ABSTRACT Hybridization is proposed as one process that can enhance a plant species’ invasive abil... more ABSTRACT Hybridization is proposed as one process that can enhance a plant species’ invasive ability. We quantified the levels of hybridization of 180 saltcedar plants (Tamarix spp.) of varying ages that span the history of an invasion along the Green River, Utah, USA. Plants ranging in establishment dates from 1930s to 2004 were analyzed using Amplified Fragment Length Polymorphisms. All plants sampled, even those established before the Green River saltcedars were numerous, were assigned as hybrids, not as parental types that are still found in more extreme southern and northern latitudes in the USA. Our collections either did not capture the earliest parental types, parental types have failed to persist, or the first introductions to the Green River were already hybrids. In any case, it appears that hybrids have been a dominant part of this local invasion history, from establishment through invasion spread stages.
Significant ecological, hydrologic, and geomorphic changes have occurred during the 20th century ... more Significant ecological, hydrologic, and geomorphic changes have occurred during the 20th century along many large floodplain rivers in the American Southwest. Native Populus forests have declined, while the exotic Eurasian shrub, Tamarix, has proliferated and now dominates most floodplain ecosystems. Photographs from late 19th and early 20th centuries illustrate wide river channels with largely bare in-channel landforms and shrubby higher channel margin floodplains. However, by the mid-20th century, floodplains supporting dense Tamarix stands had expanded, and river channels had narrowed. Along the lower Green River in eastern Utah, the causal mechanism of channel and floodplain changes remains ambiguous due to the confounding effects of climatically driven reductions in flood magnitude, river regulation by Flaming Gorge Dam, and Tamarix invasion. This study addressed whether Tamarix establishment and spread followed climate- or dam-induced reductions in annual peak flows or whether Tamarix was potentially a driver of floodplain changes. We aged 235 Tamarix and 57 Populus individuals, determined the hydrologic and geomorphic processes that controlled recruitment, identified the spatial relationships of germination sites within floodplain stratigraphic transects, and mapped woody riparian vegetation cohorts along three segments of the lower Green River.
The oldest Tamarix established along several sampling reaches in 1938, and 1.50–2.25 m of alluvium has accreted above their germination surfaces. Nearly 90% of the Tamarix and Populus samples established during flood years that exceeded the 2.5-year recurrence interval. Recruitment was most common when large floods were followed by years with smaller peak flows. The majority of Tamarix establishment and Green River channel narrowing occurred long before river regulation by Flaming Gorge Dam. Tamarix initially colonized bare instream sand deposits (e.g., islands and bars), and most channel and floodplain changes followed the establishment of Tamarix. Our results suggest that Tamarix recruitment was triggered by large annual floods that were followed by years with lower peak flows, not by periods of low flow alone. Tamarix appears to have actively invaded floodplains, while Populus colonization has been limited. Thus, Tamarix invasion may have greatly influenced floodplain development and riparian vegetation composition along the lower Green River since the early 20th century.
Hybridization is proposed as one process that can enhance a plant species’ invasive ability. We q... more Hybridization is proposed as one process that can enhance a plant species’ invasive ability. We quantified the levels of hybridization of 180 saltcedar plants (Tamarix spp.) of varying ages that span the history of an invasion along the Green River, Utah, USA. Plants ranging in establishment dates from 1930s to 2004 were analyzed using Amplified Fragment Length Polymorphisms. All plants sampled, even those established before the Green River saltcedars were numerous, were assigned as hybrids, not as parental types that are still found in more extreme southern and northern latitudes in the USA. Our collections either did not capture the earliest parental types, parental types have failed to persist, or the first introductions to the Green River were already hybrids. In any case, it appears that hybrids have been a dominant part of this local invasion history, from establishment through invasion spread stages.
ABSTRACT Hybridization is proposed as one process that can enhance a plant species’ invasive abil... more ABSTRACT Hybridization is proposed as one process that can enhance a plant species’ invasive ability. We quantified the levels of hybridization of 180 saltcedar plants (Tamarix spp.) of varying ages that span the history of an invasion along the Green River, Utah, USA. Plants ranging in establishment dates from 1930s to 2004 were analyzed using Amplified Fragment Length Polymorphisms. All plants sampled, even those established before the Green River saltcedars were numerous, were assigned as hybrids, not as parental types that are still found in more extreme southern and northern latitudes in the USA. Our collections either did not capture the earliest parental types, parental types have failed to persist, or the first introductions to the Green River were already hybrids. In any case, it appears that hybrids have been a dominant part of this local invasion history, from establishment through invasion spread stages.
Significant ecological, hydrologic, and geomorphic changes have occurred during the 20th century ... more Significant ecological, hydrologic, and geomorphic changes have occurred during the 20th century along many large floodplain rivers in the American Southwest. Native Populus forests have declined, while the exotic Eurasian shrub, Tamarix, has proliferated and now dominates most floodplain ecosystems. Photographs from late 19th and early 20th centuries illustrate wide river channels with largely bare in-channel landforms and shrubby higher channel margin floodplains. However, by the mid-20th century, floodplains supporting dense Tamarix stands had expanded, and river channels had narrowed. Along the lower Green River in eastern Utah, the causal mechanism of channel and floodplain changes remains ambiguous due to the confounding effects of climatically driven reductions in flood magnitude, river regulation by Flaming Gorge Dam, and Tamarix invasion. This study addressed whether Tamarix establishment and spread followed climate- or dam-induced reductions in annual peak flows or whether Tamarix was potentially a driver of floodplain changes. We aged 235 Tamarix and 57 Populus individuals, determined the hydrologic and geomorphic processes that controlled recruitment, identified the spatial relationships of germination sites within floodplain stratigraphic transects, and mapped woody riparian vegetation cohorts along three segments of the lower Green River.
The oldest Tamarix established along several sampling reaches in 1938, and 1.50–2.25 m of alluvium has accreted above their germination surfaces. Nearly 90% of the Tamarix and Populus samples established during flood years that exceeded the 2.5-year recurrence interval. Recruitment was most common when large floods were followed by years with smaller peak flows. The majority of Tamarix establishment and Green River channel narrowing occurred long before river regulation by Flaming Gorge Dam. Tamarix initially colonized bare instream sand deposits (e.g., islands and bars), and most channel and floodplain changes followed the establishment of Tamarix. Our results suggest that Tamarix recruitment was triggered by large annual floods that were followed by years with lower peak flows, not by periods of low flow alone. Tamarix appears to have actively invaded floodplains, while Populus colonization has been limited. Thus, Tamarix invasion may have greatly influenced floodplain development and riparian vegetation composition along the lower Green River since the early 20th century.
Hybridization is proposed as one process that can enhance a plant species’ invasive ability. We q... more Hybridization is proposed as one process that can enhance a plant species’ invasive ability. We quantified the levels of hybridization of 180 saltcedar plants (Tamarix spp.) of varying ages that span the history of an invasion along the Green River, Utah, USA. Plants ranging in establishment dates from 1930s to 2004 were analyzed using Amplified Fragment Length Polymorphisms. All plants sampled, even those established before the Green River saltcedars were numerous, were assigned as hybrids, not as parental types that are still found in more extreme southern and northern latitudes in the USA. Our collections either did not capture the earliest parental types, parental types have failed to persist, or the first introductions to the Green River were already hybrids. In any case, it appears that hybrids have been a dominant part of this local invasion history, from establishment through invasion spread stages.
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Papers by Adam Birken
The oldest Tamarix established along several sampling reaches in 1938, and 1.50–2.25 m of alluvium has accreted above their germination surfaces. Nearly 90% of the Tamarix and Populus samples established during flood years that exceeded the 2.5-year recurrence interval. Recruitment was most common when large floods were followed by years with smaller peak flows. The majority of Tamarix establishment and Green River channel narrowing occurred long before river regulation by Flaming Gorge Dam. Tamarix initially colonized bare instream sand deposits (e.g., islands and bars), and most channel and floodplain changes followed the establishment of Tamarix. Our results suggest that Tamarix recruitment was triggered by large annual floods that were followed by years with lower peak flows, not by periods of low flow alone. Tamarix appears to have actively invaded floodplains, while Populus colonization has been limited. Thus, Tamarix invasion may have greatly influenced floodplain development and riparian vegetation composition along the lower Green River since the early 20th century.
The oldest Tamarix established along several sampling reaches in 1938, and 1.50–2.25 m of alluvium has accreted above their germination surfaces. Nearly 90% of the Tamarix and Populus samples established during flood years that exceeded the 2.5-year recurrence interval. Recruitment was most common when large floods were followed by years with smaller peak flows. The majority of Tamarix establishment and Green River channel narrowing occurred long before river regulation by Flaming Gorge Dam. Tamarix initially colonized bare instream sand deposits (e.g., islands and bars), and most channel and floodplain changes followed the establishment of Tamarix. Our results suggest that Tamarix recruitment was triggered by large annual floods that were followed by years with lower peak flows, not by periods of low flow alone. Tamarix appears to have actively invaded floodplains, while Populus colonization has been limited. Thus, Tamarix invasion may have greatly influenced floodplain development and riparian vegetation composition along the lower Green River since the early 20th century.