You may need to repot it in a faster draining soil. Avocados are usually grown in coastal areas with a lot of sandy soil. Lighten the soil a bit and this will give you a chance to look at the roots. If ant are rooted cut them off until you get to healthy roots and sprinkle with cinnamon, let it sit for a day or so. Then water sparingly until the roots heal.

I'm no expert but it looks like the tree is suffocating. It must have been planted too deeply to begin with then the mulch dressing is really finishing it off. If it were me I would remove the mulch and rake away some of the top soil almost to the point were the feeder roots are visible and as far out as the drip line. Then I would put a light top coating of wood chips (not shredded which could compact) over the top. This might seem drastic but you have nothing to lose since it looks like if you don't do something you'll probably lose the tree anyway. The tree looks like some kind of Poplar. Very pretty. I love the conical shape. Perfect for the space. It would be a shame to have to get rid of a tree like that.

See my response to your orange tree post. Patty S.

I remembered subsequent to posting that I had the same problem last year with another avocado tree. Same discoloration and drying out. I had applied little/no fertilizer for the duration of its life if I recall correctly, yet it had the same problem. Even still, I will withhold fertilizer, as RodneyJS suggested, to see if it helps at all. The internet seems to suggest avocados will tolerate full sun. It's definitely getting sun from morning to night in its location, including strong afternoon sun. I am going to try, despite its preference for full sun, to move it to a spot where it gets sun in the morning and midday and partial shade in the afternoon. Will this help? Also, as you can see from the picture, it is on a black asphalt roof that gets very hot (too hot to walk on barefoot on a sunny day). Could it be getting too hot? Again, all my citrus trees seem to be happy as ever with all of the same conditions and care, but I'm just wondering.