UNIVERSITY OF GOTHENBURG
Department of Economy and Society, Human Geography &
Department of Earth Sciences
Geovetarcentrum/Earth Science Centre
A small-scale study of
microclimatic effects on
vegetation changes in
tundra ecosystems
Helen Niemi
ISSN 1400-3821
Mailing address
Geovetarcentrum
S 405 30 Göteborg
Address
Geovetarcentrum
Guldhedsgatan 5A
B771
Bachelor of Science thesis
Göteborg 2013
Telephone
031-786 19 56
Telefax
031-786 19 86
Geovetarcentrum
Göteborg University
S-405 30 Göteborg
SWEDEN
Abstract
The earth is experiencing a warming of the climate, which is occurring almost twice the
global rate in Arctic and Polar regions and is for example causing changes in ecosystems. In
tundra areas an expansion of shrubs is expected and has already been observed as several
locations around the world. However, studies have shown that the climate driven shrub
expansion in the Arctic show large regional variations where shrubs are especially increasing
where the ambient temperature is already high. In this study, named A small-scale study of
microclimatic effects on vegetation changes in tundra ecosystems, it is therefore investigated
if microclimate plays a major role in the climate driven shrub expansion by comparing
microclimate data to vegetation changes. The data used has been collected through in situ
observations in the southern part of the Swedish mountain range, Fulufjället and Långfjället.
Soil- and air temperature data, which in this study represents the microclimate, has been
obtained for approx. one year during 2011-2012 while vegetation cover data has been
obtained year 1995 and year 2011. The findings from the data analyzes indicates that snow
cover plays a large role in affecting the microclimatic temperatures. It was also found that
microclimate is not controlling climate driven shrub expansion. It is, however, possible that
graminoids are experiencing an expansion with an increase of soil temperature, especially
during the warmest months of the year. It is also possible that a thicker snow cover may
enhance expansion of some plant functional types since a thicker snow cover can cause
increases in soil temperatures.
Keywords: climate warming, tundra ecosystem, climate driven shrub expansion,
microclimate.
3
Sammanfattning
Jorden genomgår en uppvärmning av klimatet vilken sker nästan dubbelt så snabbt i arktiskaoch polarområden och leder bland annat till förändringar i ekosystem. I tundraområden
förväntas en expansion av buskar ske och detta har redan observerats på flera ställen runt om i
världen. Dock har man i studier kommit fram till att den klimatdrivna expansionen av buskar i
arktiska områden visar på stora regionala variationer och är särskilt tydlig där den omgivande
temperaturen redan är hög. I föreliggande studie, vars titel är En småskalig studie av
mikroklimatiska effekter på vegetationsförändringar i tundra ekosystem, undersöks därför om
mikroklimat kan ha en stor betydelse för expansionen av buskar genom att jämföra
mikroklimatdata mot vegetationsförändringar. Datan som används har samlats in genom in
situ observationer i den södra delen av den svenska bergskedjan, Fulufjället och Långfjället.
Jord- och lufttemperaturdata, som i föreliggande studie representerar mikroklimat, har samlats
in under ca. ett års tid under åren 2011-2012 medan vegetationsdata har samlats in år 1995
och 2011. I studien visade analyserna av den insamlade datan att snötäcke har en betydande
inverkan på mikroklimatiska temperaturer. Det visade sig också att mikroklimat inte styr den
klimatdrivna expansionen av buskar. Dock är det möjligt att gräs upplever en expansion med
en ökning av marktemperaturer, särskilt under de varmaste månaderna av året. Det är också
möjligt att ett tjockare snötäcke kan förstärka expansionen av vissa vegetationstyper eftersom
ett tjockare snötäcke kan leda till ökningar av marktemperaturer.
Nyckelord: global uppvärmning, tundra ekosystem, klimatdriven expansion av buskar,
mikroklimat.
4
Preface
This study is a 15 hec Bachelor thesis in Geography, performed at the department of Earth
Sciences at Gothenburg University. The climate warming and its effects is a highly topical
subject and I especially find changes in ecosystems interesting, so when I saw that this project
needed a writer I decided that this is what I want my thesis to be about. I also became more
interested when I found out that there is little knowledge concerning microclimatic effects on
tundra vegetation.
The study is a part in a larger project that my supervisor, Associate Professor Robert Björk, is
leading. The role I have had has been to analyze data. The data itself has been collected by a
team of biologists.
It has been a really interesting experience writing this thesis and I would like to thank
Associate Professor Robert Björk for good supervision, useful advices, and for always having
a positive attitude.
I also wish to thank PhD student Tage Vowles for the availability and the willingness to help
answering my too many questions.
Thanks also to my close friend Henrik Kostet who’ve been proofreading the thesis over and
over again.
Thank you
Gothenburg University, June 2013
Helen Niemi
5
Table of contents
1.
Introduction ....................................................................................................................... 7
1.1 Aim ................................................................................................................................... 8
2.
Microclimate, climate driven shrub expansion, and reindeer grazing ........................ 9
2.1 Microclimate ..................................................................................................................... 9
2.1.1 Reindeer grazing and microclimate ......................................................................... 10
2.2 Climate driven shrub expansion ..................................................................................... 11
2.2.1 Reindeer grazing and vegetation changes ................................................................ 11
3.
Study areas ...................................................................................................................... 13
3.1 Geographical overview ................................................................................................... 13
3.2 Vegetation overview ....................................................................................................... 15
4.
Methods ............................................................................................................................ 18
4.1 Selecting study areas and dividing them into plots ........................................................ 18
4.2 Vegetation cover ............................................................................................................. 20
4.3 Temperature data ............................................................................................................ 21
4.4 Analyzing data ................................................................................................................ 22
5.
Results .............................................................................................................................. 24
5.1 Herbivore grazing ........................................................................................................... 24
5.2 Comparing climates (air temperatures) .......................................................................... 25
5.3 Air- and soil temperature in the microclimates .............................................................. 29
5.4 Vegetation change and microclimate ............................................................................. 32
5.4.1 Low shrubs ............................................................................................................... 32
5.4.2 Graminoids ............................................................................................................... 34
6.
Discussion......................................................................................................................... 37
7.
Conclusions ...................................................................................................................... 44
8.
References ........................................................................................................................ 45
6
1. Introduction
According to the Intergovernmental Panel on Climate Change (IPCC) the Earth has
experienced a warming of the annual surface temperature with 0.74°C between the years 1906
and 2005. Even if the warming has not been even or uniform around the entire planet, it has
proceeded at an unusual pace (Trenberth et al. 2007). In the Arctic and Polar regions, the
temperature is increasing almost twice the global rate and this is causing longer growing
periods and additional changes in ecosystems and vegetation composition (Anisimov et al.
2007). One of the changes of ecosystems that are expected with a warming of the climate is
an expansion of shrub abundance in the Arctic and Polar regions. This has already been
observed at several locations (Anisimov et al. 2007). There are other studies that also suggest
that expansion of shrubs is indeed climate driven. Hallinger et al. (2011) found that climate is
the most likely factor for the expansion of shrubs that have been documented. They found that
shrub establishment at higher altitudes and radial and vertical growth of shrubs in northern
Sweden is driven by the climate (Hallinger et al. 2011). In a study by Elmendorf et al. (2012a)
it was found that tundra vegetation during a 20-year period, in response to climate warming,
showed large regional variations. The study also found that different vegetation types
responded differently to the warming and that shrubs only increased with warming where the
ambient temperature was already high (Elmendorf et al. 2012a).
This study is a part in a Formas1 project in which empirical ecosystem studies and ecosystem
modeling are combined to improve the understanding on how climate warming can affect the
Swedish mountains. The name of the project is “Ecosystem responses to herbivory and
climate change along the Swedish mountains”. Since shrubs responded with an increase with
higher ambient temperature in Elmendorf’s et al. (2012a) study, it may be the microclimate
that is affecting the expansion of shrubs. Sturm et al. (2000) found that substantially higher
soil temperatures caused by thicker snow cover during winter may enhance shrub growth
(Sturm et al. 2000). Since there is little knowledge in the subject of matter, the main aim of
this study is to find out if microclimate is affecting vegetation changes in tundra areas, and if
microclimate plays a role in the climate driven shrub expansion.
1
A governmental research council that finances research projects concerning, for example, environment and
sustainable development.
7
In the study, the focus is on tundra ecosystems in two sites in the Swedish mountain range;
Fulufjället and Långfjället, which both are located in the county of Dalarna. These sites have
both been divided into six plots each from where vegetation cover and microclimate data have
been collected through in situ observations. The vegetation cover data have been obtained
year 1995 and year 2011 while the microclimate data, which is represented by air temperature
measured just above the canopy and soil temperature measured 2 cm in the soil, have been
obtained in each plot for approx. a one year period during the years of 2011-2012. Data have
been collected at other sites along the Swedish mountain range as well. However, due to time
restrictions only Fulufjället and Långfjället were selected for this study according to their
geographical resemblance.
1.1 Aim
To be able to know if the shrub expansion is driven by microclimate, it is first of interest to
find out how large the differences are between local climates, represented by site temperature,
and the microclimates in the plots. It is also of importance to compare the microclimates
within each site to find out if there are any differences in temperatures between the plots.
Further, the main aim of this study is to find out if the vegetation changes between 1995 and
2011 are affected by the microclimate. The hypothesis of the study is that the warmer the
microclimate, the greater the expansion of vascular plants (taller plants) in the tundra have
been.
In the study, the questions sought to be answered are:
-
Are there any temperature differences between the microclimates and the local
climates at the sites?
-
Are there any temperature differences between the microclimates of the plots in the
sites?
-
Are there any connections between the temperatures measured at microclimatic level
and the vegetation changes at the sites? If yes, may thickness of snow cover play a
role?
-
Is the shrub expansion driven by microclimate?
-
Are any of the different measuring methods of microclimate more representative in
terms of effects on the vegetation (just above canopy or 2 cm in the soil)?
-
Does herbivore (vegetation-eating animals) grazing in the areas have any affects on
the microclimates or the vegetation changes?
8
2. Microclimate, climate driven shrub expansion, and reindeer
grazing
2.1 Microclimate
Microclimate is the climate that characterizes the state of the air layers in adjacent to a surface
that transforms energy, for example the ground or an object. An energy transforming surface
here means a surface that transforms insolation to energy (or heat). A microclimate usually
has a horizontal extent of 1 cm to 100 meter and a vertical extent of 1 cm to 10 m (Mattsson
1979). In this particular study, microclimates represent areas that are 22x22 meters in
horizontal extent and 30-40 cm in vertical extent. According to Mattsson (1979) a local
climate represents somewhat larger areas than microclimates. They usually have a horizontal
extent of 100 m to 10 km and a vertical extent of 1 dm to 1 km. Microclimates rarely require
long periods of observations compared to regional climates that require several years or
decades of measurements (Mattsson 1979).
Air temperature variations that occur in or between microclimates are mostly regulated by
insolation and radiation. However, other factors, such as humidity and wind speed, can also
influence microclimates. Whether a surface is bare or covered by vegetation, changes the
energy transformation and thus the microclimate. When a surface is bare, it is only that
surface that affects the energy transformation. If the surface is covered by vegetation, the
vegetation itself also affects the energy transformation and thus the temperature and the
microclimate (Mattsson 1979). On a sunny day, the warmest temperature is usually located
around the canopy while the cooler temperature is located further down in the plant
community. This is because the insolation cannot penetrate the vegetation cover. During the
night it is the lower layers of the plant community that has the coolest temperatures since cool
air is heavy and sinks. A contributing factor for the cooler temperatures to be found within the
vegetation can also be the transpiration of the plants. Transpiration, which creates humidity,
has a cooling affect. The denser the vegetation is, the larger the differences are between the
coolest and the warmest temperatures in a plant community. During winters, the differences in
temperature extremes in a vegetation community are not as large since the insolation is lower
during this time of the year. While the vegetation itself affects the temperatures within a plant
community in several ways, the temperature above the canopy is often only affected by the
weather, especially insolation and wind speed. On a surface that is covered by vegetation, the
9
vegetation itself reduces the wind speed both in and over the vegetation which can affect the
temperatures (Mattsson 1979).
Sturm et al. (2000) conducted a study in Arctic Alaska to find out if there is an interaction
between snow and shrubs. In April 1996, when snow depth reached its maximum, the snow
depth, density, thermal conductivity and other properties of the snow cover was measured
along intersecting transverse lines through three vegetation types. In July the same year
properties of the vegetation types (canopy height, stem thickness etc) were recorded along the
same line. In the study it was found that where wind transport of snow is common, shrubs that
are taller and more abundant traps greater amounts of drifting snow which thickens the snow
cover. The snow cover works as a thermal isolator which leads to increases in soil
temperature. According to Sturm et al. (2000) this conclusion is well established.
2.1.1 Reindeer grazing and microclimate
In a study made by Olofsson et al. (2004) it was found that, in tundra locations in northern
Norway, reindeer grazing did not change the soil temperature on a yearly basis between July
2000 and July 2001. However, a variation in soil temperature in different grazing treatments
between the months was observed. During the months July 2000 and June-July 2011 the soil
temperature in heavily grazed zones was significantly higher than in moderately grazed zones.
In another study, made by Stark (2002), it was found that heavy reindeer grazing can increase
the soil temperature in tundra locations in northern Finland and Norway. Van der Wal et al.
(2001) conducted a study on Svalbard where reindeer- and barnacle geez grazing was
excluded in certain areas in a seven year period. After the seven years, in August 1999, the
soil temperatures were measured and it was found that grazed areas had a 0.9 °C warmer soil
temperature than un-grazed areas. Van der Wal et al. (2001) also found that, during an
experiment where soil temperature was manipulated, arctic-meadow grass (Poa arctica) and
polar cress (Cardamine nymanii) decreased with 50% in biomass when the soil was chilled
(Van der Wal et al. 2001). All these mentioned studies suggest that reindeer grazing is
affecting soil temperature.
As explained before, vegetation affects insolation and wind speed (Mattsson 1979). Reindeer
grazing means that reindeers consume vegetation, which means that the vegetation is
removed. This can lead to changes in density of the vegetation which, according to Mattsson
(1979) may change wind speed and insolation conditions. This may change the microclimate
and thus lead to changes in temperature.
10
2.2 Climate driven shrub expansion
With global warming a longer growing period is predicted which is supposed to lead to
changes in ecosystems and vegetation. According to the IPCC (Anisimov et al. 2007) the
temperature in Arctic- and Polar regions is increasing almost twice the global rate and this is
causing an increase of shrub abundance. A study from Alaska, for example, showed that
shrubs have increased in 70% of 200 locations investigated (Anisimov et al. 2007).
In a study made by Hallinger et al. (2010) in Abisko, northern Sweden, it was found that
during the last decades shrubs have increased at higher elevations and that shrub growth
correlated positively with warm summer temperatures and thicker winter snow cover. In the
study it is also suggested that if climate change continues as projected, there is potential for
large-scale ecosystem changes (Hallinger et al. 2010). In another study also made by
Hallinger et al. (2011) it is concluded that climate is the most likely driver for establishment
of shrubs at higher elevations and also for the increases in radial and vertical shrub growth
that have been observed and documented in northern Sweden.
The results from a study made by Elmendorf et al. (2012a) indicated that changes in tundra
vegetation during a 20-year period, in response to climate warming, shows large regional
variations and that different vegetation types responded differently. Shrubs, for example, only
increased with warming in areas where ambient temperature already was high (Elmendorf et
al. 2012a). In another study by Elmendorf et al. (2012b) it was shown that an increase of
shrubs and forbs, during a 30-year period, in the arctic tundra biome is associated with a
warming of summer temperatures. However, according to their study, the association was
dependent on climate zones, moisture, and also presence of permafrost.
In the study by Sturm et al. (2000), already mentioned, they did not only find that tall shrubs
traps snow which increases soil temperature; they also found that substantially higher soil
temperatures during the winter may enhance shrub growth due to winter decomposition and
nutrient release. In their study they found the deepest snow to be associated with the tallest
and densest shrubs. That higher soil temperatures may enhance shrub growth is, however,
speculative.
2.2.1 Reindeer grazing and vegetation changes
Eriksson et al. (2007) conducted a short-term study in where they investigated the effects of
reindeer grazing on vegetation communities in the Swedish mountain range. The study
11
included Fulufjället and Långfjället. In a five-year period during the 1990s it was found that
reindeer grazing only had marginal or no short-term effects on the vegetation communities in
these areas. It is pointed out by the authors that exclusion of grazing during a short period
does not change the diversity or composition of vegetation. They conclude that in order to get
an understanding of herbivore grazing on vegetation, long-term studies need to be conducted.
Olofsson et al. (2009) studied the effect of warming during the last decade on the vegetation
in northern Sweden and northern Norway. It was also studied how grazing by herbivores
affected the shrub expansion. Their results showed that shrub abundance increased during the
last decade, which correlates with the warming. However, the results also showed that
reindeer grazing has an effect on the expansion of shrubs in tundra ecosystems since the
increase of shrubs were more pronounced when grazing was excluded. They therefore suggest
that shrub expansion is controlled by an interaction between both climate and herbivores.
According to Stark (2002) reindeer grazing, investigated in 40- and 10-year periods, in tundra
ecosystem in northern Finland and Norway resulted in a shift from dwarf shrub domination to
graminoid domination. The changes were more pronounced in heavily grazed areas.
Therefore, Stark (2002) suggests that herbivore grazing can indeed cause shifts in tundra
vegetation. In a study made by Olofsson et al. (2004) it is suggested that moss-rich tundra
turns into productive grasslands due to intense reindeer grazing. In Olofssons’s et al. (2004)
study they investigated changes during a 40-year period.
Eriksson et al. (2007) pointed out that the investigations of the effects of herbivores on
vegetation communities have to be extended into longer time periods than in their own study.
Stark (2002), Olofsson et al. (2004) and Olofsson et al. (2009) all investigated the effects
during at least one decade and they all found that grazing is indeed affecting vegetation
communities.
12
3. Study areas
3.1 Geographical overview
Fulufjället and Långfjället are two mountains both located in the Scandinavian mountain
range in the county of Dalarna, close to the Norwegian border (figure 1).
Figure 1. Map showing the location of Långfjället and Fulufjället.
Långfjället is located at 800-1010 meters above sea level. The bedrock consists of Dala
granite. Fulufjället is located at 800-930 meters above sea level. Here, the bedrock consists of
Dala sandstone. The soils in both areas have a podsol profile throughout with till at the base.
Because of severely weathered and chemically acidic bedrock, both these areas are unable to
form rich vegetation (Eriksson et al. 2007). Due to that westerly winds from the Atlantic are
forced upwards and slowed down, and also due to the decrease of temperature with higher
altitudes, the summer temperature is relatively low in the study areas. The winter temperature
is considered as relatively high in both areas because of the maritime effect from the Atlantic
and also because the temperature usually is higher with an increase in altitude since cold air is
heavy and have a tendency to sink down in the valleys (Eriksson et al. 2007). The climate
13
station closest to the study areas is Särna located approx. 26 km from Fulufjället and approx.
63 km from Långfjället. Since the vegetation data obtained in this study is collected 1995 and
2011 and microclimate data obtained approx. a one year period during 2011 and 2012, figure
2 shows the summer and winter mean temperatures during these years.
15
10
Degrees °C
5
0
Winter
-5
Summer
-10
-15
Year
Figure 2. The mean temperatures during summer (Jun-Aug) and winter (Dec-Feb) measured at Särna climate
station. The winter 1995 includes the months December 1994 and January and February year 1995, the winter
1996 includes the months December 1995 and January and February 1996 etc. Summer temperature from year
2000 is missing. Data source:SMHI (Sveriges Meteorologiska och Hydrologiska Institut).
In figure 2 the summer mean temperature during the period is +13.3 °C. The warmest
summers occurred during year 2002 and 2006 with approx. +15 °C. The annual winter mean
during this time span is -9.5 °C. The warmest winter occurred during the year 1998 and 2008
with approx. -6.4 °C. The normal summer mean2 temperature in the study areas is approx.
+11.1 °C (SMHI 2009-07-07a-c) while the normal annual winter mean3 temperature in the
areas is approx. -9.3 °C (SMHI 2009-07-07d-f). According to data from Särna climate station,
the annual mean precipitation during 1995 and 2012 was approx. 611 mm (SMHI 2011-1231). The normal annual precipitation mean4 in the areas is 600-900 mm (SMHI 2009-07-13).
2
Normal summer mean (Jun-Aug) is according to the SMHI the mean during the reference period 1961-1990.
Normal winter mean (Dec-Feb) is according to the SMHI the mean during the reference period 1961-1990.
4
Normal precipitation mean is according to the SMHI the mean during the reference period 1961-1990.
3
14
3.2 Vegetation overview
In Fulufjället and Långfjället there are different types of ecosystems, for example grass
heaths, dry heaths, and mountain birch forest. The ecosystem of interest for this study is dry
heath, hereafter referred to as tundra. Figure 3 and 4 show pictures from the study areas.
Figure 3. Fulufjället (Photo: Tage Vowles).
Figure 4. Långfjället (Photo: Stefan Hamreus).
15
The study areas are each divided into six plots, three which have been fenced to exclude
grazing from large herbivores such as reindeer.
In the study areas the tundra is mostly dominated by vascular plants (taller plants): low
shrubs, such as Vaccinium myrtillus (blueberry), Empetrum nigrum (crowberry), Calluna
vulgaris (ling) and Vaccinium vitis-idaea (lingonberry); the taller Betula nana (dwarf birch);
different kinds of forbs (herbaceous plants); dwarf shrubs; and graminoids (grasses). Nonvascular plants (lower plants) such as lichens and mosses are also very common in the bottom
layer of the vegetation communities (Eriksson et al. 2007). The composition of the plant
communities in both study areas is very similar. Table 1 (Fulufjället) and 2 (Långfjället) show
what the vegetation cover of each category looked like in every plot in the year of 2011. The
vegetation cover in some plots exceeds 100% (table 1 and 2) since some of the taller species
may be covering the lower species that are located closest to the ground in the vegetation
community.
Table 1. The cover (%) of each vegetation category in each plot in Fulufjället 2011 (F = fenced). Source: T.
Vowles unpublished data.
Dwarf
shrubs
Low
shrubs
Tall
shrubs
Forbs
Graminoids
Lichens
Mosses
Plot 1 (F)
0
56
4
0
5
40
8
Plot 2 (F)
0
53
10
0
5
43
1
Plot 3 (F)
0
46
13
0
3
47
0
Plot 4
0
46
5
0
3
43
4
Plot 5
0
50
6
0
2
54
5
Plot 6
0
32
15
0
1
60
1
Table 2. The cover (%) of each vegetation category in each plot in Långfjället 2011. Source: T. Vowles
unpublished data.
Dwarf
shrubs
Plot 1
0
Low
shrubs
102
Plot 2 (F)
1
Plot 3
Tall
shrubs
Forbs
Graminoids
Lichens
Mosses
3
0
2
20
19
77
13
0
1
42
6
0
94
11
0
1
16
14
Plot 4
0
88
18
0
2
25
7
Plot 5 (F)
0
84
19
0
2
28
4
Plot 6 (F)
0
98
26
0
2
33
8
16
The growing season is the period when the vegetation is the most active. It starts sometime
when the daily mean temperature continuously exceeds approx. +4 °C. The growing season
then ends when the temperature continuously falls below +4 °C. However, to determine
exactly when the growing season starts and ends is difficult. The growing season in the two
study areas have been estimated to be around 130-150 days in 1991-2000 (Eriksson et al.
2007). According to Eriksson et al. (2007) humidity, the share of precipitation that does not
evaporate, is of great importance during the growing season and it has been calculated to be
equal in both areas (around 150-200 mm).
Långfjället is an important area for reindeer grazing. The reindeer consumes most of the
tundra vegetation but especially shrubs, such as Betula nana, Vaccinium myrtillys and
Empetrum nigrum, lichens, and grasses. Its menu varies during the different seasons.
Fulufjället, however, is rarely visited by reindeer. Although, feces from other herbivores such
as hare and moose, have been found here (Eriksson et al. 2007).
17
4. Methods
The main data used in this study is temperature data from an approx. one year period during
the years 2011-2012 as well as vegetation cover data from year 1995 and year 2011, both
which have been obtained through in situ observations in Fulufjället and Långfjället. In this
study it is the temperature data that represents the microclimate.
4.1 Selecting study areas and dividing them into plots
The study areas were selected in 1994. Each area was parted into six quadratic plots based on
resemblance of vegetation. The plots were constructed in a way so that the diagonals were
faced in a north-south and east-west direction. The plots are 25x25 meters, however, the study
area within each plot is a 22x22 m net area with 1.5 meters from the edge of the study area to
the plot edge. This decreases the edge effect and also makes it easier to move around without
having to affect the vegetation. After a further vegetation analysis, the six plots in each area
were then divided into pairs based on composition of vegetation. In the pairs, one plot was left
open while the other one was fenced to avoid large herbivores, such as reindeer (table 3).
Small herbivores still had free access. Plot coordinates are shown in table 3.
Table 3. Information about coordinates and whereas the plots are fenced or not fenced.
The plots in Fulufjället are located between 917-926 meters above sea level while the plots in
Långfjället are located between 837-865 m.a.s.l.
The two following figures, figure 5 and 6, illustrates roughly where the plots are located in
relation to one another in the areas. The figures are not made to scale, however, the distance
specified in the figures are more exact.
18
Figure 5. An overview of how the plots are located in relation to one another in Fulufjället. Plot 1, 2, and 3 are
fenced while plot 4, 5, and 6 are not fenced. The black dot represents a control object from where distance to the
plots was measured.
Figure 6. An overview of how the plots are located in relation to one another in Långfjället. Plot 2, 5, and 6 are
fenced while plot 1, 3, and 4 are not fenced.
19
4.2 Vegetation cover
The net areas (22x22 meters) in each plot were divided into 484 quadratic subplots in the size
of 1x1 meter. Out of these 484 subplots, 20 subplots where randomly selected to estimate the
vegetation cover in percent through observation. If more than half of the selected subplots
consisted of stones, sticks, or paths, a new subplot was randomly selected. The vegetation in
each plot cannot be less than 100%, although the total percentage can be more than 100%
since some taller species may be covering the lower species in the ground layer of the
vegetation community. The vegetation has been grouped using the Plant Functional Type
method (Chapin et al. 1996) which is a method widely recognized by arctic ecologists. The
vegetation is categorized based on their functionality; size, woodiness, deciduousness, ability
to survive disturbances, temperature response, drought response etc. The positive aspect with
this method is that vegetation species that are similar to one another are placed under the same
category. A negative aspect is that the plant functional types are restricted to a relatively small
number of categories. This means that species present in a very small number in a plot may be
excluded or placed under one of the categories even if it is ecologically different (Chapin et
al. 1996). The plots in the study areas are established according to composition of vegetation,
which means that the negative aspect of plant functional types does not affect this study. The
shrubs have not been categorized according to Plant Functional Types. They have been
grouped according to their maximum potential height (Elmendorf et al. 2012a). See table 4 for
grouping of the vegetation.
Table 4. The grouping of the vegetation in this study.
The vegetation observed in the 20 subplots of one plot represents the vegetation cover of the
entire plot. The same approach in estimating vegetation cover has been used in both 1995 and
2011 and the vegetation was observed from the end of June to the middle of August at both
occasions. The subplots where observation has taken place have been randomly selected both
20
these years. A negative aspect with selecting the subplots randomly is that the vegetation
change is not followed in the same subplots from 1995 to 2011. A positive aspect is that since
they are randomly selected, the subplots should represent the vegetation cover in the plots
equivalently. The person that has made the vegetation observation was not the same 1995 as
2011. Different observers can have made different visual estimates which may have affected
the results from the observations slightly. It still is observations of the vegetation cover, which
means a certain degree of generalization. These issues are not that substantial that it were to
change the validity of this study.
4.3 Temperature data
Temperature has been measured every hour at a 2 cm depth in the soil and 30-40 cm in the air
just above the canopy in every plot from June 2011 to May 2012. The devices have been
placed in the middle of each plot so that the temperature measured is as representative as
possible for the entire plot. The soil temperature represents the temperature around the roots
of the vegetation while the air temperature represents the temperature that is experienced by
the upper part of the vegetation. The devices used are Tinytag Plus 2 Extern (for soil
temperature) and Tinytag Plus 2 (for air temperature). The Tinytag Plus 2 Extern has an
accuracy of 0.2 °C while the Tinytag Plus 2 has an accuracy of 0.45 °C. Figure 7 shows what
the measuring devices in the plots look like. The air temperature measuring device is
protected from direct insolation by a white plastic cup (figure 7) open in the bottom and with
three holes at the top, which allows air to flow through the devices and not get trapped in the
protection. The protection has been fixed to avoid it from getting blown off by the wind. In
some cases they have been fixed somewhat tilted if it did not
work to fasten them straight. The fact that the protection in
some cases has been fixed somewhat tilted could have effects
on the air flow and therefore the measurements for some plots.
Figure 7. The measuring devices that measures air temperature (device
under bucket on stick) and soil temperature (yellow device on ground) in
each plot (Photo: Paloma Alvarez Blanco).
21
The temperature measured in each plot represents the prevailing microclimates of the plots.
The area (or site) temperature, which here represents the local climate, including all six plots
in each area has been measured with one temperature device in Fulufjället and one in
Långfjället with Tinytag Plus 2 (same as air temperature measured in the plots). For the
temperature data to be as representative as possible, the device is placed in the centre of the
area 2 meters above the ground. This measuring device is overshadowed in the same way as
the air temperature devices in the plots (figure 7). They are connected to loggers that collect
the temperature information. However, the local climate has only been measured from July
2011 to May 2012 in Fulufjället and from July 2011 to the middle of October 2011 in
Långfjället. Due to an herbivore bite, the soil temperature device in Plot 5 in Fulufjället
stopped working in the middle of September 2011 and was never fixed. Due to human errors,
the air temperature measuring in Plot 6 in Långfjället stopped in the middle of October 2011.
The plots where there has been a loss of data have been excluded from the analysis during the
periods from when data is missing.
4.4 Analyzing data
The obtained data has been processed in Microsoft Office Excel 2007. As a first step, the
hourly microclimate data collected was calculated into daily mean temperatures and from
these numbers the monthly, seasonal, and annual means were calculated. Also, the change
(increase or decrease) of each vegetation category in each plot was calculated by using the
vegetation cover data from 1995 and 2011.
To assess the differences between the climates, the microclimate data (temperature measured
in the plots) have been compared to local climate data in each site. The microclimates in the
plots within each area have also been compared. The temperature data used in these
comparisons was monthly and seasonal means. When comparing the microclimates to the
local climate, the temperature difference between each plot’s air temperature and the local
climate was calculated and used in graphs that were analyzed. When comparing the
microclimates to each other, the seasonal mean temperature was used in the graphs that were
analyzed. It is of interest to assess if there first of all are any differences between the climates
before comparing the different microclimates to vegetation changes.
The vegetation changes between 1995 and 2011 were compared to the microclimate based on
their groupings (Table 4). The changes of every vegetation category in both study areas were
22
compared to the annual and all the seasonal air- and soil temperature means in approx. 130
graphs that were carefully analyzed. Since climate data is missing from two of the plots
during some periods, these plots have been excluded in the graphs that are comparing data
from periods when data was missing in the plots.
Large herbivores have access to three plots in each area and therefore the analysis takes
grazing into consideration throughout. However, while Långfjället is frequently grazed by
reindeer, Fulufjället is mostly grazed only by other herbivores such as hare and elk (Eriksson
et al. 2007). An indicator of grazing affecting the microclimates could be if the fenced plots
have different microclimates than the non-fenced ones throughout the study. Whether grazing
is affecting the vegetation change or not would also be revealed throughout the analysis. All
results are visualized in graphs.
There is little knowledge about microclimatic effects on climate driven shrub expansion or
vegetation changes. It is therefore hard to determine how efficient this chosen method is. The
biggest concern is if vegetation data from 1995 to 2011 is comparable with microclimate data
from 2011-2012. This issue is, however, further discussed in chapter 6.
23
5. Results
In most of the graphs there is either a sun or a snowflake followed by an F or an L. This is to
indicate if the graph involves snow free months or winter months and the letter is to indicate
which site the graph involves (F=Fulufjället, L=Långfjället).
5.1 Herbivore grazing
When analyzing the data, there were no trends that showed that grazing from reindeer and
other herbivores have had any affects on neither the microclimates nor the vegetation change
(figure 8 and 9). This can be seen throughout the analysis of microclimates and vegetation
changes compared to microclimates. The microclimates in the fenced plots do not stand out
compared to the non-fenced. None of the plant functional types examined have been affected
either depending on whether the plots are fenced or not. Reindeer prefer eating lichens, which
is a non-vascular plant type (Andersson et al. 2007), and figure 8 and 9, to exemplify, shows
that lichens have not decreased or increased more or less in the non-fenced plots compared to
the fenced plots. In fact, lichens have decreased in 9 out of 12 plots (figure 8 and 9).
Lichens change in %
10
5
0
-5
-10
-15
-20
Figure 8. The lichens change from 1995 to 2011 in Fulufjället. The fenced plots are plot number 1, 2, and 3.
24
Lichens change in %
10
5
0
-5
-10
-15
-20
Figure 9. The lichens change from 1995 to 2011 in Långfjället. The fenced plots are plot number 2, 5, and 6.
Therefore, it can in this study be concluded that, in Fulufjället and Långfjället, grazing by
herbivores have affected neither the microclimate nor the vegetation change.
5.2 Comparing climates (air temperatures)
Only months where microclimate (air temperature) and local climate are comparable with
each other have been included. The choices of months are therefore dependent on available
local climate data. The microclimates are the air temperatures measured in each of the plots
while the local climates are the site temperature measured at 2 m above the site surface.
During the summer temperature comparisons, low shrubs have been included since this is the
plant functional type that generally dominates the plots and since low shrubs could, by its
height, affect the microclimates (chapter 2). During the winter comparisons tall shrubs has
been included since, despite a minor cover of this plant functional type, tall shrubs may work
as a snow trap according to Sturm et al. (2000).
In Fulufjället (figure 10) in July, plot 5 is approx. 0.8 °C warmer than the local climate. All
other plots are between 0.4 and 0.5 °C warmer than the local climate. Between the warmest
(plot 5) and coolest plot (plot 2 and 3) in July, the difference is approx. 0.4 °C. In August, plot
5 is approx. 0.6 °C warmer than the local climate. During August, the temperatures between
the plots vary more than in July. In August the difference between the warmest (plot 5) and
the coolest plot (plot 4) is approx 0.4 °C. In September, plot 5 is approx. 0.2 °C warmer than
25
the local climate. During this month, half of the microclimates are colder than the local
climate while the other half is warmer. The warmest plot in September (plot 5) was approx.
0.4 °C warmer than the coolest plot (plot 4). In July and August, all the plots are warmer than
the local climate. During all months, plot 5 stands out compared to the other plots, however, it
is not this plot that has the largest or least cover of low shrubs. No connection between cover
of low shrubs and air temperature measured in the plots is seen. Plot 5 is, however, the plot
located at the highest altitude of all plots in Fulufjället (926 m.a.s.l.).
Figure 10. The magnitude of the temperature differences between the local climate (site) and the air temperature
measured in each plot (microclimate) during July to September 2011 in Fulufjället. The 0-line represents the
local climate. The plots are sorted according to the cover (%) of low shrubs in 2011. In the graph, the differences
have been calculated from the monthly mean air temperatures. In the graph, the fenced plots have a quadratic
shape while the non-fenced plots are circular.
The same temperature trend is seen in Långfjället during these months (figure 11); there are
differences between the local climate and the microclimates while there are also differences
between the microclimates. During July and August, all plots are warmer than the local
climate while in September, all of the plots except from plot 5 are cooler than the local
climate. The warmest plot during July (plot 5) was approx. 0.4 °C warmer than the coolest plot
(plot 4) and approx. 0.6 °C warmer than the local climate. In August the warmest plot (plot 5)
was approx. 0.2 °C warmer than the coolest plot (plot 2). In September, the warmest plot (plot
5) was approx 0.2 °C warmer than the coolest plot (plot 2). No connection between cover of
26
low shrubs and air temperature measured in the plots is seen. Plot 5 in Långfjället is not the
plot located at the highest altitude.
Figure 11. The magnitude of the temperature differences between the local climate (site) and the air temperature
measured in each plot (microclimate) during July to September 2011 in Långfjället. The 0-line represents the
local climate. The plots are sorted according to the cover (%) of low shrubs in 2011. In the graph, the differences
have been calculated from the monthly mean air temperatures. In the graph, the fenced plots have a quadratic
shape while the non-fenced plots are circular.
During the winter, the magnitudes of the differences are much larger (figure 12 and 13). In
December in Fulufjället (figure 12), all plots are slightly cooler than the local climate. The
warmest plot in December (plot 1) was approx. 0.7 °C warmer than the coldest plot (plot 4).
During January and February, the magnitudes of the differences are very large. Plot 1, 2, and
3 (the fenced plots) are several degrees warmer than the local climate. In January they are 3-4
°C warmer while in February, they are 2-5 °C warmer. The temperature difference between
the warmest plot (plot 2) and coldest plot (plot 5) were, in January approx. 3.6 °C. In
February, the warmest plot (plot 2) and the coldest plot (plot 6) had an approx. 4.5 °C
temperature difference. No connection between the cover of tall shrubs and temperature is
seen.
27
Figure 12. The magnitude of the temperature differences between the local climate (site) and the air temperature
measured in each plot (microclimate) during December to February 2011 in Fulufjället. The 0-line represents the
local climate. The plots are sorted according to the cover (%) of tall shrubs in 2011. In the graph, the differences
have been calculated from the monthly mean air temperatures. In the graph, the fenced plots have a quadratic
shape while the non-fenced plots are circular.
In Långfjället (figure 13) data during the winter months was missing from plot 6, this plot was
therefore excluded. Also, site temperature was missing from these months so therefore figure
13 does only present the microclimate’s air temperature and the differences between them, it
does not present the differences between microclimates and local climate. When comparing
the microclimates between the plots, in December, the temperature difference between the
warmest plot (plot 4 and 5) and the coldest plot (plot 1 and 3) was only 0.1 °C. The
temperature difference between the warmest plot (plot 5) and the coldest plot (plot 3) was
approx. 1.2 °C in January. The temperature difference between the warmest plot (plot 5) and
the coldest plot (plot 3) was in February approx. 1.9 °C. Plot 5 stands out as the warmest plot,
especially in January and February. The plot with the largest cover of tall shrubs (plot 5) is
amongst the warmest during the three months investigated; this plot is also amongst the
fenced plots.
28
Figure 13. The direct temperature measured in each plot (microclimate) during December to February 2011 in
Långfjället. The plots are sorted according to the cover (%) of tall shrubs in 2011. In the graph, the differences
have been calculated from the monthly mean air temperatures. In the graph, the fenced plots have a quadratic
shape while the non-fenced plots are circular.
5.3 Air- and soil temperature in the microclimates
Figure 14 and 15 is a comparison concerning the two measuring methods. In the graphs each
dot is representing the mean soil- or air temperature from December to February. Since plot 5
was missing soil temperature data in Fulufjället, this plot was excluded from figure 14, and
since plot 6 was missing air temperature from this period, this plot was excluded in figure 15.
As can be seen in Fulufjället (figure 14), the soil temperature in all plots is several degrees
warmer than air temperature. The three plots (plot 1, 2 and 3) with the highest soil
temperature (approx. 0.4 °C in all three plots) are also the plots with the highest air
temperatures (approx. between -4.4 and -5.5 °C). That the air temperature in plot 4 and 6
stands out as these plots’ air temperatures are obviously colder compared to the other plots.
This could also be seen in figure 11. The plot with the largest cover of tall shrubs is the plot
with the coldest air and soil temperature. In Långfjället (figure 15), the soil temperature in all
plots is several degrees warmer than air temperature. Plot 5 is the warmest plot both according
to air- (approx. -6.3 °C) and soil (approx. -0.2 °C) temperature. In figure 15, plot 5 is also the
plot with the largest cover of tall shrubs (approx 19%). Plot 2, is the plot with the second
highest soil temperature (approx. -0.4 °C).
29
Figure 14. Air- and soil temperature in Fulufjället. The monthly mean temperature from December to February
is used. The plots on the X-axis are sorted with the plot that has the least cover of tall shrubs (2011) to the left,
and the plot with largest cover of tall shrubs to the right. The fenced plots are represented as quadrates.
Figure 15. Air- and soil temperature in Långfjället. The monthly mean temperature from December to February
is used. The plots on the X-axis are sorted with the plot that has the least cover of low shrubs (2011) to the left,
and the plot with largest cover of tall shrubs to the right. The fenced plots are represented as quadrates.
30
Comparing the different measuring methods during the summer months showed different
results. Here, the differences between soil- and air temperature are not several degrees as
during winter, but the differences still vary. Also, during summer, air temperature is
constantly warmer than soil temperature. See figure 16 for Fulufjället and figure 17 for
Långfjället. The air temperatures between the plots in both sites are steady between approx.
12.3 °C and approx. 12.6 °C while the soil temperatures varies between 9.9 °C and approx.
10.9 °C in both sites. The differences between the microclimates, according to air
temperature, do not vary as much as according to soil temperature. In both Fulufjället and
Långfjället plot number 1 is the plot with the largest cover of low shrubs (approx. 56 % in
Fulufjället and approx. 102% in Långfjället). In Fulufjället (figure 16), plot 1 is the coolest
plot together with plot 4 (12.3 °C) according to air temperature. It is, however, obvious in
figure 16 that plot 1 has the warmest soil temperature in Fulufjället (approx. 10.9°C). The plot
with the second highest soil temperature at this site is plot 2 which also has the second largest
cover of low shrubs. In Långfjället (figure 17) plot 1 does not have the warmest nor coolest
air temperature despite the large cover of low shrubs. In this site, plot 4 has the warmest soil
temperature (approx. 10.9°C).
Figure 16. A comparison between air- and soil temperature in Fulufjället. The monthly mean temperature from
June to August is used. The plots on the X-axis are sorted with the plot that has the least cover of low shrubs
(2011) to the left, and the plot with largest cover of low shrubs to the right. The fenced plots are represented as
quadrates.
31
Figure 17. A comparison between air- and soil temperature in Långfjället. The monthly mean temperature from
June to August is used. The plots on the X-axis are sorted with the plot that has the least cover of low shrubs
(2011) to the left, and the plot with largest cover of low shrubs to the right. The fenced plots are represented as
quadrates.
5.4 Vegetation change and microclimate
A total of ca 130 graphs were created where each vegetation category’s change in percent
from 1995 to 2011 in each plot was compared to the microclimate measured. Here, six graphs
with the most interesting results are presented. In Fulufjället, soil temperature data is missing
from plot 5 and therefore this plot has been excluded from the graphs.
5.4.1 Low shrubs
Figure 18 shows that, in Fulufjället, at least the two plots with the highest annual soil
temperature mean are the same plots that have the largest increase of low shrubs. These two
plots are also amongst the three fenced plots. However, in Långfjället the connection between
soil temperature and the expansion of low shrubs was the opposite (figure 19). Here, the
warmest plots instead had the smallest increase of low shrubs.
32
Low shrubs change in %
70
60
50
Plot1
40
Plot2
30
Plot3
20
Plot4
10
Plot6
0
2,8
3,0
3,2
3,4
3,6
3,8
Annual soil temperature mean in °C
Figure 18. Low shrubs change from 1995-2011 in % (Y-axis) compared to the annual soil temperature mean in
°C (X-axis) in Fulufjället. In the graph, the fenced plots have a quadratic shape while the non-fenced plots are
Low shrubs change in %
circular. The darker the color of the plot, the larger the increase of vegetation has been.
70
60
Plot1
50
Plot2
40
Plot3
30
Plot4
20
Plot5
10
Plot6
0
2,8
3,0
3,2
3,4
3,6
3,8
Annual soil temperature mean in °C
Figure 19. Low shrubs change from 1995-2011 in % (Y-axis) compared to the annual soil temperature mean in
°C (X-axis) in Långfjället. In the graph, the fenced plots have a quadratic shape while the non-fenced plots are
circular. The darker the color of the plot, the larger the increase of vegetation has been.
Comparing the low shrubs change to different seasons did not show any trends that indicate
an increase of low shrubs with warmer temperatures.
33
5.4.2 Graminoids
Figure 20 and 21 are comparisons between the changes of graminoids to the annual soil
temperature mean.
Graminoids change in %
5
4
3
Plot1
2
Plot2
1
Plot3
Plot4
0
Plot6
-1
2,5
3,0
3,5
4,0
Annual soil temperature mean in °C
Figure 20. Graminoids change from 1995-2011 in % (Y-axis) compared to the annual soil temperature mean in
°C (X-axis) in Fulufjället. In the graph, the fenced plots have a quadratic shape while the non-fenced plots are
circular. The darker the color of the plot, the larger the increase of vegetation has been.
Graminoids change in %
5,0
4,0
Plot1
3,0
Plot2
2,0
Plot3
1,0
Plot4
0,0
Plot5
-1,0
Plot6
2,5
3,0
3,5
4,0
Annual soil temperature mean in °C
Figure 21. Graminoids change from 1995-2011 in % (Y-axis) compared to the annual soil temperature mean in
°C (X-axis) in Långfjället. In the graph, the fenced plots have a quadratic shape while the non-fenced plots are
circular. The darker the color of the plot, the larger the increase of vegetation has been.
34
Figure 20 shows that the three plots with the highest soil temperature have experienced the
largest increase of graminoids in Fulufjället. These plots are also the fenced plots at this site.
In Långfjället (figure 21), the two coolest plots have had a decrease in graminoids while the
rest of the plots have had an increase. Plot 1 is the warmest plot and it is this plot that has had
the largest increase of graminoids.
The effect that soil temperature has on graminoids in Fulufjället was most obvious according
to the annual soil temperature mean (figure 20), but also during the snow free months (figure
Graminoids change in %
22).
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
-0,5
-1,0
Plot1
Plot2
Plot3
Plot4
Plot5
9,0
9,5
10,0
10,5
11,0
Plot6
June to august soil temperature mean
Figure 22. Graminoids change from 1995-2011 in % (Y-axis) compared to Jun-Aug soil temperature mean in °C
in Fulufjället. In the graph, the fenced plots have a quadratic shape while the non-fenced plots are circular. The
darker the color of the plot, the larger the increase of vegetation has been.
In figure 22 there is somewhat of a trend that suggests that the plots with the highest soil
temperatures are the ones where graminoids increased the most, especially plot 1 and 2. A
similar trend was seen when the graminoid changes was compared to the soil temperature
means in March to May. However, while the soil temperature shows a trend, the air
temperature in most seasons showed an obvious decrease of graminoids with increasing
temperature in Fulufjället. In Långfjället (figure 23), the mean soil temperature in June to
August did not show any connection with the graminoid changes as it did in Fulufjället, nor
did air temperature. In figure 23, the third warmest plot (plot 3) even had a decrease in
graminoids.
35
Graminoid change in %
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
-0,5
-1,0
Plot1
Plot2
Plot3
Plot4
Plot5
Plot6
9,0
9,5
10,0
10,5
11,0
June to august soil temperature mean
Figure 23. Graminoids change from 1995-2011 in % (Y-axis) compared to Jun-Aug soil temperature mean in °C
(X-axis) in Långfjället. In the graph, the fenced plots have a quadratic while the non-fenced plots are circular.
The darker the color of the plot, the larger the increase of vegetation has been.
Most of the results from the ca 130 graphs show large variations in weather the vegetation
change is connected with microclimate. Although, the most interesting finding is that
graminoids show trends that suggest that it is affected by the soil temperature measured in the
plots. The air temperature on both sites from all plots and during all seasons compared to
vegetation change showed very diffuse results and no conspicuous trends in vegetation
change and microclimate were observed.
36
6. Discussion
One potential drawback of this study may be that the vegetation change data is covering year
1995 to 2011, a 16 year time span. The climate data have, however, only been collected
during approx. one year during 2011-2012. In the study it is assumed that the microclimatic
differences have been constant during all the 16 years. Whether this assumption is legitimate
or not cannot be answered in this study. It requires microclimate measurements all the way
back from 1995 to answer this question, which is not possible here. Although, the temperature
measured by the closest climate station, Särna, during the one year from when microclimate
data have been collected at the study sites could be compared to the temperatures measured in
Särna all the way back to 1995. A comparison could show how representative the period from
when microclimate data have been collected is compared to all the other years between 1995
and 2012. If the period from when microclimate data have been obtained has been
exceptionally warm or cold, this could have had an impact on the finding in this study.
The summer 2011, from where microclimate data representing summer temperatures in this
study is used, had a mean temperature of 14.1 °C (figure 2) which is 0.8 °C warmer than the
summer mean during the whole period 1995 to 2012. There are, however, at least three
summers in the time span that had a warmer mean temperature than 2011. The summer air
temperature mean in the plots of the study areas have been between approx. 12.3 °C and
approx. 12.6 °C which is cooler than the summer mean temperature of 13.3 °C during 1995
and 2012 measured as Särna climate station. The winter 2012, from where microclimate data
in this study is used, had a mean winter temperature of -8.9 °C (figure 2) which is 0.6 °C
warmer than the winter mean during the whole period 1995 to 2012. There are, however eight
years between 1995 and 2012 that have had an even warmer mean winter temperature. The
one year from when microclimate data have been collected has not been unusual temperature
wise compared to all the years from 1995. Now if the period from when microclimate data
have been collected is representative enough, and if the assumption mentioned above is
legitimate, it is possible that the findings in this study concerning a connection between
microclimate and vegetation changes are tenable.
In the study, no trends were found that suggest that herbivore grazing have effects on neither
microclimates nor the vegetation change. Previous studies by Stark (2002) and Olofsson et al.
(2009), however, suggest the opposite. They both found that grazing affects soil temperatures.
Mattsson (1979) wrote that vegetation covered surfaces have different microclimates
37
compared to surfaces not covered by vegetation. In this case, grazing would lead to removal
of vegetation in the plots that are not fenced, and may lead to changes in the microclimates.
No differences were seen between the fenced and non-fenced plots. In the same studies made
by Stark (2002) and Olofsson et al. (2009) it is said that grazing can lead to shifts in the
vegetation. In Fulufjället and Långfjället, this have not been seen either which is exemplified
in figure 8 and 9. Lichens have neither increased nor decreased depending on whether the
plots are fenced. That grazing has not affected the vegetation in Fulufjället and Långfjället is
also supported by Eriksson et al. (2007) that investigated the very same areas and concluded
that reindeer grazing have only had marginal or no effects on the vegetation communities in a
five-year period during the 1990s. However, in this study the vegetation changes have been
investigated from 1995 to 2011 which is a longer time span than Eriksson et al. (2007) used,
but still, grazing have not had any effects in the study areas. A theory to why grazing have not
affected neither the microclimates nor the vegetation change may be that the frequency of
grazing have been different in the areas investigated in previous studies.
Furthermore, there are differences found between the air temperatures measured in the plots
and the local climates measured at the sites (figure 10-13). Differences between microclimates
at each site were also found, as well as differences between the air- and soil temperatures
measured in each plot in the sites (figure 14-17).
During the warmer months (July and August), the air temperature in all plots in both study
areas were warmer than the local climate (figure 10-11). According to Mattsson (1979), the
vegetation affects the energy transformation and therefore the temperature, which may be the
reason to why the plots are warmer than the local climate during these months. Or it can be
the 0.45 °C accuracy of the air temperature devices that causes the small differences. At the
examined sites, the cover of low shrubs in 2011 was generally larger than the cover of all the
other vegetation categories examined (table 1-2). However, the differences in air temperature
between the plots during the warmer months do not seem to have anything to do with the
cover or low shrubs. In Fulufjället (figure 10) plot 5 stood out as warmer than the rest of the
plots during July to September, this plot does not have the largest nor the least cover of low
shrubs on the site. This plot is located at the highest altitude of all the plots in Fulufjället.
However, Eriksson et al. (2007) writes that temperature during summer decreases with height
(Eriksson et al. 2007) which means that it is most likely not the altitude that is making plot 5
stand out. In Långfjället (figure 11), there is also a plot that stands out as the warmest during
the same months, plot 5. This plot, as were the case in Fulufjället, does not have the least nor
38
the largest cover of low shrubs here. In Långfjället plot 1 have an approx. 102% cover of low
shrubs, however, this plot is neither the warmest nor the coolest during July to September.
There is therefore no clear connection between the cover of low shrubs and the air
temperature differences between the plots. Also, the plot that stands out as warmer is not
located at the neither highest nor lowest altitude amongst the plots in Långfjället. All the
small differences between the microclimates in the plots do most likely depend on the
accuracy of the air temperature measuring devices. Even if a trend were to be seen concerning
the air temperature during summer and the cover of low shrubs, it would not be reliable to
draw any conclusions.
During the winter months, the differences between the air temperatures in the plots and the
temperature representing the local climate are much larger, especially in January and February
(figure 12-13). The most plausible explanation to this is that the plots that are several degrees
warmer had snow covering the air temperature devices, and therefore, the device measured
the snow temperature instead of the air temperature. If there should have been other causes
behind these irregularities than snow, it would most likely have shown during December and
also during snow free months as well, which it did not. Sturm et al. (2000) have concluded
that tall shrubs traps more snow and thicken the snow cover, which has an isolating effect on
soil temperature. However, in Fulufjället (figure 12) it is not the tall shrubs that causes the
snow to thicken since the plot with the largest amount of tall shrubs (plot 6: 15%) is not
amongst the three plots that stands out as much warmer during January and February. Instead,
the plot with the least cover of tall shrubs (plot 1: 4%) is amongst the warmest plots. All the
plots that are substantially warmer than the rest are all the fenced plots. It is therefore most
plausible that the fences work as a snow traps which thickens and covers the temperature
devices. In Långfjället (figure 13) plot 5 stands out in January and February as warmer than
the rest of the plots. This can either depend on three things: plot 5 is one of the two fenced
plots at this site, it is also the plot with the largest cover of tall shrubs, and lastly; the
temperature difference between plot 5 and the other plots are not that large, which therefore
can be a result of the accuracy of the Tinytags.
It is also found that there are differences between the air- and soil temperatures measured in
each plot in the study areas (figure 14-17). During the winter, the soil temperature is always
warmer than the air temperature whether the air temperature devices are covered by snow or
not. As Sturm et al. (2000) emphasizes; snow has an isolating capacity. The difference
between air- and soil temperatures is most certainly a result of that the snow is keeping the
39
soil from becoming as cold as the air. In figure 14, for example, the plots with coldest soil
temperature (plot 4 and 6) most likely has a thinner snow cover than the fenced plots that are
much warmer, as was mentioned above. A thinner snow cover would therefore mean less
isolation from the cold air and lead to colder soil temperatures. The same phenomena can be
seen in Långfjället (figure 15) where the warmest soil- and air temperature is found in plot 5,
which here depends on either the fence, the cover of tall shrubs, or the accuracy of the device,
as mentioned earlier. However, why plot 2 stands out as the plot with the second warmest soil
temperature is indefinite since the air temperature in this plot does not stand out. Therefore it
does not suggest that the air measuring device was covered by snow in this plot.
During the summer (figure 16-17) there are small differences in air temperature between the
plots which are in the range of the accuracy for the Tinytags. Therefore, no reliable
conclusions can be drawn. The temperature differences between soil- and air temperature are
not as small and are therefore not within the accuracy range. According to Mattsson (1979)
there are differences in the temperatures within and above a vegetation community. Within
the vegetation community, the transpiration and the shading effect that is caused by the
vegetation itself may be what keeps the soil from becoming cooler than the air above. This
theory is most likely what the differences between air- and soil temperatures in the plots
depend on. The differences in soil temperatures between the plots are larger and the accuracy
range of the soil temperature measuring devices is also smaller. Why the soil temperature
varies more in Långfjället (figure 17) during summer may depend on the density of the
vegetation cover just above the soil temperature measuring device. If the vegetation is less
dense, the less the shading effect is, and the more the insolation can reach the ground and
warm up the soil. This is the most reasonable theory that can be drawn from the data
collected. However, the explanation may be something else that cannot be explained here. In
Fulufjället during summer (figure 16), the two plots with the warmest soil temperature have
the largest cover of low shrubs. Though, since the same trend is not seen in Långfjället, where
the cover of low shrubs is larger, it most likely is not the cover of low shrubs in the entire
plots that are affecting the soil temperature. As mentioned above, it can be the vegetation
cover just above the Tinytags.
When comparing vegetation changes to the microclimate, it was in this study found that
graminoids seems to be the vascular plant that is most consistent with the hypothesis of the
study. The graminoids showed that they have a tendency to change with annual soil
temperature in both Fulufjället and Långfjället, which indicates an expansion with warmer
40
annual soil temperature (figure 20-21). In Fulufjället (figure 20), the difference in percentage
between the plots that had the smallest and largest increase of graminoids were around 3%
while the annual soil temperature difference between these plots were around 0.5 °C. In
Långfjället (figure 21), the difference in percentage was also around 3% while the soil
temperature difference was around 0.4 °C. A 3% increase of graminoids to a 0.4 – 0.5°C
annual soil temperature difference seems fairly reasonable. When comparing the graminoid
change to different seasons, the snow free period shows a trend that graminoids are increasing
with an increase in soil temperature in Fulufjället (figure 22). Here, the differences in soil
temperature between the plots are substantially larger which rules out the 0.2 °C accuracy of
the measuring device. It is possible that this period may be the most important to when
graminoids are the most susceptible to soil temperature in terms of growth. In Långfjället the
most important period was harder to determine (figure 23). The results concerning graminoids
may be consistent with Van der Wal et al. (2001) study that found a decrease of Arctic
meadow grasses when the soil was chilled with 0.9 °C. However, when comparing the
changes of graminoids to air temperature during the summer, the results were reversed. It
showed that the graminoids are decreasing with increases in air temperature. As mentioned,
the air temperatures during summer are not to trust due to the accuracy of the Tinytags.
Furthermore, when examining the expansion of low shrubs it is clear that, in Fulufjället, the
two plots where low shrubs had the largest expansion are also the plots with the highest
annual soil temperature (figure 18). The difference in percentage between the plots that had
the smallest and largest expansion is around 13% while the annual soil temperature difference
between these plots were around 0.7 °C. In contrast, in Långfjället (figure 19) the plot that
had the largest increase of low shrubs (approx. 65%) is 0.4 °C cooler than the plot with the
smallest increase. That the cover of low shrubs year 1995, when the first vegetation cover
observation took place, was different in Fulufjället compared to Långfjället has not affected
how much the low shrubs have expanded during the 16 year time span. Instead, the accuracy
of the measuring device may have played a role here in Långfjället since the annual soil
temperature differences between the plots are small and within the accuracy range.
Comparisons of the expansion of low shrubs to the mean soil-, and also, air temperature
during different seasons did not show any other trends. No other recorded vegetation change
showed any seasonal trends to mean soil- and air temperatures.
41
In a study Sturm et al. (2000) suggests an increase in soil temperature caused by a thickness
of snow cover that is caused by taller shrubs that may, in turn, enhance shrub expansion
(Sturm et al. 2000). Vegetation can affect snow cover which affects soil temperature, and vice
versa. In this study, it was found that in Fulufjället three plots were warmer (plot 1, 2 and 3)
during the winter according to both air and soil temperature (figure 12 and 14). These three
plots are the fenced plots at this site and, as mentioned, there is a large possibility that the
fences have trapped snow which have thickened the snow cover and caused both air- and soil
temperatures to increase in these plots and not in the non-fenced. The tall shrubs are,
however, not more abundant in the warmer plots here which means that it is most likely not
the vegetation that affects the snow cover in this particular site. During the summer (figure
16) plot 2 and 1 are the warmest plots according to soil temperature and these two had the
largest cover of low shrubs according to the vegetation cover data collected 2011. When
looking at how much the low shrubs increased in Fulufjället between 1995 and 2011 (figure
18), it is clear that the two plots with the highest annual soil temperature had the largest
increase. These two are also amongst the three fenced plots. The increases of graminoids in
Fulufjället have also been largest in the three fenced plots that are also the plots with the
warmest annual soil temperatures (figure 20). During summer (figure 22), two of the fenced
plots with the highest soil temperature have, again, seen the largest increase of graminoids.
Could the increases of low shrubs and graminoids in the fenced plots Fulufjället be an effect
from a thicker snow cover caused by the fences that in turn causes higher soil temperatures?
In Långfjället, the effect of fences working as snow traps where not as obvious in Fulufjället.
In Långfjället it is possible, but not certain, that plot 5 had thicker snow cover, as explained
before. This is visible in figure 15. Here, it is also plot 5 that had the largest cover of tall
shrubs. However, it is more likely that plots 5 stands out here due to the fence or the accuracy
of the measuring device than due to cover of tall shrubs. The interaction between snow cover
and vegetation is interesting and should be further investigated in these areas. If, for example,
the fences in Fulufjället have caused the snow cover to thicken during a majority of the 16
year of recorded vegetation change in this study, an interaction between snow cover and low
shrubs and graminoids may be possible. A question, however, arises; if low shrubs and
graminoids have seen larger increases in fenced plots, may it depend on herbivore grazing?
Most likely not since Långfjället is frequently visited by reindeer and no trend is seen here. In
Fulufjället visitation by reindeer are rarer.
42
According to Mattson (1979), vegetation can contribute in changing microclimate in the air
temperatures as mentioned earlier. However, in Fulufjället and Långfjället, the microclimatic
differences between the air temperatures in the plots during summer showed no connection to
the cover of taller vegetation such as low shrubs. Lichens did, however, decrease in nine of
the twelve plots (figure 8 and 9) and since low shrubs increased substantially in some of the
plots where lichens decreased, it can mean that the microclimate around the lichens has been
affected if the ambient composition of low shrubs has changed during the 16 years. If the
lichens decreased due to a shading effect it can indeed mean that air temperature in
microclimate is affected by vegetation in some extent. If the air temperature Tinytags were
calibrated more accurately it is possible that an interaction between vegetation and
microclimate would have been observed.
The problem caused by accuracy of air temperature devices makes the soil temperatures the
most representative of the microclimates throughout the study.
Why climate driven shrub expansion shows large regional variations in response to a climate
warming, as Elmendorf et al. (2012a) concluded, depends on something else than the
microclimates even if Elmendorf et al. (2012a) found that shrubs increased where the ambient
temperature was already high. Even if soil temperature may affect the expansion of
graminoids, it is possible that multiple factors are influencing the shrub expansion in the
tundras at the same time, not soil temperature alone. In further studies, however, snow depth
should be included since this study showed that the depth of snow cover most likely affects
soil temperature, which in turn may have effects on some plant functional types. When
conducting microclimatic studies in which microclimates located close to one another is
compared, it is also recommended that the measuring devices is calibrated so that the range of
the accuracy is not as large as is has been in this study. Then maybe, an interaction between
microclimate and vegetation would be prominent. Also, if devices are calibrated very
carefully and accurately it is also recommended that the insolation protection on the air
temperature devices is being placed in the exact same way in all locations so that all devices
have the exact same conditions prevailing in affecting the air temperature. Since Eriksson et
al. (2007) writes that humidity is of importance during the growing season, a microclimatic
study where humidity is included may also help bring more knowledge to the subject of
matter.
43
7. Conclusions
There are differences in microclimates (plot air temperature) of the plots and the local climate
measured at the sites. There are also differences between the microclimates (both air- and soil
temperatures) in each site. What causes the differences during the summer is most likely the
measurement accuracy of the air temperature. During the winter months, there is a large
possibility that the temperature differences are controlled by snow cover. It is not the
microclimate itself that is controlling the shrub expansion. However, it is possible that the soil
temperature during the warmest months of the year is having an influence of the expansion of
graminoids which seem to increase with an increase of soil temperature. It is also possible that
a thicker snow cover may enhance expansion of some plant functional types since a thicker
snow cover can cause increases in soil temperatures. The most representative microclimate
measuring method for this study is soil temperature. The soil temperature measurements are
more reliable and it is only soil temperature that showed connections between some
vegetation changes and the hypothesis of the study. In Fulufjället and Långfjället, grazing by
herbivores has neither affected the microclimates nor the vegetation changes.
44
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