October 2014 Nature Column as published in the Woburn Advocate
Living in New England we have all come to expect beautiful fall foliage. But why exactly do we have such colorful trees this time of year, and why are some years better than others?
A lot of people think that it is the onset of cold weather that triggers the colors. Temperature does play a part, but it is not the whole story! Other things such as day length (less light is a major factor), rainfall during the spring and summer (good moisture is essential during the growing season), rainfall during the fall (a slightly dry fall is better), and the temperature difference between night and day (cool nights, warm days but no frost) as autumn progresses. All these variables interact to give a spectacular and always different autumn display. Or a so-so, rather drab season. Or, as in most years, something in-between!
Trees are smart! They know exactly what they need and how to get it. All spring and summer a pigment in leaves called chlorophyll converts sunlight and water into starches (in a process called photosynthesis) to feed the tree and make it grow. Trees are very efficient at this. This pigment is what gives leaves, and things like green beans, spinach, broccoli, lettuce, etc., their green color! But what about the other colors? Where do they come from? Why do some trees turn just yellow, some all red, some just brown. This kaleidoscope of oranges, yellows, browns, reds, crimson, purples, etc. comes from different pigments other than the chlorophyll. One of these is called xanthophyll, and one is carotene. These yellow and orange (respectively) pigments are always present in leaves. They are also what give things like carrots, squash, daffodils, corn, etc. their colors. Most of the year the stronger chlorophyll overwhelms them so all you see is green. (But think about early spring and how yellow some leaves appear at first before the chlorophyll gets built up in them). Then comes fall! In all its glory! As the days get shorter and cooler, a tree starts preparing for winter just like people. You prepare your yard by putting lawn furniture away, raking up all the leaves, etc.; you pull down the storm windows on your house, check the heating system, etc. The signals that nature puts out foretelling of the coming winter, cause the veins that carry fluids into and out of a leaf to gradually close off as a layer of cells forms at the base of each leaf. Chlorophyll is no longer being produced. As it fades, the yellows and oranges start to show through! But what about the reds, you ask? Reds, crimson and purples are the result of another pigment called anthocyanin. This pigment, however, is not normally in a leaf, hiding under the chlorophyll like the xanthophylls and carotinoids. A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays. During these days, lots of sugars are produced in the leaf but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions-lots of sugar and lots of light-spur production of the brilliant anthocyanin pigments, which tint the leaves (as well as things like beets & eggplant) in shades of reds, purples, and crimson.
Eventually this separation layer is complete and the connecting tissues are sealed off. Then the leaf is ready to fall. Sometimes just its weight will bring it fluttering to the ground. Sometimes a good wind helps a lot of leaves that are almost to that point, fly off of the tree to go swirling about.
What trees turn what colors? Each kind of tree has a certain color that it usually turns in the fall. One of the first trees to start changing color is the Red Maple. Depending on that magic combination of light and temp, they can be lots of yellow with a little bit of red or orange scattered throughout, or the whole tree can be blazing crimson! The Red Maples have been beautiful for over a week, now. Most of the woods around the Pond are what is called Oak/Hickory woods. Most oaks turn a dull red to brown and hickories turn golden yellow. Also in that yellow spectrum are the birches, cottonwoods and aspen. The Silver Maples along the Causeway turn a pale yellow. A commonly planted non-native tree, the Norway Maple also turns yellow, but much later in the season than other maples. We don't really have the flaming oranges and reds of the Sugar Maples, but if you want to see some without traveling to NH, try Woodbrook Cemetery over on Salem Street. It has plenty of towering Sugar Maples that light up the area with their color!
The next full moon is the Full Beaver Moon on November 8th.
Living in New England we have all come to expect beautiful fall foliage. But why exactly do we have such colorful trees this time of year, and why are some years better than others?
A lot of people think that it is the onset of cold weather that triggers the colors. Temperature does play a part, but it is not the whole story! Other things such as day length (less light is a major factor), rainfall during the spring and summer (good moisture is essential during the growing season), rainfall during the fall (a slightly dry fall is better), and the temperature difference between night and day (cool nights, warm days but no frost) as autumn progresses. All these variables interact to give a spectacular and always different autumn display. Or a so-so, rather drab season. Or, as in most years, something in-between!
Trees are smart! They know exactly what they need and how to get it. All spring and summer a pigment in leaves called chlorophyll converts sunlight and water into starches (in a process called photosynthesis) to feed the tree and make it grow. Trees are very efficient at this. This pigment is what gives leaves, and things like green beans, spinach, broccoli, lettuce, etc., their green color! But what about the other colors? Where do they come from? Why do some trees turn just yellow, some all red, some just brown. This kaleidoscope of oranges, yellows, browns, reds, crimson, purples, etc. comes from different pigments other than the chlorophyll. One of these is called xanthophyll, and one is carotene. These yellow and orange (respectively) pigments are always present in leaves. They are also what give things like carrots, squash, daffodils, corn, etc. their colors. Most of the year the stronger chlorophyll overwhelms them so all you see is green. (But think about early spring and how yellow some leaves appear at first before the chlorophyll gets built up in them). Then comes fall! In all its glory! As the days get shorter and cooler, a tree starts preparing for winter just like people. You prepare your yard by putting lawn furniture away, raking up all the leaves, etc.; you pull down the storm windows on your house, check the heating system, etc. The signals that nature puts out foretelling of the coming winter, cause the veins that carry fluids into and out of a leaf to gradually close off as a layer of cells forms at the base of each leaf. Chlorophyll is no longer being produced. As it fades, the yellows and oranges start to show through! But what about the reds, you ask? Reds, crimson and purples are the result of another pigment called anthocyanin. This pigment, however, is not normally in a leaf, hiding under the chlorophyll like the xanthophylls and carotinoids. A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays. During these days, lots of sugars are produced in the leaf but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions-lots of sugar and lots of light-spur production of the brilliant anthocyanin pigments, which tint the leaves (as well as things like beets & eggplant) in shades of reds, purples, and crimson.
Eventually this separation layer is complete and the connecting tissues are sealed off. Then the leaf is ready to fall. Sometimes just its weight will bring it fluttering to the ground. Sometimes a good wind helps a lot of leaves that are almost to that point, fly off of the tree to go swirling about.
What trees turn what colors? Each kind of tree has a certain color that it usually turns in the fall. One of the first trees to start changing color is the Red Maple. Depending on that magic combination of light and temp, they can be lots of yellow with a little bit of red or orange scattered throughout, or the whole tree can be blazing crimson! The Red Maples have been beautiful for over a week, now. Most of the woods around the Pond are what is called Oak/Hickory woods. Most oaks turn a dull red to brown and hickories turn golden yellow. Also in that yellow spectrum are the birches, cottonwoods and aspen. The Silver Maples along the Causeway turn a pale yellow. A commonly planted non-native tree, the Norway Maple also turns yellow, but much later in the season than other maples. We don't really have the flaming oranges and reds of the Sugar Maples, but if you want to see some without traveling to NH, try Woodbrook Cemetery over on Salem Street. It has plenty of towering Sugar Maples that light up the area with their color!
The next full moon is the Full Beaver Moon on November 8th.