Nature Afoot

Surviving the dry times

Bridget — Sun, 04 Dec 2011 03:12:57 +0000

Unlike people, many trees can survive for months without available water. In places where the ground freezes in winter, so that moisture is not available to be drawn up through the roots into the tree, winter is a kind of drought.

This American sycamore has dropped all its leaves by early winter

Deciduous trees solve this problem by hunkering down for the duration: They drop their leaves. Sap retreats to the tree’s roots. While bears hibernate in their dens, next year’s leaves wait, tightly furled in their winter buds, for the spring thaw.

Winter buds on an American sycamore

In an arid climate, trees use other strategies to survive. Inland Southern California has a very dry, Mediterranean climate. Only a few inches of rain fall every year, and only in the winter. Summers are long, bone dry, and brutally hot. So some trees and shrubs survive by dropping their leaves in dry times. This palo verde, Parkinsonia aculeata, in Riverside, California, is just waking up from its summer slumber after November rains.

Mexican palo verde

Most of the green color in this picture comes from the trunk, branches, and twigs. This tree is “dry season deciduous.” It drops its leaves when there isn’t enough moisture to support them. The leaves stay on the tree for only a short time, so some of the work of photosynthesis is carried out by the green woody parts.

But it’s been raining in Riverside and the ground is moist, so the palo verde is leafing out. If you look closely, you can see leaves. Actually, these are tiny leaflets on very long, compound leaves.

The palo verde is leafing out

Palo verde is Spanish for green stick or pole. The USDA Plants database calls this species Jerusalem thorn, which I suppose refers to the vicious thorns that grow at the base of each leaf. I prefer an older name, Mexican palo verde, because the tree grows mostly in Mexico and in the parts of the U.S. that used to be in Mexico. And it looks like a green stick most of the year.

What’s the tree of your place?

Bridget — Thu, 03 Nov 2011 21:52:16 +0000

What kind of tree do you think of when you think of the place where you live, or any other place you know well? What kind of tree would you want in the background if you were making a movie about that place? Here on the Lake Ontario plain where I live, it might be a maple, possibly a Red Maple, Acer rubrum, like this grand old tree.

a tree in its place

Bridget — Thu, 11 Aug 2011 18:39:36 +0000

The tree in the picture at the top of this page is a Bur Oak, Quercus macrocarpa. This particular specimen is twisted and grizzled, gradually dropping branches as it is shaded out by taller trees.
Bur Oak belongs to the place in the American Midwest where the prairies meet the eastern forest. Driving west on I-90 from New York state, there’s a moment, somewhere in Ohio, where suddenly I see bur oaks and think, we’re in the Midwest now.
Along back roads and boundary lines in Wisconsin, and next to farmhouses, you see these sturdy, dark-leaved oaks. But no one plants them in the subdivisions that replace corn fields.