Color Guard
The weekend trip closed with a drive home through the Alaska Range, and the steep scenery around Isabel Pass looked as glorious as it usually does--except for one little flaw. Here and there, like pale flames along the creek banks, willows gleamed golden in the evening light. On the river's gravel bars and beside the road, dwarf fireweed leaves had turned a sunburned purple.
The first of August, and fall colors were already signaling a change of season on the high ground. "Not fair," I groused to the driver. "Why do the doggone plants have to start changing colors so early?"
That question led to some further discussion, plus an answer or two, thus reminding me yet again of the first item I'd like to have along on any trip; a scientist. Perennial plants, ones like willows and fireweed that grow again spring after spring, gamble with their lives every year. When they're living at high latitude and altitude, the stakes are high and the risks great. The colorful plants of August in Isabel Pass are living at the edge of the possible.
Their game has only a few simple rules. Grow as fast as you can, bloom and set seeds to continue the line, and stash away every spare crumb of energy you can to get through the winter. Winners get to try again next spring; losers die. Wild cards do show up in the game, such as a hungry moose chomping away a year's effort or a moving river undermining three generations, but much of the game goes to the plants that best bet their effort.
Flowering takes energy, but lots of flowers are likely to lead to many offspring. How much to bet on tomorrow? How much to save for today? Defensive chemicals keep the bugs at bay, but take energy to manufacture. Build too strong a dose of natural insecticide this summer and there'll be no spare food for lasting the long months of winter. Build too little and bugs can strip away all the food-making leaves.
Unlike human gamblers, plants cannot make foolish decisions. They can be inefficient; they can lose, and die, but they can't think about it. Their choices have been programmed by evolution, and they are descended from a long line of winners.
What I saw in Isabel Pass was a range of bets. Not all the willows had turned yellow. The ones that had done so were betting that winter would be early. They were closing down the chlorophyll factories in their leaves, leaving the less efficient photosynthetic yellow pigments, the carotenoids, to do what they could until the leaves fell. A killing frost would not be so harmful to these early-yellowed willows; they'd already withdrawn much of what they needed from their now more easily sacrificed leaves.
The willows still fully green were betting on a later winter. They were laying more on the table, packing away more supplies for winter than their conservative yellowed brethren, but risking a far higher portion if snow caught them fully leafed and green. The fireweed plants were making similar gambles, green and growing for broke versus empurpled and throttled conservatively back. (Plants with a high proportion of blue or dark red in their autumnal colors have unmasked their supplies of anthocyanins, pigments also usually hidden by the intense green of chlorophyll.)
Since every winter is a little different, the plant communities in the pass represent a range of color-change timings that have succeeded over the centuries since the glaciers uncovered the gravels. If the climate continues to warm, eventually the conservative early changers will be outcompeted by the plants hanging on to summer colors a bit longer. Then maybe Isabel Pass will seem purely green on the first of August, but probably not in our lifetimes.
