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Introduction This study was performed in the Guisane Valley of The French Alps during May 2000. Current and past trends of agriculture in the Alps, provided the basis for this report. Alpine agriculture uses the method known as terracing which allows steep fertile slopes created by glacial processes to be levelled to a less steep angle for use in grazing or planting. These terraces of the Alpine slopes are covered or scattered by scree. Farmers remove the scree, piling it up at the perimeter of the terraced fields. These rock piles are the basis for the study. Stone pile without extensive succession
Aim of Study - To test the hypothesis by studying the rock piles and the succession which has occurred
on them, identifying the species, any patterns in their growth or zoning of specification, and also as an extension
looking at factors affecting these features, namely aspect, temperature etc. The site chosen for the study was a field close to Le Freyssinet on the North facing slope of the Guisane Valley, altitude 1420 metres, which had a large number of stone piles. The piles were obviously old and had evidence of the full range of stages during succession. It also seemed to demonstrate how aspect affects the growth on the rock piles, and so the site A preliminary inspection of the vegetation, the most important species, features and the place where these were
best seen at the site were noted.
Primary succession is the change of an area from a bare surface to a mature ecosystem. The Alpine Stone Piles are artificial features which have created a nucleus for a new primary succession. The stones create a bleak abiotic environment. Lichens are among the classical early colonists of rock in primary succession and it is these symbiotic stress tolerator organisms, the primary sere which pave the way for higher organisms such as flowering plants, so that an inorganic abiotic substrate can become a diverse climax community. In Alpine zones, grasses, sedges, herbaceous plants and dwarf shrubs thrive. The flowering plants have become adapted to their environment by creeping flat on the ground or in cushions, with roots often extending widely in shifting scree or permeating rock crevices (Huxley 1984). Water shortage, brought about by factors such as low precipitation, high winds (which enhance transpiration), very thin soils or frozen soils (in Winter) prevent water from being absorbed by the roots (Moore (1982). The area which was studied contained various plant life, including lichens, juniper, Lichens are two different organisms (fungus and alga) combined, this is known as symbiosis, and these organisms cannot survive without each other. Lichens grow on exposed surfaces such as rocks, walls or trees and can survive harsh weather conditions, contributing to the weathering of solid rock.. The rock pile studied was well colonised with various species of plant life, able to withstand the conditions
of the Alpine zone provided. In order to show the transition in vegetation at the site a detailed study of the species along a transect was done using quadrats. To lay the transect out, a long tape measure was placed over the site starting in the surrounding area leading to the stone pile and finishing on the south side in the surrounding vegetation. This will give us a comparison. A Quadrat is placed along this transect and a detailed study in to the species type is carried out with a percentage cover estimated. The identification and cover estimates must be as accurate as possible because the site is small and transitions from one species to the next may otherwise be missed. A 0.5m x 0.5m quadrat was used as it is relatively small and would be easier to observe such changes. The percentage cover was taken to enable a Braun-Blanquet value to be given (see Table A). Also an abundance level could be taken from these results (see Table B). The quadrats are placed side by side along the transect. This method accentuates the transitions in vegetation type.
A profile transect was also carried out to determine the changes of level over the site. An Abney level and levelling staffs (marked canes) are used to do this, the canes are placed at regular intervals along the transect and using the Abney level against one cane, the observer fixes the Abney level on the same mark on another cane until the bubble is between the two marks, an angle is taken with a positive or a negative value. The profile can be determined and plotted on a graph, This shows the gradient of the slopes and could help us
to determine why some species are more dominant at different gradients. The temperature of the soil was taken in
the morning and at midday to see the difference at each end of the transect. We did this using a specialised soil
thermometer. Our project methods aimed to collect sufficient, meaningful qualitative and quantitative data.
The profile measurements allowed an accurate graphical profile to be made. This profile demonstrates the slope shape and helps in the visualisation of how aspect may affect the rock pile. The values obtained from the survey were manipulated using trigonometry to give the graph entitled "profile of the stone pile from North to South on the North facing slope". Trigonometry was used to decipher each point on the graph which corresponds to the hypotenuse of a triangle.
The temperature readings of the soil were different on the North and South sides of stone pile and there is a visible difference between the two sides and the type of species they have. The soil temperature at 10.00 am on the South facing side was 30.8 degrees C, compared to 14.5 degrees C on, the North facing side. The kite diagram allows us to see were each species is most abundant, this is were the width is thickest and this can therefore tell us on which area of the stone pile the species prefers or is most dominant in growth. When the kite diagrams have been constructed for all species there should be some evidence of zonation, the scale of the horizontal scale is the same for the profile as each quadrat was 0.5m this means that the pattern of abundance for each species can be compared with the profile and any trends can then be detected. The kite diagrams were plotted by using table (b) a value from 1-5 as given to the cover of each species.
The quadrat results show that the succession occurring on the rock piles is different to that of the surrounding grasslands. Species such as lichens and mosses were instigating succession of the bare surface as they would have done on the grasslands in/the past. Different species occurred on the rock pile which were not to be found in the quadrats before and after the rock pile. This proves that the habitat is a different one to that of the surroundings and is able to support different species with different adaptations and needs. Typically the small plants were not to be found on the grasslands and for that reason the rock piles although not natural habitats are important ones. The rock piles are a very diverse environment and should have high conservation values and protection from removal. The study of aspect's role in the formation of the habitat has found that there is a degree of visible evidence of the effects of aspect. The stone pile has very distinct zone on it, each having different appearances and species. The South facing side which receives more sunlight than the North facing had Spruce trees, higher plants and shrubs. This suggests that it is in a later stage of succession, however aspect is one of many factors in determining that and is probably not the most influential. The temperature increase during the day was greater on the South facing slope therefore plants that can with stand such temperature fluctuations will be found here. On the stone pile there is a band of bare stones which has not experienced succession like the other areas. This is most probably due to succession approaching from opposite sides of the rock pile. If this is correct the band of rock eventually experience all the stages of succession. From the kite diagrams there is evidence of zonation. There are four distinct zones visible. On the lower slope
of the North side grass and several flowering plants are abundant, with grass as the most dominant species. Further
up the stone pile these species become sparse or unable to grow. The second zone contains some lichens and some
mosses, showing the earlier stages of succession. This indicates that succession is moving up the stone -pile.
Dominant species in this zone are mosses such as Cteniduim moluscum and Braychythecum albicans. As the gradient
become steeper the succession has slowed down and made it harder for primary colonisers to become established,
this is the third zone, a band of bare stones with primary colonisers such as Lichens. The fourth zone may have
a few less obvious zones in it that can not quite be determined from the kite diagrams. In this zone mosses and
grasses appear again suggesting that succession is also moving back down the stone pile. In this zone shrubs are
also visible such as Juniper, Raspberry and Gooseberry . There was also a lot of detritus and bare soil due to
the 1arger shrubs blocking out light to the soil surface making it hard for smaller plants and grasses to become
established. This zone shows the much later stages of succession. On the South side of the stone pile there were
no distinct zones, this may be due to the gradient being less steep than the North side, but could also be due
to the management of the stone pile as there is evidence that the farmer has been dumping vegetation there, accelerating
succession as it is enriched with nutrients.1
The conclusions made from this study are that the stone piles as artificial features, have undergone succession
in a different way to the natural Alpine grasslands surrounding them. The stone piles have provided different species.
Another conclusion is that although artificial, these stone piles are important and should be conserved for their
species diversity. The conclusion with regards to how aspect has affected the habitat, is that the aspect and other
factors have caused the different vegetation types on the North and South Facing sides. The South Facing side has
experienced succession more rapidly then the North. Huxley, A. (1984). Green Inheritance. William Collins Sons & Co Ltd, London. Moore, D. M. (1982). Green Planet. Cambridge University Press, London. Colinvaux, (1973). Introduction to Ecology. John Wiley & Sons, New York. Grime. J. P et a/ (1988). Comparative Plant Ecology. Unwin Hyman Ltd, London. Janick. J. et a/ (1969). Plant Science. W.H. Freeman and Company, San Francisco.
Appendix 2 - Table showing Abundance value for species in each quadrat.
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