Fall is a great time to study oak trees – and there is a lot to discover at Six Sigma Ranch. Leaves are turning yellow on the blue oaks by our front gate and on the majestic valley oaks in Asbill Valley a little deeper into the Ranch. All summer, the rare black oaks have been hiding their green leaves among the other trees on the hillsides but, for a short while in the fall, they will stand out with their bright orange and red colors, and you suddenly can’t miss them.
Some oak trees, the live oaks, do not take part in the fall color show, but keep their dark green colors all year round.
This is all pretty basic, we used to think: Deciduous trees turn colors and shed their leaves in the fall, while evergreens stay, well… always green.
Then, a couple of years ago, we stumbled upon a few trees with a behavior somewhere in between the two: Their leaves turned into a yellowish green in the fall, but after that, they stayed on the trees most of the winter instead of falling off… It took some help from an expert to figure out the mystery!
The Solution
Kerry Heise of UC Davis helped us figure out what is going on.
The tree, oracle oak, is actually exactly what it seems to be, Kerry explained – a hybrid between deciduous black oak and an evergreen specie, interior live oak.
When you look at the leaves, it seems intuitively very probable that the one in the middle represents a hybrid between the black oak on the left and the interior live oak on the right.
With Kerry’s help, we have now identified eight different species of oak on the ranch. That’s pretty exciting for nature lovers who grew up in Denmark where all oak trees look the same!