Question

summary sentence: (the author is saying that...) no ecosystem remains static or the same. however, under normal conditions all parts of an ecosystem act and react upon each other through gradual changes until they reach a relative stability. this process is called ecological succession. two major types of ecological succession exist: primary and secondary. in primary succession, the pioneer stage begins when organisms invade an area not previously occupied, such as a sandy area left exposed by a retreating glacier. in secondary succession, the pioneer stage begins when organisms invade an area that was previously occupied, such as an abandoned farm field. in both types of succession, the intermediate stages occur as the area is gradually changed by successive communities of organisms. for example, the grasses and shrubs present in the early stages eventually die; as they decompose, they build up the thickness and nutrient content of the soil. eventually the soil becomes thick and rich enough to support trees; small trees are followed by large trees. when a community is established in which each species maintains a relatively stable number of individuals, the ecosystem has reached its climax. secondary succession achieves climax much more rapidly than primary succession because an area that was previously occupied is richer in nutrients than an area that was not previously occupied.

Explanation:

The text defines ecological succession, its two types (primary and secondary), stages (pioneer, intermediate, climax), and notes secondary succession reaches climax faster due to more nutrients.

Answer:

The author is saying that ecological succession is the process by which an ecosystem changes until it reaches relative stability, with two types (primary and secondary), stages like pioneer, intermediate, and climax, and secondary succession reaching climax faster as previously - occupied areas are more nutrient - rich.