1. Unit 3 Science Investigation Skills
Topic F: Plants and their environment

2. Learning objectives:
To identify the factors that may affect plant growth
and distribution.
To describe ecological plant sampling techniques.
To explain the importance of random sampling and
sample size.

3. Why is ecology important?
Ecology is the study of ecosystems and biodiversity, the abundance of different species, and interactions between living organisms in all kinds of habitats. We need to understand how plant, animal and microscopic organisms interact together, and how their populations are affected by global and local environmental changes. The ballooning population of humans is having a huge impact on the biosphere. We must measure and understand this impact, to improve the welfare and chances of survival of all species, including our own.

4. Why are plants important?
Photosynthesis is one of the most important chemical reactions on Earth.
Most photosynthesis on land is carried out by plants.
Photosynthesis is the source of two products:
glucose, the energy source vital for almost all food chains
oxygen, required by all aerobic organisms.
Plants provide a habitat, shelter or shade for many other species, reduce erosion and flooding, and help to reduce global warming by absorbing carbon dioxide.
They are also a source of building materials, medicines and many other commercial products.

5. Factors that may affect plant growth and distribution
Consider ryegrass, used in a typical garden lawn.
Biotic (living) factors that affect ryegrass include:
abundance of consumer species What effect might a large population of wild rabbits have on the lawn?
abundance of competing species Why do most gardeners dislike dandelions in the garden?
human behaviour. What effect does mowing have on ryegrass growth?

6. Factors that may affect plant growth and distribution
Abiotic (non-living) factors that affect ryegrass include:
aeration of the soil How do gardeners aerate a lawn? Which soil animals also help?
temperature and light intensity Why doesn’t a lawn need to be mowed over the winter?
amount of moisture When are sprinklers used in a garden?
pH and mineral content of the soil. How can gardeners improve soil fertility?

7. Ecological plant sampling techniques
To study the abundance of different plant species in a habitat, and measure the effects of various biotic and abiotic factors, ecologists use a variety of equipment and methods. Plants can be easier to study than animals, as they are generally ‘rooted to the spot’. However, there are still many skills required by ecologists to measure plants’ abundance in a meaningful way.

8. Types of plant survey
There are two main types of ecological surveys used for plants: random sampling and transects. Random sampling is used to estimate abundance of a species within a fixed area. It can be used to follow changes over time, season by season or year by year, or to compare abundance between different areas, such as comparing abundance of daisies in a grazed field with an ungrazed field.

9. Transects are used to measure change in abundance over an area displaying a change or gradient in an abiotic factor. An example would be soil salinity which would be high in land near a seashore and would decline in land further away from the seashore. Sampling could be used to measure the effect of the changing salt levels on the abundance of a particular plant species.
Point, frame or grid quadrats can be placed at regular intervals along a transect line, for instance, every 5m along a 50m length of tape.

10. Sample size 4 x 100 = 400 daisy plants
The most accurate way to count the number of daisy plants in a field would be to divide the field into squares and count the daisies in every square. However, this would be very time-consuming and laborious.
So it is usual to count species in a number of sample sites. A mean value can then be calculated and used to estimate the count for the whole area.
For example: in a 100m2 field (10m x 10m), 20 1m2 sites were surveyed. The mean number of daisy plants in the 20 sites was 4 (in 1m2). Therefore, the total number of daisy plants in the field is estimated to be:
4 x 100 = 400 daisy plants

11. Deciding how many sites to survey
The more sites you sample, the stronger the data.
But as your data accumulates, you can judge whether or not it is worth counting further sites.
This involves calculating a running mean and finding whether or not the mean is fluctuating within acceptable limits (e.g. +/- 5%). If the mean values are within these limits, this indicates that further sampling would not significantly improve the accuracy of the data.

12. Random sampling
Like all scientists, ecologists need to make sure they work in an unbiased way. Imagine you are asked to survey a field to measure the abundance of daisies. You need to count daisies in at least 20 1m2 sample sites. The field is used as cow pasture, and there are patches of nettles, a bramble hedge and boggy areas. What could influence your choice of sites to sample? Why is it important to select sites randomly? By counting species in randomly selected sites, you can get more representative data.

13. How are random sites chosen?
The sites to be sampled in a habitat can be chosen randomly by the following method:
Divide the area into a huge grid, using strings or tapes held by tent pegs. 1m x 1m is a commonly used dimension of squares.
The grid is numbered so that the corners of each square will be defined by unique pairs of co-ordinates, e.g. 2, 7.
The co-ordinates of the squares to be sampled can be selected using a random number generator.

14. Sampling techniques and equipment
Open and gridded quadrats
The open quadrat is used to count plant species
(or slow-moving animals such as slugs), and there
are various sizes that can be used. Common sizes
for small plants such as daisies are 0.5m x 0.5m or
0.25m x 0.25m. In gridded quadrats, the square is divided into smaller squares, making it easier to count small plants. Estimates of plant coverage can also be made
using open or gridded quadrats.
Open and gridded quadrats can be used for random sampling or transects.

15. Point frame or point quadrat
The point frame is used to count plant species.
It consists of a vertical frame with (usually) 10 pins inserted into holes in the horizontal support.
The count is made by counting the number of pins in contact with the species of interest.
In the diagram, the count would be 3.
The point frame is usually used in transects.
Point quadrat
The point quadrat is used to count plant species.
It consists of a vertical frame with (usually) 10
pins inserted into holes in the horizontal support.
The count is made by counting the number of pins in contact with the species of interest.
In the diagram, the count would be 3.
The point quadrat is usually used in transects.