Forests cover about a quarter of the world's land surface, excluding Greenland and Antarctica. Global forest cover has been reduced by 20 percent since pre-agricultural times, and possibly as much as 50 percent. Forest area has increased slightly since 1980 in industrial countries, but has declined by almost 10 percent in developing countries. Tropical deforestation probably exceeds 130,000 km2 a year. Less than 40 percent of forests globally are relatively undisturbed by human action. The great majority of forests in the industrial countries, except Canada and Russia, are reported to be in "semi-natural" condition or converted to plantations. Many developing countries today rely on timber for export earnings. At the same time, millions of people in tropical countries still depend on forests to meet their every need. The greatest threats to forest extent and condition today are conversion to other forms of land use and fragmentation by agriculture, logging, and road construction. Logging and mining roads appear to lead the way in opening up intact forest to pioneer settlement and increases in hunting, poaching, fires, and exposure of flora and fauna to pest outbreaks and invasive species.