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With climatic warming, wildfire occurrence is increasing in the boreal forest of interior Alaska. Loss of catchment vegetation during fire can impact streams directly through altered solute and debris inputs and changed light and temperature regimes. Over longer time scales, fire can accelerate permafrost degradation, altering catchment hydrology and stream nutrient dynamics. In 2004, the 217,000 ha Boundary Fire burned 65% of an established study site in the Caribou-Poker Creeks Research Watershed. We used this opportunity to investigate the impact of wildfire on stream chemistry and metabolism in boreal forest catchments. Wildfire impacts on chemistry were evaluated by examining solute chemistry in four catchments from 2002 to 2007. Ecosystem metabolism was measured over the summer of 2005 in one burned and two unburned catchments. Wildfire led to stream nitrate concentration increasing up to threefold, whereas dissolved organic carbon (DOC) and dissolved organic nitrogen concentrations decreased post-fire. Average stream gross primary production in the burned catchment was double that of the unburned sites (2.4 and 1.2 g O2 m−2 day−1, respectively). Respiration rate was also elevated in the burned stream (6.6 g O2 m−2 day−1) compared with the control streams (1.2 and 4.5 g O2 m−2 day−1). Climatic warming has the potential to impact boreal forest streams through permafrost thaw and increased fire frequency, leading to altered solute inputs and production and respiration rates.
Blowing and drifting snow continues to be a transportation and safety hazard with significant economic costs. Critical design criteria for the construction of a living (vegetated) snow fence are reviewed and presented using the most currently available design equations. Coupled with an analysis of climate and topographical data, the design criteria are applied to an area in Rocky Mountain National Park historically prone to snow drifting. The long-term average snow accumulation season (period beginning with the first blowing snow and ending with maximum drift density) was calculated from air temperature as between 4 November and 10 April, and these dates compared well with those based on nearby snow observations. Over the snow accumulation season, the potential for snow transport based on wind characteristics was 21.4 tonnes m−1 (all wind directions), of which 21.0 tonnes m−1 occurred along a mean drifting direction of 259° (nearly perpendicular to the road at the study site). The potential for snow transport based on snow characteristics (754 tonnes m−1) exceeded the potential for snow transport based on wind characteristics, thus indicating that wind was the primary factor controlling drift formation. Using a snow transport of 23.9 tonnes m−1, determined using the long-term average snow water equivalent plus one standard deviation (occurred in three out of 25 years of observations), the required snow fence height needs to be 1.61 m tall, set back 56.4 m from the road. The fence will have a trapping efficiency of 79% when an effective porosity of 50% is achieved. Comparisons of these design parameters to snow drift conditions created behind a structural fence indicated that living snow fence design parameters are likely appropriate and realistic.
Leaf area index (LAI) and total foliar nitrogen (TFN) are important canopy characteristics and crucial variables needed to simulate photosynthesis and ecosystem CO2 fluxes. Although plant communities dominated by Cassiope tetragona are widespread in the Arctic, LAI and TFN for this vegetation type have not been accurately quantified. We address this knowledge gap by (i) direct measurements of LAI and TFN for C. tetragona, and (ii) determining TFN-LAI and LAI–normalized difference vegetation index (NDVI) relationships for typical C. tetragona tundras in the subarctic (Sweden) and High Arctic (Greenland and Svalbard).
Leaves of C. tetragona are 2–6 mm long and closely appressed to their stems forming parallelepiped shoots. We determined the LAI of C. tetragona by measuring the area of the leaves while still attached to the stem, then doubling the resulting one-sided area. TFN was determined from leaf N and biomass. The LAI-NDVI and TFN-LAI relationships showed high correlation and can be used to estimate indirectly LAI and TFN. The LAI-NDVI relationship for C. tetragona vegetation differed from a generic LAI-NDVI relationship for arctic tundra, whereas the TFN-LAI relationship did not. Overall, the LAI of C. tetragona tundra ranged from 0.4 to 1.1 m2 m−2 and TFN from 1.4 to 1.7 g N m−2.
Assisted revegetation is particularly difficult in subarctic and arctic ecosystems where the impact of anthropogenic activities can be extensive and natural plant regeneration is slow. The construction of a military base in the 1950s at Kuujjuarapik–Whapmagoostui in northern Quebec destroyed most of the vegetation cover. Afterwards, other anthropogenic disturbances linked to the village expansion (housing, ATV traffic, pedestrian trampling) have slowed down the recovery process. To provide residents with low-cost but efficient assisted revegetation techniques, we evaluated the performance (seedling emergence, survival, and biomass production) of three indigenous plant species (Leymus mollis, Lathyrus japonicus, Trisetum spicatum) submitted to different levels of mineral and organic fertilizer additions in both a greenhouse experiment and a field plantation in the village. In the greenhouse experiment, moderate mineral fertilization had positive impacts on seedling emergence and both aboveground and belowground biomass of L. mollis. The magnitude of this impact on biomass was greater when mineral fertilization was combined with organic fertilization. The effects of mineral fertilization were negative on the other two species, especially at higher fertilization levels. However, after two growing seasons, a moderate level of mineral fertilizer in the field plantation had positive effects on the cover and aboveground biomass of all three species. Overall, organic fertilization from the substrate of a nearby marsh did not enhance plant performance in either experiment. Planting seeds of L. mollis or T. spicatum in combination with a moderate level of mineral fertilization at the time of planting provides a low-cost assisted revegetation treatment for subarctic villages.
During the last millennium, climatic fluctuations occurred in the Arctic that presumably affected ecosystems and people. Paleoclimatologists recognize that the impacts of these fluctuations were not consistent across space or time; however, archaeologists often cite climatic fluctuations as an impetus for Thule migration and more recent regionalization across the Arctic. An interdisciplinary International Polar Year project is examining possible correlations between climate and cultural changes on Melville Peninsula. To better evaluate the role climate played in cultural change on Melville Peninsula and to place emerging data in context, we present here new syntheses of paleoclimatic and archaeological data from adjacent regions to determine how the data sets articulate. A comparison of high-resolution paleoclimatic records suggests dissimilarities in climatic histories across this transitional area, with Little Ice Age cooling possibly occurring 1–2 centuries earlier west of Melville Peninsula than to the east. Although paleoclimates in the Baffin region to the east may have been more variable, the maritime climate may have contributed to a resource-rich environment, resulting in continuous human occupation. The more stable, and possibly cooler, continental climate to the west of Melville Peninsula could explain the relatively fewer Thule sites. This area, however, was relatively densely used throughout the coldest part of the past millennium and the historic period, likely owing to technological specialization and access to European material culture.
At least four active glaciers are present in the Prokletije Mountains of northern Albania. These glaciers exist at altitudes between 1980 and 2420 m a.s.l.—well below the regional equilibrium line altitude—on shaded northeast-facing slopes prone to avalanche. Glacier-climate modeling suggests that these glaciers require annual accumulation of between 4137 and 5531 mm (water equivalent) to balance melting. A significant proportion of this accumulation is likely to be sourced from windblown snow and, in particular, avalanching snow. It is estimated that the total accumulation needed to balance melting is potentially up to twice the value received from direct precipitation. The presence of these glaciers—some of the southernmost in Europe—at altitudes well below the regional equilibrium line altitude, highlights the importance of local controls on glacier development.
This study presents a new pine (Pinus sylvestris L.) ring-width chronology and a summer temperature reconstruction for the last 400 years from the Khibiny Low Mountains (Kola Peninsula, NW Russia). Pine trees from sites at the altitudinal timberline of Khibiny Mountains show pronounced climatic signals in tree-ring width. We found a strong positive correlation with summer temperature of July–August (r = 0.58). The reconstruction shows lower summer temperatures from a.d. 1630 to 1840, a subsequent warming up to the mid-20th century and a cooling trend afterwards. According to our data, a temperature increase is observed during the past decade. The good coherence of multi-decadal to secular trends of our reconstruction and series of observed solar activity indicate that solar activity may have been one major driving factor of past climate on Kola Peninsula.
We studied the seed bank of abandoned fields in four successional stages (habitat A: 1 year; habitat B: 10 years; habitat C: 20 years; and habitat D: mature meadow) in eastern Tibetan Plateau. The seed density in seed banks decreased with successional age, but species richness and diversity increased, and the highest species diversity and species richness appeared in habitat C. Similarity between the seed bank and vegetation decreased gradually with succession in the whole. The vegetation is more similar to the seed bank in the shallow layer than to the seed bank in the deeper soil, which shows that the vegetation contributes less to the seed bank as soil depth increases. The seed bank was mainly composed of first successional species during the whole successional range. Species of the later successional stages contributed little to the seed bank. Most of species from early successional stage produced longer-lived seeds, which stayed viable in the soil for a long period (more than 20 years). Hypotheses about changes in seed bank during succession, predicting decreasing species richness and seed diversity, were not confirmed. The hypothesis that density of buried seeds declined during succession was confirmed. We conclude that seed bank plays an important role on vegetation in the early succession stage. In the later succession stages, seed bank's role becomes weaker and weaker, and which likely relies on vegetative reproduction and dispersal.
Ecological factors determining the growth of arctic shrubs remain poorly understood, thereby obscuring the current predictions about climate change effects. I conducted a study on the Yamal Peninsula, West Siberia, to find out which factors determine the growth and height of upright willows (Salix glauca and S. lanata). I sampled willow thickets at different slope positions at 13 sites along a 300-km-long north-south transect. The measurements included the height of willow shrubs and the length and diameter of shoots.
The length and diameter of willow shoots increased southwards and with increasing distance from the sea. At the top of the slope and in areas with shallow thaw, the height and growth of willow were low compared to other slope positions and to areas with deep thaw. An increasing level of reindeer (Rangifer tarandus) grazing intensity was associated with decreased height and growth of willow and also associated with reduced foraging activity of willow grouse (Lagopus lagopus).
The results show that even though increasing summer warmth is likely to enhance willow growth, there are other factors such as distance from the sea that also affect the growth and height of willow. The results suggest that reindeer grazing may locally counteract the effects of climate change.
Twelve jack pine (Pinus banksiana) tree-ring chronologies were developed from sites on rock outcrops near Yellowknife, Northwest Territories, Canada. The average chronology length is approximately 180 years spanning the period 1825–2005. The longest extends to 1679, whereas the shortest covers the period 1936–2005. All of the site chronologies are significantly correlated with June, total May–July, June–July, and June–August precipitation, although relations with the single month of June are strongest. June precipitation was reconstructed using a regionally averaged tree-ring chronology. The reconstruction captures 42% of the variance in the instrumental climate record and based on Rbar and EPS statistics is considered robust from 1819 to 2005. Periods of lower June precipitation occurred in 1927–1979, 1880–1893, 1842–1865, 1801–1821, 1776–1796, and 1698–1739. Positive June precipitation anomalies are reconstructed for 1980–1995, 1890–1926, 1822–1841, 1756–1775, and 1687–1697. Throughout the period of reconstruction, there is strong multi-decadal agreement between June precipitation in Yellowknife and other dendrohydrological records from western North America and records of Pacific climate variability. This suggests that large-scale atmospheric patterns influenced by sea surface temperatures (SSTs) in the Pacific basin have controlled continental-scale precipitation patterns at decadal time scales in the Yellowknife region over the past three centuries or more.
Here we present the first tree-ring series (1850–2003) of stable carbon (δ13C) and oxygen (δ18O) isotope ratios from a high-latitude treeline site in northwestern Canada. Both δ13C and δ18O were measured at annual resolution from whole-ring α-cellulose of three white spruce trees (Picea glauca [Moench] Voss) growing in the Mackenzie Delta. There is a strong positive association between δ13C and maximum summer temperatures. This relation likely results from the influence of temperature-induced drought stress on stomatal conductance. Mean summer relative humidity is also significantly correlated, inversely, with δ13C reflecting its direct influence on stomatal conductance. The δ18O record is strongly and positively correlated with early-spring to mid-summer minimum temperatures likely owing to the temperature dependence of δ18O in precipitation and uptake of this water during the growing season. Mean summer relative humidity is also significantly and inversely correlated with δ18O due to leaf water evaporative enrichment. Our δ13C and δ18O records contain a large amount of climate-driven variability indicating their considerable potential to infer past climate changes in the Mackenzie Delta region.
The ectomycorrhizal communities in alpine habitats have been relatively little studied. As global change is predicted to have a large impact in Arctic and alpine environments, it is important to document the fungi of these climatic regions to monitor changes and to understand upcoming successions. This study investigates the ectomycorrhizal community of Dryas octopetala and Salix reticulata on cliff ledges in a mid-alpine setting using the internal transcribed spacer region of nuclear ribosomal DNA for the identification of the fungal component of ectomycorrhizal root tips. It is shown that the community is relatively species rich, with 74 molecular operational taxonomic units (MOTUs)/species, and that it is dominated by Cenococcum geophilum, Thelephoraceae spp., Cortinarius spp., and Sebacinales spp. Furthermore, the dominating species have low specificity regarding the tested hosts and seem likely to be able to facilitate the succession of the alpine tundra to subalpine forest by serving as mycorrhizal partners for establishing pioneer trees.
Several members of the subgenus Amphilaena (Saussurea; Asteraceae) growing at high elevations in the Himalayan region have semi-translucent bracts covering their inflorescences, the function of which is not fully understood. We investigated the thermal benefits of these bracts in Saussurea velutina in situ in the Hengduan Mountains, SW China, and compared the reflectance spectra and anatomical characters of bracts and rosette leaves in the laboratory. After removal of bracts in the field the average inflorescence daytime temperature was 2.5 °C colder than in control plants with intact bracts. Manually opened treatment inflorescences grew slower and set significantly fewer seeds than control inflorescences with bracts intact. The mesophyll of bracts is a single cell layer with a lower reflectance in the infrared range than rosette leaves. We show that the semi-translucent bracts in S. velutina function to ensure warmer temperatures for floral and seed development at high elevations in the Hengduan Mountains.