Marram grass (Ammophila arenaria):

• is a tough, perennial grass species found on coastal sand dunes
• requires sunlight for photosynthesis
• absorbs water and essential minerals from highly permeable sand through its deep root network
• is grazed by wild rabbits and is vulnerable to mechanical damage from human foot traffic.

Give two abiotic factors and two biotic factors that could affect the population size of marram grass.

Ecologists investigated the populations of marram grass in two different sections of a sand dune ecosystem:

• Zone A (Mobile Dunes): an active, highly dynamic dune close to the shoreline with high wind exposure and constant sand movement
• Zone B (Fixed Dunes): a mature, stable dune further inland with developed soil cover and negligible sand movement

Plan an investigation using a $0.25m\times 0.25m$ quadrat to compare the mean number of marram grass plants per $m^2$ in Zone A and Zone B.