You are going to measure the plant biodiversity of a playing field or an area of parkland. Biodiversity is a measure of the number and variety of different organisms living in an area. This means you will need to be able to recognise different species of plants, and you will also need to measure their population size (how many of each species are there?). Your teacher will assign you an area of a habitat to investigate.
Plant identification
You may be able to use a field guide to help you identify the species you observe, or your teacher may be able to help you name them. If you are not able to name a plant, draw a simple sketch of one of its leaves (and/or flowers) and give it a letter identifier, e.g. Species ‘A’. You could also take a photograph of it, then you might be able to identify it fully at a later date.
The ACFOR scale
This is a subjective method of describing the population of a species within an area. When using the ACFOR scale, you need to decide which of the following words best describes the abundance of each species you identify:
Abundant – the species is found in high numbers in the habitat.
Common – the species is found often, but it is not particularly abundant.
Frequent – it is relatively easy to find the species as it occurs throughout the habitat, though it is not commonplace.
Occasional – the species is found in the habitat, but not enough to describe it as frequent.
Rare – the species is found in the area of study, but not very often at all.
Method
ATry not to damage the habitat you are studying; do not pick any of the plants you observe!
BYou will need to fully explore your assigned area of habitat to define the limits of your area.
CLook carefully at the ground and record (as described above) every different species you can see.
DFor each species, assign the best description for level of abundance.
EIf time, ask your teacher for another area to record.
Considering your results
1What sort of graph could you use to display your data?
2aWhat conclusions can you draw about the abundance and about the variety of plants in the part of the habitat you studied?
bDoes the same biodiversity exist in other parts of the habitat? Suggest, with reasons, why it does or does not. You may need to look at data collected by other groups.
Evaluation
3What problems did you encounter when using the ACFOR scale to describe the abundance of each species?
4Can you suggest a different method of measuring plant abundance?
You are going to estimateearthworm population density in an area of grassland. You will use quadrats to sample the area.
Apparatus
2 tablespoons mustard powder / bucket / quadrat / Health and safetyWash your hands thoroughly when you have finished.
large plastic milk bottle / scissors / stop clock
stirrer / tap water
Method
ARandomly determine a place to put your quadrat down in the area you are investigating.
BUse scissors to cut the grass in the quadrat area down to soil level. The soil surface should be easily visible and accessible.
CFill the bucket about halfway up with tap water. Place mustard with a little water into the large plastic bottle and shake to mix them. Then carefully add the mix to the bucket of water and stir to mix thoroughly. Then almost fill the bucket to the top with tap water.
DPour the mustard mixture slowly and carefully over the prepared area of ground, as evenly spread as possible. Mark each plot to ensure that the same area is not repeatedly flushed with mustard water. Worms (if present!) should start to emerge within 1 minute.
ECount how many worms emerge during a 3-minute period. Fully-emerged worms should be picked up and moved out of the clear area to ensure that they do not get counted twice.
Recording your results
1Pool results with the rest of the class so that you get a reasonable amount of data to analyse.
Considering your results/conclusions
2Use the class data to calculate a mean population density for earthworms in the area you investigated. You will need to calculate the area of each quadrat and decide on an appropriate unit for expressing population density. Remember that you are observing the number of earthworms per area of the top surface and not per volume.
Evaluation
3Explain any problems you encountered with the technique you used.
4Suggest an alternative method and explain how it would provide a more accurate estimate of population density.
A group of students investigated the distribution of plants along a 100-metre strip of land, crossing from heathland into woods. They recorded the frequency and percentage cover of the plants, using 1-metre square quadrats.
A plant was recorded in the frequency column if it was found in a quadrat. For example, bluebell was found in 5 of the 100 quadrats. The percentage of cover was estimated for each quadrat. For example, if a plant covered all of one quadrat and half of a second quadrat out of 100 quadrats, its percentagecover would be 1% + 0.5% = 1.5%.
Their results are given below.
Plant name / Frequency (%) / Cover (%)bluebell / 5 / 3
bracken / 8 / 6
bramble / 13 / 10
elder / 2 / 1
foxglove / 9 / 5
gorse / 57 / 40
heather / 61 / 35
oak / 1 / 0.5
sedge / 13 / 4
thistle / 11 / 4
willowherb / 17 / 2
wood sorrel / 4 / 1
1Plot a bar graph, line graph or pie chart for both frequency and cover, giving a reason for your choice of graph or chart in each case.
2Which plant covered seven quadrats completely and half-covered six further quadrats?
3A plant that is found in many quadrats but has a low percentage of cover is likely to be spread thinly. Plants with high percentage of cover, such as heather, are likely to be growing in clumps that cover a large part of each quadrat.
aUse the data to name one plant that is spread thinly.
bUse the data toname one plant other than heather that grows in clumps.
Extra challenge
4The total percentage cover is 111.5%, not 100%. Explain how this is possible.
The grids on the next page show the distribution of a plant species (represented by dots) found in two different ‘fields’. Follow the instructions and answer the questions that follow.
Prediction
1Looking at the grids, which field do you think has the largest plant population?
Method
AGenerate 10 pairs of coordinates using random numbers – for example using dice or randomly hitting numbers on a calculator.
BUse your coordinates to determine which squares ('quadrats') you will sample in field X. Count the number of ‘plants’ (dots) in each randomly determined region and record the results.
CRepeat the above steps for field Y.
Recording your results
2Draw up a suitable table for all of your results.
Considering your results/conclusions
3For each field, work out the average number of plants per square in your sample, and use this value to calculate an estimate for the total number of plants.
4Do your estimates support your prediction?
5If the fields and plants were real, what possible factors could influence how many plants were found in each area? For each factor you suggest, explain why it would have an effect.
Extra challenge
5How confident are you about the accuracy of your estimates? Explain your answer.
6If the total area sampled in each case were the same, do you think it would be better to use 10 small samples or one large sample? Why?
7Why do you think it is important to randomly select sampling points?