Wildlife - Plant Surveys

• all plant survey methods assume you can identify the plants first
• different methods suitable for different situations
  • dependent on the type of plant community and the way you intend to use the results
• amount of time available, as well as time of year
  • plants grow at various times of year

• need to be repeatable so that different workers can survey the same site at various times or different sites can be compared
• usually carried out using standard methods, such as:
  • species list
  • species list with visual estimates of cover
  • quadrat sampling
  • national vegetation classification
  • marking and mapping individuals

• quickest method of surveying plants is to list the plant species
• decide which groups are important to record
  • may be only one group, such as trees, or it may include all plants from mosses and ferns to herbaceous plants and woody trees and shrubs
• will indicate species richness (species diversity) of your study site
• will not indicate relative abundance (amounts) of species
  • in theory, two sites could have the same species but look quite different if different plants dominate

• surveyor lists species in the study area and gives an estimate of the % cover of each species
• several different scales for recording abundance
• ADVANTAGES: methods are rapid so are useful for studying large areas of vegetation, results are sufficient to make judgements of the wildlife value of a site
  
• DISADVANTAGES: can be subjective. Different people have different estimates of cover. Surveyor may miss rare plants.
• DAFOR: in the DAFOR system each species is given a rating according to whether it is Dominant, Abundant, Frequent, Occasional, or Rare
  
• Domin: the Domin scale is more objective than the DAFOR scale because it is based on percentage cover

Domin Value

Cover-abundance

10

91-100%

9

76-90%

8

51-75%

7

34-50%

6

26-33%

5

11-25%

4

4-10%

3

<4% frequent

2

<4% occasional

1

<4% rare

• not possible to survey all the plants in a study area so you have to take samples
• when planning a survey you need to consider:
  • type of quadrat
  • quadrat size
  • number of quadrats
  • measurements of abundance
  • sampling design
  • transects
• positives
  • save time
  • can be more accurate by placing multiple quadrats
• negatives
  • miss rare plants
  • two nearby areas are not always the same
  • different conditions, including light levels and water levels

• rigid frame made of wood, metal, or plastic
  
  • may be defined on the ground with tapes or string, especially where the quadrats are large
• often square, but can be rectangular or any other shape as long as you know its area.

• thin metal rod is lowered vertically through vegetation
  • theoretically a frame quadrat of infinitesimally small area
• record each plant species the point 'hits' on the way down
  • usually a frame is used
    • consists of a metal bar with holes along its length through which you thread the point quadrat

• frame quadrats which are fixed in place or which can be replaced on fixed markers such as corner posts
• used in monitoring programmes, for example, monitoring the population of a given species over time, or monitoring area regeneration

• different types of vegetation require different quadrat sizes
  • larger plants or more sparsely distributed plants require larger quadrats
• sizes most often used:
  • 10cm x 10cm = bryophytes (mosses) or lichens
  • 0.5m x 0.5m up to 2m x 2m = grassland
  • 10m x 10m up to 50m x 50m = trees and tall shrubs
• 'maximum return for minimum effort'
  • small samples can be taken for the same amount of effort as fewer large samples
    • more smaller samples give less statistical error than fewer large samples
    • smaller samples have greater 'edge effect'
      • Edge effect: when an animal or plant is at the edge of the quadrat, a decision has to be made as to whether it should be counted, more often than not it tends to be counted
        
• ADVANTAGES: 
  
  • less harmful to most species compared to other methods
  • relatively simple compared to other methods
  • one of the most affordable techniques
  • allows researchers to study plant and animal populations over large areas
• DISADVANTAGES:
  
  • can be physically demanding
  • quadrats that are too large, too small or spaced inappropriately result in errors
  • larger species require larger plots
  • randomly spaced quadrats that are too small might miss too many individuals
  • researchers who are inconsistent when counting or omit species that lie only partially within the boundaries may introduce errors

• need to take enough samples for statistical analysis, without wasting time
• estimating the optimum:
  • place a series of quadrats randomly across sampling area
  • record the cumulative number of species as you study each quadrat in turn
    • eventually reach a point where you have identified all the common species and further sample yields little increase

• Density
  • number of individual plants in the unit area
  • can be useful when you can distinguish discrete individuals such as trees, but is difficult to count individual plants when plants spread vegetatively, such as grass
• Frequency
  
  • the measure of the number of percentages of the samples (quadrats) in which a given species is present
  • rapid and indicates the distribution of species but ignores the species abundance and is biased against species with a clumped distribution
• Biomass
  
  • a measure of the dry weight of all the plants in a given area at a given time
  • depends on harvesting the plants at ground level, then sorting, drying and weighing them.
    • time-consuming
    • very destructive so is rarely used in environmental studies
• Cover
  • estimate of the area covered by a plant when viewed directly from above
  • useful measure because it takes into account both size and density of plants
  • favours species that spread or those with larger leaves

• three systems of sampling
• Random
  • simple random sample is a subset of individuals chosen from a larger set, each individual is chosen randomly
  • need to ensure that your sample is representative of the whole plant community
  • in random sampling every point in a study area has an equal chance of being included in the sample
  • true randomness is difficult to achieve without some human bias
• Stratified Random Sampling
  
  • involves dividing a population into smaller groups called strata
    • organised based on the shared characteristics or attributes of the member in the group
  • if the study area has variation, for example different soil types
• Systematic sampling
  
  • sample taken as part of a systematic methodology
  • quadrats placed at a regular pattern across the study area
  • not truly representative of the study area because the regular samples may coincide with natural regularity
  • may be useful when the purposes is to map variation in plant abundance across a study area