X Tree, X Tree

Read all about it! 
That tree's going down. It's only a matter of time*  

X = mass/weight of tree
Y = length of tree 
Z = time
X + Y + Z = Timber!
*A year ago a cyclist could take the inside track, closest to the tree.  Not so, now.

This tree's going down, called the architect as he stood beneath. (extra 1) 
That tree's going down, repeated the second cyclist as he rode by. (extra 2)