The Science of Fall
As we turn the calendar from August into September, it feels like the unofficial end of summer. While warm weather typically persists, September comes with a host of changes for your trees and landscape. Have you ever wondered why we see such vibrant fall colors? Or why leaves drop at all? Read on to learn more about this transitional season, what it means for your trees, and how Tree House can help.
Colors
Our team makes themselves at home in a fall colored oak
A striking visual phenomenon, fall colors are one of the hallmarks of seasonality and change. But do you know the science behind why our trees get such striking displays? To start, it is important to understand why leaves are green in the first place. The answer lies in a pigment called chlorophyll. Chlorophyll is found in leaf tissue, and is the primary mechanism behind photosynthetic production. Thus, chlorophyll is essential for plant and tree life, as it directly facilitates the conversion of sunlight to usable sugars.
As we move further into fall, however, temperatures will begin to drop, days will get shorter, and crucially, the northern hemisphere will receive less direct sunlight. All of these factors result in a breakdown of chlorophyll. As chlorophyll becomes less prominent, other pigments become more visible. These are the reds, oranges, and yellows we see, all of which can be referred to as carotenoid pigments. Rainfall amounts and average daytime and night temperatures are also influential factors; fall colors may be more striking following sunny days and moderate temperatures. Dry and hot weeks can sometimes lead to more muted color. No matter what, be on the lookout!
Why Do Leaves Drop?
Be sure to enjoy the colors while they last! Before too long, trees will shed their leaves as they ready for a long winter. Deciduous (trees that lose their leaves) trees, in an effort to best prepare themselves for winter, have many adaptations to ensure their resources are optimized for survival. A key example is leaf drop. By ridding themselves of leaves, deciduous trees are setting themselves up for optimal water and energy conservation. A key part of this process lies in a specialized area at the base of the leaf called the abscission zone. Essentially a unique layer of cells that are capable of separating, this process of separation responds to hormones in the tree, and when those hormones slow in fall, those abscission cells separate, dropping leaves and sealing over the connection point to protect the tree. But, what about the browned and withered leaves you see held during winter? When you see dry leaves still hanging on year-round, you are observing a characteristic called marcescence. Generally uncommon, these dry and dead leaves will typically be blown off during winter winds. You’ll see them in Madison on young saplings and oak trees.
But What About Evergreens?
Can you spot the climber amongst the fall foliage?
Unlike broad leaf, or deciduous, trees which change colors and lose leaves, evergreen species such as pines, spruces, and firs will hold their leaves year-round. Why? The answer lies in water. Evergreens feature specialized leaves, more commonly referred to as needles. These needles function similarly to broad leaves, but are smaller, thicker, and feature a thick, waxy layer which allows for greater water retention by the tree. Additionally, cells held inside these needles contain more acidic compounds below the freezing point of water, so there is less of a risk of tree wounding over the winter as water freezes and expands. So, contrasting the annual leaf drop by deciduous trees, conifers and evergreens lose smaller amounts of older needles throughout the year, and are able to hold more photosynthetic tissue through harsh Wisconsin winters. Though there are some deciduous evergreens, they are exceptions to the rule.
Fall-Proofing
With a grasp of the basic science behind the changes we observe every fall, it's time to discuss what it means for you as a tree owner. To start, what can you do as a tree owner? An easy care step, but vastly important, is to think about nutrients. Adding fresh, organic mulch around the base of your tree can help add nutrients to the soil, and brings a host of other benefits that range from combating soil compaction to reduced soil temperature. Another step you can take on your own is to ensure the water needs of your trees are met. Counterintuitively, that may mean dialing back on your waterings of younger trees, or reducing the overall length of any irrigation or sprinkler system you may have in place. Due to cooler weather patterns and less intense sunlight, soils hold onto moisture more effectively in fall. Accounting for this means you can avoid flooding your trees’ root systems.
How Can Tree House Arbor Science Help?
Color change typically begins in mid-late September. If your trees have non-green leaves much before then, there may be a larger issue at play that we can help diagnose and address. Assuming your trees are following a typical timeline, however, there are a number of other ways you can maximize your trees’ health during the fall. With leaves off, you will likely have an easier time seeing a tree’s branches and inner structure. Do you see any dead wood? Cracks? Fungal bodies? While you may be able to detect some of these issues, our team of arborists are trained in exactly what to look for. So if there’s any concern at all, be sure to get in touch. Additionally, the upcoming snow and ice weight can stress your trees, causing breaks and damage. It is important to stress here that Tree House Arbor is of a pruning-first mindset. We much prefer to prune, cable, brace, or otherwise help get your tree ready for fall transitions and eventual winter rather than see trees damaged. If you have any concerns, questions, or want to learn more, please reach out to us in whatever way is most convenient for you!