Alpine Treeline Warming Experiment
Internship at Lawrence Berkeley National Laboratory including
field work at University of Colorado Mountain Research Station
29th of July to 31st of December 2010
___________________________________________________________________________
Lawrence Berkeley
National Laboratory
One Cyclotron Rd
Berkeley, CA 94720, USA
University of Colorado
Mountain Research Station
818 County Road 116
Nederland, CO 80466, USA
___________________________________________________________________________
Intern:
Fabian Züst
Haldenstrasse 14
9552 Bronschhofen
fabian.zuest@access.uzh.ch
Adviser:
Dr. Margaret S. Torn
Program Head Climate and Carbon Sciences
Lawrence Berkeley National Laboratory
mstorn@lbl.gov
Internship ATWE
Fabian Züst
Abstract
The Alpine Treeline Warming Experiment (ATWE) was installed in 2008 to 2009 on Niwot Ridge
above Boulder, Colorado. It uses infrared heaters to warm soil and plant surfaces by an amount comparable to current average projections of climate warming in the year 2100. The project analyses the
effect of warming to subalpine trees and tries to enhance current knowledge on the influence of warming to the subalpine and alpine ecosystem.
Due to excellent contacts of Prof. Dr. Michael Schmidt to Dr. Margaret S. Torn from Lawrence Berkeley National Laboratory (LBNL), California, I got the possibility to travel to the United States of
America to work for the ATWE as a field student assistant for five months. The internship was split up
into two parts.
From the end of July to the end of October 2010, I worked at the ATWE field site, located on Niwot
Ridge, Colorado. The area of Niwot Ridge builds a big area for alpine research with the University of
Colorado Mountain Research Station (MRS) as its base for data analyses and housing. For three
months I performed seedling data collection, tree observations, soil sampling and preparation work for
the next field season at an elvetation of 3000 to 3600 m.
For November and December 2010, I changed my work location from Colorado to LBNL in Berkeley,
California. I was responsible to build a geospatial database for the ATWE as base for several analyses
and maps. Besides that main task, I got the possibility to go out to field sites and visit the American
Geophysical Union (AGU) Fall Meeting in San Francisco.
Being part of a big research project like the ATWE gave me a unique impression how research works
and enhanced my skills to perform field work. Due to researchers from different directions of science
were involved in the project, I had a lot of interesting talks and learnt a lot about different fields in biogeosciences.
Table of contents
1.
Alpine Treeline Warming Experiment
2
2.
Working tasks at ATWE, Niwot Ridge, Colorado
2.1.
Surveys on seedlings and germinates
2.2.
Soil coring sterile/non sterile
2.3.
Finding locations and setting up back ground recruitment plots
2.4.
Observation of trees and finding locations for cone collection
2.5.
Cone collecting, processing and organising
2.6.
Out planting of seeds
2.7.
Driving the project vehicle back to Merced, California
4
4
5
5
5
6
6
7
3.
Working tasks at Lawrence Berkeley National Laboratory, California
3.1.
ATWE geospatial database
3.2.
Blogget Experimental Forest field site
3.3.
American Geophysical Union (AGU) Fall Meeting San Francisco
8
8
10
10
4.
Preliminary results from 2010 data
4.1.
Timing of snowmelt
4.2.
Germination
4.3.
Survival
4.4.
Preliminary conclusions
11
11
11
12
12
5.
Conclusion
13
6.
Acknowledgments
13
7.
References
14
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Internship ATWE
Fabian Züst
1. Alpine Treeline Warming Experiment
The Alpine Treeline Warming Experiment (ATWE) was installed in 2008 to 2009 on Niwot Ridge
above Boulder, Colorado. It uses infrared heaters to warm soil and plant surfaces by an amount comparable to current average projections of climate warming in the year 2100. The project follows three
basic questions:
- Will subalpine trees, currently restricted from cooler, higher elevations, move into alpine habitat
and replace alpine land species as a result of climate warming?
- Will subalpine trees be stressed by warmer temperatures and be less successful in their existing
elevational ranges as a result of climate warming?
- Will ecosystem properties modify the effects of climate warming on subalpine or alpine species
within and beyond their current elevational ranges?
To find potential answers and enhance current knowledge, 80 3 m diameter plots across three sites,
ranging from 3060 m to 3540 m were established. 20 plots were established near the lower limit of
Engelmann spruce and Limber pine distributions, in the lower subalpine site (LSA) or forest site respectively. Another 20 plots were placed near the upper limit of those two species in the upper subalpine site (USA) or treeline site respectively. Above the upper limit of subalpine trees, 40 plots were
placed in the alpine site (ALP).
In all sites two environmental treatments, heating and watering, are applied. At each site, one quarter
of the plots are heated, one quarter are watered, one quarter receive both heat and water, and one quarter receive no treatment as controls. In fall 2009 and 2010 respectively, seeds from two distinct populations of Limber pine (low/10000ft vs. high/11000 ft elevation) and two distinct populations of
Engelmann spruce (low/10000ft vs. high/11000 ft elevation) were sown in 20 plots each site. The 20
alpine species research plots in the ALP site received no outside sources of seed.
Fig. 1: Schematic overview and project set up of the ATWE. The forest site (LSA), treeline site (USA) and
alpine site (ALP) contain 80 plots in total treated in four scenarios H, W, HW, and C. 40 of the plots are
heated with six infrared heating panels each plot. Seed from warm and cold edge are sown in four quads.
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To trace environmental conditions in the three sites, the following core field measurements are recorded; climate is measured by recording air temperature, relative humidity, wind speed, and photosynthetically active radiation every 15 minutes. In all of the experimental plots soil microclimate at 510 cm and 15-20 cm depths are measured. In addition to that, snow, soil and vegetation properties are
measured too.
During the growing season, seedling germination and survival, growth rate, rate of photosynthesis, and
water stress are monitored. Trees from which seeds are collected are genotyped using a range of nuclear, chloroplast and mitochondrial DNA markers. The project also follows alpine species phenology
(timing of flowering), physiology, and relative abundance.
Fig. 2: Alpine site (ALP) with 40 plots. Viewing direction southwest.
Fig. 3: Treeline site (USA). Unheated plot in
foreground, heated plots are visible in the
background.
Fig. 4: Forest site (LSA). Heated plots with
cages that protect seeds from predators like
squirrels.
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2. Working tasks at ATWE, Niwot Ridge, Colorado
To collect the data required for analysing the previously introduced main research questions of the
project, up to 12 people are working for the Alpine Treeline Warming Experiment (ATWE) on Niwot
Ridge.
The ATWE field crew is structured into three sub crews; vegetation, infrastructure, and seedling crew
that share different responsibilities. The vegetation crew is mainly performing surveys on the native
Alpine Tundra vegetation at ALP and USA field site. The infrastructure crew is responsible for running the infrared heaters, replacing and adjusting of heaters if needed, controlling functionality of data
loggers, and transport water up to the field sites. The seedling crew is responsible for doing surveys on
fall out planted1 or spring transplanted2 seedlings which includes recording germination and lifetime of
seedlings, managing cone collection of target species, processing seeds, and out plant them in fall into
the plots.
I was mainly part of the three person seedling crew. My co-workers Miles, Armin and me shared responsibilities and organised different tasks. Main work tasks continuously changed during the field
season. When I arrived at the end of July 2010, the peak growing and germination of fall out planted
seedlings respectively transplanted seedlings was already over and the focus changed form performing
surveys to 2010 fall out plant preparation work. My major work tasks are described in the following
sub chapters.
2.1. Surveys on seedlings
As main task of the seedling crew, the seedlings at every plot were surveyed systematically once a
week. One plot contains four quads with seeds from two distinct populations of Limber pine
(low/10000ft vs. high/11000 ft elevation) and two distinct populations of Engelmann spruce
(low/10000ft vs. high/11000 ft elevation). Every quad in a plot contains 100 cells where 94 cells contain 5 seeds and potentially 5 seedlings. For every seedling, presence or absence was recorded to follow its development.
In addition to that, we were also responsible for the water treatment. As introduced, the ATWE follows four different treatments: heated only, heated and watered, watered only, and control. To simulate more precipitation, 4.5 gallon water was dispersed over every watered plot once a week.
Fig. 5: Limber pine seedling, forest
site (LSA), September 2010.
1
2
Fig. 6: Engelman spruce seedling, forest site (LSA), September
2010.
Fall out planted refers to seedlings that germinated from seeds sown in fall.
Spring transplanted refers to seedlings that were first grown in a greenhouse and then transplanted into the plots.
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2.2. Soil coring sterile/non sterile
Another variable the ATWE monitors is the soil carbon content at every plot to analyse if the manipulation of climatic variables cause changes in soil carbon content. In addition to that, quantity and variety of soil micro organisms are getting analysed. Regarding soil micro organisms, changes in quantity
and variety influences patterns of decomposition and could cause a loss or accumulation of soil carbon.
As a side task, I was responsible for taking the sterile and non sterile soil samples. The samples were
taken with a 1.5 cm diameter soil corer in a depth of 10 cm.
For the sterile samples, after every sample the soil corer and all instruments had to be sterilised with
ethanol. From every core, a homogenised sub sample was taken and frozen in a cooler box cooled with
dry ice. For the non sterile samples, no sterile cleaning was required. After every sample, the soil corer
was cleaned with water.
2.3. Finding locations and setting up back ground recruitment plots
To get more knowledge about the natural movement and spread of different tree species at the alpine,
treeline and forest site elevation level, the ATWE established several natural recruitment plots at every
elevation level. A natural recruitment plot is an area of 30 m times 30 m with random point locations
at the inside. After setting up a plot, one square meter around every random point is analysed for
Engelman spruce and Limber pine seedlings respectively other species as Lodgepole pine or sub alpine fir that are present in the area.
2.4. Observation of trees and finding locations for cone collection
To set up the ATWE plots for the field season 2011, cones of the two target species Limber pine and
Engelman spruce had to be collected from trees and the seeds extracted.
For some reason, Limber pine trees from high and low elevation didn’t develop a lot of cones in the
year 2010. Due to that fact, we started monitoring and observing a lot of areas by the end of August.
With an average of 20 seeds per cone, we had to find about 1400 cones to be able to extract the 28’000
seeds needed for every species and elevation level. After we extended our search radius up to 15 kilometers, we were finally able to spot enough cones to be collected by the end of September.
For Engelman spruce, the amount of cones wasn’t a problem. Every single tree had up to 500 cones.
The difficulty with these cones was a worm inside the cones eating the seeds. From outside, there
weren’t any indicators to differentiate between good or bad cones. The only solution was to find trees
with better cones based on sub sampling.
Fig. 7: 5iwot Ridge. View from Caribou mining area. Treeline site (USA) is marked with a circle. To find
additional areas with Limber pine trees, we analysed the surrounding forests using satellite images. Areas
with pines are less dense than areas with fir or spruce. The meadow at the lower left is covered with Limber pine trees where we found several cones.
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2.5. Cone collecting, processing and organising
The most difficult thing when collecting cones is to find the optimal time to pick them from the trees.
To make sure that the seed is mature, the cotyledon of the seed has to be developed at least 80 percent
and the endosperm white and firm. To find the right time to pick the cones, we took sub samples from
different trees and elevations to analyse the stage of development. Cutting the seeds respectively cones
lengthwise, the endosperm gets visible.
Fig. 8: Limber pine cone. The cotyledon of the
seed is almost developed, but the endosperm is still
too soft and milky. The cone is not mature yet.
Fig. 9: Engelman spruce cone. 2 mm sized seed
with wing sits on top of the cone.
After a collecting period of four weeks, we collected about 1400 Limber pine cones from low elevation, 1500 cones from high elevation and about 8000 Engelman spruce cones from high elevation. Dry
and warm weather conditions combined with strong winds made the cones developing very fast.
Within 5 days, cones changed from completely closed to open, loosing their seeds and getting worthless for us. Working long days, two weekends and strengthened with additional manpower, we finally
made sure to pick all cones from our previously explored areas.
To extract the seeds out of the cones, cones were dried under controlled conditions. Limber pine seeds
were extracted directly up at the Mountain Research Station. Due to their small size, Engelman spruce
cones were sent to a facility to extract the seeds mechanically.
2.6. Out plant of seeds
Before snow started accumulating at the filed sites, the seeds had to be out planted. For Limber pine
from low and high elevation, 5 seeds each cell were planted. Due to a high amount of empty seeds, the
amount of planted seeds of Engelman spruce from low and high elevation was extended to 10 respectively 20 seeds each cell.
Fig. 10: Placed grid to plant the seeds in cells
of 10 cm size. In every quad, one species
from low or high elevation was planted.
Fig. 11: Engelman spruce seeds (left) and Limber pine
seeds (right). 5eedles give a reference for the size of the
seeds.
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By the beginning of October, all seeds were extracted and we started sowing seeds at alpine site (ALP).
Good weather conditions, less snowfall and an efficient work strategy made possible that we finished
sowing all plots by the third week of October.
2.7. Driving the project vehicle back to Merced, California
Due to the three field sides are located higher than the MRS and to carry material to these locations,
we used a four wheel drive Nissan Pathfinder from UC Merced, California, to ride up the main part of
the distance. By the end of the field season, the car had to be driven back to Merced.
Because I continued with my internship at Lawrence Berkeley National Laboratory, California, for
November and December, I took the job to drive the vehicle from Colorado to California.
Compensating weekend workdays, the project heads gave me one week off that I had 10 days to cross
Colorado, Utah, Arizona, Nevada and California. On my way I drove through fascinating landscapes
and visited several spectacular National Parks as Arches NP (Utah), Canyonlands NP (Utah),
Monument Valley (Arizona), Natural Bridges Monument (Utah), Capitol Reef NP (Utah), Bryce
Canyon NP (Utah), Zion NP (Utah), Grand Canyon NP (Arizona) and Death Valley NP (Nevada). It
was spectacular to see all these massive rock formations shaped by wind and water over millions of
years and great to expand my impression and knowledge about different kinds of landscapes.
Fig. 12: Clockwise from top to bottom: Arches 5P (Utah), Monument Valley (Arizona), Bryce Canyon 5P
(Utah), Grand Canyon 5P (Arizona) and Death Valley 5P (5evada).
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3. Working tasks at Lawrence Berkeley National Laboratory, California
For November and December, my new workplace was Lawrence Berkeley National Laboratory
(LBNL), California. Due to the need of the ATWE for a geospatial database, my main work task was
to build the database, integrate spatial data from different sources and create maps for internal use and
publications. Besides this main work task, I got the possibility to go to field sites and visit the American Geophysical Union (AGU) fall meeting in San Francisco.
3.1. ATWE geospatial database
The Alpine Treeline Warming Experiment (ATWE) is located at Niwot Ridge, spread out over 4 kilometers, spans an elevation gradient of 500 meters between the treeline site (LSA) and alpine site (USA)
and consists of 20 respectively 40 plots each site. To manage the plots at each site, to create overview
and detailed maps, and to perform further analyses referring topography or vegetation, there was a
need for a geospatial database that stores geospatial data in a defined spatial reference.
Design and overview
The ATWE geospatial database was designed as a file geodatabase using ESRI ArcGIS version 9.3.1
to integrate and manage all data. Data from different data sources was integrated into a thematic structured folder system and transformed to the same geospatial reference. Through the same geospatial
reference, data sets can be combined properly and used for visualization, mapping, modelling or different spatial analyses.
The following list provides an overview of the thematic folder system:
- Geology: Geologic data digitized from 1:24000 USGS Ward quad, CO.
- Landcover: Projected USGS Colorado land cover data in 30 m resolution. Data covers the whole
State of Colorado.
- Map: Several USGS topographic maps and central state boundaries. USGS topographic maps are in
1:24000 and 1:100000 scale.
- Orthoimagery: Othoimages of Niwot Ridge and surrounding area from 2002, 2004 and 2008 in 0.3
m to 0.6 m resolution.
- Experiment_site: GPS points of all sites including plots and infrastructure, off site locations (background recruitment plots, seed traps, cone collection areas), and raw GPS data files. In addition to
that, a file database contains data tables with data related to the ATWE that can be joined to the
geospatial datasets for further analyses. The key attribute to join data tables to spatial datasets is defined in the data overview table.
A definition of each attribute (description and unit) is integrated in the FCDC metadata file, accessible in ArcCatalog.
- Soil: Niwot Ridge soil data digitized from 1:10,000 soil maps.
- Terrain: Digital Elevation Models (DEM) in 10 m to 30 m resolution, Digital Surface Model
(DSM) in 2m resolution, Digital Terrain Model (DTM) in 2 m resolution and filtered/unfiltered
LIDAR elevation and canopy model in 1 m resolution. Other useful data products as contours,
shaded reliefs or expositions were generated out of the data sets.
- Vegetation: Vegetation coverage on Niwot Ridge digitized from 1:10,000 maps.
All geospatial data sets share the same geospatial reference and are projected on Universal Transverse
Mercator (UTM) Zone 13 with North American Datum (NAD) 1983.
- Projected Coordinate System (PCS): NAD_1983_UTM_Zone_13N
- Geographic Coordinate System (GCS): GCS_North_American_1983
Metadata was integrated in most of the data files using the FGDC ESRI format. A data overview table
provides information if metadata is integrated or stored separate as .htm or. txt file in the referring folder.
Conversion and processing of GPS data
All locations of plots and infrastructure were measured with a Trimble GPS unit in spring 2010. The
raw data was stored on a hard drive at the Mountain Research Station.
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By the end of the field season, I analysed the raw GPS data, performed a geographic correction and
exported the corrected locations of all ATWE facilities as a data format that is compatible in ESRI ArcGIS.
This dataset is a main part of the database; it provides information about every plot for example treatments or pattern of sowing. With a key attribute, additional data can be joined to every plot and be
analysed.
Integrating datasets and transforming to a common datum and coordinate system
A big variety of different thematic datasets was available, but didn’t share the same datum and coordinate system. This can cause trouble when combining or manipulating datasets. As usual for the region
where the ATWE is set up, the Universal Transverse Mercator (UTM) Zone 13 with North American
Datum (NAD) 1983 was defined as spatial reference.
Before adding a dataset to the geo database, I analysed its coordinate system and, if required, transformed it into the defined spatial reference.
Integrating native metadata files
To guarantee an efficient use of the dataset, native metadata was integrated to every dataset or was
created using the FGDC ESRI format.
Creating maps
The completed database provided the base for creating several maps for the ATWE. According to
needs of Lara M. Kueppers and Cristina Castanha, I created different maps for internal and external
use:
- Small size experimental site overviews in color and greyscale to be used in publications.
- Large scale site overviews with exact location of plots and infrastructure facilities for internal use.
- Cone collection overview maps of the years 2008, 2009 and 2010 to trace the source of seeds
used for fall and spring outplant.
- Visualisation of snowmelt pattern 2010 at alpine site may used in a publication.
Fig. 13: Small size site overview maps. Maps
were created in different color schemes and
level of detail depending on scale.
Fig. 14. Detailed alpine site (ALP) overview including
plots, treatments and schematic wiring.
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Glad to say, the created small size experimental site overviews were already used by Lara M. Kueppers and Cristina Castanha for a presentation respectively poster session at American Geophysical Union (AGU) fall meeting in December 2010.
3.2. Blogget Experimental Forest field site
Located at Blogget Experimental Forest, North El Dorado county, California, a long term research
project (10 years) is set up to explore decomposition of needles and wooden debris using labelled plant
material. After nine years, a bear damaged the data logger that collects data from soil sensors and had
to be repaired. For one day, I joined Cristina Castanha to assist doing the rebuilding of the measurement facilities. One week later, I returned by myself to complete the tasks with an assistant from the
technical facilities of LBNL. I performed or assisted the following tasks:
- Replacing plastic box that covers and protects the data logger.
- Rebuilding conduit and wires that connect the sensors with the data logger.
- Placing one additional temperature sensor/logger each site.
- Rewiring data logger, checking functionality and reloading the software.
- Building a bear fence to protect the data logger from another attack of a bear.
Compared to field sites in Switzerland, Blogget Experimental Forest is an extremely remote area.
Conditions as no cell phone service, 1.5 hours drive from the next village and 3.5 hours drive from
Berkeley made an exact preparation mandatory. Even though we had to shoot with some trouble out in
the forest, we finally managed to run the facility again.
Fig. 15: Data logger, ready to be
rewired.
Fig. 16: Rewired datalogger.
Fig. 17: Rebuilt measurement
facility including electric bear
fence.
3.3. American Geophysical Union (AGU) fall meeting San Francisco
The 2010 AGU fall meeting took place at the Moscone Convention Center, San Francisco from the
13th to 17th of December. The meeting is the largest worldwide conference in the geophysical sciences,
attracting nearly 20000 scientists, educators, students, and policy makers.
For the time of the meeting, Cristina Castanha organised a batch that I was able to visit the meeting
with its lectures and poster sessions. Due to the meeting was in the second last week of my internship,
I had to finish several tasks to complete the ATWE geospatial database project and went to the meeting for one day. The variety of topics that are presented at the meeting is overwhelming. Out of the
nearly countless presentations, I selected lectures in the fields of Biogeosciences, Hydrology, Global
Environmental Change, and Natural Hazards. Even though it was hard to follow the argumentation of
every presentation, visiting such a big conference opened my mind for the scientific world and provided me unique information of different scientific fields I am interested in.
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4. Preliminary results from 2010 data3
By the end of November, almost all data collected during summer 2010 was entered and preliminary
analyses done. For the American Geophysical Union (AGU) fall meeting in San Francisco, Cristina
Castanha analyzed the data and presented the results at the AGU poster session.
4.1. Timing of snowmelt
Heating by the use of infrared heaters advanced snowmelt by 3 months at the forest site (LSA), by 1
month at the alpine site (ALP), and by 4 months at the treeline site (USA). Picture 18 shows the visual
effect of the infrared heaters in fall 2010.
Topography at field sites influences snowmelt too. Concave and convex shapes cause different radiation and accumulation of snow during winter. Figure 19 illustrates the snowmelt pattern at alpine site
for the 20 unheated plots.
Fig. 19: Snowmelt pattern alpine site (ALP),
2010.
Fig. 18: Visual difference of snowmelt pattern between heated and control plot, treeline site (USA),
September 2010.
4.2. Germination
Referring Figure 20, heating advanced timing of germination for both species Limber pine and Engelman spruce.
Over all sites, germination rates of Limber pine were higher than germination rates of Engelman
spruce. This difference was greatest in alpine site and lowest in treeline site.
Overall germination rates at forest site were as high as at treeline site. Alpine site had a lower overall
germination rate than the other two sites.
Species responses to treatment varied by site: In the forest, additional heat and water enhanced Limber
pine germination. In the treeline, heat enhanced pine germination but depressed spruce germination.
No effect of treatment was observed in the alpine site.
3
Data source chapter preliminary results, except for photography and visualization snowmelt:
C. Castanha1, M. J. Germino, M. S. Torn, S. M. Ferrenberg , J. Harte, L. M. Kueppers (2010): Subalpine Conifer Seedling
Demographics: Species Responses to Climate Manipulations Across an Elevational Gradient at Niwot Ridge, Colorado.
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4.3. Survival
In addition to generally poor germination, Engelman spruce seedlings suffer total mortality with heating, except in the alpine site, where watering enhanced survival (Figure 21).
Treatment effects on Limber pine survival as a fraction of germinants or as fraction of seeds were
similar in the alpine and the forest sites, where water enhanced seedling survival. In the treeline heat
depressed survival as fraction of germinants but promoted germination, and the net effect was higher
survival of pine under heating.
Fig. 20: Cumulative Germination of Limber Pine andFig. 21: Survial as a fraction of germinants and as a
Engelman Spruce accross the three sites.
fraction of seeds.
4.4. Preliminary conclusions
Species effect
The ability to germinate and survive within and above the existing ranges of Limber pine and Engelman spruce is higher for pine than spruce.
Elevation effect
Site had a complex effect on seedling success. For both species germination was greatest and survival
was lowest in the treeline site.
Warming effects on geographic ranges
For Engelman spruce, an expansion above high edge is unlikely. If seeds of Limber pine are dispersed,
pine may invade into alpine tundra.
For Limber pine, with warming infilling at treeline is likely, but not for Engelman spruce.
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5. Conclusion
By the end of December I couldn’t believe how fast five month can pass. Changing work tasks, two
work locations, field and GIS work, travelling, and friendly people around me let time fly.
Being part of big research project like the ATWE gave me a unique impression how research works
and how many people have to be involved to collect data. Different work tasks at the field site improved my knowledge about organising day tasks, structuring field work, taking samples, and how to
treat samples depending on their kind. Due to researchers from different directions of science were involved in the project, I had a lot of interesting conversations and enhanced my knowledge about new
scientific fields.
My GIS skills from a focus study at University of Zurich helped a lot when I was building the geo database for the ATWE and creating several maps. It was a great experience to see that the education
from my Bachelor studies can be used and learnt a lot about solving problems using ArcGIS and enhanced my knowledge about working with GIS software.
Driving the project car back to California was a unique adventure and was optimal to combine work
with travelling. Because I didn’t expect to see a lot of areas between Colorado and California, it was
even more spectacular to see all the National Parks with their fascinating landscape and rock formations.
I can recommend such an internship to everyone. It is a unique experience and perfect to enhance
knowledge about scientific fields, improve language skills and to get in touch with a new country and
its culture.
6. Acknowledgments
I want to thank several people who made this internship possible for me. First, I want to thank Margaret S. Torn from Lawrence Berkeley National Laboratory, who invited me as guest student assistant to
LBNL and gave me her trust to work for the ATWE during five months. Second, I want to thank Michael W. I. Schmidt, Bettina Weibel and Samuel Abiven from University of Zurich who made initial
contacts and gave me very good recommendations after I applied for the internship. Third, I want to
thank Cristina Castanha from LBNL and Lara M. Kueppers from UC Merced for the excellent collaboration over big distances and their trust to delegate me several responsibilities.
Additionally I want to thank all my co-workers up at Niwot Ridge who made efficient work in a team
possible, treated me as a friend from the first day on and invited me to countless off work activities.
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7. References
C. Castanha, M. J. Germino, M. S. Torn, S. M. Ferrenberg , J. Harte, L. M. Kueppers (2010): Subalpine Conifer Seedling Demographics: Species Responses to Climate Manipulations Across an Elevational Gradient at Niwot Ridge, Colorado
Alpine Treeline Warming Experiment (ATWE):
https://alpine.ucmerced.edu/pub/htdocs/index.html. Access: 20.12.2010.
American Geophysial Union (AGU) Fall Meeting 2010:
http://www.agu.org/meetings/fm10/. Access: 01.05.2011.
University of Colorado Mountain Research Station (MRS):
http://www.colorado.edu/mrs/stationinfo.html. Access: 01.05.2011.
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