Plotless Sampling

This technique is mainly used for woodland, where individual plants can be more widely spaced out. There are four main methods of plotless sampling:
1. Point-centred quarter method: measures from the sampling point to the nearest individual in a quadrat. This is possibly the most accurate, but it can be biased where plants are evenly distributed.
2. Nearest individual method: measures from the sampling point to the nearest individual.
3. Nearest neighbour method: measures from the sampling point to the nearest neighbour of an individual. Requires identification of random individuals from which measurements are made; it is biased towards isolated individuals.
4. T-square (random pairs) sampling method: This is a more time-consuming version; measures from the sampling point to the nearest individual; an imaginary line is drawn through the sampling point (at right angles to the first sample) and then the nearest neighbour found on the other side of the line. A minimum of 10 samples are suggested.



Picture showing the nearest individual and nearest neighbour from a sampling point

If species are clumped:
• Nearest neighbour overestimates density.
• Point-centred underestimates density.

If species are evenly distributed:
• Nearest neighbour underestimates density.
• Point-centred overestimates density.

T-square: This combines the attributes of the point-centred quarter method and nearest neighbour method.
Plotless Sampling:
Advantages
• Cheap.
• Relatively easy.
• Avoids use of quadrats in difficult areas.
Disadvantages
• Suffer from bias.
• You might encounter variable undergrowth (e.g. brambles, thickets) making it difficult to reach some plants.