Where are my quadrats? Positional accuracy in fieldwork


Correspondence author. E-mail: m.e.dodd@open.ac.uk


1. There has been much written about sampling design, spatial scale and the need for permanent plots in long-term monitoring but very few authors have considered how to locate and re-find positions in the field accurately. Indeed, many attempts at re-sampling exact positions set up many years previously have failed.

2. Various field measurement systems were compared including 50-m tape, consumer-grade GPS, total-station theodolite and differential GPS.

3. Both total station and differential GPS were able to measure and relocate quadrats accurately to within a few centimetres over distances of hundreds of metres or more.

4. Of over 500 1 × 1 m vegetation monitoring quadrats set out and location re-recorded by differential GPS at sites across UK, only 1% had positional errors of more than 0·2 m. None of these quadrat locations relied on permanent markers. Differential GPS has the advantage of speed and delivering coordinates in latitude/longitude or local coordinate system directly.

5. Accurately located quadrats can be resurveyed many years in the future just using the original coordinates without worrying about ‘permanent’ markers that rarely turn out to be truly permanent. If more researchers used these techniques, then there is huge potential for establishing networks of accurate long-term monitoring positions, which could provide information on a wide range of topics, such as vegetation dynamics and environmental change even if these were not the original research objectives.