Vegetation dynamics in the southern Rocky Mountains: Late Pleistocene and Holocene timberline fluctuations.

Persistent Link:
http://hdl.handle.net/10150/184610
Title:
Vegetation dynamics in the southern Rocky Mountains: Late Pleistocene and Holocene timberline fluctuations.
Author:
Fall, Patricia Lynn.
Issue Date:
1988
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Plant macrofossils and pollen from six small basins in western Colorado are used to trace the history of vegetation and climate over the last 15,000 years. The late-glacial upper timberline was 2800 m, and sparse krummholz Picea grew up to 3200 m. Summer temperatures were 3° to 5°C cooler than today. The late Pleistocene climate was influenced by winter storms from the Pacific. Precipitation shifted to a summer-dominated pattern by at least 9000 yr B.P. with the development of the summer monsoon. Plant fossils from bogs and lakes located near modern ecotones track the elevations of the temperature-controlled upper timberline and the moisture-controlled lower forest through the Holocene. Between 9000 and 4000 yr B.P., the Picea engelmannii-Abies lasiocarpa forest covered a broader elevational range, with upper timberline 200-300 m higher than today. Mean annual temperatures were 1.8°C warmer, and mean summer temperatures were 2.1°C warmer, than today. Temperatures were still about 1°C warmer prior to 2000 yr B.P. The lower limits of the montane and subalpine forests were 100-200 m below their modern elevations from 9000-4000 yr B.P. Mean annual precipitation was 50-100 mm greater. By 2600 yr B.P. the modern lower forest borders were established. Modern pollen dispersal, transportation, and deposition was sampled in atmospheric collectors, moss polsters, and surface lake sediments. Annual accumulation rates range between 1000 and 5000 grains cm⁻²yr⁻¹. Modern influx (grains cm⁻²yr⁻¹)averages: 1100 in alpine tundra, 2700 in the subalpine forest, 3400 in the montane forest, and 200 in shrub steppe. Pollen spectra in atmospheric traps and moss polsters reflect local vegetation, and provide effective modern analogs for pollen accumulation in peat bogs. In forested environments 80-90% of the pollen deposition in small lakes (< 5 ha) with no inflowing streams comes from atmospheric input. Pollen spectra in open vegetation are distorted by pollen from other vegetation types. At least half of the pollen deposition in small alpine lakes comes from taxa growing up to 1500 m lower in elevation.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Timberline -- Rocky Mountains.; Vegetation and climate -- Colorado.; Paleoecology -- Colorado.; Vegetation dynamics -- Colorado.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Geosciences; Graduate College
Degree Grantor:
University of Arizona

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleVegetation dynamics in the southern Rocky Mountains: Late Pleistocene and Holocene timberline fluctuations.en_US
dc.creatorFall, Patricia Lynn.en_US
dc.contributor.authorFall, Patricia Lynn.en_US
dc.date.issued1988en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractPlant macrofossils and pollen from six small basins in western Colorado are used to trace the history of vegetation and climate over the last 15,000 years. The late-glacial upper timberline was 2800 m, and sparse krummholz Picea grew up to 3200 m. Summer temperatures were 3° to 5°C cooler than today. The late Pleistocene climate was influenced by winter storms from the Pacific. Precipitation shifted to a summer-dominated pattern by at least 9000 yr B.P. with the development of the summer monsoon. Plant fossils from bogs and lakes located near modern ecotones track the elevations of the temperature-controlled upper timberline and the moisture-controlled lower forest through the Holocene. Between 9000 and 4000 yr B.P., the Picea engelmannii-Abies lasiocarpa forest covered a broader elevational range, with upper timberline 200-300 m higher than today. Mean annual temperatures were 1.8°C warmer, and mean summer temperatures were 2.1°C warmer, than today. Temperatures were still about 1°C warmer prior to 2000 yr B.P. The lower limits of the montane and subalpine forests were 100-200 m below their modern elevations from 9000-4000 yr B.P. Mean annual precipitation was 50-100 mm greater. By 2600 yr B.P. the modern lower forest borders were established. Modern pollen dispersal, transportation, and deposition was sampled in atmospheric collectors, moss polsters, and surface lake sediments. Annual accumulation rates range between 1000 and 5000 grains cm⁻²yr⁻¹. Modern influx (grains cm⁻²yr⁻¹)averages: 1100 in alpine tundra, 2700 in the subalpine forest, 3400 in the montane forest, and 200 in shrub steppe. Pollen spectra in atmospheric traps and moss polsters reflect local vegetation, and provide effective modern analogs for pollen accumulation in peat bogs. In forested environments 80-90% of the pollen deposition in small lakes (< 5 ha) with no inflowing streams comes from atmospheric input. Pollen spectra in open vegetation are distorted by pollen from other vegetation types. At least half of the pollen deposition in small alpine lakes comes from taxa growing up to 1500 m lower in elevation.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectTimberline -- Rocky Mountains.en_US
dc.subjectVegetation and climate -- Colorado.en_US
dc.subjectPaleoecology -- Colorado.en_US
dc.subjectVegetation dynamics -- Colorado.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.identifier.proquest8907955en_US
dc.identifier.oclc701909397en_US
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