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Environmental Limits of Tall Shrubs in Alaska's Arctic National Parks.

ABSTRACT: We sampled shrub canopy volume (height times area) and environmental factors (soil wetness, soil depth of thaw, soil pH, mean July air temperature, and typical date of spring snow loss) on 471 plots across five National Park Service units in northern Alaska. Our goal was to determine the environments where tall shrubs thrive and use this information to predict the location of future shrub expansion. The study area covers over 80,000 km2 and has mostly tundra vegetation. Large canopy volumes were uncommon, with volumes over 0.5 m3/m2 present on just 8% of plots. Shrub canopy volumes were highest where mean July temperatures were above 10.5°C and on weakly acid to neutral soils (pH of 6 to 7) with deep summer thaw (>80 cm) and good drainage. On many sites, flooding helped maintain favorable soil conditions for shrub growth. Canopy volumes were highest where the typical snow loss date was near 20 May; these represent sites that are neither strongly wind-scoured in the winter nor late to melt from deep snowdrifts. Individual species varied widely in the canopy volumes they attained and their response to the environmental factors. Betula sp. shrubs were the most common and quite tolerant of soil acidity, cold July temperatures, and shallow thaw depths, but they did not form high-volume canopies under these conditions. Alnus viridis formed the largest canopies and was tolerant of soil acidity down to about pH 5, but required more summer warmth (over 12°C) than the other species. The Salix species varied widely from S. pulchra, tolerant of wet and moderately acid soils, to S. alaxensis, requiring well-drained soils with near neutral pH. Nearly half of the land area in ARCN has mean July temperatures of 10.5 to 12.5°C, where 2°C of warming would bring temperatures into the range needed for all of the potential tall shrub species to form large canopies. However, limitations in the other environmental factors would probably prevent the formation of large shrub canopies on at least half of the land area with newly favorable temperatures after 2°C of warming.

SUBMITTER: Swanson DK

PROVIDER: S-EPMC4574981 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:One of the most palpable effects of warming in Arctic ecosystems is shrub expansion above the tree line. However, previous studies have found that reindeer can influence plant community responses to warming and inhibit shrubification of the tundra.We revisited grazed (ambient) and ungrazed study plots (exclosures), at the southern as well as the northern limits of the Swedish alpine region, to study long-term grazing effects and vegetation changes in response to increasing temperatures between 1995 and 2011, in two vegetation types (shrub heath and mountain birch forest).In the field layer at the shrub heath sites, evergreen dwarf shrubs had increased in cover from 26% to 49% but were unaffected by grazing. Deciduous dwarf and tall shrubs also showed significant, though smaller, increases over time. At the birch forest sites, the increase was similar for evergreen dwarf shrubs (20-48%) but deciduous tall shrubs did not show the same consistent increase over time as in the shrub heath.The cover and height of the shrub layer were significantly greater in exclosures at the shrub heath sites, but no significant treatment effects were found on species richness or diversity.July soil temperatures and growing season thawing degree days (TDD) were higher in exclosures at all but one site, and there was a significant negative correlation between mean shrub layer height and soil TDD at the shrub heath sites. Synthesis. This study shows that shrub expansion is occurring rapidly in the Scandes mountain range, both above and below the tree line. Tall, deciduous shrubs had benefitted significantly from grazing exclosure, both in terms of cover and height, which in turn lowered summer soil temperatures. However, the overriding vegetation shift across our sites was the striking increase in evergreen dwarf shrubs, which were not influenced by grazing. As the effects of an increase in evergreen dwarf shrubs and more recalcitrant plant litter may to some degree counteract some of the effects of an increase in deciduous tall shrubs, herbivore influence on shrub interactions is potentially of great importance for shaping arctic shrub expansion and its associated ecosystem effects.

Project description:BackgroundWild berries are a valued traditional food in Alaska. Phytochemicals in wild berries may contribute to the prevention of vascular disease, cancer and cognitive decline, making berry consumption important to community health in rural areas. Little was known regarding which species of berries were important to Alaskan communities, the number of species typically picked in communities and whether recent environmental change has affected berry abundance or quality.ObjectiveTo identify species of wild berries that were consumed by people in different ecological regions of Alaska and to determine if perceived berry abundance was changing for some species or in some regions.DesignWe asked tribal environmental managers throughout Alaska for their views on which among 12 types of wild berries were important to their communities and whether berry harvests over the past decade were different than in previous years. We received responses from 96 individuals in 73 communities.ResultsBerries that were considered very important to communities differed among ecological regions of Alaska. Low-bush blueberry (Vaccinium uliginosum and V. caespitosum), cloudberry (Rubus chamaemorus) and salmonberry (Rubus spectabilis) were most frequently identified as very important berries for communities in the boreal, polar and maritime ecoregions, respectively. For 7 of the 12 berries on the survey, a majority of respondents indicated that in the past decade abundance had either declined or become more variable.ConclusionsOur study is an example of how environmental managers and participants in local observer networks can report on the status of wild resources in rural Alaska. Their observations suggest that there have been changes in the productivity of some wild berries in the past decade, resulting in greater uncertainty among communities regarding the security of berry harvests. Monitoring and experimental studies are needed to determine how environmental change may affect berry abundance.

Project description:When balancing environmental preservation and economic development, it is critical to evaluate how taxpayers value national park land and for what they are valuing it. One key component of this evaluation is to calculate a "passive use value," or the willingness to pay (WTP), for protection of land that may never directly be used, and to determine what benefits of land protection motivate this passive use value. We estimated the WTP for a 5% expansion of Denali National Park in Alaska (an expansion of 325,340 acres) using a questionnaire and the contingent valuation method. The survey first educated respondents on Alaskan geography, the current status of protected land and wildlife in Alaska, and common arguments for and against National Park expansion. The survey then described a proposal to expand the Denali National Park and asked a series of questions designed to bound the respondents WTP. Finally, the survey asked respondents to answer questions about what motivated their support or disapproval for the program. Multiple methodologies were used to estimate the national average WTP, resulting in a WTP range of a single payment of $77 to $409. This is estimated to be a total WTP of $15.1 billion to $79.3 billion for all individuals aged 18 to 64 in the United States, or $363.1 million to $1.91 billion per year in 2017 dollars. Respondents to the survey indicated that their support is driven primarily by increased protection from oil spills (85.8% deemed this very important or important), by increasing and protecting Alaska's biodiversity (84.3%), and preserving Alaska's beauty (84.2%). These results can help inform recent, current, and future debates about land use. President Obama significantly expanded land protections, while President Trump is continuing to scale back land protections, including opening up untouched land in Alaska in the Arctic National Wildlife Refuge for oil drilling. These results suggest that there are significant passive use values that should be considered when deciding whether to expand or reduce protection of land. Given that passive use values are significant, this suggests that the economic benefits must be large to tip a cost-benefit analysis in favor of reduced land protections.

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Environmental Limits of Tall Shrubs in Alaska's Arctic National Parks.

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