Hopland Research and Extension Center

We propose to carry out a series of experiments that test central questions shared by both conceptual ecology and ecological restoration, and to replicate these experiments identically for at least five consecutive years.  This will be the first long-term examination of year effects in ecological experiments, as well as more general test of particular ecological questions across sites and years. There will be two sets of core experiments, carried out in different systems. The first is a study of priority effects in perennial grasslands. The second is a study of recruitment limitation in an oak species with a troubling century-long recruitment gap.  For each of these two core experiments we will establish five replicates (each year) at each of four sites in northern California, and we will do this repeatedly for (at least) five consecutive years.  At the same time, we will initiate five replicates of specific targeted experiments at each site. These will initially be based on our a priori understanding of the limiting factors in the systems, but as the experiments progress, we will use these targeted experiments to test hypotheses arising from inter-annual differences observed in our core experiments. Although we are requesting funds for five years, we anticipate running this experiment for ten years or more, both monitoring the established experiments and continuing our replications across years.

Cork has been of great importance to California's finer wine makers, but the source, cork oak (Quercus suber L.), is native only to the eastern Mediterranean in Europe and North Africa.  Much cork oak acreage has been and is still being lost in the Mediterranean region, and many cork oaks have been eliminated by an introduced root pathogen.  The only range-wide germplasm collection ever attempted was assembled in 1992-1994, but field genebanks established in Portugal failed.  The cork oak germplasm collection at Hopland R&E Center is the only extant, broad-based collection of cork oak genetic resources.  It includes a broad genetic base from 19 locations and in addition to conserving cork oak genetic resources it will provide data on genetic variation in the species.  Determining the adaptability of these materials to California is a necessary first step in the development of a domestic industry.

This proposal is a request to continue the work and complete the objectives outlined in the proposal for HREC Project # 35-03, submitted in March 2003, with Project Completion Report submitted 4/4/05.  Phytolith analysis, extracting biogenic silica from soils and examining the soil phytoliths in relation to reference phytoliths from plants, has considerable potential for paleoecological reconstruction of pre-European settlement vegetation in California, but to date there is minimal literature on phytolith work in the state.  We propose to do a baseline study and build a reference collection of phytoliths produced by dominant plants from four HREC vegetation types.  This reference collection will be used to catalog and count phytolith shapes found in already collected and processed soil samples from the four vegetation types to delineate phytolith assemblages for each type.  The utility of knowledge of vegetation type phytolith assemblages will be tested by attempting to reconstruct the vegetation present prior to clearing on Watershed II.  The annual rate of grass phytolith deposition in the soil will be calculated for formerly dense woodland sites that have been grassland for 40+ years since clearing.  Additionally, landslide scars will be examined and sampled to assess the feasibility of using phytoliths to record major vegetation changes in the chronologically stratified colluvium.

The primary economic use of most hardwood rangelands in the coastal foothills is livestock production.  The economic rent for this activity is relatively low in the neighborhood of $10-$15/acre/year.  Owners and managers of hardwood rangelands may be able to increase their income on a small portion of their lands by producing higher value crops.  However, there are few crops that can be produced in the dry Mediterranean like climate that characterizes this region without irrigation, which is generally prohibitively costly.  Some conifers have demonstrated the ability to grow rapidly in fairly dry environments where average rainfall is around 25 inches annually.  Such trees may be suitable for wood production on short rotations or for Christmas trees.  This study evaluates the ability of four species of conifers to survive and grow in unirrigated field plots.

Invasive species research has just begun to successfully utilize an evolutionary perspective to understand the origin of invasiveness in plants and animals, including several species in CA.  The focus of this study is CA wild radish (Raphanus sativus), a hybrid-derived species in which invasiveness has evolved since introduction to the state.  Two hypotheses will be tested by the project to account for the evolution of invasiveness:  hybridization and rapid adaptive evolution.  Experiments conducted will be part of an ongoing effort to test the second of these two hypotheses.  Overall, this project seeks to understand the underlying mechanisms for the evolution of invasiveness and to apply this knowledge to the development of control approaches for this species as well as others that have evolved invasiveness.

This research seeks to understand the genetic basis of adaptation to heterogeneous environments.  Avena barbata occurs in California as two readily identifiable genotypes (termed "Mesic" and "Xeric"), associated with environments that differ in moisture availability.  In previous work, we have crossed these genotypes, and mapped the genes underlying fitness variation in this cross using native sites at HREC and SFREC.  I propose to continue this fieldwork in two important ways.  First, I will conduct additional replicate field trials to understand the extent of temporal (year to year) variation in the strength, direction and target of selection.  So far, we have data for two growing seasons with contrasting weather patterns, and I propose to collect data for two more.  Second, fieldwork to date has collected only final measures of plant performance (final size, and seed output).  I will spend one full field season at HREC and SFREC monitoring the growth of the genotypes, to determine which traits expressed during the plants life cycle contribute to fitness variation.  This will permit an understanding of the traits that link genes with fitness.

The purpose of this study is to explore the formation of ecotypes in blue oak.  Acorns were collected from 27 populations of blue oak throughout the range of the species in California.  Nine individuals of each population were planted on 1 meter centers to form squares that were replicated 10 times, at random, to establish the common garden.  The assumption of a common garden experiment is that difference in growth and rates of physiological processes will be the result of differences in the genotypes of the plants.  Furthermore, natural selection will result in the formation of ecotypes (genetic populations) that have adaptations to variations among local habitats.    Results to date suggest that genetic variation in blue oak is better described as ecoclinal (gradual variation along environmental gradients) rather than ecotypic (abrupt variation along environmental gradients).  Statistical significant difference in growth, timing of bud break, nutrient uptake, and transpiration rate occurred among certain population, but these variations did not suggest ecotypic differentiation.  Current research involves the use of molecular techniques to distinguish the various populations. I wish to maintain the common garden as a source of tissue for molecular analysis.  I would also like to maintain the populations to observe response to potential drought or above average precipitation over the next seven years. 

Ecological studies have shown that G. politella is an effective pollinator of L. parviflorum.  G. politella pollinate Lithophragma plants passively while ovipositing though the corolla.  G. politella has a mutualistic effect on the plant, when it pollinates, and an antagonistic effect when it eats the seeds.  Whether the overall effect of the interaction is locally mutualistic depends upon the presence of co-pollinators that pollinate the flowers but do not oviposit into flowers. In some populations where co-pollinators are abundant, they can swamp the mutualistic effects of Greya on seed set. In the northern geographic range, the interaction ranges from antagonism to commensalism to mutualism among habitats.  Continuing with these studies, the objective of the proposed work is to evaluate how the network structure of the interaction differs in outlier populations of the plants at the very southern and western edges of the ranges of the moths. At that range edge, the moths have shifted from their normal Lithophragma host plant (Lithophragma parviflorum) onto a different Lithophragma species (Lithophragma cymbalaria in Sedwick Reserve, and L. heterophyllum in Hopland Reserve and Hasting location).

Plant invasions are well known for their often dramatic aboveground effects on plant community composition, but their belowground effects remain largely uncharacterized. Root-associated microbes can affect plant fitness, plant community composition, and are critical to 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 processes in soil. To examine this link, we used monocultures and mixtures of exotic and native species maintained for four years in California grasslands with known differences in mycorrhizal communities. We measured how different soil microbial communities changed gross rates of nitrogen cycling using the 15N pool dilution method in combination with in-growth cores designed to include nested subsets of the soil biota: bacteria, bacteria and mycorrhizal fungi, bacteria and mycorrhizal fungi and roots. We found that the altered mycorrhizal community associated with exotic grasses in California halved rates of gross nitrogen mineralization. Exotic grasses also doubled gross rates of nitrification by increasing the abundance of nitrifying bacteria in soil. This can translate into a dramatic change in ecosystem nitrogen budgets when exotic grasses are dominant by increasing nitrogen loss from the system and decreasing plant available nitrogen. Changes to belowground microbial communities and their resulting effects on ecosystem processes may be the invisible legacy of exotic plant invasions. Understanding these changes is likely to be an important step in developing successful eradication and restoration efforts.

Barbed goatgrass (Aegilops triuncialis), is a cleistogamous annual grass with a native range throughout Europe, Asia and the Mediterranean Basin.  A. triuncialis is now considered a serious noxious range weed due to its poor palatability for livestock. A. triuncialis has very low forage quality and has begun to invade large areas of rangeland formerly dominated by other annual grasses. It has also been classified as a plant pest of greatest ecological concern in California because of its unique capacity to invade serpentine soil habitats that are "hot spots" of endemic plant diversity.  By addressing the questions posed in this project, we will provide much needed information on evolutionary mechanisms by which founding infestations of goatgrass, although initially genetically depauperate, can adapt and spread into these serpentine habitats.  We will provide a unique, comprehensive test of the potential adaptive role of maternal environmental effects in invasion dynamics and will explore the possibility that mutation accumulation in quantitative traits may be an important source of genetic variation facilitating adaptive spread in goatgrass. By examining both of these mechanisms simultaneously in goatgrass, we will provide important fundamental information on their relative roles in plant adaptation during invasions.   From a management perspective we will also have a much better understanding of the interplay between genetic variation and plasticity and the role that both play in promoting the invasion of A. triuncialis into California range and wildlands.

Barb goatgrass (Aegilops triuncialis) is fast becoming a major plant pest in California grasslands, yet its impacts on critical ecosystem processes remain poorly understood.  We seek to address this gap by conducting field and laboratory experiments in which we will use stable isotopes as tracers to quantify the impacts of goatgrass on C and N cycling. Research has suggested that goatgrass may have significant impacts on soil microbial communities, especially arbuscular mycorrhizal fungi, which may not only facilitate its colonization of new habitat but also contribute to its net effect on soil nutrient properties. This in turn may affect the success of post-eradication restoration efforts. As a component of our field and laboratory experiments, we will use molecular methods to identify and quantify the impacts of goatgrass on mycorrhizal community composition and functional attributes. Our research will contribute to our understanding of the basic biology and ecology of this invasive species as well as provide information useful to land managers engaged in restoration efforts.

In most ecosystems, litter senesced at the end of the growing season is assumed to be the main source of carbon and recycled nutrients.  However, experiments conducted by Eviner and Vaughn at HREC demonstrate that self-thinning of grass seedlings provide N and C inputs that are similar in magnitude to the C and N derived from senesced litter.  In the late spring, 70% of aboveground plant N is retranslocated from senescing litter to seeds. Over 90% of these seeds germinate in the fall and these seeds and seedlings likely take up and store N during the early rains, when a significant amount of litter-derived N is leached from the system. Intense seedling competition through the growing season results in mortality of approximately 75% of the seedling, resulting in a steady release of highly labile C and N. Since seedling density largely drives seedling thinning, shifts in seed density (through management- or environment- induced changes in seed production, or density of seeds planted in restoration) likely have large impacts on plant growth and nutrient cycling. Similarly, seed granivory's impact on seed density can have strong impacts on the grassland community and ecosystem. The proposed experiment will manipulate seed density to determine the impacts of seed density on plant density, growth, size, and fecundity, as well as nitrogen cycling and leaching throughout the growing season. In addition, a set of seed density manipulations will occur in rodent exclosures—allowing us to assess the impact of seed granivory on plant and soil dynamics.

With the ever-increasing demand on water supplies in California, the focus on efficient water use has intensified.  California's population continues to grow at a rapid rate, but the supply of water for its citizens is limited.  To make certain enough water is available for Californians as well as to encompass the all of the other water needs; studies are being conducted to determine new strategies for using water appropriately. To help improve landscape irrigation efficiency, recommendations to apply water based on evapotranspiration modified by a plant (species) or landscape coefficient have been made.  The widely used reference, Water Use Classifications of Landscape Species, WUCOLS, (Costello and Jones, 1999), lists coefficients for many ornamental species and provides additional valuable information on landscape irrigation.  Unfortunately, these coefficients are not research based.  Knowing this, the UC Landscape Workgroup initiated a project to test commonly used landscape plants irrigated with four fractions of reference evapotranspiration (ETo).  Based on weather data collected at nearby CIMIS stations, irrigation treatments of 20%, 40%, 60%, and 80% of ETo are applied to commonly used landscape plants.  To study regional variations, project sites will be located in different areas of the state including South Coast (South Coast Research & Extension Center), Low Desert (U.C. Riverside Coachella Valley Agricultural Research Station), Central Valley (U.C. Davis), North Coast (U.C. Hopland Research & Extension Center), UCCE Ventura Co. Hansen Farm with an additional alternative site at the U.C. Riverside Agricultural Experiment Station. The physical design of the plots and selection of the plants tested are standardized for each site.

Fourteen winegrape cultivars of Mediterranean origin will be planted in a replicated trial to evaluate their suitability for use in CA.  Vine performance and fruit quality will be evaluated including yield per vine, dormant pruning weights, cluster number and weight, berry size, percent brix sugar, pH, and titratable acidity.  Phenological data will include budbreak, flowering, veraison and harvest.  The vineyard will be available for tours by interested persons.  Progress reports and data will also be made available.

Flavor development in wine grapes sometimes lags behind sugar accumulation, so grapes have to be picked after the sugar levels have become quite high.  1-MCP (1-methyl cyclopropene) affects the ripening process in many fruits and some preliminary data shows effects on grapes during the growing season.  We propose to test whether the application of MCP in a Rohm and Haas formulation would alter the accumulation of color or tannin during the ripening process. Fruit will be treated at veraison and at two week intervals afterwards.  Phenolics including color and tannin will be measured vs. sugar in the fruit, and the same phenols measured in wine made from the fruit. 

Mendocino and Lake County winegrowers are quite involved in alternative farming practices.  There are nearly 3200 acres of certified organically farmed grapes, and another 500 acres of Demeter certified biodynamically farmed grapes.  Growers extol the benefits of these farming systems including improved environmental quality, improved fruit quality, improved soil quality, economically viable yields, and improved worker safety.  This study looks at all three farming systems, and evaluates:  vine performance, measured by yield, cluster counts, stem counts, pruning weights; fruit quality including % brix, titratable acidity, pH, total tannins, acid profiles; wine quality, including alcohol, pH, acidity, tannins; soil fertility and health, including NPKS, micronutrients, biological activity and diversity, organic matter content, soil porosity and bulk density, soil resistance, and water holding capacities; pest management evaluation including mites, leaf hoppers, incidence of powdery mildew, eutypa, and seasonal pest and disease disorders.