METHOD OF SAMPLING VEGETATION SAMPLING:
(QUADRATE AND LINE INTERSECT METHOD)
The process in which a predetermined number of observations are obtained from a
larger population is called as sampling.
It depends upon the type of analysis being performed.
METHODS OF SAMPLING:
There are two types of sampling methods:
• Probability sampling
• Non-probability sampling
1. PROBABILITY SAMPLING:
It includes random selection that allow you to make statistical results about the whole
group.
2. NON-PROBABILITY SAMPLING:
It includes non-random selection based on simple criteria that allow you to collect
initial data.
VEGETATIVE SAMPLING:
It is based on the idea that the changes in vegetation (biomass, VWC (volumetric water
constant), and plant structure) are negligible within a week that is why same paddock
(an enclosed area used for pasturing animals) is re-sampled after one week.
IMPORATANCE OF SAMPLING VEGETATION: -
• They are important in wetlands in many physical and chemical processes.
• For aquatic organisms, they provide habitat and structure.
• They stabilize shorelines (area where water and coast meet) and reduces
the erosive force of waves.
• It helps to characterize all types of vegetation in different study areas.
• It helps people to readily identify plants with minimum training as plants
are present in almost all the wetlands.
METHODS OF SAMPLING VEGETATION: -
It includes:
1. Transect method
It is further divided into:
• Line transect or line intersect
• Belt transects
2. Bisect method
3. Trisect method
4. Ring counts method
5. Quadrat method
It can be of 4 types:
• List quadrat
• List-court quadrat
• Chart quadrat
• Clip quadrat
LINE TRANSECT METHOD/ LINE INTERSECT METHOD:
DISCOVERY:
This method was developed by canfield in 1940 to estimate the cover in the grasslands
of S-W USA and it is widely used in shrublands and in the progress of applications.
DESCRIPTION:
It is a method of sampling elements in a region in which an element is sampled if the
transect interacts the element. It is a common way to determine the cover by laying a
transect and see how many plants intersects with the transect.
It is a type of transect method.
it is used for the measurement of grass or grass like plants, shrubs, trees.
The following vegetation characteristics are covered by this method:
• Basal cover
• foliar cover
• Canopy cover
Figure 1 types of cover
AREAS WHERE IT IS USED:
It is used in semi-arid bunchgrass-shrub vegetation.
LINES: -
It can be single, multiple, l-shaped or of unequal length.
TRANSECT LENGTH:
It depends on the vegetation and the type of plants which are to be measured. For
example, 15m transects are suitable in dense vegetation whereas 30-50m are required
to obtain a representative sample in thin thinly scattered vegetation.
USE OF LINE INTERSECT METHOD:
It is used in ecology to measure the percent vegetation coverage, coarse woody debris
(CWD) coverage, and plant abundance.
General steps to conduct a line intersect in field:
• Take 2 measurements for each item of interest. Now cover the length and
width of the items perpendicular to the transect.
• The start and end point for each time a plant intersect the line is recorded
as the total distance of the intercept. It can be calculated in the lab.
• When we read the distances along the transect, read only along one edge
of the tape. The tape should not be moved inadvertently to include or exclude the
certain plants.
• Now in the same way, measure the bare ground.
• If there are multiple items of interest repeat step 1 and 2.
• Lines should be thin; it has no width at all. They are used to calculate the
basal and canopy cover but also use to determine the foliar cover for the species
having dense canopies and large leaves.
• Now cover is calculated as:
Cover of species = total distance of specie / total distance of line
• Now determine the percentage cover for each line and take average to
determine the cover of the total landscape.
figure 1 : line intersect
INFORMATION COLLECTED FROM LINE TRANSECT METHOD INCLUDES:
The number of times a specie appears along the line.
The increase and decrease of distance between the individuals of species.
The percentage of the occurrence of different species in relation to the
total species.
The appearance and disappearance of different species that are present
along the line.
ADVANTAGES OF LINE INTERSECT METHOD:
• It is more economical.
• It is easy to learn and simple to use.
• It provides an accurate estimate of cover.
• It is used as standard comparison when testing other methods for the
determination of cover.
• Greater species turnover.
• Larger area is covered in a relatively short time.
• It is applicable throughout the year.
• Use in many types of habitat.
• It can be used in hilly area.
• Permanent transects can cover for a longer period of time
DISADVANTAGES OF LINE INTERSEPT METHOD:
• In this method, distances are not correctly measured.
• Movement of observer may disturb the animals.
• Chances of missing rare species are more.
• It is difficult to detect small changes.
• Rare plant species may not intersect by the points and are not sampled.
• It can be time consuming specially in dense vegetation.
Figure 2 line intercept
TERMS USED IN LINE INTERSECT METHOD:
Cover = Sum of intersect lengths for a specie/total length of the
transect×100
Density = Ȃ/1 (unit area/total transect length)
(Where M = max width of the plant perpendicular to transect line)
Relative Density = species density / total density for all species.
PROCEDURE:
• In this the vegetation is sampled only on a line (without any width).
• A line is placed over the vegetation with a steel tape or long rope and it is
fixed with the help of a short pin or a bolt or hooks.
• This line touches the plants on its way from one point to other point.
• Now the observer starts recording these plants from one end and will
move to the other end.
• Cover is calculated by adding all intercept distances divided by total
length of the transect
Figure 3 Transect Line
QUADRAT SAMPLING METHOD:
It is a method by which we can directly count organisms in a certain proportion of
habitat.
It is used for the estimation of
No. of population
Population Density
Population Frequency
Population distribution
QUADRAT:
• It is a square in which species of interest are counted.
• It is a frame which is laid down to mark out the specific area of
community to be sampled.
Figure 4 Quadrat
SHAPE OF QUADRAT:
They may be:
Square
Rectangular
Circular
Figure 5 Shapes of Quadrat
USE OF QUADRAT METHOD:
It is used to determine the differences and similarities in the composition
and structure of different plant communities or related or unrelated
vegetation.
It is used for sampling:
plants
slow moving animals
some aquatic organisms.
TYPES OF QUADRATES:
• List quadrat:
In this we enlist the names of species that grow in the quadrat
• List-court quadrat:
In this we record the no. of individuals of each specie present in each quadrat.
• Chart quadrat:
In this we record the areas that are covered by grasses, mosses on a graph paper. This
graph helps us to compare any change in the structure of community.
• Clip quadrat:
In this we measure the weight of each specie all species are pulled out of the ground
and its dry or fresh weight is measured.
SIZE OF QUADRAT:
It is determined by drawing a species area curve. It is done by sampling the vegetation
present inside the quadrat.
Quadrat can be of any size. Common sizes include
• 25 by 25 cm
• 50 by 50 cm
• 1 by 1 m
GENERAL STEPS:
• First of all, choose a sampling region and make a grid line along the area.
• Now select a random area and place the quadrat there.
• Now count the individuals that are present inside the quadrat.
Figure 6 Edge Effect
There is present an edge effect. Species that are present inside the quadrat are counted
but those species that are present at the edges or outside the quadrat are not counted.
• Now repeat step 2 and 3.
• Now measure the total size of the area occupied the population in square
meter.
• Now calculate the population by using the equation:
Population = average organisms per quadrat × total area ÷ quadrat area
TERMS USED IN QUADRAT METHOD:
• Counts – it tells the number of individuals of a species.
• Cover – the percent (%) area of the quadrat occupied by a plant species.
• Density – estimated by quantifying the number of individuals of a species
per unit area.
• Frequency – the proportion of quadrats sampled in which the species is
represented.
(frequency = no. of plots in which species occur / total no. of plots
sampled)
(relative frequency = frequency value for a specie / total frequency values for all
species × 100) • Relative cover- is the proportional cover of an individual species as a
percentage of total plant cover so it is expressed as a percentage, ranging from 0 –
100%.
ADVANTAGES OF QUADRAT METHOD:
It is simple to use.
Quadrat plots are uniform in size and shape and distributed throughout
the area which make it straightforward.
Affordable because it requires less material.
DISADVANTAGES OF QUADRAT METHOD:
Not useful to study fast moving animals as they not stay inside the
quadrat.
Too large or too small in size quadrats result in errors because large
species require larger plots. Randomly spaced quadrats that are too small
might miss many individuals.
