"Old and Valuable" Whomping Willow - But Why?

[Brenda M.]

No: HPFGUIDX 109562

Hi all!

Feels good to be back after another long break, lol...  Before I 
become completely forgotten, will drop a post and fly away...

I started reading CoS, second time round.  I have been noticing much 
more details and insights than before, I'm glad.  Then something 
occurred to me.

Apologies for lack of exact quotation, but when Snape is lecturing 
them about damaging the Whomping Willow, he describes it as "old and 
valuable".  Also Harry's description has it "ancient tree".

But why?

We know it was planted the year Lupin came to Hogwarts.  So that will 
be about 24-25 years ago.  It must have come from somewhere else -- I 
suppose that's a common sense, tree of that magnitude will take quite 
a long time to grow.  So how old of trees are thought to 
be 'ancient'?  Any botanist?

And why valuable?  Sure, it provides the entrance to Shrieking Shack, 
but is there more than meets the eye?  It rings a pair of odd bells, 
seeing how Snape describes it 'valuable'.  Severus Snape, of all 
people, who would love to squash it if possible, I bet.

Any thoughts?

Brenda