I hiked that a couple of years ago, we took 3 days. We were in the trees on the south and west sides, on the north they had been blown away, and there was only low vegetation on the Plains of Abraham on the east.

It surprised me, but there is a much better view of the crater from Johnston Ridge than closer.

And there is some very, very rugged country in there. Hasn't weathered, still unstable higher up on the flanks. Spectacular.

Just south of St. Helens, on Mt. Hood, the treeline is 6,000 feet. Farther south, on Mt. Whitney, I recall the treeline being about 10,000, and even farther south, on Orizaba in Mexico, the treeline is near 13,000. (On that mountain you can drive to Piedra Grande (Big Rock) which is 14,300 feet.)

4,800 is pretty close for St. Helens. What grows there is Noble Fir, looks like a Christmas tree farm. Trees are very sensitive to elevation, for some reason of which I'm not aware. A difference of a 1,000 feet can affect size, health and species rather dramatically.

Nice to see another folk on HZ who has messed around the Cascades. Happy Trails!