Trees have fascinated me since I was a small child. (Coming from a 
Nordic country with a lot of trees and forests, this is probably not suprising). But, of course, people have always been fascinated by trees. Culturally the 
world tree - connecting heaven and earth - is an ancient symbol present in several religions and mythologies. The 
tree of knowledge and the 
tree of life are related symbols in many religions and philosophies. 
Trees have also inspired thousands of poets and writers. Here are two of my favourite tree poems by 
Michael S. Glaser:
The Presence of Trees
I have always felt the living presence 
of trees
the forest that calls to me as deeply 
as I breathe,
as though the woods were marrow of my bone 
as though
I myself were tree, a breathing, reaching 
arc of the larger canopy
beside a brook bubbling to foam 
like the one
deep in these woods, 
that calls
that whispers home
A Blessing for the Woods
Before I leave, almost without noticing, 
before I cross the road and head toward 
what I have intentionally postponed— 
Let me stop to say a blessing for these woods: 
for crows barking and squirrels scampering, 
for trees and fungus and multi-colored leaves,
for the way sunlight laces with shadows 
through each branch and leaf of tree, 
for these paths that take me in, 
for these paths that lead me out.
I will not here discuss problems connected with the destruction of rainforests. However, I dould like to highlight another worrysome development:  Many valuable and useful tree species are seriously threatened. 
Despite their importance over 8,000 tree species, 10% of the world's total, are threatened with extinction. Even more worryingly 1,002 species are listed as critically endangered – likely to go extinct unless urgent action is taken now to save them.
The information above and below is by 
The Global Trees Campaign, the only international campaign dedicated to saving threatened trees. 
- millions of people around the world rely on food, medicine or other products that can only be derived from a particular species of tree; 
- the life-cycle of many animals or plants is inextricably tied to certain trees; 
- many timber users (both industrial and subsistence scale) need wood with special properties; 
- in many cultures, particular trees play an important spiritual role, such as the kapok tree in South America, which is believed to link heaven and earth.
PS
The 
Willow tree is probably the most wellknown "medical" tree - and has been so since ancient times. 
Image by Zest-pk flickr