This fall season has truly been one of the most whacked out that I can remember. It’s not just late, it’s helter-skelter, with some trees unwilling to follow any sort of rhyme or reason, and others performing in a fairly predictable manner. It’s maddening for those of us who think we know it all. I mean, we’ve seen the most consistent variable play out: as long as the earth continues the usual track around its nearest star, all other factors—day and nighttime temperatures, sunlight, wind, rain—should be minor players, right?
Well, as us seasoned old timers have witnessed this year, the earthly nuances are just as important as the celestial.
The tree we call “the canary in the coal mine” is a little runt of a Chinese pistachio that grows out of a rhyolite cliff along the catwalk in Queen Creek canyon on the Main Trial. It’s a dwarf about three feet tall that grows as fast as rust, but it is the very first pistachio to turn color, quickly reaching a zenith of deep burgundy before any other tree. For me and the rest of the staff, it’s the official kickoff for the rest of the pistachios to follow. This year, it was well on its way to full fall coloration on November 21, before any other pistachios were even feeling the urge. Moisture, or the lack thereof, can trigger an early entry into fall coloration, and it may be the dominant factor at play with this rock-impacted specimen. But If there is domino effect, this is the first tree to fall.
Our top box office draw for fall color is across from the Herb Garden, where two giant Chinese pistachios dominate the tree canopy and amaze Fall Festival goers with their orange to red leaves during Thanksgiving weekend. The trees are adjacent to each other and their respective canopies and autumn coloration comingle as one. The busy festival going on beneath them (and beneath another four Chinese pistachios nearby) has music, hot-spiced cider, donuts, apple pie—everything but the hayride—and the timing of hosting this event a few days after Thanksgiving has proven itself over time. One tree, in particularly, usually fills the back of the music stage with an arching branch of glowing orange leaves spiked with red. It’s a set designers dream, all courtesy of mother nature, and usually timed perfectly for this event.
But this idyllic scene never materialized on the cue that we arranged for it. One of the two pistachios had begun to color up on the sunny side of the tree, (the side facing the creek), but the other, the one that backed up the stage, still looked as green as the fourth of July. The crazy thing is that these two trees are usually in lock step in regards to color timing, each revealing their pulpy blood orange pigments, equally backlit in the low sun of afternoon like the stained glass of a gothic chapel.
The dominant yellow-gold color generators are the honey locusts, Gleditsia triacanthos var. inermis, and these were also late by a few weeks, too. The photo in this post was taken November 21, and this tree can start to turn as early as late October in some years. But, of course, not this year.
Today, December 12, the pistachio trees at the Suspension Bridge have completely left their chlorophyll behind, revealing the orange carotenoid pigments that are hidden beneath the green, and the burgundy and red anthocyanin pigments that are promoted by clear blue skies with plenty of sun. These trees are right on time, typically at the their best during the first or second week of December. From the High Trail or the Faul Suspension Bridge, the view dominates twenty degrees of the skyline. Catch these trees around noon, and the sun hits them squarely and evenly, giving all four trees studio-quality lighting as they frame the north end of the bridge.
In past years, I have had to desaturate some of my photos (the opposite of Photoshop enhancement) of these trees because the color was so vivid that it looked fake. Now that’s a good problem to have.
So what’s unique about this year?
Because of the earth’s tilt and its orbit around the sun is all but constant, this un-homogeneous fall season can only be blamed on the weather. But even it has components that can be exonerated. The skies have been mostly clear and sunny for the past six weeks, so eliminate clouds and gray dreariness as perpetrators. There hasn’t been pouring rain, fierce winds, freezing temperatures (until a mild frost on the last day of November), so rule them out. The only variable left is temperature.
For most of the month, November stayed warm, both at day and at night, with highs around 70 and lows in the low 50s. It wasn’t until the last few days of November that daytime temperatures dipped into the high 50s with lows from the low 30s to low 40s. This is the crispy weather we’ve been waiting for, and in the first week of December, the color change started to snowball.
Peak colors are right on time for the suspension bridge and the cottonwoods in the creek, but these are predictably late in the season every year. Nothing new here. (Three cheers for normalcy!) The other natives that give us some hue of yellow, like willows and Arizona ashes, usually color up before the cottonwoods, but they are just catching up. The picnic area and the demonstration are still a day or two away from the maximum saturation levels. Because they are late, they will probably last longer, barring any extremes in weather. So while much of the colder parts of the country wish for a white Christmas, Boyce Thompson Arboretum may be the recipient of a lingering colorful one.
As for the red canary along the catwalk, it is usually bare by now, but at last check it still had most of its leaves. Autumn isn’t a tidy package this year, but it should make up for it by lasting far into December.