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Master Thesis
Vegetation dynamics after forest fire in comparison to the pre- fire state
Author(s): Temperli, Christian
Publication Date: 2007
Permanent Link: https://doi.org/10.3929/ethz-a-005517791
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Vegetation dynamics after forest fire in comparison to the pre-fire state Diploma thesis, department of environmental science ETH, Zürich, carried out at the Swiss Research Institute WSL
Christian Temperli December 2007
Reference: Co-reference:
Prof. Dr. Harald Bugmann Dr. Thomas Wohlgemuth ETH Zürich WSL Swiss Federal Research Institute Institut f. Terrestrische Ökosysteme Disturbance Ecology Universitätstrasse 16 Zürcherstr. 111 CH-8092 Zürich CH-8903 Birmensdorf Switzerland Switzerland
The regeneration of vegetation after the forest fire above Leuk, VS, Switzerland in 2003: Comparison to the pre-fire state and analyses with respect to climate, fire intensity and CWD.
Cover picture: Fire patch above Leuk, VS, Switzerland on August 1, 2007.
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Abstract
Christian Temperli (2007): Vegetation dynamics after forest fire in comparison to the pre-fire state. Diploma thesis, departement of Environmental Science ETH, Zürich.
A wild fire caused by arson destroyed in August 2003 300 ha of forest above the central alpine town of Leuk, Switzerland. The burned montane to sub-alpine forest ranged from 800 m.a.s.l. up to the timberline at 2100 m.a.s.l. at the south facing slope of the Valais main valley. As the succession processes along the large ecological gradient are of great interest in times of increased wild fire frequency they have been monitored since 2004. Additionally the local climate has been recorded by means of temperature and precipitation sensors installed in the fire patch. In line with this diploma thesis the vegetation data was compared to the pre-fire state and mainly analysed with respect to climate and fire intensity. Most species (re-)colonised the fire patch in the first two post-fire years. The highest species richness and vegetation covers were recorded at the most humid sites at high altitudes where temperatures and fire intensity were low. Until 2007 also the unfavourable hot and dry sites at lower altitudes where most of the soil was combusted by the fire were colonised by many species. The vegetation is still sparse at these sites though. The development of the species richness depends strongly on the scale in consideration. Whereas the species richness one year after the fire was surprisingly nearly as high as before the fire at a scale of 25 a it took four years to reach the pre-fire state on the small scale of 0.3 a. In the past two years high dominances of Epilobium angustifolium and Calamagrostis varia at higher altitudes and Conyza canadensi s and Rubus sp . at lower altitudes have developed. These species do not impede the regeneration of early colonising trees ( Populus tremula, Salix sp . and Betula pendula ). In contrary, the number of tree saplings found at the favourable sites at high altitudes was very high and regular succession climaxing in Norway spruce and Larch forest can be expected. Below 1200 m.a.s.l. the direction of the succession tends to Oak forest though.
Keywords: Biodiversity, forest, regeneration, climate, fire, Valais .
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Contents
ABSTRACT ...... 3 CONTENTS ...... 4 1. INTRODUCTION ...... 6 2. METHODS ...... 9
2.1. STUDY AREA ...... 9 2.1.1. Geography ...... 9 2.1.2. Climate ...... 10 2.1.3. Soils ...... 11 2.1.4. Vegetation ...... 11 2.1.5. Fire impact on soils and vegetation ...... 12 2.2. DATA COLLECTION ...... 13 2.2.1. Vegetation data ...... 13 2.2.2. Geographical data ...... 14 2.2.3. Climate data...... 15 2.3. DATA PREPARATION ...... 17 2.3.1. Vegetation data ...... 17 2.3.2. Climate data...... 19 2.4. DATA ANALYSIS ...... 21 2.4.1. Statistical methods ...... 21 2.4.2. Used measures ...... 21 3. RESULTS ...... 25
3.1. BIODIVERSITY ...... 25 3.2. HERB LAYER COVER ...... 26 3.3. HETEROGENEITY OF THE VEGETATION ...... 27 3.3.1. Patchiness ...... 27 3.3.2. Similarity within plots ...... 28 3.4. SPECIES COMPOSITION ...... 29 3.4.1. Similarity between post- and pre-burn species composition ...... 29 3.4.2. Ecological groups ...... 30 3.5. DOMINANT SPECIES ...... 35 3.5.1. Dominance-diversity relation ...... 35 3.5.2. Species richness and Epilobium angustifolium cover ...... 36 3.5.3. Effect of Epilobium angustifolium cover on the cover of other species ...... 37 3.5.4. Regeneration of trees and Epilobium angustifolium cover ...... 37 3.5.5. Species richness and Rubus sp. cover ...... 38 3.5.6. Effect of Rubus sp. cover on the cover of other species ...... 38 3.5.7. Tree regeneration and Rubus sp. cover...... 38 3.6. TREES BEFORE AND AFTER THE FIRE ...... 38 3.6.1. Tree layer before the fire in 1996 ...... 38 3.6.2. Tree regeneration ...... 39 3.7. ELEVATION ...... 42 3.7.1. Species richness ...... 42 3.7.2. Herb layer cover ...... 42 3.7.3. Tree regeneration ...... 43 3.8. CLIMATE ...... 44
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3.8.1. Climate model ...... 44 3.8.2. Thermal photography data ...... 45 3.8.3. Climate and species richness ...... 46 3.8.4. Climate and herb layer cover ...... 47 3.8.5. Climate and tree regeneration ...... 48 3.9. FIRE ...... 49 3.9.1. Fire and elevation ...... 49 3.9.2. Fire intensity and species richness ...... 49 3.9.3. Fire intensity and herb layer cover ...... 50 3.10. COARSE WOODY DEBRIS (CWD) ...... 51 4. DISCUSSION ...... 52
4.1. BIODIVERSITY ...... 52 4.1.1. Biodiversity before and after the fire ...... 52 4.1.2. Biodiversity and climate ...... 52 4.1.3. Biodiversity and fire intensity...... 52 4.2. VEGETATION COVER ...... 53 4.2.1. Developing of the herb layer cover from the pre-fire state to 2007 ...... 53 4.2.2. Vegetation cover and climate ...... 53 4.2.3. Vegetation cover and fire intensity ...... 54 4.2.4. Vegetation cover and height and CWD ...... 54 4.3. VEGETATION STRUCTURE AND SPECIES PROPAGATION ...... 55 4.4. SPECIES COMPOSITION ...... 55 4.5. DOMINANT SPECIES ...... 58 4.6. TREE REGENERATION ...... 59 4.6.1. Tree regeneration at different conditions ...... 59 4.6.2. Tree species ...... 59 4.7. REMARKS ON THE CLIMATE MODELS ...... 61 5. CONCLUSION ...... 63 6. ACKNOWLEDGMENTS ...... 64 7. REFERENCES ...... 65 APPENDIX...... A-1
A 1 SURVEY FORM ...... A-1 A 2 SITE INFORMATION OF PLOT LOCATIONS AND CLIMATE STATIONS ...... A-3 A 3 CORRECTIONS MADE TO SPECIES LIST AND RELEVÉS ...... A-5 A 4 NEW AND LOST SPECIES ...... A-9 A 5 SPECIES LISTS ...... A-12 A 6 TREE REGENERATION ...... A-20 A 7 CLIMATE MODEL GRAPHS AND R-OUTPUTS ...... A-21
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1. Introduction
In August 2003 a wildfire caused by arson destroyed 300 ha of forest above the central-alpine town of Leuk in the canton of Valais, Switzerland. The exceptionally hot and dry summer weather in 2003 did its part so that the fire could proceed from just above Leuk at an elevation of 800 m.a.s.l. up to the timberline at 2100 m.a.s.l. Out of the 800 wildfires in the canton of
Valais in the past 100 years this was by far the largest (GIMMI et al . 2004) and according to
SCHÖNENBERGER UND WASEM (1997) the occurrence of wildfires in Switzerland increased recently. The lower part of the burned forest protected the town of Leuk from rock slide. To maintain the stability of the bare slopes measures have been taken but still a great interest exists to know how and how fast the forest regenerates. The burned area ranges over an elevation of 1300 m and therefore includes the montane and sub-alpine vegetation zone. In 1995 and 1996 the forested area between the localities of Albinen, Leuk and Guttet which includes the area burned in 2003 was surveyed and floristically well documented by
GÖDICKEMEIER (1998). She described the original vegetation as a continuous gradient characterised by three larger units: Pine-forest (Pinus sylvestris ) between 1000 and 1550 m.a.s.l., spruce-forest (Picea abies ) ranging from 1400 to 1800 m.a.s.l. and open larch-forest
(Larix decidua ) from above 1800 m.a.s.l. up to the timberline. The re-colonisation of plants into the burned area proceeds differently depending on the elevation and the fire intensity
(WOHLGEMUTH et al. 2005). The further study of the regeneration processes could therefore provide results that can help to understand the fire ecology of a large part of the central Alps. For these reasons the Swiss Federal Institute for Forest Snow and Landscape Research (WSL) decided in 2004 to start the research project “Forest fires in the Valais” (“Waldbrand im Wallis”) as part of the research program “Forest dynamics”. Several subprojects to assess the regeneration from different points of view have been set up: A representative vegetation monitoring, an assessment of the invertebrate diversity, the fire impact on soil properties, a local climate model and the continuous surveillance by means of aerial photographs.
(WOHLGEMUTH et al . 2005) The aim of the project is the assessment of the speed of re- colonisation and the ecological resilience with respect to biological and environmental factors such as mycorrhiza infestation and climatic influences.
In 2004, one year after the fire, sparse but surprisingly diverse pioneer vegetation was documented by KÜTTEL (2004) in line with his diploma thesis. When SERENA (2005) was on the fire patch during the field work of her diploma thesis in 2005, the second year after the
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fire, the vegetation has exploded. The species richness even exceeded the pre-fire state on a large scale and the vegetation cover multiplied compared to the year before.
Also in the fourth year after the fire significant changes in the upcoming vegetation were expected. Therefore the stratified sampling plots defined by GÖDICKEMEIER (1998) have been surveyed again. To be able to explain developments by measured climatic environmental factors rather than proxy site factors such as elevation, aspect and slope as it has been done in the precious studies (KÜTTEL 2005 and SERENA 2005) the data of 12 climate stations installed on the fire patch in spring 2005 should be incorporated additionally. Except for that data on species and vegetation should be analysed by similar objectives as in 2005:
These are a) the development of the species composition, richness and abundance from the time before the fire until 2007 with respect to three plot scales. b) The species composition with regard to spatial variable climate, fire intensity and cover of burned trees and woody litter (CWD) and c) the regeneration of tree species over time and in respect to climate and CWD. Based on these objectives the following working-hypotheses have been set up:
• The biodiversity is higher in 2007 than in 2005 and it varies with climatic influences and fire intensity. I expect more species to have colonised the fire patch. As the fire intensity still affects the species diversity negatively and decreased with
altitude (WOHLGEMUTH et al. , 2005) the species richness increases with elevation. • The vegetation cover is denser than in 2005 and varies with climatic influences, fire intensity and CWD. Very hot and dry conditions impede the establishment of a dense herb layer. I expect the vegetation to be taller at sites of high CWD that seems to provide protection from strong wind, radiation and precipitation and therefore mitigates soil erosion. • At the small scale the vegetation became more heterogeneous (patchier) as more competitive species could supersede or overgrow other less competitive species. On a larger scale i.e. the whole study area a homogenisation of the species composition is expected as species have spread and re-colonised sparsely vegetated places like ridges and knolls. • The species composition changed compared to 2005. It is more similar to 1996 than it was in 2005. The species richness and cover of different ecological groups
(L ANDOLT 1991) will change compared to the previous years.
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• Dominant species influence the species richness and composition and the regeneration of trees. Dense Rubus sp . thickets grew larger and impede other species in general and the establishment of tree saplings in particular. In contrast high abundances of Epilobium angustifolium seem to facilitate the establishment of trees. • There are more tree saplings and root sprouts in 2007 than in 2005 and their distribution is determined by temperature, humidity and fire intensity. There are more recorded tree saplings of early colonising tree species ( Salix sp., Populus tremula, Betula pendula ) than in 2005 expected. Heat and low humidity prevents the regeneration of trees. Furthermore a shift from the former montane Pinus sylvestris -forest towards a forest consisting of Oak species ( Quercus sp. ) is expected.
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2. Methods
2.1. Study area
615000 616000 617000
58
55 71 57 ! ! <
80 ! 54 67 ! < 56 89 ! <
91 ! 53
104 ! 250 !!251 109 !
115 ! 257 !
131000 52 131000 51
! !!129 ! 262 107 ! 263 106 ! ! 138! 135 ! 139 147 ! 144 145 ! 148 ! 151 ! 49 ! !141 <269 ! 128 ! 50 152 !
272 !!273 ! ! 163 48 164 ! 150 < 47 277 !
130000 Legend 130000
615000 616000 617000 0250 500 1.000 ± Meters
Figure 1: Locations of the precipitation and temperature measuring climate stations and the survey plots defined by GÖDICKEMEIER (1998) on the forest fire patch above Leuk, VS (Reproduced with authorisation of Swisstopo: BA071737).
2.1.1. Geography
The forest fire patch is situated on the southern aspect slope of the east-west orientated Valais main valley. The study area is defined as the forested area that was burned above Leuk, VS, in 2003 (46°20’N, 7°39’E). The area comprises 300 ha of forest within the communities of Leuk, Guttet-Feschel and Albinen, VS, Switzerland (Figure 1). The 60 ha area designated as “Bannwald” in the lower part of the fire patch protected the community of Leuk from rock slide and avalanches. The area is laterally bordered by two ridges that most likely prevented the fire from spreading to the adjacent forest. The fire started below “Bannwald” above the 9
locality of Leuk Stadt at 800 m.a.s.l. and within several hours climbed up the channel like terrain to the timberline at 2100 m.a.s.l. The fire patch is accessible from several forestry and hiking tracks and the road from Thel to Albinen.
2.1.2. Climate
The climate at the valley bottom is characterised by high daily and annual temperature variations. Cold winters, hot summers, low precipitation and a distinct wind system are the main properties of the continental climate of the Valais valley at low elevations. With ascending altitude the continental climate fades to a typical high mountain climate of low mean annual temperatures and high precipitation (KIENAST 1985). The comparison of the climate graphs of the meteorological stations next to the study area illustrates this (Figure 2).
Figure 2: Climate graphs of Sierre and Leukerbad, VS (based on WERNER 1994, p 14).
The available precipitation and temperature measurements on the fire patch allow the following statements on the local climate:
45
40
35
30 Station 47 (1020 m.a.s.l) 25 Station 50 (1215 m.a.s.l)
20 Station 52 (1435 m.a.s.l)
15 Station 53 (1690 m.a.s.l) Precipitation [mm] Precipitation
10 Station 55 (1865 m.a.s.l) Station 58 (2085 m.a.s.l) 5
0 01.06.2005 08.06.2005 15.06.2005 22.06.2005 29.06.2005 06.07.2005 13.07.2005 20.07.2005 27.07.2005 03.08.2005 10.08.2005 17.08.2005 24.08.2005 31.08.2005 07.09.2005 14.09.2005 21.09.2005 28.09.2005
Figure 3: Daily precipitation measured from the 1.6.2005 to the 30.9.2005 at six climate stations set up along the elevation gradient in the fire patch. 10
In the period between Mai 2005 and April 2007 the hottest day on the fire patch was the 28.7.2005 with an average temperature of 26 °C at an elevation of 1020 m.a.s.l. and 18 °C at 2085 m.a.s.l. Ground temperatures around 50 °C have been measured throughout the whole study area though. The coldest day was on the 28.12.2005 when the daily mean at 1020 m.a.s.l was -8.5 °C and -17 °C at 2085 m.a.s.l. The precipitation sum in summer 2005 (June to September) at 1020 m.a.s.l. was 278 mm and 367 mm at an altitude of 2085 m.a.s.l.
35 Air temperature [°C] 35 Ground temperature [°C] 35 Soil temperature [°C] 30 30 30 25 25 25 Station 47 20 20 20 (1020m.a.s.l.) 15 15 15 Station 52 (1435m.a.s.l.) 10 10 10 Station 58 5 5 5 (2058m.a.s.l.) 0 0 0 01.06.2005 30.09.2005 01.06.2005 30.09.2005 01.06.2005 30.09.2005
Figure 4: Temperatures above ground (2 m), at surface (5 cm above ground) and in the soil (5 cm depth) during the vegetation period 2005 (1.6.2005 – 30.9.2005) on three altitudinal levels.
As displayed on Figure 4 the air, ground and soil temperatures show high daily variations. They are most distinct just above ground whereas the soil absorbs those fluctuations. The mean temperature on the fire patch during the vegetation period is 13.5 °C in the air, 15.5 °C at surface and 16 °C in the soil.
2.1.3. Soils
The bedrock in the study area is predominated by limestone (B URRI 1992) and at lower elevations Quaternary rock debris (GÖDICKEMEIER 1998) and moraine material (Tom Wohlgemuth, pers. comm.). The soils developed after the last ice age on carbonatic rocks. Before the burning between 900 and 1500 m.a.s.l. rendzina soils with the lime limit on the surface and therefore slightly alkaline topsoil were present. The spruce forest between approximately 1500 and 2000 m a.s.l. grew on cambisols topped by a slightly acidic humus layer. Near the timberline above 2000 m a.s.l. the cambisols were podsolised and the topsoil in the larch forest is acidic which only allowed the formation of a minor humus layer only
(GÖDICKEMEIER 1998 and WERNER 1994).
2.1.4. Vegetation
Before the fire the vegetation showed the typical characteristics of the montane (800 to 1500 m.a.s.l.) and the subalpine (1500 to 2200 m.a.s.l.) vegetation zones of the central part of the
Valais main valley as described in WERNER (1994) (Figure 5). Thus, at the very bottom of the 11
study area the colline oak fo rests merged in to the montane S cotch pine forest th at stretched to an approximate altitude of 1500 m.a.s.l. Norway s pruces and near the timberline E uropean larches formed then the subalpine forest. GÖDICKEMEIER (1998) structured the vegetation according to the dominating tree species and came to similar results. In summary, overlapping Scotch pine (Pinus sylvestris ), Norway spruce (Picea abies ) and E uropean larch ( Larix decidua ) forests formed a vegetational gradient ranging from 800 m.a.s.l. at the bottom of the study area up to the timberline .
Figure 5: Nord-south profile of the Valaisian Alps showing the theoretical altitudinal vegetation zones (Based on WERNER 1994, p. 27).
2.1.5. Fire impact on soils and vegetation
According to WOHLGEMUTH et al . (2005) the fire combusted 80% of the o rganic top soil. The mixture of remaining ash with mineral soil compartments raised the pH about 1.5 units. Nutritional elements essential for plant growth such as P, K, Mg, Ca, and N were oxidised by the fire and are now available for the upcoming vegetat ion (BERLI 1996). Furthermore chemical processes formed a hydrophobic top layer that promoted water runoff that in turn led to soil erosion.
Except for a few groups of trees mainly at the top of the study area the fire destroyed the whole tree layer. Most of t he burned trees still stand upright. In the lower part some tree s were felled perpendicular to the slope to prevent rock slide, avalanches and soil erosion . Mould attacked others (mainly Scotch pines) which were then felled by squalls though. The veget ation cover on the ashy soils was sparse one year after the fire. Nevertheless, t he total number of species at a scale of 25 a was surprisingly nearly as high as before the fire whereas at the small scale only half of the pre-fire species richness was reached. The species richness increased with elevation as it did in the original forest vegetation. KÜTTEL (2004) also found 12
the vegetation to be more similar to the pre-fire state at high elevations and explained it by the decreasing fire intensity in high altitudes. In the second year after the burning the species richness already exceeded the pre-fire state at a scale of 5 a. At lower altitudes the vegetation development in general and the tree regeneration in particular is thought to be influenced if not limited by drought and heat. The high fire intensity in the middle part of the fire patch between 1200 and 1600 m.a.s.l. is clearly visible in the vegetation development that lags behind strongly at these sites (SERENA 2005 and WOHLGEMUTH et al . 2005).
2.2. Data collection
2.2.1. Vegetation data
To be able to compare the data to the previous studies by SERENA (2005), KÜTTEL (2004) and
GÖDICKEMEIER (1998) the sampling design has been adapted.
2.2.1.1. Sampling design
GÖDICKEMEIER (1998) defined two sample designs. To be able to capture the full floristic range of her study area the whole ecological space had to be covered. To achieve this she applied a stratification method using the site parameters altitude, slope and aspect which have been calculated by means of a 25 m grid digital elevation model (SWISSTOPO ). The second sampling design was defined systematically and based on a 250 m grid. The coordinates were calculated based on the projected coordinate system Swiss Grid (CH1903+LV95).
In 2004, KÜTTEL surveyed the 53 samples located in the fire patch and marked them with a labelled T-profile bar for future surveyors. For analysis he eliminated 13 of these 53 sample plots (restricted sample) as they came to lie in unburned forest patches or edges, on the timberline or on tracks. According to KÜTTEL (2004) the fire did not affect the vegetation at these places enough so that it could be reckoned as a vegetational shift in comparison to the pre-fire vegetation. SERENA (2005) surveyed the plots of the restricted sample (n=40) and analyses in this study refer to this sample. The coordinates of the sampling sites are listed in the appendix (Table A 1). To reveal the relevance of the considered scale at each sample site, vegetation data on a sample plot was collected within concentric circles of 0.3, 2 and 5 a. In 1996 and 2004 an additional circle of 25 a was surveyed. As the cover and diversity of the vegetation has increased drastically in the past 3 years the workload would not have been manageable in the field season.
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2.2.1.2. Survey methods
Three concentric circles spanning areas of 0.3 a, 2 a and 5 a, respectively, were delineated at each sample site using 30 m measuring tapes and flags. The following parameters were recorded:
• The average height and the cover of the tree (was except for one living tree inexistent), shrub, and herb layer in meters and percentages of the observed area, respectively. The
tree layer is made up of trees (phanerophytes as in LAUBER and WAGNER 2001) with a minimum height of 5 m. The shrub layer consists of trees and shrubs (nano- phanerophytes) and woody chamaephytes with a maximum height of 0.5 to 5 m whereas the herb layer includes all herbaceous and gramineous species. Phanerophytes, nano-phanerophytes and woody chamaephytes less than 0.5 m in height contributed to the herb layer.
• The presence and cover of all vascular plants and ferns according to BRAUN -
BLANQUET (1964): Plants were determined to the level of sub- or semi-species using
the following literature: HESS et al . (1998), LAUBER and WAGNER (2001), EGGENBERG
and MÖHL (2007) and KRÜSI (2006). If determination was not possible the next higher
taxon was recorded. The nomenclature refers to Flora Helvetica by LAUBER and
WAGNER (2001)
• CWD as a percentage of the observed area.
• The number of tree saplings and root sprouts distinguishable into one of the following height classes: 0-20 cm, 20-50 cm, 50-100 cm, 100-150 cm and >150 cm.
All field data were collected between the 25.6.2007 and the 10.8.2007 by Christian Temperli and Nicklaus Hardegger.
2.2.2. Geographical data
The coordinates of the sample sites were adopted from GÖDICKEMEIER (1998). At each sample site aspect and slope were measured by KÜTTEL (2004) and incorporated in this study too. The coordinates of the climate stations (cf. chapter 2.2.3.1. Climate station) were defined by Ueli Wasem whereas aspect and slope were derived from coordinates by means of the ® digital elevation model DTM-AV (SWISSTOPO ) using ESRI ArcMap™ 9.2.
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2.2.3. Climate data
2.2.3.1. Climate station
In spring 2005 twelve climate stations were installed on the fire patch. As displayed on Figure 1 stations were placed at six elevation levels (two replications per level). On each level one is equipped with precipitation measuring instruments additionally to the digital iButton ® temperature data loggers. The iButtons ® of the type DS1922L, programmable sensors with a built in battery, suit very well for temperature measurements at a high number of different locations and over long time periods as they work automatically and are relatively cheap in ® acquisition as well. According to GEHRIG (2004) this type of iButton guaranties a measurement accuracy of 0.5 °C in a temperature range of -10 °C to 65 °C. The air temperature is measured in 2 m height underneath a shelter by two iButtons ®, the ground temperature 5 cm above ground by one iButton ® facing upwards and another facing downwards and the soil temperature is measured in 5 cm depth with one iButton ® (Figure 6 and Figure 7).The temperature and precipitation sums are recorded hourly.
Figure 6: Temperature and precipitation measuring Figure 7: iButtons® facing upwards (left) and station located in the fire patch above Leuk, VS (by G. downwards (right) measuring the ground Schneiter, 5.10.2005). temperatures in the fire patch above Leuk, VS (by G. Schneiter, 5.10.2005). 2.2.3.2. Thermal photography
On the 15.8.2007 Tom Wohlgemuth and Daniel Scherrer shot between 10 and 15h every minute one thermal photograph of the fire patch from the top of the opposite mountainside (Illhorn, 46°15’46”N, 7°36’58”O). The sky was cloudless during the whole day (Tom Wohlgemuth, pers. comm.).
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615000 616000 617000 The thermal photographs were geographically referenced using ESRI®
!! ! 132000 132000 ! ! ArcMap™ 9.2 (Figure 8). Landmarks like !
! ! road intersections, roofs, rocks and forest ! !! ! ! edges visible on an already geo-referenced !
131000 ! 131000 ! !!! ! aerial photograph of 2005 and on the ! ! ! ! ! ! ! ! ! ! ! ! ! ! 1:25:000 topographical map (SWISSTOPO ) !!! ! ! Legend ! ! Gödickemeier plot locations that could clearly be allocated to structures
130000 Fire patch 130000 Temperature [°C] High : 27,115 on the thermal photograph served as Low : 12,901 control points. Having selected 15 points 615000 616000 0617000250 500 1.000 ± Meters an automatic spline transformation was Figure 8: Geo-referenced thermal image shot from applied to the thermal photographs so that “Illhorn” by T. Wohlgemuth and D. Scherrer showing the ground temperatures of a large part of the fire pixels with temperature information fitted patch on the 15.8.2008 at 13.00h with a resolution of 7meters (Reproduced with authorisation of SWISSTOPO : to the underlying projected coordinate BA071737). system “Swiss Grid” (CH1903+LV95) with a resolution of approximately 7 m.
2.2.3.3. Available data
Table 1: Gaps in temperature time series. Listed are the For this thesis the hourly temperatures of affected stations (Figure 1) and data loggers: Air temperature (ATA, ATB), ground temperature iButton® all stations and data loggers from the facing upwards (GTU) and downwards (GTD) and soil temperature (ST). 21.5.2005 to the 30.4.2007 and daily
Station number/data No data available from precipitation records from the 21.5.2005 to logg er the: 51/ATA, ATB, GTU, GTD, 1.10.2005 – 4.10.2005 the 31.5.2006 have been available. The 60 51/GTDST 21.6.2006 – 30.4.2007 52/ST 22.6.2006 – 30.4.2007 (5 data loggers on twelve stations) 52/GTU 5.10.2005 – 30.4.2007 temperature and the six precipitation time 54/GTU 29.9.2005 – 30.4.2007 53/GTD 31.3.2007 – 30.4.2007 series were checked for gaps and measuring errors. Table 2: Time periods of lacking or implausible precipitation sums. The gaps in the temperature measurements Station number No data on the: are according to Gustav Schneiter (pers. 53, 55 31.12.2005 and 16.2.2006 comm.) due to yet unsolved technical 58 31.12.2005 – 19.2.2006 53 4.3.2006 – 21.3.2006 problems reading the data from the loggers 53 9.5.2006 – 11.5.2006 to the storage device (Table 1). 55, 58 4.3.2006 – 31.5.2006 16
The precipitation time series were compared in order to find time periods with lacking data and to check plausibility in precipitation sums (Table 2).
The measuring errors of the precipitation sensors concerned the top three stations above 1690 m.a.s.l. and occurred in wintertime. Due to snow pressure the precipitation collecting containers were damaged and the measurements were either stopped or falsified (Gustav Schneiter, pers. comm.). The presence of snow was also visible in the temperature time series during winter and spring. Ground and soil temperature loggers measured temperatures around 0 °C for days to weeks due to the insulating effect of snow cover.
After revision, temperature and precipitation time series were complete for all stations and data loggers from the beginning of the measurements till 29.9.2005. The air temperature was recorded at all stations for the whole measuring period except for a minor interruption of four days at station 51 (Table 1).
In addition, the ground temperatures covering the study area continuously were at hand. With respect to this spatial data, the south-eastern part, the tip in the very south and some rather large part in the North and West of the fire patch are excluded (Figure 8).
2.3. Data preparation
2.3.1. Vegetation data
2.3.1.1. Digitalisation and corrections
The field data available on paper forms (Figure A 1) were digitised and vegetation tables were created using VEG 4.12 1. For further processing the vegetation tables were exported to Microsoft ® Office Excel ® 2007. In a first step the original vegetation tables of 1996, 2004, 2005 and 2007 were joined. Then the list of species determined during the four survey periods was corrected: The determined taxa were brought to the same level. Taxa according to
WELTEN and SUTTER (1982, 1984) and WAGNER (1994) not present in the study area were replaced by a reasonable substitute. The list of species recorded on the fire patch by 2 WOHLGEMUTH et al. (based on the survey of 153 quadrates of 200 m from 2004 to 2006) served as reference. As the species list of the previous survey was available for each plot uncertainties with respect to doubtful determinations could be tracked down directly in the
1 Version 4.12, 5.9.2004, developed by Hans Märki, Märki Informatik (www.maerki.com). The software is free of charge in terms of the “GNU Gerneral Public License”, cf. www.gnu.org. 17
field. In a second step the four relevés of each plot were compared. Incompletely or doubtfully determined species were corrected.
Furthermore the species aggregates “ Salix appendiculata/caprea Grp. ” and “ Epilobium montanum/collinum Grp.” were defined and the “ Hieracium murorum Grp.” aggregate was adapted from GÖDICKEMEIER (1998). The following specifications explain the introduction of these aggregates:
Salix appendiculata/caprea Grp. was defined because GÖDICKEMEIER (1998) and KÜTTEL
(2004) determined Salix caprea throughout the study area; SERENA (2005), I and Nicklaus Hardegger (2007) determined most likely the same individual trees as Salix appendiculata ; S. caprea and S. appendiculata show the same morphological characteristics together with S. bicolor , S. Starkeana and S. laggeri which can be excluded from the study area geographically though (HESS et al. 1998, WELTEN and SUTTER 1982, 1984 and WAGNER , 1994).
Epilobium montanum/collinum Grp . was defined as Epilobium montanum and Epilobium collinum were not distinguishable with a satisfactory certainty.
Species of the genus Hieracium similar to Hieracium murorum were aggregated to
Hieracium murorum Grp . by GÖDICKEMEIER (1998). The affected species and the aggregation statements are listed in Table A 3 besides all corrections made to the original species lists.
The corrections of the individual relevés are listed in Table A 4.
After all revisions a final vegetation table uniting the 0.3, 2 and 5 a relevés of 1996, 2004, 2005 and 2007 served as basis for further vegetation analysis.
2.3.1.2. Ecological grouping
To analyse changes in species compositions plant species were allocated to ecological groups as used in the Red List of threatened ferns and flowering plants (LANDOLT 1991). This classification is rather rough as a lot of species populate a wide range of different ecological niches but should nevertheless be adequate enough to show the change in habitat characteristics formed by the fire and the subsequent succession process. Within this study neophytes, crop plants and plants that could not be determined to the species level were
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pooled to an additional group called “Others”. Group specific properties are described in
LANDOLT (1991) and SERENA (2005).
2.3.1.3. Cover transformations
Table 3: Transformation of the ordinal Braun-Blanquet As the cover of single plant species had cover values to percentages of the observed area. been estimated according to the ordinal Braun-Blanquet Percentage of the cover value observed area Braun-Blanquet scale the values were 0 0 r 0.05 transformed to the percentage of the + 0.5 observed area as shown in (Table 3). Those 1 3 percentages were used to calculate 2 15 3 37.5 abundances of individual species and the 4 62.5 cover of ecological groups. As a second 5 87.5 measure of the herb layer cover accumulated cover percentages of all species in the herb layer of an observed area were used (accumulated B-B.).
2.3.2. Climate data
Due to the limited data availability and due to the fact the growing season and therewith most climate sensitive season for plants being from April to October (WERNER 1994) temperature and precipitation data from the 1.6.2005 to the 30.9.2005 were used for further analysis. To this period of time it is referred as “vegetation period” in this thesis.
2.3.2.1. Bioclimatic parameters
The temperature time series of the vegetation period 2005 have been aggregated to a set of 28 parameters such as mean temperatures, degree sums, maxima, minima and number of heat hours (above 25 and 40 °C). The two air temperature measurements were averaged; same holds for the two ground temperature measurements of upwards and the downwards facing iButtons ®. An explorative procedure of correlating the parameters among each other and to elevation, aspect and slope was conducted to eliminate those of bad topography dependency and redundant information content. This resulted in a set of four temperature parameters presented in Table 4.
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Besides the precipitation sum of the vegetation period (P) the ratio of precipitation and potential evapotranspiration (P/PE) was used as a parameter for humidity: Following the instructions of THORNTHWAITE and MATHER (1957) PE was calculated from monthly air temperature means and geographical latitude for each station. BIGLER et al. (2006) used this rather simple measure in their study on drought effects on Scots pine ( Pinus sylvestris ) stands in the Valais, too, and found it appropriate even after comparison with more sophisticated measures.
Table 4: Bioclimatic parameters used for modeling.
Parameter Unit Mean air temperature of the vegetation period °C Mean ground temperature of the vegetation period °C Mean soil temperature of the vegetation period °C Number of hourly measures > 40°C Precipitation sum of the vegetation period mm Precipitation/potential evapotranspiration of the vegetation period (P/PE)
2.3.2.2. Climate models
In a first step regression models were calculated using elevation and aspect as predictors. The kind of relations of the climate parameters with the site parameters were evaluated by consulting scatter plots and searching for the best describing regression models whereas p- values and determination coefficients (R 2) served as quality criterion.
Secondly the climate parameters were spatially interpolated to the sample site locations using the calculated model formulas.
As spatially continuous temperature values of the study area were available a regression model with the temperatures of the five heat pictures as dependent and elevation and aspect determined by means of the digital elevation model DTM-AV as explanatory variables were calculated for improvement of the climate models based on the climate measuring stations. The spatially high resolution of temperature data were expected to allow a more accurate modelling of the temperature-aspect relation.
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2.4. Data analysis
2.4.1. Statistical methods
The used t-tests and linear regression model fits were computed using the language environment R version 2.5.1 2. All tests were conducted on the 95% confidence level ( α=0.05).
2.4.2. Used measures
2.4.2.1. Biodiversity
As a measure of biodiversity the species richness, Shannon’s diversity index and the evenness were applied. The species richness is defined as the number of species on a given area and Shannon’s diversity index and the evenness were calculated as follows:
Shannon’s diversity index: