Sierra Nevada Science Symposium 2002: Science for Management and Conservation
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POSTER SESSION: Climate and Landscape Change Over Time
Abstracts for each of the posters can be viewed below by clicking on the title of the poster.



Extreme Variability in Tree-ring Chronologies from Different Physical Settings
Andrew G. Bunn*, Lindsey A. Waggoner, and Lisa J. Graumlich, The Big Sky Institute, Montana State University, P.O. Box 173490, 106 AJM Johnson Hall, Bozeman, MT 59717-3490, USA; *ph: 406-994-2374, *email: abunn@montana.edu


Long chronologies of annually resolved past-climate proxies derived from tree rings are key to assess the role of temperature and precipitation variability and trends on subalpine forests. Especially important contributors to the time-series data are tree-ring records from high elevation, long-lived conifers in western North America. Although high elevation trees are generally considered good recorders of past climate, little research has investigated the influence of kilometer-scale physical setting on the sensitivity of tree-ring chronologies. Using proxies for soil moisture and radiation derived from a digital elevation model, we systematically collected increment cores for twelve tree-ring chronologies in extreme biophysical settings from three sites in the Sierra Nevada Mountains of California. We present a multivariate analysis of the chronologies and show the importance of considering the physical template, especially as it relates to soil moisture, as a patterning agent of this key paleoclimatic resource. Preliminary results indicate that soil moisture affects chronology sensitivity, climactic inference and points to the need to account for physical setting when sampling.




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The Sierra Nevada Global Change Research Program
Nathan L. Stephenson* and Jon E. Keeley, USGS Western Ecological Research Center, Sequoia and Kings Canyon Field Station, Three Rivers, CA 93271, ph: (559) 565-3176, *email: nstephenson@usgs.gov. Jan W. van Wagtendonk, USGS Western Ecological Research Center, Yosemite Field Station, El Portal, CA 95318. Dean L. Urban, Nicholas School of the Environment, Duke University, Durham, NC 27708. Thomas W. Swetnam, Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721. Lisa J. Graumlich, Big Sky Institute and Mountain Research Center, Montana State University, Bozeman, MT 59717.


The Sierra Nevada Global Change Research Program began in 1991 as a component of the National Park Service's (now U.S. Geological Survey's) Global Change Research Program. The program's core study areas are Sequoia, Kings Canyon, and Yosemite national parks. Our goal is to understand and predict the effects of environmental changes on montane forests. To reach this end, our program consists of integrated studies organized around three themes: paleoecology, contemporary ecology, and modeling. The paleoecological theme takes advantage of the Sierra Nevada's rich endowment of tree-ring and palynological resource to develop and understanding of past climatic changes and the consequent responses of fire regimes and forests. The contemporary ecology theme takes advantage of the Sierra Nevada's substantive climatic gradients as "natural experiments," allowing us to evaluate climatic mechanisms controlling forest structure, composition, and dynamics. The modeling theme integrates findings from the paleoecological and contemporary studies, and is a vehicle for scaling up our mechanistic findings to regional landscapes and predicting which parts of montane landscapes may be most sensitive to future environmental changes. To date, the program has produced several results both of broad interest to biologists and useful to land managers.




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Climate Change and the Bay-Delta Watershed: An Animated Poster
Noah Knowles*, Dan Cayan, and Mike Dettinger, Scripps Institution of Oceanography/USGS, 9500 Gilman Dr., La Jolla, CA 92093-0224; *email: noah@ucsd.edu.


California's primary hydrologic system, the San Francisco estuary and its upstream watershed, is vulnerable to the regional hydrologic consequences of projected global climate change. Projected temperature anomalies from a global climate model are used to drive a combined model of watershed hydrology and estuarine dynamics. This poster presents computer animations representing these projections at several spatial scales over the coming century. By 2090, a projected temperature increase of 2.1_C results in a loss of about half of the average April snowpack storage, with greatest losses in the northern headwaters. Consequently, spring runoff is reduced by 5.6 km3, with associated increases in winter flood peaks. The smaller spring flows yield spring/summer salinity increases of up to 9 psu, with larger increases in wet years. The use of animations provides a powerful means of communicating the broad scope of these hydrologic and estuarine impacts of climate change in California.




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Climate Change as an Ecosystem Architect: Examples from High-Elevation Pine Forests
Constance Millar*, Diane Delany, and Robert Westfall, USDA Forest Service, PSW Research Station, *Box 245, Berkeley, CA 94701, *ph:(510) 559-6435, *email: cmillar@fs.fed.us. John King, Lone Pine Research, Bozeman, MT.


Advances in ecology and conservation during the 20th century motivated a shift from viewing nature as static and typological to dynamic and processual. Static concepts, however, still constrain our understanding of natural dynamism and limit our conservation successes. Recent advances in earth system sciences, which characterize recurrent climate change as a central physical force on earth, have not been well incorporated into evolutionary and ecological theory, nor yet translated into regional conservation and management practice.

We describe preliminary results from several studies of pine ecosystems in the high Sierra Nevada and adjacent Basin ranges as examples of forest response to historic climate change. In all studies, we used standard tree-ring and ecological plot analysis methods. We document correlated growth response and meadow/snowfield invasions of whitebark pine and lodgepole pine during four multi-decadal climate periods in the 20th century, and decadal cycles in limber pine growth related to dry and wet periods over the past two centuries. Century-scale growth variability of limber pine forests over the past 4,000 years correlates with major temperature and precipitation cycles as derived from independent climate indicators. Major demographic shifts of limber pine include cyclic extirpation and recolonization events that appear correlated to multi-decadal climate phases. Such natural variability has not been figured into conservation baselines and planning.





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Sagebrush Expansion in Meadows of the Kern Plateau, Southern Sierra Nevada
Heather Swartz, Dept. of Environmental Science Policy and Management, Univ. of California Berkeley, 151 Hilgard Hall #3110, Berkeley, CA 94705-3110; ph: (510)643-5430, email: hswartz@socrates.berkeley.edu. Eric Berlow, Univ. of California White Mountain Research Station. Carla D'Antonio, USDA-ARS, Reno, Nevada and Univ. of California, Berkeley, Dept. of Integrative Biology.


Over the last century there has been significant vegetation change and stream incision in meadows of the Kern Plateau in the southern Sierra Nevada. Rothrock's sagebrush, Artemisia rothrockii, has expanded extensively into areas of wet meadow vegetation. Lowered water tables as a result of stream incision contribute to shrub expansion, but sagebrush also invades unincised areas. This research project examines rates and spatial patterns of sagebrush expansion and factors correlated with local changes in sagebrush distribution.

Using Geographic Information Systems, we rectified repeat aerial photographs to identify change in sagebrush distributions. Our initial comparison of time points shows many new areas of sagebrush as well as isolated local recovery of wet meadow vegetation.

To characterize areas of sagebrush expansion, we measured environmental and landscape variables in sites with and without recent expansion. Preliminary results show that areas of new sagebrush are intermediate in soil moisture, relative elevation, and sagebrush density between intact herbaceous vegetation and older sagebrush. They occur on all geomorphic surfaces including floodplains, newly incised terraces and older terraces. We are now using classification trees to identify combinations of variables that best predict conditions for sagebrush expansion. These classification trees can provide a management tool to reduce further sagebrush expansion.




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The Thermodynamics of Snowpack at Gin Flat, Yosemite National Park, Winter and Spring 2002
Michael D. Dettinger, US Geological Survey, Scripps Institution of Oceanography, La Jolla, CA 92093-0224; email: mddettin@usgs.gov; ph: (858) 822-1507. Frank Gehrke, California Cooperative Snow Surveys, California Department of Water Resources, Sacramento, CA.


The Gin Flat automated snow-telemetry site, at 7,050 feet above sea level in Yosemite National Park, has been augmented during the past two years to measure components of the water and radiation budgets of the snowpack in addition to the precipitation, temperatures, and snow-water content measurements typical of such sites. New measurements at Gin Flat include snow thickness, incoming solar radiation, and net radiation to the snow surface. Together, the measurements at Gin Flat characterize gross water and radiative-heat budgets of the winter snowpack, as well as snow density. During 2002, temperatures within the (6-ft) snowpack also were monitored at one-foot vertical intervals, as indicators of the time and depth varying thermodynamics of the snowpack. The measurements at Gin Flat, taken together, illustrate multi-day downwelling of cold into the Sierra Nevada snowpack during two prolonged cold snaps, but, for the most part, the snowpack remained essentially at 0ºC throughout the winter and spring. Additional instrumentation such as that operatred at Gin Flat is proving robust to the elements and provides new insights into the workings of Sierra Nevada snowpacks. Augmentations have now been included at several more sites, including Tuolumne Meadows and Dana Flat in Yosemite National Park.




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Snow, Topography, and the Diurnal Cycle in Streamflow
Jessica Lundquist, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive MC-0213, La Jolla, CA 92093; ph: (858) 534-1504; email: jlundquist@ucsd.edu. Michael Dettinger, United States Geological Survey. Daniel Cayan, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive MC-0213, La Jolla, CA 92093; United States Geological Survey. Noah Knowles, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive MC-0213, La Jolla, CA 92093.


Hourly measurements of river discharge provide a widely available, but as yet underutilized, source of information about snowmelt processes, providing direct information on basin output at a fine temporal scale. The timing of streamflow variation within each day reflects the daily timing of snowmelt maxima and minima, modulated by travel times through the snowpack, hillslopes, and stream channel to the gauging stations where they are measured. The daily timing of the diurnal cycle consequently reflects the seasonal evolution of travel times and, by extension, the evolution of snowpack and snowcover conditions within contributing watersheds.

Traditional theories, based on numerical models and localized, small-basin observations, report that the hour of day of maximum flow becomes earlier as the snowpack thins, reflecting shorter travel times for surface melt to reach the base of the snowpack. However, an examination of hourly discharge from 100 basins in the Western United States, ranging in size from 1 km2 to 10,812 km2, reveals a more complex situation. Depending on basin size and topography, diurnal timing often depends strongly on the discharge magnitude and on the snowmelt location.

In most of the basins examined, at the end of the melt season, the hour of maximum discharge shifts to later in the day, reflecting increased travel times as the snowline retreats to higher elevations. The rate of this retreat is more rapid in dry years than in wet years and may provide a measure of how basin snow-cover and soil moisture respond to inter-annual climate variations.




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The Historic Variability of Vegetation in Glass Creek Meadow, Inyo National Forest, California, and its Role in Resource Management Planning
Wallace Woolfenden, Mountain Heritage Associates, P.O. Box 429, Lee Vining, CA 93541; ph: (760) 647-3035; email: wwoolfenden@fs.fed.us.


The study of past variability of ecosystems is important for understanding ecosystem dynamics that occur at timescales greater than the timescale at which they are usually observed, evaluating present ecosystem conditions, and planning for their sustainability. The history of Glass Creek Meadow vegetation was interpreted from a 3000-year pollen sequence extracted from radiocarbon-dated sediment cores in order to examine the value of historic reference conditions in managing this type of ecosystem. In the top section of the sequence an interval of low pollen concentration above a volcanic ash bed and mixed with volcanic tephra marks the effect of the Glass Creek eruption of about 600 years ago. An increase in willow pollen followed by an increase in aster and saltbush pollen is the major indicator of vegetation change during and after the eruption. Between 100 and 225 years ago a large spike of sedimentary charcoal and a decrease in fir and buttercup pollen indicates a fire effect on the meadow and surrounding pine-fir forest. A decrease in willow pollen to low levels by 300 years ago to the present, along with fairly stable proportions of forb, grass, and sedge pollen, contradict the assessment of the meadow as having been overgrazed.




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Effects of Altered Summer Precipitation on Sierra Nevada Shrubs
Michael E. Loik, Dept. of Environmental Studies, University of California, Santa Cruz, CA 95064; ph: (831) 459-5785; email: mloik@cats.ucsc.edu.


Current GCMs predict a 25 to 50% increase in precipitation for California by 2095. How the actual spatial and temporal patterns of precipitation change will affect plants are uncertain. An increase in summer monsoon activity is considered likely for the eastern Sierra Nevada. Although increased precipitation could be beneficial for plants, not all species equally utilize summer rain. I tested hypotheses regarding increased summer precipitation on photosynthesis for Artemisia tridentata and Purshia tridentata. Supplemental water was added over the range of 0 to 200% of average precipitation, over 1 to 14 days, and at three elevations; water relations, photosynthesis, and stress within PSII were measured. Photosynthesis as a function of added water increased more for A. tridentata compared to P. tridentata. Both species responded maximally at 2 d following addition. Several small additions elicited more of a response compared to one large addition. Photosynthesis was greater for plants at higher elevations. Future patterns of photosynthesis in response to increased summer rainfall will be species-specific and will depend importantly on the timing, magnitude, and spatial scale of actual precipitation changes. Results will contribute to the development of restoration plans for recovery of damaged habitats.




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High Temperature Tolerance for Purshia tridentata Exposed to Increased Summer Precipitation Across an Elevation Gradient
Gitane L. Royce, Graduate Research Assistant, Desert Research Institute, University of Nevada, 2215 Raggio Pkwy, Reno, NV 89512; ph: (775) 673-7413; email: groyce@dri.edu. Michael E. Loik, Department of Environmental Studies, University of California, 1156 High Street, Santa Cruz, CA 95064.


Current GCMs predict increased precipitation for California by the year 2050. Our research focused on the impacts of climate change on the arid shrub Purshia tridentata (Rosaceae). Three sites were chosen spanning a total of 1400 m elevation. We tested the hypotheses that (1) P. tridentata at low elevation are better able to survive high temperatures than at high elevation, and (2) increased precipitation will enhance the tolerance of high temperatures. In situ watering manipulations were used to determine the potential impact of increased precipitation on P. tridentata. Thermal stress was assessed by measuring damage to cell and chloroplast membranes, as well as the ability to uptake CO2. At 45°C CO2 flux was -0.104 _mol m-2 s-1 for plants at 1725 m and -3.056 _mol m-2 s-1 for plants at 3070 m. FV/FM was enhanced by 5.5 % for 1725 m, 10.3% for 2600 m, and 24.8% for 3070 m when compared with untreated plants at 45°C (P<0.0409). Based on electrolyte leakage the LT50 was 56°C at 1725 m, 54°C at 2600 m, and 49°C at 3070 m. These results indicate that plants at lower elevation sites are better able to withstand extreme high temperatures, and that enhanced tolerance to high temperatures due to increased precipitation will be most prominent for upper elevations.




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Climate, Snow, Water, and Chemistry Observations in Yosemite National Park: A monitoring network for environmental change
Dan Cayan* and Jessica Lundquist, UCSD - SIO, La Jolla, CA 92093-0224; ph: (858) 534-4507; *email: dcayan@ucsd.edu. Mike Dettinger, USGS, La Jolla, CA. Dave Clow, USGS, Denver, CO. Frank Gehrke, California Cooperative Snow Surveys. Steve Hager, David Peterson, and Richard Smith, USGS, Menlo Park, CA. Mark Butler, Yosemite National Park.


Yosemite National Park sits astride the high Sierra Nevada and encompasses the pristine watersheds of two important rivers, the Merced and the Tuolumne. Its pristine conditions, together with the access that park roads and trails provide to the high country, make it a unique setting for scientific studies of the range. During the 2001 Yosemite Park Research Planning Workshop, the Park was identified as having a special role in the earth sciences as a locus for trans-Sierran studies and for studies of the responses of natural systems to global to regional climate change. The Park environs also have the potential to be a barometer for hydrologic variations at spatial scales spanning the range to the whole of western North America, and time scales ranging from hours to decades.

Indeed, the presence of the almost century-long meteorological stations and streamflow gauging stations in the Merced River basin have provided much of the incentive for studies that--to date--have demonstrated the remarkable potential of the Park for earth science investigations. However, these relatively few observation sites need now to be augmented with more monitoring sites, and additional parameters, in both the Merced and Tuolumne River basins. To fulfill this promise, meteorological, snowpack, and hydrologic conditions within the Park are being monitored in more detail and greater consistency than in the past, or elsewhere (at this scale) in the range.

Our ability to interpret and predict streamflow, snowpack, flood, geochemical, and related ecological processes in the Park has grown as a result of recent scientific research within the Park boundaries. With this increased ability comes increased need for data, often for real-time data, if our growing understanding is to be adequately translated into useful information for use by the Park, region, and Nation. Reaching the required level
of monitoring is likely to be an incremental process, as we develop support, methods, and a track history of monitoring success that will justify the ultimate goals.

The initial components that will form the core of this effort include meteorological, snow, hydrological, and stream chemistry. In the near term, better communications are needed to harvest these data in real time. Presently they are transmitted via scheduled bursts of GOES telemetry or during infrequent manual downloads from memory contained in self-recording instruments. Ultimately the aim is to imbed many of these instruments into a near-continuous real time network that will be ported to the Internet. While this suite of physically-based observations are ones that we are implementing immediately or in the near future, the communications and other infrastructure" that is envisioned is designed to accommodate other physical or biological sensors and their data streams.




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Climate and Wildfire in California and the Western U.S.
Anthony Westerling, Alexander Gershunov, Daniel Cayan, Michael Dettinger, and Tim Barnett, Scripps Institution of Oceanography, 9500 Gilman Dr., La Jolla, CA 92093-0224; ph: (858) 822-4057; email: leroy@ucsd.edu. Thomas Swetnam, Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721.


It is well known that climate influences are pervasive in western U.S. wildfire regimes. In this research, wildfire histories and reconstructions for a variety of temporal and spatial scales are used to describe climate-wildfire relationships on annual to decadal time scales for California and the western U.S. A twenty-one year gridded 1 x 1 degree monthly fire history compiled from federal agency fire reports recreates the seasonality and interannual variability of wildfire in the western U.S. A 75-year record of area burned aggregated by state for 1916-1990 and regional fire scar indices for 1700-1900 indicate strong links between variability in climate and wildfire regimes on decadal scales. Correlations between anomalous wildfire frequency and extent and the Palmer Drought Severity Index (PDSI) illustrate the importance of prior and accumulated precipitation anomalies for future wildfire season severity. Links to current and antecedent seasons' moisture conditions vary widely with differences in predominant fuel type, and can be exploited to estimate statistical models of seasonal wildfire area burned. We present statistical models reconstructing 18th and 19th century wildfire area burned using PDSI reconstructed from tree rings which correlate strongly with regional fire scar indices for the same period, and a statistical forecast model for predicting area burned by ecosystem province in the western United States a season in advance.




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The Southern Sierra Repeat Photography Project: Vegetation Changes Over the Past 125 Years
Monica M. Bueno, Nathan Stephenson, Jon E. Keeley, and Anne Pfaff*, United States Geological Survey, Western Ecological Research Center, Sequoia-Kings Canyon Field Station, Three Rivers, California, 93271; ph: (559)565-3171; *email: ahpfaff@usgs.gov


In this project we used repeat photography to reconstruct historical changes in southern Sierra Nevada plant communities over the past 125 years. The study area encompassed foothill and forest plant communities from the Stanislaus River south to the Kern River. The primary focus was a comparison of vegetation changes in the ponderosa pine forests and oak-chaparral communities of Kings Canyon with those already documented for Yosemite Valley. These two valleys share similar geologic and human histories, although Yosemite Valley has undergone extreme changes in drainage not experienced by Kings Canyon. In addition to qualitatively describing each of the photo pairs, we quantitatively analyzed some pairs using a simple, dot-grid-overlay counting method. We conclude that the density and cover increases in the plant communities seen in Kings Canyon are not as dramatic as those documented for Yosemite Valley, raising questions about the roles of fire suppression versus hydrology in affecting vegetation changes in the latter.

Other less detailed areas of inquiry were a look at changes in foothill chaparral communities and the chaparral-conifer ecotone; and an examination of early vegetation conditions and subsequent change in Giant Sequoia groves. We found landscape level vegetation changes in many of the photo comparisons.




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