(3) Biodiversity surveying: Method 2
Surveying using transects in ecology
A belt transect is a path/gradient along which one counts and records occurrences
of the species of study.
You might wish to study how the distribution of
organisms changes by sampling across a transect.
A transect is used to survey a wider area in a
more systematic way than just doing a few quadrats.
e.g you can use a sequence of quadrats along a
transect to find out how organisms are distributed across a change in
habitat due to an abiotic factor - bright light to shade, damp to
dry ground, change in soil composition (due to underlying differences in
geology e.g. limestone and sandstone)
Below is a photograph of a field of wild flowers.
I've drawn on the photograph how you use a 1 m2
quadrat along the line of a transect to survey the species of
wild flowers from the hedge at the top to the bottom of the field.
You can visually see that the distribution
(concentration) of white and yellow flowers changes as you come down the
field and these can be accurately counted to give you quantitative
data.
Photo of the Cornfield wild flower project
Hutton-le-Hole - Ryedale Folk
Museum (August 2019) well worth a visit.
20 cm x 20 cm squares in the 1 m2 quadrat
You can count the number of each species in 1 m2
(100 x 100 = 10,000 cm2) areas or randomly sample the smaller
0.04 m2 (20 x 20 = 400 cm2) areas.
Doing a transect survey
In the preceding section I've described how to
use a quadrat.
Here you lay out a long string line from the
starting point to the end point.
Using a long tape measure you measure out 1,
2, 3 m etc. and place a 1 m2 quadrat at these points.
Count the organisms e.g. plant species you are
interested in and then move the quadrat on 1 m further down the
line.
You can survey every metre or 2 or 3 metres if
its a very long transect.
From your results you can plot graphs
of organism density (species/m2) versus
distance down the transect (m).
You could also measure the light intensity
down the transect using a light meter, at the same distance
intervals you were measuring the plant density.
You can then compare the two graphs and
see if there is any connection between the plant species density and
the intensity of light falling on the transect.
The calculations are just the same as I've shown
in the preceding (1)
Quadrats section.
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