| dc.description.abstract | High-mountain areas are hotspots of biodiversity and provide critical ecosystem services. These high-mountain areas are very sensitive to climate change. This causes temperature rise and strong changes
in precipitation patterns, which leads to glacier retreat and snow cover reduction. Another
consequence of climate change is greening, which is an increase in productivity of vegetation. This
causes enhanced growth and spreading of vegetation. Besides the climatic conditions, greening
depends on interactions between soil, vegetation and topography. This research aims to improve the
insights in the relationships between soil, vegetation and topography in an alpine environment.
Data was collected on a field research in the Meretschibach catchment in Valais, Switzerland. Five
different vegetation classes (bare, pioneer, grass, shrub and forest) were defined previously, from which
42 locations were randomly selected based on spectral characteristics using NDVI images. At these 42
locations plots of 2x2 m were installed. In these plots, various measurements of the surface cover,
topography and soil characteristics were executed. Also, soil samples were collected, which were used
to derive additional soil characteristics using experiments in the laboratory. To find out whether there
are relationships between the measured soil, vegetation and topographic parameters a statistical
analysis was executed, which consist of a correlation, boxplot, cluster, PCA and NMDS analysis. In the
PCA and NMDS ordinations, the topographic and surface cover parameters were plotted passively as
explanatory variables and the soil parameters as response variables.
One of the main findings is that the predefined vegetation classes are no good predictor for the soil
characteristics. However, the correlation and boxplot analyses show that several soil characteristics can
be related to vegetation. Moreover, vegetation cover has a large explanatory power for the variance in
the soil parameters. This is also the case for rock cover, which has a negative association with vegetation
cover.
From the different topographic parameters (elevation, slope angle, aspect and slope form), only
elevation has a strong explanatory power on the variance of the soil data. This is mainly caused by
climatic conditions which vary with elevation. Generally, slope angle and aspect cause an mosaic of
microclimates that result in a strong variation in soil characteristics. However, the outcomes of the
statistical analysis did not show the impacts of slope angle and aspect. The elevation dependent
climatic conditions influence plant growth and consequently, several soil characteristics like the organic
matter content and the soil depth. Besides, the soil microbial activity depends soil temperature and
moisture, which is also influenced by the elevation dependent climatic conditions. This controls the soil
nutrient cycle and therefore, the soil development. All together, they cause elevation to have a large
explanatory power on the variance in soil data.
It is expected that greening will intensify in the Meretschibach catchment due to climate change.
Upward migration of vegetation is likely to occur at locations where the snow cover duration shrinks
due to climate change. Furthermore, stable soils that are relatively developed are the most favorable
conditions for plant colonization. Greening causes increased evapotranspiration rates in the catchment.
Therefore, decreased precipitation together with increased evapotranspiration during summer in the
future, will cause a reduction in runoff from the catchment. This may result in browning, which is a
decrease in productivity of vegetation. Greening is also beneficial for increasing soil depth and the
water holding capacity of soils. Consequently, it will reduce the runoff from the catchment and
therefore, gr | |
