Four objects, three of which are trees.
I know Mackenzie wanted the golfer to be able to maneuver their ball from the tee to set up angles. I may not know exactly what he intended for the surrounds of the hole, but i can prudently assume it wasn't meant to impinge upon those options, other than as may occur over time as the trees he left grew.
In this case, the three trees had become a "nuisance" by 1949, something I believe Mackenzie anticipated. What he didn't anticipate, and didn't intend, was the further addition of trees on both the left and right sides of the hole effectively limiting the options off of the tee.
Here's what I wrote on the hole a couple of years ago:
"I actually think that this is one hole at Augusta where placing a premium on placement of the tee shot is appropriate (the method of doing so is still up for debate). The reward is a shot at the green, the penalty for poor execution is to have to lay up (with birdie still an option). That being said, the second into the 15th green is one of a few standout moments in the closing stretch of the tournament. There's a fine line between building up the excitement and still asking the golfer to execute shots in order to be in a position to make a move.
As we've seen in recent years, the tournament committee has the ability to change the conditioning around the 15th to make the hole easier or harder, depending on the intentions of the year. With a bit of rough on the bank, the penalty for a miss short is alleviated slightly. Of course, if you haven't maneuvered through the obstacle course in the fairway, the length of the grass on the bank has little effect.
Reading Dan's comments makes me think that the nature of this hole should be dominated by the pin positions, and the fairway should be set up so that the player has the opportunity to place their tee shot in the ideal position for attacking the day's location. I think I'd rather hear the commentators discussing how Player A's drive leaves them a tough angle into the narrow left side of the green, as opposed to hearing them discuss how they are going to play their layup from the pine straw."