March 15th
March is the month of oaks along our creeks, awakening from their winter dormancy to bloom. Three types of oak trees are commonly found adjacent to creek channels; valley, black and coast-live oak.
The most abundant species is the valley oak. A mature valley oak can be 200-300 years old. They are deciduous, losing the last of their leaves in November. In March buds burst open and bright green leaves unfurl. Valley oaks leaf out on an individual schedule. Two trees standing side by side may get their leaves weeks apart. Flowers are produced as the leaves begin to open. The female flower is inconspicuous, occurring on the fine branches and twigs. The male flowers hang down in cascades called catkins. The pollen produced by the catkins travels by wind to pollinate and fertilize the female flowers, resulting in an acorn. Acorns are an important food source to many animals, including deer, raccoon, scrub jay, acorn woodpecker, wild turkey, wild pig, humans and many types of insects to name just a few.
The valley oak is capable of growing in the floodplain, enduring inundation that may last from 3-5 months. During the winter the leafless tree is dormant with metabolic activities slowed to a minimum. The valley is the tallest tree growing in the riparian corridor, creating an emergent canopy layer above the ash, willow, rose and other species.
The black oak, named for the black color of the trunk, is found above the flood plain. It may grow in the company of coast-live or valley oaks. The black oaks produce leaves in early March, before the valley oaks. The leaves are distinctly pink as they initially open and quickly turn green as they grow. The leaves are large with distinctive spines on the leaf lobe tips. In the fall the black oaks exhibit the most colorful display of fall colors, turning red, yellow and orange. The black oak, like the valley, generates female flowers and hanging male catkins, producing acorn that will mature and fall in September.
The coast-live oak does not lose all its leaves in the fall. Instead leaves fall and are replaced throughout the year. The leaf is small and leathery with spines around the margins. They appear much more hard-wearing than the valley and black oak leaves. In the spring the coast-live oak will also be decorated with cascades of male catkins hanging down from the branch tips. You will find the coast-live oak above the floodplain where land rises to form a hill or hummock.
Acorn production varies greatly from year to year. Not all trees produce flowers every year and the reasons are poorly understood. When flowers are produced the acorn crop is ultimately affected by the amount of spring rainfall. In wet springs much of the pollen will be washed away, resulting in a smaller acorn crop.