The Role of Fire and a Nonnative Grass as Disturbances in Semi-Desert Grasslands

Persistent Link:
http://hdl.handle.net/10150/195861
Title:
The Role of Fire and a Nonnative Grass as Disturbances in Semi-Desert Grasslands
Author:
Geiger, Erika L.
Issue Date:
2006
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:
Disturbances are key processes that alter environmental conditions which have consequences for species interactions; therefore, disturbances are important to maintenance of biological diversity. Climate, fire, livestock grazing, introduction of nonnative species, and humans all influence semi-desert grasslands of the southwestern United States. In southeast Arizona, a nonnative perennial grass, Lehmann lovegrass (Eragrostis lehmanniana), was introduced in the 1930s in an effort to restore degraded rangelands. I quantified annual fluctuations of Lehmann lovegrass and the response of native plants along a gradient of dominance by this nonnative grass. Biomass and richness of native plants declined with increasing dominance by Lehmann lovegrass. Substantial increases in biomass by Lehmann lovegrass in response to above-average rainfall did not result in decreases in native plants. Fire is an important disturbance in semi-desert grasslands. Herbaceous plants are favored over trees and shrubs in areas with frequent fires, therefore fire maintains grassland physiognomy. Humans have manipulated natural fire regimes however, by altering their frequency, season, and spatial extent. I experimentally investigated the possibility of a positive feedback cycle in grasslands invaded by Lehmann lovegrass by assessing whether the presence of Lehmann lovegrass was enhanced by fire to the detriment of native plants. In the two years post-fire, the proportion of Lehmann lovegrass on burned sites did not increased compared to unburned sites or to pre-fire conditions. I also detected no changes in species richness, diversity, or biomass of native plants in response to fire for 2-3 years after fires. Changes in biomass of all plants varied among years, especially due to exceptionally wet conditions during spring 2001, and varied if fires were set in spring versus summer. Lastly, I investigated the response of Agave palmeri to fire, a species that provides forage for a migratory bat that is federally endangered. Survival of agave varied with soil type, fire season, and size of the plant. In general, agave can tolerate up to 85% damage before mortality. Germination of agave seed was decreased by fire. Based on my research, I recommend setting fire at natural frequency and season for the maintenance of semi-desert grasslands.
Type:
text; Electronic Dissertation
Keywords:
Natural Resources
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Natural Resources; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
McPherson, Guy R.

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleThe Role of Fire and a Nonnative Grass as Disturbances in Semi-Desert Grasslandsen_US
dc.creatorGeiger, Erika L.en_US
dc.contributor.authorGeiger, Erika L.en_US
dc.date.issued2006en_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.abstractDisturbances are key processes that alter environmental conditions which have consequences for species interactions; therefore, disturbances are important to maintenance of biological diversity. Climate, fire, livestock grazing, introduction of nonnative species, and humans all influence semi-desert grasslands of the southwestern United States. In southeast Arizona, a nonnative perennial grass, Lehmann lovegrass (Eragrostis lehmanniana), was introduced in the 1930s in an effort to restore degraded rangelands. I quantified annual fluctuations of Lehmann lovegrass and the response of native plants along a gradient of dominance by this nonnative grass. Biomass and richness of native plants declined with increasing dominance by Lehmann lovegrass. Substantial increases in biomass by Lehmann lovegrass in response to above-average rainfall did not result in decreases in native plants. Fire is an important disturbance in semi-desert grasslands. Herbaceous plants are favored over trees and shrubs in areas with frequent fires, therefore fire maintains grassland physiognomy. Humans have manipulated natural fire regimes however, by altering their frequency, season, and spatial extent. I experimentally investigated the possibility of a positive feedback cycle in grasslands invaded by Lehmann lovegrass by assessing whether the presence of Lehmann lovegrass was enhanced by fire to the detriment of native plants. In the two years post-fire, the proportion of Lehmann lovegrass on burned sites did not increased compared to unburned sites or to pre-fire conditions. I also detected no changes in species richness, diversity, or biomass of native plants in response to fire for 2-3 years after fires. Changes in biomass of all plants varied among years, especially due to exceptionally wet conditions during spring 2001, and varied if fires were set in spring versus summer. Lastly, I investigated the response of Agave palmeri to fire, a species that provides forage for a migratory bat that is federally endangered. Survival of agave varied with soil type, fire season, and size of the plant. In general, agave can tolerate up to 85% damage before mortality. Germination of agave seed was decreased by fire. Based on my research, I recommend setting fire at natural frequency and season for the maintenance of semi-desert grasslands.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectNatural Resourcesen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineNatural Resourcesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairMcPherson, Guy R.en_US
dc.contributor.committeememberSteidl, Robert J.en_US
dc.contributor.committeememberMcLaughlin, Steven P.en_US
dc.contributor.committeememberKupfer, John A.en_US
dc.contributor.committeememberHubbard, J. Andrewen_US
dc.identifier.proquest1856en_US
dc.identifier.oclc659746406en_US
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