Question
Jim,

I have a very large Fir tree about 90 feet in my very small suburban back yard (50X70).  It is at the edge of the property and has a pretty big lean to it.  It's been this way for many years so I'm not immediately concerned, but I imagine it's still growing.  The top15+ feet has forked so now there are 2 trunks.

I wondered if it's feasible and appropriate to top off 20 feet?  Would that destroy the viability of the tree over time?  
Thanks for your consideration,
Dave W

Answer
It is feasible BUT I recommmend high NOT to top your tree. The growth of a tree is from the top (meristem) and if it is cut you will see growth problems begin. Not only will it make it look bad but the cut will allow fungi to enter and set up rot in the trunk. Here is one web link that agrees with this position. http://www.pnwisa.org/tree-care.html