Dynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patterns
Woody 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 ab...
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ndltd-UTEXAS-oai-repositories.lib.utexas.edu-2152-ETD-UT-2010-08-18872015-09-20T16:55:44ZDynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patternsGonzález, Ana VerónicaCentral TexasSavannasWoody plant encroachmentJuniperus asheiEdwards PlateauWoody plantsWoody plant coverInvasive plantsInvasive speciesWoody 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.text2010-11-10T21:52:25Z2010-11-10T21:52:34Z2010-11-10T21:52:25Z2010-11-10T21:52:34Z2010-082010-11-10August 20102010-11-10T21:52:34Zthesisapplication/pdfhttp://hdl.handle.net/2152/ETD-UT-2010-08-1887eng |
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English |
format |
Others
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Central Texas Savannas Woody plant encroachment Juniperus ashei Edwards Plateau Woody plants Woody plant cover Invasive plants Invasive species |
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Central Texas Savannas Woody plant encroachment Juniperus ashei Edwards Plateau Woody plants Woody plant cover Invasive plants Invasive species González, Ana Verónica Dynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patterns |
description |
Woody 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. === text |
author |
González, Ana Verónica |
author_facet |
González, Ana Verónica |
author_sort |
González, Ana Verónica |
title |
Dynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patterns |
title_short |
Dynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patterns |
title_full |
Dynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patterns |
title_fullStr |
Dynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patterns |
title_full_unstemmed |
Dynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patterns |
title_sort |
dynamics of woody plant encroachment in texas savannas : density dependence, environmental heterogeneity, and spatial patterns |
publishDate |
2010 |
url |
http://hdl.handle.net/2152/ETD-UT-2010-08-1887 |
work_keys_str_mv |
AT gonzalezanaveronica dynamicsofwoodyplantencroachmentintexassavannasdensitydependenceenvironmentalheterogeneityandspatialpatterns |
_version_ |
1716821212134375424 |