ABSTRACTS
CIRMOUNT SESSION AGU 2009
Climate Change and Biogeophysical Impacts Across Elevation and Latitude:
Are Mountains Different From Poles?
Presiding:
J S Littell, University of Washington, Seattle;
J A Hicke, University of Idaho, Moscow;
J D Lundquist, Civil and Environmental Engineering, University of Washington, Seattle;
C T Driscoll, Syracuse;
J L Campbell, USDA Forest Service, Durham;
G T Pederson, Northern Rocky Mountain Science Center, U.S. Geological Survey, Bozeman
Water and geochemical responses to seasonal changes across the rain-snow transition in the Southern Sierra
Nevada
Bales, R C (rbales@ucmerced.edu), University of California, Merced, CA, United States
Hunsaker, C T (chunsaker@fs.fed.us), Pacific Southwest Research Station, USDA Forest Service, Fresno, CA, United
States
Meadows, M (mmeadows@ucmerced.edu), University of California, Merced, CA, United States
Kerkez, B (bkerkez@gmail.com), University of California, Berkeley, CA, United States
Glaser, S D (glaser@ce.berkeley.edu), University of California, Berkeley, CA, United States
Liu, F (fliu@ucmerced.edu), University of California, Merced, CA, United States
The hydrologic and geochemical response of rain-dominated versus snow-dominated catchments was investigated using
multi-year measurements of precipitation, snow accumulation and melt, streamflow, soil moisture and meteorological
variables. Research was carried out at the Kings River Experimental Watersheds (KREW), an integrated ecosystem
project for long-term research on nested headwater streams in the Southern Sierra Nevada. KREW is also the site of the
Southern Sierra Critical Zone Observatory (CZO). Snow at lower elevations exhibits multiple accumulation and melt
cycles throughout the cold season, with soil moisture response similar across events and locations. Snow at higher
elevations exhibits a single main melt period in spring, with streamflow lagging that at lower elevations. Soil moisture
declines rapidly in the first week after snowmelt is completed, followed by a more-gradual decline thereafter. Local
differences in the timing of snowmelt and soil drying between north versus south aspects and shaded versus open sites
are both about one month, comparable to elevation differences in the average response. Interannual variability in timing is
also similar. Evapotranspiration follows snowmelt and temperature patterns. Ionic concentrations are consistently higher
in the rain-dominated sites. Two aspects of the elevational gradients offer lessons for how catchments will respond to
climate warming, precipitation and snowmelt patterns. Soil moisture response to climate change is also indicated by
aspect differences. Interannual differences provide indications of how geochemical fluxes in streamwater will respond to
warming.
Expectations and reality for high latitude versus high elevation global change
Bunn, A G (andy.bunn@wwu.edu), Environmenal Sciences, Western Washington University, Bellingham, WA, United
States
Lloyd, A H (lloyd@middlebury.edu), Biology, Middlebury College, Middlebury, VT, United States
Arctic and alpine ecosystems are often treated as analogs of each other, in large part because they share a similar
vegetation transition from forested to low-stature tundra communities. Despite the superficial similarities, the response of
the two types of ecosystems to future climate change will likely differ because of differences in ecosystem history,
function, and extent. The role of feedbacks differs substantially between the two as the Arctic terrestrial system is
dominated by feedbacks which have the potential to significantly alter the rate and magnitude of future climate change. If
invoked, these feedbacks will substantially alter and augment northern high latitude change far above the background
forcing from increased greenhouse gas concentrations. The same is not obviously true for mountains, both because of the
difference in areal extent and because of differences in soil characteristics that affect the potential for carbon cycle
feedbacks. The climatic controls over biophysical processes may differ in subtle but important ways between the two
systems despite the overriding importance of temperature as a control in both ecosystems. For example, changes in the
position of the treeline ecotone in the Sierra Nevada during the late Holocene occurred in response to variation in both
temperature and moisture, whereas treeline advance and retreat in Arctic regions appears to be primarily a function of
temperature. Despite those differences, it appears likely that changes in Arctic and alpine ecosystems will have large
influences on the global system. The consequences of changes in alpine ecosystems will be amplified by their large
importance in controlling global water supplies. More than 50% of the world’s freshwater supplies, for example, are
derived from mountainous regions. Any change to those regions might have disastrous effects on human welfare. Global
impacts of changes in Arctic regions are amplified by the aforementioned feedbacks on the climate system, which have
the potential to increase the rate of warming in high latitudes by several fold, with cascading effects on the global climate
system. We will review some of the similarities and differences in arctic and alpine systems by showing data on predicted
changes to the physical, floral, and faunal aspects of both systems paying particular attention to the role of feedbacks and
forcings.
The Persistent Life of Snow
Hiemstra, C A (hiemstra@cira.colostate.edu), Cooperative Institute for Research in the Atmosphere, Colorado State
University, Fort Collins, CO, United States
Liston, G E (liston@cira.colostate.edu), Cooperative Institute for Research in the Atmosphere, Colorado State University,
Fort Collins, CO, United States
Elder, K (kelder@fs.fed.us), Rocky Mountain Research Station, USDA Forest Service, Fort Collins, CO, United States
Sturm, M (matthew.sturm@usace.army.mil), Cold Regions Research and Engineering Laboratory, US Army Corps of
Engineers, Fairbanks, AK, United States
Snow is an essential element linking mountains and poles. In high-elevation and high-latitude environments, snow is the
dominant precipitation form, and observations suggest snowpacks in both these areas are being altered with climate
change directly (higher temperatures) and indirectly (vegetation change). Snow’s substantial control on energy balance,
water resources, and ecosystem processes make it a key variable in understanding climate change ramifications in both
mountain and polar systems. In spite of its broad importance, snow remains difficult to accurately quantify on many
landscapes and over a wide range of spatial and temporal scales. Because of its interactions with the atmosphere and
surrounding landscape, snow is inherently dynamic and a challenge to measure and model. In both mountainous and
Arctic domains, it is often transported by wind and interacts with topography and vegetation to form a heterogeneous
distribution in both space and time. This heterogeneous distribution imparts numerous effects on ecosystem structure and
function and land-atmosphere surface fluxes; it also obfuscates analyses of long-term trends. Both middle latitude
mountains and the Arctic are experiencing changes in vegetation, precipitation, and air temperature. These accompany
attendant changes in the timing and spatial distributions of snow properties, characteristics, and quantities. We will
describe tools, techniques, challenges, and outcomes of measuring and modeling snow accumulation and ablation in
snowy environments ranging from low to high elevations and middle to high northern latitudes, with a particular focus on
the common snow-related impacts of climate and vegetation changes in these two environments. We will look at middleand high-latitude snow-vegetation interactions within shrubland environments and present improved ways to represent
snow-atmosphere interactions within these landscapes. We will describe the potential ramifications of widespread bark
beetle outbreaks in mountainous environments; Arctic snow trends; and how emerging Arctic vegetation and sea-ice
changes are modifying terrestrial snow covers and their subsequent influences on atmospheric, hydrologic, and
ecosystem processes.
Interactions of climate, vegetation, and fire during the Holocene: lessons from high-latitude and high-elevation
ecosystems
Higuera, P E (phiguera@uidaho.edu), Forest Resources, University of Idaho, Moscow, ID, United States
Chipman, M L (mchipman@life.illinois.edu), Plant Biology, University of Illinois, Urbana, IL, United States
Allen, J (Jennifer_allen@nps.gov), Regional Fire Ecologist, National Park Service, Fairbanks, AK, United States
Brubaker, L (lbru@u.washington.edu), Forest Resources, University of Washington, Seattle, WA, United States
Whitlock, C L (whitlock@montana.edu), Earth Sciences, Montana State University, Bozeman, MT, United States
Hu, F (fshu@life.illinois.edu), Plant Biology, University of Illinois, Urbana, IL, United States
Recent climate change in high-latitude and high-elevation ecosystems has led to significant increases in the frequency of
large, severe wildfires, highlighting the need to understand the biophysical controls of fire regimes across multiple
temporal scales. Paleoecological records reveal the interactive impacts of climate and vegetation on fire regimes, and
they provide a context for evaluating the consequences of ongoing and future climate change. Here we highlight new
findings from high-resolution fire-history records from lake sediments in arctic ecosystems of Alaska and subalpine forests
of the Rocky Mountains. Post-glacial climate change (last 15 ky) in each region influenced fire regimes directly, by altering
summer temperatures and moisture patterns, and indirectly, by promoting large-scale shifts in vegetation. In the Alaskan
Arctic, vegetation change strongly mediated the impacts of millennial-scale climate change on fire regimes, by changing
the quantity and quality of fuels on the landscape. For example, fire frequencies decreased in the south-central Brooks
Range with the development of deciduous woodlands ca. 10 ka BP, despite evidence of warmer, drier summers than at
present. In the U.S. Rocky Mountains, Holocene vegetation change was less dramatic, and fire-history records from
subalpine forests underwent more subtle changes. Nonetheless, the direct and indirect influence of climate is evident on a
range of time scales in Yellowstone and Rocky Mountain national parks. Area burned over the past 750 years in
Yellowstone, for example, was significantly above average during decades with extreme drought. Overall, both systems
display evidence of strong climate-fire relationships at multiple time scales, but large-scale shifts in vegetation have had a
greater impact on fire regimes in Alaska than in the Rocky Mountains.
Relationships of Periglacial Processes to Habitat Quality and Thermal Environment of Pikas (Lagomorpha,
Ochotona) in Alpine and High-Latitude Environments
Millar, C I (cmillar@fs.fed.us), Sierra Nevada Research Center, USDA Forest Service, Albany, CA, United States
Smith, A T (a.smith@asu.edu), School of Life Sciences, Arizona State University, Tempe, AZ, United States
Hik, D S (david.hik@ualberta.ca), Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
Patterned-ground and related periglacial features such as rock-glaciers and fractured-rock talus are emblematic of cold
and dry arctic environments. The freeze-thaw processes that cause these features were first systematically investigated in
the pioneering work of Linc Washburn. Unusual internal and autonomous micro-climatic and hydrologic processes of
these features, however, are only beginning to be understood. Such features occur also in temperate latitude mountains,
often in surprising abundance in regions such as the Great Basin (NV, USA) and San Juan Mtns (CO, USA), where they
occur as active as well as relict (neoglacial or Pleistocene) features. Rock-dwelling species of pikas (/Ochotona/) in
temperate North American and Asian mountains and in North American high-latitudes have long been known for their
preference for talus habitats. We are investigating geomorphic, climatic, and hydrologic attributes of these periglacial
features for their role in habitat quality and thermal environment of pikas. PRISM-modeled and observed climatic
conditions from a range of talus types for /Ochotona princeps/ in California and the western Great Basin (USA) indicate
that, 1) thermal conditions of intra-talus-matrix in summer are significantly colder than talus-surface temperatures and
colder than adjacent slopes and forefield wetlands where pika forage; 2) near-talus-surface locations (where haypiles are
situated) are warmer in winter than intra-talus-matrix temperatures; 3) high-quality wetland vegetation in talus forefields is
promoted by year-round persistence of outlet springs, seeps, and streams characteristic of active taluses. The importance
of snowpack to winter thermal conditions is highlighted from these observations, suggesting a greater sensitivity of habitat
in dry temperate regions such as eastern California and Nevada USA to warming winter minimum temperatures than in
regions or elevations where snowpacks are more persistent. In regions where warming air temperatures cause declining
snowpacks over talus in the future, pika winter habitats may be exposed not only to colder surface- air temperatures, but
to sub-freezing air circulation from within talus matrices. An important implication is that periglacial features in which pikas
inhabit have different thermal environments and unique internal air circulation compared to slopes and ambient surface air
above taluses. This suggests that talus environments might have micro-climatic conditions in the future quite different
from those modeled for the general mountain or arctic contexts in which they occur. We bring together new observations
from North American temperate mountain- and high-latitude pika species, and from rock- and soil-dwelling species in the
highlands of Asia, to speculate on population ecology in the face of changing climates in these disparate regions.
Managing for Climate Change in Western Forest Ecosystems; The Role of Refugia in Adaptation Strategies
Millar, C I (cmillar@fs.fed.us), Sierra Nevada Research Center, USDA Forest Service, Albany, CA, United States,
Morelli, T (tmorelli@fs.fed.us), Sierra Nevada Research Center, USDA Forest Service, Albany, CA, United States
Managing forested ecosystems in western North America for adaptation to climate change involves options that depend
on resource objectives, landscape conditions, sensitivity to change, and social desires. Strategies range from preserving
species and ecosystems in the face of change (resisting change); managing for resilience to change; realigning
ecosystems that have been severely altered so that they can adapt successfully; and enabling species to respond to
climate changes. We are exploring one extreme in this range of strategies, that is, to manage locations, species,
communities, or ecosystems as refugia. This concept is familiar from the Quaternary literature as isolated locations where
climates remained warm during cold glacial intervals and wherein species contracted and persisted in small populations.
References to refugia have been made in the climate-adaptation literature but little elaborated, and applications have not
been described. We are addressing this gap conceptually and in case-studies from national forest and national park
environments in California. Using a classification of refugium categories, we extend the concept beyond the original use to
include diverse locations and conditions where plant or animal species, or ecosystems of concern, would persist during
future changing climatic backgrounds. These locations may be determined as refugial for reasons of local microclimate,
substrate, elevation, topographic context, paleohistory, species ecology, or management capacity. Recognizing that
species and ecosystems respond to climate change differently, refugium strategies are appropriate in some situations and
not others. We describe favorable conditions for using refugium strategies and elaborate specific approaches in Sierra
Nevada case studies.
Patterns of cold-air drainage and microclimate in mid-latitude versus high-latitude mountains: contrasts and
implications for climate change
Pepin, N C (nicholas.pepin@port.ac.uk), Geography, University of Portsmouth, Portsmouth, United Kingdom
Predictions of current spatial patterns of climate are difficult in areas of complex relief in all parts of the world, because of
the interweaving influences of topography, elevation and aspect. These influences vary temporally as a result of the
seasonal and diurnal cycles in radiation balance. In periods of negative energy balance, surface decoupling can occur as
cold air drainage develops low-level temperature inversions, and the surface temperature regime beneath the inversion
becomes divorced from free atmospheric forcing. Both the spatial scale and temporal persistence of this decoupling vary
according to latitude, and although the physical processes that influence inversion formation are similar in polar areas and
mid-latitude mountains, the contrasting seasonal and diurnal forcings make the end results very different. Examples are
contrasted from detailed field temperature measurements (~50 sites per field area) taken over several years in areas of
complex relief in the eastern Pyrenees (~42.5 deg N), the Oregon Cascades (also ~42.5 deg N) and Finnish Lapland (70
deg N and above the Arctic circle). In the former two locations decoupling is mostly diurnally driven, and small-scale
topography is important in mediating the effects. Summer decoupling is brief and spatially limited, whereas winter
decoupling can be more spatially extensive. There are strong relationships between synoptic conditions, as measured by
objective flow indices at the 700 mb level (derived from NCEP/NCAR reanalysis fields) and the patterns of decoupling,
which allow us to assess the effects of past and potential future circulation change on spatial patterns of future climate
warming. In Finnish Lapland the decoupling regime most clearly approaches the mid-latitude pattern around the
equinoxes when there are clear day and night periods. In winter and summer however (the polar night and polar day) with
the muting of the diurnal cycle, processes are more poorly understood. Winter cold pools can develop and strengthen
over days until eventually they extend over and above the topography. Strangely, there are also indistinct relationships
with circulation indices at this time. While build-up can take days, destruction is often immediate and is dynamically
forced. In summer, localized decoupling occurs on clear nights even though the sun is above the horizon, but micro-scale
patterns are different than in mid-latitudes. The above comparison shows that polar areas are very different in their microtemperature regimes than mid-latitude mountains and in their relationships of these regimes with circulation. Thus we
expect detailed spatial patterns of climate change may be very different in the two regions.
Potential effects of Rising CO2 and Climate Change Interactions with Atmospheric Deposition in Northeastern
U.S. over the 21st Century Using a Dynamic Biogeochemical Model (PnET-BGC)
Pourmokhtarian, A (apourmok@syr.edu), Civil & Environmental Engineering, Syracuse University, Syracuse, NY, United
States
Driscoll, C T (ctdrisco@syr.edu), Civil & Environmental Engineering, Syracuse University, Syracuse, NY, United States
Campbell, J L (jlcampbell@fs.fed.us), Northern Research Station, US Forest Service, Durham, NH, United States
Hayhoe, K (katharine.hayhoe@ttu.edu), Geosciences, Texas Tech University, Lubbock, TX, United States
Climate is an important regulator of hydrology and biogeochemical processes within forest ecosystems, therefore the
functionality of terrestrial ecosystems is altered by changes in climate. The ecological responses to climate change have
been assessed by observational, gradient, laboratory and field studies; however, models are the only practical approach
that can predict concurrent exposure to multiple environmental factors and consider interactive effects between climate
change, atmospheric deposition and CO2 fertilization effects. Therefore, dynamic biogeochemical watershed models are
potentially powerful tools to help to understand the long-term effects of climate change on ecosystems. In this study, we
use a biogeochemical model (PnET-BGC) coupled with long-term measurements to evaluate the effects of potential future
changes in temperature, precipitation, solar radiation, atmospheric deposition and atmospheric CO2 on pools and fluxes
of major elements at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire. Future emissions scenarios
were developed from monthly output from two atmosphere-ocean general circulation models (AOGCMs; HadCM3, PCM)
in conjunction with potential lower and upper bounds of projected atmospheric CO2 (550 and 970 ppm by 2099,
respectively). We also evaluated the interaction of climate change with changes in acidic deposition. Estimates of
atmospheric deposition are based on a “business-as-usual” deposition scenario. We compared the results of the
“business as usual” scenario with two additional scenarios which consider additional moderate and aggressive emission
controls on sulfate and nitrate. AOGCM results over the 21st century indicate an average increase in temperature ranging
from 1.9 to 6.9°C with simultaneous increases in precipitation ranging from 12.5 to 13.9% above the long term mean
(1970-1999). Long-term measurements and watershed modeling results show a significant shift in hydrology with earlier
spring discharge (snowmelt), greater evapotranspiration and longer growing season (due to CO2 fertilization), and later
snowpack development. Model results also show an increase in NO3- leaching over the second half of the century due to
increases in net mineralization and nitrification. The extent of this response is dependent on the fertilization effect that
increasing atmospheric CO2 has on forest vegetation. The watershed responses of other major elements such as SO42and Ca2+, and chemical characteristics such as pH and ANC varied based on future climate and deposition scenarios.
Model predictions showed that equivalent decreases in sulfate deposition were twice as effective as decreases in nitrate
on recovery of soil and streamwater chemistry. Model projections also suggest marked decreases in soil exchangeable
calcium, magnesium and potassium with simultaneous decline in soil base saturation and Ca/Al ratio over the next
century.
Hydrochemical responses to climate change in high-elevation catchments of the Colorado Front Range.
Williams, M W (markw@snobear.colorado.edu), University of Colorado, Boulder, CO, United States
Potential climate impacts on the hydrochemistry of two seasonally snow covered catchments is evaluated using 24 years
of data from the Niwot Ridge Long Term Ecological Research Site, Colorado. At the larger (220 ha), higher elevation
(3570 m) GL4 catchment annual discharge did not change significantly based on nonparametric trend testing. However,
October streaflow volumes and groundwater storage did increase, despite drought conditions near the end of the record in
2000-2004. In contrast, at the smaller (8 ha), lower elevation (3400 m) MART catchment, annual discharge decreased
significantly over the study period with the most substantial changes in July-September. The study period was separated
into "wet", "normal", and "dry" years based on the 75th and 25th quartiles of annual precipitation. Results indicate that
MART is particularly sensitive to changes in precipitation with dry years exhibiting decreased snowmelt peak flows, earlier
snowmelt timing, decreased annual discharge, and reduced late-season flows. GL4 was less susceptible to changes in
precipitation and surprisingly late-season flow volumes (Sept.-Oct.) were not significantly different between wet, normal,
and dry conditions. Surprisingly, during dry years both the concentrations and annual fluxes of Ca2+ and SO42- increased
in the outflow of GL4, but not at the Martinelli catchment. These changes in hydrochemistry were particularly pronounced
during the low-flow period. Streamwater chemistry in GL4 during drought years resembled that of permafrost, suggesting
augmented flow during the fall due to permafrost melt. This study shows that seasonally snow covered catchments are
particularly sensitive to changes in climate, but the hydrochemical response may depend on landscape characteristics.
POSTER SESSION
Recent increase in maximum temperature at the tropical treeline of North America
Biondi, F (fbiondi@unr.edu), University of Nevada, Reno, NV, United States
There are only a handful of weather stations above 3000 m in the entire American Cordillera, from Alaska to Tierra del
Fuego. I present a surface instrumental record of high elevation (treeline) ecoclimatic variables for the tropics of North
America. Besides its high elevation (3760 m) and tropical (19.5°N) features, this site is also located in the North American
Monsoon System, making the data relevant to a broad suite of environmental issues. Automated half-hour data collected
on Nevado de Colima, Mexico, from 2001 to 2009 show an increase in maximum temperature during the dry winter
season, while incoming solar radiation remained stationary. Since minimum temperature did not increase as much, the
daily range of air temperature has expanded over time. At this elevation, with average daily barometric pressure of 655 ±
1.4 hPa, maximum temperatures reflect the annual and daily energy cycle because of the dominant role of ground heating
caused by incoming shortwave radiation. In fact, spring is the warmest season in this area, as it is followed by pronounced
cooling during the summer monsoon because of increased cloudiness. The observed warming is associated with reduced
wind speed, especially around solar noon, and is therefore most likely driven by reduced atmospheric flow, suggesting
that the energy and water balance of high elevation tropical ecosystems are changing in unexpected ways. Further
measurements and regional modeling experiments are therefore needed, given the staggering consequences this could
have for any resource managers and policy makers concerned with trans-boundary (Mexico-US) terrestrial, coastal, and
oceanic issues.
Small mammals and high elevation vegetation in Yosemite National Park could be responding to smaller
temperature increases than previously reported
Conklin, D R (david.conklin@oregonstate.edu), Oregon State University, Corvallis, OR, United States
Daly, C (daly@nacse.org), Oregon State University, Corvallis, OR, United States
Recent research related the dynamics of Sierra Nevada subalpine conifers to 20th century warming, and used
temperature records from Yosemite National Park headquarters and two other locations outside the Park to estimate a
3.7°C rise in average minimum temperature. More recently, observed elevational shifts of small mammals in Yosemite
National Park were linked to the same upward trend in minimum monthly temperatures. However, our analysis of spatially
explicit, monthly time series of temperatures, derived using the PRISM model, suggests that the large increase in
minimum monthly temperatures may be limited to Yosemite Valley, where the Park headquarters itself is located. PRISM
bases its interpolations on observations from 195 temperature recording stations within and near Yosemite National Park.
Minimum monthly temperatures over most of the Park do not show a centennial-scale trend, but for the final quarter of the
century they do trend upwards by 1°C. Our new estimate of the spatial and temporal pattern of 20th century changes in
minimum temperatures in the Park could affect conclusions about the relative importance for subalpine conifers of the
centennial trend compared to interdecadal variability of temperature. It also raises a question of whether the elevational
shifts of the mammals took place only in the latter part of the century, and in response to smaller temperature increases. It
challenges us to accept that these plants and animals are responding to smaller changes in minimum temperatures than
previously estimated or else to find reasons other than an increase in minimum temperatures for the changes that have
been documented, by these and other studies, over the last century in Yosemite.
Using an Inverse Geochemical Reaction Path Model to Analyze the Effects of Climate Change on High-elevation
Catchments in the Southern Rocky Mountains
Driscoll, J M (driscoll@hwr.arizona.edu), Hydrology and Water Resources, University of Arizona, Tucson, AZ, United
States
Meixner, T (tmeixner@hwr.arizona.edu), Hydrology and Water Resources, University of Arizona, Tucson, AZ, United
States
Brooks, P D (brooks@hwr.arizona.edu), Hydrology and Water Resources, University of Arizona, Tucson, AZ, United
States
McIntosh, J C (mcintosh@hwr.arizona.edu), Hydrology and Water Resources, University of Arizona, Tucson, AZ, United
States
Williams, M W (markw@snobear.colorado.edu), Institute of Arctic and Alpine Research, University of Colorado, Boulder,
CO, United States
Molotch, N P (noah.molotch@colorado.edu), Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO,
United States
Sickman, J O (jsickman@ucr.edu), Environmental Studies, University of California, Riverside, CA, United States
High-elevation catchments are particularly responsive to changes in climate, which alters the snowmelt dynamics that
drive geochemical reactions in these sensitive ecosystems. Snowmelt timing and duration can be altered by the amount of
snowpack available for melt as well as the rate at which melt occurs. This study aims to assess the impact of changes to
these snowmelt dynamics through the use of a reaction path model (RPM). The inverse geochemical RPM approach
within PHREEQC was used to find estimates of mineral weathering rates and stoichiometry and infer the hydrologic
structure of the catchments studied. Chemical and hydrologic data from two NSF Critical Zone Observatories, Green Lake
4 (GL4) in the Boulder Creek watershed in Colorado and the Valles Caldera (Valles) at Redondo Peak in New Mexico
were chosen to evaluate the impact of physical differences in snowmelt dynamics on weathering and hydrologic
connectivity. The influence of total snow amount on weathering and connectivity was evaluated using wet (1996) and dry
(2002) winters in GL4, the impact of the rate of snowmelt was evaluated by assessing a variety of aspect directions
(around Redondo Peak) in the Valles, and a comparison of the relative latitude of these catchments was also used to
determine the amplitude of effects from south to north in the Rocky Mountains. We hypothesize that increased snowmelt
rates due to variations in aspect will lead to differences in catchment residence times, and that longer residence times will
lead to more contact time between water and weathering minerals and therefore produce more weathering products. The
amount of mineral weathering within a catchment is therefore indicative of relative residence time; however, when
comparing catchments, assumptions regarding bedrock lithology, temperature and other chemical inputs are necessary.
The geochemical connectivity of waters in the catchments is dependent on the amount of snowmelt and transit time, with
the number of connections hypothesized to be fewer with less snowpack. Further analysis of the changes in the specific
mineral weathering reactions that occur in these conditions will lead to conclusions on the impact of changing snowmelt
dynamics due to climate change on the buffering capacity of alpine catchments.
Multi-Scale Influences of Climate, Spatial Pattern, and Positive Feedback on 20th Century Tree Establishment at
Upper Treeline in the Rocky Mountains, USA
Elliott, G P (elliottg@missouri.edu), Geography, University of Missouri, Columbia, MO, United States
The influences of 20th century climate, spatial pattern of tree establishment, and positive feedback were assessed to gain
a more holistic understanding of how broad scale abiotic and local scale biotic components interact to govern upper
treeline ecotonal dynamics along a latitudinal gradient (ca. 35°N-45°N) in the Rocky Mountains. Study sites (n = 22) were
in the Bighorn, Medicine Bow, Front Range, and Sangre de Cristo mountain ranges. Dendroecological techniques were
used for a broad scale analysis of climate at treeline. Five-year age-structure classes were compared with identical fiveyear bins of 20th century climate data using Spearman’s rank correlation and regime shift analysis. Local scale biotic
interactions capable of ameliorating broad scale climate inputs through positive feedback were examined by using
Ripley’s K to determine the spatial patterns of tree establishment above timberline. Significant correlations (p < 0.01)
between tree establishment and climate were confined to the Front Range, where a positive correlation exists with
summer (June-Aug) and cool season (Nov-Apr) temperature range (Tmax-Tmin). Additionally, trees in the Front Range
are almost exclusively situated in a random spatial pattern above timberline (4/5 sites). Random spatial patterns imply that
positive feedback is of minimal importance and that trees are more closely aligned with broad scale changes in abiotic
conditions. This tight coupling between climate and treeline vegetation in the Front Range helps explain synchronous
ecological (tree establishment) and climate regime shifts (temperature) during the early 1950s. Similar to the Front Range,
a majority of trees at upper treeline in the Bighorn Mountains are in a random spatial pattern, but their existence appears
to be dependent on shelter availability in the lee of boulders. This contingency helps explain the lag time between a
regime shift to more favorable temperatures and subsequent peaks in tree establishment. The Medicine Bow and Sangre
de Cristo Mountains primarily contain clustered spatial patterns of trees above timberline, which indicates a strong
reliance on the amelioration of abiotic conditions through positive feedback with nearby vegetation. Although clustered
spatial patterns likely originate in response to harsh abiotic conditions such as drought or constant strong winds, the local
scale biotic interactions within a clustered formation of trees appears to override the immediate influence of broad scale
climate. This is evidenced both by a lack of significant correlations between tree establishment and climate in these
mountain ranges, as well as the considerable lag times between initial climate regime shifts and corresponding shifts in
tree age structure. Taken together, this research suggests that the influence of broad scale climate on upper treeline
ecotonal dynamics is contingent on the local scale spatial patterns of tree establishment and related influences of positive
feedback. These findings have global implications for our understanding of how vegetation patterns will respond to various
global climate change scenarios.
Plant Water Use Efficiency Response to the Atmospheric CO2 Concentration is Greater in High Altitude
Environments
Feng, X (xiahong.feng@dartmouth.edu), Earth Sciences, Dartmouth College, Hanover, NH, United States
Wang, G (gawang@cau.edu.cn), Resources and Environment, China Agricultural University, Beijing, China
Intrinsic water-use efficiency of plants (A/g ratio, where A is CO2 assimilation rate and g is stomatal conductance of H2O)
quantifies the amount of carbon assimilated per unit leaf area per unit time per unit cost of water. There has been a large
body of work showing that intrinsic plant water use efficiency (WUE) increases with increasing atmospheric CO2
concentration. This conclusion has strong implications for quantifying the effects of terrestrial carbon sequestration and
plant transpiration under the condition of continuously increasing anthropogenic CO2. Less attention has been given to
assessing whether the plant response to the atmospheric CO2 increase differs as a function of environmental variables,
such as temperature, precipitation and altitude. One would expect interactions between the CO2 concentration and other
environmental variables, and the joint effects on the plant WUE might be different from the effect of CO2 concentration
alone. However, these interactions can be quite complicated and difficult to predict; even the sign of response remains
uncertain. For example, one would expect that plants growing under a dry climate may benefit from the CO2 increase
more than those under wet climate, and thus A would increase more in a dry climate. Stomata density of leaves typically
decreases with increasing CO2 concentration, causing g to decrease, and A/g to increase. However, it is not known if
stomata density decreases more or less under dry or wet climate conditions. Similar uncertainties or lack of knowledge
apply to temperature effects. In this work, we adopt an empirical approach using carbon isotopic ratios in tree rings. Over
50 tree-ring δ13C series are compiled from the literature. The response of δ13C to atmospheric conditions (CO2
concentration and δ13C) is obtained, and the rates of change of the WUE are obtained at several different times between
AD 1800 and 2000. These rates are then compared statistically with location’s mean annual temperature, annual
precipitation and altitude, in addition to the rate of change in the atmospheric CO2 concentration. The multiple linear
regression results show that the majority of the WUE increase is explained by the change in CO2 concentration, and the
magnitude of the CO2 effect is close to the theoretically predicted value. The rate of change of WUE has no significant
response to either temperature or precipitation. However, there is a significant positive contribution of altitude to the rate
of increase of WUE; i.e., the WUE increases faster in high altitude than in low altitude locations. This is probably caused
by the fact that high altitude plants are CO2 starved due to low CO2 partial pressure. It is possible that an increase in CO2
concentration induces a greater boost in A in high altitude plants relative to low altitude ones.
Climate Change Responses of Hydrologic Flowpaths in Mountainous and Polar Regions
Godsey, S (godseys@eps.berkeley.edu), UC-Berkeley, Berkeley, CA, United States
Gooseff, M N (mgooseff@engr.psu.edu), Pennsylvania State University, State College, PA, United States
Kirchner, J W (james.kirchner@wsl.ch), Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL),
Birmensdorf, Switzerland
Tague, C (ctague@bren.ucsb.edu), UC-Santa Barbara, Santa Barbara, CA, United States
Hydrologic processes in mountainous and polar regions may respond differently to changes in the catchment energy
budget that are anticipated to occur as climate changes. In the Sierra Nevada Mountains of California, warmer winter
temperatures are expected to shift the phase of precipitation from snow to rain across a range of elevations. We examine
whether this phase change will alter subsequent low flow regimes during the dry Mediterranean summers of this region.
We show that changes in the phase of precipitation as well as changes in evapotranspiration losses from vegetation are
key drivers in the hydrologic response of these mountains to climate change. In northern Alaska, the depth of the active
layer above permafrost evolves over space and time, affecting subsurface flowpaths. Large changes in water or energy
flows may lead to catastrophic loss of ground ice, known as thermokarst development. Thermokarst features can deliver
large pulses of sediment and nutrients to lakes and streams, and further alter the hydrology because they expose
previously insulated permafrost to the ground surface, and thus higher heat fluxes. Here we show the spatial and temporal
development of the active layer inside of and outside of thermokarst features over the course of the warming season. We
explore the importance of changes in subsurface topography as a driver of hydrologic response to climate change in arctic
tundra catchments.
Biotic Responses of Headwater Streams to Geophysical Alteration and Disturbance Related to Climate Change
Gresswell, R E (bgresswell@usgs.gov), US Geological Survey, Northern Rocky Mountain Science Center, Bozeman, MT,
United States
Sedell, E R (tsedell@gmail.com), Department of Ecology, Montana State University, Bozeman, MT, United States
Cannon, S (cannon@usgs.gov), US Geological Survey Landslide Hazards Program, Denver, CO, United States
Hostetler, S W (steve@coas.oregonstate.edu), US Geological Survey, National Research Program, Water Resources
Center, Corvallis, OR, United States
Williams, J E (JWilliams@tu.org), Trout Unlimited, Ashland, OR, United States
Haak, A L (ahaak@tu.org), Trout Unlimited, Boise, ID, United States
Kershner, J L (jkershner@usgs.go), US Geological Survey, Northern Rocky Mountain Science Center, Bozeman, MT,
United States
Climate change will potentially alter physical habitat availability for trout species (both native and nonnative) in the western
USA, and ultimately affect population distribution and abundance in watersheds across the region. To understand the
biological consequences of habitat alteration associated with climate change, we have developed models linking
contemporary patterns of occurrence and abundance to geomorphic variables (e.g., aspect, elevation, and slope) and
stream conditions derived from the habitat (e.g., temperature, discharge, and flood regimes). Because headwater streams
may be especially susceptible to catastrophic disturbances in the form of debris flow torrents that have the potential to
radically alter the physical structure of channels and sometimes extirpate local fish populations, we are focusing fine-scale
spatial analyses in the high elevation systems. Risks of such disturbances increase exponentially in landscapes that have
experienced recent wildfires when high-intensity precipitation or runoff events occur. Although predicting the timing,
extent, and severity of future wildfires or subsequent precipitation and runoff events is difficult, it is possible to identify
channels within stream networks that may be prone to debris flows. These channels can be identified using models based
on characteristic storm and burn scenarios and geographic information describing topographic, soil, and vegetation
characteristics. At-risk channels are being mapped throughout the stream networks within the study areas in the
headwaters of the Colorado River to provide information about the potential for catastrophic population disturbance in
response to variety of wildfire and post-wildfire storm scenarios.
Explaining the Spatial Variability in Stream Acid Buffering Chemistry and Aquatic Biota in the Neversink River
Watershed, Catskill Mountains, New York State
Harpold, A A (aah38@cornell.edu), Biological & Environmental Engineering, Cornell University, Federal Way, NY, United
States
Walter, M T (mtw5@cornell.edu), Biological & Environmental Engineering, Cornell University, Federal Way, NY, United
States
The Neversink River Watershed (NRW) originates at the highest point in the Catskill Mountains and is sensitive to
changing patterns in acidic deposition, precipitation, and air temperature. Despite reductions in fossil fuel emission since
the Clean Air Act, past acidic deposition has accelerated the leaching of cations from the soil and reduced the stores of
base cations necessary for buffering stream acidity. The goal of this study was to investigate connections between
different watershed ‘features’ and the apparently complex spatial patterns of stream buffering chemistry (specifically, acid
neutralizing capacity ANC and Ca concentrations) and aquatic biota (macroinvertebrate and fish populations). The ten
nested NRW watersheds (2.0 km^2 to 176.0 km^2) have relatively homogeneous bedrock geology, forested cover, and
soil series; therefore, we hypothesized that differing distributions of hydrological flowpaths between the watersheds
control the variability in stream buffering chemistry and aquatic biota. However because the flowpath distributions are not
directly measurable, this study used step-wise linear regression to develop relationships between watershed ‘features’
and buffering chemistry. The regression results showed that the mean ratio of precipitation to stream runoff (or runoff
ratio) from twenty non-winter storm events explained more than 81% of the variability in mean summer ANC and Ca
concentrations. The results also suggested that steeper (higher mean slope) more channelized watersheds (larger
drainage density) are more susceptible to stream acidity and negative impacts on biota. A simple linear relationship (using
no discharge or water chemistry measurements) was able to explain buffering chemistry and aquatic biota populations in
17 additional NRW watersheds (0.3 km^2 to 160.0 km^2), including 60-80% of the variability in macroinvertebrate
populations (EPT richness and BAP) and 50-60% of the variability in fish density and species richness. These results
have several important implications for understanding the effects of climate change on buffering chemistry and aquatic
biota in this well-studied watershed. First, the results demonstrate that geomorphological and hydrogeological ‘features’
control the spatial variability of stream buffering chemistry, suggesting that acidification ‘hot-spots’ could be predicted a
priori. Second, the connection between event-scale processes (runoff ratio) and average stream chemistry imply that
changing precipitation patterns in the Catskills may have uneven effects on long-term buffering chemistry between ‘flashy’
and ‘damped’ watersheds. Specifically, an increasing trend in precipitation in the last 25 years in the Catskill Mountains
makes it difficult to compare base cation recovery across NRW streams, even if the concentrations are normalized by
discharge. The results of this study could improve the modeling of base cation recovery in surface waters in other
mountainous Northeastern U.S. watersheds with future reductions in acidic deposition and differing climate scenarios.
Predicting Individual Tree and Shrub Species Distributions with Empirically Derived Microclimate Surfaces in a
Complex Mountain Ecosystem in Northern Idaho, USA
Holden, Z (zaholden@fs.fed.us), U.S. Forest Service, Missoula, MT, United States
Cushman, S (scushman@fs.fed.us), USFS Rocky Mountain Research Station, Missoula, MT, United States Evans, J
(jeffrey_evans@tnc.org), The Nature Conservancy, Ft. Collins, CO, United States
Littell, J S (jlittell@u.washington.edu), CSES Climate Impacts group, University of Washington, Seattle, WA, United States
The resolution of current climate interpolation models limits our ability to adequately account for temperature variability in
complex mountainous terrain. We empirically derive 30 meter resolution models of June-October day and nighttime
temperature and April nighttime Vapor Pressure Deficit (VPD) using hourly data from 53 Hobo dataloggers stratified by
topographic setting in mixed conifer forests near Bonners Ferry, ID. 66%, of the variability in average June-October
daytime temperature is explained by 3 variables (elevation, relative slope position and topographic roughness) derived
from 30 meter digital elevation models. 69% of the variability in nighttime temperatures among stations is explained by
elevation, relative slope position and topographic dissection (450 meter window). 54% of variability in April nighttime VPD
is explained by elevation, soil wetness and the NDVIc derived from Landsat. We extract temperature and VPD predictions
at 411 intensified Forest Inventory and Analysis plots (FIA). We use these variables with soil wetness and solar radiation
indices derived from a 30 meter DEM to predict the presence and absence of 10 common forest tree species and 25
shrub species. Classification accuracies range from 87% for Pinus ponderosa , to > 97% for most other tree species.
Shrub model accuracies are also high with greater than 90% accuracy for the majority of species. Species distribution
models based on the physical variables that drive species occurrence, rather than their topographic surrogates, will
eventually allow us to predict potential future distributions of these species with warming climate at fine spatial scales.
Phosphorous in the Sierra Nevada: Forms, mechanisms, and timing of release in high-elevation soils
Homyak, P M (Peter.homyak@email.ucr.edu), Environmental Sciences, University of California, Riverside, Riverside, CA,
United States
Sickman, J O (jsickman@ucr.edu), Environmental Sciences, University of California, Riverside, Riverside, CA, United
States
Melack, J M (melack@lifesci.ucsb.edu), Ecology, Evolution & Marine Biology, University of California, Santa Barbara,
Santa Barbara, CA, United States
In high-elevation lakes of the Sierra Nevada (California) a change in nutrient loading has resulted in mild eutrophication
with concomitant shifts from P to N limitation, but the source of P is currently unknown. Temperature, runoff patterns, and
the timing of snowmelt influence N and P biogeochemistry in high-elevation ecosystems, which can modify cycling of P in
soils and result in altered P availability. To determine whether changes in P cycling, in response to climatic changes, can
lead to the mild eutrophication documented in Sierran lakes, we analyzed P pools in entisols and inceptisols in the
Emerald Lake Watershed, a representative high-elevation catchment, in Sequoia National Park. Our objective is to
address how P is mobilized and transformed in soils and how these processes are modified by variations in climate and
hydrology. Results from sequential P fractionation extractions indicate that on average 692 µg P g^-1 of soil are available
in organic soils and 547 µg P g^-1 of soil are available in mineral soils. In organic soils, 71 % of the total P is freely
exchangeable or associated with Fe and Al, 19 % is Ca-associated P, and 10 % exists in recalcitrant pools. In mineral
soils, 58 % of the total P is freely exchangeable or associated with Fe and Al, 32 % is associated with Ca, and 10 % exists
in recalcitrant pools. Our results suggest that the majority of the total P in high-elevation soils is found in pools that can be
affected by climatic and hydrologic changes. Future research will incorporate lake sediment P chemistry as well as freezethawing and drying-rewetting experiments on soils to assess microbial P turnover and the potential effect of climate
change on P availability in Sierran soils.
IPY-Back to the Future: Determining decadal time scale change in ecosystem structure and function in high
latitude and high altitude tundra ecosystems
Johnson, D R (drjohnson2@utep.edu), Systems Ecology Lab, University of Texas at El Paso, El Paso, TX, United States
Villarreal, S (svillarreal3@miners.utep.edu), Systems Ecology Lab, University of Texas at El Paso, El Paso, TX, United
States
Lara, M (mjlara@miners.utep.edu), Systems Ecology Lab, University of Texas at El Paso, El Paso, TX, United States
Webber, P J (webber@msu.edu), Department of Plant Biology, Michigan State University, East Lansing, MI, United States
Callaghan, T (terry_callaghan@binternet.com), Abisko Scientific Research Station, Abisko, Sweden
Hik, D (dhik@ualberta.ca), Department of Biology, University of Alberta, Edmonton, AB, Canada
Tweedie, C E (ctweedie@utep.edu), Systems Ecology Lab, University of Texas at El Paso, El Paso, TX, United States
In the absence of long-term monitoring, revisiting, re-sampling and assessing environmental change that has occurred at
Arctic and alpine research sites established several decades ago represent a largely untapped change detection capacity.
The primary objective of the “International Polar Year - Back to the Future” project, a three-year IPY project (#214), is to
determine how key structural and functional characteristics of high latitude/altitude tundra ecosystems have changed over
the past 25 or more years and assess if such trajectories of change are likely to continue in the future. This poster
presents an update of the resampling efforts undertaken in several Arctic (Barrow, Alaska, Atqasuk, Alaska and Baffin
Island, Canada) and alpine locations (Niwot Ridge, Colorado and Kluane Lake, Canada). This poster presentation will
highlight several shared and contrasting patterns of change documented the IPY-BTF sites highlighted above, as well as
several other IPY-BTF sites (Greenland, northern Russia, and Scandinavia), and presented at a fall 2009 IPY-BTF
synthesis meeting.
Climate controls on anomalously high productivity in the mixed conifer forests of the Sierra Nevada
Kelly, A E (a.kelly@uci.edu), Earth System Science, University of California, Irvine, Irvine, CA, United States
Goulden, M L (mgoulden@uci.edu), Earth System Science, University of California, Irvine, Irvine, CA, United States
The Mediterranean climate of California’s Sierra Nevada Mountains supports a dense conifer forest that contains some of
the largest trees in the world. Well-established ecological relationships, such as the Miami Model, predict relatively low
NPPs for these forests (~250 g/m^2 /yr to 1300 g/m^2 /yr) due to winter cold limitation and summer drought. However, the
observed rates of NPPs are quite high (up to 2000 g/m^2 /yr), raising the question of what environmental conditions and
plant adaptations promote such a high NPP. We hypothesize that the trees in these forests are neither as cold-limited nor
water-limited as surface weather station data suggest. Eddy covariance observations at the top of a 55 m tall
micrometeorological tower located at 2050 m elevation indicate daytime CO2 uptake continues year round, and is not
limited by winter cold or summer drought. Comparisons of temperature measurements on the tower with operational
balloon soundings indicate that tree canopies are often in the free troposphere, which buffers the temperatures they
experience and moderates winter cold limitation and summer evapotranspiration.
Meteorological Controls On The Energy Balance And CO2 Over Alpine Tundra At Niwot Ridge, Colorado
Knowles, J F (John.Knowles@colorado.edu), Geography, University of Colorado, Boulder, CO, United States Blanken, P
(blanken@colorado.edu), Geography, University of Colorado, Boulder, CO, United States
Williams, M W (markw@snobear.colorado.edu), Geography, University of Colorado, Boulder, CO, United States
Ecosystems in topographically complex (mountainous) terrain are likely responsible for a majority of land-atmosphere
CO2 exchange (net ecosystem exchange; NEE) across the western United States due to high inputs of winter
precipitation as snowfall. NEE in these regions has been historically difficult to quantify using the eddy covariance (EC)
method, however, due to complexities in surface terrain that lead to irregularities in streamline air flow, particularly
advective fluxes during periods of low turbulent mixing. This research evaluated the applicability of the EC method at an
alpine tundra site in conjunction with the Niwot Ridge Long Term Ecological Research Project (LTER), and subsequently
investigated meteorological factors controlling the observed NEE. Persistent high wind speeds, a relatively short turbulent
flux footprint, and the nearly flat ridge-top location of the study site resulted in 85% mean annual energy balance closure
and general fulfillment of basic EC methodological requirements. In all, the alpine tundra was a net source of C to the
atmosphere during 2008. Peak rates of summertime CO2 sequestration and wintertime CO2 respiration were of
comparable magnitude. Rates of CO2 sequestration during the growing season increased non-linearly with increasing soil
temperature, in agreement with results from other alpine tundra studies. CO2 sequestration was 22% less during the
relatively longer 2007 growing season, highlighting a possible inverse relationship between alpine growing season length
and CO2 sequestration on Niwot Ridge.
Climate and 20th century establishment in alpine treeline ecotones of the Western US
Littell, J S (jlittell@u.washington.edu), University of Washington, Seattle, WA, United States
Pederson, G T (gpederson@usgs.gov), United States Geological Survey, Bozeman, MT, United States Graumlich, L J
(lisag@cals.arizona.edu), University of Arizona, Tucson, AZ, United States
Germino, M J (germmatt@isu.edu), Idaho State University, Pocatello, ID, United States
Rowland, E (erowland@cals.arizona.edu), University of Arizona, Tucson, AZ, United States
Climate affects the location and demography of treeline by affecting the balance between seedling establishment and
mortality. In this study, we evaluated the nature of and climatic associations with conifer establishment at nine treelines in
the western US. Late twentieth century pulses of establishment occurred at all nine treelines, and the location of new
establishment is almost entirely within 50-100m of trees that established prior to the 19th or early 20th century. The
timing, species, and magnitude of the pulses varied among treelines. At the scale of the western US, the pulses in
aggregate appear to be related to increasing temperature, but detailed analysis at the level of each treeline suggests a
more complicated relationship between site-level climatic and biotic factors. We describe the role of growing season heat
sums, spring-summer snowpack persistence, and summer water balance within the different treelines and relate
establishment both to climate and to microsite conditions.
Structural and Geomorphic Controls in Altitudinal Treeline: a Case Study in the Front Ranges of the Canadian
Rocky Mountains
Macias Fauria, M (mmaciasf@ucalgary.ca), Biogeoscience Institute, University of Calgary, Calgary, AB, Canada
Johnson, E A (johnsone@ucalgary.ca), Biogeoscience Institute, University of Calgary, Calgary, AB, Canada
Altitudinal treelines occur on mountain slopes. The geological history of mountain systems sets both the distribution of
slope angles, aspects and lengths, and the physical characteristics of the bedrock and regolith on which trees have to
establish and grow. We show that altitudinal treeline is largely controlled at an ecosystem level by structural and slope
(i.e. gravitational) geomorphic processes operating at a range of temporal and spatial scales, which have direct influence
on the hydrological properties of the substrate (affecting the trees’ water and energy budget), as well as on substrate
stability, both of which affect recruitment and growth of trees. The study was conducted over a relatively large area of >
200 km2 in the Front Ranges of the Canadian Rocky Mountains, selected to contain the regional diversity of slopes and
substrates, which is the result of hundreds of millions of years of sea deposition, subsequent mountain building, and deep
erosion by glaciations. Very high-resolution remote sensing data (LiDAR), aerial orthophotos taken at several times since
the late 1940s, and ground truthing were employed to classify the terrain into process-based geomorphic units. High
resolution, landscape-scale treeline studies are able avoid potential biases in site selection (i.e. selection of sites that are
not representative of the overall regional treeline), and consequently capture the coupling between trees and the
environment at an ecosystem (regional) level. Moreover, explicitly accounting for slope and substrate-related processes
occurring in the studied mountain region is paramount in order to understand the dynamics of trees at their altitudinal
distribution limit. Presence of trees in each unit was found to be controlled by a set of parameters relevant to both
hydrological and slope processes, such as contributing area, slope angle, regolith transmissivity, and aspect. Our results
show no treeline advance over the last 60 years in the region, as most of the area is controlled by geological processes
and not by physiological temperature thresholds. Temperature could potentially affect presence of trees at high elevations
through its effects on the physical properties of the slopes on which trees grow. However, this effect is at a much longer
timescale than those implied in current studies of treeline response to global warming. Finally, continuous recruitment of
trees following lightning-caused wildfires during the first half of the 20th century has resulted in increased high altitude
forest stand density.
Climate induced changes in high-elevation lake chemistry and the importance of sulfide weathering
Mast, A (mamast@usgs.gov), Colorado Water Science Center, US Geological Survey, Denver, CO, United States
Holland-Sears, A (ahollandsears@fs.fed.us), White River National Forest, US Forest Service, Glenwood Springs, CO,
United States
Despite downward trends in precipitation sulfate concentrations across Colorado, high-elevation lakes in several
wilderness areas in the region show sharp increases in lake-water sulfate concentrations during 1985-2008. Similar
increases in sulfate concentrations have been reported for numerous alpine lakes in Europe, which have been attributed
to enhanced weathering rates, increased biological activity, and/or melting of permanent ice features caused by
increasing air temperatures. Analysis of climate records from Colorado SNOTEL stations shows increases in annual air
temperature of 0.43 to 0.93 °C per decade over most mountainous areas suggesting climate also may be a factor for the
Colorado lakes. Sulfur isotopic data for a subset of lakes reveals that sulfate is largely derived from the weathering of
pyrite, which is associated with hydrothermally altered and mineralized bedrock. Unlike the weathering of silicate minerals,
pyrite breakdown is largely dependent on oxygen availability and can be accelerated by fluctuating groundwater levels,
which enhance exposure of mineralized rock to oxygen as water levels decline. We suggest that during warmer, drier
years the water table declines enhancing pyrite oxidation and build up of soluble salts in the unsaturated zone. During the
subsequent snowmelt, these salts are flushed from soils and sediments resulting in increased solute concentrations in
lakes. If climate change in mountainous areas results in increased summer warming or a greater frequency of drought
years, then the magnitude of sulfate export from mineralized watersheds may continue to increase. Because pyrite is
often associated with other base-metal sulfides and its breakdown generates acidity, climate changes could result in
increased acidity and trace metal concentrations in surface water to levels where impacts on aquatic life may become
evident. Futhermore, climate change may act to decrease critical loads in these mineralized watersheds unlike the
increases in critical loads predicted for high-elevation European watersheds.
Climate Change and the Water Vapor Feedback at High Altitudes and Latitudes
Miller, J R (miller@marine.rutgers.edu), Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, United
States
Rangwala, I (imtiazr@envsci.rutgers.edu), Environmental Sciences, Rutgers University, New Brunswick, NJ, United
States
Chen, Y (chen.yonghua@gmail.com), Columbia University, New York, NY, United States
Russell, G (russell@giss.nasa.gov), NASA/GISS, New York, NY, United States
Future climate change is likely to be enhanced in high northern latitudes, and there is evidence of similar enhancement at
high altitudes. In both regions there are positive feedbacks on surface temperature associated with snow and ice cover,
clouds, and atmospheric water vapor. We combine observations and global climate model simulations to examine some
of the connections and feedbacks among these variables for the present climate and for a future climate in which
atmospheric greenhouse gases are increasing. We focus on two sites—the Tibetan Plateau and the Arctic Ocean. The
well-known snow/sea-ice albedo feedback mechanism accounts for some of the projected future temperature increases in
both regions. Increased water vapor, cloud cover, and cloud optical depth also play roles by increasing the flux of
downward longwave radiation. For the future climate, the strength of the feedbacks can change with time. Similarities and
differences between the feedbacks at the high latitude and high altitude locations are discussed, with a particular
emphasis on the water vapor feedback.
Drivers of aboveground primary production and litter accumulation in grass dominated systems
O'Halloran, L R (riesl@science.oregonstate.edu), Oregon State University, Corvallis, OR, United States
Borer, E (borer@science.oregonstate.edu), Oregon State University, Corvallis, OR, United States
Chu, C (chuchj04@lzu.cn), Lanzhou University, Lanzhou, China
Cleland, E E (ecleland@ucsd.edu), UCSD, San Diego, CA, United States
DeCrappeo, N (ndecrappeo@usgs.gov), USGS, Corvallis, OR, United States
MacDougall, A (amacdo02@uoguelph.ca), University of Guelph, Guelph, ON, Canada
McCulley, R L (rebecca.mcculley@uky.edu), University of Kentucky, Lexington, KY, United States
Seabloom, E (seabloom@science.oregonstate.edu), Oregon State University, Corvallis, OR, United States Wolkovich, E
M (wolkovich@nceas.ucsb.edu), NCEAS, Santa Barbara, CA, United States
Global trends in vegetation structure and function across major biomes spanning broad latitudinal and climatic gradients
have been well characterized in the literature. However, controls on these vegetation characteristics within a specific
biome are not well understood. Grasslands, for example, persist in diverse biogeographic regions throughout the world
and experience a range of abiotic conditions that are likely to control regional-scale patterns in biodiversity and primary
production. Here, we explore the relationship of climatic characteristics such as mean annual precipitation, interannual
variability in precipitation, and mean seasonal temperature to ecosystem traits including plant species diversity, cover,
aboveground primary production, and litter accumulation and estimated loss using a global network of 45 grassland sites.
Our preliminary results suggest that although all of the sites are grass-dominated ecosystems, the variables controlling
major ecosystem functions, such as aboveground primary production and litter accumulation, vary significantly among
sites. This global scale study demonstrates the importance of within-biome variation in response to abiotic conditions,
highlights the need for incorporation of this type of variability into existing dynamic global vegetation models, and provides
validation data for such models.
Are All Headwater Catchments the Same? Elevational Controls on Organic and Inorganic Nutrients in Headwater
Catchments in the Boulder Creek Watershed, Colorado Front Range
Parman, J (jordan.parman@colorado.edu), Geography, University of Colorado, Boulder, CO, United States
Williams, M W (markw@snobear.colorado.edu), Geography, University of Colorado, Boulder, CO, United States
High-elevation ecosystems have become the focus of recent biogeochemical research due to their unique and complex
processes, but also because these systems may serve as an early warning system for the potential effects of climate
change. In the Colorado Front Range, it is expected that alpine areas will continue to experience greater annual
precipitation, as well as an increase in atmospheric deposition of inorganic nitrogen (Williams and Tonnessen, 2000). Past
studies have shown that these mountain systems tend to amplify such environmental changes in specific areas of the
landscape. The Landscape Continuum Model (LCM, Seastedt et al., 2004) proposed a conceptual framework for how
mountain ecosystems accumulate and redistribute exogenous material from the atmosphere and endogenous material
derived from the mountain itself, emphasizing the importance of transport processes and redeposition of nutrients and
water across highly varying and complex terrain. Here, we test the LCM by comparing and contrasting changes in organic
and inorganic nutrients in stream waters of headwater catchments along an elevational gradient in the Colorado Front
Range. We simultaneously collected water samples at four gauged headwater catchments: (1) Green Lakes Valley (3,500
m); (2) Como Creek (2,900 m); Gordon Gulch (2,400 m); and Betasso (1,830 m). All water samples were analyzed for
DOC, DON, DOP, nitrate, and ammonium. Additionally, spectroscopic techniques were used to determine the quality of
DOC. These measurements, along with supporting information on soil C:N ratios and climate data, allow us to determine
how elevational position controls: (a) the redistribution of exogenous materials from the regional environment such as
nitrate in wetfall; and (b) endogenous sources originating from montane areas such as DOC and DON, while controlling
for catchment size, aspect, and underlying geology. Seastedt, T. R., W. D. Bowman, T. N. Caine, D. McKnight, A.
Townsend & M. W. Williams (2004) The landscape continuum: A model for high-elevation ecosystems. Bioscience, 54,
111-121. Williams, M. W. & K. A. Tonnessen (2000) Critical loads for inorganic nitrogen deposition in the Colorado Front
Range, USA. Ecological Applications, 10, 1648-1665.
The role of cold-air drainage in explaining spatial patterns of temperature trends in the Western U.S.
Pepin, N C (nicholas.pepin@port.ac.uk), Geography, University of Portsmouth, Portsmouth, United Kingdom Daly, C
(daly@nacse.org), Geosciences, Oregon State University, Corvallis, OR, United States
Lundquist, J D (jdlund@u.washington.edu), Civil Engineering, University of Washington, Seattle, WA, United States
Understanding spatial patterns of climate change in the western U.S. is of fundamental importance to understanding
impacts on the landscape. Because much of the western U.S. is topographically complex, and shows distinct
microclimates, there is no reason therefore to expect past or future patterns of change to be spatially smooth. In particular
cold air drainage in mountain valleys causes decoupling of the temperature regime in many locations from the free
atmosphere. This is a major feature of the western U.S. climate which is often dominated by relatively cloud-free high
pressure conditions. We investigate here whether this decoupling has seen significant temporal change in the past, and
the implications of such a change for patterns of warming observed across the western U.S. We analyse temperature
trends from 494 long-term weather stations in the western U.S. for the period 1948-2006, from the GHCNv2 dataset,
supplemented by additional COOP stations. There is a range of topographic incision and elevation in the sites chosen. At
each location we derive monthly synoptic indices representative of the degree of anticyclonicity vs cyclonicity using
NCEP/NCAR 700 mb reanalysis pressure fields. The number of anticyclonic days minus the number of cyclonic days (AC) is strongly related to temperature anomalies at exposed convex sites and hilltops where the free atmosphere controls
the temperature signal. At cold air drainage sites which tend to be in topographic concavities the relationship is much
weaker. We use the gradient of the A-C/temperature relationship to represent a coupling index which is high at exposed
free-air locations and low at cold-air drainage locations. There are clear relationships between the past rate of warming
and this coupling index across the western U.S. but these are seasonally determined. On a mean annual basis there are
no strong relationships between temperature trend magnitude, elevation, the degree of topographic incision or the
coupling index. However, in winter the rate of warming is generally weaker at cold-air pool locations, but especially when
snow cover plays a major role (an ice-box effect). In fall the relationship is reversed with cold air pools warming more
rapidly relative to exposed free-air locations. Summer, when small-scale convection dominates the climate, shows no
patterns. Our results show that future change may be different (either amplified or muted dependent on season and/or
surface characteristics) in locations prone to cold-air drainage, in comparison with the free-atmosphere, and in order to
achieve successful downscaling of future climate change such processes need to be understood.
20th Century Trends In The Maximum And Minimum Temperatures In Colorado’s San Juan Mountains
Rangwala, I (rangwala.imtiaz@gmail.com), UCAR, Boulder, CO, United States
Miller, J R (miller@marine.rutgers.edu), Marine Sciences, Rutgers University, New Brunswick, NJ, United States
We examine the maximum (Tmax) and minimum (Tmin) temperature changes in San Juan Mountain (SJM) region of
southwestern Colorado between 1895-2005. We analyze monthly averaged observations from 6 National Weather
Service (NWS) stations between 1895-1949, and 25 NWS stations between 1950-2005. These changes are evaluated on
annual, seasonal and monthly bases. Annually, our results suggest a long-term gradual warming trend in Tmin and no
such discernable trend in Tmax. However, between 1990 and 2005, the region experiences a rapid warming trend with
both Tmax and Tmin increasing by 1 degree C. Between 1950 and 1985, there is a regional cooling trend during which
there are significant decreases in Tmax and almost no trend in Tmin. Similar to the annual trends, only Tmin shows a
gradual warming trend during the 20th century during all seasons. Furthermore, during fall and summer, there is a lower
correlation between Tmax and Tmin as compared to winter and spring. Between 1990-2005, Tmax increases more than
Tmin during summer and spring, whereas Tmin shows greater increases during winter. We also examine Tmax and Tmin
trends from 23 Snow Telemetry (SNOTEL) sites in the region between 1984-2005. We find strong correlation between
NWS and SNOTEL observations, both annually and seasonally. Between 1990-2005, the largest warming at the SNOTEL
sites occurs during summer while it is largest during winter at the NWS sites. Spatially, there are similar increases in
Tmax and Tmin except in the central mountain region, where increases in Tmin started earlier and are greater. Physical
mechanisms for these observed trends in Tmax and Tmin will be discussed.
Holocene Paleoenvironment of the North-central Great Basin: Preliminary Results from Favre Lake, Northern
Ruby Mountains, Nevada
Starratt, S (sstarrat@usgs.gov), U S Geological Survey, Menlo Park, CA, United States
Wahl, D (dwahl@usgs.gov), U S Geological Survey, Menlo Park, CA, United States
Wan, E (ewan@usgs.gov), U S Geological Survey, Menlo Park, CA, United States
Anderson, L (la@gmail.gov), Environmental and Earth System Science, Stanford University, Stanford, CA, United States
Wanket, J (jwanket@csus.edu), Geography, California State University, Sacramento, CA, United States Olson, H
(holson@usgs.gov), U S Geological Survey, Menlo Park, CA, United States
Lloyd-Davies, T (tlloyddavies@usgs.gov), U S Geological Survey, Menlo Park, CA, United States
Kusler, J (jkusler@gmail.com), Geography, California State University, Sacramento, CA, United States
Little is known about Holocene climate variability in north-central Nevada. This study aims to assess changes in
watershed vegetation, fire history, lake levels and limnological conditions in order to understand secular to millennial-scale
changes in regional climate. Favre Lake (2,899 m a.s.l.; 12 m deep; 7.7 hectares) is a flow-through lake in the northern
Ruby Mountains. The primary sources of influent, both of which appear to be intermittent, are Castle Lake (2,989 m a.s.l.)
and Liberty Lake (3,077 m a.s.l.). The bedrock of the three lake basins is early Paleozoic marble and Mesozoic granite
and metamorphic rocks. Bathymetric maps and temperature, pH, salinity, and conductivity profiles have been generated
for Favre Lake. Surface samples and a series of cores were also collected using a modified Livingstone piston corer. The
presence of the Mazama ash in the basal sediment (~4 m below the sediment/water interface) indicates the record
extends to ~7,700 cal yr B.P. Magnetic susceptibility (MS) and loss-on-ignition data indicate that the sediments in the
lowest part of the core contain primary and reworked Mazama ash. About 2,000 years ago CaCO3 increased from 2 to
3% of the inorganic sediment. The upper 25 cm of the core are marked by an increase in MS which may indicate
increased erosion due to grazing. Between about 7,700 and 6,000 cal yr B.P. the diatom flora is dominated by a diverse
assemblage of benthic species. The remainder of the core is dominated by Fragilaria, suggesting that lake level rose and
flooded the shelf that surrounds the depocenter of the lake. This is supported by changes in the abundance of the aquatic
fern Isoetes. Pinus and Artemisia dominate the pollen record, followed by subordinate levels of Poaceae, Asteraceae,
Amaranthaceae, and Sarcobatus. The late early Holocene (7,700-6,000 cal yr B.P.) is dominated by Pinus which is
present in reduced amounts during the middle Holocene (6,000-3,000 cal yr B.P.) and then returns to dominance in the
late Holocene (post-3,000 cal yr B.P.). Future research will include analysis of both macro- and micro-charcoal
abundances. The charcoal record will augment the suite of data presented here by providing independent evidence of
variability in precipitation regimes and drought history. An additional set of cores from a perennial wetland on the eastern
edge of the range, Ruby Marsh, will provide a low elevation paleoclimatic counterpoint to this alpine site.
Effects of Climate Change on Alpine Lakes in the Georgia Basin, British Columbia, Canada
Strang, D M (donnastrang@trentu.ca), Environmental and Life Science, Trent University, Peterborough, ON, Canada
Aherne, J (jaherne@trentu.ca), Environmental and Life Science, Trent University, Peterborough, ON, Canada
Alpine lakes are sensitive to the effects of climate change due to their dilute nature, dependence on glacial processes as
well as their susceptibility to changes in temperature and precipitation. The Georgia Basin, located in the south-western
corner of British Columbia, Canada is an area influenced by four mountain ranges. In the fall of 2008, a synoptic water
quality survey was conducted on alpine lakes in the basin (n = 72), with elevations ranging from 90 to 2005 m.a.s.l. (mean
= 1145 m), and catchment glacier coverage ranging between 0 and 62 % (mean = 3.7%). The lakes were characterized
by low conductivities (mean = 9.42 µS cm-1), low DOC levels (mean = 1.12 mg L-1) and low acid-neutralizing capacities
(mean = 63.0 µeq L-1). During the 20th century, air temperature in the Georgia Basin increased by 1.5 degrees C and
precipitation increased between 5-35 % (depending on season). General circulation models predict that both air
temperature and precipitation will continue to increase; winter temperatures increasing between 2.4 and 6.0 degrees C,
summer temperatures increasing between 0.6 and 4.2 degrees C, and precipitation increasing by 100-200 mm
(depending on season) by 2050. The purpose of this study is to assess the sensitivity and response of alpine lake
catchments in the Georgia Basin to increased temperature and precipitation. Specifically, the study will focus on the
potential changes in alpine lake chemistry across biogeoclimatic zones based on current observations of water chemistry,
soil mineralogy, soil carbon and nitrogen pools and measurements of air, surface water and soil temperatures. The study
will also assess the potential changes in catchment weathering rates under increased temperature. The results of this
study will aid in the understanding of how climate change will affect these relatively unstudied ecosystems as well as
acknowledge data gaps. It will also serve as a platform for more in depth examination of the potential ramifications of
climate change on the alpine regions in the Georgia Basin as well as other high elevation mountainous regions around the
world.
Downscaling to the Climate Near the Ground: Measurements and Modeling Along the Macro-, Meso-, Topo-, and
Microclimate Hierarchy
Van de Ven, C (cvandeven@albion.edu), Geological Sciences, Albion College, Albion, MI, United States
Weiss, S B (stu@creeksidescience.com), Creekside Center for Earth Observation, Menlo Park, CA, United States
Most climate models are expressed at regional scales, with resolutions on the scales of kilometers. When used for
ecological modeling, these climate models help explain only broad-scale trends, such as latitudinal and upslope migration
of plants. However, more refined ecological models require down-scaled climate data at ecologically relevant spatial
scales, and the goal of this presentation is to demonstrate robust downscaling methods. For example, in the White
Mountains, eastern California, tree species, including bristlecone pine (Pinus longaeva) are seen moving not just upslope,
but also sideways across aspects, and downslope into areas characterized by cold air drainage. Macroclimate in the
White Mountains is semi-arid, residing in the rain shadow of the Sierra Nevada. Macroclimate is modified by mesoscale
effects of mountain ranges, where climate becomes wetter and colder with elevation, the temperature decreasing
according to the regionally and temporally-specific lapse rate. Local topography further modifies climate, where slope
angle, aspect, and topographic position further impact the temperature at a given site. Finally, plants experience
extremely localized microclimate, where surrounding vegetation provide differing degrees of shade. We measured and
modeled topoclimate across the White Mountains using iButton Thermochron temperature data loggers during late
summer in 2006 and 2008, and have documented effects of microclimatic temperature differences between sites in the
open and shaded by shrubs. Starting with PRISM 800m data, we derived mesoscale lapse rates. Then, we calculated
temperature differentials between each Thermochron and a long-term weather station in the middle of the range at
Crooked Creek Valley. We modeled month-specific minimum temperature differentials by regressing the Thermochronweather station minimum temperature differentials with various topographic parameters. Topographic position, the
absolute value of topographic position, and slope combined to provide a very close fit (r2>0.9) to measured inversions of
>8°C. Although topoclimatic maximum temperature models have been more elusive, regressions with degree hours
greater than zero (DH>0) have been modeled with September insolation and slope (r2=0.7). In paired experiments,
Thermochrons also recorded the temperature differences between the environment under sagebrush (Artemisia
tridentata) and in the open, with an average minimum temperature difference of 2.1°C, and maximum temperature
difference of 4.5°C. When we incorporate hourly weather station data, the strength of the inversion is weakened by wind,
higher relative humidity, and cloudiness. This hierarchical modeling provides a template for downscaling climate and
weather to ecologically relevant scales.