This survey was concerned with looking at the changes in soil and vegetation on a transect located at Dead Mans Hill (See map A). The aim was to record the type and quantity of vegetation and to analyse the quality of soil on the transect. Using this information it would be possible to examine the relationship between the vegetation and soil, this would also give an indication to the condition of the heathland.
Dead Mans Hill is located 30 miles south of Salisbury in the New Forest. The landscape is open with raised land in the distance covered by Oak, Scotch pine and Birch trees. The main vegetation immediately visible was heather, gorse and bracken, all characteristic of heathland. The Bracken was beginning to die off, the Gorse still had a few yellow flowers and the Heather showed no signs of grazing. The location of the transect was on a gentle slope. At the bottom of the slope the land was wet and boggy; here the vegetation was mainly grass, rushes and sedges. Surface water was visible which had a brown /orange colour. The only wildlife visible was New Forest ponies, which roam freely over the forest. Signs of a rabbit population were also visible.
Heathland is only found in temperate climates in Western Europe below an altitude of 300m and is an important habitat for animals such as the Nightjar, Stone-curlew, Dartford Warblour and Smooth Snake. Heathland is not a natural landscape; there is evidence of it being present as far back as the Bronze Age. Earthworks such as barrows and other structures were sited on the heath so as to be seen from a distance; the soils beneath these earthworks contain podzols, which only form where ling is present on heathland. Two such podzols in the Breckland were dated to 900BC.
To conserve heathland it has to be managed, if it isn’t managed it will eventually revert back to woodland; this process is known as succession. Over the past 200 years 9/10ths of European heathland has been lost, as a result the New Forest heathland is now the largest in Europe.
The vegetation that grows on the heath used to be harvested at regular periods, Ling was used as fuel and thatch, Bracken was also used as fuel and to produce potash used in glassmaking. Grazing of animals used to be more common on heathland, all these factors helped manage the heath. The land use has now changed, grazing of animals isn’t common and the population of rabbits was reduced by Myxomatosis, as a result Bracken, Heather and Grasses have taken over the heath replacing the short and varied vegetation that used to be present 11. Heathland has also been fragmented by roads and building, this produces lots of boundaries from which the woodland begins to encroach, once this happens it is very difficult to reverse, for example Hampstead Heath in London. Heathlands are usually located on sandy soil, this soil has very good drainage and as a result nutrients are washed away leaving a nutrient poor soil. This soil is also usually acidic having a pH 3.5-6.5, where water gathers the pH tends to be higher making the soil even less fertile. As a result Heathlands tend to be exposed areas, with nutrient poor soil which can only sustain small plants.
FIELD METHODS AND DATA COLLECTION
To obtain the data a belt transect was used. The transect was laid from the bottom of the slope for a distance of 100m up the slope. At 5m intervals a quadrat was placed on the transect line; the percentage cover of the different types of vegetation was recorded. This method has limitations because the records are subjective, different people have different opinions with regards to percentage cover. The belt transect was on a small scale and as a result common plants such as Gorse and Bracken may not have been within the transect, therefore not recorded even though they were present on the heathland. The records could give a false impression of the vegetation cover as a whole. To overcome this limitation a larger belt transect should be used. During different times of the year plants will be at different stages of growth, the dominant species may change throughout the year. To over come this limitation, a survey needs to be carried out at regular intervals to allow for seasonal change.
With a thermometer the surface temperature was recorded within the quadrat, the soil temperature was also recorded at a depth of 5-10cms. This method has limitations, different people may read the thermometer differently, and the depth the thermometer was placed into the soil was variable and could effect the record of soil temperature.
From each quadrat a soil sample was taken for analysis to discover the pH value, water content and content of organic matter. The soil sample was split into two, one half was weighed then placed in an oven and dried at a temperature of 90.C. After 8 hours the soil sample was taken out of the oven, weighed again and the difference between the 2 weights revealed the water content of the soil. The same soil sample was then placed over a Bunsen burner and burnt for 5 minutes, any organic material in the soil would be burnt off. After the burning the sample was weighed again and the difference in weight revealed the amount of organic matter in the soil.
To discover the pH of the soil the other half of the sample was used, 2cm3 of soil and 1cm3 of barium sulphate were placed into a test tube. The barium sulphate ensures the soil particles separate, this is known as flocculation. 10cm3 of distilled water and 5cm3 of an indicator solution were then added, the test tube was given a good shake then allowed to settle for 5 minutes. The colour of the water was compared against a colour chart, which gave the pH of the soil. From these results we could asses how fertile the soil was.
To measure the gradient of the slope a 5m rope, spirit level and two 1m rulers were used. One end of the rope was held in place on the ground at sample station number 21, the rope was then pulled tight and leveled using the spirit level. The vertical distance between the ground at station 20 and the end of the rope was recorded. This was repeated all the way down the transect line, in-between each sample station. The results were plotted onto graph paper, which gave an impression of the gradient. The problems encountered using this method were, getting the rope level over a distance of 5m as it was flexible and where the gradient was small, vegetation was at a height that obstructed the rope. The results on the graph paper didn’t have a true scale and so the image of gradient appears slightly steeper than in reality. Not much could be done to allow for these limitations.
The results obtained showed that certain vegetation grew only at certain points on the transect line, for instance Bell Heather was only recorded above sample station 13, whilst Cross Leafed heather was more common below station 13. Dead grass was mainly recorded above station 13. Very little bare ground was recorded, the main types of vegetation seems to be heathers and grass (see table 1.5, bar chart 1.6).
Organic matter in the soil was evenly spread throughout the transect (See table 2.0 and line graph 1.7). There seemed to be higher water content in the soil from sample stations 1-10 which were at the bottom of the slope, although every 20m the water content seems to peak then drop off again (See table 3.0 and line graph 1.7). There seemed to be a relationship between organic matter and water content, as organic content increased so did the water content. The pH of the soil was mainly between 4.5 – 5.5, at station 2 it was found to be 6.5 (See table 3.0). The temperature of the soil and surface temperature were constant with little variation from sample 1 to sample 21, the surface temperature being 1 or 2 degrees higher that the soil. (See line graph 1.7 and table 2.0)
The vertical distances between sample stations were plotted on graph paper to give an impression of the gradient (See table 1.8 and illustration 1.9).
At station 20 there was a large increase in water content even though this was near the top of the slope, we would expect this station to be dryer than most of the stations yet it has one of the highest water content results.
The collected data was as expected and corresponds with the background information. The pH tests on the soil showed that it was acidic as expected. The soil was fine and sandy, this would have good drainage and as a result nutrients would be washed away making the soil only suitable for certain types of vegetation. At the bottom of the slope where the water gathered the vegetation was as expected, Cotton Grass, Sphagnum moss, Bog Asphodel, Sundew and Molinia Caerulea (purple moor grass) were present, all being native to wet, acidic conditions. As the investigation moved up the slope the vegetation changed, Ling was present throughout the study but became dominant further up the slope as the conditions became dryer and more favourable. Lichen was observed around the base of the heather stems in the higher stations, it’s colour was light green-yellow as a result of the acidic conditions 10. Bell heather which favours dry conditions was only recorded above station 12 half way up the slope. Cross leaved Heather which is native to bogs and wet heaths was mainly recorded below station 9 at the bottom of the slope which had a higher water content.
The relationship between organic matter and water content in the soil could be explained as follows. The more organic material that is present in the soil would effect the drainage and so retain water, more organic material, more water.
Surface temperature was slightly higher above station 9. Above station 9 Ling and Bell Heather were more common, the heather would act as insulation trapping a pocket of air between the ground and its leaves. This pocket of air would retain heat and result in a slightly higher surface temperature where there is good cover of heather. The soil temperature was on average 14.C except at stations 16 and 20, which showed an increase of 3-4 .C, at these stations there was also a noticeable increase in organic matter and water content. The increase in temperature may be a result of the organic matter below the surface decomposing and producing heat. At these stations something seems to be preventing drainage, podzols may be present at these stations and responsible for the higher water content of the soil. A podzol is produced by a combination of acidic soil and Ling heather. The chemistry of Ling heather favours podzolization, rain dissolves organic acids out of leaf mould, leached humus and iron compounds out of the topsoil. These are deposited lower down in the soil and cement soil particles together to form ‘pans’. These ‘pans’ or podzols are characteristic to heathland and slow down drainage 11. Next to these stations we observed Cross Leafed heather which prefers wet conditions and a reduction in Bell heather which prefers dry conditions.
The bare ground recorded can be explained by trampling, from humans and the ponies, which live on the heath and tend to take the same route time and time again.
From the main findings such as the pH of the soil, vegetation distribution and the discovery of possible podzols we can conclude that the land studied is characteristic of heathland. From the information obtained, the heathland seems to be in good condition supporting a variety of plants, none of which seemed to be dominant. The heathland is being managed to maintain it; the ponies although having an impact couldn’t be responsible on their own as their population isn’t large enough.
WORD COUNT 2022.
10 Grasses, Ferns, Mosses and Lichens of Great Britain and Ireland
Roger Phillips 1994 Pan Books
11 The History of the Countryside Rackham 1986 Dent & Sons
12 Flora of the British Isles Clapham, Tutin & Warburg
Cambridge University Press 1958
Gorse; Found in grassy places on edges of heaths usually on lighter less calcarelous soils 12.
Ling; European shrub, pollinated by wind & animals. Native to heaths on acid soils upto 3400ft. Dominant on well-drained acid soils 12.
Bell heather; native to heaths, dry soil upto 2200ft. Has crimson, purple flowers 12.
Cross-leafed heather; native to bogs and wet heaths. Rarely grows on dryer heaths 12.
Tormentil; Likes light acid soil, not heavy calcarelous soils 12.