Since the tropical rainforests are the most diverse ecosystems on Earth   and about 80% of the world's known biodiversity could be found in tropical rainforests,   removal or destruction of significant areas of forest cover has resulted in a degraded  environment with reduced biodiversity.   A study in Rondônia , Brazil, has shown that deforestation also removes the microbial community which is involved in the recycling of nutrients, the production of clean water and the removal of pollutants. 
Reforestation won't completely fix the damage, though. For example, Daley points out that forests cannot sequester all of the carbon dioxide humans are emitting to the atmosphere through the burning of fossil fuels and a reduction in fossil fuel emissions. It is still necessary to avoid buildup in the atmosphere. Reforestation will not help with extinction due to deforestation, either. "Unfortunately, we have already diminished the population of many species to such an extreme that they might not recover, even with a massive reforestation effort," Daley told Live Science.