Latitudinal variation in southern Rocky Mountain forests /

Source: OAI

ABSTRACT Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 1988. Includes bibliographical references (leaves 212-223).

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    ABSTRACT: We examined the influence of twentieth-century climate on upper treeline dynamics in the southern Rocky Mountains to better understand the role of temperature and precipitation on tree establishment and to determine whether bioclimatic thresholds have been exceeded as a result of warming during the twentieth century. By using dendrochronological techniques, we reconstructed tree establishment at upper treeline on six mountain peaks within the Front Range and Sangre de Cristo Mountains. We compared age–structure data with climate using Spearman's rank correlation coefficients between annual and seasonal climate indexes and tree establishment dates at both regional (southern Rockies) and landscape scales (mountain range). Regime-shift analysis detected thresholds in temperature, precipitation, and tree establishment data. Tree establishment has increased substantially at upper treeline throughout the southern Rockies, leading to varying degrees of treeline advance upslope. Tree establishment in the Front Range significantly correlates with temperature, but no significant correlations with temperature variables exist in the Sangre de Cristos. Significant inverse correlations exist with precipitation but remain confined to north-facing slopes in both mountain ranges. Synchronous regime shifts (within five years) occurred in the Front Range between temperature and tree establishment during the early 1950s (1950–1954), suggesting that increasing temperatures provided a possible mechanism for abrupt increases in establishment. This research highlights the intraregional variability in treeline sensitivity to climate in the southern Rocky Mountains and the usefulness of using a multiscale approach coupled with regime-shift analysis to examine the influence of twentieth-century climate on treeline. Examinamos la influencia del clima del sigloXX en la dinámica de la línea superior de árboles en el sur de las Montañas Rocosas para entender mejor el rol de la temperatura y precipitaciones en la existencia de árboles y determinar si los umbrales bioclimáticos han sido excedidos como resultado del calentamiento durante el siglo XX. Mediante el uso de técnicas dendrocronológicas hemos reconstruido la presencia de árboles en el límite superior de la línea de árboles en seis picos de montañas en la Front Range y las montañas de Sangre de Cristo. Para esto comparamos data de estructura de edad con el clima usando coeficientes de rango de correlación de Spearman entre índices de clima anual y estacional y las fechas de existencia de árboles a escala regional (Rocosas del sur) y escala de paisajes (cadenas de montañas). El análisis de cambio de régimen detectó umbrales en temperatura, precipitación, y fechas de establecimiento de árboles. El establecimiento de árboles ha aumentado sustancialmente en la línea superior de árboles en todas las Rocosas del sur, llevando a grados variados del avance de la línea de árboles cuesta arriba. El establecimiento de árboles en la Front Range se correlaciona significativamente con la temperatura, pero no ocurre lo mismo para Sangre de Cristo. Existen correlaciones inversas significativas con las precipitaciones pero estas quedan confinadas a las laderas con frente al norte en ambas cadenas de montañas. Cambios de régimen sincrónico (en cinco años) ocurrieron en la Front Range entre la temperatura y la ocurrencia de árboles durante los primeros años de la década de 1950 (1950–1954), sugiriendo que el incremento de temperaturas alimentó un posible mecanismo para el incremento abrupto de existencias. Esta investigación resalta la variabilidad intrarregional en la sensibilidad de la línea de árboles al clima en el sur de las Montañas Rocosas y la utilidad del uso de un enfoque multiescalar junto con el análisis de cambio de régimen para examinar la influencia del cambio de clima del siglo XX en la línea de árboles.
    Annals of the Association of American Geographers 11/2011; 101:1181-1203. · 2.17 Impact Factor
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    ABSTRACT: Objective: Our purpose was to characterize vegetation compositional patterns, tree regeneration, and plant diversity, and their relationships to landscape context, topography, and light availability across the margins of four stand-replacing subalpine burns. Location: Four 1977 to 1978 burns east of the Continental Divide in Colorado: the Ouzel burn, a burn near Kenosha Pass, the Badger Mountain burn, and the Maes Creek burn. Methods: Vegetation and environmental factors were sampled in 200 0.01-ha plots on transects crossing burn edges, and stratified by elevation. We utilized dissimilarity indices, mixed-effects models, and randomization tests to assess relationships between vegetation and environment. Results: Three decades after wildfire, plant communities exhibited pronounced compositional shifts across burn edges. Tree regeneration decreased with increasing elevation and distance into burn interiors; concomitant increases in forbs and graminoids were linked to greater light availability. Richness was roughly doubled in high-severity burn interiors due to the persistence of a suite of native species occurring primarily in this habitat. Richness rose with distance into burns, but declined with increasing elevation. Only three of 188 plant species were non-native; these were widespread, naturalized species that comprised <1% total cover. Conclusions: These subalpine wildfires generated considerable, persistent increases in plant species richness at local and landscape scales, and a diversity of plant communities. The findings suggest that fire suppression in such systems must lead to reduced diversity. Concerns about post-fire invasion by exotic plants appear unwarranted in high-elevation wilderness settings.
    Journal of Vegetation Science 01/2010; · 2.82 Impact Factor
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    ABSTRACT: A Landsat Thematic Mapper (TM) based digital land cover map has been created for the state of Wyoming, USA, at moderate spatial (l-km2 minimum mapping unit) and high typal (41 land cover types) resolution as part of the Wyoming Gap Analysis Program (WGAP). This map presents opportunities for regional characterization of land cover, especially vegetation, and for examination of ecological phenomena that manifest themselves over large areas. Using the digital land cover data, we describe Wyoming vegetation and examine positions of three prominent physiognomic transitions in Wyoming: the elevation of upper and lower treeline, and the position of the biogeographic boundary between shruband grass-dominated vegetation. By area, the three leading land cover types in Wyoming are Artemisia tridentata ssp. wyomingensis sagebrush (33.4 %), mixed grass prairie (17.5 %) and Pinus contorta forest (6.5 %). Average upper-treeline elevation in Wyoming is 2947 m, and decreases with increasing latitude at an average rate of about 0.5 m/km, less than the rate of about 0.9 m/km reported by Peet (1978) for a gradient from Mexico to Canada. Lower-treeline occurs at an average elevation of 2241 m, and decreases with increasing latitude and with southerly aspect. In Wyoming, shrub-dominated communities are more likely to occur than grass-dominated communities as summer precipitation decreases below 282 mm. All of these relationships are subtle, and it appears that for particular areas, local factors are more important than regional climatic trends in explaining the position of phytogeographic boundaries.
    Journal of Vegetation Science 02/2009; 8(1):133 - 146. · 2.82 Impact Factor