There is no single effect
Logging is not one event with one result. The effect on wildlife depends on how much is cut, how it is cut, what kind of forest it was, how the area regrows and what the surrounding landscape looks like. The same harvest can be a setback for one species and a benefit for another. Some animals need the old trees and dense shade that logging removes; others thrive on the sunny, shrubby growth that follows. Any honest summary has to be conditional, and local conditions matter more than general rules.
During felling
The most immediate effects occur when the work takes place.
- Direct disturbance. Noise, machinery and people displace many animals, and nests, dens and burrows can be destroyed. Cutting during the breeding season tends to cause more harm than at other times, because eggs, nestlings and young animals cannot escape. The sensitive periods vary by species and region.
- Loss of structure. Large trees, cavity trees, snags and logs disappear, along with the nests and shelter they offered. Cavity-using birds and bats, canopy-dwelling animals and species that depend on the forest floor all lose habitat to different degrees. The importance of deadwood habitat means that removing standing and fallen dead wood can have long-term effects.
- Changed conditions. Opening the canopy raises temperatures and light levels at ground level and dries the surface. Animals sensitive to dryness, such as many amphibians, are often among the first to be affected.
Roads and access
Roads built for logging can matter as much as the cutting itself, and in some cases more.
Roads fragment forest, add edges and create barriers to movement. They also bring traffic, which kills animals, and open remote areas to hunters, settlers and people collecting forest products. In some tropical regions, hunting pressure that follows logging roads has been identified as a major cause of declines in larger mammals and birds, sometimes greater than the direct effect of the felling. Roads can also act as routes for invasive species. The care taken when building forest roads and skid trails influences erosion and stream sedimentation too, which can harm fish and other aquatic life in forest streams.
Closing or restricting roads after harvest, where it is practical, is one of the commonly suggested ways to reduce these pressures.
The stages of regrowth
After logging, the forest does not simply return to its earlier state. It goes through stages, in a process of forest succession, and each stage favors different animals.
Early stage (open, young regrowth). Light-loving plants, shrubs and seedlings grow quickly. Species that use open, shrubby habitat, along with some seed-eating birds and browsing animals, may increase, and some animals that need young forest depend on disturbances like this one. This stage often produces more food near the ground, for example berries and tender shoots.
Middle stage (dense, closed canopy). The stand thickens, light at ground level drops and the understory can become sparse. In some forests, this phase supports fewer species than either earlier or later stages.
Late stage (older, structurally complex). Over many decades, larger trees, canopy gaps, standing dead wood and layered structure develop again. Species that need old-forest features return only gradually, and some may take far longer than the usual harvest rotation to recover. How long recovery takes varies greatly among forest types, and in some cases the original conditions may not return at all.
Who tends to do better and who worse
General patterns reported in many studies, though not universal, include:
- Specialists tied to old-growth forests, large hollow trees, deep shade or very humid conditions tend to decline after intensive logging.
- Generalists and species that use open or edge habitat often remain stable or increase.
- Large-bodied animals, wide-ranging predators and animals that are hunted are often more sensitive, especially when roads increase access.
- Animals with low mobility, such as some salamanders and invertebrates, may take a long time to recolonize cut areas.
Because responses differ so much, the total number of species in a logged area can look similar to unlogged forest even when the community has changed in important ways.
Practices that can reduce harm
Many of the following are commonly recommended, although effectiveness depends on how they are applied.
- Selective or partial harvest that leaves much of the canopy, as in continuous cover forestry, tends to preserve more forest conditions than clearing everything at once. The contrast between harvest systems is covered in the comparison of shelterwood systems.
- Retention. Leaving some large living trees, snags, logs and patches of uncut forest provides lifeboats for species that would otherwise lose everything.
- Reduced impact logging methods, such as planning routes in advance, directional felling and limiting the area of soil disturbed, tend to lower damage to remaining trees and to the ground.
- Buffer strips along streams and wetlands protect water and the animals that use these areas, as with riparian buffers.
- Timing. Avoiding the main nesting or breeding periods in sensitive areas reduces direct losses.
- Landscape planning. Spreading harvests in space and time, and keeping some mature forest, maintains habitat for species that need it. Leaving connected strips of intact forest can also keep animals moving.
- Controlling access. Limiting hunting and closing temporary roads once work is finished helps reduce secondary pressure.
Forest certification schemes sometimes include requirements of this kind, though what they require and how strictly they are enforced varies. Good evidence on any one practice is often limited to particular species and regions.
Keeping it in perspective
Responsible, planned forestry can coexist with healthy wildlife in many landscapes, particularly when part of the forest is left unharvested. By contrast, poorly planned or illegal logging, especially when followed by conversion to other land uses, can cause long-lasting losses. The difference lies less in the act of cutting than in the intensity, the planning, the aftercare and whether the forest is allowed to regrow.