When we talk about deforestation, we usually mean logging for timber or clearing trees for agriculture and human habitation. If a section of rainforest, for instance, is chopped down and then left alone, it may take just a few decades to grow back. But thousands of years will pass before it returns to its original glory, according to studies carried out in the Brazilian Atlantic Forest and Panama.

Forests in their various forms cover 31 percent or 4 billion hectares of the world's land surface. That's down from 5.9 billion hectares in pre-industrial times. Around 46-58,000 square miles of forest are lost each year, which is equivalent to 48 football fields every minute, says WWF. A lot of the trees won't grow back, as they've been cleared to make way for agriculture, cattle ranges or human development.

Forests provide habitat for people and wildlife. They are home to some of the world's most endangered animals and around 1.6 billion people rely on the essential services they have to offer, including traditional medicine and food. When lands are deforested, surrounding communities also experience changes in rainfall and can face water shortages. That's because the lush tree canopy helps evaporate groundwater that generates rain. Forests also control water run-off, filter water and prevent soil erosion. Without the stabilizing force of roots, soil can simply wash or blow away, leading to mudslides or expanding desert. 

Forests are important from a global perspective too because they are the first natural line of defense against carbon dioxide, which trees soak up. When a tree is cut down, the carbon returns to the atmosphere. An estimated 15 percent of greenhouse gas emissions are the result of deforestation, which in turn contributes to global warming and changing climate patterns. South America's Amazon rainforest plays a crucial role in storing carbon and preventing climate change. But this year saw the largest loss of trees there since 2008. 

Africa isn't immune to deforestation either. The Congo Basin is the continent's green heart. It contains up to 20 percent of the world's tropical forests and is one of the most important ecosystems on the planet. While deforestation rates there have been the lowest of any other major forest region in the world since the 1990s, threats abound. Clear-cutting for small-scale subsistence agriculture, charcoal, fuel, urban development and mining are all driving deforestation in the Congo rainforest. But industrial logging is also playing a major role. Logging roads have opened up previously untouched areas of the rainforest to hunting, leading to poaching epidemics in some areas. This in turn effects indigenous communities living in the forests.

So, it seems, even if trees grow back in the long run, their loss has a major impact globally and locally.