What impact do humans have on succession?

Answer 1

This seemingly simple question has a complicated answer.

Succession is the process by which one plant community replaces another over time in a given space, i.e. grassland to deciduous forest to coniferous forest. Natural events, such as forest fires, can reset the succession cycle back to a grassland, for instance, at any point in the cycle.

Humans can impact succession in a number of ways by suspending succession in one phase or another or by causing an event that restarts the succession cycle (i.e. starting a forest fire).

Suspending succession: We suspend succession when we promote one type of ecological community over another. For example, we manage some forests for the purpose of harvesting timber at a later time. Here, the emphasis is on mature, full-bodied trees that have balanced competition from neighboring trees. These trees will be harvested before they begin to fall down and begin to turn the forest into an old-growth forest where new growth comes up where old trees fall in the forest. Promoting and attempting to sustain this type of forest prohibits plants and animals that specialize in old-growth forests from getting established.

Another interesting way in which we impact succession has been the impetus to extinguish all forest fires since the early 1900s. Fires are naturally occurring and are an important way in which forest ages are regulated naturally, which, in turn, regulates the mosaic of food sources and wildlife habitats that occur. Putting out fires for most of the last century has resulted in larger forest fires more recently and decreased plant & animal diversity.

Restarting succession: We also can restart succession by starting wildfires, either intentionally or unintentionally. While not inherently bad in the grand scheme of nature - after all, nature in many cases depends on fire - it is a way in which man impacts succession.