Pioneer & Climax Communities
What are pioneer communities?
- In pioneer communities (i.e. in the early stages of succession), gross productivity is low due to the unfavourable initial conditions and low density of producers (low gross primary productivity)
- However, the proportion of energy lost through community respiration is also relatively low
- This means that net productivity in pioneer communities is relatively high
- This allows the pioneer community system to grow and accumulate biomass
What are climax communities?
- In climax communities (i.e. in the later stages of succession), gross productivity may be relatively high, due to a high density of producers (high gross primary productivity) and consumers (high gross secondary productivity)
- However, this relatively high gross productivity is balanced by the large amounts of energy lost from the climax community system through respiration
- This causes the net productivity of a climax community to approach 0
- As this happens, the productivity–respiration (P:R) ratio approaches 1
- This ratio reaches 1 when biomass and energy is being produced by the system at the same rate as it is being used
- If the ratio >1, then excess energy and biomass is being produced
- If the ratio <1, then more biomass and energy is being consumed than is being produced
- To reach a stable (climax) community, there has to be an equilibrium between the community production and the community respiration
- There is no one climax community, but rather a set of alternative stable states for a given ecosystem
- What the climax community eventually looks like depends on a large variety of factors, including climate, the local soil properties, and a range of random events that can occur over time (e.g. extreme weather events, human interventions)
- What the climax community eventually looks like depends on a large variety of factors, including climate, the local soil properties, and a range of random events that can occur over time (e.g. extreme weather events, human interventions)
Changes occurring in a community as it develops from a pioneer community into a climax community through the process of succession
Comparison of Pioneer and Climax Communities
Feature | Pioneer Communities | Climax Communities |
Stage in succession | Early stages | Later Stages |
GPP | Low | High |
NPP as a % of GPP | High | Low |
Species Richness and Diversity | Low | High |
Niches | Fewer, wider | Many, narrow |
Size of organisms | Small | Large |
Species composition | Fewer species, adapted to harsh conditions | More species, adapted to stable conditions |
Total biomass (amount of organic matter) | Low | High |
Soil depth | Shallow | Deep |
Soil quality |
Poor (little nutrients and organic material) |
High (nutrient-rich and full of organic matter) |
Growth rate | Rapid | Slower |
Energy flow | Simple and linear | Complex and cyclic |
Nutrient cycling | Less efficient, open system (external inputs) | More efficient, closed system (nutrients are recycled) |
Dominant organisms | Lichens, mosses, algae, bacteria, and fungi | Woody plants, trees, and shrubs |
Stability | Unstable, prone to disturbance and colonisation | Stable, resistant to disturbance and colonisation |
Examples | Pioneer species like lichens and mosses on rocks | Ancient oak forests |