1. Virtual Field Trip Nitrogen deposition and heathlands
© Carl Corbidge
© Amy Rogers
© Amy Rogers
© Amy Rogers

2. What are you going to do?
You are going to be learning about a very important habitat – lowland heathland.
You will be collecting data and conducting analyses to investigate how nitrogen deposition is affecting the vegetation of two lowland heathland sites.
© Amy Rogers

3. Objectives You will be finding out:
what nitrogen deposition is, and why it is a problem for heathlands;
how nitrogen affects the growth of a plant species (heather);
how to identify common heathland plant species;
how to collect vegetation data using quadrats;
how to analyse data (graphically and statistically) to investigate the effect of nitrogen deposition on heathland vegetation.

4. What is nitrogen deposition?
Atmosphere
Biosphere
Over the past few decades there has been an increase in emissions of man-made nitrogen-containing compounds into the atmosphere, notably nitric oxide (NO), nitrogen dioxide (NO2) and ammonia (NH3).
The nitrogen contained in these compounds can leave the atmosphere and enter the biosphere where it can be absorbed by plants – this process is known as nitrogen deposition.

5. Naturally occurring nitrogen gas (N2) only enters the biosphere after being fixed by micro-organisms or lightening.
Nitrogen-containing compounds such as nitrous oxides (NOx) and ammonia (NH3) can enter the biosphere by both wet (i.e. via precipitation) and dry deposition (i.e. the direct deposition of gases) = nitrogen deposition. N2
NH3 & NOX

6. Why is nitrogen deposition a problem for heathlands?
Healthy heathland soils are nutrient poor – this allows plants like to heather to outcompete faster growing plants (such as grasses and bracken) and dominate the heathland.
If soil nutrient levels increase, faster growing species (grasses, bracken, birch trees) may invade and turn the heathland into a different habitat (woodland).
Nitrogen deposition can increase soil nutrient levels and so threatens the existence of the heathland habtiat.

7. ? Nitrogen deposition: Nitrous Oxide (NOx)
Which of these sources was the greatest emitter of nitrous oxide (NOx) in England and Wales in 2005?
Industry
Domestic & Commercial
Road Transport
Other Sources
10%
21%
51%
18%
Source: Data for Neighbourhoods and Regeneration (

8. ? Nitrogen deposition: Ammonia (NH3) 51% 71% 81% 91% 61%
In 2007, 289 thousand tonnes of ammonia were emitted in the UK (excluding natural sources). ?
What percentage of these emissions came from agriculture
51%
71%
81%
91%
61%

9. The effect of nitrogen deposition on heather growth
Activity A
The effect of nitrogen deposition on heather growth
© Carl Corbidge
© Amy Rogers
© Amy Rogers
© Amy Rogers

10. The effect of nitrogen on heather
Between 2009 and 2010 a scientist from the University of Nottingham conducted a laboratory experiment to investigate how nitrogen deposition affected the growth of common heather (Calluna vulgaris).
Videos explaining his research are available at the following website:
Please watch ‘The Dirt Collector II’ and ‘The Dirt Collector III’. ‘The Dirt Collector I’ also provides background information on the study.

11.    The effect of nitrogen on heather
Questioning the experimental methodology 
Suggest reasons why the scientist collected several soil samples from each site rather than just one larger soil sample from each site.
Suggest why the scientist collected seeds from one heather plant at one site, rather than from several heather plants at multiple sites.
Describe some of the ways in which the experiment was controlled.  

12. The effect of nitrogen on heather
Questioning the experimental methodology
Q: Suggest reasons why the scientist collected several soil samples from each site rather than just one larger soil sample?
A: As well as being affected by atmospheric nitrogen deposition, the nutrient content of soils at small scales could be affected by other factors. These could include manure from animals, or the presence of a nitrogen fixing shrub such as gorse. By taking several soil samples, the potential effect of these local scale effects can be averaged out.
Return to classroom discussion slide

13. The effect of nitrogen on heather
Questioning the experimental methodology
Q: Suggest why the scientist collected seeds from one heather plant at one site, rather than from several heather plants at multiple sites.
A: Heather plants may vary in their health and vigour. This may effect the health of the seeds they produce, which may in turn affect how well they germinate and how quickly the seedlings grow. If seeds from different heather plants had been used, it may have been difficult to work out if variation in heather seedling germination and growth was due to the experimental nitrogen levels or the initial condition of the seeds.
Return to classroom discussion slide

14. The effect of nitrogen on heather
Questioning the experimental methodology
Q: Describe some of the ways in which the experiment was controlled.
A: Controls include:
Collecting heather seeds from one plant at one site rather than several plants at several sites;
Growing seedlings in a growth room rather than a greenhouse. This allowed control of the environmental conditions (e.g. temperature, light);
Rotating the seedlings to account for any potential variation in the environmental conditions within the growth room;
Using purified and de-ionised water to ensure that the only nutrients available to the heather seedlings were those within the soil samples.

15. The effect of nitrogen on heather
Analysing the data
The data collected by the scientist is shown on page 3 of your workbook. Use the data shown to answer Questions A1 - A6.

16. ? Laboratory analysis vs. Field investigation
The previous questions analysed the results of a laboratory experiment. Your next task will be to analyse the results of a field investigation.
In pairs/groups, discuss some of the benefits and potential problems of both laboratory and field-based experimentation / investigation. ?

17. Laboratory Experiments
Field Observations
Pros
Can establish cause and effect
Behaviours/responses are natural.
Allows for precise control of variables
Experiments can be replicated
Experiments can be repeated under the same conditions
Cons
Artificial system
Too many variables to control – makes it difficult to establish cause and effect
Behaviours/responses may not be ‘natural’
Not as easily replicated
Not easily repeated under the same conditions

18. Activity B: Virtual Field Trip
The effect of nitrogen deposition on heather and bracken percentage cover
© Carl Corbidge
© Amy Rogers
© Amy Rogers
© Amy Rogers

19. Activity B: Virtual Field Trip
The main aim of this activity is to…
…investigate whether the nitrogen content of heathland soil affects the plant species community.
We will be investigating whether or not nitrogen deposition affects the abundance of two plant species: heather and bracken.
We will be comparing the heathland plant community on two sites with different levels of nitrogen deposition.

20. Site 1 – Low N deposition (2.4 Kg N ha-1 year-1)
Site 2 – High N deposition (8.4 Kg N ha-1 year-1)
Key
Surrounding habitat
Heathland
Extent of field site
Site 1 and 2 have been based upon data for the sites listed as sites b and o in Table 1 of the student workbook.
Previous studies indicate that Site 1 has a lower nitrogen deposition rate than Site 2. Suggest reasons why this might be. ?

21. The effect of N deposition on bracken and heather percentage cover
To conduct this investigation we need to be able to identify the two focal plant species: bracken and heather.

22. Identification training: Bracken
Stiff, upright, triangular- shaped fronds produced from an underground rhizome.
Fronds emerge in May.
In autumn the fronds turn reddish-brown and die back to ground level.
Plant can reach over 1.5 m high.
© Peter Crittenden
Bracken
(Pteridium aquilinum)

23. Identification training: Heather
There are three species of heather that may be found on our field sites.
You do not need to be able to identify between these species.
Cross-leaved heath
(Erica tetralix)
Common heather
(Calluna vulgaris)
Bell Heather
(Erica cinerea)
© Roger Key
© Peter Crittenden

24. Identification training: Heather
For the purposes of this study, we do not need to identify the different species of heather. All three species have the following characteristics:
© David Glynne Fox
Small purple or pink flowers
Small, narrow, linear green leaves.
Cross-leaved heath
(Erica tetralix)

25. ? The effect of N deposition on bracken and heather percentage cover
Before we begin….. ?
What null hypothesis are we testing?
H0 = Nitrogen deposition does not affect the percentage cover of heather and bracken (i.e. the distribution of heather and bracken is the same regardless of the level of nitrogen deposition).

26. ? The effect of N deposition on bracken and heather percentage cover
Before we begin…..
What kind of things might we need to plan/think about before starting an investigation such as this one? ?
The two main things we need to think about are:
How will we measure percentage cover? What is our sampling unit?
How should our samples be arranged? What is our sampling strategy?

27. How will we measure plant percentage cover?
We will be using quadrats (0.5 x 0.5 m) to measure the percentage cover of heather and bracken,
Place the quadrat over the area of vegetation to be surveyed.
Look at the quadrat from directly above.
The total area of ground within the quadrat is 100%.
For each plant species, estimate the % area of the quadrat that it covers.
© Peter Crittenden

28. ? ? ? Using quadrats to measure percentage plant cover
Estimate the percentage cover of heather in this quadrat. ?
© Peter Crittenden
Did everyone in your class give the same answer? How varied were the estimates of percentage cover? ?
Percentage cover is a speculative measure – the results will vary depending upon who is taking the measurements. When collecting percentage cover data it is important that the same person collects all the data, to make sure that it is consistent.
Can you think of a way to make it easier to estimate the percentage cover? ?

29. ? Using quadrats to measure percentage plant cover
© Peter Crittenden
Should we include plants which are rooted outside the quadrat, but whose leaves fall over the quadrat? ?
The bracken plant indicated by the yellow arrow is not rooted inside the quadrat, but some of the fronds fall inside the quadrat. Should this frond be included in the percentage cover calculations?
Typically, studies would not include individuals that are not rooted inside the quadrat into percentage cover calculations. However, it is more important that data collection is consistent, i.e., if calculations of one quadrat include plants that fall over the quadrat, but that are not rooted inside it then all quadrats should follow the same methodology.

30. ? How many quadrats of data should we collect?
Within each site, how many quadrats of data should we collect? Should we collect, 1, 5, 10 or more? ?
The more the better! More quadrats mean more information about the effect of nitrogen deposition on the percentage cover of heather and bracken. In practice, the number of quadrats you collect will depend on factors such as the size of the study site and the amount of time you have for data collection.
In this study you will be collecting 10 quadrats per site.

31. ? How should we position our quadrats?
Within each site, how will you position your 10 quadrats? ?
There are two main ways of positioning your quadrats:
Systematically Randomly
The technique you use will depend on the question you are trying to answer.

32. Systematic sampling
Systematic sampling is used when studying changes along an environmental gradient. For example, does the percentage cover of heather change as you move downhill?
A sampling line is established parallel to the environmental gradient. Quadrats are placed at regular intervals along the sampling line
Can you think of any other studies that may use systematic sampling? ?
Environmental gradient

33. Random sampling
Random sampling is often used when comparing sites that are different in some way. For example, comparing the plant species richness of two fields that are under different management regimes.
When comparing sites, why might it be important that samples are collected randomly? ?
Random sampling ensures that every position within the study site has an equal chance of being sampled. This will avoid collecting a biased sample.

34. How do we sample randomly?6 5 4 3 2 1
Divide the site into a grid and use random numbers to generate co-ordinates
(e.g., [2,3]).
Position quadrat at these co-ordinates.
‘Throwing’ quadrats is not really random!
Image source: www-saps.plantsci.cam.ac.uk

35. Practice time!
Can you identify the heather and bracken in this quadrat? ?
© Peter Crittenden
Bracken
Heather
What do you estimate the percentage cover of heather and bracken is? ?
Warning: Not all heather plants will have flowers!

36. Open the document ‘quadrats.ppt’ to start collecting your data!

37. The effect of N deposition on bracken and heather percentage cover
Analysing the data
Complete questions B1 – B4 in your workbook.
The extension activity is provided as a separate worksheet. It uses the Mann-Whitney U-Test to determine whether or not the observed differences in the percentage cover of heather and bracken between Site 1 and Site 2 are statistically different.
Extension activity available (optional)

38.   The effect of N deposition on bracken and heather percentage cover
Questioning the experimental methodology
Were there any anomalous results?
What were the potential sources of error in your investigation, and how may they have affected the validity and reliability of your data?
What were the limitations of your methodology and the site selection? How may these limitations have affected your ability to assess whether nitrogen deposition affects the percentage cover of heather and bracken?  

39. The effect of N deposition on bracken and heather percentage cover
Questioning the experimental methodology
Potential sources of error could include:
Percentage cover is a subjective measure – could affect reliability of heather and bracken abundance measures.
‘Boundary decisions’ – when individuals overlap the edge of the quadrat do you include them or not?
How might the time of year affected the percentage cover of different species?
Incorrect plant identification.
Return to project evaluation slide

40. The effect of N deposition on bracken and heather percentage cover
Questioning the experimental methodology
Limitations of the study include:
Ten quadrats per site is a relatively small sample size.
Have not collected our own data on nitrogen deposition – are working on the assumption that a previous study was correct.
Only two sites investigated – can this really tell us about the effect of nitrogen deposition in all heathlands?
Return to project evaluation slide

41. Activity C
The effect of nitrogen deposition on plant diversity and species composition of lowland heathland
© Carl Corbidge
© Amy Rogers
© Amy Rogers
© Amy Rogers

42. Activity C The main aim of this activity is to…
…investigate whether the nitrogen content of heathland soil affects the plant species community.
We will be investigating whether or not nitrogen deposition affects the plant diversity and species composition of lowland heathlands.
We will be comparing the heathland plant community on two sites with different levels of nitrogen deposition.

43. The effect of N deposition on plant diversity and species composition
Does nitrogen deposition affect the diversity and species composition of lowland heathland vegetation? ?
What null hypothesis are we testing?
H0 = Nitrogen deposition does not affect the diversity and species composition of lowland heathland vegetation.

44. What is species richness?
We will be comparing the plant diversity on two heathland sites.
What is ‘diversity’? To understand ‘diversity’ we need to first understand species richness and species evenness.
Species richness = the number of different species in a given area.
Area 1
Species richness = 4
Area 2
Species richness = 6
The diagrams above show the distribution of individual plants within a habitat. Each dot represents an individual (e.g. an individual plant). Each colour represents a different species. Dots of the same colour belong to the same species.

45. ? What is species evenness?
Species evenness is the relative abundance with which each species is represented in each area.
Area 3
Species richness = 4
Number of individuals = 16
Area 4
Species richness = 4
Number of individuals = 16
Area 3 has greater species evenness. ?
Areas 3 and 4 have the same species richness and the same number of individuals. Which area has the greatest species evenness?

46. ? What is species diversity?
Species diversity – the number of different species in an area (i.e. species richness) weighted by some measure of species evenness.
Area 3
Species richness = 4
Number of individuals = 16
Area 4
Species richness = 4
Number of individuals = 16
Area 3 is more diverse than Area 4. If students struggle with this, try asking the question in different ways. Which area has more variation? Which area would be more valuable to conserve? ?
Which area do you think is more diverse, Area 3 or Area 4?

47. How do you measure species diversity?
Species diversity is often measured by the Simpson’s Index of Diversity (D). OR
Where N is the total number of individuals of all species found and n is the total number of organisms of a particular species found.
The higher the value of the index, the greater the diversity of the community.

48. Species diversity – worked example
Area 4
Area 3
Species n
n(n-1) 4 12
Total 16 48
Species n
n(n-1) 2 9 72 1 4 12
Total 16 86
Please choose the worked example that uses the formula detailed in your syllabus.

49. Species diversity – worked example
Area 3
Area 4
Species n
n/N
(n/N)2 4
0.25
0.0625
Total (N) 16
Species n
n/N
(n/N)2 2
0.125
0.0156 9
0.5625
0.3164 1 4
0.25
0.0625
Total
(N) 16 86
Please choose the worked example that uses the formula detailed in your syllabus.

50. Complete question C1 – C3 in your workbook.
The effect of N deposition on plant diversity and species composition
Analysing the data
A quadrat was used to investigate the percentage cover of different plant species in Site 1 and Site 2.
Table 4 in your workbook shows the percentage cover of different plant species in one quadrat taken from each site.
Complete question C1 – C3 in your workbook.

51. The effect of N deposition on plant diversity and species composition
Questioning the methodology
What were the potential sources of error in your investigation, and how may they have affected the validity and reliability of your data?
What are the limitations of your methodology and site selection? How may these limitations have affected your ability to assess whether nitrogen deposition affects the heathland plant species community.  

52. The effect of N deposition on plant diversity and species composition
Questioning the methodology
Potential sources of error could include:
Percentage cover is a subjective measure.
What to do when leaves of different species overlap one another?
Incorrect identification of species.
How might the time of year affect the percentage cover of different species?
Return to project evaluation slide

53. The effect of N deposition on plant diversity and species composition
Questioning the methodology
Limitations of the study include:
A single quadrat per site does not allow us much confidence in the diversity calculations made.
Have not collected our own data on nitrogen deposition – are working on the assumption that a previous study was correct.
Only two sites investigated – can this really tell us about the effect of nitrogen deposition in all heathlands?
Return to project evaluation slide