November-December 2005 CA Grasslands Newsletter
CA Grassland Newsletter
Remember that archives of the CA Grassland newsletter can be found at http://cbc.berkeley.edu/grass
1) Newest CA grassland ecologists?
2) Dinosaur poop!
3) Publications – 12 this time.
(1) 2 birth announcements in our community:
Congratulations to Meredith Thomsen and Josh Minor for the birth of their son, Soren Minor. By the way, Meredith will begin a faculty position at the University of Wisconsin-La Crosse in January, so wish her a bon voyage (firstname.lastname@example.org), and urge her to keep her hand in California grasslands from afar!
And, congratulations to…me! Janette and I are the proud parents of Elise Autumn Corbin. She hasn’t visited Tom’s Point yet, but soon!
(2) Dinosaur poop! Thanks to CNGA for this note:
CNGA member Jeffrey Caldwell brought to our
attention the amazing news that astonished scientists have found remains of
grasses -- phytoliths, signature chemicals -- in the dung of Indian sauropod
dinosaurs ... indicating at least five different types, including grasses
related to bamboo and rice ... the oldest known fossils of grasses are dated 55
million years, while most dinosaurs were believed to live 65 to 71 million years
ago ... and dinosaurs were thought to have died out long before grasses appeared
Ancient Grazers: Find adds grass to dinosaur menu <http://www.sciencenews.org/articles/20051119/fob1.asp>
Canals, Eviner, Herman, and Chapin. 2005. Plant colonizers shape early N-dynamics in gopher-mounds. Plant and Soil 276: 327-334.
Abstract: Disturbances by fossorial mammals are extremely common in many ecosystems, including the California annual grassland. We compared the impact of juveniles of four common plant colonizers (Aegilops triuncialis, Cerastium glomeratum, Aphanes occidentalis and Lupinus bicolor) on the pools and fluxes of N in mounds created by pocket gophers (Thomomys bottae Mewa). The mechanisms and magnitude of biotic N retention differed among plant species. In mounds colonized by Cerastium, Aphanes and Lupinus, the microbial N pool was significantly larger than the plant N pool, as is typical in California grasslands in the early spring, whereas in mounds colonized by Aegilops, there was a more equal distribution of biotic N between plant and microbial pools. A 1-day N-15 pulse field experiment demonstrated that plant species significantly differed in their effects on the distribution of isotopic N, with the N-fixing Lupinus leaving most (82%) N-15 as inorganic N in soil, whereas more N-15 was immobilized in plants or otherwise removed from the available soil pool in mounds colonized by other species. The impacts of early colonizers on N dynamics suggest that the identity of plant species that initially colonize gopher mounds may have important consequences on the dynamics of the overall grassland community.
Corbin, Thomsen, Dawson, and D’Antonio. 2005. Summer water use by California coastal prairie grasses: fog, drought, and community composition. Oecologia 145: 511-521.
Abstract: Plants in the Mediterranean climate region of California typically experience summer drought conditions, but correlations between zones of frequent coastal fog inundation and certain species' distributions suggest that water inputs from fog may influence species composition in coastal habitats. We sampled the stable H and O isotope ratios of water in non-photosynthetic plant tissue from a variety of perennial grass species and soil in four sites in northern California in order to determine the proportion of water deriving from winter rains and fog during the summer. The relationship between H and O stable isotopes from our sample sites fell to the right of the local meteoric water line (LMWL) during the summer drought, providing evidence that evaporation of water from the soil had taken place prior to the uptake of water by vegetation. We developed a novel method to infer the isotope values of water before it was subjected to evaporation in which we used experimental data to calculate the slope of the delta H versus delta O line versus the LMWL. After accounting for evaporation, we then used a two-source mixing model to evaluate plant usage of fog water. The model indicated that 28-66% of the water taken up by plants via roots during the summer drought came from fog rather than residual soil water from winter rain. Fog use decreased as distance from the coast increased, and there were significant differences among species in the use of fog. Rather than consistent differences in fog use by species whose distributions are limited to the coast versus those with broader distributions, species responded individualistically to summer fog. We conclude that fogwater inputs can mitigate the summer drought in coastal California for many species, likely giving an advantage to species that can use it over species that cannot.
Young and Evans. 2005. Initial mortality and root and shoot growth of valley oak seedlings outplanted as seeds and as container stock under different irrigation regimes. Native plants. Spring 2005:83-90.
Abstract: Direct seeding of valley oak (Quercus lobata Nee [Fagaceae], commonly used in restoration in the Central Valley of California, may be preferable to using container stock, at least in non-irrigated sites and where acorn predation can be controlled. In a stratified random experiment we tested initial growth and survival of oaks either: 1) outplanted as acorns; 2) outplanted as 3mo-old container seedlings; 3) outplanted as 3mo-old container seedlings that had been transplanted into larger containers 6 wk before outplanting; and 4) outplanted as 1-yr-old container seedlings (commercial stock). We subjected each of these to 3 different irrigation regimes: 1) none; 2) drip; or 3) overhead. Half of the irrigated oaks were watered for 1y, and half for 2y. In nonirrigated plots, oaks grown from acorns that survived initial seed predation survived significantly better than oaks planted from containers. Across stock type (acorns, plants of different sizes of containers), initial differences in plant height remained after 18mo of growth, but growth rates were similar. Oaks grown in containers usually had more branched and more distorted root systems but all stock types successfully produced deep roots. Irrigated plants grew faster than nonirrigated plants. Plants weaned from irrigation during their second year grew as well thereafter as those that were never irrigated.
Moyes, Witter, and Gamon. 2005. Restoration of native perennials in a California annual grassland after prescribed spring burning and solarization. Restoration Ecology 13: 659-666.
Abstract: Grasslands dominated by exotic annual grasses have replaced native perennial vegetation types in vast areas of California. Prescribed spring fires can cause a temporary replacement of exotic annual grasses by native and non-native forbs, but generally do not lead to recovery of native perennials, especially where these have been entirely displaced for many years. Successful reintroduction of perennial species after fire depends on establishment in the postfire environment. We studied the effects of vegetation changes after an April fire on competition for soil moisture, a key factor in exotic annual grass dominance. As an alternative to fire, solarization effectively kills seeds of most plant species but with a high labor investment per area. We compared the burn to solarization in a study of establishment and growth of seeds and transplants of the native perennial grass Purple needlegrass (Nassella pulchra) and coastal sage species California sagebrush (Artemisia californica). After the fire, initial seed bank and seedling densities and regular percent cover and soil moisture (0-20 cm) data were collected in burned and unburned areas. Burned areas had 96% fewer viable seeds of the dominant annual grass, Ripgut brome (Bromus diandrus), leading to replacement by forbs from the seed bank, especially non-native Black mustard (Brassica nigra). In the early growing season, B. diandrus dominating unburned areas consistently depleted soil moisture to a greater extent between rains than forbs in burned areas. However, B. diandrus senesced early, leaving more moisture available in unburned areas after late-season rains. Nassella pulchra and A. californica established better on plots treated with fire and/or solarization than on untreated plots. We conclude that both spring burns and solarization can produce conditions where native perennials can establish in annual grasslands. However, the relative contribution of these treatments to restoration appears to depend on the native species being reintroduced, and the long-term success of these initial restoration experiments remains to be determined.
Dickert. 2005. Giant garter snake surveys at some areas of historic occupation in the grassland ecological area, Merced Co. and Mendota Wildlife Area, Fresno Co., California. California Fish and Game 91: 255-269.
Abstract: The Threatened (California and Federal listings) giant garter snake, Thamnophis grigas, is endemic to still and slow-moving waterways of California's Central Valley, such as sloughs, canals, and cattail and tule marshes. Giant garter snakes have experienced substantial habitat loss in the San Joaquin Valley and are seemingly no longer present in some sites where they were documented in the mid-1970's. In 2001 we conducted giant garter snake surveys on both publicly and privately owned lands in the Grassland Ecological Area and at the Volta Wildlife Area, both located in western Merced County, as well as at two sites in Fresno County; Mendota Wildlife Area and Alkali Sink Ecological Reserve. We performed visual surveys for giant garter snakes in early morning when basking snakes were most visible. In addition, at 18 study sites we set floating funnel traps for giant garter snakes along approximately 19 km of wetland edge. We did not encounter any giant garter snakes during our visual surveys. We trapped 15 giant garter snakes; 14 at the Mendota Wildlife Area and I in the southern Grassland Ecological Area. We recorded morphological measurements, physical characteristics, and implanted PIT tags into all captured giant garter snakes prior to release at the point of capture. Wed id not capture any juvenile giant garter snakes nor did we recapture any giant garter snakes; the snake that was captured in the southern Grassland Ecological Area was nota recapture although giant garter snakes were captured at this site in previous surveys. Giant garter snakes were definitively documented on the Mendota Wildlife Area in 2001, the first year since the mid-1970's. However, we have not found giant garter snakes at the Volta Wildlife Area since 1999, despite conducting surveys therein 2000 and 2001. The late summer timing of trapping efforts could explain this result. Giant garter snakes still persist in some San Joaquin Valley locations thus future research efforts should strive to understand their current status, distribution, and the threats to their continued survival. This basic information is needed to protect populations of giant garter snakes in the San Joaquin Valley through effective land management decision making on existing giant garter snake habitat and for the restoration of giant garter snake habitat in areas where it is currently absent or degraded.
Fleskes, Gilmer and Jarvis. 2005. Pintail distribution and selection of marsh types at Mendota Wildlife Area during fall and winter. California Fish and Game 91: 270-285.
Abstract: To help guide management of Mendota Wildlife Area (MWA), we determined distribution patterns and use relative to availability (i.e., selection) of lake vs. shallow marsh, and shallow marsh by dominant understory vegetation and percentage of emergent cover during September through March, 1991-94 for 145 female northern pintails, Anas acuta. Pintails were radio tagged during August - early October at MWA (n = 116), other San Joaquin Valley areas (n = 27), or Suisun Marsh (n = 2). Before duck hunting season (i.e., Prehunt), pintail distribution at MWA generally tracked marsh flooding although distribution was more concentrated during the day than night. During duck hunting season (i.e., Hunt), pintails that had not left MWA sought sanctuary on units closed to shooting and at night dispersed throughout the area; most returned to sanctuary units on both shoot (Wednesdays and weekends) and nonshoot days. Pintails present during Posthunt (i.e., after Hunt ended) dispersed throughout MWA. Pintails avoided the central lake in favor of the more shallow marsh units throughout MWA. Among the marsh units, pintails selected open and avoided heavily vegetated units at night. Open marsh units Were also selected during the day during Posthunt and, except in 1993, during Prehunt. However, closed or hemi marshes were selected during day during Hunt. Marshes where swamp timothy, Heleochloa schoenoides, was the dominant or prominent understory plant were always selected and received more use by pintails than any other marsh type. Watergrass, Echinochloa crusgalli, marsh was avoided during the day but, along with timothy marsh, selected at night most years. Selection of marsh where alkali bulrush, Scirpus patudosus, or other non-timothy or non-watergrass plants were primary understory plants ranked in the middle during the day but were avoided at night. Our finding that foraging pintails selected swamp timothy is consistent with food habits and habitat use reported elsewhere, but the greater use of watergrass marsh at MWA than in the Grassland Ecological Area indicates regional differences in management or pintail ecology. Exodus of pintails coinciding with start of Hunt indicates that some aspect of the sanctuary or other habitats were lacking at MWA, and will need to be improved to maintain pintail use all winter.
Marty, Collinge, and Rice. 2005. Responses of a remnant California native bunchgrass population to grazing, burning and climatic variation. Plant Ecology 181: 101-112.
Abstract: This study examined the interactive effects of grazing intensity and burning on a remnant population of the California native bunchgrass Nassella pulchra. We measured growth, reproduction and mortality of permanently marked bunchgrasses and measured bunchgrass seedling recruitment and density in permanent quadrats. We burned half of the treatment plots in late spring 1998. Grazing treatments were implemented in 1998, 1999 and 2000 at four different intensities: ungrazed, light rotational grazing (31% average biomass removal), heavy rotational grazing (42% average biomass removal), and continuously grazed. Both burning and grazing affected the bunchgrass population. Bunchgrass mortality was 10% higher in burned vs. unburned plots but was not significantly different among grazing treatments. Seedling density was 100% higher in burned vs. unburned plots 2 years after the burn, however seedling densities never attained pre-burn levels. Seedling densities did not differ significantly among grazing treatments, but grazing reduced the height and reproduction of the mature bunchgrasses. Adult bunchgrass density did not differ significantly in any of the treatments but experienced a five-fold decrease over the 4 years of the experiment. Although the continuous grazing treatment reduced the number of culms produced per plant by 75% from the baseline year, the effect on culm production in the continuous grazing treatment was not consistently greater than the rotational grazing treatments. The interaction of grazing and burning had no significant impacts on the N. pulchra populations except on the diameter of adult bunchgrasses which was highest in the lightly grazed, unburned treatments 2 years following the burn. All response variables except bunchgrass height followed a similar pattern in time over the 4 years of the experiment regardless of treatment, peaking in 1998 and then declining in 1999 and 2000. We believe the above average rainfall and below average temperatures experienced late in the growing season in 1998 provided conditions that favored the native bunchgrasses. Overall, we found few interactive effects of grazing and burning but the separate treatments did affect bunchgrass growth, reproduction and mortality, and these effects were modulated by the ubiquitous effects of climatic fluctuations.
Montaldo, Rondena, Albertons, and Mancini. 2005. Parsimonious modeling of vegetation dynamics for ecohydrologic studies of water-limited ecosystems. Water Resources Research. 41: art # 10416.
Abstract: The structure and function of vegetation regulate fluxes across the biosphere-atmosphere interface with large effects in water-limited ecosystems. Vegetation dynamics are often neglected in hydrological modeling except for simple prescriptions of seasonal phenology. However, changes in vegetation densities, influencing the partitioning of incoming solar energy into sensible and latent heat fluxes, can result in long-term changes in both local and global climates with resulting feedbacks on vegetation growth. This paper seeks a simple vegetation dynamics model (VDM) for simulation of the leaf area index (LAI) dynamics in hydrologic models. Five variants of a VDM are employed, with a range of model complexities. The VDMs are coupled to a land surface model (LSM), with the VDM providing the LAI evolution through time and the LSM using this to compute the land surface fluxes and update the soil water contents. We explore the models through case studies of water-limited grass fields in California (United States) and North Carolina (United States). Results show that a simple VDM, simulating only the living aboveground green biomass (i.e., with low parameterization), is able to accurately simulate the LAI. Results also highlight the importance of including the VDM in the LSM when studying the climate-soil-vegetation interactions over moderate to long timescales. The inclusion of the VDM in the LSM is demonstrated to be essential for assessing the impact of interannual rainfall variability on the water budget of a water limited region.
Ahearn et al. 2005. Land use and land cover influence on water quality in the last free-flowing river draining the western Sierra Nevada, California. Journal of Hydrology 313: 234-247.
Abstract: and use and land cover across 28 sub-basins within the Cosumnes Watershed, CA (1989 km(2)) were correlated to nitrate-N and total suspended solids (TSS) loading between water years 1999 and 2001. The impact of human development on stream water quality was evident as both agricultural area and population density predicted TSS loading in a linear mixed effects model. In contrast to the TSS model, the nitrate-N loading model was more complex with agriculture, grassland, and the presence or absence of waste water treatment plants (WWTPs) all contributing. The lack of correlation between population density and nitrate-N loading indicates that human habitation of the landscape does not impact stream nitrate levels until a WWTP is built within the sub-basin. During dry water years the models predict a linear reduction in TSS loading but the correlations to agriculture and population density remain positive. In contrast, nitrate is positively correlated to grasslands during average water years and negatively correlated during dry water years. Analysis of constituent fluxes from the upper watershed versus the lower watershed indicates that silica is derived primarily from the uplands and that during dry water years the upper watershed is an important source of dissolved organic carbon (DOC) and nitrate. The lower watershed contributes the majority of the sediment and nutrients during both dry and average water years, the one caveat being that during dry years the lower basin becomes a nitrate sink. (c) 2005 Elsevier B.V. All rights reserved.
Dukes et al. 2005. Responses of grassland production to single and multiple global environmental changes. PLOS Biology 3: 1829-1837.
Abstract: In this century, increasing concentrations of carbon dioxide (CO2) and other greenhouse gases in the Earth's atmosphere are expected to cause warmer surface temperatures and changes in precipitation patterns. At the same time, reactive nitrogen is entering natural systems at unprecedented rates. These global environmental changes have consequences for the functioning of natural ecosystems, and responses of these systems may feed back to affect climate and atmospheric composition. Here, we report plant growth responses of an ecosystem exposed to factorial combinations of four expected global environmental changes. We exposed California grassland to elevated CO2, temperature, precipitation, and nitrogen deposition for five years. Root and shoot production did not respond to elevated CO2 or modest warming. Supplemental precipitation led to increases in shoot production and offsetting decreases in root production. Supplemental nitrate deposition increased total production by an average of 26%, primarily by stimulating shoot growth. Interactions among the main treatments were rare. Together, these results suggest that production in this grassland will respond minimally to changes in CO2 and winter precipitation, and to small amounts of warming. Increased nitrate deposition would have stronger effects on the grassland. Aside from this nitrate response, expectations that a changing atmosphere and climate would promote carbon storage by increasing plant growth appear unlikely to be realized in this system.
Henry, Juarez, Field and Vitousek. 2005. Interactive effects of elevated CO2, N deposition and climate change on extracellular enzyme activity and soil density fractionation in a California annual grassland. Global Change Biology 11: 1808-1815.
Abstract: Elevated CO2, N deposition and climate change can alter ecosystem-level nutrient cycling both directly and indirectly. We explored the interactive effects of these environmental changes on extracellular enzyme activity and organic matter fractionation in soils of a California annual grassland. The activities of hydrolases (polysaccharide-degrading enzymes and phosphatase) increased significantly in response to nitrate addition, which coincided with an increase in soluble C concentrations under ambient CO2. Water addition and elevated CO2 had negative but nonadditive effects on the activities of these enzymes. In contrast, water addition resulted in an increase in the activities of lignin-degrading enzymes (phenol oxidase and peroxidase), and a decrease in the free light fraction (FLF) of soil organic matter. Independent of treatment effects, lignin content in the FLF was negatively correlated with the quantity of FLF across all samples. Lignin concentrations were lower in the aggregate-occluded light fraction (OLF) than the FLF, and there was no correlation between percent lignin and OLF quantity, which was consistent with the protection of soil organic matter in aggregates. Elevated CO2 decreased the quantity of OLF and increased the OLF lignin concentration, however, which is consistent with increased degradation resulting from increased turnover of soil aggregates. Overall, these results suggest that the effects of N addition on hydrolase activity are offset by the interactive effects of water addition and elevated CO2, whereas water and elevated CO2 may cause an increase in the breakdown of soil organic matter as a result of their effects on lignin-degrading enzymes and soil aggregation, respectively.
Bedard-Haughn, Tate and van Kessel. 2005. Quantifying the impact of regular cutting on vegetative buffer efficacy for nitrogen-15 sequestration. J of Environmental Quality 34: 1651-1664.
Abstract: This study used the stable N-15 isotope to quantitatively examine the effects of cutting on vegetative buffer uptake of NO3--N based on the theory that regular cutting would increase N demand and sequestration by encouraging new plant growth. During the summer of 2002, 10 buffer plots were established within a flood-irrigated pasture. In 2003, IN-labeled KNO3 was applied to the pasture area at a rate of 5 kg N ha(-1) and 99.7 atom % N-15. One-half of the buffer plots were trimmed monthly. In the buffers, the cutting effect was not significant in the first few weeks following IN application, with both the cut and uncut buffers sequestering 'IN. Over the irrigation season, however, cut buffers sequestered 2.3 times the N-15 of uncut buffers, corresponding to an increase in aboveground biomass following cutting. Cutting and removing vegetation allowed the standing biomass to take advantage of soil 'IN as it was released by microbial mineralization. In contrast, the uncut buffers showed very little change in N-15 sequestration or biomass, suggesting senescence and a corresponding decrease in N demand. Overall, cutting significantly improved N-15 attenuation from both surface and subsurface water. However, the effect was temporally related, and only became significant 21 to 42d after IN application. The dominant influence on runoff water quality from irrigated pasture remains irrigation rate, as reducing the rate by 75% relative to the typical rate resulted in a 50% decrease in total runoff losses and a sevenfold decrease in N-15 concentration.