Mature and Old Growth Forests

This piece discusses concepts, indicators, and challenges for defining mature and old-growth forests. Most existing definitions combine social and environmental values with qualities like advanced age, tree size, and structural diversity. While Forest Inventory and Analysis provides nationally consistent data helping define these forest types at a granular level, mapping at a finer scale and capturing inherent heterogeneity may require collecting more data, including additional measurements, adjustments to criteria at local scales, and incorporation of social and traditional ecological knowledge.

Agency scientists estimate that 45 percent of forest land stewarded by the Forest Service and Bureau of Land Management is mature—and nearly two-thirds may be mature and old growth. The study authors determined mature forest extent by working backwards; they modeled the prior characteristics of forests defined as old growth and estimated where these conditions now occur.

This study describes an approach for using National Forest System regional old-growth definitions that were developed using science and refined through planning processes; and applying these definitions with FIA data to quantify old-growth forests. Using this method, agency scientists estimate 10 million hectares—or 17 percent—of National Forest System land qualifies as old-growth forest. This study marks the first to harmonize diverse old-growth forest definitions and inventories.