Red maple are some of the first trees to flower in the spring, and the flowers are fun to see. However, in a cold spring like this one, I don’t get too excited about red maple flowers as a sign of spring. Aspen flowers, on the other hand, I do get excited about, and I saw some last Saturday.
Cumulative heat sum is a major signal for trees to initiate growth in the spring. To keep it simple, a tree can sense how much warmth it has received, and when it reaches its threshold cumulative heat value, it begins to grow. In aspen, “Maximum air temperatures above 12° C (54° F) for a period of about 6 days appear to be the principal factor governing timing of flowering.” (Silvics of North America, http://www.na.fs.fed.us/spfo/pubs/silvics_manual/volume_2/populus/tremuloides.htm) Of course we’ll still have some cool days, but the medium term forecast shows real spring like temperatures are on their way. Hoooray!