Source: UNIVERSITY OF CALIFORNIA, DAVIS submitted to
DEMOGRAPHY OF ARID-LAND SHRUBS: BASIC RESEARCH IN PLANT ECOLOGY WITH APPLICATIONS FOR RESTORATION AND MANAGEMENT OF DEGRADED ARID-LAND ECOSYSTEMS IN CALIFORNIA
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0168762
Grant No.
(N/A)
Project No.
CA-D-EVE-5963-H
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 2009
Project End Date
Dec 31, 2011
Grant Year
(N/A)
Project Director
Toft, C.
Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671
Performing Department
Evolution and Ecology
Non Technical Summary
With the predicted advent of global warming, combined with the continued growth of the human population in California, more demands will be made on scarce water supplies. At the same time, the public expects higher environmental quality and use of scenic and natural resources. Because most of this state is arid, pressures on water use from agriculture and urbanization have considerable repercussions on the state?s economy, politics and law. A prime example is the diversion of water from Sierra Nevada streams, including those feeding Mono Lake in the Mono Basin, to support the large cities and agricultural areas of southern California. In the past, water allocations were made based on the largest good for the public sector, but today the public demands that actual environmental costs and impacts on smaller communities be considered in the allocation of water rights. My current research project builds on 30 years of study of sand-dune ecosystems surrounding Mono Lake, in the eastern Sierra, in an area that has undergone considerable desertification as water is exported primarily to urban areas of southern California. This research will be crucial in designing permanent restoration of sand-dune ecosystems on dry lakebeds and other ecosystems degraded by desertification, where the intention is to create inexpensive and most importantly 'walk away' solutions to mitigating air pollution from dust generated by degraded ecosystems.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
10307101070100%
Goals / Objectives
This 5-year project investigates the dynamics of native arid-land ecosystems in the eastern Sierra Nevada of California. This research: 1) addresses the still unresolved debate on the occurrence of and mechanisms of plant succession in deserts; and 2) tests hypotheses on the demography of perennial desert shrubs, from seeding establishment, recruitment of juveniles into the reproductive class, growth and reproduction of adults, and senescence. The 30-year span of data collection also enables reliable projections about long-term climate change and its effect on California's arid-land ecosystems. The basic research contributions from this project have direct application to restoring natural ecosystems to ameliorate the impacts of stream diversions and groundwater pumping that cause 'desertification' of large areas of the arid West. The primary application will be to aid restoration of self-sustaining ecosystems that suppress the generation of toxic dust (PM10 and smaller) on dry lakebeds or in areas adversely affected by groundwater pumping or grazing. OBJECTIVES: 1) To document long-term demographics of perennial shrub populations and recruitment, survivorship of seedlings along the environmental gradient created by the receding Mono Lake; 2) to use the projected transgression of Mono Lake after the 1994 water rights decision as a natural (uncontrolled) experiment to document effects of ground-water depth on recruitment of seedlings to phreatophytic status (defined as reaching groundwater); 3) to test hypotheses about the recruitment of juveniles into the reproductive class, in particular whether episodic short-term climatic fluctuations caused by ENSO determines the timing of recruitment of reproductives; 4) to build predictive models of long-term demographic trajectories of rabbitbrush, as a representative perennial, arid-land shrub, to explore among other things the effect of projected climate change due to global warming on arid-land ecosystems; and 5) to apply information obtained at Mono Lake to design lakebed restoration protocols in the Owens Valley and other degraded arid-land ecosystems.
Project Methods
1) Two sites of different successional stages (500 years and 50 years since transgression of Mono Lake) will continue to be monitored for several environmental variables including depth to ground water and soil quality using standard methods in physical geography and ecological studies; 2) at these two sites, we will continue collection of basic demographic data on previously marked shrubs (adults and large juveniles), specifically size of canopy, flowering and survivorship. Standard statistical methods and canonical vegetation ordination will be used to analyze these data ; 3) at these two sites, we will continue to follow seedlings mapped in the previous phase of study and annually to mark new seedlings to add to this census, again using standard field methods; 4) a predictive population projection matrix model will be created and tested with a complete re-census of the 50-year-old plot, which has recruited many unmarked individuals into the juvenile and reproductive class since 1993. We will use RAMAS or specially written software.

Progress 10/01/09 to 12/31/11

Outputs
Target Audience: Nothing Reported Changes/Problems: Dr. Toft passed away in 2011. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? N/A

Publications


    Progress 01/01/10 to 12/31/10

    Outputs
    OUTPUTS: There have been no outputs or dissemination of the project in the first-year reporting period of the 5-year project. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

    Impacts
    Work to date has focused on analysis of data, and preparation of a manuscript, with results as follows: Findings to date determined the causes of spatial aggregation of seedlings of Ericameria nauseosa spp. consimilis and followed its consequences for their growth and survival in a sand-dune ecosystem near Mono Lake, California. Establishing seedlings were highly spatially aggregated, a result of where seeds were retained, germinated and survived. Microsites varied in suitability for seed retention and seedling survival. Seeds were retained in depressions and under snags (dead shrubs), but seedlings did not survive there. In contrast, microsites under the canopy of shrubs or on berms promoted both seed retention and seedling survival, whereas interspaces (devoid of vegetation) promoted neither. This initial aggregation of seedlings had large and long-lasting consequences for their subsequent growth and survival. Seedlings within aggregations were less likely to die with more close neighbors (i.e., inverse density dependence) within a 30-cm radius early in the growing season. Later in the season, seedlings with close neighbors were more likely to die (i.e., direct density dependence) within a 7-cm radius. Density-independent mechanisms (., drought) also contributed to seedling mortality in all years of the study. Variation in density-dependence effects on survival occurred at different spatial and temporal scales, obscuring the underlying processes determining the spatial distribution of seedlings and causing seedling mortality to appear density independent on a landscape scale. Although direct and inverse density dependent processes were transient in their effects on one life history stage of C. nauseosus, these processes had profound consequences that resonate throughout the life history of this long-lived perennial plant, ultimately determining which individuals survived to reproduce more than a decade after germination. These results are unexpected and may be applied to restoration of shrublands degraded by overgrazing, diversion of water, and other land changes with urbanization or use of public lands. Restoration by replanting seedlings to reduce air pollution, erosion, or other impacts can be informed by this study. Such restoration is challenging in arid-land ecosystems, but studies of in situ natural shrubland ecosystems such as those in the eastern Sierra can provide a basis for success in restoration in numerous locations in California, including coastal and inland Central Valley shrublands.

    Publications

    • No publications reported this period


    Progress 01/01/08 to 12/31/08

    Outputs
    OUTPUTS: We continue to publish results from our long-term study (24 years) on demography of two species of perennial desert shrubs, rabbitbrush ERICAMERIA NAUSEOSA and greasewood, SARCOBATUS VERMICULATUS. Rebecca Balogh Benard and I published in 2008 a paper on the survival and spatial dynamics of seeds and first-year seedlings, including tests of density dependence in the growth and survival of seedlings during this brief life history phase. Another remains in preparation [Benard, R.B. and C.A. Toft, in prep. Seedling establishment in a desert perennial shrub: causes and consequences of spatial aggregation]. We are testing (using stage-structured population models) the hypothesis that a brief period of density-dependence nevertheless has profound effects on population dynamics of E. NAUSEOSA, in spite of these plants living in a harsh, variable environment in which one would expect the effects of density independent mortality to wipe out any signal of competition or facilitation. The problem of incorporating variability into a stage-structured model has turned out to be difficult to do. I am currently working with a colleague on such a model, collaborating with her skills in this kind of modeling and my supplying our 24-year sequence of data. Other on-going projects include a spatial-demographic population genetics study of S. VERMICULATUS, and 5-year re-census of E. NAUSEOSA testing predictions of our model. Our results continue to contradict the 'dogma' about desert shrubs still prominent in many textbooks. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Targeted audiences include: non-governmental organizations involved with ecological restoration and state, county and federal agencies involved with remediation of erosion, air pollution or other environmental impacts. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

    Impacts
    Applications of this research are primarily in the restoration of native vegetation on dry desert lakebeds to suppress dust pollution and uphold public trust values. If we understand the development of arid-land ecosystems through time by learning the demographic patterns of key shrub species, this perspective will allow us to design cost-effective restoration where diversion of water for urban and agricultural use has degraded natural habitats and created environmental hazards such as air pollution from dust. Our results also will contribute to understanding and predicting the effects of global warming, by applying our knowledge of past long-term climate change and plant population responses to it.

    Publications

    • Benard, R.B. and C.A. Toft. 2008. Fine-scale spatial heterogeneity and seed size determine early seedling survival in a desert perennial shrub (ERICAMERIA NAUSEOSA: Asteraceae). Plant Ecology 194:195-205.


    Progress 01/01/07 to 12/31/07

    Outputs
    This year we published results from the second of our long-term study (24 years) on demography of two species of perennial desert shrubs, the rabbitbrush ERICAMERIA NAUSEOA and greasewood, SARCOBATUS VERMICULATUS. My former graduate student Rebecca Balogh Benard and I wrote 3 manuscripts on the survival and spatial dynamics of seeds and first-year seedlings, including tests of density dependence in the growth and survival of seedlings during this brief life history phase. Two of these papers are published and appeared in 2007 and 2008, respectively. The third is still in preparation. We are ready to start the final phase of the project: analyzing our 24-years of results with a complete population-dynamics model using all life history stages. We found that a brief period of density dependent mortality experienced by the seedlings in their first years of life had significant effects that potentially resonate throughout the life history of E. NAUSEOA, in which some individuals live more than 100 years. Although fleeting in this context, this period of density-dependence should therefore have profound effects on population dynamics, in spite of these plants living in a harsh, variable environment in which one would expect the effects of density independent mortality to wipe out any signal of competition or facilitation. We are currently testing (using stage-structured population models) the hypothesis that a brief period of density-dependence nevertheless has profound effects on population dynamics, in spite of these plants living in a harsh, variable environment in which one would expect the effects of density independent mortality to wipe out any signal of competition or facilitation. Desert shrubs are not uniformly spaced on the landscape in spite of the influence of density dependence, in part because of significant environmental heterogeneity. Our results continue to contradict the 'dogma' about desert shrubs still prominent in many textbooks.

    Impacts
    Applications of this research are primarily in the restoration of native vegetation on dry desert lakebeds to suppress dust pollution and uphold public trust values. If we understand the development of arid-land ecosystems through time by learning the demographic patterns of key shrub species, this perspective will allow us to design cost-effective restoration where diversion of water for urban and agricultural use has degraded natural habitats and created environmental hazards such as air pollution from dust.

    Publications

    • Benard, R.B. and C.A. Toft. 2007. Effect of seed size on seedling performance in a long-lived desert perennial shrub (ERICAMERIA NAUSEOSA: Asteraceae). International Journal of Plant Sciences 186:1027-1033.
    • Benard, R.B. and C.A. Toft. 2008. Fine-scale spatial heterogeneity and seed size determine early seedling survival in a desert perennial shrub (ERICAMERIA NAUSEOSA: Asteraceae). Plant Ecology 194:195-205.


    Progress 01/01/06 to 12/31/06

    Outputs
    We are ending the second phase of our long-term study (24 years) on demography of two species of perennial desert shrubs, the rabbitbrush ERICAMERIA NAUSEOA and greasewood, SARCOBATUS VERMICULATUS. The two major projects of this phase are 1. Filling in the last piece of the life history puzzle, the survival and spatial dynamics of seeds and first-year seedlings, including tests of density dependence in the growth and survival of seedlings during this brief life history phase; and 2. Analyzing our 24-years of results with a complete population-dynamics model using all life history stages. The most remarkable result in project 1 was the finding that a brief period of density dependent mortality experienced by the seedlings in their first years of life had significant effects that potentially resonate throughout the life history of E. NAUSEOA, in which some individuals live more than 100 years. Although fleeting in this context, this period of density-dependence should therefore have profound effects on population dynamics, in spite of these plants living in a harsh, variable environment in which one would expect the effects of density independent mortality to wipe out any signal of competition or facilitation. We are currently testing this hypothesis using stage-structured population models, but this work is in progress with no results to report. In spite of this importance of competition, desert shrubs are not uniformly spaced on the landscape, in part because of significant environmental heterogeneity. Our results continue to contradict the 'dogma' about desert shrubs still prominent in many textbooks.

    Impacts
    Applications of this research are primarily in the restoration of native vegetation on dry desert lakebeds to suppress dust pollution and uphold public trust values. If we understand the development of arid-land ecosystems through time by learning the demographic patterns of key shrub species, this perspective will allow us to design cost-effective restoration where diversion of water for urban and agricultural use has degraded natural habitats and created environmental hazards such as air pollution from dust.

    Publications

    • Benard, R.B. and C.A.Toft. 2007. Fine-scale spatial heterogeneity and seed size determine early seedling survival in a desert perennial shrub (ERICAMERIA NAUSEOSA: Asteraceae). Plant Ecology. IN PRESS.


    Progress 01/01/05 to 12/31/05

    Outputs
    We are completing the second phase of our long-term study (23 years) on demography of two species of perennial desert shrubs, the rabbitbrush CHRYSOTHAMNUS NAUSEOSUS and greasewood, SARCOBATUS VERMICULATUS. This year was devoted to analyzing data and preparing three manuscripts on seedling establishment and survival. The most remarkable result during this phase was the finding that a brief period of density dependent mortality experienced by the seedlings in their first 3 years of life had significant effects that resonated throughout the life history of C. NAUSEOSUS, in which some individuals live more than 100 years. Early density dependence of both types (direct, i.e.. competitive thinning, and inverse, i.e., nurse plants) determined which individuals reached reproductive age. Although fleeting in this context, this period of density-dependence should therefore have profound effects on population dynamics, in spite of these plants living in a harsh, variable environment in which one would expect the effects of density independent mortality to wipe out any signal of competition or facilitation. We will be testing this hypothesis in the next phase of the long-term study by using stage-structured population models. In spite of this importance of competition, however, desert shrubs are not uniformly spaced on the landscape, in part because of significant environmental heterogeneity. Our results continue to contradict the "dogma" about desert shrubs still prominent in many textbooks.

    Impacts
    Applications of this research are primarily in the restoration of native vegetation on dry desert lakebeds to suppress dust pollution and uphold public trust values. If we understand the development of arid-land ecosystems through time by learning the demographic patterns of key shrub species, this perspective will allow us to design cost-effective restoration where diversion of water for urban and agricultural use has degraded natural habitats and created environmental hazards such as air pollution from dust.

    Publications

    • No publications reported this period


    Progress 01/01/04 to 12/31/04

    Outputs
    This project is long-term study (22 years) on demography of two species of perennial desert shrubs, the rabbitbrush CHRYSOTHAMNUS NAUSEOSUS and greasewood, SARCOBATUS VERMICULATUS. In 2004, we the mechanisms of seedling establishment, including germination of seeds, seedling growth and survival, and we tested for competition, through the collaborative research of my graduate student, Rebecca Balogh. Our research investigated how environmental heterogeneity, intraspecific competition, and variation among individuals all interact to influence the initial spatial distribution and establishment of seedlings. Using field observations and experiments, Balogh showed that: 1) environmental heterogeneity causes seeds to be unevenly distributed in the landscape; Unexpectedly, seeds did not accumulate in depressions or on saltgrass mats but rather under living shrubs even though the seeds are wind dispersed; 2) microsites promoting seed retention are not those that promote seedling survival; Seeds initially do better under shrubs but then lose that advantage as they get older, compared to seeds in other microsites 3). intraspecfic variation among seedling size and/or time of emergence interact with density to influence a seedling's survival within aggregations, but we are as yet unable to detect any effect of competition among seedlings; 4). variation in seedling emergence time and initial seedling size interact with environmental heterogeneity to influence seedling establishment. Analysis of these preliminary results will continue in 2005.

    Impacts
    Applications of this research are primarily in the restoration of native vegetation on dry desert lakebeds to suppress dust pollution and uphold public trust values. If we understand the development of arid-land ecosystems through time by learning the demographic patterns of key shrub species, this perspective will allow us to design cost-effective restoration where diversion of water for urban and agricultural use has degraded natural habitats and created environmental hazards such as air pollution from dust.

    Publications

    • No publications reported this period


    Progress 01/01/03 to 12/31/03

    Outputs
    This project is long-term study (22 years) on demography of perennial shrubs in arid, California rangeland. Applications of this research are primarily in the restoration of native vegetation on dry desert lakebeds to suppress dust pollution and uphold public trust values. This research investigates two species, the rabbitbrush CHRYSOTHAMNUS NAUSEOSUS and greasewood, SARCOBATUS VERMICULATUS, and the ecology of their establishment on former shorelines of a receding Mono Lake. In 2003, we continued long-term demographic studies of the older shrubs and published a paper on 18 years of data. This research showed that seedlings compete strongly for their first three years, but, however short, this competition has life-long consequences, determining which shrubs reach reproductive age, and when. We discovered that size-differentials early in life determine which individuals survive this competition. This finding is crucial to designing viable restoration plans. In 2003 we continued to explore the mechanisms of seedling competition, through the research of my graduate student, Rebecca Balogh. This research will determine how environmental heterogeneity, intraspecific competition, and variation among individuals all interact to influence the initial spatial distribution and establishment of seedlings. Using field observations and experiments, we are testing the following hypotheses: 1) environmental heterogeneity causes seeds to be unevenly distributed in the landscape; 2) microsites promoting seed retention will not necessarily promote seedling survival; 3) intraspecfic variation among seedling size and/or time of emergence interact with density to influence a seedling's competitive ability and survival within aggregations; 4) variation in seedling emergence time and initial seedling size interact with environmental heterogeneity to influence seedling establishment. The seedling project is in progress and will be completed in 2004.

    Impacts
    The broad perspective of this project is to understand the development of arid-land ecosystems through time by learning the demographic patterns of key shrub species. This perspective will in turn permit cost-effective restoration where diversion of water for urban and agricultural use has degraded natural habitats and created environmental hazards such as air pollution from dust.

    Publications

    • No publications reported this period


    Progress 01/01/02 to 12/31/02

    Outputs
    In this period, we completed two major phases of my long-term research (22 years) on demography of perennial shrubs in arid California rangeland, specifically rabbitbrush CHRYSOTHAMNUS NAUSEOSUS and greasewood, SARCOBATUS VERMICULATUS. 1) a test for stage-specific spatial patterns of rabbitbrush, which reveals the factors that determine its establishment, growth, survival and reproduction, and 2) DNA fingerprinting of old crowns of greasewood to test hypotheses on early establishment and mortality that determine spatial dispersion of this species. 1) For rabbitbrush we are testing hypotheses about early establishment of long-lived shrubs, in particular the degree to which growth and survival are determined by density-dependent processes (competition for scarce resources, primarily water or facilitation by nurse plants or spatial variation in suitable sites for establishment) versus density-independent processes (primarily desiccation from extreme water shortage). Rabbitbrush seedlings begin life in highly aggregated spatial distributions and become randomly dispersed in increasingly older stages. In this period, we definitively demonstrated that rabbitbrush seedlings compete for water (or water-borne minerals) for a 1-3 year period after germination. Although brief, this competition is associated with a size differential that persists through life, affecting how soon the juvenile rabbitbrush is able to access deep soil moisture, a condition necessary for long-term survival and reproduction. 2) For greasewood, we are testing the hypothesis that greasewood builds sand dunes (because it promotes and thrives with burial) by conducting a DNA fingerprinting study of 2 populations of different ages (500 years and 50 years, respectively). We discovered that adjacent crowns are in fact buried branches of the same individual and that there is some additional spread of greasewood by runners. However, both modes of growth and asexual reproduction are not as common as we hypothesized and that very old shrubs are still significantly spatially aggregated, in sharp contrast to rabbitbrush at the same location, and contradicting dogma about long-lived desert shrubs.

    Impacts
    The broad perspective of this project is to understand the development of arid-land ecosystems through study of the demographic patterns of key shrub species. This perspective will in turn permit cost-effective restoration where diversion of water for urban and agricultural use has degraded natural habitats and created environmental hazards such as air pollution from dust.

    Publications

    • Toft, C.A. and T. Fraizer. 2003. Stage-specific spatial dispersion and density dependence in a population of perennial desert shrub (CHRYSOTHAMNUS NAUSEOSUS ASTERACEAE). Ecology. In press.


    Progress 01/01/01 to 12/31/01

    Outputs
    Our long-term research on demography of perennial shrubs in arid, California rangeland is in its 21st year. This research investigates two species, the rabbitbrush CHRYSOTHAMNUS NAUSEOSUS and greasewood, SARCOBATUS VERMICULATUS, and the ecology of their establishment on former shorelines of a receding Mono Lake. In this 5-year phase, we are focusing on two aspects. 1) The initial establishment of seedlings and growth and survival through the first year, particular of rabbitbrush and 2) DNA fingerprinting of old crowns of greasewood, spanning two extremes of the different life history stages of perennial shrubs and the processes governing those phases. For rabbitbrush we are testing hypotheses about early establishment of long-lived shrubs, in particular the degree to which growth and survival are determined by density-dependent processes. 1) Competition for scarce resources, primarily water, or 2) facilitation by nurse plants or spatial variation in suitable sites for establishment) versus density-independent processes (primarily desiccation from extreme water shortage). So far we have found that seed germination and seedling establishment are governed by a combination of processes, on different spatial scales. Seedling recruitment is episodic, being more likely in wet, El Nino years and less likely in dry La Nina years. We are building a population model to discover which life history stage is most influential in population growth projections, in order to understand the dynamics of how rabbitbrush establishes in arid-land ecosystems after disturbances. For greasewood, we are testing the hypothesis that greasewood builds sand dunes by promoting and thriving with burial. Therefore the older the population, the more buried and larger are individual crowns; we are testing this hypothesis by conducting a DNA fingerprinting study of 2 populations of different ages (500 years and 50 years respectively). We completed a manuscript on the past 7-year portion of the study in which we test hypotheses on expected spatial patterns of different age classes of rabbitbrush. Seedlings begin life in highly aggregation spatial distributions, and through a combination of density-independent thinning and opposing density dependent thinning, shrubs become randomly dispersed in increasingly older cohorts and populations. This result is contrary to the expected pattern from competition for water; we conclude that competition for water does not influence the long-term population dynamics of these perennial shrubs, however, we need to test this hypothesis on greasewood.

    Impacts
    The broad perspective of this project is to understand the development of arid-land ecosystems through time by learning the demographic patterns of key shrub species. This perspective will in turn permit cost-effective restoration where diversion of water for urban and agricultural use has degraded natural habitats and created environmental hazards such as air pollution from dust.

    Publications

    • No publications reported this period


    Progress 01/01/00 to 12/31/00

    Outputs
    This project documents demography of perennial shrub populations, including recruitment and survivorship of seedlings along the environmental gradient created by a receding Mono Lake. The broad perspective of this project is to understand the development of arid-land ecosystems through time and in particular to understand their response to disturbance. This perspective will in turn permit cost-effective restoration where diversion of water for urban and agricultural use has degraded natural habitats and created environmental hazards such as air pollution from dust. In this reporting period, I published one paper on development of the shoreline ecosystems at Mono Lake (Toft and Elliott-Fisk in press), which demonstrated that plant succession in the strictest sense occurs in desert ecosystems and that some processes occur remarkably rapidly. These results are crucial for the design of cost-effective and self-perpetuating restoration of native vegetation on desiccated lakebeds in the western U.S. We are continuing this work by investigating spatial demography of SARCOBATUS VERMICULATUS and CHRYSOTHAMNUS NAUSEOSUS, focusing on the establishment of seedlings in their first year when mortality is highest and seedlings are most dependent on upper soil moisture. I submitted a NSF grant this past cycle to fund the shrub demography work and completed another manuscript on the spatial demography of two populations or C. NAUSEOSUS of different ages and stages of succession. We found that contrary to expectation, adult shrubs are not uniformly distributed across the landscape; although water limits survival, growth and reproduction, we cannot find any population-level evidence for competition for water, including self-thinning. Seedlings start out life highly aggregated, and in some cases, competition appears to occur briefly in the densest aggregations. My students and I are building population models to determine if this brief period of competition has any permanent effects on the population.

    Impacts
    Results from our study of development of vegetation on former shorelines of Mono Lake will allow the design of restoration programs for dry lake beds to prevent air pollution from toxic dust, as occurs at Owens Lake. Restoration of native vegetation on dry lake beds is an inexpensive, self-maintaining solution to suppression of dust pollution, and it is also consistent with public trust values.

    Publications

    • Toft, C.A. and Elliott-Fisk, D.L. 2001. Patterns of vegetation along a spatiotemporal gradient on shoreline strands of a desert basin lake. Plant Ecology. In press.


    Progress 01/01/99 to 12/31/99

    Outputs
    The primary objective of this project is to document demographics of perennial shrub populations and recruitment, survivorship of seedlings along the environmental gradient created by a receding Mono Lake. We continue long term monitoring of adult shrubs and seedling recruitment in populations of SARCOBATUS VERMICULATUS and CHRYSOTHAMNUS NAUSEOSUS at 3 key sites that differ in age in time since exposure by the receding lake. The broad perspective of this project is to understand the development of arid-land ecosystems through time and in particular to understand their response to disturbance. We found that a natural variation in temperature and precipitation coupled with variations ground water, which fluctuates with diversion of water from the Mono Basin to the City of Los Angeles, has profound effects on the growth and survival of perennial shrubs and recruitment of their seedlings into the population. Currently we are experiencing a series of wet and cool years that have greatly enhanced growth, survivorship and recruitment. Recruitment into these desert shrub populations is therefore highly episodic, with the first successful recruitment since 1985 occurring in 1997 and continuing through the 99 field season. We found that S. VERMICULATUS builds dunes thereby enhancing its own growth and survival and perhaps that of the other species of shrubs. Because its growth is enhanced by burial with sand, S. VERMICULATUS forms large canopies on dune tops, making it difficult for us to determine its exact demographic patterns. We are using DNA fingerprinting to determine the exact population structure of S. VERMICULATUS. Results from our study challenge the long-held view that succession does not occur in arid-land environments and that perennial desert shrubs develop uniform spatial distributions because of competition for water.

    Impacts
    Results from our study of development of vegetation on former shorelines of Mono Lake will allow the design of restoration programs for dry lake beds to prevent air pollution from toxic dust, as occurs at Owens Lake. Restoration of native vegetation on dry lake beds is an inexpensive, self-maintaining solution to suppression of dust pollution, and it is also consistent with public trust values.

    Publications

    • No publications reported this period


    Progress 01/01/95 to 12/30/95

    Outputs
    This project seeks to understand mechanisms of plant establishment and ecosystemdevelopment on newly exposed playas of arid-land lakes, using the Mono Lake Basin as a model system. Initial funding for this project was provided by the U.S.D.A. in a multidisciplinary effort. My responsibility is to document and test hypotheses on the demography of shrub populations of varying ages at 6 sites along an environmental gradient produced by the recession of Mono Lake. In the 1995 field season, we completed the third year of descriptive study of the demography of populations of two species of shrubs, SARCOBATUS VERMICULATUS and CHRYSOTHAMNUS NAUSEOSUS, both of which are significant species on arid rangelands. We have another census planned in the 1996 field season. Preliminary analyses based on our initial data has shown that shrub populations are limited by the availability of water and the depth of the water table (which varies with the amount of water exported from the Mono Basin). We are investigating whether establishment of juvenile shrubs occurs only under transient conditions based on the depth of the water table, which varies with the level of Mono Lake. This work is in collaboration with ecophysiological experimentation by J.H. Richards (LAWR) and L.A. Donovan (U. Georgia). This year we completed the first major paper describing the sand-dune ecosystems (with D.L. Elliott-Fisk).

    Impacts
    (N/A)

    Publications

    • TOFT, C.A. 1995. Review of "INTRODUCTION TO ANIMAL PARASITOLOGY." J.D. Smyth. Cambridge University Press, Cambridge and New York., 1994. 549 pp.
    • MANGEL, M., TALBOT, L.M., MEFFE, G.K., AGARDY, M.T., ALVERSON, D.L., BARLOW, J., BOTKIN, D.B., BUDOWSKI, G., CLARK, T., COOKE, J., CROZIER, R.K., DAYTON, P.K., ELDER, D.L., FOWLER, C.W., FUNTOWICZ, S., GISKE, J., HOFMAN, R.J., HOLT, S.J. TOFT, C.A. and JAEGER, R.G. 1996. Writing for scientific journals I: The Manuscript. Herpetological Mongraphs. IN PRESS.