Fall Color Report
Dr. Howard Neufeld is Professor of Plant Eco-physiology at Appalachian State University, but he is also known as The Fall Color Guy. For the third year in a row WataugaRoads.com is teaming up with Dr. Neufeld to provide information as the colors start changing.
Conceived by Howard Neufeld and Michael Denslow
Map Constructed by Michael Denslow
Maps via Foliage Network – http://www.foliagenetwork.net
Leaf Color Report
This week is the first in which I can report the leaves they are a’changing; at least at the highest elevations. As noted by Jesse Pope, in my post yesterday, there is visible leaf color now starting to show up at the highest elevations, around 5, 000’ and on down to around 4,000’. Below 4,000’, most trees are still predominantly green. As noted last week, burning bushes continue to redden ahead of schedule, and more red maples are showing splotches of color. What is unusual about most of these red maples, many of which are varieties of urban trees planted for their fall leaf color display, is the extremely dull red of the leaves so far. Generally, red maples end up a bright red color. Perhaps these dull red leaves will brighten up in the next few weeks, something I will keep an eye on.
There is a beautiful Virginia Creeper vine that totally covers the trunk and branches of a tree, right off US 421 west of Boone. In fact, it’s the banner photo on my academic fall color page (http://biology.appstate.edu/fall-colors). What I have noticed is that last Sunday, this vine was essentially all green. Then, beginning on Monday, it began to redden up, and each day it has become more and more red. It is an interesting transition to watch, since I pass by it on the way to and from work. Although I don’t have a record of when it changed last year, it seems to me that this year it is turning early by at least a week or two.
I didn’t get a chance to take photos this week, as I was accompanying my wife to a conference of UNC Hispanic faculty at UNC-Charlotte. Also, I know I haven’t completed my trilogy of tree water relations essays, but will some time later this fall. Something about my day job taking up most of my free time?
So far, contrary to the recent climate outlook, September has not been excessively warm in the High Country. In fact, it was really cool and cloudy today, with temperatures only in the high 50s. If these cool temperatures persist, and we see a little more sun, we should be on track for good fall color.
For those who want a short (< 500 words) summary of the state of fall leaf colors here in the mountains of western NC, I will post my observations at the beginning of my report each week. Then, below the report, I will provide an essay on trees that some of you may find interesting. This way, you can get right to the fall color report and not have to wade through my science essays. This past week, the weather has moved back to a more normal pattern for this time of year and we’re back to our usual “dog days” of August. As a result, there is not much to report with respect to fall colors aside from what I wrote last week.
The forests here are still very green. Jesse Pope reports from Grandfather Mountain that: “We do have some more leaf change on red maples, and also just plain leaf loss on them. Many of the maple trees above 4800 ft have already shed 50% of their foliage. Not sure what’s going on there. No other trees are changing drastically yet. The buckeyes are starting to show just a smidge of color but nothing too drastic. I think we are still a couple weeks out from any real noticeable changes here at Grandfather.”
Kathy Mathews, from Western Carolina University, and Jonathan Horton, from UNC-Asheville, also report little progress to date on fall colors around Asheville and Cullowhee. Jonathan did mention yellowing on tulip poplars in the Bent Creek Experimental Forest (a unit of the US Forest Service that has some nice walking and biking trails, and which is adjacent to the NC Arboretum), and he saw some few Virginia creepers turning red.
I think it must be drier at lower elevations, as I also saw many tulip poplars in the Piedmont this weekend with yellow leaves. So, leaf lookers, hang in there. Over the next two weeks, we should begin to see trees turning at the highest elevations (5,000 ft or so) and then watch it progress downwards each week.
Tree Science – How Trees Use Water
Last week I gave a fairly extended explanation of how water moves from the roots of a tree to the leaves and out into the atmosphere. This week, I’d like to explain what physical and biological factors affect the rate at which that water moves through the trees. This will involve some knowledge of fluid dynamics and plant physiology, but hang in there; it’s actually fun to know!
My mantra here is that structure and function are tightly intertwined. That means we have to learn the structure of the cells that transport the water if we want to understand why they function like they do. The cells that conduct water in plants are known as xylem cells and we’re all familiar with them –tree xylem, for example, is wood! Interestingly, xylem cells are dead at maturity, and this contributes to their efficiency. Being dead, they have no cellular contents and are essentially just hollow structures with walls made out of cellulose and lignin, the two main components of wood. The walls provide rigidity to the cells and contribute to the ability of trees to grow to great heights without crushing themselves. The lack of cell contents allows these cells to conduct water with high efficiency.
Conifers, which evolved prior to the emergence of angiosperms (the flowering plants), contain a primitive type of xylem cell called a tracheid. Tracheids are long, narrow, and hollow cells, ranging 10-30 um in diameter). Figure 1 shows a typical tracheid. They also have end walls. For water to move from cell to cell, it has to pass through small openings in the wall, called pit pores (see Figure 2). As we will see below, the presence of end walls and having to move through the pits present obstacles to the movement of water for these types of plants.
Angiosperms, on the other hand, in addition to tracheids, contain a more recently evolved xylem cell called a vessel element (see Figure 1 again). These cells are much wider (100 up to 800 um diameter), shorter, and often have no cell walls on either end. Vessel elements also contain pits and water can not only move through the vessel element, but can cross over to other vessel elements through the pits.
Vessel elements can be stacked together to form what we call “vessels”. An analogy would be if you stacked toilet paper tubes one on top of the other. Each tube would be a vessel element and the set of joined tubes a vessel. A vessel is bounded on either end by vessel elements that do have a porous end wall. Such walls may act to restrict the movement of air bubbles in the xylem. Some vessels are just two or three cells long, whereas in some tree species, such as ash trees, they can be 10 m long! The evolution of vessel elements probably contributed to the ability of flowering plants to dominant certain landscapes, as we’ll discuss below.
At this point, we know something about the anatomy of these xylem cells, but how does their anatomy affect the movement of water through them? For that, we turn to the engineering field of fluid dynamics. Luckily, we can handle this type of engineering verbally and without formal mathematical equations (although I’ll show an equation to you anyway, for those of you who like math).
If you’ve ever been to a fast food restaurant, you’ve probably seen those small stir straws. Few of you would want to use those straws in your drink, because you know that it would be hard to suck the drink up the straw. In contrast, if you had a regular straw, with its much larger diameter, it would be much easier to get the drink into your mouth. Why is that?
Well, we need to know two things about how water flows in tubes before we can figure this out. First, water along the sides of the straw will rub against the walls, creating friction, and that will slow these water molecules down compared to those in the center of the straw. Second, water in the middle of the straw is drawn up the straw by the vacuum applied when you suck on the straw, and the entire column of water moves because of cohesion with other water molecules.
Now, that single layer of water at the straw’s edge that is moving slower will slow down the next layer inward of water because of shear, which is what happens when one layer of water rubs against another. That layer will interact with the next most layer, and slightly slow it down too. However, because water is somewhat slippery the frictional resistance of one layer of water against another is much smaller than that with the walls of the straw and as one moves to the center of the straw, these effects are drastically reduced. As a result, water moves faster at the center of a tube than at the edges. See Figure 3, which shows the velocity of water as a function of the distance from the side of a tube.
If you have a very narrow tube, a greater percentage of all the water in the tube will be interacting with the sides and as a result, more of the water in the straw will be moving slowly. Going back to the straw analogy, it means you will have to suck much harder to get the same flow rate in a narrow straw as compared to a wide straw, since you have to overcome more frictional resistance. Therefore, to get the same flow rate in a narrow tube as in a large one, you have to exert a greater tension (or pressure if you’re pushing the water). In fact, from a fluid dynamics point of view, if you keep the pressure constant, but decrease the radius of a tube by half, you reduce the flow by 16 times! Conversely, if you double the radius, flow increases by 16 times! Mathematically, we’re saying that the flow of water is proportional the radius raised to the fourth power: F α r^4. This means that doubling the radius is the same as raising two to the fourth power (2^4 = 16). Note: ^ means raise to this power.
For a tree, this has enormous consequences. It means that at any given tension in the xylem, it will be the larger diameter xylem cells that are conducting most of the water. If you compare tracheids to vessel elements, the implications are obvious: flowering plants (the only ones to have evolved vessel elements) will have a much greater capacity to move water (at equivalent tensions) than will conifers and ferns, which have only the much narrower tracheids. In fact, the fastest sap in the world has been found in the kiwi vine, which has vessel elements nearly 800 um wide (or 0.8 mm). This down-under vine can have rates of flow exceeding 20 mm/s (>50 m/h or 164 ft/h). In fact, kiwi vines have the fastest sap in the west (and north, and south, and east!). In deciduous trees, whose xylem diameters are usually less than 500 mm, and often between 100 and 400 um, rates of flow are slightly lower (25 to 40 m/h or 82 to 131 ft/h).
In contrast, conifers and ferns, with their more primitive and narrower tracheids, cannot move water nearly as fast. Rates of movement in pine trees, for example, are only around 1 mm/s (~6 m/h or ~20 ft/h). Why are sap velocities so much higher in vines and deciduous trees? Well, remember, vessel elements are much wider than tracheids, and a much smaller percentage of the water is in contact with the walls. This means the water can flow more freely, and less tension is needed to move large volumes up the plant. Also, the lack of end walls further reduces the tortuosity of the pathway (how contorted a path the liquid must traverse), and instead of having to move primarily through pits, as water must do in tracheids, it can flow freely down the wide, hollow vessels.
Mathematical Diversion for the Adventurist:
You can confirm mathematically why water flows faster through vessels than tracheids if you remember your geometry. For a cell with a radius of r, the circumference (which you can consider the single layer of water touching the walls), will be: C = 2πr. For a tracheid that has an r=10 um, C = 63 um. The volume of water in a cell can be approximated by the cross-sectional area (A) of the cell, and the formula for that is A=πr^2. For this cell, A=314 um^2. If you have a vessel element with r=125 um, C = 785 um and A=49,807 um^2. Now, take the ratio of A to C for both cells to get an idea of how much water is in the cell compared to how much is interacting with the walls. For the tracheid, the ratio is 314/63 = ~5. For the vessel element, it is 49,807/785 = ~63. Thus you can see that there is about 12 times more “free” water in a vessel element than in a tracheid, which is why water can flow faster in a wider tube (i.e., cell!).
The large frictional resistance in tracheids greatly slows down the velocity of the sap in ferns and conifers. This means that in response to a large transpirational demand (i.e., a lot of dry air out there), angiosperms will be able to transport water more easily and faster to the leaves than will conifers. Also, when water is plentiful, angiosperms will have the luxury of being able to open their stomata to take in carbon dioxide for photosynthesis, and not have to “worry” about all the water that is being lost via transpiration in that process. If a conifer did this, the loss of water from the needles would exceed the capacity of the xylem to replace the water lost via transpiration, and the tree would dry out. Of course, this is a greatly simplified explanation, but the you get the general idea of how wood anatomy can determine how trees move water in their trunks.
Figures from: http://plantsstructureandreproduction77.wikispaces.com/structure2 and pits in the walls of a softwood tracheid (hollow fibre). in Keey et al. 2000. Left most: tracheids and vessels; middel: how water moves up a tree; Right most: pits in a conifer tracheid.
Next week : What happens to a tree if it gets drought stressed? Is there a trade-off between xylem efficiency and safety? How does evolution solve such a dilemma?
Sometimes nothing happens of much note from one week to the next. That’s the story line for this week’s fall leaf color report. Another word I might use to describe fall leaf color for this week would be “ibid”, which according to the English Oxford Dictionary, means “In the same source (used to save space in textual references to a quoted work that has been mentioned in a previous reference).” In other words, you could read last week’s report and that would fill you in on this week!
Of course, time does march on (I wonder how many clichés I can fit into one essay?) and some things did change. The red and sugar maples that were turning last week continue to do so this week and many of them are now predominantly red/orange rather than green. A few trees are even nearly defoliated already! I think the phenology researchers should pay more attention to what is happening this summer and refine their models, which have given June and July temperatures little impact on the timing of fall leaf color. Perhaps these months are more important than we have realized! Yet, despite these unusual early turning trees, the rest of the forests around here are still quite green this week.
Last week I said I would fill you in on some interesting aspects of tree water relations. So, here goes. You only need to know some anatomy, fluid dynamics, physics, mechanical engineering, biomechanics, natural selection, and the concept of an evolutionarily stable strategy! But luckily, you do not need to know any rocket science, so this should be a breeze to understand.
First off, trees do not “push” water to the tops of their crowns. If that were so, water would shoot out of the trunk if you cut into one, just as if you had nicked a garden hose with the water turned on. But as loggers will attest, this does not happen in a healthy tree. Furthermore, since water is essentially incompressible, the trunk of a tree would expand as each individual xylem cell (the wood that conducts water up a tree) bulged outward from the pressure. But when we measure trees that are actively transpiring they actually shrink instead! That suggests they are under tension (negative pressure); and if that is true, then trees must be pulling, not pushing, water up their trunks. One way to think about this is to imagine stretching a rubber band, which puts it under tension. As it gets longer from the tension, it also gets thinner. The same can be said for water under tension: it stretches and the water column gets thinner, causing the tree trunk, in turn, to shrink.
But for those of you who lived or still live on farms and remember pumping water up by hand, the deepest well you could have was just 10 m, or ~33’. If it was any deeper, the weight of the water column would be so great that it would break. But if that is so, then how do trees like redwoods and eucalyptus, which can be more than 100 m tall (up to 370’), pull water up up to the tops of their crowns, which are much higher than 10 m?
The answer lies in the fact that if you transport water in wood composed of billions of very small diameter cells (known as tracheids in conifers, vessel elements in angiosperms) then you can support a column of water under tension (negative pressure) to a very great height! Tracheid diameters can range from 20-80 microns (0.0009”) while the largest vessel elements (which occur in vines) can approach 500 microns (or nearly 0.02”). To test whether cells of these diameters can support a column of water more than 100 m high, scientists have induced high tensions in water filled glass capillaries (with tube diameters equivalent to that of xylem cells) and also in detached branches from trees with a continuous column of water in their wood, by spinning them in centrifuges. The results of these studies show that water is more than able to maintain a continuous column, under tension in the xylem, for lengths longer than that of even the tallest trees.
The other properties that are important for moving water in plants involve what are known as the colligative properties of water. For example, water is attracted to other materials by the process of adhesion (which is why water will wick up a paper towel) and also to other water molecules by cohesion (which is why you can suck water up a straw). In very narrow conduits, like xylem cells, the upward-pulling forces of adhesion and cohesion exceed that of the downward gravitational forces. This means that not only can a tree maintain a continuous column of water from the roots to the leaves, but it can transport that water upward nearly 400’ against the downward gravitational force.
But what forces are actually responsible for making the water move upwards? To understand this part of the process requires knowing what happens when a water molecule evaporates from the leaf. As a water molecule goes from the liquid state (as it is in the xylem) to the gaseous state (or vapor phase) when it evaporates into the atmosphere, the surface tension at the air-water interface in the leaf is disrupted by the loss of that molecule, which results in an unstable energy state. To regain the more stable energy state, a water molecule in the liquid column must move in to replace the one that left, and every time that happens, it pulls other water molecules up the water column by cohesion. Now, multiply this by the trillions of water molecules leaving a leaf every minute, and cohesive forces acting on the entire water column in the trunk, and you get a lot of water moving up that tree in a continuous column. In fact, a large tree can transpire over 100 gals of water (378 liters) per day!
What is truly amazing about this process is that it requires no metabolic energy on the part of the plant. Tracheids and vessel elements, for example, are dead, hollow, cells at maturity. Paul Kramer, a famous plant physiologist from Duke University, showed that a plant with dead roots (killed by hot water) could move water up its stem as long as its xylem was not clogged by debris.
But for water to move from root to leaf to atmosphere (through what we call the Soil-Plant-Atmosphere-Continuum, or SPAC), energy must be expended, and forces must act on the water. When forces cause something to move, that is, in physics terms, “work”. In formal terms, Work = Force x Distance. Given that trees can move water 100 m against the force of gravity, they must be doing a lot of work!
So how do trees do this work without expending their own energy? In the simplest of terms, it is the sun that provides that energy, by heating the air and drying it out. Inside a leaf, the relative humidity of the air is ~100%, but rarely is the air that wet in the atmosphere outside the leaf (unless you live in New Orleans!). That means there is almost always a gradient in the concentration of water from the leaf to the air, and water will always diffuse passively (that is, spontaneously) down that gradient. Thus, as long as the concentration of water is higher in the leaf than outside the leaf, water will evaporate from it. In reality, trees are like giant wicks inserted in the ground, moving water out of the soil and up the their trunks, against the force of gravity, by using the drying power of the air, whereupon the water is released into the atmosphere.
Now, if a large tree transpires 100 gals of water a day, it must be moving that water very rapidly and efficiently. To understand how that is accomplished, see next week’s leaf color report. That is the part of the story for which you will need to understand fluid dynamics and mechanical engineering. But no worry! I will explain it in such a way that everyone will understand how trees (and in fact, all vascular plants) move water through xylem cells with very small diameters. If you have ever watered plants with a hose and put your finger over the end to make the water shoot further out at a higher velocity, then you know all that’s required to understand the hydraulics of trees! And I promise – no calculus required!
Next week: further reports on fall leaf color and part two of our essay on tree water relations. This one will be on the trade-offs between moving water at high velocities through the xylem and withstanding drought stress; or in evolutionary terms, why there is no free lunch when it comes to tree water relations (cliché again!).
I’m sorry I didn’t have any tree photos last week. Your intrepid reporter was laid low by a recalcitrant kidney stone, which was surgically removed this past Tuesday. He’s feeling much better now and today when out and about looking for iconic photos of trees. See the photo album that I will upload after this post.
It is an understatement to say that this has been a relatively cool summer. Using the metric of daily mean temperature, this July was the coldest since the Boone station began keeping records 34 years ago, and in Jefferson, which has 82 years of records, it was the 3rd coolest July. For the state as a whole, it was the 11th coolest in the last 120 years! The NC State Climate Office reports that this is due primarily to lower maximum temperatures and not unusually low minimum temperatures at night. However, here in the mountains, we did get into the high 40s for a few days in July.
The cool temperatures may have resulted from a polar vortex phenomenon that causes the jet stream, which tends to separate warm from cool air, to dip lower into the United States. Some feel that as the Polar Regions continue to warm rapidly (more so than in the tropics), that this will cause greater instability in the path of the jet stream, and could, paradoxically, lead to more instances of cooling in this region. I know this may give climate change deniers ammunition to continue their campaign to discredit those who have documented significant human-induced climate change, but in reality, it simply shows off their ignorance of weather and climate science. Just remember, even though locally we’re having a cool summer, globally, temperatures worldwide continue to rise. Last year tied with 2003 as the fourth warmest on record, and 13 of the last 14 warmest years on record have all occurred since 2000!
Will the cool July affect the timing of autumnal leaf colors, or the quality? No one knows for sure. August is continuing on a mild streak right now, and it’s an important month for prepping the trees for fall color. When August and September are cool and sunny, we get our best leaf colors.
This week I am seeing some prominent coloring on dogwoods, red and sugar maples and on burning bushes; the dogwood in my yard is starting to show some red color, as are the ones across the street from me in the cow pasture. The maples I mentioned last week continue to turn as do isolated ones in the woods. But the majority of trees are still quite green now, as they should be. I have uploaded an album of some pictures I took this Sunday of trees turning color in the Boone area. This phenomenon has been noticed by others as far north as Pittsburgh, NY and Canada. They too had very cool July’s and people are reporting trees turning color several weeks earlier than usual. Others are documenting a failure of tomatoes to ripen on time. This may turn out to be one of our more unusual and interesting autumns.
Last week I said I would tell you why some black locust trees are turning brown. There is a native insect, called the locust leaf miner (Odontota dorsalis), which is a type of beetle, and whose larvae attack the leaves and eat them from the inside out, causing them to turn brown and then drop off prematurely. They usually peak in activity in late July and August which is why there are so many brown locust trees right now. However, it’s my opinion that the incidence is much less this year; perhaps the frost in late April that we had here killed some of the insects, or the cold is reducing their impact. I took some pictures of damaged locust leaves, and also of the mature insects sitting on them and they are in the album of tree pictures mentioned above.
Black locust is an interesting tree species because it can fix nitrogen out of the air through nodules on their roots that contain Rhizobia, a bacterial genus that does the actual fixing. This mutualistic relationship is based on the fact that the bacteria get carbohydrates from the plant while the plant gets nitrogen from the bacteria. This process can enrich the soil in nitrogen, because when the roots die and decay, or when leaves fall to the ground, they are enriched in nitrogen and make it more fertile.
Black locust trees are indigenous to the southern Appalachians, but have been planted outside their native range in both North America and Europe, where they are now one of the most invasive trees species known. Cameron Houser, an Appalachian State University Biology graduate student, just completed her Master’s thesis on this species. She showed that when it invades areas outside its native range, it substantially increases the nitrogen content of forest soils compared to adjacent forests where locust trees are absent. Such enrichment may greatly alter ecosystem nutrient cycling processes, as well as have consequences for the species composition of these invaded forests. That a native tree species can be invasive in its own continent is unusual, since we usually think of most invasives as alien species that are come over from either Asia or Europe.
Next week: further reports on leaf color and some thoughts on tree water relations.
Photos: Dr. Howard Neufeld
Red Maple at intersection of King and Poplar Grove Road showing reddening of upper and outer leaves.
Closeup of leaves turning red.
Tree adjacent to Galileo Bar and Grill parking lot that has completely turned red in the upper portion of the crown by August 17, 2014. See how the lower leaves are still totally green while the upper crown is totally red.
Sugar maple leaves turning yellow-orange on King Street across from Galileo’s Bar and Grill, Aug 17, 2014.
Here is that red tree at Galileo’s again, with a neighboring tree that is still mostly green. Strange!
Black locust leaves behind Broyhill Center on campus of Appalachian State University showing leaf miner damage, Aug 17, 2014.
These are the locust leaf miner adult beetles. Notice how they have damaged the leaves.
Sugar maple turning early on Bodenheimer Drive right next to entrance to parking lot by Chancellor’s home on the campus of Appalachian State University, Aug 17, 2014.
“Well, after a restful winter/spring, and with summer starting to fade, it’s time to renew our weekly fall leaf color reports. I hope everyone had a good off-season and that you’re ready for our autumnal displays this year. So, what’s the situation this week, and what does that portend for the fall?
This summer started off fairly dry and we were actually in a low level drought until some rains came later in July. You may also remember just how cool July was (I’m checking to see if it was a record cool) and some people wrote me asking what that meant for fall colors (I don’t think too much). Already, you can see scattered color developing, particularly on red and sugar maples. There’s even one red maple on the east side of US 321 between Patterson and Blowing Rock that is at peak (I repeat, peak!) color for reasons not are not clear to me. Other maples are showing significant coloring, especially along Rivers Street in Boone, but also at other locations in Watauga County. Some of the horticultural red maple varieties are starting to turn red on the outer portions of their crowns, and these usually turn much later in the year.
It’s not clear why these trees turn so early. The trees along Rivers Street color up every year around this time, yet the majority of the trees in the forest still peak at our usual time, which for Boone is mid-October. It is possible that when trees are stressed, such as by salt from the DOT during the winter, or by being planted in compacted soils, that they turn early. I don’t think the fact that these trees are turning early suggests that fall colors will come early this year. That depends more on what the weather conditions will be like for the rest of August and through September.
If the weather turns sunny and cool in August and September, colors should arrive on time and be vibrant, with bright reds contrasted against oranges and yellows. If it is rainy and warm, peak colors may be delayed and subdued.
Final thoughts: some recent scientific papers studying the timing of autumnal colors suggest that temperatures, especially in the fall, are the most correlated with the timing of colors. Warm falls delay the colors, cool ones accelerate them. Rainfall has much less of an effect on timing. Since we aren’t in a major drought, which can cause the leaves to fall prematurely, we still have the potential for an excellent fall leaf color season here in the southern Appalachians.
Next week: why the black locust trees are turning brown.”
August 6, 2014 – The summer of 2014 will be remembered more for cooler temperatures that the record setting rains in 2013. Attention is turning quickly toward fall and what might it bring.
Dr. Howard Neufeld is not only Professor of Plant Eco-physiology at Appalachian State University, but he is also known as The Fall Color Guy. For the third year in a row WataugaRoads.com is teaming up with “The Fall Color Guy” to provide information as the colors start changing.
WataugaRoads.com ask Dr. Neufeld what we might see with fall colors this year due to the more cooler temperatures instead of all the rain received last summer.
“As for the wet weather, there have been some publications since last year on the impacts of weather on fall color (especially timing, not so much quality). Precipitation has only minor effects on timing in the fall. Temperature is more important. So, at this point, I don’t see anything to make me think that fall colors will be adversely affected, either in timing or quality.
What happens in mid- to late August and in September, temperature-wise, will be more important, especially for quality (notably the intensity of the red colors)”.
Dr.Neufeld shared some thoughts just before fall season of 2013 that are still relevant this upcoming season:
“1. People think fall colors are good when they last a long time, and have plenty of brilliant reds interspersed with the oranges and yellows. So, the quality will depend on how much “redness” we have this fall.
2. Trees tend to make more red colors (anthocyanins) in the fall when it’s cool and sunny, and if we have a slight but not severe drought.
3. Sunny days means more photosynthesis, and more sugars produced in the leaves, and sugars induce anthocyanin production.
4. A slight drought impairs uptake of nitrogen (we think) and some experiments suggest that plants low on N make more anthocyanins.
5. Usually, fall colors peak around Oct 11-14 in the Boone area; sooner by a few days up to a week at higher elevations, later at lower ones. Nice colors can stick around for a week or more, although the peak usually comes and goes in just a few days, weather permitting (no high winds for example)”.
An early look at some trees starting to change on the ASU campus on August 6, 2014. Photos: Kara Harmon
*article from NOAA*
Cool Autumn Weather Reveals Nature’s True Hues
A favorite American pastime in fall is to pack a picnic basket and set off with loved ones on a Sunday drive along one of the nation’s many scenic byways. It’s a time of year when people enjoy crisp cool weather and marvel at the transforming landscape as tree leaves turn from lush green to gorgeous shades of yellow, orange, red, purple and brown.
While we relish the opportunity to frolic in a big pile of freshly raked leaves, we don’t often think about the science behind why leaves change color and eventually fall from their branches. The answer may surprise you!
Recipe for Fabulous Foliage: Cool Nights and Sunny Days
Weather factors such as temperature, sunlight, precipitation and soil moisture influence fall color arrival, duration and vibrancy. According to United States National Arboretum, a wet growing season followed by a dry autumn filled with sunny days and cool, frostless nights results in the brightest palette of fall colors. Changes in weather can speed up, slow down or change the arrival time of fall’s colorful foliage. For example:
Drought conditions during late summer and early fall can trigger an early “shutdown” of trees as they prepare for winter. This causes leaves to fall early from trees without reaching their full color potential.
Freezing temperatures and hard frosts can kill the processes within a leaf and lead to poor fall color and an early separation from a tree.
True Colors Come From Inside
Trees actually begin to show their true colors in autumn, and here’s why.
The four primary pigments that produce color within a leaf are: chlorophyll (green); xanthophylls (yellow); carotenoids (orange); and anthocyanins (reds and purples). During the warmer growing seasons, leaves produce chlorophyll to help plants create energy from light. The green pigment becomes dominant and masks the other pigments.
Trees must replenish the chlorophyll because sunlight causes it to fade over time. As days get shorter and nights become longer, trees prepare for winter and the next growing season by blocking off flow to and from a leaf’s stem. This process stops green chlorophyll from being replenished and causes the leaf’s green color to fade.
The fading green allows a leaf’s true colors to emerge, producing the dazzling array of orange, yellow, red and purple pigments we refer to as fall foliage.
Following the Feast of Fall Colors
Fall’s color “parade” varies from region to region and year to year, depending on weather conditions. For areas under calm and dry high pressure, cool nights and sunny days can lengthen fall color displays. Cold or warm fronts can produce strong winds and heavy rain that cause leaves to fall off trees more rapidly.
November 13, 2013 – Since the leaf peak season has passed this is the final report on conditions for the High Country on this page.
November 2013. Graphics from The Foliage Network
October 26, 2013. Graphics from The Foliage Network
October 23, 2013. Graphics from The Foliage Network
Autumn Color viewed from space Sunday October 20 in Western NC via the Modis Visible Satellite image. Image courtesy of Brad Panovich
October 19, 2013. Graphics from The Foliage Network
October 16, 2013. Graphics from The Foliage Network
“This week, plus the coming weekend, should be our peak fall leaf color times here in the Boone/Blowing Rock and Grandfather Mountain areas. A drive along the Blue Ridge Parkway will present excellent viewing, especially at 3,000’ and up. Colors are still developing at lower elevations, and won’t peak for another week or so, but the views should be great nonetheless. Sugar maples are really gearing up now. In Boone, along King Street, and also on the Blowing Rock Highway, there are several large sugar maples that just explode in yellow-orange brilliance at this time, and you can see them this week if you come up. Red maples are having a great year, and many are now peaking in the Boone area. A lot of yellow color is coming through now as the birches, beeches, tulip poplars, hickories and magnolias begin to show. Some of the oaks are also starting to color up, and the red, scarlet and black oaks will be the last major bursts of color on the landscape.
Kathy Mathews says that “we will reach “peak” by next weekend [in the Cullowhee/Sylva area]. A lot of trees are dropping their leaves,” and she says “it would be best to advise tourists to come up next weekend, I think. She says she’s “astonished we haven’t had a frost yet to bring on a real peak of simultaneous color! A frost may not happen until the end of the month, but many trees will be finished by then.” Kathy then drove “over the mountains on Hwy 64 south to Clay County this weekend, between Franklin and Hayesville, and the pass where the AT crosses highway 64 near the Standing Indian Recreation Area is just gorgeous now. That area is in true peak, with lots of bright colors.”
Jonathan Horton reports that Asheville is still predominantly green, but there is color on the surrounding hills. Oaks and hickories are coloring up and adding to the other trees that already show color (maples, sourwoods, dogwoods). Later today I’ll have a report from the Cashiers/Highlands area. The government shutdown is preventing me from reporting about Great Smoky Mountains National Park, but my intuition says the high elevations are peaking now, so this weekend should also be good for a drive up to Newfound Gap. Cades Cove will most likely peak later as it’s at low elevation in the Park.
We’ve had very moderate temperatures these last few weeks, even excessively warm the prior week. I think that delayed the progression of color development by several days as the peak is yet to appear here in the Boone area, and the average date of appearance is between the 10th and 14th of October. Also, as Kathy Mathews from WCU points out, we have not had a hard frost yet, which can synchronize leaf colors somewhat (it can also speed up leaf loss too). We did get down to 34oF a few mornings ago, and I’m sure it went below freezing at the higher elevations like Banner Elk. But the long-range forecast shows temperatures above 40oF for the next week or so. There is a front moving in, and there could be rain late Wednesday and some of Thursday, and even a chance this coming weekend (sorry, I can’t do anything about Mother Nature!). But nothing too major (and no severe winds) so come on up and enjoy the best show nature ever devised!”
October 12, 2013. Graphics from The Foliage Network
October 10 from Brad Panovich WCNC TV Charlotte
October 9, 2013. Graphics from The Foliage Network
October 5, 2013. Graphics from The Foliage Network
October 2, 2013. Graphics from The Foliage Network
“This is the first weekend of autumn and also the first time I can report that fall leaf color in the mountains is beginning to show in earnest, especially above 4,000’ elevation. Check out the photo attached which I took at Tynecastle, at the intersection of Rts. 105 and 184, near Banner Elk, and just west of Grandfather Mountain State Park. The sugar and red maples are coming out and should peak at the higher elevations by next weekend. American ash is turning also (a dull purplish color), and the mountain ash fruits are like red beacons against the background of spruce and still green oaks. They are quite spectacular this year, perhaps a result of all that rain earlier in the summer (Grandfather Mountain, for example, received 29” of rain in July alone!). There are four species of maples on Grandfather Mountain (red, sugar, striped, and mountain) which turn varying shades of orange and red (often both), although striped maple is unique in that its large leaves only turn a brilliant yellow only.
You may also see the evergreen rhododendrons (R. maximum and R. catawbiense) dropping their older leaves now. That is normal at this time of year, and you can tell which is which by the color: the senescent leaves of R. maximum are yellow while those of R. catawbiense have a reddish hue to them. Also, the leaves of R. maximum are longer while the other species has shorter, more oval leaves. Sassafras is also turning, and you can find leaves ranging from dark green, to yellow, to orange to red, all on the same tree! Huckleberry bushes are now peaking and have a deep burgundy color. There is a good display of these shrubs on the rock outcrops on Beacon Hill, just off the Blue Ridge Parkway east of Grandfather Mountain. Finally, you may have seen tree trunks covered in a deep red vine (note the picture at the top of my academic fall color page (http://biology.appstate.edu/fall-colors). This is Virginia creeper, and it’s peaking now throughout the High Country.
Down by Cullowhee and Sylva, Kathy Mathews reports that she is seeing “many trees and shrubs turning yellow (tulip poplar, cherry, birch, walnut) and red (dogwoods, sourwoods, red maple, burning bush, etc.), but the chlorophyll is still present as well, so the red colors are looking somewhat dull.” She feels that their peak is still several weeks away.
Based on the rate of development of leaf color, I think visitors will enjoy peak colors by next weekend at the higher elevations, especially on the slopes of Grandfather (and particularly on the east-facing slopes), at the higher elevations in Elk Knob State Park just north of Boone and on Roan Mountain on the border of NC and TN and finally, in the Smokies, also at the higher elevations. Colors won’t be at their peak in Boone and Highlands until the weekend after next. One positive thing going for us is that the weather for this coming week is forecast to be sunny and cool, which is perfect for color development.”
September 28, 2013. Graphics from The Foliage Network
September 26, 2013. Graphics from The Foliage Network
September 21, 2013. Graphics from The Foliage Network
“The forecast for this week is, in a nutshell, the same as last week: Green! Trees in the High Country still have most of their leaves, and there is isn’t much to report right now. Yellow buckeyes are about the only tree species to show a significant change: most have started losing their leaves (remember, these trees are early to leaf out, and early to lose them in the fall – the botanical equivalent of early to bed, early to rise!). However, they also get a leaf fungal disease, so their leaves do not provide much color. Dogwoods and burning bushes are coming along and increasing in color each week, and the occasional sugar or red maple have some orange/red leaves. Otherwise, as I stated above, the word is still GREEN.
The long-range forecast for the southeastern portion of the country, including the southern Appalachians, is for above-normal amounts of precipitation. That doesn’t bode well for great fall leaf color, because sunny and cool conditions are what lead to good fall leaf color. But so far the weather has been near perfect for good fall color, so let’s hope that we don’t get too much rain in the next few weeks. If not, we should have a great fall color season this year!
As I was driving back from a short visit to the coast on Sunday, I was thinking of how green the mountains looked as I headed up US 421 into Watauga County. That started me thinking of all things green: How Green Was My Valley, the Grass is Always Greener on the Other Side of the Fence, and It Isn’t Easy Being Green (https://www.youtube.com/watch?v=51BQfPeSK8k, with Kermit the Frog). What phrases can you think of that relate to “green”?
Have a great week! Don’t forget, you can check out essays on the science of fall color at my other fall color site, as well as a list of what colors each tree turns: https://www.youtube.com/watch?v=51BQfPeSK8k”
Map conceived by Howard Neufeld and Michael Denslow, constructed by Michael Denslow
September 14, 2013. Graphics from The Foliage Network
September 7, 2013. Graphics from The Foliage Network
The summer of 2013 will go down as the wettest on record for the area, and for many residents it will go down as one that was not a summer at all. Attention is turning quickly toward fall and what might it bring.
Dr. Howard Neufeld is not only Professor of Plant Eco-physiology at Appalachian State University, but he is also known as The Fall Color Guy. Along with sharing his expertise with the NC Division of Tourism each fall, in 2012 he allowed WataugaRoads.com to share his insight and information.
Once again in 2013 WataugaRoads.com is teaming up with The Fall Color Guy to provide information as the colors start changing. On Monday of this week (July 29, 2013) WataugaRoads.com asked the question about what we might see with fall colors this year due to the amount of rain received.
“1. People think fall colors are good when they last a long time, and have plenty of brilliant reds interspersed with the oranges and yellows. So, the quality will depend on how much “redness” we have this fall.
2. Trees tend to make more red colors (anthocyanins) in the fall when it’s cool and sunny, and if we have a slight but not severe drought. This year, cloudy, rainy, no drought!
3. Sunny days means more photosynthesis, and more sugars produced in the leaves, and sugars induce anthocyanin production.
4. A slight drought impairs uptake of nitrogen (we think) and some experiments suggest that plants low on N make more anthocyanins.
5. If it is rainy, then there is less photosynthesis, fewer sugars, and more nitrogen uptake (soils are wetter for longer), and hence, trees may make fewer anthocyanins.
6. So, if the weather keeps consistent, we may see duller red colors this fall. The oranges and yellows should be as usual, as they do not depend as much on light or drought.
7. How long the fall color will last is another thing, and also, it is unknown if a wet summer will change the timing of fall colors.
8. Usually, fall colors peak around Oct 11-14 in the Boone area; sooner by a few days up to a week at higher elevations, later at lower ones. Nice colors can stick around for a week or more, although the peak usually comes and goes in just a few days, weather permitting (no high winds for example).
9. If the wet conditions extend the growing season, then the initiation of fall colors might be delayed by several days, or, if trees decide that they’ve got all they need for this season, they may initiate fall colors early instead. We just don’t know at this point. It will also depend on what the weather does in late August through September.”
Aug 6, 2013. Photo: Kenneth Reece
On Tuesday July 30, 2013 Anita Presnell shared these photos of some early changes from Valle Crucis Park.
You can find more information from The Fall Color Guy at the following links: