Your friend had a field full of pioneer tree species. Those trees stopped his field from being a meadow (a badly, badly damaged meadow) but they have to die to make way for the real forest building species.
For instance, a pioneer tree dies. A hemlock, which likes to grow on fallen trees (nurse logs) takes its place. When the hemlock grows old and dies, your old-growth species might establish in the same spot, or it may wait to replace whatever grew after the hemlock.
https://en.wikipedia.org/wiki/Fir_wave
For more information, this book: https://www.goodreads.com/book/show/9698421-nature-guide-to-... has wonderful information about how northern forests change over time.
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.
Agree about the clusters. I am most familiar with the northern forests of New England (strictly as an amateur) and they are a wonderfully dynamic place. From big events like the Hurricane of '38, to small wind storms, fires, ice storms, and just an individual tree getting old and falling over, they are in a wonderful constant state of flux.
One of the saddest things is the loss (or coming loss) of so many important species. The American Chestnut and Elms are long since gone. The Hemlock and Ash are also under threat from pests and the Beech may be as well.
Between 1990 and 2015 forests in Europe gained 90,000 square kilometer. A whole Portugal worth of additional forest.
https://www.weforum.org/agenda/2019/07/forest-europe-environ...
In less naturally forested areas we have to be careful not to upset things like peat and bogs which are even better at CO2 than forests.
You can accelerate mature forest creation by planting native and more late cycle trees to prime the pump. I have a buddy who inherited ~50 acres in central NY after college. It had limited road frontage and sale value, so he basically pays the taxes by leasing ~10 acres to a farmer, and spent about $15k planting black walnut, oak, etc. It probably
Large scale farms at least. Some things like cheesemaking are still viable, because you only need a handful of cows to make an enormous amount of cheese.