Every organism in an ecosystem has a role or niche it fulfills, that is important to the sustainability of that ecosystem. If a particular tree species is removed by deforestation, or due to a disease, loss of habitat will occur for songbirds and insects that live on or in that tree. The root-systems of trees keeps the soil from eroding and also helps to absorb rainwater, which prevents runoff. The shade provided by the tree provides habitat for plants that grow in low-light conditions such as mosses and ferns. One of the reasons there is such a huge loss of songbirds is that tropical rainforests are being cut down at unprecedented rates and those rainforests provide winter habitat for the songbirds which migrate there. It is another explanation for the death of so many Monarch butterflies. Therefore, it is obvious that biodiversity is the key to a healthy ecosystem.