Ast the Arbotist

A time to turn comes early


 

 

It’s not your imagination: the leaves on many trees are turning yellow earlier than normal.

I’m not talking about conifers like Monterey or Aleppo pines or any other evergreen tree that doesn’t lose its leaves every year. If you see a pine that is all yellow, it’s too late; the tree is dying or dead.

I’m speaking specifically about deciduous trees that drop their leaves every fall as part of their natural life cycle.

I’ve been getting calls and emails for three weeks from people wondering what is wrong with their trees because they’re noticing yellowing leaves. Some of the trees do have problems such as chlorosis, which could be caused by a lack of iron or nitrogen, seen quite often on citrus trees and some liquidambar trees, for example.

And there is no doubt that many trees are suffering from the lack of rain last winter, which compounds the drought conditions that we are feeling in Southern California.

What is unusual are the otherwise healthy-looking deciduous trees that usually don’t display fall colors until the end of September or early October but appear to be in early stages of dormancy right now.

Just driving around this week I’ve seen some London plane trees, California sycamores, valley oaks and Chinese pistache that are starting to turn.

There are even a few liquidambar trees in my neighborhood that have turned that beautiful burgundy color they normally show off later in the year.

Leaves on deciduous trees turn colors in the fall when the chlorophyll leaches out of them. Chlorophyll creates the green color that overpowers the actual color of a leaf. As the chlorophyll goes away, the leaf turns its natural color.

For most trees in Ventura County, those colors are varying shades of yellow and orange, with some red and burgundy thrown in for good measure.

Until just a few years ago, I used to collect acorns to plant and to give away to those who wanted them. Every year I could count on collecting acorns from valley oaks in September and coast live oaks in October—until this year.

On July 30, I was looking at some valley oaks that already have mature acorns on them. Acorns being produced so early in the year is most unusual, and some are already beginning to fall off the trees.

This is not the case with every oak that I see, but the number of oaks that have mature acorns already is very interesting.

Why does it seem like the internal clock on some trees is off by at least a month?

Keep in mind that the major function of leaves on a tree is to produce food through the process called photosynthesis. As long as the roots are providing water and there is sufficient sunlight to maintain the normal photosynthetic process, then those little food factories called leaves can do their jobs very efficiently.

Have you noticed the weird weather we’re having this year? This upper plateau we call the Conejo Valley is experiencing different weather than I ever recall.

I have always counted on what we call “June Gloom,” where all the mornings in June are foggy, with a chance of drizzle followed by warm afternoons.

But this year we also had May Gray and July Something, and now we are into August Whatever. Since May, we’ve had more gloomy mornings than any year in the past.

But trees don’t have a brain; they can’t make decisions based on fact as humans do.

What they do very well, though, is react to various kinds of positive and negative outside stimuli, and adjust the best way they can.

My theory is that there is a combination of environmental conditions tricking some trees into “thinking” it is already autumn.

So far, the daytime temperatures this summer have been quite mild compared to past years. Combine that with the fact that for more than three months, the days have seemed shorter to trees because they have not had enough actual sunlight for the leaves to produce as much food as they usually do. When leaves don’t produce, trees will cut them off and let them fall.

The big problem is that if trees drop their leaves earlier than they should, they could miss out.

We may get a really hot finish to August and September, and many trees will miss a great opportunity to create the much-needed starch reserves that get them through the rough times.

It will be kind of like showing up to an all-you-can eat smorgasbord five minutes before closing time and missing out on a whole bunch of really good food.

I guess we’ll just have to wait and see how it all turns out.

David D. Mortimer is a certified arborist and a certified tree risk assessor with more than 35 years’ experience in the tree care industry. Email questions to dmortimer@theacorn.com.


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