Skill:
• Analysis of data showing primary succession
Ecological succession describes the process by which a sequence of increasingly complex communities develop over time
- The climax community is reached when succession has ended and the community has all of its characteristics
Primary Succession
Primary succession occurs when communities develop on entirely new land without any established soil
- This may occur at river deltas, glaciers, sand dunes or on exposed rock
The organisms which first colonise the region are called pioneer species and typically consist of lichen or moss
- As the lichen and moss die, they decompose, which creates the first organic soil capable of sustaining plant growth
As plant species colonise the area, the litter produced by their growth and their decomposing remains will cause changes:
- Soil depth will increase (as plants add humus to the soil) and soil pH will become altered
- Soil mineral content will increase and rocks will begin to be broken down by the action of roots
- The soil will become aerated and water retention is increased (drainage is reduced)
These changes will allow for the growth of larger plants, which will reduce erosion through the binding action of their roots
- Not all plant species will thrive in unison – larger plants will eventually outcompete smaller shade intolerant plants
Overview of Primary Succession
Primary Succession Data
A primary succession sequence can be identified according to the distribution of plants at a site of ecological nascency
- This is any location where a new community may emerge from uninhabitable land – such as a coastal sand dune or glacier
- The regions closer to the site of ecological nascency will be in the earlier chronological stages of succession
Glacial retreat exposes bare rock for colonisation, so regions further from the glacier have had more time to develop life
- Hence regions further from the glacier are expected to contain larger trees common to a climax community, while regions closer to the glacier are expected to contain plant life common to the earlier stages of primary succession
Primary Succession Following Glacial Retreat
Diagram:
All
Alder only
Spruce only
Hemlock only