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Forest succession is one of ecology's most reliable predictions. Pioneer species (light-demanding, short-lived) give way to intermediate, then to climax (shade-tolerant, long-lived) species over decades to centuries.
After a major disturbance, sun-loving pioneers (aspens, birches, pines) colonize first. Their shade creates conditions for intermediate species (oaks, maples, hickories). The shade these create, in turn, allows climax species (sugar maple, beech, hemlock in the Eastern US) to establish and eventually dominate. The sequence varies by region, soil, and disturbance type — but the directional pattern is one of ecology's most reliable findings.