system
Given the following post, respond as if you're commenting on Reddit:
human
Why is so much of the American West dominated by coniferous forests?

It seems like the West has a much higher proportion of conifers than deciduous forests east of the Great Plains do. Is this only because of generally higher levels of elevation and aridity?
gpt
It's all about water. conifers grow slowly but year-round (different sap), even in winter but very slow. deciduous trees need water during the warm months, and out west it does not rain during the warm months. So  deciduous can't compete very well. You are noticing the difference in rainfall seasonality. In the rainy east, deciduous outgrow the conifers because they use cheap, disposable leaves.