Are you aware you can view the maps and owner info online: http://host.cdmsmithgis.com/enfieldct/
Enter your address and zoom in to your home. Click on the properties around you and get owner info.

You may want to check in with your owners' association president or legal agent because as a "planned development" the Pheasant Hill may have certain buffer requirements to maintain around the perimeter. Might involve replacing certain vegetation that comes down, etc...

Northern Connecticut Land Trust appears to own land behind homes on the other side of the street. However Ms. Puziak's home would appear to back up to Meadow Road lots.

http://gis.vgsi.com/enfieldct/Parcel.aspx?pid=14660

http://www.northernctlandtrust.org/

I contacted NCTLT and had Richard (super nice guy) come out to see if they owned the land and they don't, unfortunately. Here's where my trail runs dry every time haha

This 8 acre marsh was a gift made by George Leaska on 12/20/1994. It is a nature preserve located off of Weymouth Road. The steward in the 2014 annual report is listed for this property is Albert Grant 860-623-5487

Could be CREC if you are at the end of the street

And the piece of land off King Street that also abuts Pheasant Hill was conveyed to the Trust in 2012 by KEI-BO & WU INC.

But where are you having the tree issue? You said it was right behind your home... Is that accurate?

Yes! THAT'S the name - Kei-Bo & Wu Inc! Couldn't recall the name to save my life, thank you! The tree issue is a few gigantic trees that are either totally dead or currently dying. The last two winters have really made these trees a threat to the house. Not to mention the weeds/overgrowth that has plagued the area has made the land unusable. Tried to grow a garden but I couldn't keep ahead of the weeds and it killed everything.

(Paul) CREC doesn't own it either, the homes were built in 1997, long before the school was built. Though I wish it were that easy! The 8 acre marsh is owned by NCTLT :)

Looks like Kei Bo & Wu Inc. has dissolved: http://www.connecticutcorps.com/corp/148874.html

I'm assuming that means that the town absorbs it in a way?

The Town doesn't appear to be involved at all.
Judging by the Land Transactions the property appears to have been conveyed in 2012 to the NCTLT. You can see them identified here:

http://gis.vgsi.com/EnfieldCT/Parcel.aspx?pid=30062

If you went to the Town Clerk and asked to see Book & Page: 2554/0867 you could view the detailed legal description of the boundaries, etc.

The condo association property behind unit #16 abuts the rear yard of 5 Meadow Road. There is a right of way between 16 and 18 Wemouth Road that belongs to the condo association and enters the property near the rear of #16. It appears the trees behind #16 are the property of the condo association.

Check with someone from the condo associations as they would be the responsible party.