We tested the hypothesis that the traits of managers and the types of agencies they represent wou... more We tested the hypothesis that the traits of managers and the types of agencies they represent would have measurable impacts on the outcomes of restoration in 243 sites across the Southwestern US where invasive Tamarix spp. trees had been removed. Change in cover for invasive species, tamarix, and native cover were the dependent variables, based on the difference in these values between the treatment site and a corresponding reference site. Most other columns are either environmental variables (lowercase) or manager variables (all caps). Manager data was collected via surveys and interviews.
Spatial modeling has proven to be useful in understanding the drivers of plant populations in the... more Spatial modeling has proven to be useful in understanding the drivers of plant populations in the field of ecology, but has yet to be applied to understanding variation in biocontrol impact. In this study, we employ multi-scale analysis (Moran’s Eigenvector Maps) to better understand the variation in tree canopy exposed to defoliation by a biocontrol beetle (Diorhabda spp.). The control of the exotic tree Tamarix in riparian areas has long been a priority for land managers and ecologists in the American southwest. Diorhabda spp. was introduced as a bio-control agent beginning in 2001 and has since become an inseparable part of Tamarix-dominated river systems in the southwest. Between 2013 and 2016 tamarisk dieback was assessed at 79 sites across Grand County, Utah, arguably the epicenter of Diorhabda impact in the U.S. Canopy cover of Tamarix was between 73 and 81% at these sites, with the percent that was live cover fluctuating by year with a minimum of 42%. Using a traditional general linear model, we found that readily and commonly measured environmental factors could explain only up to 26% of the variation in Tamarix live canopy each year. The number of defoliations was correlated with an increase rather than a decrease in percent live canopy, suggesting compensatory growth. Spatial structure alone explained 22–40% of variation. We found fine scale spatial structure at less than 10 km and broad scale spatial structure from 10 to 30 km. Combining both traditional and novel spatial statistical methods we increased that percentage to 43–63%, depending on year. These results suggest that scientists and land managers must look beyond commonly measured environmental variables to explain non-random biocontrol impact in this system. In particular, this study points to the potential for biotic interactions and variation in flood cycles for further exploration of the identified spatial structure.
: Changes in historical disturbance regimes have been shown to facilitate non‐native plant invasi... more : Changes in historical disturbance regimes have been shown to facilitate non‐native plant invasions, but reinstatement of disturbance can be successful only if native colonizers are able to outcompete colonizing invasives. Reintroduction of flooding in the southwestern United States is being promoted as a means of reestablishing Populus deltoides subsp. wislizenii, but flooding can also promote establishment of an introduced, invasive species, Tamarix ramosissima. We investigated competition between Populus and Tamarix at the seedling stage to aid in characterizing the process by which Tamarix may invade and to determine the potential ability of Populus to establish itself with competitive pressure from Tamarix. We planted seedlings of Tamarix and Populus in five ratios at three densities for a total of 15 treatments. The growth response of each species was measured in terms of height, above‐ground biomass, and tissue concentrations of nitrogen and phosphorous. These measurements across treatments were modeled as three‐dimensional response surfaces. For both species, Populus density was more important than Tamarix density for determining growth response. Both species were negatively affected by increasing numbers of Populus seedlings. Due to the larger size of the native Populus, we predict that its superior competitive ability can lead to its dominance when conditions allow native establishment. Our results suggest that even in the presence of an invader that positively responds to disturbance, reestablishment of historical flooding regimes and post‐flood hydrology can restore this ecosystem by promoting its dominant plant species.
We investigated the relative role of manager traits and decisions for explaining the impact of ri... more We investigated the relative role of manager traits and decisions for explaining the impact of riparian restoration. To do this, we used the difference in vegetation between post-restoration and controls for 243 pairs of sites to create a success index. We then determined how much variability in success could be explained by physical variables that directly impact vegetation (environment and weed removal) versus human variables (characteristics of the people who managed those sites and their management decisions). More than 60% of the variability in vegetation change could be explained, with human variables increasing adjusted R-square values of physical-only models by an average of 47%. Restoration "success" was positively associated with an increase in the number of collaborators, the number of information sources used, and the relative priority of plant-related goals. Worse outcomes were associated with an increase in the number of roles the manager held, monitoring frequency, and with higher manager education level. These results point to the indirect impacts of the human element, and specifically supports recommendations to include multiple partners and set specific goals. To our knowledge, this is the first time the importance of human characteristics as drivers of restoration outcomes has been quantified.
Questions: Have species expanded their ranges upward in elevation? Have aand b-diversity changed ... more Questions: Have species expanded their ranges upward in elevation? Have aand b-diversity changed over time? Have species richness changes along the gradient shown distributional patterns? Have community compositions changed over time, and if so, which plant families are responsible for variation? Do herbaceous changes correspond to increased warming, overstorey shifts and disturbance events at each site? Location: Long-term Ecological Research (LTER) sites near Niwot Ridge, CO, US. Methods: We surveyed four herbaceous plant communities along an elevational gradient for species composition, diversity and frequency. Our results were compared to those found in 1981 and 1996 in the same plots to determine longterm community change at each site and along the elevational gradient. We evaluated changes in elevational species range expansion, community diversity, and composition. We related herbaceous change to tree data and site-specific literature on climate and disturbance to analyze change patterns and drivers. Results: Our investigation showed the upward range expansion of eight species. Alpha-diversity changes were site-specific, while species richness changes along the gradient did not exhibit distinctive patterns. Each community changed significantly (P < 0.05) in composition and in b-diversity. Shade-tolerant families increased in dominance at the three lower sites, which reflected succession-driven canopy closure. Changes correlated to increased warming, overstorey shifts and disturbance. Conclusions: Herb aceous communities have changed in dynamic ways, as evidenced by shifts in composition, diversity and distribution. We confirm the need for more long-term studies that can offer robust insights into the interplay between change drivers, such as climate, biotic interactions and disturbance, which work in concert to determine community assemblage.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 12, 2019
Los autores de las comunicaciones son los únicos responsables de los puntos de vista y opiniones ... more Los autores de las comunicaciones son los únicos responsables de los puntos de vista y opiniones planteadas, selección de las soluciones técnicas o de gestión, o planteamiento de los trabajos de investigación presentados en cada uno de los artículos que componen esta publicación. Es posible que el CIREF no comparta algunas soluciones u opiniones. Todas estas comunicaciones fueron aceptadas por el Comité Científico del Congreso Restauraríos y se presentan de forma íntegra como las han redactado sus autores.
Elevated soil salinity is often associated with Tamarix invasion; however, it's unclear whether s... more Elevated soil salinity is often associated with Tamarix invasion; however, it's unclear whether soils are more saline because of Tamarix or other environmental factors. Surface soil salinity was investigated along a flow-regulated, arid river with dense Tamarix of varying age to determine which factors best explain soil salinity. Flooding was the most important predictor, reducing salinity by nearly 70%. Soils under Tamarix had lower salinity than adjacent areas without woody cover in non-flooded areas suggesting that evaporation in arid environments may contribute more surface salts than Tamarix or may exacerbate plant inputs. Under most conditions, higher salinities were found under Tamarix than natives. An exception to this pattern was that soils under the smallest trees were more saline for natives. Relationships between soil salinity and stem size suggest that salts increase over time under Tamarix unless they are removed by flooding. However, the most mature stands had lower salinity than expected, reflecting some additional mechanism. Soil texture and distance from the river were important, but interacted strongly with other factors. The observed relationships between surface soil salinity and Tamarix stem size, a predictor of aboveground age, suggest Tamarix plays an active role in floodplain salinization within the sampled area.
Riparian Research and Management: Past, Present, Future: Volume 1
Fifty years ago, riparian habitats were not recognized for their extensive and critical contribut... more Fifty years ago, riparian habitats were not recognized for their extensive and critical contributions to wildlife and the ecosystem function of watersheds. This changed as riparian values were identified and documented, and the science of riparian ecology developed steadily. Papers in this volume range from the more mesic northwestern United States to the arid Southwest and Mexico. More than two dozen authors-most with decades of experience-review the origins of riparian science in the western United States, document what is currently known about riparian ecosystems, and project future needs. Topics are widespread and include: interactions with fire, climate change, and declining water; impacts from exotic species; unintended consequences of biological control; the role of small mammals; watershed response to beavers; watershed and riparian changes; changes below large dams; water birds of the Colorado River Delta; and terrestrial vertebrates of mesquite bosques. Appendices and references chronicle the field's literature, authors, "riparian pioneers," and conferences.
We present the ideas, conditions, and environments that motivated our co-creation of a Center for... more We present the ideas, conditions, and environments that motivated our co-creation of a Center for a Regenerative Future at the University of Denver. There is an emerging consensus among scholars and a widening realization among younger generations that the concept of sustainability has exhausted its utility as a framework and rhetorical narrative for creating a viable future for humanity. Growing levels of eco-anxiety related to climate change, loss of biodiversity, and their social and economic consequences suggest that efforts to achieve ‘sustainability’ or ‘sustainable development’ are not succeeding. Dominant sustainability paradigms typically rest on an anthropocentric culture–nature dualism and a mechanistic worldview that perpetuates a growth-based economic system that is socially inequitable and ecologically destructive. Regenerative paradigms offer holistic understandings of Earth systems, with accompanying commitments to social and ecological justice. They support the deve...
Abstract Control of invasive species within ecosystems may induce secondary invasions of non-targ... more Abstract Control of invasive species within ecosystems may induce secondary invasions of non-target invaders replacing the first alien. We used four plant species listed as noxious by local authorities in riparian systems to discern whether 1) the severity of these secondary invasions was related to the control method applied to the first alien; and 2) which species that were secondary invaders persisted over time. In a collaborative study by 16 research institutions, we monitored plant species composition following control of non-native Tamarix trees along southwestern U.S. rivers using defoliation by an introduced biocontrol beetle, and three physical removal methods: mechanical using saws, heavy machinery, and burning in 244 treated and 79 untreated sites across six U.S. states. Physical removal favored secondary invasions immediately after Tamarix removal (0–3 yrs.), while in the biocontrol treatment, secondary invasions manifested later (> 5 yrs.). Within this general trend, the response of weeds to control was idiosyncratic; dependent on treatment type and invader. Two annual tumbleweeds that only reproduce by seed ( Bassia scoparia and Salsola tragus ) peaked immediately after physical Tamarix removal and persisted over time, even after herbicide application. Acroptilon repens , a perennial forb that vigorously reproduces by rhizomes, and Bromus tectorum , a very frequent annual grass before removal that only reproduces by seed, were most successful at biocontrol sites, and progressively spread as the canopy layer opened. These results demonstrate that strategies to control Tamarix affect secondary invasions differently among species and that time since disturbance is an important, generally overlooked, factor affecting response.
Considering humans as components of ecosystems is not new; geographers have been doing it in huma... more Considering humans as components of ecosystems is not new; geographers have been doing it in human ecology departments for decades (see Field and Burch 1988). There have also been many volumes dedicated to the subject (McDonnel and Pickett 1993, Schnaiberg and Gould 1994, Catton 1982, Wilson 1988). Recently there has been a development in the field of ecology to consider humans as a part of ecosystems, rather than simply agents of destruction, including the full complexity of human interactions (including social, cultural, and economic) with the environment (chapter 17 this volume, Folke et al. 1996, Turner and Carpenter 1999, Pickett et al. 1999, Haeuber and Ringold 1998). The goal of this chapter is to provide a framework for the types of interactions between humans and biodiversity. We use biodiversity as an umbrella term encompassing genetic, species, and landscape diversities (chapter 1 this volume). In particular, we emphasize human–biodiversity interactions in the context of ...
III Congreso Ibérico de Restauración Fluvial, Jun 12, 2019
Los autores de las comunicaciones son los únicos responsables de los puntos de vista y opiniones ... more Los autores de las comunicaciones son los únicos responsables de los puntos de vista y opiniones planteadas, selección de las soluciones técnicas o de gestión, o planteamiento de los trabajos de investigación presentados en cada uno de los artículos que componen esta publicación. Es posible que el CIREF no comparta algunas soluciones u opiniones. Todas estas comunicaciones fueron aceptadas por el Comité Científico del Congreso Restauraríos y se presentan de forma íntegra como las han redactado sus autores.
We tested the hypothesis that the traits of managers and the types of agencies they represent wou... more We tested the hypothesis that the traits of managers and the types of agencies they represent would have measurable impacts on the outcomes of restoration in 243 sites across the Southwestern US where invasive Tamarix spp. trees had been removed. Change in cover for invasive species, tamarix, and native cover were the dependent variables, based on the difference in these values between the treatment site and a corresponding reference site. Most other columns are either environmental variables (lowercase) or manager variables (all caps). Manager data was collected via surveys and interviews.
Spatial modeling has proven to be useful in understanding the drivers of plant populations in the... more Spatial modeling has proven to be useful in understanding the drivers of plant populations in the field of ecology, but has yet to be applied to understanding variation in biocontrol impact. In this study, we employ multi-scale analysis (Moran’s Eigenvector Maps) to better understand the variation in tree canopy exposed to defoliation by a biocontrol beetle (Diorhabda spp.). The control of the exotic tree Tamarix in riparian areas has long been a priority for land managers and ecologists in the American southwest. Diorhabda spp. was introduced as a bio-control agent beginning in 2001 and has since become an inseparable part of Tamarix-dominated river systems in the southwest. Between 2013 and 2016 tamarisk dieback was assessed at 79 sites across Grand County, Utah, arguably the epicenter of Diorhabda impact in the U.S. Canopy cover of Tamarix was between 73 and 81% at these sites, with the percent that was live cover fluctuating by year with a minimum of 42%. Using a traditional general linear model, we found that readily and commonly measured environmental factors could explain only up to 26% of the variation in Tamarix live canopy each year. The number of defoliations was correlated with an increase rather than a decrease in percent live canopy, suggesting compensatory growth. Spatial structure alone explained 22–40% of variation. We found fine scale spatial structure at less than 10 km and broad scale spatial structure from 10 to 30 km. Combining both traditional and novel spatial statistical methods we increased that percentage to 43–63%, depending on year. These results suggest that scientists and land managers must look beyond commonly measured environmental variables to explain non-random biocontrol impact in this system. In particular, this study points to the potential for biotic interactions and variation in flood cycles for further exploration of the identified spatial structure.
: Changes in historical disturbance regimes have been shown to facilitate non‐native plant invasi... more : Changes in historical disturbance regimes have been shown to facilitate non‐native plant invasions, but reinstatement of disturbance can be successful only if native colonizers are able to outcompete colonizing invasives. Reintroduction of flooding in the southwestern United States is being promoted as a means of reestablishing Populus deltoides subsp. wislizenii, but flooding can also promote establishment of an introduced, invasive species, Tamarix ramosissima. We investigated competition between Populus and Tamarix at the seedling stage to aid in characterizing the process by which Tamarix may invade and to determine the potential ability of Populus to establish itself with competitive pressure from Tamarix. We planted seedlings of Tamarix and Populus in five ratios at three densities for a total of 15 treatments. The growth response of each species was measured in terms of height, above‐ground biomass, and tissue concentrations of nitrogen and phosphorous. These measurements across treatments were modeled as three‐dimensional response surfaces. For both species, Populus density was more important than Tamarix density for determining growth response. Both species were negatively affected by increasing numbers of Populus seedlings. Due to the larger size of the native Populus, we predict that its superior competitive ability can lead to its dominance when conditions allow native establishment. Our results suggest that even in the presence of an invader that positively responds to disturbance, reestablishment of historical flooding regimes and post‐flood hydrology can restore this ecosystem by promoting its dominant plant species.
We investigated the relative role of manager traits and decisions for explaining the impact of ri... more We investigated the relative role of manager traits and decisions for explaining the impact of riparian restoration. To do this, we used the difference in vegetation between post-restoration and controls for 243 pairs of sites to create a success index. We then determined how much variability in success could be explained by physical variables that directly impact vegetation (environment and weed removal) versus human variables (characteristics of the people who managed those sites and their management decisions). More than 60% of the variability in vegetation change could be explained, with human variables increasing adjusted R-square values of physical-only models by an average of 47%. Restoration "success" was positively associated with an increase in the number of collaborators, the number of information sources used, and the relative priority of plant-related goals. Worse outcomes were associated with an increase in the number of roles the manager held, monitoring frequency, and with higher manager education level. These results point to the indirect impacts of the human element, and specifically supports recommendations to include multiple partners and set specific goals. To our knowledge, this is the first time the importance of human characteristics as drivers of restoration outcomes has been quantified.
Questions: Have species expanded their ranges upward in elevation? Have aand b-diversity changed ... more Questions: Have species expanded their ranges upward in elevation? Have aand b-diversity changed over time? Have species richness changes along the gradient shown distributional patterns? Have community compositions changed over time, and if so, which plant families are responsible for variation? Do herbaceous changes correspond to increased warming, overstorey shifts and disturbance events at each site? Location: Long-term Ecological Research (LTER) sites near Niwot Ridge, CO, US. Methods: We surveyed four herbaceous plant communities along an elevational gradient for species composition, diversity and frequency. Our results were compared to those found in 1981 and 1996 in the same plots to determine longterm community change at each site and along the elevational gradient. We evaluated changes in elevational species range expansion, community diversity, and composition. We related herbaceous change to tree data and site-specific literature on climate and disturbance to analyze change patterns and drivers. Results: Our investigation showed the upward range expansion of eight species. Alpha-diversity changes were site-specific, while species richness changes along the gradient did not exhibit distinctive patterns. Each community changed significantly (P < 0.05) in composition and in b-diversity. Shade-tolerant families increased in dominance at the three lower sites, which reflected succession-driven canopy closure. Changes correlated to increased warming, overstorey shifts and disturbance. Conclusions: Herb aceous communities have changed in dynamic ways, as evidenced by shifts in composition, diversity and distribution. We confirm the need for more long-term studies that can offer robust insights into the interplay between change drivers, such as climate, biotic interactions and disturbance, which work in concert to determine community assemblage.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 12, 2019
Los autores de las comunicaciones son los únicos responsables de los puntos de vista y opiniones ... more Los autores de las comunicaciones son los únicos responsables de los puntos de vista y opiniones planteadas, selección de las soluciones técnicas o de gestión, o planteamiento de los trabajos de investigación presentados en cada uno de los artículos que componen esta publicación. Es posible que el CIREF no comparta algunas soluciones u opiniones. Todas estas comunicaciones fueron aceptadas por el Comité Científico del Congreso Restauraríos y se presentan de forma íntegra como las han redactado sus autores.
Elevated soil salinity is often associated with Tamarix invasion; however, it's unclear whether s... more Elevated soil salinity is often associated with Tamarix invasion; however, it's unclear whether soils are more saline because of Tamarix or other environmental factors. Surface soil salinity was investigated along a flow-regulated, arid river with dense Tamarix of varying age to determine which factors best explain soil salinity. Flooding was the most important predictor, reducing salinity by nearly 70%. Soils under Tamarix had lower salinity than adjacent areas without woody cover in non-flooded areas suggesting that evaporation in arid environments may contribute more surface salts than Tamarix or may exacerbate plant inputs. Under most conditions, higher salinities were found under Tamarix than natives. An exception to this pattern was that soils under the smallest trees were more saline for natives. Relationships between soil salinity and stem size suggest that salts increase over time under Tamarix unless they are removed by flooding. However, the most mature stands had lower salinity than expected, reflecting some additional mechanism. Soil texture and distance from the river were important, but interacted strongly with other factors. The observed relationships between surface soil salinity and Tamarix stem size, a predictor of aboveground age, suggest Tamarix plays an active role in floodplain salinization within the sampled area.
Riparian Research and Management: Past, Present, Future: Volume 1
Fifty years ago, riparian habitats were not recognized for their extensive and critical contribut... more Fifty years ago, riparian habitats were not recognized for their extensive and critical contributions to wildlife and the ecosystem function of watersheds. This changed as riparian values were identified and documented, and the science of riparian ecology developed steadily. Papers in this volume range from the more mesic northwestern United States to the arid Southwest and Mexico. More than two dozen authors-most with decades of experience-review the origins of riparian science in the western United States, document what is currently known about riparian ecosystems, and project future needs. Topics are widespread and include: interactions with fire, climate change, and declining water; impacts from exotic species; unintended consequences of biological control; the role of small mammals; watershed response to beavers; watershed and riparian changes; changes below large dams; water birds of the Colorado River Delta; and terrestrial vertebrates of mesquite bosques. Appendices and references chronicle the field's literature, authors, "riparian pioneers," and conferences.
We present the ideas, conditions, and environments that motivated our co-creation of a Center for... more We present the ideas, conditions, and environments that motivated our co-creation of a Center for a Regenerative Future at the University of Denver. There is an emerging consensus among scholars and a widening realization among younger generations that the concept of sustainability has exhausted its utility as a framework and rhetorical narrative for creating a viable future for humanity. Growing levels of eco-anxiety related to climate change, loss of biodiversity, and their social and economic consequences suggest that efforts to achieve ‘sustainability’ or ‘sustainable development’ are not succeeding. Dominant sustainability paradigms typically rest on an anthropocentric culture–nature dualism and a mechanistic worldview that perpetuates a growth-based economic system that is socially inequitable and ecologically destructive. Regenerative paradigms offer holistic understandings of Earth systems, with accompanying commitments to social and ecological justice. They support the deve...
Abstract Control of invasive species within ecosystems may induce secondary invasions of non-targ... more Abstract Control of invasive species within ecosystems may induce secondary invasions of non-target invaders replacing the first alien. We used four plant species listed as noxious by local authorities in riparian systems to discern whether 1) the severity of these secondary invasions was related to the control method applied to the first alien; and 2) which species that were secondary invaders persisted over time. In a collaborative study by 16 research institutions, we monitored plant species composition following control of non-native Tamarix trees along southwestern U.S. rivers using defoliation by an introduced biocontrol beetle, and three physical removal methods: mechanical using saws, heavy machinery, and burning in 244 treated and 79 untreated sites across six U.S. states. Physical removal favored secondary invasions immediately after Tamarix removal (0–3 yrs.), while in the biocontrol treatment, secondary invasions manifested later (> 5 yrs.). Within this general trend, the response of weeds to control was idiosyncratic; dependent on treatment type and invader. Two annual tumbleweeds that only reproduce by seed ( Bassia scoparia and Salsola tragus ) peaked immediately after physical Tamarix removal and persisted over time, even after herbicide application. Acroptilon repens , a perennial forb that vigorously reproduces by rhizomes, and Bromus tectorum , a very frequent annual grass before removal that only reproduces by seed, were most successful at biocontrol sites, and progressively spread as the canopy layer opened. These results demonstrate that strategies to control Tamarix affect secondary invasions differently among species and that time since disturbance is an important, generally overlooked, factor affecting response.
Considering humans as components of ecosystems is not new; geographers have been doing it in huma... more Considering humans as components of ecosystems is not new; geographers have been doing it in human ecology departments for decades (see Field and Burch 1988). There have also been many volumes dedicated to the subject (McDonnel and Pickett 1993, Schnaiberg and Gould 1994, Catton 1982, Wilson 1988). Recently there has been a development in the field of ecology to consider humans as a part of ecosystems, rather than simply agents of destruction, including the full complexity of human interactions (including social, cultural, and economic) with the environment (chapter 17 this volume, Folke et al. 1996, Turner and Carpenter 1999, Pickett et al. 1999, Haeuber and Ringold 1998). The goal of this chapter is to provide a framework for the types of interactions between humans and biodiversity. We use biodiversity as an umbrella term encompassing genetic, species, and landscape diversities (chapter 1 this volume). In particular, we emphasize human–biodiversity interactions in the context of ...
III Congreso Ibérico de Restauración Fluvial, Jun 12, 2019
Los autores de las comunicaciones son los únicos responsables de los puntos de vista y opiniones ... more Los autores de las comunicaciones son los únicos responsables de los puntos de vista y opiniones planteadas, selección de las soluciones técnicas o de gestión, o planteamiento de los trabajos de investigación presentados en cada uno de los artículos que componen esta publicación. Es posible que el CIREF no comparta algunas soluciones u opiniones. Todas estas comunicaciones fueron aceptadas por el Comité Científico del Congreso Restauraríos y se presentan de forma íntegra como las han redactado sus autores.
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