Late Leaf Change

This image was taken October 7, 2017 in Teton Valley. Compared to leaf color change last year and several years previous, this seems to be about 2 weeks later.

---

Journal entry September 24, 2016: “Teton National Park is in the best color I have ever seen. I think the peak time is from September 21-27.”

 

Journal entry September 23, 2017: “The cottonwoods in the Park (Grand Teton) have a tinge of yellow, but the aspens have hardly started to turn at all.”

 

We just returned from the Park on October 3^rd and the colors still haven’t peaked. And this is happening in Island Park, Teton Valley and along the South Fork as well. Color change is LATE. I just don’t get it. I have been tracking the autumn color change for several years and I thought I had it pegged.

In fact, according to the National Arboretum, color change is triggered mostly by day length. There is a threshold of hours of light/dark that seems to be a consistent trigger. If that is the case though, why is the color change over two weeks late when day length is as predictable as sunrise?

First, a little background on what leaf color change is all about.  Leaves contain chlorophyll, and chlorophyll converts sunlight into sugars that the leaf sends to roots and stems for storage. Chlorophyll is green, so one might assume that the leaves must somehow change the green into the yellows, oranges, reds and purples of a resplendent autumn.

In reality, yellow and orange pigments are always present, they are just masked by the green chlorophyll. Red and purple colors come from anthocyanins and form from sugars trapped in the leaf.

Trapped in the leaf? The communication between leaf and the rest of the plant declines when lengthening darkness signals a rapid cell division at the juncture of leaf and branch. Like pulling the spark plug wire, these cells, called the abscission layer, effectively disconnect the leaf from the rest of the plant, ensnaring any remaining sugars. Eventually, the abscission layer will cause the leaf to fall from the plant.

So, what happens to the chlorophyll? Like colored paper fading in sunlight, hardworking chlorophyll constantly breaks down and the leaf makes more. Once the leaf is disconnected from the plant, chlorophyll production ceases and the remaining chlorophyll quickly fades, unmasking the base color. Cold temperatures can also stop the production of chlorophyll.

Botanists tell us that cool or frosty weather, rain or drought may influence the intensity of the fall colors, but do they impact the timing of the fall color change?

A quick check of the internet showed that this isn’t the first time colors have been slow to change. In several cases, experts speculated that warm nights were the cause. So, I compared September 2016 and September 2017 temperatures for Idaho Falls. To my surprise, I found that the two were nearly identical for coldest temperature, minimum average temperature, maximum temperature and average temperature, debunking the theory that warmer nights were the cause.

Now, I know that you are expecting some earth-shattering revelation about the cause of the late color change, but I admit, I am stumped. The only difference I can find is that this summer, believe it or not, we received over an inch more rain than last year. However, September 2016 was a little wetter than this year. Does that mean anything? I dunno, but it is kind of reassuring that despite all we know about the natural world, nature still holds some cards close to her chest.

---

Wildlife License Plates

Great news! as of 2024, there are three NEW designs for license plates. They still are bluebird, cutthroat trout and elk, but they are beautiful.

Idaho Wildlife license plates provide essential funding that benefits the great diversity of native plants and wildlife that are not hunted, fished or trapped—over 10,000 species or 98% of Idaho’s species diversity. Game species that share the same habitats (such as elk, deer, antelope, sage-grouse, salmon, trout) also benefit from these specialty plates.

No state tax dollars are provided for wildlife diversity, conservation education and recreation programs. Neither are any revenues from the sale of hunting or fishing licenses spent on nongame species. Instead, these species depend on direct donations, federal grants, fundraising initiatives—and the Idaho Wildlife license plates.

Both my vehicles have Bluebird Plates. I prefer the bluebird because the nongame program gets 70 percent of the money from bluebird plates, but only 60 percent of the money from elk and trout plates - 10 percent of the money from elk plates supports wildlife disease monitoring and testing programs (to benefit the livestock industry) and 10 percent from cutthroat plates supports non-motorized boat access.

Incidentally, in 2014, the Idaho Legislature denied the Department of Fish and Game the ability to add new plates or even to change the name of the elk and cutthroat plates (very specific) to wildlife and fish plates, a move that would have allowed for changing images occasionally and generating more revenue. It would seem that they believe that we Idahoans don't want a well funded wildlife program.

I think it is time we let the Legislature know that Idahoan support wildlife funding and that we would like to see these generic plates come to fruition.