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Development of Quantitative and Qualitative measures of Human Impact on Wimbledon Common.

Extracts from this document...

Introduction

Individual Study.     Krimal Patel

Individual Study.

Development of Quantitative and Qualitative measures of Human Impact on WimbledonCommon.

Abstract

A vegetation analysis has been performed at four sites on Wimbledon Common SW19 London, to assess the suitability of quantitative methods for determining human impact on the succession climax.

Systematic stratified sampling based on the method of Querouille (1949) has been used

Based on 25 sample points per site. A test of Yoda’s law; C=Wρ –3/2  has been performed on tree stands, where ρ  = density of a stand, C= dry weight of matter and w is a constant, by using a correlation test. Log (combined diameters) as the dependent variable (y) and log (distance between pairs) as the independent (x) variable. Three out of four sites gave high values of r, indicating that Yoda’s law may operate on the sample sites. This is thought to reflect human management of the common over 200 years as well as the mechanism of self-thinning.

Using the point quadrat method (Curtis 1949) estimates of density d were obtained as:

d= 1 /  l 2    where l =   ∑ li   /  n , where n = sample no and l i the determined lengths from the sample points. This showed discrimination between open and closed sites. A frequency analysis was carried out on this data to find the relative dominance of species X as:

Relative dominance of species x= sum of circumferences for that species/ sum of circumferences for all species.

Following the procedures of Clark and Evans (1954) these density estimates were tested for normality or a random distribution using the statistic:

C=(rn- E(rn))/ (σ/√N,)

rn and E(rn ) the mean and expectation of the lengths of up to three nearest neighbours.

Further following the procedure of Thomson (1956) using a chi squared distribution a further test of randomness was performed on nth nearest neighbours.

...read more.

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Field Data Sheet: Nearest Neighbour Analysis. (Site Designator):-

Tree no

Circumference (cm)

r n1

dn1

r n2

dn2

r n3

dn3

1

2

3

4

5

6

7

8

9

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Field Data-Sheet : Base Cover. Site:

Ground Cover %

1

2

3

4

5

6

7

8

9

Average

Leaf Litter

Branches/twigs

Bare ground

Short grass

Long grass

Soft rush

Brambles

Holly

Tree saplings

Ferns

gorse

Trampling Score

The trampling scale index.

  1. No impact on vegetation- flower heads present and stems of plant not broken.
  2. 2. Vegetation affected-plants are mainly grasses, stems bent
  3. 3 1%-25% of topsoil expose-plants very short or cushion form, some damage
  4. 26%_50% of topsoil exposed-plants very short or cushion form clear damage.
  5. 51%-75% of topsoil exposed-plants very short or cushion form, very clear damage.
  6. 76%-100% of topsoil exposed-plants very short or cushion form, severe damage.

Results and Discussion.

The original results are presented as carried out in the field. These have been copied onto an excel spreadsheet for analysis and converted where appropriate into SI units.

...read more.

Conclusion

  1. Causton, D.R. (1988). Introduction to Vegetation Analysis. Unwin Hyman. London.
  1. Cochran, W.G. (1963) Sampling Techniques. 2nd edn. Wiley New York and London.
  1. Bordeau, P.F. (1953). A test of random versus systematic ecological sampling. Ecology, 34, 499-512.
  1. Lambert, J.M. (1972). Theoretical models for large-scale vegetation survey. In: Mathematical models in ecology ED by JNR Jeffers pp57-109. Blackwell Scientific Publications, Oxford.
  1. Smartt, P.F.M. and Grainger, J.E.A. (1974) Sampling for Vegetation Survey: Some aspects of the behaviour of unrestricted and stratified techniques. J. Biogeog.11, 193-206.
  1. Cottam,G. and Curtis J.T., (1949) A method for making rapid surveys of woodlands by means of randomly selected trees. Ecology, 30, 101-104.
  1. Cottam, G. and Curtis J.T.,(1955) Correction for various exclusion angles in the random pairs method. Ecology 36,767.
  1. Morsita M. (1957) A new method for the estimation of density by the spacing method applicable to non-randomly distributed populations. Seiro-Seitai 7, 134-44.
  1. Sutherland, W.J. (1996). Ecological Census Techniques. CUP. Cambridge.
  1. Kershaw, K.A. (1964). Quantitative Dynamic Ecology. Edwin Arnold London.
  1. Wratton, S.D. and Fry, G.L. (1980). Field and Laboratory exercises in Ecology. Edward Arnold. London.
  1. Thomson, H.R. (1956), Distribution of distance to nth neighbours in a population of randomly distributed individuals. Ecology. 37, 391-4.
  1. Ashby, M. (1969) An introduction to plant ecology. 2nd edn . Macmillan. London.
  1. Studies in Plant Demography (1985) A festshrift for John L. Harper. Ed.by James White. Academic Press. London.
  1. Clark,P.J., and Evans, F.C., (1954) Distance to nearest neighbour as a measure of spatial relationhips in populations. Ecology 35: 445-453.
  1. 19 Perssin,O., (1971). The Robustness of estimates of density by distance measurements. Stataistical Ecology. Ed by G.P. Patil et al. Vol 2 pp 175-90. Pennsylvania State University Press.

Acknowledgements.

Science Museum Library. South Kensington.

To Rajan, For assisting in Data Recording on Wimbledon Common.


[1]  A unit of trees.

[2] Density is the measure of number per unit area.

[3] Cover is defined as the proportion of ground occupied by perpendicular projection on to it of the aerial parts of individuals of the species under consideration.

...read more.

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