On working forest land, the rotation length between harvests is an economic decision. It also determines which forest conditions ever appear, and therefore which birds can breed there at all.
Rotation length is set by growth and interest
A stand is harvested when the value of continued growth no longer justifies the delay in receiving the money, given the landowner's cost of capital.
Fast-growing species on productive sites reach that point in a few decades. Slower species on poor sites take much longer, which is why rotations vary widely.
Tax treatment, land value and the owner's need for cash all push in the same direction, generally toward shorter rotations rather than longer ones.
Structure develops on a schedule
A young stand is dense and even-aged. As it grows, competition kills smaller trees, the canopy closes and the understory is shaded out.
Only much later do gaps open where individual large trees die, letting light reach the floor and creating the uneven structure of an older forest.
Standing dead trees and large fallen logs accumulate over the same long period, and both are essential to a substantial group of forest species.
Short rotations remove the later stages
Harvesting before gap dynamics begin means a forest cycles repeatedly through its early and middle stages and never reaches the later ones.
Cavity-nesting birds requiring large dead trees, and species dependent on complex understory beneath an old canopy, find nothing suitable regardless of how much forest exists.
The result is a region that is heavily forested by area while lacking habitat for the species associated with mature forest.
Early stages have their own specialists
Recently harvested and regenerating stands support a distinct group of birds requiring dense low cover, and several of those species have declined as abandoned farmland matured.
Harvesting therefore creates habitat as well as removing it, which is why the conservation question is about the mix of ages present rather than about cutting itself.
A region dominated by a single rotation age is the actual problem, whether that age is young or old.
Retention practices bridge the gap
Leaving scattered large live trees, snags and downed wood through a harvest carries structural elements from one rotation into the next.
Extended rotations on a portion of a holding, or reserved patches within it, produce older conditions without requiring the whole property to forgo income.
These practices cost the landowner real money in deferred or forgone harvest, which is why cost-share programs and certification requirements are the usual route to adoption.