While environmental conditions like stress from an abnormally dry and hot summer can cause trees to show their color and shed their leaves in late summer, true fall color is brought on by the shortening of the days. Any color or leaf drop before October is most like the tree shutting down its resources early as a form of protection. By late summer the tree has already produced the majority of the nutrients that it needs to survive over winter, and the early shut down protects the tree from any other stressing events.
Decreased amounts of sunlight in the fall trigger a chemical change in the leaves. The green chlorophyll that is visible all spring and summer begins to get broken down by a chemical called carotenoid, which is lingering in the background and is always present in a leaf.
“Trees such as hickory, birch and beech are all trees that show off their carotenoids with hues of yellow, brown, and orange,” said Casey Burdick, ODNR’s Fall Color Forester.
Shades of red and purple are brought on by a different chemical reaction that produces a chemical called anthocyanin. To develop the deepest shades of red and purple, bright sunny days in late summer help break down the chlorophyll causing the leaves of trees rich in sugar, including maples, oaks, sweetgums, and dogwoods to show these brilliant contrasting colors.
In woodlands, where there are trees rich in carotenoids and anthocyanins, the combination of fiery reds, golds, and bronzes can light up a vista, creating the typical autumn landscape so familiar to Ohioans. With more than 100 species of trees in the state, it is no wonder Ohio’s Fall Color season is so spectacular.
What makes the leaves fall from the trees? As fall approaches, the sap starts to thicken and slows its flow. This protects the tree from freezing over the winter. When this occurs, thickened sap clogs the leaf veins. The leaves then become saturated with sugar created by the chlorophyll. During this process the union between the branch and leaf seals off and the weight of the leaf, in combination with wind and rainstorms, eventually causing it to drop to the ground.
Which Tree Species Turn Which Colors in the Fall?
While many of Ohio’s hardwood (deciduous) trees can be divided into two color groups – reds and yellows – others reflect both colors as well as varying shades of orange, purple and dark russets. Here are a few of Ohio’s more common trees and the colors you can expect to see on their leaves.