Moss and nutrition until your tree reaches the earth (clay, loam etc.)- the nutrient packs I send with the Trees do their best to mimic the nutrients it gets from the earth. Fish Bone Meal based, etc...
And moss- I originally thought looked cool, but actually it's living and it thrives on the moisture it gets from the Tree.
Best time for removal is in when tree is dormant (Late Winter- Spring-before Leaves emerge), your Tree will bloom and thrive put out much more new healthier growth. It doesn't matter where you bought your Tree, I'm just looking out for your tree (investment).