Four species of exotic cordgrass (Spartina sp.) occur in the San Francisco estuary in addition to... more Four species of exotic cordgrass (Spartina sp.) occur in the San Francisco estuary in addition to the California native Spartina foliosa. Our goal was to map the location and extent of all non-native Spartina in the estuary. Hybrids of S. alterniflora and S. foliosa are by far the most numerous exotic and are spreading rapidly. Radiating from sites of deliberate introduction, S. alterniflora and hybrids now cover ca. 190 ha, mainly in the South and Central Bay. Estimates of rate of aerial increase range from a constant value to an accelerating rate of increase. This could be due to the proliferation of hybrid clones capable of rapid expansion and having superior seed set and siring abilities. The total coverage of 195 ha by hybrids and other exotic cordgrass species is slightly less than 1 % of the Bay’s tidal mudflats and marshes. Spartina anglica has not spread beyond its original 1970s introduction site. Spartina densiflora has spread to cover over 5 ha at 3 sites in the Central ...
The Third International Conference on Invasive Spartina convened to provide a forum for the best ... more The Third International Conference on Invasive Spartina convened to provide a forum for the best and latest Spartina research, and an opportunity to discuss new developments in Spartina science with marsh land managers and technical experts who had extensive experience with this invasive genus. The theme of the conference, “Linking science and management, ” reflected the desire of the organizers to improve both fields through increased exposure and interaction with each other, continuing and extending a focus on uniting managers and researchers that was established at earlier international conferences on this subject. The first international Spartina conference was held in 1990 in Seattle, Washington, and the second in 1997 in Olympia, Washington. We are pleased to have hosted the Third International Conference on Invasive Spartina here in San Francisco, California in 2004. The success of this event was the result of hard work and support of a number of individuals and organizations...
Conservation of rare plants requires an understanding of how the species responds to natural and ... more Conservation of rare plants requires an understanding of how the species responds to natural and artificial disturbance dynamics. For chaparral species this includes the natural disturbances of fire and shrub canopy closure during the interfire period, and the effect of shrub clearing for fuel reduction. Packera layneae is a federally listed rare herbaceous perennial subject to all these disturbances; its center of distribution is upon the gabbro soils surrounding Pine Hill in western El Dorado County, CA an area known as a hotspot of botanical diversity. Combining genetic data with mapping following a 2007 wildfire in Shingle Springs, we found that the species survives fire and chaparral overgrowth due to underground rhizomes and caudices that resprout after fire and enable its persistence under dense chaparral canopies; as well, seed recruitment of new genetic individuals occurred within discrete patches. Seedlings were not found the spring following the 2007 fire, suggesting fire...
We examined the effects of hand clearing and pile burning of chaparral on plants and wildlife on ... more We examined the effects of hand clearing and pile burning of chaparral on plants and wildlife on the perimeter of Pine Hill 1-2 years after clearing. Pine Hill is home to four federally listed plant species, necessitating botanical surveys prior to clearing activities to prevent harming these species. We found over 65 new locations for the listed plants. We compared vegetation within burn scars, in cleared only plots, and in intact chaparral (control) and the germination and survival of a listed species, Ceanothus roderickii (Pine Hill Ceanothus). The density of C. roderickii seedlings was far lower in the cleared, unburned treatment than in the burned treatments, while mature C. roderickii was only present in unburned treatments and mature chaparral. Intact chaparral had higher cover but lower species richness of both native and exotic species than all disturbed treatments. The cleared only treatment had almost three times the cover by exotic grasses as did the burned treatments, and cover by presumably palatable, native and exotic species, was almost twice that of the burned treatments; mature chaparral contained few palatable plants, i.e. those identified as having wildlife value by Conrad (1987). Increased availability of palatable plants in treated areas may have contributed to 3-4 times higher probabilities of detection by cameras of herbivores in treated versus intact chaparral; which may have attracted smaller predators (bobcats [Lynx rufus] and grey foxes [Urocyon cinereoargenteus]) that were positively associated with western grey squirrel (Sciurus griseus) detections. Large carnivore detections were higher in areas with higher mule deer (Odocoileus hemionus) detections. Larger animals (pumas [Puma concolor], black bears [Ursus americanus], and mule deer) were detected 2-4 times more in treated areas, likely due to the physical impediment of mature chaparral. Invasion of nonnative grasses and increased wildlife usage may have been accelerated through the creation of firebreaks; continued monitoring will investigate long-term effects.
Cordylanthus palmatus is an annual plant that inhabits seasonally flooded wetlands with saline an... more Cordylanthus palmatus is an annual plant that inhabits seasonally flooded wetlands with saline and alkaline soils in California, USA. In 1986, the plant was listed as endangered due to the small size or threats to its five remaining populations. The goal of our research was to inform conservation strategies by examining genetic diversity and structure and their potential response to demographic and environmental stochasticity. We used nuclear DNA markers to measure genetic characteristics. To explore potential influences on genetic variation and structure we assessed fluctuations in population size and interspecific hybridization between C. palmatus and C. mollis ssp. hispidus. We found geographically separate populations of C. palmatus were genetically distinct, with a FST of 0.23, indicating substantial genetic structure among populations. Within populations, there was no evidence of isolationbydistance. However, two adjacent vernal pools contained genetically distinct sub-populat...
The Third International Conference on Invasive Spartina convened to provide a forum for the best ... more The Third International Conference on Invasive Spartina convened to provide a forum for the best and latest Spartina research, and an opportunity to discuss new developments in Spartina science with marsh land managers and technical experts who had extensive experience with this invasive genus. The theme of the conference, " Linking science and management, " reflected the desire of the organizers to improve both fields through increased exposure and interaction with each other, continuing and extending a focus on uniting managers and researchers that was established at earlier international conferences on this subject. The success of this event was the result of hard work and support of a number of individuals and organizations. The Conference Organizing Committee helped to guide the development of the conference and addressed organizational issues as they arose. The Science Program Committee developed the conference program, selected presentations and special guest presen...
In 2014 a DNA-based phylogenetic study confirming the paraphyly of the grass subtribe Sporobolina... more In 2014 a DNA-based phylogenetic study confirming the paraphyly of the grass subtribe Sporobolinae proposed the creation of a large monophyletic genus Sporobolus, including (among others) species previously included in the genera Spartina, Calamovilfa, and Sporobolus. Spartina species have contributed substantially (and continue contributing) to our knowledge in multiple disciplines, including ecology, evolutionary biology, molecular biology, biogeography, experimental ecology, biological invasions, environmental management, restoration ecology, history, economics, and sociology. There is no rationale so compelling to subsume the name Spartina as a subgenus that could rival the striking, global iconic history and use of the name Spartina for over 200 years. We do not agree with the subjective arguments underlying the proposal to change Spartina to Sporobolus. We understand the importance of both the objective phylogenetic insights and of the subjective formalized nomenclature and hope that by opening this debate we will encourage positive feedback that will strengthen taxonomic decisions with an interdisciplinary perspective. We consider that the strongly distinct, monophyletic clade Spartina should simply and efficiently be treated as the genus Spartina.
San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spar... more San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spartina foliosa, has been the recipient of introductions of S. alterniflora and S. densiflora. Hybrids have arisen between the native and these exotic species. Sterile F1 S. densiflora 9 foliosa hybrids have formed numerous times in a number of marshes, while introgressing S. alterniflora 9 foliosa hybrids are fully fertile and invaded widely in SFB, especially onto naturally-open low tidal flats by inundationtolerant hybrids. Sarcocornia pacifica, pickleweed, dominates the mid-to-upper marsh zones where the hypersaline conditions that occur during the summer drought, characteristic of this climate, exclude S. foliosa. Here we report on two glasshouse experiments investigating the salinity tolerance of hybrid Spartina. Some hybrids of both origins grew well and flowered at high salinity levels while the parental species grew little and did not flower. Our results imply that midzone marshes are also vulnerable to invasion by salinity-tolerant Spartina hybrids. Herbicide control implemented over the last 10 years targeting both the exotic species and their hybrids have reduced their extent. However, efforts in monitoring and management of exotic Spartina and its hybrids must continue as vast areas of tidal marsh restoration are underway and planned in SFB; colonization by Spartina hybrids tolerant to inundation and/or salinity will greatly alter restoration trajectories. These concerns are all the more vital given projections of climate change and its effects on salinity and sea level rise in SFB salt marshes.
Chloropyron palmatum (Ferris) Tank & J.M Egger (formerly Cordylanthus palmatus [Ferris] J. F. Mac... more Chloropyron palmatum (Ferris) Tank & J.M Egger (formerly Cordylanthus palmatus [Ferris] J. F. Macbr.) is an annual plant that inhabits seasonally flooded wetlands with saline and alkaline soils in California. In 1986, the plant was listed as endangered under the U.S. Endangered Species Act. We aimed to inform conservation strategies for the species' five remaining populations by examining the genetic diversity and structure of the populations (on the basis of nuclear DNA markers) and their potential response to demographic and env ironmental stochasticity. We also assessed fluctuations in population size and whether there was evidence of hybridization between C. palmatum and Chloropyron molle (A. Gray) A. Heller subsp. hispidum (Pennell) Tank & J.M. Egger (formerly Cordylanthus mollis A. Gray subsp. hispidus [Pennell] T.I. Chuang & Heckard). Populations of C. palmatum were genetically distinct with a F ST of 0.23, indicating substantial genetic structure among populations. Within populations, there was no evidence of isolation by distance. However, individuals in two adjacent vernal pools were genetically distinct. The pattern of genetic variation within populations suggests that the historical frequency and extent of seed dispersal by overland flooding has strongly affected the genetic structure of populations. Despite founder effects and population bottlenecks, small and large populations had similar levels of genetic variation. We found no evidence of hybridization. All extant populations of C. palmatum are genetically variable and distinct. We recommend that hydrologic connectivity be considered if seeds are collected and sowed with the intent of increasing the size of natural populations or creating experimental populations.
Hybrids between alien cordgrass, Spartina alterniflora, introduced in the 1970s, and native Calif... more Hybrids between alien cordgrass, Spartina alterniflora, introduced in the 1970s, and native California cordgrass, S. foliosa are a menace to the ecology of San Francisco Bay, spreading to aggressively invade open mud, displacing native species, hindering flood control, navigation, and other uses of this habitat. We proposed to determine the key elements of the ecology of the hybrid cordgrass invasion: ecological amplitude of parental species and hybrids, dynamics of seedling movement and recruitment, and broad spread of hybrids around the Bay and up the Sacramento Delta. Our previous field and molecular work suggested that vigorous hybrids grow taller and more densely than either parental species; they should have greatest competitive abilities and tidal range. To experimentally compare ecological amplitudes among cordgrass plants, we measured vegetative vigor and sexual reproduction of cordgrass genotypes planted in common gardens on the intertidal plane. To identify essential components of seedling recruitment, we planned to characterized seed movement on the tides, persistence in the soil seed bank, and germination and establishment of cordgrass genotypes in experimental field plots. To document the rate and extent of the spread of hybrids around the Bay, we annually surveyed and genetically characterized cordgrass seedlings and plants in marshes where hybrids were established as well as previously un-invaded marshes.
The genetic structure of Senecio layneae, a rare plant endemic to the fire adapted chaparral in t... more The genetic structure of Senecio layneae, a rare plant endemic to the fire adapted chaparral in the central foothills of the Sierra Nevada, California, USA, was investigated over the entire known range of the species. Genetic variation was assessed using 63 ISSR and 42 RAPD polymorphic DNA markers. Multivariate analysis differentiated populations from each of three counties and grouped two populations from El Dorado County together. ISSR markers more accurately portrayed population membership patterns than did RAPD markers. A species-wide FST of 0.28 (by AMOVA) and a Fsx of 0.22 within El Dorado County showed that significant genetic differentiation exists in the species and between local (within 5.5 km) populations. These results argue for maintenance of disturbed openings in the chapparal which this federally listed, threatened species can recolonise after fire, and for the use of local seed sources (within 5.5 km) for re-introduction efforts. Additionally, the preservation of mul...
We examined the population genetic structure of Sonoma sunshine (Blennosperma bakeri), and Burke&... more We examined the population genetic structure of Sonoma sunshine (Blennosperma bakeri), and Burke's goldfields (Lasthenia burkei), two endangered annual plant species mostly restricted to vernal pools of the Santa Rosa Plain, Sonoma County. Conservation of existing populations and additional population establishment on protected mitigation lands are now under way. To inform these efforts we developed nuclear DNA markers to characterize the distribution of genetic variation among populations in space and in time. The Sonoma Valley population of B. bakeri was distinct from those on the Santa Rosa Plain (PhiPT = 0.19, P < 0.001) and notable genetic structure existed among populations within the Santa Rosa Plain (PhiPT = 0.11, P < 0.001). Range-wide, geographically separate populations of L. burkei were genetically distinct (PhiST = 0.22, P < 0.001). The variation was divided between the difference among Lake and Sonoma County populations (PhiST = 0.11), and within Sonoma Co...
Wyethia reticulata (Asteraceae), Ceanothus roderickii (Rhamnaceae), and Calystegia stebbinsii (Co... more Wyethia reticulata (Asteraceae), Ceanothus roderickii (Rhamnaceae), and Calystegia stebbinsii (Convolvulaceae) are rare plants endemic to the gabbroic chaparral of western El Dorado County, California. All three are threatened by ongoing residential development and fire suppression. I examined vegetative growth and flowering of these species before fire, and the survival, growth, and development of seeds, seedlings, and resprouted stems after fire. Fire was necessary for recruitment from seed in all three species. While seedling recruitment may not be required for maintenance of extensively clonal, resprouting W. reticulata populations, without fire-stimulated germination, populations of both C. roderickii and C. stebbinsii were mostly represented only in the seed bank in mature chaparral. Recovery patterns of other species of obligately seeding chaparral species suggest that in addition to habitat loss, a principle threat to species in this functional group are short-interval fires...
Abstract Chloropyron palmatum (Ferris) Tank & J.M Egger (formerly Cordylanthus palmatus [Ferr... more Abstract Chloropyron palmatum (Ferris) Tank & J.M Egger (formerly Cordylanthus palmatus [Ferris] J. F. Macbr.) is an annual plant that inhabits seasonally flooded wetlands with saline and alkaline soils in California. In 1986, the plant was listed as endangered under the U.S. Endangered Species Act. We aimed to inform conservation strategies for the species’ five remaining populations by examining the genetic diversity and structure of the populations (on the basis of nuclear DNA markers) and their potential response to demographic and environmental stochasticity. We also assessed fluctuations in population size and whether there was evidence of hybridization between C. palmatum and Chloropyron molle (A. Gray) A. Heller subsp. hispidum (Pennell) Tank & J.M. Egger (formerly Cordylanthus mollis A. Gray subsp. hispidus [Pennell] T.I. Chuang & Heckard). Populations of C. palmatum were genetically distinct with a FST of 0.23, indicating substantial genetic structure among populations. Within populations, there was no evidence of isolation by distance. However, individuals in two adjacent vernal pools were genetically distinct. The pattern of genetic variation within populations suggests that the historical frequency and extent of seed dispersal by overland flooding has strongly affected the genetic structure of populations. Despite founder effects and population bottlenecks, small and large populations had similar levels of genetic variation. We found no evidence of hybridization. All extant populations of C. palmatum are genetically variable and distinct. We recommend that hydrologic connectivity be considered if seeds are collected and sowed with the intent of increasing the size of natural populations or creating experimental populations.
The cordgrasses in the genus Spartina have become model organisms for studying biological invasio... more The cordgrasses in the genus Spartina have become model organisms for studying biological invasions from both ecological and genetic perspectives. Here we characterize 11 disomic loci in Spartina alterniflora that show promise for population studies and for studying hybridization events between S. alterniflora and S. foliosa. Comparisons among invasive and native S. alterniflora populations showed that levels of allelic variation are lower in invasive populations. In addition, nearly all loci that amplified in S. foliosa populations and in a swarm of S. alterniflora × × × × foliosa hybrids were polymorphic. We also found that several loci amplified successfully in other Spartina species.
The aim of this study was to explore the origin of the invasive Spartina densiflora by analysing ... more The aim of this study was to explore the origin of the invasive Spartina densiflora by analysing samples from the native region (South America) and from a recently colonized area (California). A combination of various molecular data (chloroplast and nuclear sequences, molecular fingerprint) and ploidy level estimations was used to answer the question whether the reticulate phylogenetic pattern previously detected in S. densiflora was restricted to California, or alternatively, whether a more ancient hybrid origin preceded formation of this species in its native area. We found that this species is heptaploid in both its native and introduced range. Identification of nuclear homeologous sequences indicate that this species has a reticulate origin in its native range, involving a lineage related to the hexaploid clade formed by S. alterniflora, S. foliosa, and S. maritima, and another lineage related to the sub-Antarctic endemic S. arundinacea that provided the chloroplast genome. The samples from California displayed similar multilocus patterns to the samples from Chile, supporting the hypothesis that this species originated on the southeast American coast (Argentina), from where it eventually spread to the west coast of South America (Chile) first and to the Northern Hemisphere (California) later.
Four species of exotic cordgrass (Spartina sp.) occur in the San Francisco estuary in addition to... more Four species of exotic cordgrass (Spartina sp.) occur in the San Francisco estuary in addition to the California native Spartina foliosa. Our goal was to map the location and extent of all non-native Spartina in the estuary. Hybrids of S. alterniflora and S. foliosa are by far the most numerous exotic and are spreading rapidly. Radiating from sites of deliberate introduction, S. alterniflora and hybrids now cover ca. 190 ha, mainly in the South and Central Bay. Estimates of rate of aerial increase range from a constant value to an accelerating rate of increase. This could be due to the proliferation of hybrid clones capable of rapid expansion and having superior seed set and siring abilities. The total coverage of 195 ha by hybrids and other exotic cordgrass species is slightly less than 1 % of the Bay’s tidal mudflats and marshes. Spartina anglica has not spread beyond its original 1970s introduction site. Spartina densiflora has spread to cover over 5 ha at 3 sites in the Central ...
The Third International Conference on Invasive Spartina convened to provide a forum for the best ... more The Third International Conference on Invasive Spartina convened to provide a forum for the best and latest Spartina research, and an opportunity to discuss new developments in Spartina science with marsh land managers and technical experts who had extensive experience with this invasive genus. The theme of the conference, “Linking science and management, ” reflected the desire of the organizers to improve both fields through increased exposure and interaction with each other, continuing and extending a focus on uniting managers and researchers that was established at earlier international conferences on this subject. The first international Spartina conference was held in 1990 in Seattle, Washington, and the second in 1997 in Olympia, Washington. We are pleased to have hosted the Third International Conference on Invasive Spartina here in San Francisco, California in 2004. The success of this event was the result of hard work and support of a number of individuals and organizations...
Conservation of rare plants requires an understanding of how the species responds to natural and ... more Conservation of rare plants requires an understanding of how the species responds to natural and artificial disturbance dynamics. For chaparral species this includes the natural disturbances of fire and shrub canopy closure during the interfire period, and the effect of shrub clearing for fuel reduction. Packera layneae is a federally listed rare herbaceous perennial subject to all these disturbances; its center of distribution is upon the gabbro soils surrounding Pine Hill in western El Dorado County, CA an area known as a hotspot of botanical diversity. Combining genetic data with mapping following a 2007 wildfire in Shingle Springs, we found that the species survives fire and chaparral overgrowth due to underground rhizomes and caudices that resprout after fire and enable its persistence under dense chaparral canopies; as well, seed recruitment of new genetic individuals occurred within discrete patches. Seedlings were not found the spring following the 2007 fire, suggesting fire...
We examined the effects of hand clearing and pile burning of chaparral on plants and wildlife on ... more We examined the effects of hand clearing and pile burning of chaparral on plants and wildlife on the perimeter of Pine Hill 1-2 years after clearing. Pine Hill is home to four federally listed plant species, necessitating botanical surveys prior to clearing activities to prevent harming these species. We found over 65 new locations for the listed plants. We compared vegetation within burn scars, in cleared only plots, and in intact chaparral (control) and the germination and survival of a listed species, Ceanothus roderickii (Pine Hill Ceanothus). The density of C. roderickii seedlings was far lower in the cleared, unburned treatment than in the burned treatments, while mature C. roderickii was only present in unburned treatments and mature chaparral. Intact chaparral had higher cover but lower species richness of both native and exotic species than all disturbed treatments. The cleared only treatment had almost three times the cover by exotic grasses as did the burned treatments, and cover by presumably palatable, native and exotic species, was almost twice that of the burned treatments; mature chaparral contained few palatable plants, i.e. those identified as having wildlife value by Conrad (1987). Increased availability of palatable plants in treated areas may have contributed to 3-4 times higher probabilities of detection by cameras of herbivores in treated versus intact chaparral; which may have attracted smaller predators (bobcats [Lynx rufus] and grey foxes [Urocyon cinereoargenteus]) that were positively associated with western grey squirrel (Sciurus griseus) detections. Large carnivore detections were higher in areas with higher mule deer (Odocoileus hemionus) detections. Larger animals (pumas [Puma concolor], black bears [Ursus americanus], and mule deer) were detected 2-4 times more in treated areas, likely due to the physical impediment of mature chaparral. Invasion of nonnative grasses and increased wildlife usage may have been accelerated through the creation of firebreaks; continued monitoring will investigate long-term effects.
Cordylanthus palmatus is an annual plant that inhabits seasonally flooded wetlands with saline an... more Cordylanthus palmatus is an annual plant that inhabits seasonally flooded wetlands with saline and alkaline soils in California, USA. In 1986, the plant was listed as endangered due to the small size or threats to its five remaining populations. The goal of our research was to inform conservation strategies by examining genetic diversity and structure and their potential response to demographic and environmental stochasticity. We used nuclear DNA markers to measure genetic characteristics. To explore potential influences on genetic variation and structure we assessed fluctuations in population size and interspecific hybridization between C. palmatus and C. mollis ssp. hispidus. We found geographically separate populations of C. palmatus were genetically distinct, with a FST of 0.23, indicating substantial genetic structure among populations. Within populations, there was no evidence of isolationbydistance. However, two adjacent vernal pools contained genetically distinct sub-populat...
The Third International Conference on Invasive Spartina convened to provide a forum for the best ... more The Third International Conference on Invasive Spartina convened to provide a forum for the best and latest Spartina research, and an opportunity to discuss new developments in Spartina science with marsh land managers and technical experts who had extensive experience with this invasive genus. The theme of the conference, " Linking science and management, " reflected the desire of the organizers to improve both fields through increased exposure and interaction with each other, continuing and extending a focus on uniting managers and researchers that was established at earlier international conferences on this subject. The success of this event was the result of hard work and support of a number of individuals and organizations. The Conference Organizing Committee helped to guide the development of the conference and addressed organizational issues as they arose. The Science Program Committee developed the conference program, selected presentations and special guest presen...
In 2014 a DNA-based phylogenetic study confirming the paraphyly of the grass subtribe Sporobolina... more In 2014 a DNA-based phylogenetic study confirming the paraphyly of the grass subtribe Sporobolinae proposed the creation of a large monophyletic genus Sporobolus, including (among others) species previously included in the genera Spartina, Calamovilfa, and Sporobolus. Spartina species have contributed substantially (and continue contributing) to our knowledge in multiple disciplines, including ecology, evolutionary biology, molecular biology, biogeography, experimental ecology, biological invasions, environmental management, restoration ecology, history, economics, and sociology. There is no rationale so compelling to subsume the name Spartina as a subgenus that could rival the striking, global iconic history and use of the name Spartina for over 200 years. We do not agree with the subjective arguments underlying the proposal to change Spartina to Sporobolus. We understand the importance of both the objective phylogenetic insights and of the subjective formalized nomenclature and hope that by opening this debate we will encourage positive feedback that will strengthen taxonomic decisions with an interdisciplinary perspective. We consider that the strongly distinct, monophyletic clade Spartina should simply and efficiently be treated as the genus Spartina.
San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spar... more San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spartina foliosa, has been the recipient of introductions of S. alterniflora and S. densiflora. Hybrids have arisen between the native and these exotic species. Sterile F1 S. densiflora 9 foliosa hybrids have formed numerous times in a number of marshes, while introgressing S. alterniflora 9 foliosa hybrids are fully fertile and invaded widely in SFB, especially onto naturally-open low tidal flats by inundationtolerant hybrids. Sarcocornia pacifica, pickleweed, dominates the mid-to-upper marsh zones where the hypersaline conditions that occur during the summer drought, characteristic of this climate, exclude S. foliosa. Here we report on two glasshouse experiments investigating the salinity tolerance of hybrid Spartina. Some hybrids of both origins grew well and flowered at high salinity levels while the parental species grew little and did not flower. Our results imply that midzone marshes are also vulnerable to invasion by salinity-tolerant Spartina hybrids. Herbicide control implemented over the last 10 years targeting both the exotic species and their hybrids have reduced their extent. However, efforts in monitoring and management of exotic Spartina and its hybrids must continue as vast areas of tidal marsh restoration are underway and planned in SFB; colonization by Spartina hybrids tolerant to inundation and/or salinity will greatly alter restoration trajectories. These concerns are all the more vital given projections of climate change and its effects on salinity and sea level rise in SFB salt marshes.
Chloropyron palmatum (Ferris) Tank & J.M Egger (formerly Cordylanthus palmatus [Ferris] J. F. Mac... more Chloropyron palmatum (Ferris) Tank & J.M Egger (formerly Cordylanthus palmatus [Ferris] J. F. Macbr.) is an annual plant that inhabits seasonally flooded wetlands with saline and alkaline soils in California. In 1986, the plant was listed as endangered under the U.S. Endangered Species Act. We aimed to inform conservation strategies for the species' five remaining populations by examining the genetic diversity and structure of the populations (on the basis of nuclear DNA markers) and their potential response to demographic and env ironmental stochasticity. We also assessed fluctuations in population size and whether there was evidence of hybridization between C. palmatum and Chloropyron molle (A. Gray) A. Heller subsp. hispidum (Pennell) Tank & J.M. Egger (formerly Cordylanthus mollis A. Gray subsp. hispidus [Pennell] T.I. Chuang & Heckard). Populations of C. palmatum were genetically distinct with a F ST of 0.23, indicating substantial genetic structure among populations. Within populations, there was no evidence of isolation by distance. However, individuals in two adjacent vernal pools were genetically distinct. The pattern of genetic variation within populations suggests that the historical frequency and extent of seed dispersal by overland flooding has strongly affected the genetic structure of populations. Despite founder effects and population bottlenecks, small and large populations had similar levels of genetic variation. We found no evidence of hybridization. All extant populations of C. palmatum are genetically variable and distinct. We recommend that hydrologic connectivity be considered if seeds are collected and sowed with the intent of increasing the size of natural populations or creating experimental populations.
Hybrids between alien cordgrass, Spartina alterniflora, introduced in the 1970s, and native Calif... more Hybrids between alien cordgrass, Spartina alterniflora, introduced in the 1970s, and native California cordgrass, S. foliosa are a menace to the ecology of San Francisco Bay, spreading to aggressively invade open mud, displacing native species, hindering flood control, navigation, and other uses of this habitat. We proposed to determine the key elements of the ecology of the hybrid cordgrass invasion: ecological amplitude of parental species and hybrids, dynamics of seedling movement and recruitment, and broad spread of hybrids around the Bay and up the Sacramento Delta. Our previous field and molecular work suggested that vigorous hybrids grow taller and more densely than either parental species; they should have greatest competitive abilities and tidal range. To experimentally compare ecological amplitudes among cordgrass plants, we measured vegetative vigor and sexual reproduction of cordgrass genotypes planted in common gardens on the intertidal plane. To identify essential components of seedling recruitment, we planned to characterized seed movement on the tides, persistence in the soil seed bank, and germination and establishment of cordgrass genotypes in experimental field plots. To document the rate and extent of the spread of hybrids around the Bay, we annually surveyed and genetically characterized cordgrass seedlings and plants in marshes where hybrids were established as well as previously un-invaded marshes.
The genetic structure of Senecio layneae, a rare plant endemic to the fire adapted chaparral in t... more The genetic structure of Senecio layneae, a rare plant endemic to the fire adapted chaparral in the central foothills of the Sierra Nevada, California, USA, was investigated over the entire known range of the species. Genetic variation was assessed using 63 ISSR and 42 RAPD polymorphic DNA markers. Multivariate analysis differentiated populations from each of three counties and grouped two populations from El Dorado County together. ISSR markers more accurately portrayed population membership patterns than did RAPD markers. A species-wide FST of 0.28 (by AMOVA) and a Fsx of 0.22 within El Dorado County showed that significant genetic differentiation exists in the species and between local (within 5.5 km) populations. These results argue for maintenance of disturbed openings in the chapparal which this federally listed, threatened species can recolonise after fire, and for the use of local seed sources (within 5.5 km) for re-introduction efforts. Additionally, the preservation of mul...
We examined the population genetic structure of Sonoma sunshine (Blennosperma bakeri), and Burke&... more We examined the population genetic structure of Sonoma sunshine (Blennosperma bakeri), and Burke's goldfields (Lasthenia burkei), two endangered annual plant species mostly restricted to vernal pools of the Santa Rosa Plain, Sonoma County. Conservation of existing populations and additional population establishment on protected mitigation lands are now under way. To inform these efforts we developed nuclear DNA markers to characterize the distribution of genetic variation among populations in space and in time. The Sonoma Valley population of B. bakeri was distinct from those on the Santa Rosa Plain (PhiPT = 0.19, P < 0.001) and notable genetic structure existed among populations within the Santa Rosa Plain (PhiPT = 0.11, P < 0.001). Range-wide, geographically separate populations of L. burkei were genetically distinct (PhiST = 0.22, P < 0.001). The variation was divided between the difference among Lake and Sonoma County populations (PhiST = 0.11), and within Sonoma Co...
Wyethia reticulata (Asteraceae), Ceanothus roderickii (Rhamnaceae), and Calystegia stebbinsii (Co... more Wyethia reticulata (Asteraceae), Ceanothus roderickii (Rhamnaceae), and Calystegia stebbinsii (Convolvulaceae) are rare plants endemic to the gabbroic chaparral of western El Dorado County, California. All three are threatened by ongoing residential development and fire suppression. I examined vegetative growth and flowering of these species before fire, and the survival, growth, and development of seeds, seedlings, and resprouted stems after fire. Fire was necessary for recruitment from seed in all three species. While seedling recruitment may not be required for maintenance of extensively clonal, resprouting W. reticulata populations, without fire-stimulated germination, populations of both C. roderickii and C. stebbinsii were mostly represented only in the seed bank in mature chaparral. Recovery patterns of other species of obligately seeding chaparral species suggest that in addition to habitat loss, a principle threat to species in this functional group are short-interval fires...
Abstract Chloropyron palmatum (Ferris) Tank & J.M Egger (formerly Cordylanthus palmatus [Ferr... more Abstract Chloropyron palmatum (Ferris) Tank & J.M Egger (formerly Cordylanthus palmatus [Ferris] J. F. Macbr.) is an annual plant that inhabits seasonally flooded wetlands with saline and alkaline soils in California. In 1986, the plant was listed as endangered under the U.S. Endangered Species Act. We aimed to inform conservation strategies for the species’ five remaining populations by examining the genetic diversity and structure of the populations (on the basis of nuclear DNA markers) and their potential response to demographic and environmental stochasticity. We also assessed fluctuations in population size and whether there was evidence of hybridization between C. palmatum and Chloropyron molle (A. Gray) A. Heller subsp. hispidum (Pennell) Tank & J.M. Egger (formerly Cordylanthus mollis A. Gray subsp. hispidus [Pennell] T.I. Chuang & Heckard). Populations of C. palmatum were genetically distinct with a FST of 0.23, indicating substantial genetic structure among populations. Within populations, there was no evidence of isolation by distance. However, individuals in two adjacent vernal pools were genetically distinct. The pattern of genetic variation within populations suggests that the historical frequency and extent of seed dispersal by overland flooding has strongly affected the genetic structure of populations. Despite founder effects and population bottlenecks, small and large populations had similar levels of genetic variation. We found no evidence of hybridization. All extant populations of C. palmatum are genetically variable and distinct. We recommend that hydrologic connectivity be considered if seeds are collected and sowed with the intent of increasing the size of natural populations or creating experimental populations.
The cordgrasses in the genus Spartina have become model organisms for studying biological invasio... more The cordgrasses in the genus Spartina have become model organisms for studying biological invasions from both ecological and genetic perspectives. Here we characterize 11 disomic loci in Spartina alterniflora that show promise for population studies and for studying hybridization events between S. alterniflora and S. foliosa. Comparisons among invasive and native S. alterniflora populations showed that levels of allelic variation are lower in invasive populations. In addition, nearly all loci that amplified in S. foliosa populations and in a swarm of S. alterniflora × × × × foliosa hybrids were polymorphic. We also found that several loci amplified successfully in other Spartina species.
The aim of this study was to explore the origin of the invasive Spartina densiflora by analysing ... more The aim of this study was to explore the origin of the invasive Spartina densiflora by analysing samples from the native region (South America) and from a recently colonized area (California). A combination of various molecular data (chloroplast and nuclear sequences, molecular fingerprint) and ploidy level estimations was used to answer the question whether the reticulate phylogenetic pattern previously detected in S. densiflora was restricted to California, or alternatively, whether a more ancient hybrid origin preceded formation of this species in its native area. We found that this species is heptaploid in both its native and introduced range. Identification of nuclear homeologous sequences indicate that this species has a reticulate origin in its native range, involving a lineage related to the hexaploid clade formed by S. alterniflora, S. foliosa, and S. maritima, and another lineage related to the sub-Antarctic endemic S. arundinacea that provided the chloroplast genome. The samples from California displayed similar multilocus patterns to the samples from Chile, supporting the hypothesis that this species originated on the southeast American coast (Argentina), from where it eventually spread to the west coast of South America (Chile) first and to the Northern Hemisphere (California) later.
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Papers by Debra Ayres