🎒 Base knowledge and understanding

✅ Tasks

🌿 Content

🔑 Key terms

🎯 Context

This lesson uses sand dunes at Studland Bay, Dorset as a unifying example. Sand dunes are one of the best places to see both zonation and succession in a single landscape. As you walk inland from the sea, the communities change. This spatial pattern also mirrors a temporal pattern, because the dunes furthest from the sea are the oldest.

Zonation: changes along an environmental gradient

<aside> <img src="/icons/leaf_green.svg" alt="/icons/leaf_green.svg" width="40px" />

2.5.1 Zonation refers to changes in community along an environmental gradient.

Zonation occurs due to a range of factors, such as changes in elevation, latitude, tidal level, soil horizons or distance from a water source.

</aside>

https://www.google.com/maps/@50.6679873,-1.9492585,1135m/data=!3m1!1e3?entry=ttu&g_ep=EgoyMDI2MDIxMS4wIKXMDSoASAFQAw%3D%3D

Imagine walking from the shoreline at Studland Beach inland through the sand dunes. As you walk, conditions change: salt spray decreases, wind exposure reduces, soil depth increases, humus content rises and moisture availability changes. These changing abiotic conditions support different communities at different points along the gradient.

This is zonation: changes in community along an environmental gradient. Zonation is a spatial phenomenon. It describes what we can observe at one moment in time as we move from one place to another.

Examples of environmental gradients:

Gradient Example
Distance from the sea Sand dune zonation at Studland Bay
Elevation Vegetation zones on a mountainside
Tidal level Rocky shore zonation (splash, intertidal, subtidal)
Latitude Biome distribution from equator to poles
Soil horizons Changes in organisms with soil depth

  1. In your own words, define zonation.

  2. Suggest three abiotic factors that might change as you walk inland from the sea across a sand dune system.

  3. Zonation is described as a spatial phenomenon. What does this mean?

Transects and data collection

<aside> <img src="/icons/leaf_green.svg" alt="/icons/leaf_green.svg" width="40px" />

2.5.2 Transects can be used to measure biotic and abiotic factors along an environmental gradient in order to determine the variables that affect the distribution of species.

Consider data in tables or figures related to zonation, including kite graphs.

</aside>

To investigate zonation, we use transects. On a sand dune, a transect is laid at 90° to the sea, running inland through the dune zones. At regular intervals along the transect, we place quadrats and record biotic factors (species present, percentage cover) and abiotic factors (soil pH, soil depth, wind speed, soil moisture).

Multiple parallel transects are needed for valid, representative data.

The data below were collected by students along three parallel transects through the dunes at Studland Beach on the south coast of England, using 1 m² quadrats at 10 m intervals.

Table 2.5: Data from Studland Beach

Distance from the sea / m Average slope angle / ° % cover of marram grass % cover of heather
0 5 0 0
10 15 37 0
20 5 63 0
30 5 48 0
40 3 8 34
50 -7 0 43
60 3 0 100
70 -5 0 100
80 -2 10 35
90 0 0 68

Negative slope angles indicate a downward slope (a dune slack, where the land surface dips towards the water table).

  1. At what distance from the sea does marram grass reach its peak percentage cover?

  2. At what distance does heather first appear?

  3. Describe the relationship between the distribution of marram grass and the distribution of heather. Do they overlap? What might this suggest?

  4. What does a negative slope angle tell us about the dune profile at that point?

Kite diagram task