Wildlife - Plant Surveys

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Types of 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
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Survey Types

  • 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
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Survey Types: Species List

  • 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
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Survey Types: Value Estimates of Cover

  • 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

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Quadrats

  • 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
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Frame Quadrats

  • 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.
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Point Quadrat

  • 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
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Permanent 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
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Quadrat Size

  • 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
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Number of Quadrats

  • 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
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Measure of Abundance

  • 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
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Sampling Design

  • 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
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