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#### Evolution of trees.

##### Links

See also the theory of evolution of vascular plants here and also here.
A really excelent page on the evolution of life and plants here.
A chapter about evolution of flowering plants here. from the book the evolution of plants.
Click here for a beautifully illustrated timeline with concepts like the "silurian" and so on.

##### My summary of the evolution of trees.

Trees are of course non-marine plants: they live on land and not in the sea.

The first plants to invade the land did so about 430 million years ago in the silurian, before vertebrates invaded the land. Only after vascular tissue and after that roots evolved could trees evolve.

After the invasion of land by plants a big adaptive radiation followed, in Devonian times. The first trees (big plants [30 meters] with woody stems) evolved about 360 million years ago and had roots and leafs (begin carboniferous). Amongst these first trees were lycopods, now species from this group are only known as small mosses (Selaginella or spike moss).

Lycopod trees could only live in moist-environments because they reproduced by spores, which need moisture to enable sperms to move to the egg.

In the devone a second innovation came about: the seed. The seed enabled plants to colonize non-wet land, beginning a total change of much of the lands since plants play an important part in the formation of soil because they slow down erosion. The first seedplants evolved trees with seeds which thus colonized the lands and formed the first vast forests. One of the first kinds of large trees was Archaeopteris (if you google that name you can find more information easily).

In the carboniferous important swamp trees were lycopods. There were also calamites the size of a small tree (horse-tail related). Cordaites was the first of the group gymnosperms (naked-seeds) that colonized the land for quite a while.

At the end of the permian time (280 million years ago, when the first reptiles appeared, but no dinosaurs yet), lycopod trees had declined and cordaites had dissappeared. Gymnosperms, including confers, took over land environments.

about conifers:

http://www.botanik.uni-bonn.de/conifers/taxa.htm

http://www.botanik.uni-bonn.de/conifers/cu/index.htm

http://www.uni-muenster.de/GeoPalaeontologie/Palaeo/Palbot/books_fr.htm

from http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPaleo4.html :

Plant life of the Permian (248 million years ago) took on an increasingly modern "look" with the rise of a number of gymnosperm (naked seeded) plants during the late Carboniferous and their diversification during the Permian. Indeed, the late Carboniferous "extinction" is almost inapplicable to terrestrial plants. The arborescent lycopds of the carboniferous coal swamps disappeared before the end of that period. The Permian saw the spread of conifers and cycads, two groups that would dominate the floras of the world until the Cretaceous period with the rise of the flowering plants. The first conifers had small leaves similar to those seen in the modern plant Auracaria, the Norfolk Island pine.

The Cupressaceae are found in the fossil record since the Jurassic.

Pinaceae are known in the fossil record since the Cretaceous.

At the end of the perminan the biggest mass extinctnio took place. See:

http://www.uni-muenster.de/GeoPalaeontologie/Palaeo/Palbot/ewald3.htm

The mesozoic era was the time of the dinosaurs. Pangea broke into many fragments and the mammals appeared, but did not flourish yet. The ferns that dominated as plants were accompanied by angiosperm trees from groups like the Cycads, Conifers and Ginkos. Cycads are rare now, see http://www.cycad.org/Photos/photos.htm, and there is only one species of ginko left (wich originated 60 million years ago). With exception of the pine family, all modern conifer families were already present before 245 million tears ago. The cycads dominated the jurassic period though, along with ferns and dinosaurs.

During the end of the mesozoicum, the cretaseous era, conifers take over as dominant trees from the cycads for a hunfred million years or so. Then about 100 million years ago the flowering plants, angiosperms, appear. They quickly radiate and today there are 200.000 species.

The success of flowering plants over conifers is believed to be due to several factors: they give their seed more nutrition and by "double fertilization" they can do this quite quickly. Where conifers have reproductive cycles of 18 months, flowering plants can grow and produce seeds more than once a year: therefore they can colonize barren land much quicker. A second factor is the spreading of pollen by means of insects. This has greatly accelerated species-formation in both insects as flowering plants. Such accelerated species formation is believed to accelerate adaptation rates. The flowering plants indeed radiated into 200.000 species where conifers are limited to hundreds of species. Since the evolution of a tree-sized species in different plant-families is a form of parallel evolution, this has resulted in many tree-species that can excell in specific environments (niches) and therefore outcompete conifers and the like.

A third factor (private communication with Dr C.V Looy) is the more efficient vascular tissue flowering plants evolved over conifers.

At the end of the mesozoic era, 66 million years ago, gymnosperma trees have largely take over from the conifers. Amongst the genera that had evolved were platanus, the oak family, hollies (like American holly or hulst), the walnut family, palm trees and the family that now includes birches and alnus. 50 of the 500 families of flowering plants had already evolved. At that time mammals were about to take over the animal kingdom.

Other families of species originate much later. The first plant fo the rose-order came about some 37 million years ago. At that time only half the number of species known today had evolved. Amongst those were also the grasses that took their ecological niche in this ear from 66 to 58 million years ago. 20 to 25 millios years ago ther number of herb species, or small non-woody plants, exploded because a drier climate shrunk forest and opened up new ecological niches. Today more then 10.000 species of grasses alone exist. At that time the compositae appeared, now with 13000 species of weeds like daisies/asters/sunflowers and lettuces.

Source: Earth and Life through time by Steven Stanley, 1986, Freeman. Isbn 0-716720353