age, and was present in both males and females, although the seasonal pattern differed by sex. ConclusionsOur findings of a significant seasonal pattern in suicide behavior, with monthly variation (summer peak) in non-fatal suicide behavior among younger age groups, and among both males and females can assist planners in targeting subpopulations for prevention at different times of the year.

Evidence of soil nutrient availability as the proximate constraint on growth of treeline trees in northwest Alaska: reply.

Evidence of soil nutrient availability as the proximate constraint on growth of treeline trees in northwest Alaska: reply.