The Purples of Autumn

As leaves start the show of shifting colors there are other subtle changes going on as plants prepare for dormancy. The purple hues of Hobblebush - Virburnam alnifolium are an early example of autumn. Pigments called anthocyanins are building up in the leaves. Anthocyanins are responsible for the shades reds, pinks and purples in the leaves. It is colorless until a sugar molecule attaches to its structure. In the fall, sugar created in the leaf during the day through the process of photosynthesis, cannot escape from the leaf at night because chilly temperatures slow down the movement of sap. From the sugars trapped in the leaves, anthocyanin is transformed into brilliant flaming reds or striking purplish hues. We are seeing this transformation in the red maples and hobblebush at lower elevations and in the blueberries and diapensia at higher elevations.

Diapensia matt on Bigelow

Lawn 9/9/09.

Buds are another sign of impending dormancy. Found at the ends of hobble bush twigs, buds are fully formed, ready to weather the winter season. Buds have actually formed in preparation for next spring. Once the low angle winter sunlight and freezing temperatures have given way to greater day length and more moderate conditions, the buds will break. Tiny leaves will emerge and photosynthesis will begin yet again. In the meantime the buds signal a time of dormancy for the plant. These rather large buds are also a favorite food for browsers such as moose.

Fall Foliage Update 2009
Check in for weekly fall foliage updates from AMC Naturalists. We will post weekly photos from Pinkham Notch and across the AMC backcountry huts. Check back and follow fall across the White Mountains.

Colors are still very subtle looking across at the Presidentials from Square Ledge in Pinkham Notch, but with the recent chain of cool nights and sunny days changes will soon be dramatic. The photo below was taken 9/11/09.