Secondary forest

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Secondary forests are forests that have regrown after a disturbance, such as logging, farming, or other land clearing. They grow back mostly through natural processes, rather than being rebuilt from scratch. They are different from old-growth (primary) forests, which have not recently been disrupted, and from forests that are still in the process of developing after a disturbance.

Regrowth happens through a process called succession. When a clearing opens the canopy, sunlight reaches the forest floor and pioneer plants start first, followed by shrubs and then trees. Over time, trees similar to the original forest can reappear. In many places it takes 40 to 100 years for a secondary forest to begin to resemble an old-growth forest, though in some cases it can take much longer, especially if soil nutrients are depleted.

Secondary forests typically look different from primary forests. They often have trees that are closer together, less undergrowth, and usually only one forest canopy layer. The species in the canopy are also usually different from those in a primary forest.

These forests are common where land was degraded by agriculture or logging. They also form in areas where forests were lost to shifting cultivation or other disturbances, and they can result from natural disturbances too, though the processes and outcomes may differ.

Biodiversity in secondary forests can recover over time, and these forests still provide important benefits. They help protect watersheds, support some native wildlife, boost landscape connectivity, and can offer wood or other resources to nearby communities. However, they are generally less diverse and have different species compositions than old-growth forests, and some plant–soil interactions may not fully recover.

Restoration can be helped by practices like agroforestry or actively planting native species alongside natural regeneration. These approaches can improve biodiversity and ecosystem services, and they can support local livelihoods. But the success of recovery depends on local conditions such as soil quality, water, forest size, seed sources, edge effects, and management.

Secondary forests also play a role in climate change. They store carbon in soil and biomass and can help offset emissions, though they don’t equal the carbon storage of old-growth forests. There is concern when secondary forests are cleared again, such as for rubber plantations, because stored carbon can be released.

In summary, secondary forests regrow after disturbance and provide important ecosystem services, but they are different from old-growth forests and recovery can vary greatly depending on site conditions and management.