The vascular plant emerged around 400 million years ago and started Earth's forest-building process during the Silurian geologic period. Although not yet a "true" tree, this new member of the terrestrial plant kingdom became the perfect evolutionary link with developing tree parts and considered the first proto-tree.
The earth's first real tree continued to develop during the Devonian period and scientists think that tree was probably the extinct Archaeopteris. This tree species followed later by other tree types became the definitive species comprising a forest.