Has this fall been more vibrant than others? The leaves have been changing colors since the last week of September and for the past three weeks have created the backdrop for truly breathtaking views of our surrounding landscape. We are blessed to live in Northeast Ohio this time of year and have our climate and biome to thank for the fall spectacle. Leaves are putting on their annual fall show throughout the northeastern US and southeastern Canada. Ohio is just part of the Temperate Deciduous Forest biome that blankets this section of North America with green each summer and reds, oranges and yellows each fall. Temperate means that this biome experiences 4 distinct seasons. Deciduous describes trees that lose their leaves in the fall. The Temperature Deciduous Forest biome extends essentially from the Mississippi River eastward and from parts of southern states (Georgia, Alabama, Mississippi) into Quebec and Ontario, Canada.
As you read this, the majority of leaves will be coloring the ground and the arduous task of raking has begun. The blowing warm front and rain from this past weekend marked the beginning of the end for the colorful display. All this change may have you thinking about the reasons why leaves change color.
There are three main factors for the multicolored farewell to our deciduous trees each autumn: leaf pigments, photoperiod and weather. The timing of color change is ultimately regulated by the calendar. As we learned in a previous article, the length of daylight has been decreasing since the summer solstice in June. The length of darkness triggers a biochemical process that begins the color-change and soon paints the landscape. This timing is unvarying. Like clockwork, we can expect leaves to begin changing in late September with peak color usually the first two weeks of October. As we know, we usually bundle up for the first cold nights and frost during this time, but it is the increasing darkness that alerts the trees to prepare for winter dormancy by ultimately dropping their leaves.
Ingredients for nature’s fall fireworks
The biochemistry process involves three main pigments: chlorophyll, carotenoids, and anthocyanins. Pigments are what plants produce to collect energy from the sun to power the photosynthesis factory and make food. Mix these energized pigments with a dash of carbon dioxide from the air and some drops of water from the soil and the result is a healthy dose of the simple sugar called glucose. A byproduct of photosynthesis is oxygen, which is dispersed into the atmosphere through the leaves. Glucose is moved throughout the tree and used to power growth and seed production. Some glucose is converted and stored in the plant as starch. Chlorophyll gives leaves their dominant green appearance. Chlorophyll absorbs highly energetic blue and red wavelengths of sunlight and transforms it into chemical energy to create bonds between carbon, hydrogen and oxygen to manufacture sugars. Leaves appear green because they are reflecting the green wavelength. Carotenoids produce yellow, orange and brown colors and anthocyanins yield predominantly red hues. All of these pigments may be present throughout the summer, but chlorophyll usually dominates and the green masks other colors.
As night lengthens, chlorophyll production slows and eventually stops. Chlorophyll is an interesting molecule in that it has magnesium at the center. Magnesium is not a common element in our environment. The risk of losing the magnesium as their leaves flutter away in autumn breezes is too great. So, in the fall trees destroy their chlorophyll and reabsorb the magnesium (as well as some nitrogen and other minerals) for storage in the roots during winter. The green color slowly fades, revealing the colors of carotenoids and anthocyanins. Anthocyanins are produced in late summer and fall in response to bright sunlight and excess sugars in the leaves.
In autumn, many trees can be identified by color. Oaks typically turn scarlet and brown; hickories bronze; aspen and tulip poplar yellow; dogwood purplish red; beech light tan. Maples show more variation. Sugar maples display yellow, orange and red. Red maples turn a brilliant red. Additionally, timing of color change varies by species. Tupelo (aka, Sourwood) leaves begin to turn vivid red colors while most other leaves remain fully green. Oaks and beeches are often the last trees to change, sometimes even holding on to their brown leaves through much of winter.
The brilliance of colors that develop during autumn is related to weather conditions during the time the chlorophyll in the leaves is dwindling, namely temperature and moisture. Warm, sunny days and cool, crisp (but not freezing) nights result in the most spectacular color displays. During this time, an abundance of sugar is produced in the leaves. Sugars build up because the leaf veins are constricting and the movement of sugars is sluggish during cool nights. Lots of sugar plus lots of bright sunlight results in the production of anthocyanins and hues of red, purple and crimson. Moisture throughout the growing season, not just during fall, appears to have an effect on color as well although this is more difficult to pinpoint. In general, the brightest autumn colors are produced when dry, sunny days are followed by cool, dry nights.
All good things must come to an end
Delicate leaf tissues don’t stand a chance in the cold of winter, so eventually the leaf veins close entirely and a layer of cells forms at the base of each leaf stem (petiole) and twig. This is called the abscission zone. Once this separation layer is complete, the leaf is ready to fall. Strong autumn breezes usually signal a swift end to the weeks of pleasant color.
All those leaves that fall to the ground are not wasted. As they decompose, they restock soil nutrients and enhance the humus layer of the forest floor that serves as a sponge and maintains soil moisture. Additionally, the leaf litter becomes food for soil organisms that are important throughout the forest ecosystem. Think about the amount of biomass and nutrients that get raked across your yard each October. Don’t waste it by stuffing it in bags and setting curbside for removal. Rather, rake the leaves into your flower beds and vegetable gardens. It’s the cheapest and most natural way to mulch and ‘fertilize’ your soil.
Information about fall foliage can be found at the National Forest Service (http://www.fs.fed.us/) and The Foliage Network (http://www.foliagenetwork.com/). Can’t get enough of the fabulous colors? Find camera views from Canada to North Carolina at Leaf Peepers (http://www.leafpeepers.com/cams.htm).
Other Nearby Nature…
Click! Print! Win! The Friends of the Field Station are sponsoring a Hiram College Field Station Photo Contest through November 1. All photos must be taken at the James H. Barrow Field Station property on Wheeler Rd. between Hiram and Garrettsville. Entrants can submit up to 4 photos in two categories: landscape and flora/fauna. Prizes include, among other things, Nikon 8x40mm Action Ultra-Wide-View binoculars. For an entry form and more information, phone 330.569.6003 or email firstname.lastname@example.org.
Explore the Burton Wetlands – Saturday, October 27 (9:00-11:00am) – Explore trails and pathways of the Burton Wetlands, the largest and one of the most important wetlands of the Lake Erie watershed. The area provides habitat for bald eagles, river otters, sandhill cranes, and a host of other wildlife. Glacial lakes, bogs, swamp forests, marshland and the old and new Cuyahoga River are all part of this fascinating complex. We will explore several segments of this important wetland complex, including the riparian areas along the Cuyahoga River, upland forests, and a glacial bog lake. Fee: $8 for nonmembers, $5 for members of Friends of the Field Station. Phone 330.569.6003 or email email@example.com to register.