FACULTY OF HEALTH AND OCCUPATIONAL STUDIES
Department of Occupational and Public Health Sciences
BROWSING DAMAGE BY MOOSE IN SWEDISH BOREAL FOREST
María Sánchez Luque
2017/2018
Examensarbete i biologi ,G2E,15 hp Biologi
Program
Supervisor: Lars Hillström Examiner: Mikael Lönn
ABSTRACT
The browsing damage by moose (Alces alces) is an actual and real problem that is happening in Swedish boreal forests nowadays. The browsing can be done for different types of cervids like roe deer, moose and goats, but we will focus on the browsing damage by moose because it is the main browser on pine stand and is causing the biggest problem in Sweden due to the high moose population that currently exist. The moose is the biggest species in the deer family and one of the most spread species in Sweden. We performed our study in fifteen plantation areas of Scots pines (Pinus sylvestris) in Gävleborg county, Sweden. Some of these plantations have a natural origin, whereas others have been created by human. The increase of browsing damage by moose have several consequences including effects on the ecological community and huge economic consequences, as the forest companies are losing, billions of Swedish crowns per year because of the browsing damage on the pine trees. The aim of this study was to investigate how the browsing damage by moose on Scots Pines varies depending on the density of the different deciduous tree species. Some of the most important results that I obtained were a negative relation between the number of deciduous trees and the browsing damage in Scots pine, the positive relation between the number of damaged deciduous trees very close to the Scots pine studied and the browsing damage in Scots pine and finally, the positive relation between the old browsing damage and new browsing damage in Scot pine. In general, I can conclude that when the number of deciduous trees increases in an area, the browsing damage in Scot pine decreases.
RESUMEN
El impacto del ramoneo del alce (Alces alces) es un problema real que está sucediendo en los bosques boreales Suecos hoy en día. El ramoneo puede ser provocado por diferentes tipos de cérvidos como el corzo, alce, cabras, sin embargo en este estudio nos hemos centrado en el impacto del ramoneo del alce ya que es el principal problema en Suecia debido a la alta población de alces existente. El alce es la mayor especie de la familia Cervidae (de los cérvidos) y es una de las especies más extendidas en Suecia.
Nosotros hemos llevado a cabo nuestro estudio en 15 áreas de replantación de pinos silvestres (Pinus sylvestris) in el condado de Gävleborg. Algunas de estas
replantaciones tienen origen natural y otras han sido creadas por el hombre. El
incremento del impacto del ramoneo por el alce tiene varias consecuencias incluyendo efectos en la comunidad ecológica y enormes consecuencias económicas para por ejemplo las empresas forestales la cuales pierden billones de coronas suecas por año a causa del impacto del ramoneo en pinos. El objetivo de este estudio fue investigar como el impacto del ramoneo del alce en Pinos silvestres varía dependiendo de la cantidad de diferentes especies de árboles de hoja caduca. Algunos de los más importantes
resultados que obtuve fueron, la relación negativa entre el número de árboles de hoja caduca y el impacto del ramoneo en el pino silvestre, la relación positiva entre el número de árboles de hoja caduca dañados situados muy cerca del pino silvestre
estudiado y el impacto del ramoneo en el pino silvestre y por último, la relación positiva
entre el impacto del ramoneo viejo y el impacto del ramoneo nuevo del alce en el pino silvestre. En general, puedo concluir que el incremento de árboles de hoja caduca en un área produce un descenso del impacto del ramoneo del alce en el pino silvestre.
PREFACE
I would like to dedicate a few words to all the people who have been with me and have supported me at all times in the realization of this study. I chose Gävle as an Erasmus destination since it seemed like a great place to improve and expand my knowledge and to finish my last year of the biology degree.
First of all to thank my supervisor of this study and professor of other subjects, Lars Hillström for introducing us, increasing our interest in the world of biology and helping us to carry out this study, from sampling plantings with us to teaching us theoretical concepts for our study.
Secondly, to thank our examinator Mikael Lönn, also professor of other subjects for helping us and teaching us theoretical concepts that have allowed us to complete this study.
Finally, I would like to dedicate a few words to my family, who has always supported me throughout my study period and helped me through the most difficult times and to my other Erasmus family, for their support and for making this Erasmus an unforgettable experience.
INDEX
1. Introduction
1.1 Background
Moose (Alces alces) - Description
- Biology -Habitat - Status
Browsing
Forest and forestry in Sweden - Forest conditions
- Wood utilisation in Sweden 1.2 Aims and objectives
2. Materials and Methods 3. Results
4. Discussion and Conclusion 5. References
6. Supplements
1. INTRODUCTION
The moose (Alces alces) is the biggest species in the family Cervidae in Sweden.
The moose population has increased since the beginning of 20th century but the highest increase was from the 1960s to the 1980s and the forest damage increased at the same time, above all, in pine regenerations (Hörnberg, 2001). However, since 1980s, the population of moose has decreased a lot. In Sweden, currently, the moose population contains around 400,000 individuals before the hunting season, but as around100,000 of the population are shot during the hunting season, the population during winter
contains around 300,000 mooses. Normally, around 100,000 calves are born in the spring, and the moose population in Sweden is the most dense moose population in the world.
This high moose population size in Sweden can be explained by a number of factors such as the loss of natural predators like the Wolf (Canis Lupus), or Bears (Ursus arctos), or the increased availability of alternative food resources (non-forest) and population management strategies (Herfindal et al., 2015). This growth of the moose population has important consequences for the Swedish forest, on the one hand, for the nature because different factors like plant growth and survival, succession trajectories, soil properties, nutrient cycles, habitat suitability of landscapes for animal species can be modified (Persson, Danell and Bergstrom, 2000) and on the other hand, for the economy because this problem affect to the forest industry, specifically to the quality and quantity of wood that is used by the forest industry.
In winter, moose mainly feed on woody plants. They are browsing on different deciduous trees, like rowan, aspen, willows, birch, and on Scot pines. They don't seem to forage on Norway Spruce (Picea abies), as it has been shown in a lot of studies that hardly any sampled Norway Spruce has shown signs of browsing damage (Bergqvist, Bergström and Wallgren, 2014) The Birch species (Betula spp.) and Scots pine are of a great economic importance for the Swedish forest industry to produce the timber that it needs. One of the big problems of the moose browsing damage is that it affects the Scots pines plantations which are intended for future industrial purposes. (Bergqvist, Bergström and Wallgren, 2014). The browsing by herbivores on Scots pine and deciduous trees can be divided into two categories: browsing that affect the quality of the butt log (browsing of the apical leader and breaking or bark stripping of the trunk) and browsing that affect the growth, but not the quality of the but log (browsing lateral shoots).The moose density and therefore its damage levels, can vary a lot depending on the studied areas of Sweden (Hörnberg, 2001).
The aim of this study was to investigate how the browsing in Scots pines varies depending on different variables, such as the deciduous trees abundance in the area, the level of browsing damage in these deciduous trees, the abundance of Scots pines, the number of moose pellets. Based on this background from earlier studies, I wanted to test some hypotheses that I could contrast in the study on observation of the sampled areas. I wanted to test the browsing damage in relation to:
a) Number of moose pellets to measure the moose activity in the plantations.
b) Number of deciduous trees at one meter distance from the pine tree to measure how the abundance of different trees around the Scots pine studied affect to the browsing damage level of the Scots pine studied.
c) The number of deciduous trees very close to the Scots pine studied to prove if a high abundance of trees very close to the Scots pine studied was an obstacle or an attraction for the moose to the Scots pine studied.
d) Browsing damage of deciduous trees very close to the Scots pine studied to check how varied the browsing damage level in the Scots pine studied according to the
browsing damage level in deciduous trees very close to the Scots pine studied.
e) Stripping level on the Scots pine studied to check if it is related to old or new browsing damage of the Scots pine studied.
1.1 BACKGROUND
MOOSE (Alces alces)
- Description
The moose (Alces alces) belongs to the class Mammalia, order Cetartiodactyla, family Cervidae and genus Alces. It has a heavy body with humped shoulders, long legs, short tail and wide hooves, which aid in walking over mud or snow.
The male moose is larger than the female and they have antlers that are shed each winter and re-grown throughout the summer and autumn.
The color of its coat ranges from blackish to reddish brown and, it has lighter under parts and lower legs. The coat, which is shed in spring, gives a really good insulation and consists of a fine wool undercoat with long guards hair.
- Biology
The moose can be active both during day and night, but it is more active at dawn and dusk. The moose is a browser and through its foraging behavior can alter the structure and dynamics of forest ecosystems because it's an animal that feed on large amounts of plants tissue to meet their energy requirements every day (Persson, Danell and Bergstrom, 2000)
The moose diet includes various trees (pine trees, deciduous trees ...) , shrub and herb species, twigs and bark in winter. Moose feed on aquatic vegetation too and they can lick mineral to obtain a supplementation of sodium.
The moose is normally solitary, although you can see small groups during the winter. The mating season is from September to October and births occur between May and June.
- Habitat
The moose prefers to live in the boreal forest, in the openings, lakes, swamps and wetlands. They are normally in forest composed by spruce, fir and pines, and they can also be in tundra and mountains, areas with seasonal snow cover.
-Status
The moose is a species of Least Concern (LC) according to the IUCN Red List
BROSWSING
The definition of browsing is when a herbivore feed on leaves, shoots, fruits of high-growing of woody plant like shrubs, pine trees, deciduous trees etc, that is, mainly non-grass plants. The browsing is mainly done by different types of cervids, like roe deer, moose and goats in some places (Apollonio et al, 2010) . However in the thesis, I will focus on the browsing damage by moose. The difference between browsing and grazing is that the browsers tend to eat leaves, bark, green stems from plants whereas grazers eat the vegetation at or near ground level. The browsers has an advantage concerning grazers because they can eat plants when the vegetation on the ground is covered by snow, although they sometimes have difficulties to reach some plants when the height make them inaccessible. Browsers often eat parts of the vegetation that are low in nutrients in contrast to the grazers, because when the grasses are accessible, they are more nutrient-rich.
FORESTS AND FORESTRY IN SWEDEN
Forestry is very important for the Swedish economy. Sweden provides ten percent of the sawn timber, pulp and paper that is traded on the global market. Forest and forestry are important for the climate change mitigation because Swedish forests have high productivity and low amount of natural disturbances. These characteristics allow high transfer of biomass from the forests through the removal of emissions of some products like steel, concrete and from fossil fuel. Swedish forests have been used by humans for a long time. The arable farming cleared the forest land; a lot of areas were requested for shifting cultivation, and forest grazing increased. Swedish forests were a source of wood for fuel, timber and it was used as hunting grounds. These forests were also used for other reasons, like to production of charcoal, tar and potash (Helmfrid, 1991).
During the 18th and 19th centuries, a lot of forests were over-exploited for farming, housing construction, wood for fuel, charcoal for the iron industry and later like a source of logs for timber and pulping. The first Forestry Act was passed in 1903, which required owners to replant after harvesting (Bernes, 2011).
- Forest conditions
The Swedish landscape is characterized by lakes, wetland areas and shallow and nutrient-deficient soils. There are eight vegetation zones in Sweden: Arctic alpine, Alpine, North Boreal, Boreal, North-South Boreal, South Boreal, Boreo-Nemoral and Nemoral zones. The boreal zone and its sub-zones cover the major part of the land area and the most common trees are coniferous trees. Our study has been performed in Gävleborg county so, it's between the South Boreal and the Boreo-Nemoral zone.
The volume of different tree species in Sweden is represented by: Norway Spruce (40%), Scots pine (38%), Birch (12%), and other deciduous species (6%), Dead trees (3%) and Pinus contorta (1%). The total land area used is mostly: Productive forest land (57%), other land (15%), Unproductive forest land ( 12%), Agricultural land (7%), Other wooded land (6%) and Buildings, roads (3%).
- Wood utilization in Sweden
The wood that the forest industry use and is obtained from the Swedish forest can be divided according its destiny in wood that goes to the sawmill, the pulp mills or firewood, poles etc and constitute 45%, 45% and 10% respectively. The logs are
combined with bark, while crowns and branches are extracted from the forest like forest fuel and they are used for energy generation. The wood chips produced from the sawlog go to the pulp industry.
1.2 AIMS AND OBJECTIVES
The aim of this study was to analyze how the browsing damage on pine trees varies depending on the quantity of different types of trees, like deciduous trees and pine trees (i.e. Norway Spruce) in the plantation areas that I have studied.
2. MATERIALS AND METHODS
In this study, I have sampled plots that are situated in the Gävleborg County (Supplementary,. Figures 1,2,3)
I started the project in January of 2018 and I finished in June of 2018. I started in January looking for the plantations areas that I had to study later in May and June and I found around 15 interesting areas. The areas was selected beginning in January when there was a lot of snow and I could get a picture about how the moose was moving around in the plots, as could be inferred from the tracks by moose in the snow. I was studying these areas from the last week of May and the first weeks of June.
The areas that I have studied are Scots pine plantations. I distinguished the plantations in "human plantations" and "natural plantations". I made the distinction between "human plantations" and "natural plantations" for some different factors like the distribution of Scots pines in the area, the abundance and distribution of other types of trees (deciduous trees, Norway Spruce...) in the area, the topography of the area (i.e.
if the area is stony or not). I called some plantations "human plantations" because of the specific and regular distribution of the Scots pines in the plantations and because there was low quantity of deciduous trees in the plantation. However, I called some
plantations "natural plantations" because the distribution of the Scots pines in the plantation was much more irregular and there was more quantity of other types of trees like deciduous trees.
The study performed in each plot was done with the following method. First, I decided to sample four sub-plots in each plantation. The structure of the sub-plot was circular and it had a radius of around three meters. In the centre of the plot was the Scots pine that was the focus of the study. The subplots were chosen randomly in order to get a random sample of sub-plots and an objective sample for each plot and that should constitute a represented sample of the whole plot. In each plot, the four sub-plots were chosen randomly, such that after the first plot, (chosen randomly when we entered each plot), the next sub-plot was chosen after a walk in a random direction of 50 meters, where I started to record in the second sub-plot, and after this subplot was finished, I took a new random direction and walked 50 meters to the next sub-plot, etc until I had four sub-plots in each plot. To get a measure of this distance, I measured the 50 meters with a meter band, and got a measure how many steps was need for
approaching this length with normal steps in the field, thus, I repeated this procedure four times to get four sub-plots in each plot. A few times, after I have been walking 50 meters, I didn't arrive to any Scots pine in relation to my arrived position in the plot. In the case there were several Scots pines around me, I chose one randomly of the different Scots pines.
To measure the browsing damage level in each Scots pine, I first delimited the height of the tree that I wanted to study. I decided to measure from the knees height until three internodes up the pine tree. Thereafter, I counted the total number of branches on these three internodes, and recorded the number of branches with old-browsing damage, the number of branches with new browsing damage and the branches that didn't have any browsing damage at all. In a few cases one branch had both new and old browsing damage. Then, I checked for bark stripping or broken apical shoot. Another interesting variable that was recorded was if the studied tree was
growing with other trees very close to it, as this could imply an obstacle for the moose when it tries to eat on the studied Scots pine.
After this procedure, I tried to measure the quantity of other species that there was in a circle of one meter around the studied Scots pine. To record this latter variable, the following two methods were used: In the beginning of this study, I was choosing four small sub-plots in perpendicular direction to the studied tree and I identified and counted the number of species that I found as you can see in the figure 1.
Later in the project, I identified and counted the number of species in one meter around the studied tree. You can see how I made this measure in the figure 2.
In both cases, of the above mentioned methods, I took notes about if these species had old or new browsing damage, or nothing and sometimes notes about the level of this browsing damage.
I counted the number of pellet groups that I found in the big plot too. I spent around two minutes, and I was trying to find fecal pellets in the big plots.
After the field measures, I analyzed the data with the statistical program called
"R". In the analysis, I used in some cases "linear model" and in another cases,
"generalized linear models (GLMs)" depending on the response variable. In my case I have used GLM when the response variable was a binary response (Crawley, 2005).
After this procedure, I made a variance analysis with the hypothesis of testing with a
"One-way Anova" and to compute if there was any significance variance value between the variables that I was studying. I made a graph with the option "effect graphics" and I obtained a graph through I could see how relation between the variables that I was studying varied, for instance if these variables had a positive or negative relation or which was the tendency of the graphic.
Figure 1. The big circle is the complete sub-plot. The black point in the middle is the studied Scot pine and the four black circles represent the small plots. The distance between the small plot and the studied Scot pine was around 1m.
Figure 2. The big black circle represents the complete plot.
The black point in the middle of the big plot is the studied Scot pine. The edge of the inner small circle, is where we measured the other species of trees. The small circle has a radius of one meter.
Some figures have been made in an program called "Excel", for instance the figure where I represented how the number of damaged and undamaged deciduous trees varied in the different plots.
3. RESULTS
Studied areas in the Gävleborg county illustrated in figure 1.
Figure 1. Map where we can see the distribution of different plots that we have studied in the Gävleborg county.
Relation between the total number of trees with browsing damage and the total number of trees without damage in the different areas that I have studied illustrated in figure 2.
Figure 2. The total number of damaged and undamaged deciduous trees in the different plots that have been studied. Blue color= number of damaged deciduous trees; Red color= number of undamaged deciduous trees.
The significance values that I have obtained relating different variables to browsing damage in Scots pines illustrated in table 3.
Table 3. These two tables show the significance values that I obtained relating different variables to browsing damage in Scots pines. (TBDSP: total browsing damage in Scots Pine; NBDSP: new browsing damage in Scots Pine; OBDSP: Old browsing damage in Scots Pine; BD: browsing damage; NBD: new browsing damage; S. pine: Scots pine; OBD: old browsing damage; Nº : number)
Total number deciduous
Total damaged deciduous
North-East New and old BD in deciduous Trees
New and old BD in S. pine and Birch
NBD in S.
pines
Name
TBDSP - 0.04544 +0.01175 East: +0.00002869 North: +0.007646
<0.001 S. Pine:
+0.0000974 Birch: +0.004068
- <0.001
NBDSP - East: + 0.04571
North: +0.002284
- S.Pine: +0.0003421 + 0.002569
OBDSP - East: + 0.000427 - S. pine (0.019844)
Birch (0.001162) -
Nº deciduous trees at 1m
OBD in S.
Pine
Nº pellets Nº damaged deciduous trees very close
Nº undamaged and damaged deciduous trees very close
Bark stripping
Total new and old damage on deciduous at 1m TBDSP Birch:
-0.0294
- - + 0.03441 - +0.04762
NBDSP Birch:
-0.001262
+ 0.02891 +0.0005718 - Birch
undamaged:
-0.03669
+0.02717
OBDSP - - - - -
After getting the previous table, where we see the significance values, I will comment if the relation that exist between the browsing damage on Scots pines and other variable is positive or negative. There was a significant negative association (p=0.04544) between total number of deciduous trees and browsing damage on Scots pines. Thus, when the number of deciduous trees increase, the browsing damage on Scots pines decrease (Figure 4,Table 14 (Supplementary material)).
Figure 4. The relation between the total number of deciduous trees and the total browsing damage on Scots pine.
The total browsing damage on Scots pine was significantly higher in plots situated more to the North and East ( P(East)= <0.001; P(North)= <0.001; P(East: North)=0.046) ( Figure 20, Table 21, supplementary material).
The browsing damage level in the different studied plots and I obtained a significance value of <0.001 (Figure 5, Table 13 (Supplementary material)).
Figure 5. The level of total browsing in Scots pine in different studied plots.
There was a positive association (p= 0.01175) between the browsing damage in Scots pine and the browsing damage in deciduous trees in 1 meter of the Scots pine studied. Thus, when the number of damaged deciduous trees increases, the browsing damage on Scots pine increases too (Figure 6, Table 44 (Supplementary material))
Figure 6. Relation between browsing damage on Scots pine and the number of damaged deciduous and pine trees in one meter
The association between the total number of browsing damaged deciduous trees and the browsing damage on Scots pines is positive (p= 0.03441). When the number of damaged deciduous trees located very close to the studied Scots pine increases, the browsing damage on Scots pines increases (Figure 7, Table 12 (Supplementary material)).
Figure 7. The relation between the browsing damage on Scots pine and the number of damaged deciduous trees very close to the studied Scots pine.
The new browsing damage on Scots pines increases when the level of new and old browsing damage in the deciduous trees to 1m increases (P<0.001). (see Figure 28, Table 29, supplementary material).
The old damage on Scots pines increases when the new and old damage increases on the Scots pines and Birches in 1 m (P= 0.019844 and P= 0.001162 respectively ( Figure 30, Table 31, Supplementary material).
The total browsing damage on Scots pines increases with new and old browsing damaged Scots pines and Birches that surround them (P<0.001 and P= 0.004068 respectively) (Figure 32, Table 33, Supplementary).
The new browsing damage on Scots pines increases when the Scots pines of the surroundings have new browsing damage (P= 0.002569) (Figure 34, Table 35,
Supplementary).
There is a relation between the browsing damage on Scots pine and the number of birches that surround it. The browsing damage on Scots pine decreases when the number of birches that surround it increases (P= 0.0012626) (Figure 36, Table 37, Supplementary).
The old browsing damage and the new browsing damage on Scots pines are related positively, when the old browsing damage increase, the new browsing damage increase too (P= 0.02891) (Figure 8, Table15 (Supplementary material)).
There was a significant positive relationship between the number of pellets and the new browsing damage on Scots pines such that when the number of pellets increase, the new browsing damage increase too (P= 0.0005718). (Supplementary, Figure 26, Table 27).
The browsing damage on Scots pines increases when the number of damaged deciduous trees very close to the Scots pine increases (P=0.03441) (Figure 49, Table 12, Supplementary material) and specifically, when the number of undamaged birches around the Scots pines increases, the browsing damage on Scots pine decreases (P= 0.03669) (Supplementary, Figure 40, Table 41).
4. DISCUSSION AND CONCLUSION
The new and old browsing damage varied in the different studied plots. The old browsing damage tends to decrease more than the new browsing damage
(Supplementary, Figures 22 and 24). The total browsing damage varied in the different plots (see figure 5).
The highest browsing damage was in the plot A, followed by the plot C and then the plot G. The lowest browsing damage was observed in the plots I and L (they have the same level more and less) followed by the plots H and M. The plots A,C,G and H are found in The North part of the study area, and the plots M, I and L are found in the south part of the study area.
Figure 8. The relation between the old damage and the new damage in Scots pine.
In general the browsing damage varied between the geographical coordinates, such that I obtained that the browsing damage increased in zones situated more to the North-East.
One of the reason that the level of browsing damage increased in zones more to the North could be that the amount and the time that the snow stays in areas more to the North is longer in the season than in more southern areas. The food availability of moose when the ground is covered by snow is based on woody plants like Scots pines, so it makes sense that they eat more amount of Scots pines in northern areas, where the snow is more permanent than in more southern areas, where they have a higher food availability early like deciduous trees. However, other more accurate measures such as measuring the abundance or the activity of moose in the northern and southern zones may be better to demonstrate the increase of browsing damage by moose in Northern zones because the distance between northern and southern zones could not be enough.
According to the first specific aim of the study, the level of new browsing damage should be correlated with the number of pellets (moose activity), was based on that browsing damage on Scots pine was produced by moose and not by other cervids. The browsing can be done for different types of cervids like roe deer, goat and moose (Apollonio et al. 2010).
My study showed that the browsing damage on Scots pine increased when the number of pellets increased. If the browsing damage on Scots pine increases when the number of pellets increase I can ensure that most browsing damage in pine is produce by moose and we can rule out other cervids like roe deer.
The second specific aim of this study was to investigate if the browsing damage on Scots pines decreased when the number of deciduous trees increased in the studied area.
The results from this study showed that the level of browsing damage on Scots pines decreased when the number of deciduous trees in the surroundings increased.
A prediction in this study was that the browsing damage on Scots pines should decrease when the number of deciduous trees increases, because when the moose find an area with more level of resources (more number of deciduous trees), they have more food availability and they will choose to forage on that type of trees, and more
specifically, on the more palatable of the trees. The deciduous trees are more palatable than pine trees for moose. However, if the moose find an area with only Scots pine, it will eat Scots pines. Härkonen, (2008) argued that in an area with high amount of resources, it allows the moose to cover longer distance and choose more specifically its food; the moose will eat higher percentage of the available biomass in an area with low amount of resources. In this way, when there is an area with more amount of resources (deciduous trees) for moose, they have more food availability and they will be more choosy on what type of trees to eat, it means, the more palatable for them, and on the other hand, if the moose find an area without much resources, only with Scots pine, it will eat Scots pines (Härkonen 2008). According to Andersen & Saether (1992), the moose will browse better trees quality ( better digestibility), when the availability of
browse increases. According to Härkonen (1998), an increased browsing pressure on preferred deciduous trees decreases the risk of browsing damage to pines. On the other hand, some experiments support that when there are a high availability of Scots pines in an area, the variety of trees species had a low effect on the browsing on Scots pine (Heikkie and Hhk, 1996).
One of the specific aims of this study was to see if, the browsing damage on Scots pines decreases when the browsing damage in deciduous trees increases.
This study demonstrated that the browsing damage on Scots pines decreased when the number of damaged deciduous trees increases. I divided the browsing damage in new, old and new and old damage and we obtained that the browsing damage on Scots pines increase when the new and old browsing damage increase in deciduous trees. The relation between the browsing damage in Scots pine and the number of damaged deciduous trees around one meter is positive too.
According to Heikkilä (1991), the browsing damage in Scots pine can increase in plantations where there is an admixture of preferred deciduous trees (Heikkilä, 1991).
One explanation for the increase of browsing damage on Scots pine when the damage in deciduous trees increases could be due to the high abundance of Scots pine in the studied area because when there is a high amount of Scots pines in an area, the tree species mixture hasn't a high on the moose browsing damage (Heikkilä and Härkönen, 1996).
My fourth specific objective was to investigate if the browsing damage on Scots pines decreased when they have deciduous trees very close around them. Thus, the hypothesis was that the browsing damage on Scots pines should decrease when the number of damaged deciduous trees very close to them increases.
However, the results from the present study showed that the total browsing damage on Scots pine increased when the number of damaged deciduous trees very close to the Scots pines increased and the browsing damage on Scot pines increased when the number of damaged deciduous trees increases around them. This was in opposite direction to the prediction, i.e.
That deciduous trees very close to the Scots pine could serve as a protection against moose browsing, thus this could not be confirmed in this study. One explanation for the increase in browsing damage on Scots pine when the total number of deciduous trees and especially, the number of damaged deciduous trees increases, may be that the moose is attracted to the deciduous trees, and will eat of these trees and also continue to eat on the Scots pine, because they can also forage on them, but still another explanation could be that the moose may return to forage on the Scots pine that they have been visiting previously, for example during the winter season, and on this second visit, they will prefer to forage on the deciduous trees. In fact, I have obtained that the old
browsing damage in Scots pine increase when the number of damaged deciduous trees very close to the Scots pine studied increases.
According to the fourth specific aim of this study, that the new browsing damage on Scots pines will increase when the level of old damage on Scots pine increases.
The results from this study showed that there was a positive correlation between new browsing damage on Scots pine and the old browsing damage on Scots pines.
One explanation for this positive correlation between old and new browsing damage on Scots pine is based on the moose rebrowsing (Mathisen, Milner and Skarpe, 2017). The rebrowsing occurs when the moose eat branches of a Scots pine and then returning when this tree has created more new branches and they will preferentially forage on this trees. According to Matinsen,(2017), when the amount of dominant meristem (they are in the leading shoots that are eaten by moose) decreases in a plant, the nutrient competition between the dominant meristem and apical meristem is reduced and the plant tries to produce more shoots at lower parts, it means in the heights where moose can eat the branches. And as a result, the synthesis of secondary metabolites will decrease. For these two reasons, these new branches are more palatable for browsers (moose) and they return to eat them. (Mathisen, Milner and Skarpe, 2017).
The fifth specific aim of this study was to study if the bark stripping varies with the browsing damage in Scots pine.
According to the results, of this study, the bark stripping increased with the increasing of old browsing damage in Scots pines.
According to Van Ballengerghe (1989) could be possible that the moose eat bark when the availability of browse is low, so this affirmation could explain the increase of bark stripping when the old browsing damage in Scots pine is higher because may be if a moose find a Scots pine with old damage it means that this tree has been eaten before but now it doesn't have any food for the moose, so the moose can eat the bark at least.
Suggestions for future researches, I propose some hypotheses that may be useful:
In one of the plantations of this study, there was also a territory of wolves. I didn't see any browsing damage in this area and I think it may be due to the existence of this population of wolves since the wolf is one of the moose predators, so the moose population can be lower in this area.
Another idea that I thought was that the moose may need to eat the needles of Scots pine because they can improve its digestion. The moose need a big amount of food to complete the energy requirements every day, so this food can be compacted in the stomach and these needles can contribute to remove this food compacted in the stomach and facilitate the digestion.
In conclusion, I have tried to study how the abundance of deciduous and pine trees in one area affects the level of browsing damage in Scots pines. I have obtained several interesting results like the decrease of browsing damage in Scots pine when the number of deciduous trees increases, the increase of browsing damage in Scots pines when there are damaged deciduous trees very close it and the increase of new browsing damage in Scots pine when the old browsing damage in Scots pine decreases. So, based on the results, I can conclude that the browsing in an area decreases when there are high
abundance of deciduous trees, especially birches according to the figure 4 and the table 13.
5. REFERENCES
https://www.skogsstyrelsen.se/globalassets/in-english/forests-and-forestry-in-
sweden_2015.pdf (The days that I used this webpage are 12/05/2018 and 10/05/2018).
http://www.animalbehavioronline.com/deerinsnow.html (The days that I used this webpage are 6/05/2018 and 10/05/2018)
https://www.swedishwood.com/about_wood/choosing-wood/from-log-to-plank/ (The day that I used this webpage is 29/05/2018)
Book: 'Statistic: An introduction using R'; Michael J. Crawley, 2005
https://www.wildsweden.com/about/the-wild-animals/facts-about-moose/
Bergqvist, G., Bergström, R. and Wallgren, M. (2014) ‘Recent browsing damage by moose on scots pine, birch and aspen in young commercial forests-effects of forage availability, moose population density and site productivity’, Silva Fennica, 48(1), pp.
1–13. doi: 10.14214/sf.1077.
Heikkie, R. and Hhk, S. (1996) ‘Moose browsing in young Scats pine stands in relation to forest management’, Management, 88(96).
Heikkilä, R. (1991) ‘Moose browsing in a Scots pine plantation mixed deciduous tree species’, Acta Forestalia Fennica, pp. 4–13.
Heikkilä, R. and Härkönen, S. (1996) ‘Moose browsing in young Scots pine stands in relation to forest management’, Forest Ecology and Management, 88(1–2), pp. 179–
186. doi: 10.1016/S0378-1127(96)03823-6.
Helmfrid, S. (1991) ‘Forests and forestry in Sweden’, GeoJournal, 24(4), p. 432. doi:
10.1007/BF00578267.
Herfindal, I. et al. (2015) ‘Associational relationships at multiple spatial scales affect forest damage by moose’, Forest Ecology and Management. Elsevier B.V., 348, pp. 97–
107. doi: 10.1016/j.foreco.2015.03.045.
Hörnberg, S. (2001) ‘Changes in population density of moose (Alces alces) and damage to forests in Sweden’, Forest Ecology and Management, 149(1–3), pp. 141–151. doi:
10.1016/S0378-1127(00)00551-X.
Mathisen, K. M., Milner, J. M. and Skarpe, C. (2017) ‘Moose-tree interactions:
Rebrowsing is common across tree species’, BMC Ecology. BioMed Central, 17(1), pp.
1–15. doi: 10.1186/s12898-017-0122-3.
Persson, I., Danell, K. and Bergstrom, R. (2000) ‘Disturbance by large herbivores in boreal forests with special reference to moose’, Annales Zoologici Fennici,
37(December), pp. 251–263. Available at: http://www.annzool.net/PDF/anzf37/anzf37- 251p.pdf.
Miquelle, D.G., Van Ballenberghe, V., 1989. Impact of bark stripping by moose on aspen-spruce communities. J. Wildl. Manage. 53, 577-586.
Andersen, R. and Saether, B.-E., 1992. Functional response during winter of a herbivore, the moose, in relation to age and size. Ecology, 73(2): 542-550.
R Core Team (2018). R: A language and environment for statistical
computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/.
6. SUPLEMENTARY MATERIAL
Location of differents plots that have been samples in Gäblevorg county:
- Sampled plots in Southern zone.
Figure 9. Distribution of the different studied plots sampled in the South of Gävle
- Sampled plots in Northern zone.
Figure 10. Distribution of the different plots sampled in the North of Gävle.
- Sampled plot in Northern zone
Figure 11. The furthest plot sampled to the North and other sampled plots closer to Gävle.
Table 12. Statistical values obtained from the relation between the total number of deciduous trees and the total browsing damage in Scots pine.
Table 13. This table shows the statistical results from the relation of total browsing damage and the different plots.
Table 14. Relation between browsing damage in Scots pine and total number of deciduous trees
Table 15. Statistical results from the relation between the new browsing damage and old browsing damage.
Figure 16. Relation between new browsing damage and the geographical coordinates.
Table 17. Statistical results from the relation between new browsing damage and the geographical coordinates.
Figure 18. Relation of the browsing damage in Scots pines and the geographical coordinates.
Table 19. Statistical results from the relation of the browsing damage in Scots pines and the geographical coordinates.
Figure 20. Relation of browsing damage in Scots pine and the geographical coordinates
Table 21. Statistical results from the relation of browsing damage in Scots pine with the geographical coordinates.
Name effect plot
Name
newprop
-0.2 0.0 0.2 0.4 0.6 0.8
A B C D E F G H I J K L M N O
+
Table 23. Statistical results from the level of the browsing damage in the different plots sampled.
Figure22. How the new browsing damage varies in the different plots sampled.
Figure 24. How the old browsing damage varies in the different plots sampled.
Table 25. Statistical results from the level of old browsing damage in the different plots sampled.
Figure 26. Relation between the number of pellets and the new browsing damage in Scots pine.
Table 27. Statistical results between the number of pellet and the new browsing damage in Scots pine.
Figure 28. Relation between the new browsing damage in Scots pine and the new and old browsing damage in deciduous trees and Scots pine located around the studied Scots pine.
Table 29. Statistical results from the relation between the new browsing damage in Scots pine and the new and old browsing damage in deciduous trees and Scot pine located around the studied Scots pine.
Figure 30. Relation between the old browsing damage in Scots pine and the new and old browsing damage in deciduous trees and Scot pine located around the studied Scots pine.
Table 31. Statistical results from the relation between the olds browsing damage in Scots pine and the new and old browsing damage in deciduous trees and Scots pine located around the studied Scots pine.
Figure 32. Relation between the browsing damage in Scots pine and the new and old browsing damage in deciduous trees and Scot pine located around the studied Scots pine.
Table 33. Statistical results from the relation between the browsing damage in Scots pine and the new and old browsing damage in deciduous trees and Scots pine located around the studied Scot pine.
Figure 34. Relation between the new browsing damage in Scots pine and the new browsing damage in Birch and Scots pine located around the studied Scots pine.
Table 35. Statistical results from the relation between the new browsing damage in Scots pine and the browsing damage in Birch and Scots pine located around the studied Scot pine.
Figure 36. Relation between the new browsing damage in Scot pine and the number of deciduous and pine trees.
Table 37. Statistical results from the relation between the new browsing damage in Scots pine and the number of deciduous and pine trees.
Figure 38. Relation between the browsing damage in Scots pine and the number of deciduous and pine trees.
Table 39. Statistical results from the relation between the browsing damage in Scots pine and the number of deciduous and pine trees.
Figure 40. Relation between the number of undamaged deciduous trees very close to the studied Scots pine and the new browsing damage in Scots pine.
Table 41. Statistical results from the relation between the number of undamaged deciduous trees very close to the studied Scots pine and the new browsing damage in Scots pine.
Figure 42. Relation between the old browsing damage in Scot pine and the new browsing damage in Scots pine.
Table 43. Statistical results from the relation between the new browsing damage in Scots pine with the old browsing damage in Scot pine.
Table 44. Statistical results from the relation between the browsing damage in Scots pine and the browsing damage in deciduous trees in one meter of the Scots pine studied.
Figure 45. Relation between the new and old browsing damage in deciduous trees and the browsing damage in Scots pines.
Figure 46. Statistical results from the relation between the new and old browsing damage in deciduous trees and the browsing damage in Scots pine.
1
Figure 47. Relation between damaged deciduous tree very close the Scot pine studied and browsing damage in Scots pine
Table 48. Statistical values from the relation between damaged deciduous trees very close to the Scots pine studied and browsing damage in Scots pine.
2
Figure 49. Relation between browsing damage in Scots pine and the number of damaged trees very close to the Scots pine studied.
