second-growth forest

A second-growth forest is a stand of trees that has established itself on land previously cleared by logging, fire, or agriculture. Unlike old-growth forest, which may be several hundred years old and contains trees of many age classes and species, second-growth typically consists of younger trees of fewer species, often dominated by fast-growing pioneers like aspen, birch, or pine depending on region and climate.

The distinction matters economically and ecologically. Second-growth timber reaches harvestable size (16 to 20 inches diameter breast height for softwoods) in 40 to 80 years, depending on species and site quality, versus 150 to 300 years or more for old-growth. This makes it the primary source for industrial timber in temperate zones of North America, Europe, and parts of Asia. Plantation forestry accelerates the process further by controlling species composition and density from the start.

The character of second-growth varies sharply by how the first forest was removed and what happens after. Natural regeneration often produces dense, even-aged stands vulnerable to insect and disease outbreaks. Partial harvesting, thinning, or active replanting can improve species diversity and resilience. In abandoned farmland, succession may eventually restore complexity; in frequently re-logged zones, it may not. Soil compaction, erosion, and altered hydrology from harvesting equipment persist for decades and affect the forest that grows back.

Ecologically, young second-growth typically has lower structural complexity, less coarse woody debris, and fewer old-tree specialists than primary forest. However, many wildlife species benefit from early successional habitat. As second-growth ages beyond 60 to 80 years, it can develop some attributes of older forest, though old-growth characteristics like large-diameter trees and multi-layered canopy usually require much longer to re-establish without active management.

The term entered forestry language as industrial timber harvesting became systematic in the 19th century, particularly in the northeastern United States and northern Europe. It reflects a shift from treating forests as inexhaustible reserves to managing them as renewable crops. Today second-growth and plantation forests supply the vast majority of industrial roundwood globally, making their productivity, health, and management central to timber supply forecasting and carbon accounting in the forest sector.