After his first trip to Alaska in 1930, Bob Marshall returned three times before his early death in 1939. His legacy in the Brooks Range includes the mapping of more than 30 000 km^sup 2^ of ...wilderness (Kauffman, 1992) and two books: Arctic Village (1933), which he wrote after living in Wi seman for about a year, and Arctic Wilderness (1956), which was published after Marshall's death and edited by his brother George. His biggest coup, however, was the naming of two mountains, Frigid Crags and Boreal Mountain: "The mountains became more and more precipitous until finally they culminated in the Gates of the Arctic" (Marshall, 1956:14). he went on to add: "Alaska is unique among all recreational areas belonging to the United States because Alaska is yet largely a wilderness. In the name of a balanced use of American resources, let's keep northern Alaska largely a wilderness." Marshall's call for preservation started a decade-long conservation effort in Alaska. It could be argued that purely the name "The Gates of the Arctic" has instilled a sense of adventure, wilderness, and freedom into thousands of readers and conservationists. all efforts culminated in the establishment and naming of Alaska's second-biggest national park: Gates of the Arctic National Park and Preserve. Kaufmann (1992:69) stated: "Bob Marshall is to the Brooks Range what Henry Thoreau is to the Maine woods and John Muir to the Sierra Nevada." Gates of the Arctic was awarded national monument status on 1 December 1978, and it became a national park and preserve on 2 December 1980. Bob Marshall's dream of keeping northern Alaska largely a wilderness was at least partly realized. We could find only one of the plots Marshall had established in Barrenland Creek: the other had probably washed away. The plot is situated at 67#176;59.920'N and 150#176;33.815'W on the north side of Barrenland Creek near the continental divide on top of the Brooks Range, approximately 5 km north of the current tree line and 200 m higher in elevation (1050 m asl). The current tree line is situated at the North Fork of the Koyukuk River on northand south-facing slopes. White spruce at the North Fork tree line reach 760 m elevation on north-facing slopes and 850 m on south-facing slopes. Preliminary age data suggest establishment before 1700, indicating little or no movement during at least the last 300 years. Barrenland Creek runs west to east in a U-shaped valley completely surrounded by mountains, with large gravel slides on either flank. The plot occupies 3 7times; 3 m on a floodplain north of Barrenland Creek, shortly before the creek enters its canyon. As of the summer of 2001, the four corners were marked with stone piles and three of the four still had Bob Marshall's original willow sticks protruding 50-80 cm above the ground. An old peanut can in one of the stone piles held a note from Sam Wright, reporting that he had found five spruce seedlings alive in 1989. The soil is stony and shallow and probably underlain by permafrost. The two seedlings alive in 2001 were 30 cm in height. They looked healthy and showed recent growth on their tips. An interesting side note is the fact that Les Viereck planted siblings of the seedlings he gave to Sam Wright in 1968 at the University of Alaska Fairbanks. Today they measure about 9 m in height (L. Viereck, pers. comm. September 2001).
Ziel dieser Untersuchung war 1) die Entwicklung eines räumlich expliziten, mittelmaßstäbigen Modells der Klimasensitivität von Weißfichte an der Baumgrenze im Denali Nationalpark (DNP) und Gates of ...the Arctic Nationalpark (GAAR) in Alaska und 2) mit Hilfe dieses Modells die räumlichen Veränderungen des borealen Nadelwaldes unter zukünftiger Erwärmung abzuschätzen. Dazu haben wir zuerst ein Entscheidungsmodell entwickelt, um die Beziehungen zwischen Umweltfaktoren und Baumwuchs näher zu untersuchen, und dann die Ergebnisse mit Hilfe eines GIS-Modells in den Raum extrapoliert. In DNP projiziert unser Modell mögliches Baumsterben an den Unterhängen und Baumgrenzverschiebungen und Erhöhung der Bestandsdichte an den Oberhängen. Falls sich der aktuelle Erwärmungstrend fortsetzt, kann sich die Waldfläche im Straßenkorridor um ca. 50% erhöhen, was dann zu Einschränkungen bei Wildtierbeobachtungen führen würde. In GAAR projiziert unser Modell verstärktes Baumwachstum an den Unterhängen, während sich in Mittel- und Oberhängen die Struktur des Waldes ändern könnte (größere Bestandsdichte bis zu Absterben der Bauminseln). Auf regionaler Ebene sind daher Änderungen der räumlichen Ausdehnung des borealen Waldes möglich (Verschiebung der Baumgrenze). Auf Landschaftsebene sind strukturelle Änderungen des Bestandes möglich, z.B. Verdichtung der Bestände oder begrenztes Absterben. Änderungen von Wachstumsraten einzelner Bäume aufgrund erwärmter Bedingungen können nachgewiesen werden, und weitere Erwärmung könnte diese Änderungen so intensivieren, dass Auswirkungen auf der Landschaftsebene sichtbar werden. /// Aim of this study was to develop a spatially explicit, medium-scale model of the climate sensitivity of recent white spruce growth at and below treeline in Denali National Park (DNP) and Gates of the Arctic National Park (GAAR) in Alaska and then use the model to project changes in extent of boreal forest under future warming scenarios. We developed a decision-tree model to examine tree growth-environment relationships and used a GIS to extrapolate model results into space. In DNP our results indicate possible dieback of white spruce at low elevations and treeline advance and infilling at high elevations. If recent warming continues, the road corridor in DNP would experience forest increase of about 50%, mainly along the road decreasing the possibility for visitors to observe wildlife across open tundra. In GAAR our results indicate increased rate of white spruce growth at low elevation areas while other areas would experience changes in forest structure (dieback of tree-islands, infilling of existing stands). Changes in distribution of white spruce forests in Alaska are within the range of possibility on a regional scale (treeline advance, dieback). Structural changes within existing forest are possible on a medium (landscape) scale through changes in tree density, infilling and dieback. Changes in growth performance of individual trees due to climate warming are already underway, and further warming would intensify these changes with landscape-wide consequences.
Treelines have been the focus of intense research for nearly a hundred years, also because they represent one of the most visible boundaries between two ecological systems. In recent years however, ...treelines have been studied, because changes in forest ecosystems due to global change, e.g. treeline movement, are expected to manifest first in these areas. This dissertation focuses on the elevational and latitudinal treelines bordering the boreal forest of interior Alaska. After development of a conceptional model of ecotones as three-dimensional spaces between ecosystems, we offer a historical perspective on treeline research and its broader impact in the Brooks Range, Alaska. Dendrochronological analysis of >1500 white spruce (Picea glauca (Moench Voss)) at 13 treeline sites in Alaska revealed both positive and negative growth responses to climate warming, challenging the widespread assumption that northern treeline trees grow better with warming climate. Hot Julys decreased growth of ∼40% of white spruce at treeline in Alaska, whereas warm springs enhanced growth of others. Growth increases and decreases appear at temperature thresholds, which have occurred more frequently in the late 20th century. Based on these relationships between tree-growth and climate as well as using landscape characteristics, we modeled future tree-growth and distribution in two National Parks in Alaska and extrapolated the results into the 21 st century using climate scenarios from five General Circulation Models. In Gates of the Arctic National Park, our results indicate enhanced growth at low elevation, whereas other areas will see changes in forest structure (dieback of tree-islands, infilling of existing stands). In Denali National Park, our results indicate possible dieback of white spruce at low elevations and treeline advance and infilling at high elevations. This will affect the road corridor with a forest increase of about 50% along the road, which will decrease the possibility for wildlife viewing. Surprisingly, aspect did not affect tree growth-climate relationships. Without accounting for opposite growth responses under warming conditions, temperature thresholds, as well as meso-scale changes in forest distribution, climate reconstructions based on ring-width will miscalibrate past climate, and biogeochemical and dynamic vegetation models will overestimate carbon uptake and treeline advance under future warming scenarios.
Reconstructions of past climates are based on the calibration of available proxy data. This calibration is usually achieved by means of linear regression models. In the recent paleo-climate ...literature there is an ongoing discussion on the validity of highly resolved climate reconstructions. The reason for this is that the proxy data are noisy, i.e. in addition to the variability that is related to the climate variable of interest, they contain other sources of variability. Inadequate treatment of such noise leads to a biased estimation of regression slopes, resulting in a wrong representation of the real amplitude of past climate variations. Methods to overcome this problem have had a limited success so far. Here, we present a new approach - SINOMA - for noisy serial data streams that are characterized by different spectral characteristics of signal and noise. SINOMA makes use of specific properties of the data streams temporal or spatial structure and by this is able to deliver a precise estimate of the true regression slope and, simultaneously, of the ratio of noise variances present in the predictor and predictand. The paper introduces the underlying mathematics as well as a general description of the presented algorithm. The validity of SINOMA is illustrated with two test data-sets. Finally we address methodological limitations and further potential applications.
Recently, several studies have shown changing relationships between tree growth and climate factors, mostly in the circumpolar north. There, changing relationships with climate seem to be linked to ...emergent subpopulation behavior. Here, we test for these phenomena in Northwest China using three tree species (Pinus tabulaeformis, Picea crassifolia, and Sabina przewalskii) that had been collected from six sites at Qilian Mts. and Helan Mts. in Northwest China. We first checked for growth divergence of individual sites and then investigated the relationship between tree growth and climate factors using moving correlation functions (CF). Two species, Pinus and Sabina, from two sites clearly showed growth divergence, not only in the late twentieth century as reported in other studies, but also over nearly the whole record. In divergent sites, one chronology shows more stable relationships with climate factors (usually precipitation). In non-divergent sites, nearly all relationships either vary in strength or become non-significant at one point. While this might possibly be related to increased stress on some trees due to increasing temperature, the exact causes for this shift in sensitivity remain unclear. We would like to highlight the necessity for additional studies investigating possible non-stationary growth responses of trees with climate, especially at sites that are used for climate reconstruction as our sites in Northwest China.
Aim
Plant functional groups are widely used in community ecology and earth system modelling to describe trait variation within and across plant communities. However, this approach rests on the ...assumption that functional groups explain a large proportion of trait variation among species. We test whether four commonly used plant functional groups represent variation in six ecologically important plant traits.
Location
Tundra biome.
Time period
Data collected between 1964 and 2016.
Major taxa studied
295 tundra vascular plant species.
Methods
We compiled a database of six plant traits (plant height, leaf area, specific leaf area, leaf dry matter content, leaf nitrogen, seed mass) for tundra species. We examined the variation in species‐level trait expression explained by four traditional functional groups (evergreen shrubs, deciduous shrubs, graminoids, forbs), and whether variation explained was dependent upon the traits included in analysis. We further compared the explanatory power and species composition of functional groups to alternative classifications generated using post hoc clustering of species‐level traits.
Results
Traditional functional groups explained significant differences in trait expression, particularly amongst traits associated with resource economics, which were consistent across sites and at the biome scale. However, functional groups explained 19% of overall trait variation and poorly represented differences in traits associated with plant size. Post hoc classification of species did not correspond well with traditional functional groups, and explained twice as much variation in species‐level trait expression.
Main conclusions
Traditional functional groups only coarsely represent variation in well‐measured traits within tundra plant communities, and better explain resource economic traits than size‐related traits. We recommend caution when using functional group approaches to predict tundra vegetation change, or ecosystem functions relating to plant size, such as albedo or carbon storage. We argue that alternative classifications or direct use of specific plant traits could provide new insights for ecological prediction and modelling.
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