Simply humans will also disappear. Harmful result of deforestation is the extinction of animal and plant species. They disappear because their environment and life cycles have been disturbed and they are unable to adapt to the changes. When species disappear, it is called extinction. Essential habitat is lost when forests are cut down; wildlife species lose their homes, their food sources and their place in the web of life. Even though extinction is part of life, it is happening far too quickly now. Soil erosion, flood, drought etc will occur.