: storm and (less often) fire claim vast
: tracts of these forests anyway. These fast-growing, shallow-rooted trees
: are very often blown down in storms. One of the most striking
: characteristics of a Pacific Northwest old growth forest is amount of
: blowdown and second growth that exists.

I'm really not trying to be contrary for the sake of being contrary, but I have to disagree. Neither storm nor fire claim "vast tracts" of old growth forest in the Pacific Northwest. One of the reasons the Pacific Northwest has "old growth" is precisely because there aren't influences that claim much of anything. Fire of any consequence is so rare it is almost unheard of. I realize you said "less often," but that doesn't quite capture the reality, particularly since your point seems to be human and "natural" impact is, perhaps, comparable. Old growth forest in the PNW is temperate rain forest, and it's wet, very wet. Fire simply doesn't have much impact because soggy stuff doesn't burn well. Perhaps a lightning strike might take out a single tree here and there, but vast tracts don't burn. The reason there are 800 year old trees is that they haven't been burned or blown down in storms. You simply cannot compare fire or storm to the impact of humans.

With regard to storms, I think you are confusing two very different scenarios. It is certainly true that fir trees, for example, are shallow rooted; however, the weakened stands (those most likely to blow down) are at the edge of where logging has taken place, not in the midst of old growth. A protected fir, growing in the midst of a forest isn't anywhere near as likely to blow down in a storm as a stressed, weakened fir at the edge of a clear-cut. Some of the most dangerous trees are those "decoration" firs left dotting suburban areas after the land has been cleared for houses.

The process of how a young forest becomes an old forest isn't really related to "blow downs" in the sense you use the term. It doesn't really make sense to say that there is "secondary growth" in an old growth forest. Once you cut down an old growth forest, then you get secondary growth, but I wouldn't describe this growth as "in" and old growth forest. Nor would I describe it as "characteristic" of old growth. Indeed, I can't think of anything less characteristic of an old growth forest than secondary growth. A young forest, left to it's own devices, becomes an old forest. The process of maturation involves death and decay and the ever increasing density of understory. Some of the trees thrive and become dominant; others die and feed the understory. But the trees that die aren't "secondary." "Secondary growth" refers to what appears after a disturbance, like fire or logging (and we've already ruled out fire). This new (secondary) growth is primarily deciduous, though sometimes fir, and the process begins all over again. That is, the deciduous trees and the fast growing firs are slowly replaced by what you see in an old growth forest. To make this long story short, the "blow down" you see in an old growth forest isn't "secondary" growth, but "first" growth, for lack of a better term.

So, neither fire nor storm are having any impact of a "vast tract" nature in the old growth temperate rain forests of the PNW. The only thing that has affected "vast tracts" is logging. I'm a woodworker, so I can't be anti-logging without also being a hypocrite. But I do think it's important to understand the issue. My personal opinion is that we have very little old growth left and we should protect it before it's gone. And I feel duty bound, as a woodworker, to point out the error of your characterization.