The Woodland Education Centre

ECOLOGICAL SAMPLING METHODS cont'd

Belt Transect Method

This is similar to the line transect method but gives information on abundance as well as presence, or absence of species. It may be considered as a widening of the line transect to form a continuous belt, or series of quadrats.

In this method, the transect line is laid out across the area to be surveyed and a quadrat is placed on the first marked point on the line. The plants and/or animals inside the quadrat are then identified and their abundance estimated. Animals can be counted (if they will sit still!), or collected, while it is usual to estimate the percentage cover of plant species. Cover is the area of the quadrat occupied by the above-ground parts of a species when viewed from above. The canopies of the plants inside the quadrat will often overlap each other, so the total percentage cover of plants in a single quadrat will frequently add up to more than 100%.

Quadrats are sampled all the way down the transect line, at each marked point on the line, or at some other predetermined interval (or even randomly) if time is short. It is important that the same person should do the estimations of cover in each quadrat, because the estimation is likely to vary from person to person. If different people estimate percentage cover in different quadrats, then an element of personal variation is introduced which will lead to less accurate results. The height of plants in the quadrat can be recorded and the biomass of plants can also be measured by harvesting all the plants inside the quadrat and then weighing either fresh, or dry weight in the laboratory. This is obviously a very destructive method of sampling which could not be used too often in the same place. Sampling should always be as least destructive as possible and you should try not to trample an area too much when carrying out your survey..

An example of the type of results that can be obtained from a belt transect survey is shown in below. 

This figure illustrates the distribution and abundance of cherry seedlings along a transect line. The parent cherry trees were adjacent to section number 9. The gradient of distribution apparent in the figure is a result of the dispersal of seeds outwards from this point.

3. STRATIFIED SAMPLING

Stratified sampling is used where there are small areas within a larger habitat which are clearly different. For example, scrub patches within a heathland area, or areas of bracken in a grassland. Sampling would be carried out either randomly, or systematically within each separate ‘stratum’ identified. This recognizes major differences within communities before sampling begins.

PLEASE NOTE

The Random Number Table was obtained from "Statistics for Biologists by R.C. Campbell, Cambridge University Press, 1974.