Most trees have a kigh infant mortality rate, they die from floods, droughts, but mostly are eaten as browse by deer, rabbits etc.
Browsing kills an almost immeasurably small minority of seedlings. The vast majority succumb to environmental factors, primarily lack of water and lack of sunlight. Of those that manage to germinate somewhere where survival is even possible, the vast majority are killed by disease, primarily root fungi. Only the tiny majority that actually survive to develop more than half a dozen leaves are at risk of being eaten.
A little off topic Blake, but I was always curious how the really big trees like the Redwood pumped water and nutrients from ground level to the top when a normal suction pump can manage only 30 + feet ?
In my (tropical) country, it’s typhoons and fire (natural/man-made.)
I did a ranger walk at Sequoia National Park many years ago. The ranger told us that the main cause of death for sequoias was ------ falling over. Sequoias have a water-based sap, not oil based, so they are more resistant to fire than other trees. Also bugs don’t like them very much. So the main cause of death was when the ground under them can no longer support their weight.
J.
Storms knock over plenty of trees. Or just snap them in half about 7 feet up the trunk, as happened to a maple tree in my backyard a couple months ago. We think it was probably a downdraft.
Around here, at least for right now, seems to be Dutch Elm Disease.
Next up may be the Emerald Ash Borer. As far as I know, it’s not here yet, but will be.
I read it here, but don’t have any idea how to find the post, but this is the gist of it, if I understood it correctly.
Each year the tree grows it forms another ring, which is new wood that allows for uptake of nutrients and water to support photosynthesis. As the tree gets taller, that uptake gets less efficient. As the tree gets bigger, it requires more new wood each year to create the same thickness of new growth. Since the maximum amount of new wood it can create is fixed, as the tree gets old, the new growth becomes thinner and less efficient.
Eventually, and this is a species specific thing, the necessary amount new wood becomes greater than the amount of wood the tree can create, so the tree begins to fail.
Emerald Ash Borer came thru here several years ago. Entire neighborhoods had their trees clear-cut as a defensive measure. It seems to have worked, but it was a bit of a pyrric victory 
It doesn’t work by suction. I remember something like a long chain of water molecules from the roots to the leaves, all held together with hydrogen bonds, and the water evaporating out the leaves pulls up the whole chain.
I didn’t want to do this. I wanted to be a lumberjack!