3.9 ECOLOGICAL SUCCESSION All ecosystems age in a (theoretically) predictable way called succession.

The four stages of primary succession are: 1. pioneer - begins with soil formation; small plants and species with minimal requirements 2. juvenile communities - low diversity 3. mature communities - high diversity 4. climax communities – increased stability, but some scientists argue that climax communities don’t exist; often diversity declines as dominant species exclude less adapted species. Secondary succession may interrupt any of the above stages as a result of disturbances such as forest fires, storms, flooding, or disease.

However, nature is very random. Often stability is maintained by change. Older organisms die leaving younger ones to replace them. Stability is based on three parameters, but scientists disagree whether stability must include all three. 1. inertia (resistance to change) 2. constancy (ability to live within the resources) 3. resilience (ability to bounce back)

Rain forests have high inertia because of high specie diversity, but low resilience. In a rain forest, the nutrients are stored in the vegetation rather than in the soil. Once the forest is cut, recovery is very slow because the soil is poor. This is another reason why cutting rain forests for farming is a bad idea.

This is an example of how succession might take place from a lake through a forest over time. As one ecosystem matures another may enter the pioneer stage. Many lakes were formed as depressions from receding ice. These deep holes filled with water to become large lakes. Lakes are defined by these 2 zones: Profundal zone – area with no light Limnetic zone – open water with some debris and enough light for submergent grasses and pond weeds.

As birds and insects arrive, floating plants will provide habitat, nesting sites, places for egg attachment and their food will be eaten by fish, turtles, ducks, small mammals, insects and birds.

The emergent plants then appear on the edges of the lake forming a littoral zone. As plants grow, die and decompose, layers of debris build up and raise the lake bottom enough to eliminate the profundal zone. With the elimination of the profundal zone and addition of a littoral zone, the lake becomes a pond. Emergent plants have roots under water while part of their bodies resides above the water line. If emergent plants grow all the way across the pond, a shallow marsh may result.

In some climates, ponds may become covered by grasses that dry up the land seasonally or completely. Ponds then become grasslands or meadows that have low inertia with low diversity - only grass. They have high resilience because nutrients are stored in the roots, which helps them grow back quickly.

Over time, small pine and saplings like birch, aspen, poplar and other softwood trees emerge to house small animals. In slightly damp environment, deciduous hardwoods like oaks and hickory trees will grow. In slightly drier environment, the beech and sugar maple and evergreens grow.

Succession in Coastal Zone Winds blow sand off the beach where it is trapped by sea grasses. Their roots stabilize the sand and dunes begin to form. Behind the primary, a secondary dune may be colonized by woody shrubs, eventually a maritime forest develops.