September-October 2005 CA Grassland Newsletter
1) Midwinter drought info
2) Job announcement – Range Management at Pt Reyes
3) 15 Publications this month!
1) A Meteorological Fun-fact:
You may have noticed that there is often a prolonged period during the winter rainy season that the rain abruptly shuts off and we have dry conditions for a while. Some of us have been calling it a “mid-winter drought.” But, is this a consistent feature that grassland plants must deal with every year, or just an occasional blip in an otherwise regular precipitation pattern? And, how long does this drought last?
Interestingly, Meteorologist Jan Null, of Golden Gate Weather Services, collated the daily precipitation records for San Francisco dating back to 1950 to answer that question. Go to http://ggweather.com/enso/winter_dry_spells.htm to see the full write up and data. He found that, between December and January, there is a period of at least 8 consecutive dry days EVERY YEAR between 1950 and 2003. The average length of this mid-winter drought is 17 days – potentially a long time for a young seedling!
So, don’t be surprised when your umbrella goes unused for 1-3 weeks this winter.
Range management Position at Point Reyes National Seashore
This position is being advertised as a range management specialist and biologist for both federal merit promotion candidates and nonfederal applicants.
Point Reyes National Seashore manages over 30,000 acres of agricultural lands within 90,000 acres of park lands. The Seashore is a refuge for 27 federally listed threatened and endangered species, and park staff manages a wide array of complex resource issues. The incumbent serves as the principle contact and technical advisor for all rangeland resources, preparing, revising and implementing multi-use rangeland management plans.
Additionally, the incumbent develops professional advice and recommendations for the park superintendent regarding the balance of natural and cultural resource issues pertaining to the 30 historic beef and dairy ranch properties located within Point Reyes National Seashore. The purpose of these recommendations is to ensure that the rangeland resources and multiple uses that occur on these lands are managed in a manner that is sustainable and consistent with park policy. Develops cooperative partnerships with livestock operators, park staff, representatives from other agencies, resource conservation organizations and environmental groups, in order to resolve complex resource problems and enhance both the viability of agriculture and environmental quality on rangelands. Maintains and protects natural and cultural resources within the context of range management; includes addressing water quality issues (non-point source pollution and Total Maximum Daily Loads), Best Management Practices, threatened and endangered species, and historic and pre-historic sites.
Conducts on-the-ground surveys to identify and evaluate rangelands where the vegetation and soils have significantly departed from the natural potential.
For additional information, contact:
Jane Rodgers, Vegetation Management
Point Reyes National Seashore
Point Reyes Station, CA 94956
Visit the Seashore at http://www.nps.gov/pore/
To apply for this position, please visit http://jobsearch.usajobs.opm.gov/
enter PORE 05-35 in the keyword search
Application period closes on 10/13/2005
PUBLICATIONS – We’re a productive bunch!
Gelbard JL and S. Harrison. 2005. Invasibility of roadless grasslands: An experimental study of yellow starthistle. Ecological Applications 15: 1570–1580. Abstract.Roadless habitats are commonly found to be less invaded than habitats near roads, but few studies have tested whether this pattern is due to propagule limitation or to greater invasion resistance of roadless sites. We examined reasons for the lower frequency and cover of yellow starthistle (Centaurea solstitialis) in grassland sites >1000 m vs. 10 m from roads in an inland California, USA, foothill landscape. During winter 2001 and 2002, we planted 100 Centaurea seeds in 64 pairs of 30 × 30 cm plots (uncleared and cleared of aboveground plant material) at sites stratified by distance from roads (10 m and >1000 m), soil type (nonserpentine and serpentine), and aspect (cool, warm, and neutral slopes). In nonserpentine grasslands, Centaurea survival was greater in uncleared (but not cleared) near (10 m) plots than in distant (>1000 m) plots. These findings suggest that the effect of distance from roads on survival corresponds with higher aboveground biotic resistance in distant sites than in near sites. Centaurea biomass was greater in near than in distant plots (both uncleared and cleared) on nonserpentine soil, suggesting that either abiotic resistance or belowground biotic resistance could limit its growth in distant sites. These distance effects were no longer significant in models that included two biotic covariates: native grass cover (which was higher in distant sites and negatively correlated with Centaurea performance) and bare ground (which was lower in distant sites and positively correlated with Centaurea performance). On serpentine soil, there was no effect of road proximity on the performance of planted Centaurea. Our results suggest that Centaurea seeds can germinate in nonserpentine and serpentine grasslands regardless of distance from roads. Beyond the seedling stage, however, biotic resistance associated with higher native grass cover and lower levels of disturbance may inhibit Centaurea invasion of nonserpentine grassland sites that are distant from roads.
Pyke, CR and J. Marty. 2005. Cattle grazing mediates climate change impacts on ephemeral wetlands. Conservation Biology 19:1619-1625.
Abstract: Climate change impacts depend in large part on land-management decisions; interactions between global changes and local resource management, however, rarely have been quantified. We used a combination of experimental manipulations and simulation modeling to investigate the effects of interactions between cattle grazing and regional climate change on vernal pool communities. Data from a grazing exclosure study indicated that 3 years after the removal of grazing, ungrazed vernal pools dried an average of 50 days per year earlier than grazed control pools. Modeling showed that regional climate change could also alter vernal pool hydrology. Increased temperatures and winter precipitation were predicted to increase periods of inundation. We evaluated the ecological implications of interactions between grazing and climate change for branchiopods and the California tiger salamander ( Ambystoma californiense) at four sites spanning a latitudinal climate gradient. Grazing played an important role in maintaining the suitability of vernal pool hydrological conditions for fairy shrimp and salamander reproduction. The ecological importance of the interaction varied nonlinearly across the region. Our results show that grazing can confound hydrologic changes driven by climate change and play a critical role in maintaining the hydrologic suitability of vernal pools for endangered aquatic invertebrates and amphibians. These observations suggest an important limitation of impact assessments of climate change based on experiments in unmanaged ecosystems. The biophysical impacts of land management may be critical for understanding the vulnerability of ecological systems to climate change.
Marty, JT. 2005. Effects of cattle grazing on diversity in ephemeral wetlands. Conservation Biology 19:1626-1632.
Abstract: Cattle are usually thought of as a threat to biodiversity. In regions threatened by exotic species invasion and lacking native wild grazers, however, cattle may produce the type of disturbance that helps maintain diverse communities. Across 72 vernal pools, I examined the effect of different grazing treatments (ungrazed, continuously grazed, wet-season grazed and dry-season grazed) on vernal-pool plant and aquatic faunal diversity in the Central Valley of California. After 3 years of treatment, ungrazed pools had 88% higher cover of exotic annual grasses and 47% lower relative cover of native species than pools grazed at historical levels (continuously grazed). Species richness of native plants declined by 25% and aquatic invertebrate richness was 28% lower in the ungrazed compared with the continuously grazed treatments. Release from grazing reduced pool inundation period by 50 to 80%, making it difficult for some vernal-pool endemic species to complete their life cycle. My results show that one should not assume livestock and ranching operations are necessarily damaging to native communities. In my central California study site, grazing helped maintain native plant and aquatic diversity in vernal pools.
Keeley, JE. 2005. Fire history of the San Francisco East Bay region and implications for landscape patterns. INTERNATIONAL JOURNAL OF WILDLAND FIRE 14: 285-296.
Abstract: The San Francisco East Bay landscape is a rich mosaic of grasslands, shrublands and woodlands that is experiencing losses of grassland due to colonization by shrubs and succession towards woodland associations. The instability of these grasslands is apparently due to their disturbance- dependent nature coupled with 20th century changes in fire and grazing activity. This study uses fire history records to determine the potential for fire in this region and for evidence of changes in the second half of the 20th century that would account for shrubland expansion. This region has a largely anthropogenic fire regime with no lightning- ignited fires in most years. Fire suppression policy has not excluded fire from this region; however, it has been effective at maintaining roughly similar burning levels in the face of increasing anthropogenic fires, and effective at decreasing the size of fires. Fire frequency parallels increasing population growth until the latter part of the 20th century, when it reached a plateau. Fire does not appear to have been a major factor in the shrub colonization of grasslands, and cessation of grazing is a more likely immediate cause. Because grasslands are not under strong edaphic control, rather their distribution appears to be disturbance-dependent, and natural lightning ignitions are rare in the region, I hypothesize that, before the entrance of people into the region, grasslands were of limited extent. Native Americans played a major role in creation of grasslands through repeated burning and these disturbance- dependent grasslands were maintained by early European settlers through overstocking of these range lands with cattle and sheep. Twentieth century reduction in grazing, coupled with a lack of natural fires and effective suppression of anthropogenic fires, have acted in concert to favor shrubland expansion.
Rundel, PW, AC Gibson, and MR Sharifi. 2005. Plant functional groups in alpine fellfield habitats of the White Mountains, California. ARCTIC ANTARCTIC AND ALPINE RESEARCH 37: 358-365
Abstract: An alpine fellfield community on granite substrate (elevation 3750 m) near the University of California Barcroft Laboratory in the White Mountains, of eastern California was studied during the 2000 growing season to determine whether classic perennial life forms can be treated as plant functional groups. A series of 1-m(2) quadrat samples were measured to determine common species. The four species with greatest cover were Penstemon heterodoxus var. heterodoxis. Trifolium andersonii var. heatleyae, Poa glauca subsp rupicola, and Eriogonum ovalifolium var. nivale. These and four additional common perennial species were selected for ecophysiological studies representing four distinct ecological life forms: chamaephytes. cushion plants (including mat formers), herbaceous dicot perennials, and graminoid perennials, Summer midday leaf temperatures for species with foliage held close to ground surface were up to 20 degrees C higher than air temperatures, whereas on upright species, leaves away from the ground surface closely matched ambient temperatures. For the eight species, peak values of mean maximum photosynthetic rates ranged from 11.5-25.5 mu mol CO2 m(-2) s(-1). typical of published values, although chamaephytes in the study showed higher rates comparable to herbaceous perennials. Water-use efficiency, as estimated by a ratio of internal to ambient CO2 was relatively high (c(i):c(a) ratios of 0.43-0.59) compared to published data. During the stressful end of the growing season, neither predawn nor midday shoot water potentials ever reached low levels, presenting conflicting evidence for the role of soil moisture as, a limiting factor. Overall, the data on plant functional attributes showed no strong patterns of differences between categories of life forms in the fellfield community, suggesting that classical life forms in this habitat do not represent plant functional groups.
Morghan, KJR and KJ Rice. 2005. Centaurea solstitialis invasion success is influenced by Nassella pulchra size. RESTORATION ECOLOGY 13: 524-528
Abstract: Replacement of perennial grasses with non-native annual grasses in California's Central Valley grasslands and foothills has increased deep soil water availability. Yellow starthistle (Centaurea solstitialis), a deep-rooted invasive thistle, can use this water to invade annual grasslands. Native perennial bunchgrasses, such as Purple needlegrass (Nassella pulchra), also use deep soil water, so there is an overlap in resource use between N. pulchra and C. solstitialis. Restoration of N. pulchra to annual grasslands could result in strong competitive interactions between N. pulchra and C. solstitialis, which may reduce survival, growth, and reproduction of the invader. The strength of this competitive interaction can increase as N. pulchra plants mature, increase in size, and develop more extensive root systems. We studied how the size of N. pulchra affected the success of C. solstitialis invasion over 2 years. We allowed C. solstitialis seed to fall naturally into plots containing N. pulchra plants. For each plot, we measured the number of C. solstitialis seedlings and mature plants, as well as C. solstitialis biomass and seedhead production. In both years of the study, C. solstitialis number, biomass, and seedhead production declined significantly as N. pulchra size increased. However, even C. solstitialis grown with the largest N. pulchra plants produced some seed, especially during the higher rainfall year. We conclude that restoration plantings with larger, established N. pulchra plants will be more resistant to invasion by C. solstitialis than young N. pulchra plantings, but site management must continue as long as a C. solstitialis seed source is present.
McKay JK, CE Christian, S Harrison and KJ Rice. 2005. "How local is local?" - A review of practical and conceptual issues in the genetics of restoration. RESTORATION ECOLOGY 13: 432-440
Abstract: In plant conservation, restoration (the augmentation or reestablishment of an extinct population or community) is a valuable tool to mitigate the loss of habitat. However, restoration efforts can result in the introduction of novel genes and genotypes into populations when plant materials used are not of local origin. This movement is potentially important because many plant species are subdivided into populations that are adapted to local environmental conditions. Here we focus on genetic concerns arising from ongoing restoration efforts, where often little is known about "How local is local?" (i.e., the geographic or environmental scale over which plant species are adapted). We review the major issues regarding gene flow and local adaptation in the restoration of natural plant populations. Finally, we offer some practical, commonsense guidelines for the consideration of genetic structure when restoring natural plant populations.
Malmstrom, CM, CC Hughes, LA Newton, and CJ Stoner. 2005. Virus infection in remnant native bunchgrasses from invaded California grasslands. NEW PHYTOLOGIST 168: 217-230
Abstract: (.) This study examined the effects of infection with barley and cereal yellow dwarf viruses (BYDVs) on wild grass species in California, a region in which native perennial bunchgrasses have been largely replaced by exotic annual grasses. We sought to determine whether these widespread viruses compromise the fitness of wild hosts and thus have the potential to influence grassland dynamics. Plant viruses have been long overlooked in ecological studies, and their influence on wild hosts has often been assumed to be minimal.
(.) We examined the short-term and long-term consequences of infection on field-grown individuals from 18 different populations of wild California grasses ( from seven native and one exotic species).
(.) Barley yellow dwarf virus infection was aggressive in most hosts and markedly impaired host fitness by reducing growth, survivorship, and fecundity.
(.) Previous work indicates that the presence of exotic grasses can more than double BYDV incidence in natives. Given the ubiquity of BYDVs, our results suggest that apparent competition and other virus-mediated processes may influence interactions among native and exotic grasses and potentially contribute to shifts in grassland community composition.
Malmstrom CM, AJ McCullough, HA Johnson, LA Newton, and ET Borer. 2005. Invasive annual grasses indirectly increase virus incidence in California native perennial bunchgrasses. OECOLOGIA 145: 153-164
Abstract: In California valley grasslands, Avenafatua L. and other exotic annual grasses have largely displaced native perennial bunchgrasses such as Elymus glaucus Buckley and Nassella pulchra (A. Hitchc.) Barkworth. The invasion success and continued dominance of the exotics has been generally attributed to changes in disturbance regimes and the outcome of direct competition between species. Here, we report that exotic grasses can also indirectly increase disease incidence in nearby native grasses. We found that the presence of A. fatua more than doubled incidence of infection by barley and cereal yellow dwarf viruses (B/CYDVs) in E. glaucus. Because B/CYDV infection can stunt E. glaucus and other native bunchgrasses, the indirect effects of A. fatua on virus incidence in natives suggests that apparent competition may be an additional mechanism influencing interactions among exotic and native grasses in California. A. fatua's influence on virus incidence is likely mediated by its effects on populations of aphids that vector B/CYDVs. In our study, aphids consistently preferred exotic annuals as hosts and experienced higher fecundity on them, suggesting that the exotics can attract and amplify vector populations. To the best of our knowledge, these findings are the first demonstration that exotic plants can indirectly influence virus incidence in natives. We suggest that invasion success may be influenced by the capacity of exotic plant species to increase the pathogen loads of native species with which they compete.
Constible JM, RA Sweitzer, DH Van Vuren, PT Schuyler, and DA Knapp. 2005. Dispersal of non-native plants by introduced bison in an island ecosystem. BIOLOGICAL INVASIONS 7: 699-709
Abstract: An understanding of the mechanisms of seed dispersal is critical to effectively managing populations of non-native plants. We investigated whether introduced bison on Santa Catalina Island, California, have the potential to spread non-native plants through the shedding of clumps of seed-laden hair and/or ingesting and later excreting seeds. We collected clumps of hair shaved from bison during a roundup and dislodged by wallowing activity. Greenhouse and field trials were used to test for seed viability and persistence of hair clumps in wallows. In addition to trials with bison hair, we collected samples of bison dung and tested for seed germination in a greenhouse. The majority of seeds extracted from bison hair clumps were of non-native forbs. There was a significant positive relationship between the size of hair clumps and the number of seeds extracted from the clumps, suggesting that managing the introduced bison population at a lower level will help minimize the spread of non-native plants by the species. Seeds of non-native plants were capable of germinating under conditions similar to those on Santa Catalina Island. Clumps of bison hair persisted in wallows, but did not remain intact and lost nearly 40% of their original mass. The number of germinable seeds contained in bison dung was low: 18 seeds germinated from 6 of 18 dung samples. Introduced bison appear to facilitate the dispersal of non-native plants over native plants on Santa Catalina Island. Our study suggests that a comprehensive strategy to control non-native plants must involve the management of the animal agents of plant dispersal.
Hawkes CV, IF Wren, DJ Herman, MK Firestone. 2005. Plant invasion alters nitrogen cycling by modifying the soil nitrifying community. ECOLOGY LETTERS 8: 976-985
Abstract: Plant invasions have dramatic aboveground effects on plant community composition, but their belowground effects remain largely uncharacterized. Soil microorganisms directly interact with plants and mediate many nutrient transformations in soil. We hypothesized that belowground changes to the soil microbial community provide a mechanistic link between exotic plant invasion and changes to ecosystem nutrient cycling. To examine this possible link, monocultures and mixtures of exotic and native species were maintained for 4 years in a California grassland. Gross rates of nitrogen (N) mineralization and nitrification were quantified with N-15 pool dilution and soil microbial communities were characterized with DNA-based methods. Exotic grasses doubled gross nitrification rates, in part by increasing the abundance and changing the composition of ammonia-oxidizing bacteria in soil. These changes may translate into altered ecosystem N budgets after invasion. Altered soil microbial communities and their resulting effects on ecosystem processes may be an invisible legacy of exotic plant invasions.
Bennett JR and PH Bloom. 2005. Home range and habitat use by Great Horned Owls (Bubo virginianus) in southern California. JOURNAL OF RAPTOR RESEARCH 39: 119-126.
Abstract: Great Horned Owls (Bubo virginianus) are a common, widespread species that can be found in a variety of habitats across most of North America, but little is known about their space and habitat requirements. Using rachotelemetry, location data were collected on nine male and five female Great Horned Owls to determine home range and habitat use in southern California. Owls were tracked between January 1997 and September 1998 for periods ranging from 5-17 mo. Seven owls were also followed during 13 all-night observation periods. The mean 95% adaptive kernel home-range size for females was 180 ha (range = 88-282, SE = 36) and that for males was 425 ha (range = 147-1115 ha, SE = 105). Core areas estimated by the 50% adaptive kernel averaged 27 ha (range = 7-44, SE = 7) for females and 61 ha (range = 15-187, SE = 18) for males. Owls were located in areas with varying degrees of human disturbance ranging from almost entirely urban to native oak (Quercus agrifolia) woodland. Oak/sycamore (Quercus agrifolia/Platanus racemosa) woodland and ruderal grassland (Bromus spp., Avena spp., and various other non-native invasives), were used more often than expected based on availability, but we found no correlation between home-range size and any single habitat type or habitat groups.
Fehmi JS, SE Russo, and JW Bartolome. 2005. The effects of livestock on California ground squirrels (Spermophilus beecheyii). RANGELAND ECOLOGY & MANAGEMENT 58: 352-359.
Abstract: Understanding the impacts of livestock grazing on wildlands is important for making appropriate ecosystem management decisions. Using livestock exclosures, we examined the effects of moderate cattle grazing on the abundance of California ground squirrels (Spermophilus beecheyii Richardson) and the spatial distribution of active burrows within their colonies in grassland and blue oak (Quercus douglasii Hook. & Arn.) savanna habitats in the coastal range of California over a 3-year period (1991-1994). Overall, relative population densities of California ground squirrels declined significantly throughout the experiment, but did not differ between grazed and ungrazed colonies or between habitats. There was also no significant interaction between these 2 factors. The spatial distribution of burrows, as measured by the mean nearest neighbor distance of active entrances within a colony, did not differ significantly between grazed and ungrazed colonies or between habitats, nor was the interaction significant. Thus, low to moderate levels of cattle grazing did not appear to have a strong effect on the population dynamics of California ground squirrels, and grazing may be compatible with maintenance of ground squirrel populations. Based on multivariate analysis of variance of 1994 data, live plant cover, native plant cover, and standing biomass were lower where the number of burrows was higher on grazed colonies but were little affected on ungrazed colonies. Ground squirrels may increase the impact of livestock grazing and thus reduce the capacity of the land to support other activities. However, it is clear that the effects of livestock grazing are complex and that detailed studies of potential mechanisms by which grazing impacts California ground squirrel populations are necessary.
Fierer N, OA Chadwick, and SE Trumbore. 2005. Production of CO2 in soil profiles of a California annual grassland. ECOSYSTEMS 8: 412-429
Abstract: Soils play a key role in the global cycling of carbon (C), storing organic C, and releasing CO2 to the atmosphere. Although a large number of studies have focused on the CO2 flux at the soil-air interface, relatively few studies have examined the rates of CO2 production in individual layers of a soil profile. Deeper soil horizons often have high concentrations of CO2 in the soil air, but the sources of this CO2 and the spatiotemporal dynamics of CO2 production throughout the soil profile are poorly understood. We studied CO2 dynamics in six soil profiles arrayed across a grassland hillslope in coastal southern California. Gas probes were installed in each profile and gas samples were collected weekly or biweekly over a three-year period. Using soil air CO2 concentration data and a model based on Fick's law of diffusion, we modeled the rates Of CO2 production with soil profile depth. The CO2 diffusion constants were checked for accuracy using measured soil air Rn-222 activities. The modeled net CO2 production rates were compared with CO2 fluxes measured at the soil surface. In general, the modeled and measured net CO2 fluxes were very similar although the model consistently underestimated CO2 production rates in the surficial soil horizons when the soils were moist. Profile CO2 production rates were strongly affected by the inter- and intra-annual variability in rainfall; rates were generally 2-10 times higher in the wet season (December to May) than in the dry season (June to November). The El Nino event of 1997-1998, which brought above-average levels of rainfall to the study site, significantly increased CO2 production in both the surface and subsurface soil horizons. Whole profile CO2 production rates were approximately three times higher during the El Nino year than in the following years of near-average rainfall. During the dry season, when the net rates of CO2 flux from the soil profiles are relatively low (4-11 Mg C- CO2 m(-2) h(-1)), 20%-50% of the CO2 diffusing out of the profiles appears to originate in the relatively moist soil subsurface (defined here as those horizons below 40 cm in depth). The natural abundance C-14 signatures of the CO2 and soil organic C suggest that the subsurface CO2 is derived from the microbial mineralization of recent organic C, possibly dissolved organic C transported to the subsurface horizons during the wet season.
Balser, TC and MK Firestone. 2005. Linking microbial community composition and soil processes in a California annual grassland and mixed-conifer forest. BIOGEOCHEMISTRY 73: 395-415.
Abstract: To investigate the potential role of microbial community composition in soil carbon and nitrogen cycling, we transplanted soil cores between a grassland and a conifer ecosystem in the Sierra Nevada California and measured soil process rates (N-mineralization, nitrous oxide and carbon-dioxide flux, nitrification potential), soil water and temperature, and microbial community parameters (PLFA and substrate utilization profiles) over a 2 year period. Our goal was to assess whether microbial community composition could be related to soil process rates independent of soil temperature and water content. We performed multiple regression analyses using microbial community parameters and soil water and temperature as X-variables and soil process rates and inorganic N concentrations as Y-variables. We found that field soil temperature had the strongest relationship with CO2 production and soil NH4+ concentration, while microbial community characteristics correlated with N2O production, nitrification potential, gross N-mineralization, and soil NO3- concentration, independent of environmental controllers. We observed a relationship between specific components of the microbial community (as determined by PLFA) and soil processes,particularly processes tightly linked to microbial phylogeny (e.g. nitrification). The most apparent change in microbial community composition in response to the 2 year transplant was a change in relative abundance of fungi (there was only one significant change in PLFA biomarkers for bacteria during 2 years). The relationship between microbial community composition and soil processes suggests that prediction of ecosystem response to environmental change may be improved by recognizing and accounting for changes in microbial community composition and physiological ecology.