The environmental effects of clearcutting are often cited by activists who are trying to put a stop to the practice. They include a range of negative results, from loss of habitat to an elevation in stream temperatures which can cause fish to die off, but all of them reflect major changes that will take decades to correct. Numerous activists have suggested more environmentally sustainable alternatives to clearcutting, such as selective logging, and it is the hope that as more consumers become aware of the dangers of clearcutting, they will seek out sustainably-harvested timber.

Clearcutting, or clearfelling, is a logging practice which involves completely clearing an area of trees, regardless as to their size and usability. Remaining scrub and brush are usually burnt in large burn piles that can cast a smoky haze over the area for several days. A clearcut area may be relatively small, or may span for miles, and is clearly visible through the air, along with the scars of logging roads cut to access it. The abrupt deforestation has a serious environmental impact on the surrounding area.

Clearcutting profoundly alters local rivers. If logging comes close to the banks of the river, as it often does, it eliminates the shady shield of trees, which can cause the temperature of the river to elevate. Even a few degrees can make a huge difference to native plants, fish, and amphibians, and can cause a significant population decrease. Numerous organizations monitor global rivers and have warned that extensive clearcutting could result in the extinction of some fish species, as they are driven out of their native habitats. Clearcutting also softens the banks of the river by enabling erosion, which can cause them to collapse into the water.

In addition to harming rivers, clearcutting also alters the water cycle in general. While trees are growing, they help to trap and retain water, along with precious topsoil. When trees are removed, water runs over the surface of the earth rather than filtering into the aquifer. The water runoff can cause flooding, taking valuable topsoil with it. As the water trickles downhill, it carries the topsoil into the river, turning it brown and muddy and carrying the useful nutrients out to sea. The excess of nutrients in the marine environment can be harmful to marine organisms, and cause further population damage, which can sometimes extend for several miles offshore.

Clearcutting also destroys habitat for a wide variety of animals, including many endangered species. Birds, reptiles, and mammals all face habitat destruction due to clearcutting. Many of these animals have difficulty seeking out new habitats because the surrounding areas may be clearcut or filled with human inhabitants. Some animals have adverse interactions with humans, especially large predator species and animals such as raccoons which adapt readily to human encroachment on their habitat. Others are simply incapable of adapting and quietly die off. While this alone is tragic, the effects extend into the surrounding ecosystem as well, by removing a link in the local food chain.

The results of clearcutting are not only felt in the immediate area. Clearcutting also has an impact on the quality of the atmosphere, beginning when the trees are cut down. Trees help to filter pollutants from the air, and are also an important part of the carbon cycle. Removing trees has a direct impact on the environment, especially when combined with slash-and-burn practices which result in scorched earth and in a serious increase of environmental pollutants.

Because of the numerous negative effects of clearcutting, many people concerned about the environment are trying to educate consumers about the practice. It is possible to obtain sustainable lumber, such as that labeled by the Forest Stewardship Council. By purchasing sustainably harvested lumber, consumers send a message to logging companies that they want healthy wood from healthy trees, and an environment which is healthy in the long term.