Stratified (non-random)

• Habitats are rarely uniform; smaller areas within a habitat are different from the main habitat e.g. bracken patches in a heathland area; a random sample may have none in the bracken patches - an inaccurate reflection onf the habitat
• Divide habitat into the different areas and sample each separately; e.g. heathland 200m^2 overall, bracken 50m^2 (25%) - for 12 samples: 3 (25%) would be in the bracken and 9 (75%) in the general heathland
• Advantages: All areas of habitat are sampled, no underrepresentation, disadvantage: may cause over-representation, and have disproportionate samples taken in smaller areas that look different