Dynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patterns

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dc.contributor.advisorFowler, Norma L.en
dc.contributor.committeeMemberSchwinning, Susanen
dc.contributor.committeeMemberLinder, Craig R.en
dc.contributor.committeeMemberLeibold, Mathew A.en
dc.contributor.committeeMemberMeyers, Lauren A.en
dc.creatorGonzález, Ana Verónicaen
dc.date.accessioned2010-11-10T21:52:25Zen
dc.date.accessioned2010-11-10T21:52:34Zen
dc.date.accessioned2017-05-11T22:20:39Z
dc.date.available2010-11-10T21:52:25Zen
dc.date.available2010-11-10T21:52:34Zen
dc.date.available2017-05-11T22:20:39Z
dc.date.issued2010-08en
dc.date.submittedAugust 2010en
dc.date.updated2010-11-10T21:52:34Zen
dc.descriptiontexten
dc.description.abstractWoody plant encroachment, that is, a substantial increase in the abundance of woody plants in a grassland or savanna, occurs in many parts of the world. It often has large effects on plant and animal populations and communities and on ecosystem properties and processes. However, little is known about the dynamics of woody plant encroachment and how these are affected by soils, by topography, and by the spatial pattern of the vegetation. Encroachment in turn can affect the spatial pattern of the vegetation. Using data from historical aerial photographs, I measured changes in woody plant cover and constructed, parameterized and compared a set of dynamic models of woody plant encroachment in central Texas savannas. These models predicted final woody cover from initial woody cover and the initial spatial configuration of woody plants. Then I incorporated soil and topography into these models to determine their effects. Finally, I examined the effects of encroachment on the spatial pattern of the vegetation. Incorporating negative density dependence in our models improved their fit, demonstrating that encroachment is density-dependent. A function that predicted the formation of new woody patches from a density-independent seed supply also improved the models' performance. The improvement in the models that resulted from incorporating the total length of woody-herbaceous edges confirmed that encroachment in this system occurs in part by the outward expansion of woody patches. The spatial pattern of the vegetation changed during woody plant encroachment. Spatial pattern (measured as degree of fragmentation) often had a non-linear relationship with cover. Furthermore, the spatial heterogeneity in fragmentation, that is, plot-to-plot variation in the degree of fragmentation, also changed during encroachment. Topography and soil type had, in general, little effect the dynamics of woody plant encroachment. Therefore, a relatively simple model of woody plant encroachment provided good predictions of woody cover at the end of the time periods. Other systems experiencing woody plant encroachment, forest succession, or invasion by non-native plants could be modeled using the same approach.en
dc.description.departmentBiological Sciences, School ofen
dc.format.mimetypeapplication/pdfen
dc.identifier.urihttp://hdl.handle.net/2152/ETD-UT-2010-08-1887en
dc.language.isoengen
dc.subjectCentral Texasen
dc.subjectSavannasen
dc.subjectWoody plant encroachmenten
dc.subjectJuniperus asheien
dc.subjectEdwards Plateauen
dc.subjectWoody plantsen
dc.subjectWoody plant coveren
dc.subjectInvasive plantsen
dc.subjectInvasive speciesen
dc.titleDynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patternsen
dc.type.genrethesisen

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