A University at Buffalo study reinforces that tree survival is linked to proper planting and after-planting care. If trees don’t have sufficient rooting as a drought starts, they will not have the opportunity to grow roots to a moisture source as rooting requires moisture. The study, How do conifers survive droughts? points out that existing roots, not new growth, help trees survive drought. They acknowledge scientists can't see underground, but computational models support investigation. It was published in ScienceDaily, December 2019.
The researchers looked at pines and junipers. They said, "When the model was set up with roots in the groundwater, none of the trees died off. When the model required the trees to grow the roots into the bedrock after simulations started, all the trees died off. Growing new roots, which itself requires water, took too long."