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Postglacial environmental change of a high-elevation forest, Sangre de Cristo Mountains of south-central Colorado

R. Scott Anderson, Hanna R. Soltow and Gonzalo Jimenez-Moreno
Postglacial environmental change of a high-elevation forest, Sangre de Cristo Mountains of south-central Colorado (in From saline to freshwater; the diversity of western lakes in space and time, Scott W. Starratt (editor) and Michael R. Rosen (editor))
Special Paper - Geological Society of America (December 2019) 536

Abstract

Continuous sediment, pollen, and charcoal records were developed from an 8.46-m-long sediment core taken from Hermit Lake in the northern Sangre de Cristo mountain range of Colorado. Presently, vegetation around the lake is upper subalpine forest, consisting of Picea engelmannii (Englemann spruce) with some Abies lasiocarpa (subalpine fir), and the lake lies >200 m below present tree line. We used several pollen ratios to reconstruct the relative position of the tree line and the occurrence of clay layers to infer landscape instability through time. Deglaciation of the Hermit Lake drainage began during the Bolling-Allerod interval. Between ca. 13.5 and 12.4 ka, high Artemisia (sagebrush) pollen abundance, low Picea/Pinus (spruce/pine; S/P) ratios, and sporadic occurrence of Picea macrofossils indicate alpine tundra-spruce conditions. Though the pollen record shows no transition to the Younger Dryas, the subsequent absence of Picea needle fragments suggests a lowering of tree line. By ca. 10.2 ka, a subalpine forest of Picea and Pinus grew there. Based on pollen ratios, tree line was higher than today from ca. 9.0 to ca. 3.8 ka, after which the tree line began to lower to its present elevation. Maximum expansion of the Picea-Abies subalpine forest, determined from both pollen and macrofossils, was coincident with the highest influx of charcoal particles and maximum deposition of postfire erosion (clay layers) into the lake. The period ca. 7.8-6.2 ka was the driest period, as shown by aquatic indicators, but pollen ratios suggest that ca. 6.2-3.8 ka was the warmest period of the Holocene, accompanied by high rates of burning, and consequently elevated erosion of clays into the lake. During the late Holocene, declining S/P ratios are interpreted as declining alpine tree line, while decreases in both Picea to Artemisia (S/Art) and Pinusto Artemisia (P/Art) ratios suggest climate cooling. Pollen evidence suggests expansion of the lower-elevation Colorado pinon (Pinus edulis), which has been documented as part of a widespread phenomenon noted by other studies.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 536
Title: Postglacial environmental change of a high-elevation forest, Sangre de Cristo Mountains of south-central Colorado
Title: From saline to freshwater; the diversity of western lakes in space and time
Author(s): Anderson, R. ScottSoltow, Hanna R.Jimenez-Moreno, Gonzalo
Author(s): Starratt, Scott W.editor
Author(s): Rosen, Michael R.editor
Affiliation: Northern Arizona University, School of Earth & Sustainability, Flagstaff, AZ, United States
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Published: 20191231
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
ISBN: 9780813795362
References: 98
Accession Number: 2020-010995
Categories: Quaternary geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sketch map
N38°05'17" - N38°05'17", W105°37'52" - W105°37'52"
Secondary Affiliation: Universidad de Granada, ESP, Spain
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute.
Update Code: 202008
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