Don't think I knew about fir waves, but from a human perspective, most of the interesting things happen at the edges of a forest (much of the stuff we can eat grows in clearings or edges), so windbreaks falling like dominoes makes a good deal of sense.

Where humans are involved in planting the trees, I'd expect statistical clusters, because if you plant a thousand oak trees in the same year, many will die within the same decade or so. My forestry friend in college complained about how every time trees died on campus, they'd replace them all with some other species, creating waves of dead trees every few decades, whether disease or old age, instead of a tree or two every year.

But then even without humans, nut trees are born in statistical clusters as well, ('masting' is an adaptation to overwhelm predator populations) so it stands to reason they'd die in clusters too. And a bad spring may result in more seeds germinating the following year.