A key feature of dune vegetation is the sequence of different vegetation communities or zones that occur with increasing distance landward (Figure 1). Each zone in the vegetation sequence has a different species composition that is related to the ability of plant species to withstand environmental factors prevailing in that zone.
These factors include proximity to the sea and the morphology, shape and extent of the dunes themselves. Other factors can also be important in determining zonation on dunes such as low-lying swales between dunes where the water table sometimes be close to the ground can result in distinct dune slack vegetation communities. On fixed dunes, which were typical for most of New Zealand beaches prior to human settlement, zones tend to be parallel to the shore as key environmental stresses decrease with distance landward along with dune landforms that often parallel to shore.
Vegetation on dunes
Up to three broad vegetation types running parallel to the shoreline often occur naturally from the beach landward:
- Seaward fore-dune zone of sand binders such as pingao and spinifex;
- Mid-dune with ground covers such as sand coprosma and pohuehue; and
- Back-dune with shrubs (e.g. karo, taupata) and trees (e.g. houpara, pohutukawa, ngaio).
Sampling change in vegetation and dune form along transects located perpendicular to the coast will provide an indication of the vegetation types and species in each zone. Re-measurement of these characteristics using consistent methods will show any changes that are occurring over time.
Figure 1: A dune profile from sand binding grasses on the most seaward foredune zone, to increasing ground cover and shrubs on the mid-dunes zone, to forests on the most landward zone. This continuum reflects the change in environmental conditions from seaward to landward dunes. Sampling across the dunes using transects will therefore quantify the cover and composition of vegetation across these zones.
Dune profiles
On fixed dunes, which were typical for most of New Zealand beaches prior to human settlement, zones tend to be parallel to the shore as key environmental stresses decrease with distance landward. This also occurs with dune landforms such as dune crests and swales that often run parallel to shore.
Other factors can also be important in determining zonation on dunes such as low-lying swales between dunes where the water table sometimes be close to the ground and can result in distinct dune slack vegetation communities.
A practical method has been developed to map the contour of the dunes that can be matched to the survey of vegetation cover.