When it comes to autumn color, many variables and conditions are at play. Weather and environmental conditions are key factors that influence the vibrancy of the fall season.
The basics of autumn color
When you see a green leaf, you’re seeing the green pigment chlorophyll. That’s the key component in photosynthesis. Trees continuously produce it throughout the growing season. When you see orange in a leaf, you’re actually seeing a compound called carotene. And when you see yellow, that’s from a compound called xanthophyll.
Interestingly, these compounds are in the leaves during the spring and summer as well. The green chlorophyll masks them during the growing season but is short lived. When fall arrives and the days are shorter and the sunlight is at a lower angle in the sky, photosynthesis begins to slow down, as does the production of chlorophyll. As the chlorophyll begins to dwindle, the yellows and the oranges of the xanthophyll and the carotene are finally revealed. Unlike chlorophyll, carotene and xanthophyll are more stable. They remain in the leaf until it dies or falls.
Rainy weather
If it’s a particularly rainy autumn, the chlorophyll will remain in leaves for a longer time. That shortens the window for autumn color. If frost comes in and either damages or kill the leaves, the fall show will be especially short.
On the other hand, if there hasn’t been enough rain, trees will be under stress from lack of water and drought. In these conditions, leaves are more likely to turn brown and fall with only a brief window of color.
Seasonal Temperatures
Some of the most beautiful trees in autumn have red to purple foliage. The compound anthocyanin is responsible for those hues. The appearance of anthocyanin depends greatly on weather conditions. Trees produce it in abundance when there are bright days of sunshine followed by chilly, cold temperatures at night. The sunny days result in a high sugar content in the leaves. The cooler nights keep those sugars from moving into the woody portions of the tree.
If you’re hopeful for a nice long showing of autumn color this year, keep your eye on the weather. When summer turns to fall, look for bright sunny days and cold, chilly nights along with rainfall that is neither too little nor too much!
