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Originally Posted by Windguy
Land clearing is far worse than logging, but I haven't seen no study that shows logging is beneficial.
It can be still hazardous to biodiversity of plant and animal species. Besides that there is the usual burn off that takes place for the waste materials such as branches, cutting out the road tracks etc.. which adds to climate change in the forms of carbon soot and CO2 emissions.
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Practices that effect forest health vary from area to area, what follows may not apply to Eastern US or European forests. In the Western US, our forest biology is based upon fire. In the past (pre 1850 or so) most forests would typically experience smaller, low intensity fires every 5-15 years. These fires would burn out underbrush and smaller trees, allowing larger trees to survive and typically leaving grasses between the remaining trees. Fire sources were often natural (lightning) but also from the indiginous people (Indians to us non-PC types). Fire not only kept the forests relatively clear of underbrush and small trees, but stimulated growth and propegation of the native White, Ponderosa and Lodgepole pine, as well as native grasses. In addition, it tended to kill off species that are less tolerant of fire, drought and disease. These somewhat open forests were resistant to the effect of devestating wildfires (running crown fires, which kill everything in their path and pretty well steralize the soil). These forests also provide browse and habitat for wildlife.
In more recent times, a great deal of effort and money has been spent on fire supression. In todays political environment, the amount of air pollution, as well as the threat to structures and life has resulted in greatly restricted "controlled burning", which attempts to simulate the natural conditions described above. As a result, many of our forests are way overgrown, with hundereds to thousands of small, crowded trees per acre, rather than the 20-100 that is "normal". These overgrown stands are very susceptable to disease and insect damage, and when (not if) they burn, the do so at a very high intensitity and are very destructive. These overgrown forests also provide very poor wildlife habitat; so little sunlight reaches the forest floor that no browse can grow. Around here, you will see many hillsides covered with dead and dying trees.
Logging provides a means to thin the forests and simulate the natural, fire based ecology, without the resulting air pollution, or at least by minimizing it. Waste (branches, tops), are still typically burned, but this is a fraction of the original mass of material. Some areas use forest waste as a fuel to fire boilers for heating systems, both reducing the pollution associated by uncontrolled burning (a boiler system burns far hotter and cleaner than a slash pile), while displacing fossil fuel usage. In addition, timber provides our one truely sustainable building material and once used in construction materials the carbon in the wood is effectively sequestered.
There are plenty of bad, destructive logging practices, as well as benefical ones. BMP (best management practices) attempts to define those practices which are benefical and minimize the negative environmental impact.
I have put a fair amount of effort into studying the issue; I own a small amount of forested land. Some areas have species that are not "proper" for the location and I'm loosing a lot of them to disease and insects. I have been replanting with more site-specific species and clearing the dead stuff; however I don't expect to see dramatic results in my lifetime.