Greetings Billie:
Ah yes, this is becoming quite the popular question these days, "What is the ecological value of my tree(s)."
Rather than regurgitate a bunch of information via this modestly truncated forum, might I suggest you explore the works of Dr. Kathleen Wolf et. al., at the University of Washington.
http://www.naturewithin.info/urban.html
http://www.naturewithin.info/Policy/Hedonics_Citations.pdf
In addition, you may want to procure the services of a local professional forester to assist you directly in regards to this specific tree/situation.
Best of luck!