Hi, jaywking,

This is a good kind of project, but there are a couple problems. 

1.
Many of these open spaces/nature reserves already exist on the map. If you're importing a polygon that already exists, you have to actually replace the existing one. In JOSM, that is done with "More Tools -> Replace Geometry (Ctrl+Shift+G). Right now, there are multiple overlapping open spaces at the one you mentioned in your message to me.

2.
Most of the tags on the ways you imported are incompatible with OSM data. You need to delete all the tags from the polygon (e.g., "AREA_ASSES 2.86), and add relevant OSM tags. For example:

operator=Town of Ridgefield
leisure=nature_reserve (You already got this)
name=Lakeview Road Open Space

I like to add names such as "Lakeview Road Open Space" if no other name is established for a municipally-owned open space.

Best,
Jack