2.5D Community and productivity in succession (HL) Notes

1. The type of community that develops during succession is not random.
2. It is shaped by a complex interaction of abiotic factors (such as climate, soil, topography, and disturbance events) and biotic factors (such as predation, grazing, and competition).
3. These influences determine which species can establish, survive, and dominate during different stages of succession, ultimately shaping the climax community.

Abiotic Factors Influencing Succession

1. Climatic Factors

1. Temperature, precipitation, humidity, and seasonality are primary determinants of succession pathways and final community structure.
2. These factors influence:
   1. Rate of soil development
   2. Plant growth and photosynthetic activity
   3. Species composition (e.g., tropical vs. temperate vs. arid communities)

2. Local Bedrock and Soil Properties

1. The parent rock and soil characteristics determine nutrient availability, pH, drainage, and texture.
2. These influence plant establishment and ecosystem succession.

Soil Depth and Texture

1. Deep, loamy soils allow large plants with extensive root systems.
2. Thin, rocky soils support only shallow-rooted species like grasses or mosses.

Nutrient Availability

1. Rich soils (e.g., volcanic soils) promote rapid succession toward forests.
2. Nutrient-poor soils (e.g., sandy or acidic) slow succession, supporting heathlands or shrublands.

Soil pH

1. Acidic soils (from granite or sandstone) limit plant diversity, favoring acid-tolerant species such as heather.
2. Alkaline soils (from limestone) support calcareous grasslands with unique flora.

Drainage

1. Poorly drained areas become waterlogged, limiting oxygen for roots and forming wetlands.
2. Well-drained slopes favor drought-resistant vegetation.

3. Geomorphology

Steep Slopes

1. Promote erosion and hinder soil accumulation.
2. Support only hardy, shallow-rooted species such as shrubs, lichens, or alpine grasses.

Flat Terrain

1. Promotes deep soil formation and accumulation of organic matter, enabling dense forest growth.

Aspect (Slope Orientation)

1. South-facing slopes (in the Northern Hemisphere) receive more sunlight and support xerophytic species.
2. North-facing slopes are cooler and moister, favoring shade-tolerant species.

Drainage and Waterlogging

1. Low-lying areas can accumulate water, creating oxygen-poor conditions.
2. These lead to wetlands, bogs, or mangrove swamps with specialized hydrophytic plants.

4. Fire and Weather-Related Events

1. Fires, storms, and floods can reset succession by clearing vegetation and releasing nutrients into the soil.
2. Some ecosystems are fire-adapted.
3. Fires maintain biodiversity by preventing dominance of a few species.
4. Extreme weather events (e.g., hurricanes) can knock down trees, opening the canopy and allowing light-demanding pioneer plants to re-establish.

Biotic Factors Influencing Succession

1. Biotic controls, especially from primary consumers and higher trophic levels, can reshape the structure and trajectory of succession.
2. These influences are often described as top-down regulation, where predators or herbivores control populations lower in the food chain.

1. Primary Consumers

1. Herbivores directly affect vegetation patterns by selective feeding.
2. Overgrazing prevents tree regeneration, maintaining grass-dominated systems.
3. Moderate grazing, however, can increase plant diversity by preventing competitive exclusion.

2. Higher Trophic Levels

1. Predators influence prey populations, triggering trophic cascades that reshape entire communities.
2. Predators regulate herbivore numbers, indirectly allowing vegetation to recover and forests to regenerate.

Human Influence on Succession

1. Human activities often interrupt or redirect succession, altering the type of community that develops.
2. Deforestation, overgrazing, mining, and urbanization simplify ecosystems and reduce biodiversity.
3. Controlled fires, agriculture, or logging can prevent succession from reaching climax stages.
4. Restoration ecology can help re-establish natural successional pathways by replanting native vegetation and restoring soil health.

Productivity During Succession: Changes in Gross and Net Productivity

1. As an ecosystem undergoes succession, both gross primary productivity (GPP) and net primary productivity (NPP) change over time due to changes in the community structure, species composition, and abiotic factors.
2. In early stages of succession, productivity dynamics differ significantly from those in the later stages, especially as consumers (herbivores, carnivores, etc.) become more prominent and the ecosystem matures into a climax community.

Early Stages (Pioneer Community)

1. GP is low because environmental conditions are harsh — limited nutrients, thin soil, and few producers.
2. Pioneer species (lichens, mosses) have small biomass and low photosynthetic capacity.
3. Respiration (R) is also low due to minimal biomass.
4. Therefore, NP is relatively high.
5. Most captured energy goes into growth and accumulation of biomass.
6. The system is rapidly growing and expanding in energy storage.

Mid-Stages of Succession

1. As soil develops and plant diversity increases:
   1. GP rises sharply due to greater leaf area and more photosynthetic organisms.
   2. Nutrient availability and water retention improve, accelerating biomass production.
2. NP continues to increase, but at a slower rate because respiration from producers, herbivores, and decomposers also increases.
3. The community becomes more complex and energy pathways diversify.

Late Stages (Climax Community)

1. The ecosystem reaches dynamic equilibrium, and energy input balances energy loss.
2. GP may remain high due to abundant producers (e.g., mature trees).
3. However, respiration (R) also increases significantly because of the large biomass and many consumers.
4. As a result, NP approaches zero, meaning no net biomass accumulation and the system has stabilized.

Productivity is balanced: P:R = 1 (Production equals respiration).