when do leaves appear on trees again during the spring?

Question

there are a lot of fall foliage maps that show when leaves change color. i was wondering if there are similar maps, but showing when leaves appear again during the spring

Answer 1

Plants undergo different types of dormancy depending on the typical minimum temperatures for the area. The commonest for zone 3 and higher is the quiescent period, when the buds remain dormant due to unfavourable environmental conditions. This a combination of sunlight and temperature. With less light and a decrease in temperature to between 5 & 10 C the tree struggles to support foliage with decreased photosynthesis. So there is a break-even point between available light energy and temperature that predicts actual canopy loss.

Spring bud break is the reverse, more light and warmer temperatures trigger the processes leading to bud break.

For areas with temperatures down to -38.1° C (-37F) and below the plants do more to protect themselves from freezing damage. Once fully dormant, plants count out time. This is called chilling hours. Plants in this phase can not wake up til enough cold time has passed so if a few warms hours happen they do not respond. Once their 'chill time' is met. A warm spell with longer daylight period is required to start them again.
Chill time and dormancy break is not well understood yet so even though there is an economic benefit to create an accurate modeling algorithm it has yet to be accomplished.

One thing happening with the intenet is accumulating phenology data so this can be used to create a better model. Volunteers respond with data about their area.
http://www.learner.org/jnorth/pde/PhenDataAbout.html

Answer 2

It's more difficult to determine when trees bud because budding is based on temperature, unlike leaf abscission which is based on change in length day (and thus time of year). So you're unlikely to be able to find any sort of accurate map.

With the weird weather we've been having this fall, some trees have actually been budding where I live.