La ocurrencia de “Las Vegas Bearpoppy” (Arctomecon californica) han fluctuado durante las últimas décadas, en parte debido a la variabilidad interanual de las precipitaciones que influyen en los eventos de reclutamiento y mortalidad. Sin embargo, el desarrollo en el valle de Las Vegas sigue amenazando el hábitat que sustenta a esta especie. Se solicitó incluir a A. californica en la lista de la Ley de Especies en Peligro de Extinción en 2019 y actualmente se está revisando para determinar si se justifica tal inclusión (Servicio de Pesca y Vida Silvestre de los Estados Unidos 2020). Esta revisión actualiza la información de la especie A. californica, e incluye conocimientos recientes sobre la ecología de las semillas de la especie, los requisitos de hábitat y los modelos de adecuación, propagación, reintroducción, así como la biología de sus polinizadores. Incluimos información de los últimos veinte años en estas áreas que complementan las acciones de conservación y restauración de la especie. También, identificamos temas con escasa información disponible y destacamos áreas para futuros estudios, incluyendo: preservación de la diversidad genética a través de colecciones de germoplasma, identificación de los mecanismos que impulsan su endemismo en el suelo, estudio del hábitat de los polinizadores para mantener la relación con A. californica, determinación de la fracción de semillas viables y su longevidad en las reservas de semillas del suelo, y generar predicciones de la respuesta de la población al cambio climático regional basada en modelos demográficos.
Examinamos las cuatro variedades reconocidas de Penstemon scariosus que comprenden un complejo de taxones relacionados que comparten caracteres morfológicos superpuestos: las variedades albifluvis, cyanomontanus, garrettii y scariosus. Las descripciones taxonómicas modernas y las claves asociadas no están completamente de acuerdo en cómo delimitar claramente estas variedades. Resulta especialmente importante entender la circunscripción taxonómica de la variedad albifluvis, debido a que se ha considerado su inclusión en la Ley de Especies Amenazadas. Para abordar la posición taxonómica de los taxones en este complejo de especies, examinamos la estructura genética de 66 registros de P. scariosus que representan las cuatro variedades reconocidas dentro de su área de distribución geográfica conocida, utilizando diez marcadores SSR (microsatélites). También examinamos la morfología vegetal de estos taxones a partir de 264 especímenes de herbario. Los resultados de nuestros estudios moleculares y morfológicos dan lugar a cuatro conclusiones. En primer lugar, debido al carácter genético distintivo de P. scariosus var. albifluvis y a su aislamiento geográfico, consideramos conservar su estado original a nivel de especie. En segundo lugar, nuestro estudio molecular sugiere que el área geográfica de la var. cyanomontanus es mucho mayor de lo que se conocía hasta ahora, y que consta de plantas y poblaciones con o sin tricomas glandulares característicos que se han utilizado para identificar ese taxón. En tercer lugar, tanto nuestros datos moleculares como morfométricos sugieren que las variedades garrettii y scariosus no se pueden separar de forma confiable y deberían considerarse el mismo taxón. Por último, nuestros datos moleculares revelan un genotipo distinto de la zona de Tabby Mountain, UT, que no ha sido reconocido taxonómicamente con anterioridad. Describimos este nuevo taxón y proporcionamos una clave taxonómica para separar esta nueva variedad de los otros miembros del complejo de especies.
Abstract. Clear Lake is a large (176.7-km2) natural lake in northern California, USA. An estimated 1000 pairs of Western Grebes (Aechmophorus occidentalis) and Clark's Grebes (A. clarkii) nested on the lake prior to massive applications of the pesticide dichlorodiphenyldichloroethane (DDD) to kill the Clear Lake gnat (Chaoborus astictopus) during 1949–1957. Biomagnification of DDD was implicated as the cause of several mass mortality events of grebes and short-term reproductive failure in the 1950s, although other factors such as mercury (Hg) poisoning may have contributed. Successful nesting resumed in 1960 and increased gradually, with up to 165 nests in 1967 but fewer through 1976. Subsequent surveys revealed up to 390 nests annually during 1992–1995 and up to 2675 nests annually during 1996–2010. We conducted 7–29 nest surveys annually during 2010–2019 and found a mean of 3123 nests per year. The annual number of nests varied dramatically (range 898 to 5936) and was unrelated to water level. The grebes nested at 28 sites in Clear Lake and 9 sites in associated wetlands, with proportionately more nests on Clear Lake and fewer nests in adjacent wetlands during years with low water level. Western Grebes attended 84.9% of the nests and Clark's Grebes attended 15.1%. During years with low water, there were proportionately more open water nests, which were anchored to submergent vegetation farther from shore and in deeper water than marsh nests, which were more densely placed in emergent vegetation closer to shore in shallower water. Brood surveys along the perimeter of the lake at the end of each breeding season revealed considerable variation in the number of young (1–599, x̄ = 153.9), young per nest (0.00025–0.118, x̄ = 0.04), and productivity ratio of young to adults (0.0006–0.252, x̄ = 0.07). Reproductive success was unrelated to water level. Wind-generated waves were a major cause of nest failure, destroying up to 35% of a year's nests. Predation on eggs was also a major cause of nest failure. American Crow (Corvus brachyrhynchos) was the dominant predator during the day (84% of predation events), and northern raccoon (Procyon lotor) was the dominant predator at night (98% of predation events). Nocturnal predation by mammals occurred most frequently when water level was high because nests were placed closer to shore and were more accessible. The grebes' breeding population has recovered since DDD biomagnification during the 1950s and may be larger due to 2 introduced fish species competing for plankton with benthic larvae of the Clear Lake gnat, which previously transferred large quantities of biomass from aquatic to terrestrial ecosystems during emergence. However, the grebes' reproductive success remains lower at Clear Lake than at several other breeding localities. The bioaccumulation and biomagnification of toxic chemicals and the periodic reductions of prey fish from hypoxic areas of the lake during periods of intense cyanobacterial and algal blooms may reduce reproductive success. Resumen. Clear Lake es un lago natural grande (176.7 km2) en el norte de California, EEUU. Se estima que 1000 parejas del achichilique occidental (Aechmophorus occidentalis) y achichilique pico naranja (A. clarkii) anidaron en el lago antes de las aplicaciones masivas del pesticida diclorodifenildicloroetano (DDD) para matar al díptero de Clear Lake (Chaoborus astictopus) durante 1949–1957. La biomagnificación de DDD estuvo implicada como la causa de varios eventos de mortalidad masiva de achichiliques y fallas reproductivas a corto plazo en la década de 1950, aunque otros factores pueden haber contribuido, como el envenenamiento por mercurio (Hg). La anidación exitosa se reanudó en 1960 y aumentó gradualmente, con hasta 165 nidos en 1967 pero menos hasta 1976. Los censos posteriores revelaron hasta 390 nidos anualmente durante 1992–1995 y hasta 2675 nidos anualmente durante 1996–2010. Realizamos de 7 a 29 censos de nidos anualmente durante 2010–2019 y encontramos una media de 3123 nidos por año. El número anual de nidos varió drásticamente (rango 898–5936) y no estuvo relacionado con el nivel del agua. Los achichiliques anidaron en 28 sitios en Clear Lake y 9 sitios en humedales asociados, con proporcionalmente más nidos en Clear Lake y menos nidos en humedales adyacentes durante años con bajo nivel de agua. Los achichiliques occidentales asistieron al 84.9% de los nidos y los achichiliques de Clark asistieron al 15.1%. Durante los años con poca agua, hubo proporcionalmente más nidos en aguas abiertas, que estaban anclados a la vegetación sumergida más lejos de la costa en aguas más profundas, que nidos de marismas, que estaban más densamente colocados en la vegetación emergente más cerca de la costa en aguas menos profundas. Los censos de cría a lo largo del perímetro del lago al final de cada temporada de reproducción revelaron una variación considerable en el número de crías (1–599, x̄ = 153.9), crías por nido (0.00025–0.118, x̄ = 0.04), y una tasa de productividad de jóvenes a adultos (0.0006–0.252, x̄ = 0.07). El éxito reproductivo no estuvo relacionado con el nivel del agua. Las olas generadas por el viento fueron una de las principales causas de la falla de los nidos, destruyendo hasta el 35% de los nidos de un año. La depredación de los huevos también fue una de las principales causas del fracaso de los nidos. El cuervo americano (Corvus brachyrhynchos) fue el depredador dominante durante el día (84% de los eventos de depredación) y el mapache del norte (Procyon lotor) fue el depredador dominante durante la noche (98% de los eventos de depredación). La depredación nocturna por mamíferos ocurrió con mayor frecuencia cuando el nivel del agua era alto porque los nidos se colocaron más cerca de la costa y eran más accesibles. La población reproductora de achichiliques se ha recuperado desde la biomagnificación por DDD durante la década de 1950 y puede ser mayor debido a que dos especies de peces introducidas compiten por el plancton con las larvas bentónicas del díptero de Clear Lake, que anteriormente transfirió grandes cantidades de biomasa de los ecosistemas acuáticos a los terrestres durante la emergencia. Sin embargo, el éxito reproductivo de los achichiliques sigue siendo menor que en varias otras localidades de reproducción. La bioacumulación y biomagnificación de sustancias químicas tóxicas y las reducciones periódicas de peces presa de las áreas hipóxicas del lago durante períodos de intensa proliferación de cianobacterias y algas pueden reducir el éxito reproductivo.
Gaufinia is proposed as a new genus for the Sweltsa lamba (Needham and Claassen 1925) species group, and 5 current and 6 new species are recognized based primarily on scanning electron microscopy of the male epiproct. Males of the new genus are distinguished from all other Chloroperlidae by the presence of a distinctive leaf-like aedeagal lamella. A preliminary key for males of the 11 currently recognized species is presented to assist in identification.
Seven hundred and ninety-two vascular plant taxa were documented for the Kaibab Plateau through a review of herbarium records (primarily online) and targeted fieldwork focusing on springs, natural ponds, cattle tanks, and sinkholes. Taxa not previously published or currently recorded on SEINet for the Kaibab Plateau include 7 taxa for Grand Canyon National Park, 4 taxa for the Kaibab National Forest, 51 taxa for the Kaibab Plateau, 6 taxa for Coconino County, and 5 taxa for the state of Arizona. Two hundred and thirty previously published records or records on SEINet were eliminated from the flora area by reviewing specimens that were either misidentified or mismapped.
Over 80% of the Mid-Continent Sandhill Crane (Antigone canadensis) Population (MCP), estimated at over 660,000 individuals, stops in the Central Platte River Valley (CPRV) during spring migration from mid-February through mid-April. Research suggests that the MCP may be shifting its distribution spatially and temporally within the CPRV. From 2002 to 2017, we conducted weekly aerial surveys of Sandhill Cranes staging in the CPRV to examine temporal and spatial trends in their abundance and distribution. Then, we used winter temperature and drought severity measures from key wintering and early migratory stopover locations to assess the impacts of weather patterns on annual migration chronology in the CPRV. We also evaluated channel width and land cover characteristics using aerial imagery from 1938, 1998, and 2016 to assess the relationship between habitat change and the spatial distribution of the MCP in the CPRV. We used generalized linear models, cumulative link models, and Akaike's information criterion corrected for small sample sizes (AICc) to compare temporal and spatial models. Temperatures and drought conditions at wintering and migration locations that are heavily used by Greater Sandhill Cranes (A. c. tabida) best predicted migration chronology of the MCP to the CPRV. The spatial distribution of roosting Sandhill Cranes from 2015 to 2017 was best predicted by the proportion of width reduction in the main channel since 1938 (rather than its width in 2016) and the proportion of land cover as prairie-meadow habitat within 800 m of the Platte River. Our data suggest that Sandhill Cranes advanced their migration by an average of just over 1 day per year from 2002 to 2017, and that they continued to shift eastward, concentrating at eastern reaches of the CPRV. Climate change, land use change, and habitat loss have all likely contributed to Sandhill Cranes coming earlier and staying longer in fewer reaches of the CPRV, increasing their site use intensity. These historically unprecedented densities may present a disease risk to Sandhill Cranes and other waterbirds, including Whooping Cranes (Grus americana). Our models suggest that conservation actions may be maintaining Sandhill Crane densities in areas that would otherwise be declining in use. We suggest that management actions intended to mitigate trends in the distribution of Sandhill Cranes, including wet meadow restoration, may similarly benefit prairie- and braided river–endemic species of concern.
Stopover sites provide important forage resources and protection from predators to the Aransas-Wood Buffalo population of Whooping Cranes (Grus americana) as they migrate 4000 km across the Great Plains each spring and fall. Given the Whooping Crane's expansive migration corridor, sensitivity to human disturbance, small population size, and protected status under the Endangered Species Act, it is challenging to gather detailed information regarding the particular forage resources that the cranes exploit at various stopover locations. On 22 March 2018 we observed and photo-documented an adult Whooping Crane consuming at least 5 individual juvenile channel catfish (Ictalurus punctatus) after it landed 100 m in front of our Sandhill Crane viewing blind on the south channel of the Platte River. Using the average exposed culmen length of an adult Whooping Crane for reference, we estimated that the length of the channel catfish ranged from 97 mm to 117 mm. Growth estimates developed from the Lower Platte River suggest that the depredated channel catfish were just over one year old. To the best of our knowledge, our observations represent the first definitive record of a Whooping Crane consuming fish in the Platte River, as well as the first record of a Whooping Crane depredating a channel catfish in the Great Plains. Given the relatively long distances at which Whooping Cranes are generally viewed (≥650 m), small-bodied fish may be a more common prey item during migration than indicated by current scientific literature. Our note demonstrates how wildlife photography and ecotourism can contribute to our understanding of species' natural histories.
Twice annually, the last remaining wild and self-sustaining migratory population of Whooping Cranes (Grus americana) migrates through central Nebraska on its approximately 3900-km journey between Aransas National Wildlife Refuge on the Gulf Coast of Texas and Wood Buffalo National Park in Alberta, Canada. On 27 March 2018, a juvenile Bald Eagle (Haliaeetus leucocephalus) was observed attacking a Whooping Crane on the Loup River near Rockville, Nebraska. The encounter, documented by a private landowner, was forwarded to the U.S. Fish and Wildlife Service as part of the decades-long citizen-science effort undertaken to track and record public sightings of Whooping Cranes during migration. Crane species have few avian predators, and observations of depredations upon these crane species are rare. The Whooping Crane fended off the Bald Eagle, utilizing a “jump-rake” defense; neither species appeared harmed by the clearly aggressive interaction. The episode was reflective of recent observations of Bald Eagles depredating Sandhill Cranes on the Platte River during the spring migration. To our knowledge, this is the first description in scientific literature of a Bald Eagle attacking a Whooping Crane from the Aransas-Wood Buffalo population.
Wide channels with short bank vegetation, access to nearby foraging habitat, shallow water areas ( 5000 cranes), but the ratio was statistically similar across a wide range of maximum unobstructed channel widths. Medium-sized Sandhill Crane groups (501–5000 cranes) were less influenced by in-channel vegetated islands, and these groups selected channels based on wide total unvegetated channel widths. Our results also suggest that flows ≤39.05 m3/s (cms; 1379 cfs) in channels that are 275 m in unvegetated width maximize selection ratios for medium and large crane groups, so flows above this level may not improve Sandhill Crane roosting habitat conditions during the spring migration and staging season within the central Platte River. While Sandhill Cranes stage within the central Platte River valley for a longer time interval in the spring, Whooping Cranes (Grus americana) also use the Platte River as a stopover point. Both species share similar indices for roosting habitat, such as unobstructed channel width and shallow water depths. The results of our investigation could be used to identify a range of flows and channel width configurations expected to generate the highest amount of suitable habitat for Sandhill Cranes roosting along the central Platte River.
Abstract. Stoneflies (Plecoptera) are a dominant group in running freshwaters. We report 104 stonefly species from Nevada. The fauna contains species with Sierra Nevada—Cascade range affinities, few of which penetrate far eastward, and Rocky Mountain species extending to western Nevada. Endemics, species associated with the large interior Humboldt River, and species with northern or southern boundaries in Nevada add zoogeographic complexity. From 3531 stonefly records in Nevada, we provide an annotated discussion and collection data for the species present. This material is a foundation for continuing research on Plecoptera and for monitoring vital stream ecosystems in this arid region of western North America. Collection records from this study are compiled in the Nevada Stonefly Database, which is archived and accessible at http://scholarsarchive.byu.edu/mwnan/vol10/iss1/1.
An updated faunal list containing 94 species of Odonata (60 Anisoptera and 34 Zygoptera) for Utah is pre - sented. Of the 95 Odonata species recorded in past publications as being from Utah, 8 have been removed from the Utah Odonata list, while 7 new state records have been added. Explanations for their removal are provided in the species accounts. The 7 ecoregions found in Utah are briefly described along with their wetland habitats and odonate species. Geographical distribution data by county, drainage, and ecoregion are provided for each species along with information regarding elevation range, flight season, and habitat preferences in Utah. Specific comments relevant to the distribution and abundance of each species are provided. Distribution maps illustrate collection locations against a background of county boundaries and topography. State conservation rankings using methods described by NatureServe are recommended.
Abstract. Vegetation surveys at Zion National Park (Zion), Utah, have contributed to our understanding of plant community patterns and their relationship to environmental factors. Previous authors used vegetation plot data to characterize vegetation types at Zion following conventional procedures that emphasize spatial discreteness and dominant species. We developed and applied an alternative approach for community characterization that emphasizes nondiscrete presence-absence patterns and is compatible with the individualistic concept. We reanalyzed existing plot data from Zion using coalition clustering, an algorithm that identifies groups of positively-associated species referred to as coalition groups. Each species and plot in the data set was linked to each coalition group via an “affinity” value obtained through weighted averaging. Affinity values were used to characterize environmental affinities of coalition groups through regression tree modeling and predictive mapping. We also identified species that frequently co-occurred with coalition groups (affiliate species) and those that frequently co-occurred with high cover (dominant-affiliates), viewing these as alternatives to conventional prevalent and dominant species. Following this approach, we identified 10 coalition groups at Zion that overlapped compositionally and spatially to differing degrees. Mesic environments on a gradient from low-elevation riparian zones through mid-elevation narrow canyons to high-elevation plateaus were represented by 3 overlapping groups. Two groups occupying slickrock and sand environments were detected on the Navajo Sandstone, as well as 2 on mesa tops above it. At lower elevations, 3 intergrading xeric coalition groups were distinguished. When previously classified associations of the National Vegetation Classification were clustered based on shared affinities to coalition groups, the arrangement differed from existing classification schemes but was environmentally interpretable. Although these patterns are contingent on conditions at the time of data collection, they provide a baseline that could be used for evaluating and predicting plant community change in the park. With proper attention to sampling and analysis issues, our community characterization approach could be applied in other settings as an alternative or supplement to conventional vegetation classification.
We examined allelic variation at nuclear-encoded microsatellites and sequences of mitochondrial (mt)DNA in 10 geographic samples representing 6 nominal species of the cyprinid genus Dionda. Species of Dionda are found in springs and spring-fed headwaters in the southwestern United States and Mexico and are of particular interest to conservation and management, in part because of their limited distribution and habitat specificity, and in part as indicator species of habitat quality. All 10 samples examined appear to be discrete, demographically independent populations, with greater observed FST values between or among samples within species (0.123–0.280) than threshold values above which demographic independence is indicated. All 10 exhibited microsatellite and mtDNA variation comparable to or lower than that found in other cyprinids considered to be threatened or endangered; across microsatellites, average number of alleles across populations ranged from of 2.09 to 9.76, allelic richness from 2.24 to 8.45, and gene diversity from 0.0211 to 0.606; for mtDNA, the number of haplotypes across populations ranged from 1 to 14. Estimates of historical and present-day genetic demography indicated that all 10 populations have experienced order-of-magnitude declines in effective population size, with lower bounds of time intervals for the declines in 9 of the populations ranging from 6 to 65 years. Estimates of average long-term effective population size (536 in Dionda argentosa from San Felipe Creek to 2335 in D. texensis) and effective number of breeders (22 in D. flavipinnis from Fessenden Spring to 555 in D. diaboli from Devils River) also indicated recent declines in effective size, and at least 5 of the populations appear to have undergone recent, severe bottlenecks (mean Mc range 0.806–0.848, P value range 0.000–0.0350). The observation that all 10 populations are demographically independent indicates that local extirpations likely would not be replaced by new migrants and that loss of any of the populations would represent loss of a unique genetic entity. Conservation recommendations for each of the populations are briefly discussed.
Abstract. The natural vegetation of Santa Cruz Island was severely disturbed by nonnative herbivores for well over a century. As the livestock and feral ungulates (primarily sheep, cattle, and pigs) were removed from the island over the last 30 years, many of the native plant communities began to recover naturally. Recovery has been extremely slow in other areas, especially where nonnative annual grasses and fennel (Foeniculum vulgare) dominate several hundred hectares that were under intense agricultural use (pastures and farmed lands). We experimentally tested the feasibility of speeding up the recovery process in a postagricultural area of the island's Central Valley using active restoration techniques. We assessed how weed control via herbicide application and planting of small nursery stock without irrigation might contribute to restoring natural plant assemblages in 3 different areas of the Central Valley (valley bottom, upper south-facing slope, and midsouth-facing slope). In February 2009, we planted the same 21 species of native plants in experimental plots with and without weed control at each location. In December 2009, we planted 28 species in adjacent plots after 2 seasons of weed control. We assessed natural recruitment in weeded and unweeded plots that were not planted. At all 3 locations, a single early season herbicide treatment prior to planting had strong positive effects on the survival, cover, and reproduction of planted natives compared to no herbicide treatment; the effects persisted and grew stronger in the second and third years. Repeated herbicide treatments over 2 years before planting did not result in any additional significant positive effects on native survival or growth compared to only one herbicide treatment. We saw virtually no natural recruitment of native shrubs in unplanted plots. We found that typical coastal sage scrub species performed best at the upper slope site and poorly at the valley bottom site. Grasses and shrubs tolerant of poorly drained soil did better in the valley bottom. We found that planting native species from small nursery stock without irrigation is effective for a wide range of grassland and coastal sage scrub species. All of the restoration techniques we used are cost effective and can be scaled-up to restore large areas of postagricultural lands.
Abstract. Guadalupe Island, off the Baja California peninsula, México, hosts the most important growing Laysan Albatross (Phoebastria immutabilis) breeding colony in the eastern Pacific. Since this seabird's first arrival in 1983, it has been affected by predation from feral cats (Felis catus), present on Guadalupe since the late 19th century. Heavy predation events have been recorded on the island, so we initiated a feral cat control campaign in 2003 and began collecting baseline information for developing an eradication plan. At the same time, we conducted seasonal monitoring of Laysan Albatross reproductive success in order to assess the benefits from control activities. Cat relative abundance on Guadalupe was estimated through spotlight surveys, and control was done at the southernmost end of the island around the 2 locations where Laysan Albatross nest: Colinas Negras and Punta Sur. Laysan Albatross population growth rate was calculated based on the number of reproductive individuals, while breeding success was estimated as the proportion of laid eggs that resulted in fledged chicks. A total of 203 cats were removed from the south end of Guadalupe between 2003 and 2013. During this same period, high reproductive success (0.8) was recorded for Laysan Albatross, suggesting a positive effect of cat control activities. We found significant differences in reproductive success between years with predation and no predation by feral cats. The Laysan Albatross colony on Guadalupe has grown steadily during the past 30 years, increasing from 4 to 143 breeding pairs between 1984 and 2013, respectively, and with a population growth rate of 1.10 between 2004 and 2013.
Abstract. Marine invertebrate faunas with mixtures of extralimital southern and extralimital northern faunal elements, called thermally anomalous faunas, have been recognized for more than a century in the Quaternary marine terrace record of the Pacific Coast of North America. Although many mechanisms have been proposed to explain this phenomenon, no single explanation seems to be applicable to all localities where thermally anomalous faunas have been observed. Here, we describe one such thermally anomalous fossil fauna that was studied on the second emergent marine terrace at Eel Point on San Clemente Island. The Eel Point terrace complex is a composite feature, consisting of a narrow upper bench (terrace 2a) and a broader lower bench (terrace 2b). Terrace 2b, previously dated from ∼128 ka to ∼114 ka, was thought to date solely to marine isotope stage (MIS) 5.5, representing the peak of the last interglacial period. Nevertheless, the fauna contains an extralimital northern species and several northward-ranging species, as well as an extralimital southern species and several southward-ranging species. Similar faunas with thermally anomalous elements have also been reported from San Nicolas Island, Point Loma (San Diego County), and Cayucos (San Luis Obispo County), California. U-series dating of corals at those localities shows that the thermally anomalous faunas may be the result of mixing of fossils from both the ∼100-ka (cool-water) and the ∼120-ka (warm-water) sea level high stands. Submergence, erosion, and fossil mixing of the ∼120-ka terraces by the ∼100-ka high-sea stand may have been possible due to glacial isostatic adjustment (GIA) effects on North America, which could have resulted in a higher-than-present local sea level stand at ∼100 ka. The terrace elevation spacing on San Clemente Island is very similar to that on San Nicolas Island, and we hypothesize that a similar mixing took place on San Clemente Island. Existing fossil records from older terraces elsewhere in California also show thermally anomalous elements, indicating that the scenario presented here for the last interglacial complex may have applicability to much of the marine Quaternary record for the Pacific Coast.
Santa Cruz Island, California, has been free of nonnative vertebrates since 2007, but nonnative invasive plants remain one of the most significant threats to the recovery of the island's native ecosystems. Just over one-fourth of the island's flora is comprised of nonnative, naturalized plant species. In 2007, an island-wide invasive plant survey indicated that several species were candidates for eradication based on factors such as their distribution, abundance, invasiveness, and known or projected harmful impacts on the native biota. In 2008, The Nature Conservancy (TNC) and Native Range, Inc., initiated a program to eliminate 15 invasive plant species from TNC's portion (76%) of the 246-km2 island. An additional 9 species were targeted in subsequent years. As of 2012, a total of 882 populations of 24 weed species have been mapped and treated, and 73% of these populations are considered inactive (dead), with no aboveground living biomass. The majority of the remaining active infestations are due to resurgence from the soil seed bank. Continued monitoring and annual follow-up treatments of invasive plants will be required. Utilization of a small helicopter provides surveyors and herbicide applicators with efficient access to remote infestations and a platform from which to treat populations and detect individual plants. Most important in achieving project success is consistent treatment from year to year, which prevents reproduction and recovery of infestations. Long-lived soil seed banks for some species will be a management issue for years to come. Continued commitment to eradicating these weeds and the ability to detect incipient infestations and respond rapidly to eliminate them will be key determinants of success of this program.
San Miguel Island is the westernmost of the California Channel Islands and one of the windiest areas on the west coast of North America. The majority of the island is covered by coastal sand dunes, which were stripped of vegetation and subsequently mobilized due to droughts and sheep ranching during the late 19th century and early 20th century. Since the removal of grazing animals, vegetation and biological soil crusts have once again stabilized many of the island's dunes. In this study, historical aerial photographs and field surveys were used to develop a chronosequence of the pattern of change in vegetation communities and biological soil crust levels of development (LOD) along a gradient of dune stabilization. Historical aerial photographs from 1929, 1954, 1977, and 2009 were georeferenced and used to delineate changes in vegetation canopy cover and active (unvegetated) dune extent among 5 historical periods (pre-1929, 1929–1954, 1954–1977, 1977–2009, and 2009–2011). During fieldwork, vegetation and biological soil crust communities were mapped along transects distributed throughout San Miguel Island's central dune field on land forms that had stabilized during the 5 time periods of interest. Analyses in a geographic information system (GIS) quantified the pattern of changes that vegetation and biological soil crust communities have exhibited on the San Miguel Island dunes over the past 80 years. Results revealed that a continuing increase in total vegetation cover and a complex pattern of change in vegetation communities have taken place on the San Miguel Island dunes since the removal of grazing animals. The highly specialized native vascular vegetation (sea rocket, dunedelion, beach-bur, and locoweed) are the pioneer stabilizers of the dunes. This pioneer community is replaced in later stages by communities that are dominated by native shrubs (coastal goldenbush, silver lupine, coyote-brush, and giant coreopsis), with apparently overlapping or cyclical succession pathways. Many of the dunes that have been stabilized the longest (since before 1929) are dominated by exotic grasses. Stands of biological soil crusts (cyanobacteria) are found only on dunes where vascular vegetation is already present. Biological soil crusts are not found on dunes exhibiting a closed vascular plant canopy, which may indicate that the role of soil crusts in dune stabilization on the island is transitory. Particle-size analyses of soil samples from the study area reveal that higher biological soil crust LOD is positively correlated with increasing fine grain content. The findings indicate that changes in vegetation communities may be the most rapid at earlier and later stages of dune stabilization and that regular monitoring of dunes may help to identify the interactions between vegetation and soil crusts, as well as the potential transitions between native and exotic plant communities.
