Trees that leaf out early and hold leaves late are subject to limb breaking snow loads. When this happens with trees, it means a loss of the stored energy reserves that went into producing this first set of leaves. Trees will activate reserve buds to grow another set of leaves, but this may require more stored energy than weakened trees have. The freeze-kill of leaves can be the stress that pushes a marginal tree to decline or death. Trees can only manufacture energy from the process of photosynthesis when leaves are exposed to sunlight.
Time is the only cure for trees caught with their leaves out in a freeze.
Areas such as ours that receive low amounts of natural precipitation aren't well-suited to tree growth. In the Denver area, we have few native trees - cottonwood, western hackberry, Gambel oak and ponderosa pine. The first two grow along waterways and the last two in the foothills. There just isn't enough water to support the growth of a large tree and so nature calls for grasslands. Plants adapted to a semi-arid environment of low humidity and low soil moisture levels are the basis of Xeriscape gardening.