Ecosystem Regeneration and Biogeochemical Cycles

Stages of Post-Fire Forest Regeneration

• 1. Survival: Underground elements and the seeds of pyrophytes survive, even when the floor is completely damaged.
• 2. Early Regeneration: If the soil was not totally damaged, regeneration starts. During the early years, a pasture consisting of herbaceous plants is formed. If the soil has been removed, this may not start or may take longer.
• 3. 10 to 15 Years: Low shrubs predominate and coexist with the grass. Burned logs decompose and nourish the soil. The animal population increases.
• 4. 30 to 35 Years: Large shrubs predominate, eventually becoming a tree-filled area. This stage allows for mammals such as the fox.
• 5. Forest Formation: The formation of a forest takes 50 to 60 years. Even then, another half-century would have to pass to achieve a significant ecological community.

Secondary Succession in Aquatic Environments

• 1. Sedimentation: A lagoon loses depth due to the contribution of organic matter and sediments. Rushes and reeds appear, and terrestrial animals move inward.
• 2. Bank Stabilization: Ancient banks appear where moisture-bearing trees settle. Birds and other animals typical of this environment appear as well.
• 3. Forest Maturation: As moisture recedes, a forest appears alongside its concerned fauna.

Key Abiotic Factors in Natural Ecosystems

• Texture: Sandy soil, clay, and mixed soil.
• Water and Air: Includes water-loving (hydrophilic) and drought-tolerant (xerophilic) organisms.
• Chemical Composition and pH: Salty and neutral soils.
• Salinity: Freshwater and saltwater environments.
• Light: Categorized into the Euphotic zone (max 50m, enough light), Oligophotic zone (penumbra area), and Aphotic zone (dark area from 500m).
• Temperature: Influences the amount of oxygen and temperature differences between surfaces and deep areas of oceans and seas, where currents distribute nutrients and oxygen.

The Carbon Cycle and Organic Transformation

Plants, algae, and some bacteria take CO₂ from the water and atmosphere through photosynthesis and transform it into organic compounds. This carbon goes through all trophic levels through food. Much of the carbon returns to the environment through the respiration of all living beings (Producers, Decomposers, and Consumers). Remains of bodies are buried by sediments and go through a lengthy process to form coal or oil.

In nature, the atmosphere is enriched in CO₂ thanks to volcanic eruptions and the combustion of plant material, as well as the burning of fossil fuels like oil or coal. Marine organisms also form their shells with carbon dissolved in the water.

The Nitrogen Cycle and Soil Fertility

Plants can only use nitrogen that is in the form of salts dissolved in water. During photosynthesis, plants use nitrogen to form organic compounds (proteins). Some organisms capture atmospheric nitrogen and transform it for use by plants (nitrogen-fixing bacteria of the soil, such as Rhizobium).

The organic nitrogen compounds pass through the food chain. When organisms die or produce droppings, they return to the environment. Organic nitrogen is transformed from detritus by bacterial decomposition into soil nitrates. These nitrates are eventually returned in the form of nitrogen to the atmosphere by other transforming bacteria. Nitrogen can also be fixed artificially from the atmosphere to manufacture inorganic fertilizers, which enter the nitrogen cycle once in the ground.