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 (and the largest plant species) with developing tree parts and considered the first proto-tree. Vascular plants developed the ability to grow large and tall with massive weight needed for the support of a vascular internal plumbing system.
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 during the late Devonian period. As I have mentioned, they were the first plants to overcome the bio mechanical problems of supporting additional weight while delivering water and nutrients to fronds (leaves) and roots.
Entering the Carboniferous period around 360 million years ago, trees were prolific and a major part of the plant life community, mostly located in coal-producing swamps. Trees were developing the parts that we immediately recognize today. Of all the trees that existed during the Devonian and Carboniferous, only the tree fern can still be found, now living in Australasian tropical rainforests. If you happen to see a fern with a trunk leading to a crown, you have seen a tree fern. During that same geologic period, now extinct trees including clubmoss and giant horsetail were also growing.Primitive conifers were the next tree species to appear in ancient forests around 250 million years ago (the late Permian to Triassic). Many trees, including the cycads and monkey-puzzle tree, can be found around the world and are easily recognized. Interestingly, the very familiar ginkgo tree's ancestor appeared during this geologic period and the fossil record shows the old and the new to be identical. Arizona's "petrified forest" was a product of the "rise" of the first conifers, or gymnosperms, and exposed fossilized logs are crystallized remains of the tree species Araucarioxylon arizonicum.
There was another type of tree, called an angiosperm or hardwood, making headway during the early Cretaceous or about 150 million years ago. They appeared at about the same time geologists think the earth was breaking up from a single continent called the Pangaea and dividing into smaller ones (Laurasia and Gondwannaland). Early into that Tertiary period, hardwoods exploded and diversified themselves on each new continent. That is probably the reason hardwoods are so unique and numerous across the globe.
Few dinosaurs ever made a meal on hardwood leaves because they were rapidly disappearing before and during the beginning of the new "age of hardwoods" (95 million years ago). Magnolias, laurels, maples, sycamores and oaks were the first species to proliferate and dominate the world. Hardwoods became the predominant tree species from mid-latitudes through the tropics while conifers were often isolated to the high-latitudes.
Not a lot of change has happened to trees in terms of their evolutionary record since the palms made their first appearance 70 million years ago. Fascinating are several tree species that simply defy the extinction process and show no indication that they will change in another dozen million years. I mentioned ginkgo earlier but there are others: dawn redwood, Wollemi pine and monkey puzzle tree.