Plant Sampling

• Random Sampling

  • Avoid bias, sample randomly selected so each organism has equal chance of counted representative
  • Deliberate selection may give an biodiversity overestimate
  • Disadvantage: May not cover all areas equally + low presence species may be missed
  • Habitat areas mapped with long tape measures (often 10m^2)
  • Using random co-ordinate pairs, generated by calc, quadrats positioned in sampling square
  • Wireframe quadrat is fixed size e.g. 1m^2, 0.5m^2 or 0.25m^2
  • Sample number depends on habitat size, time + species number
  • If comparing, same number should be taken in each
  • Larger sample = more representative data; possible to calc mean data to assess validity (Often 10)
  • Recording results: Need suitable results table, prepared in advance
  • Species richness, species presence recorded; qualitative, unlikely all listed
  • Species evenness, each species number recorded (more meaningful for biodiversity); quantitative
• Quantitative Sampling

  • Often state measuring plant abundance in area
  • Measured many ways
  • Counting each plant number (time-consuming)
  • Estimate percentage cover (easier in square frame)
  • Estimating percentage cover subjective
  • Some quadrats have wire divisions to make it easier
  • Could use an abundance scale to estimate relative abundance
  • ACFOR - Abundant/Common/Frequent/Obvious/Rare
  • Also could measure abundance w/ point quadrat w/ 10 needles; plant species recorded present if needle touches it
• Systemic Sampling

  • Continuous belt transect is quadrat placed along tape, so small area sampled, e.g. 0.5m^2
  • After 1st sample, quadrat flipped over, so next area sampled, etc
  • Interrupted belt transect is quadrat placed at set distances along line e.g. every 2 metres; saves time on long transects
  • Advantages: Useful if habitat shows clear environmental gradient (e.g. grassland to woodland)
  • Disadvantage: Only species on line recorded - underestimate
• Stratified Sampling

  • Habitats rarely uniform; smaller areas in a habitat different from main habitat e.g. bracken patches in heathland
  • Random sample may have no bracken patches; inaccurate
  • Divide habitat to different areas + sample each separately
  • E.g. heathland 200m^2 overall, bracken 50m^2 (25%)
  • For 12 samples: 3 (25%) in bracken + 9 (75%) in general heathland
  • Advantages: All areas sampled, no underrepresentation
  • Disadvantage: may cause over-representation + have disproportionate samples from smaller areas
• Opportunistic Sampling

  • Researcher takes samples from prior knowledge or in process of collecting data
  • Sample area they know contains particular species
  • Advantages: Easier + faster than random
  • Disadvantage: Biased data, or overestimate of biodiversity