Trees

&nbsp Trees are commonly found in areas of Middle-Earth not under the domminion of Sauron.

Description
Trees in Middle-Earth greatly resemble trees in the real world, and many of the species mentioned in Middle-Earth exist in real life. Although the Ents resemble trees, they can move, whereas true trees cannot.

"Talking" trees
Some trees, for example those in the Old Forest, were dangerous and could "talk" to other trees, drop their branches on unsuspecting passersby, and lead them to Old Man Willow.

However in most places trees were neutral -- they were neither allied with Sauron nor with anyone else -- and in most places other than the Old Forest and Fangorn, the trees couldn't communicate with one another and were virtually indifferent to anyone passing by.

Major forests of Middle-Earth
Mirkwood was by far the largest forest and it was also the most dangerous, though it's trees weren't dangerous -- it was the fact that Sauron's stronghold had been located in Mirkwood for a while that enabled Giant Spiders to spawn there.
 * Fangorn
 * Old Forest
 * Mirkwood
 * Lorien

Other locations where there were trees
Trees could be found just about everywhere, including (but not only): Trees couldn't be found in some areas, including:
 * In and around The Shire
 * Ithilien
 * Around Rivendell
 * Parts of Gondor
 * The Gray Havens
 * Along the west side of the Anduin
 * Most of Rohan (it was mostly grassland)
 * The peaks of the Misty Mountains (or any other mountain range)
 * Mordor
 * The Brown Lands