overstorys

The overstory is the uppermost layer of a forest stand, formed by the tallest trees whose crowns create the canopy that shades the forest floor. It is the dominant spatial layer in most stands and contrasts with the understory and midstory beneath. In some forests, an emergent layer rises above the main canopy.

Composition and structure of the overstory depend on forest type and succession. Overstory trees are typically mature, long‑lived species with broad crowns. Their heights surpass those of most competitors, producing a vertical stratification in which light availability decreases with height and species arrangement may vary over time.

Ecological role: The overstory regulates light, temperature, humidity, and soil moisture reaching lower layers. By intercepting rainfall and stabilizing microclimate, it influences nutrient cycling, litter input, and carbon storage. Canopy trees provide habitats and food for many canopy‑dwelling organisms and shape regeneration patterns for the understory.

Disturbances such as windthrow, fire, disease, or harvesting can remove or thin the overstory, triggering changes in stand structure and regeneration. Silvicultural practices often target the overstory to promote seedling establishment in the understory or to modify growth, quality, and yield of commercial species. Excessive thinning can raise light levels too much or destabilize the stand.

In forest measurement, the overstory is assessed alongside the understory. Terms like dominant, codominant, and suppressed describe a tree's position relative to the overstory; metrics such as canopy cover and basal area help quantify its extent and influence.

In broader usage, the term overstory appears in literature as well; for example, The Overstory is a 2018 novel by Richard Powers that uses trees and forests as central motifs.