Fall is a time when we can hear melancholy songs in our minds as the wind grows cold and leaves rain down from the trees. Maybe the moments of slight sadness come from a sense that summer has died and the dark nights of winter will soon close in on us, leaving animals shivering in the woods and snow blowing off the peaks.
Rafting trips are over for the year, biking through sunny meadows or lying in the grass with a friend… these things are past for now. But fall is so beautiful, so vivid and stark, with yellow aspen tree colors strewn across the mountains of New Mexico and Colorado in a full-on psychedelic show. Snow falls through yellow leaves.
Why do these trees change color, these aspen and Rocky Mountain maple, cottonwood and box elder? Why do they lose their leaves? These are the sorts of questions that are hiding in plain view out in nature. As we rush around do we ever pause to wonder? Kids do. What do we tell them?
A Little Background
Leaves are the solar panels of the biological world. Leaves expose themselves to the sun so that little organs in the cells of their leaves, chloroplasts, can collect sunlight and miraculously convert it to sugars that the plant uses to feed itself. Naturally humans and all animals eat the plants to get these sugars for survival. Chlorophyll is the green stuff in leaves that contains the chloroplasts.
Chloroplasts are the reason any of us exist, the reason any animals exist. Without chloroplasts, the earth would be an empty stone, floating in the black lonely void of space. These tiny little chemical machines in chlorophyll that convert sunlight into usable energy may have first evolved in mats of algae on ancient beaches more than 250 million years ago.
Falling Leaves
I digress. Why do leaves turn yellow or red in the fall? As it turns out, the green (chlorophyll) in the leaves drains away when the days get shorter and other pigments in the leaves that have been underneath the green stuff (chlorophyll) are exposed to the world. Green gone, other pigments on full display. Whole mountain sides of plant pigments attracting people by the carload.
So why don’t the colorful leaves just hang on all winter? Why do trees and other plants lose their leaves?
Trees lose their leaves because in cold climates it would be impossible to maintain the delicate cell structures inside the leaves in the freezing weather. Just as people can get frostbite (which is severe damage to the cells that make up our flesh) so too can plants have their cells destroyed when the water inside the cells freezes and breaks the cell walls and damages the “organelles” that perform all sorts of functions inside the plant cells.
Right where the leaf attaches to the little branch of the tree there is a membrane called the abscission layer. All summer nutrients from the leaf flow into the tree trunk across this layer and water from the roots flows into the leaves. The leaf feeds the tree with the sugars it manufactures. But when the days get short, hormones in the plant cause the tree to seal off the abscission layer where the leaf has been attached and the leaf falls off the tree and drifts down, dreamily through the autumn air.
The ground is then covered with leaves which gleam in the fall sun. They blow around in the wind. They blow our minds and eventually they begin to decay in wet climates, or in dry climates like ours, they are covered with snow and perhaps are burned by a creeping fire. But that’s another story.
The best places to view colors in the southern Rockies:
Red Mountain Pass in the San Juan Mountains
Aspen Vista in the Sangre de Cristo above Santa Fe
Camp May in the Jemez Mountains near Los Alamos
Crestone in the Sangre de Cristo north of Alamosa
Incredible cottonwood colors are best seen from Velarde to Pilar on NM Hwy 68.
(And don’t forget the beer and be sure to VOTE EARLY.)
