Students conducted physical geography fieldwork to investigate ecological succession and soil development across a sand dune system from the strandline inland. Below is a summary of the data they collected at 10-metre intervals.
| Distance from Strandline (m) | Percentage Vegetation Cover (%) | Soil pH |
|---|---|---|
| 0 (Strandline) | 0 | 8.2 |
| 10 (Embryo Dune) | 15 | 8.0 |
| 20 (Yellow Dune) | 55 | 7.4 |
| 30 (Grey Dune) | 90 | 6.5 |
Identify two further pieces of primary physical data that the students could collect at these sites to investigate sand dune succession and soil development.