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

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Individual Study.     Krimal Patel

Individual Study.

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


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.

Basal cover at 36 quadrats was estimated using a tenths scale. Finally a trampling index is proposed that assesses human impact. This has shown discrimination between open and closed sites. However in terms of overall trampling damage little serious impact has been seen outside of the established paths.  A conclusion is drawn that both Conservationists and ecologists will be able to use the density measurements and the techniques more generally when planning management schemes for the common as well as the vegetation data and trampling scale to readily assess the impact visitors are having on certain areas of the common.



Wimbledon Common situated in southwest London is an extensive area of open land subject to multiple recreational use. For example there is a golf course, horse riding designated paths, cycle paths and numerous footpaths, some designated some not. Conservators are appointed to resolve issues of conflict demand use and to take decisions regarding conservation.  In the absence of human interference this area would reach climax vegetation. Exactly what this would be depends upon a number of factors. The vegetation could vary on a local scale depending on the closeness to standing water, drainage qualities of the soil as well as the climate overall. The deciduous oak/beech forest is typical of southern England. Diagram 1 shows the proposed stages in this climax that could be appropriate to this area.

It is important to realise that the vegetation pattern is never a static phenomenon unchanging once established but a highly dynamic one. Individual trees for example inevitably die or fall; leaving an opportunity gap in the light space that has opened up for other species to establish. This implies a pattern of a mosaic of patches might be become established caused by catastrophes, storms epidemics and diseases and so on.

Some species actually inhibit their own re-creation at least initially. Their young saplings do not succeed paving the way for others. Beech is a case in point, thus replacement will be of ash, oak, or birch, but later these trees let the beeches back in. We can conclude that patches of oak, ash or birch are an integral part of the beechwood community.

A.S.Watt in a study of beech-woods and found that when they are 60-80 years old the field layer can support wood sorrel but after another 10-20 years these are succeeded by brambles.

The field layer may be very sparse with some species of tree for example Beech, dogs mercury, wood sorrell, wood barley grass and wood sanicle have been recorded as common, however if yews are present then not even these plants can gain a foothold. Oak (Quercus robor) has associated on the filed layer dogs mercury, wood sanicle and bluebells.

As some areas on Wimbledon Common are left by the conservators to reach their ‘natural climax ‘ whereas others are heavily trampled by humans, the opportunity exists to evaluate methods that quantify and qualify the scale of human interference. In this study a dual focus will be attempted. Firstly a look at the trees in their stands from the viewpoint of density, and secondly to look at the ground coverand assess both qualitatively and quantitatively human impact.


A logical starting point is Yoda’s self-thinning law. (1963). In this study applied to trees.  A derivation of this is given in the appendix.

Yoda postulated that that the smallest individuals in a population are the first to die, leaving the larger individuals to gain weight.

The law proposed was W= C ρ –3/2      , or; in log form log W= log C- 1.5 log ρ

Where w = dry weight of surviving plants,

            ρ = density of surviving plants

            C = a constant related to growth class of particular species being studied.

The power 3/2 could vary between species as could the constant C. In some 80 species studies the range of C has been found to lie: 3.5 <= C<= 4.3.

A 3/2 power law implies that a change of three log units in mean plant weight corresponds to a change of only 2 log units in mean plant density. Although plants in a dense population become larger with age and as the population decreases due to mortality the law implies that the total plant weight will increase because mean plant weight is increasing faster than density is falling. This phenomenon is known as self-thinning.

Incidentally there is enormous biological significance in this. For Farmers three are density limits in which young seedlings of a given species can survive. There are also implications in the filed of conservation of rare species where safe sites need to be found, for the planting of the seeds.

One of the Hypotheses under test is that there is a positive direct relationship between the size of each pair of nearest neighbours and their distance apart. In particular self-thinning as opposed to man’s imposition of pattern would be expected to comply with Yoda’s –3/2-power law. Larger individuals benefit from the death of smaller ones. Where regeneration takes place in a woodland gap a large number of seedlings immediately take advantage of the extra light but self-thinning operates during their growth to provide only one mature tree to fill the gap. The successful tree then suppresses new seedling growth.

For the analysis of tree stands the method of plotless sampling has been chosen. This method is considered appropriate to forests where there are practical difficulties in delimiting the relatively large quadrats necessary for sampling trees.

From the varied procedures mentioned in the literature given for completeness in appendix 2. Three have been chosen and suitably modified to suit the present project. By recording a minimum set of data it is possible to use any of the three methods.

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  1. Intraspecific and Interspecific crowding.

Involves plotting the relationship between the log o combined diameters of each tree and that of its nearest neighbour against the log of the distance between them. This can be done for

  1. all pairs of the same species
  2. all pairs of mixed species
  3. Combined data.

A correlation coefficient is calculated where x represents the log of combined diameter and y the log of the distance of the nearest neighbours.

Point Centred Quadrat method.

A Point is established at random in the study area. Four quadrats around the ...

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