I don't know what would cause a tree to sprout leaves earlier in the spring. And I don't know if the article explains that because of the paywall. Maybe it has

I don't know what would cause a tree to sprout leaves earlier in the spring. And I don't know if the article explains that because of the paywall. Maybe it has to do with temperature? As far as shedding leaves earlier in the fall, I heard they determine that based on when they've collected enough CO2. The more CO2 in the atmosphere, the less time it takes the trees to meet their goals.