The ever-growing human consumption and population is the biggest cause of forest destruction due to the vast amounts of resources, products, services we take from it. Half the world's rainforests have been destroyed in a century, at this rate you could see them vanish altogether in your lifetime!
Forest loss also reduces the availability of renewable resources like timber, medicinal plants, nuts and fruit, and game. Over the longer term, deforestation of tropical rainforests can have a broader impact, affecting global climate and biodiversity.
As well as the decreasing amount of oxygen since trees are a natural source for the air that we breathe.