Article

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).

0 Bookmarks
 · 
84 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract Aim  We addressed four objectives: (1) Determine the regional responses of species, size classes and a vegetation type to climate and parent material predictors, including their distributions in environmental space and the relative contributions of the predictors to explained variation. (2) Determine whether size classes of a species respond similarly to climate and parent material. (3) Assess the extent to which the predicted regional distribution of a vegetation type can be approximated by the distribution of its diagnostic species and vice versa. The establishment of a consistent relationship between the distribution of a vegetation type and its diagnostic species would facilitate change detection, management and conservation planning by allowing the use of one distribution to generate the other when data availability is limited. (4) Examine landscape-scale environmental variability in predicted species and vegetation type distributions.Location  South-western USA (Arizona, New Mexico and southern Colorado).Methods  Ecological response surface models were developed using a data base of 1409 vegetation plots to analyse biotic–environmental relationships of (1) Pinus ponderosa P. & C. Lawson and Abies concolor (Gord. & Glend.) Lindl. Ex Hildebr. size classes, (2) P. ponderosa, A. concolor and Quercus gambelii Nutt. combined size classes, and (3) a P. ponderosa forest type widely distributed in the south-western USA.Results and main conclusions Pinus ponderosa and A. concolor models generally were judged to be successful. Quercus gambelii models were judged unsuccessful, which may result from the influence of variables not modelled, such as soil moisture, disturbance, biotic factors and other site limiting factors. Size classes differed in the range of environmental conditions associated with high occurrence probabilities within and between species, reflecting differences in the effects of climate variability and anthropogenic changes, such as fire suppression, on the distribution of each size class. Pinus ponderosa alliance was predicted to be distributed over a narrower range of environmental conditions than P. ponderosa species models, therefore limiting the use of this vegetation type as a surrogate for the distribution of the dominant species, and vice versa. Maps of combinations of environmental variables that produced a high probability of P. ponderosa occurrence showed that some landscapes predicted to contain the species exhibited diverse environmental conditions over short distances. The use of regional environmental relationships to characterize areas with high local environmental variability may facilitate identification of areas of potential rapid biotic change.
    Journal of Biogeography 01/2003; 30(2):257 - 276. · 4.86 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source