Spatial and temporal dynamics of disturbance interactions along an ecological gradient

Persistent Link:
http://hdl.handle.net/10150/311565
Title:
Spatial and temporal dynamics of disturbance interactions along an ecological gradient
Author:
O'Connor, Christopher Daniel
Issue Date:
2013
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:
Interactions among site conditions, disturbance events, and climate determine the patterns of forest species recruitment and mortality across landscapes. Forests of the American Southwest have undergone significant changes over a century of altered disturbance regimes, human land uses, and changing environmental conditions. This study reconstructs the interactions between fire, spruce beetle outbreaks, climate, and anthropogenic factors and their influence on the species composition, spatial extent, and structure of four upper elevation forest types. We found that fire-climate associations changed following fire exclusion and recent high-severity fires occurred during less severe conditions than in several larger, lower severity fires in the historical record. Contemporary fires are burning with higher severity than similarly-sized historical fires, suggesting a shift toward higher-severity fire as a result of changes to forest structure and fuels over much of the upper elevation forest. In high elevation forests, the area occupied by Engelmann spruce and corkbark fir doubled in size over the four decades following fire exclusion. The increase in spruce beetle outbreak size and severity in the 20th century appears to be linked to significant expansion of host extent, accelerated growth of spruce in mixed-conifer forest, and incidence of anomalously warm summer temperatures followed by up to a decade of low precipitation. Trends toward warming, drying conditions are expected to increase the risk of future high-severity outbreaks, especially in locations of recent spruce population expansion. Forest conversion from disturbance-adapted to competition-adapted species following fire exclusion was a function of site productivity. Species assemblages in the lowest and highest productivity sites were the most stable over the century following fire exclusion. Frequent low severity fires maintained the stocking of forests in moderate productivity sites below their biological potential, conferring a degree of resistance to drought, insect outbreaks, and high-severity fire prior to fire exclusion. Current forests located on moderate productivity sites are now the most vulnerable to drought and future disturbance. Aggressive action to restore historical species composition, stocking and fire component of these forests may return resilience to this system in the face of projected changes to fire and climate dynamics.
Type:
text; Electronic Dissertation
Keywords:
fire suppression; spatial reconstruction; spruce beetle; stability; tree-ring; Natural Resources; fire severity
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Natural Resources
Degree Grantor:
University of Arizona
Advisor:
Falk, Donald A.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleSpatial and temporal dynamics of disturbance interactions along an ecological gradienten_US
dc.creatorO'Connor, Christopher Danielen_US
dc.contributor.authorO'Connor, Christopher Danielen_US
dc.date.issued2013-
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.abstractInteractions among site conditions, disturbance events, and climate determine the patterns of forest species recruitment and mortality across landscapes. Forests of the American Southwest have undergone significant changes over a century of altered disturbance regimes, human land uses, and changing environmental conditions. This study reconstructs the interactions between fire, spruce beetle outbreaks, climate, and anthropogenic factors and their influence on the species composition, spatial extent, and structure of four upper elevation forest types. We found that fire-climate associations changed following fire exclusion and recent high-severity fires occurred during less severe conditions than in several larger, lower severity fires in the historical record. Contemporary fires are burning with higher severity than similarly-sized historical fires, suggesting a shift toward higher-severity fire as a result of changes to forest structure and fuels over much of the upper elevation forest. In high elevation forests, the area occupied by Engelmann spruce and corkbark fir doubled in size over the four decades following fire exclusion. The increase in spruce beetle outbreak size and severity in the 20th century appears to be linked to significant expansion of host extent, accelerated growth of spruce in mixed-conifer forest, and incidence of anomalously warm summer temperatures followed by up to a decade of low precipitation. Trends toward warming, drying conditions are expected to increase the risk of future high-severity outbreaks, especially in locations of recent spruce population expansion. Forest conversion from disturbance-adapted to competition-adapted species following fire exclusion was a function of site productivity. Species assemblages in the lowest and highest productivity sites were the most stable over the century following fire exclusion. Frequent low severity fires maintained the stocking of forests in moderate productivity sites below their biological potential, conferring a degree of resistance to drought, insect outbreaks, and high-severity fire prior to fire exclusion. Current forests located on moderate productivity sites are now the most vulnerable to drought and future disturbance. Aggressive action to restore historical species composition, stocking and fire component of these forests may return resilience to this system in the face of projected changes to fire and climate dynamics.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectfire suppressionen_US
dc.subjectspatial reconstructionen_US
dc.subjectspruce beetleen_US
dc.subjectstabilityen_US
dc.subjecttree-ringen_US
dc.subjectNatural Resourcesen_US
dc.subjectfire severityen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineNatural Resourcesen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorFalk, Donald A.en_US
dc.contributor.committeememberFalk, Donald A.en_US
dc.contributor.committeememberLynch, Ann M.en_US
dc.contributor.committeememberSwetnam, Thomas W.en_US
dc.contributor.committeememberLoehman, Rachel A.en_US
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