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81 results for “treeline”
Age and Size of Smith Firs at Treeline in Tibet 1700-2013
The most widespread response to global warming among alpine treeline ecotones is not an upward shift, but an increase in tree density. However, the impact of increasing density on interactions among trees at treeline is not well understood. Here, we test if treeline densification induced by climatic warming leads to increasing intraspecific competition. We mapped and measured the size and age of Smith fir trees growing in two treelines located in the southeastern Tibetan Plateau. We used spatial point-pattern and codispersion analyses to describe the spatial association and covariation among seedlings, juveniles, and adults grouped in 30-year age classes from the 1860s to the present. Effects of competition on tree height and regeneration were inferred from bivariate mark-correlations. Since the 1950s, a rapid densification occurred at both sites in response to climatic warming. Competition between adults and juveniles or seedlings at small scales intensified as density increased. Encroachment negatively affected height growth and further reduced recruitment around mature trees. We infer that tree recruitment at the study treelines was more cold-limited prior to 1950 and shifted to a less temperature-constrained regime in response to climatic warming. Therefore, the ongoing densification and encroachment of alpine treelines could alter the way climate drives their transitions towards subalpine forests.
Crossing Treeline: Bacterioplankton community composition in alpine and subalpine lakes of the Rocky Mountain southern ecoregion and associated physical and chemical characteristics
This dataset includes lake water samples collected in the summer of 2016 from 16 different mountain lakes in the Rocky mountains in both Rocky Mountain National Park and the Snowy Range of southern Wyoming. Each lake was sampled twice: once in the early summer when hydrologic connections with the surrounding terrestrial environment were high and again in the late summer when hydrologic connections were low. The main goal of the study was to compare communities of bacterioplankton in alpine and subalpine lakes to determine if communities differed across treeline as soil microbes in the surrounding terrestrial environment were. To do so, we collected water samples from the deepest point of each lake, mixed it with a surface water sample and characterized bacterioplankton communities with 16S sequencing technology. Additionally, we wanted to identify abiotic factors that may correlate with community dissimilarity and characterized a suite of chemical attributes for each lake. Lake characteristics reported included surface temperature, soluble reactive phosphorous (SRP), ammonia (NH3+), pH, total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and total dissolved organic carbon (DOC), and chlorophyll a (chl-a).
Global Alpine Treeline Elevational Transects
<p>Elevational transects within alpine treeline ecotones worldwide.</p>
Data from: Radial stem growth of the clonal shrub Alnus alnobetula at treeline is constrained by summer temperature and winter desiccation and differs in carbon allocation strategy compared to co-occurring Pinus cembra
<p><strong>Data are documented in the following article:</strong></p> <p>Oberhuber W., G Wieser, F. Bernich, A. Gruber (2022) Radial stem growth of the clonal shrub <em>Alnus alnobetula</em> at treeline is constrained by summer temperature and winter desiccation and differs in carbon allocation strategy compared to co-occurring <em>Pinus cembra</em>. Forests 2022, 13, 440. doi: 10.3390/f13030440.</p> <p> </p> <p><strong>Summary:</strong></p> <p>Global change is affecting species areal distribution in many regions. A better understanding of how land-use change and climate warming affects shrub growth is essential for improved predictions of forest dynamics at the alpine treeline. Evaluation of radial stem growth of the clonal shrub <em>Alnus alnobetula</em> (= <em>Alnus viridis</em>) and the co-occurring tree species Swiss stone pine (<em>Pinus cembra</em>) within an alpine treeline ecotone revealed that mean ring width of nitrogen fixing <em>A. alnobetula</em> was about four times lower compared to <em>P. cembra</em>. Our findings are based on ring width data from <em>A. alnobetula</em> and <em>P. cembra</em> stems sampled at the alpine treeline ecotone on Mt. Patscherkofel (47°12’N, 11°27’E, Central European Alps, Austria, elevation range 2050 to 2190 m asl). Ring width time series include 86 radii from 51 stems of <em>A. alnobetula</em> (stems had mean age of 18±7 yrs) and 24 radii from 16 stems of <em>P. cembra </em>(18±4 yrs). We explain our findings by different carbon allocation strategies, i.e., preference of “vertical” stem growth in late successional <em>P. cembra</em> vs. favoring “horizontal” spread in the pioneer shrub<em> A. alnobetula.</em> By favouring clonal propagation over individual stem growth <em>A. alnobetula</em> is able to quickly spread at the alpine treeline ecotone.</p>
Nitrogen cycling at treeline. I. Study Sites and Vegetation
We studied spatial and temporal patterns of nitrogen pools and fluxes in soils at treeline and forested sites within three mountain ranges across a 785 km transect in Alaska during 2001- 2002. We measured pools of soil mineral (ammonium and nitrate) and organic (amino acid and microbial biomass) nitrogen, in situ rates of net mineralization, net nitrification, net amino acid production, and decomposition, as well as soil carbon turnover in a laboratory incubation experiment. A complete characterization of the study can be found in Loomis et al. (2006).
Nitrogen cycling at treeline. II. Percent Soil Carbon and Nitrogen
We studied spatial and temporal patterns of nitrogen pools and fluxes in soils at treeline and forested sites within three mountain ranges across a 785 km transect in Alaska during 2001- 2002. We measured pools of soil mineral (ammonium and nitrate) and organic (amino acid and microbial biomass) nitrogen, in situ rates of net mineralization, net nitrification, net amino acid production, and decomposition, as well as soil carbon turnover in a laboratory incubation experiment. A complete characterization of the study can be found in Loomis et al. (2006).
Nitrogen cycling at treeline. III. Total Soil Carbon and Nitrogen Content
We studied spatial and temporal patterns of nitrogen pools and fluxes in soils at treeline and forested sites within three mountain ranges across a 785 km transect in Alaska during 2001- 2002. We measured pools of soil mineral (ammonium and nitrate) and organic (amino acid and microbial biomass) nitrogen, in situ rates of net mineralization, net nitrification, net amino acid production, and decomposition, as well as soil carbon turnover in a laboratory incubation experiment. A complete characterization of the study can be found in Loomis et al. (2006).
Nitrogen cycling at treeline. IV. Soil Profile Descriptions
We studied spatial and temporal patterns of nitrogen pools and fluxes in soils at treeline and forested sites within three mountain ranges across a 785 km transect in Alaska during 2001- 2002. We measured pools of soil mineral (ammonium and nitrate) and organic (amino acid and microbial biomass) nitrogen, in situ rates of net mineralization, net nitrification, net amino acid production, and decomposition, as well as soil carbon turnover in a laboratory incubation experiment. A complete characterization of the study can be found in Loomis et al. (2006).
Nitrogen cycling at treeline V. Insitu Nitrogen mineralization
To assess spatial and seasonal patterns of pools and fluxes of dissolved inorganic- N (DIN), amino acid- N (AAN) and microbial biomass N (MBN), we conducted in situ soil incubations at four time periods during May 2001 - May 2002: spring thaw, peak growing season, fall senescence and over-winter. The goal was to be consistent in sampling each of these time periods within each mountain range, which was possible due to the 3-4 week lag in phenology (e.g. budbreak or initiation of senescence) between the southernmost and northernmost sites. Sites were sampled in order from south to north. During the spring 2002 sampling period, soils in the Brooks Range thawed prior to those in the White Mts. and the sampling sequence was adjusted to accommodate this. Within each treeline or forested sub-site, a 50 m transect was established parallel with the slope contour of the mountain. Six points were randomly selected along each transect, and soils were sampled near these points for the entire year. Rates of net DIN mineralization and net AAN production were measured using an in situ buried bag technique (Robertson et al., 1999). We used a 6.7 cm diameter steel corer fitted with a perforated, plastic sleeve to collect paired adjacent soil cores, and sampled below the live moss and detritus layers to a depth of 20 cm. The function of the perforated sleeve was to maintain structural integrity of the soil core during sampling. The perforated sleeve containing the intact core was then placed in a 1 mil breathable polyethylene bag followed by a fine mesh bag, gently returned to the original location, covered with litter and left to incubate. Incubation length was 4 weeks for the spring, growing season, and senescence sampling periods, and from September 2001 to early June 2002 for the over-winter sampling period. The second core in each pair was stored on ice and transported to the laboratory in Fairbanks. Soils were rocky at some sites and sampling to 20 cm was not possible; for these
Nitrogen cycling at treeline VI. Common Litter Decomposition
To assess spatial and seasonal patterns of pools and fluxes of dissolved inorganic- N (DIN), amino acid- N (AAN) and microbial biomass N (MBN), we conducted in situ soil incubations at four time periods during May 2001 - May 2002: spring thaw, peak growing season, fall senescence and over-winter. The goal was to be consistent in sampling each of these time periods within each mountain range, which was possible due to the 3-4 week lag in phenology (e.g. budbreak or initiation of senescence) between the southernmost and northernmost sites. Sites were sampled in order from south to north. During the spring 2002 sampling period, soils in the Brooks Range thawed prior to those in the White Mts. and the sampling sequence was adjusted to accommodate this. Within each treeline or forested sub-site, a 50 m transect was established parallel with the slope contour of the mountain. Six points were randomly selected along each transect, and soils were sampled near these points for the entire year. Rates of net DIN mineralization and net AAN production were measured using an in situ buried bag technique (Robertson et al., 1999). We used a 6.7 cm diameter steel corer fitted with a perforated, plastic sleeve to collect paired adjacent soil cores, and sampled below the live moss and detritus layers to a depth of 20 cm. The function of the perforated sleeve was to maintain structural integrity of the soil core during sampling. The perforated sleeve containing the intact core was then placed in a 1 mil breathable polyethylene bag followed by a fine mesh bag, gently returned to the original location, covered with litter and left to incubate. Incubation length was 4 weeks for the spring, growing season, and senescence sampling periods, and from September 2001 to early June 2002 for the over-winter sampling period. The second core in each pair was stored on ice and transported to the laboratory in Fairbanks. Soils were rocky at some sites and sampling to 20 cm was not possible; for these
Nitrogen cycling at treeline VII. Laboratory Decomposition
To assess spatial and seasonal patterns of pools and fluxes of dissolved inorganic- N (DIN), amino acid- N (AAN) and microbial biomass N (MBN), we conducted in situ soil incubations at four time periods during May 2001 - May 2002: spring thaw, peak growing season, fall senescence and over-winter. The goal was to be consistent in sampling each of these time periods within each mountain range, which was possible due to the 3-4 week lag in phenology (e.g. budbreak or initiation of senescence) between the southernmost and northernmost sites. Sites were sampled in order from south to north. During the spring 2002 sampling period, soils in the Brooks Range thawed prior to those in the White Mts. and the sampling sequence was adjusted to accommodate this. Within each treeline or forested sub-site, a 50 m transect was established parallel with the slope contour of the mountain. Six points were randomly selected along each transect, and soils were sampled near these points for the entire year. Rates of net DIN mineralization and net AAN production were measured using an in situ buried bag technique (Robertson et al., 1999). We used a 6.7 cm diameter steel corer fitted with a perforated, plastic sleeve to collect paired adjacent soil cores, and sampled below the live moss and detritus layers to a depth of 20 cm. The function of the perforated sleeve was to maintain structural integrity of the soil core during sampling. The perforated sleeve containing the intact core was then placed in a 1 mil breathable polyethylene bag followed by a fine mesh bag, gently returned to the original location, covered with litter and left to incubate. Incubation length was 4 weeks for the spring, growing season, and senescence sampling periods, and from September 2001 to early June 2002 for the over-winter sampling period. The second core in each pair was stored on ice and transported to the laboratory in Fairbanks. Soils were rocky at some sites and sampling to 20 cm was not possible; for these
White spruce demography and herbivory by snowshoe hares measured at latitudinal treeline in the Brooks Range, AK I - Site Data
Treelines in Alaska are advancing in elevation and latitude because of climate warming, which is expanding the habitat available for boreal wildlife species, including snowshoe hares (Lepus americanus). Snowshoe hares are already present in tall shrub communities beyond treeline and are the main browser of white spruce (Picea glauca), the dominant tree species at treeline in Alaska. We investigated the processes involved in a 'snowshoe hare filter' to white spruce establishment near latitudinal treeline in the Brooks Range, Alaska. Site variables collected included latitude, landscape position, vegetative cover, and the density of white spruce seedlings, saplings and trees.
White spruce demography and herbivory by snowshoe hares measured at latitudinal treeline in the Brooks Range, AK II - Sub Plot Data
Treelines in Alaska are advancing in elevation and latitude because of climate warming, which is expanding the habitat available for boreal wildlife species, including snowshoe hares (Lepus americanus). Snowshoe hares are already present in tall shrub communities beyond treeline and are the main browser of white spruce (Picea glauca), the dominant tree species at treeline in Alaska. We investigated the processes involved in a 'snowshoe hare filter' to white spruce establishment near latitudinal treeline in the Brooks Range, Alaska. We hypothesized that surrounding vegetation would influence the likelihood of spruce being browsed by hares. Therefore, at each plot we estimated ramet density for all associated woody vegetation using one square-meter subplots. Within these subplots we also counted the total number of hare fecal pellets found on the ground.
White spruce demography and herbivory by snowshoe hares measured at latitudinal treeline in the Brooks Range, AK III - Spruce Data
Treelines in Alaska are advancing in elevation and latitude because of climate warming, which is expanding the habitat available for boreal wildlife species, including snowshoe hares (Lepus americanus). Snowshoe hares are already present in tall shrub communities beyond treeline and are the main browser of white spruce (Picea glauca), the dominant tree species at treeline in Alaska. We investigated the processes involved in a 'snowshoe hare filter' to white spruce establishment near latitudinal treeline in the Brooks Range, Alaska. To understand how hare browsing may affect the rate at which seedlings escape herbivory, we measured several demographic attributes of white spruce in, including spruce height, basal diameter, browsing history and age.
Soil inorganic and organic property data for subalpine forest, treeline, and alpine zone, 1999.
This study was initiated to examine the nitrogen content of three montane soils: subalpine, treeline and alpine; and to determine if the differences in soil nitrogen content were attributed to plant community and elevation. Soil organic matter, soil carbon, bulk density, pH and soil moisture were also measured for each site. Soil samples were collected from 64 total plots [22 subalpine,15 treeline and 27 alpine sites]. The subalpine site plots included aspen, fir, lodgepole, spruce and meadow vegetation cover. The treeline site plots included fir, spruce and meadow vegetation cover. The alpine site plots included dry meadow and mesic meadow fertilization (control, N, P, NP) plots. Soil cores were removed with 3.5-cm interior diameter PVC pipe that was driven into the soil by use of a rubber mallet. The minimum depth of individual cores was 10 cm. Cores were taken at each site three times over the period between 29 June 1999 and 29 July 1999.
Genetic basis of growth reaction to drought stress differs in contrasting high-latitude treeline ecotones of a widespread conifer
<p>Raw and filtered SNP data and raw tree ring data of the analysed trees. R scripts for SNP filtering, phenotypic data and genotype-phenotype association analysis. </p>
Data from: Treeline – quo vadis? an ecophysiological approach
<p><strong>Data are documented in the following article:</strong></p> <p>Gruber A., W. Oberhuber, G. Wieser (2022) Treeline-Quo Vadis? An ecophysiological approach. Forests 2022, 13,857; doi: 10.3390/f13060857.</p> <p><strong>Summary:</strong></p> <p>At high elevation or latitude, the margin of the life-form tree is set by low temperature, with trees defined as upright woody species taller than 2-3 m. As the climate driven limit of the life-form tree at high elevation is set by low temperature, climate warming will cause treelines to move upwards. As shown in a case study in the Central European Alps, open and dense stands at treeline differ with respect to basal area growth. In an open stand recent climate warming triggered an enhancement in basal area increment of solitary <em>Pinus cembra</em> (L.) and <em>Larix decidua</em> (Mill.) trees. In contrary, in a dense stand nearby, an adequate growth response was almost lacking. This suggests that at the alpine treeline, due to competition for light, nutrients and soil water availability, the positive effect of climate warming on individual tree growth is suppressed with increasing tree density.</p>
Data for: Red foxes enhance long-term tree growth near the Arctic treeline
<p>Recent climate warming is expected to increase tree growth and productivity, substantially altering ecological function and boundaries in northern ecosystems. Temperature and precipitation largely determine the range and growth of trees in any biome, yet variations in microsite conditions can also influence tree growth on a finer scale. By altering essential resources and habitat conditions, terrestrial organisms could modify Subarctic tree growth. Red foxes (<em>Vulpes vulpes</em>) are found in most terrestrial ecosystems and are considered ecosystem engineers by enriching soil nutrients and plant composition through denning. Added soil nutrients from prey remains, feces, and urine could benefit tree growth in Subarctic regions by alleviating soil nutrient limitations. We examined growth in white spruce (<em>Picea glauca</em>) trees growing on eight red fox dens and paired control sites near Churchill, Manitoba, Canada, at the Arctic treeline. Radial growth was 55% higher for trees on dens than on control sites between 1897 and 2017, despite similarities in tree ages, densities, and regional climate across all sites. By promoting tree growth near the treeline, red foxes may influence the position of the Arctic treeline. Although the impacts on tree growth largely depend on the spatial distribution of dens and predator activity in the boreal forest, predators can create distinct microhabitats across the landscape via ecosystem engineering processes, leading to increased vegetation productivity, persisting over many decades.</p>
Insect seed and cone predation reduces reproductive potential of treeline conifers across northern Canada
<p><strong>Aim</strong>: Altitudinal and latitudinal treeline ecotones have not consistently responded to climate warming the in direction and/or magnitude as predicted by climate alone, suggesting that non-climatic mechanisms (e.g., biotic interactions) are also mediating treeline range dynamics. Through a collaborative research approach, we assessed environmental conditions associated with insect cone granivory and how this biotic interaction may govern the reproductive potential, and therefore range dynamics, of spruce-dominated treelines across northern Canada. </p> <p><strong>Location</strong>: Ten boreal forest treelines, tundra and alpine, from Yukon to Newfoundland and Labrador, Canada</p> <p><strong>Taxa</strong>: White spruce (<em>Picea</em> <em>glauca</em> (Moench) Voss), Black spruce (<em>Picea</em> <em>mariana</em> (Mill.) B.S.P.), <em>Strobilomyia</em> spp., <em>Megastigmus</em> spp.</p> <p><strong>Methods</strong>: Treeline sites were assessed for presence and magnitude of pre-seed dispersal granivory by insects, and viability of available seed was determined. We quantified stand density metrics, organic layer depth, and understory vegetation composition at each location and, subsequently, incorporated those variables into generalized linear mixed models to establish predictors of granivory magnitude and viability of available seed. </p> <p><strong>Results</strong>: Our findings reveal the widespread presence of insect granivory across sites, however, site-specific patterns of granivory were associated with increased moss cover and decreased shrub cover and stand density. While all black-spruce-dominated sites exhibited seed viability rates greater than 50%, the number of seeds produced per cone varied, suggesting that within-site abiotic conditions and biotic interaction pressures limit successful colonization of novel environments in advance of seed dispersal. </p> <p><strong>Main</strong> <strong>Conclusions</strong>: Results from the modelled relationships between cone granivory, seed viability, and environmental conditions represent an essential step toward generalizing how and when biotic interactions across subarctic treelines influence boreal tree range dynamics before seed dispersal. Connections between granivory magnitude and site-level stand density will help establish how treeline form (e.g., discrete or diffuse) may drive patterns of future insect outbreaks under continued climate warming. </p>
Forests on the move: Tracking climate-related treeline changes in mountains of the northeastern United States
<div><em>Aim</em></div> <div>Alpine treeline ecotones are influenced by environmental drivers and are anticipated to shift their locations in response to changing climate. Our goal was to determine the extent of recent climate-induced treeline advance in the northeastern United States, and we hypothesized that treelines have advanced upslope in complex ways depending on treeline structure and environmental conditions.</div> <div> </div> <div><em>Location</em></div> <div>White Mountain National Forest (New Hampshire) and Baxter State Park (Maine), USA.</div> <div> </div> <div><em>Taxon</em></div> <div>High-elevation trees – <em>Abies balsamea, Picea mariana, and Betula cordata</em>. </div> <div> </div> <div><em>Methods</em></div> <div>We compared current and historical high-resolution aerial imagery to quantify the advance of treelines over the last four decades, and link treeline changes to treeline form (demography) and environmental drivers. Spatial analyses were coupled with ground surveys of forest vegetation and topographical features to ground-truth treeline classification and provide information on treeline demography and additional potential drivers of treeline locations. We used multiple linear regression models to examine the importance of both topographic and climatic variables on treeline advance.</div> <div> </div> <div><em>Results</em></div> <div>Regional treelines have significantly shifted upslope over the past several decades (on average by 3 m/decade). Diffuse treelines (low tree densities and temperature limited) experienced significantly greater upslope shifts (5 m/decade) compared to other treeline forms, suggesting that both climate warming and treeline demography are important drivers of treeline shifts. Topographical features (slope, aspect) as well as climate (accumulated growing degree days, AGDD) explained significant variation in the magnitude of treeline advance (R<sup>2</sup> = 0.32).</div> <div> </div> <div><em>Main conclusions</em></div> <div>The observed advance of regional treelines suggests that climate warming induces upslope treeline shifts particularly at higher elevations where greater upslope shifts occurred in areas with lower AGDD. Overall, our findings suggest that diffuse treelines at high-elevations are more a of a result of climate warming than other alpine treeline ecotones and thus they can serve as key indicators of ongoing climatic changes.</div>
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