Buds: A Bridge to the Future
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
Winter is a tough time for the woody plants at Tryon Creek State Natural Area (TCSNA). The air gets both colder and, when the temperature dips below freezing, much drier. Most of the plants stop growing, and some shed their leaves. However, the plants have to be prepared for the next growing season. To prepare, they form buds as a “bridge” to the future. By September the buds are a conspicuous feature of woody plants at TCSNA .
A woody plant’s bud might merely look like a hard little blob on a branch, like this bud of a European hazel (Corylus avellana) growing near TCSNA’s main parking lot.
But the buds of TCSNA’s woody plants are actually quite interesting.
So what exactly is a “bud”?
At the tip of each branch is a small cluster of active cells called the apical meristem. At some point in the spring-summer-fall (it varies with different species), the apical meristem starts differentiating and forming a bud consisting of a variety of structures. These structures can be bud scales, leaves or flowers. These tiny structures rest over the winter, and come spring, they start growing. Even the tough-looking bud scales elongate a bit in the spring.
Below is a picture of a bigleaf maple (Acer macrophyllum) bud which is just starting to open. The different parts of the bud are labeled. The “scale to leaf” transition components have very, very tiny leaf parts at the tip of the scale, you’ll have to look closely.
Last spring I picked another newly opened bud of bigleaf maple which was slightly more advanced than the one pictured above. I took it apart to more clearly show the different components. In the picture below, the parts from the base of the bud are at the left hand side, and the other structures are arrayed in order, right up to the flower, which was at the tip. For completeness, at the base of the floral stem are two tiny meristems (not visible here) that will create next year’s buds.
Since the maples produce structures in pairs, one on each side of the stem, there are always an even number of scales and leaves. The flower is an exception to this rule. The “scale to leaf” transition phase is the most interesting. The leaves and flowers have a perfectly round “stem” connecting them to the branch of the plant. The “scale to leaf transition” structures are dwarf leaves supported by a flattened “stem” that resembles the bud scales in shape. These structures clearly demonstrate the plant’s flexibility when it comes to producing different parts. It’s not a clear “one thing or another” decision. (Note: Not all maple buds have these part-scale/part-leaf structures.)
Now it starts to get really interesting!
Okay that’s the basic pattern, but with dozens of different species of woody plants growing at TCSNA, we’ve got lots of variations in buds.
The first type of “weird bud” is the naked bud. This means a bud that has no bud scales. Our native cascara buckthorn (Frangula purshiana) produces naked buds as seen below. The leaves are fully exposed to the winter environment, but are very tough, and slightly hairy. If you want to see a cascara, go to Beaver Bridge. The cascara is about 5 feet upstream from the bridge on the side of the creek furthest from the Nature Center.
Flower Buds, Leaf Buds and Both of them!
As you saw with the bigleaf maple, some buds contain both leaves and flowers, but some contain only leaves and some contain only flowers.
Oftentimes you can tell if the bud contains flowers even before the buds open. In the picture below are two buds of Indian plum (Oemleria cerasiformis) collected from the same branch. They are just starting to expand in the spring. The big fat bud with the rounded end contains both leaves and flowers, while the skinny one contains only leaves.
Indian plum also teaches us that the term “bud break” is ambiguous at best. Below is a picture of a newly opened Indian plum “bud” containing both leaves and flowers. The young leaves including their tiny veins are clearly visible. The flowers are still contained with their own separate “buds.” So, with the Indian plum we have a bud within a bud.
The Indian plum plants are either male or female, and with rare exceptions, will have only functional male OR female flowers on a single plant.
Keeping it all together
In contrast, some plants have both male buds and female buds on the same plant. Red alder (Alnus rubra) is a good example. The alder tree has buds that only contain leaves, other buds that only contain female flowers, and other buds that only contain male flowers. The photo below shows the three different kinds of overwintering alder buds.
How else can the buds be different?
One of the most important ways that buds are different is that some species have determinate, buds and other species have indeterminate buds. Overwintering determinate buds contain all the organs (like leaves, needles, flowers, whatever) that will appear the following year. Indeterminate buds hold only a few of the organs that may appear next year.
A good example of a determinate bud is our Douglas-fir (Pseudotsuga menziesii). In the winter, all of the needles that will grow out of the Douglas-fir bud the next year are already present in primitive, miniature form call “primordia.” Pictured below is a Douglas-fir bud which I collected in late August and stripped off all its scales. Each little needle primordium will turn into an actual needle early next spring. Two of the primordia are indicated with black arrows. All of the needles destined for the 2016 branch are represented by a little bump of tissue. This entire green structure is approximately 2 mm (1/12”) in diameter. For plants with determinate buds, it is easy to see why the environment of one year is so important in influencing the growth of the plant in the following year.
In contrast, TCSNA’s black cottonwood (Populus balsamifera var. trichocarpa) has an indeterminate bud. For cottonwood this typically means that there are three or four relatively big pre-formed leaves that overwinter in the bud. Come spring, these leaves will expand very quickly, and start producing sugar for the plant. If the weather conditions are good, the apical meristem will create another leaf from scratch, and when that is done, the tree might produce a couple of more leaves, etc. This is why for indeterminate plants, shoot growth in any one year is profoundly affected by the environment in the current year, not the previous year!
Below is a whole cottonwood bud, and the same bud with the scales removed. In the second photo you can easily see two preformed leaves, two more are hidden on the backside of the bud.
The photo below shows a single, preformed cottonwood leaf in the bud. The light streak is the main vein which will go down the center of the mature leaf.
The photo below is of a black cottonwood shoot not too long after it emerged from the bud. You can see the 3 large leaves which were preformed, and the fourth, smaller, leaf which formed after the bud broke.
For the woody plants at TCSNA, the overwintering buds ARE the future. It is amazing that the fate of something as large as a tree rests within the tiny buds which bridge the gap between the growing seasons. All things considered, buds deserve a lot more attention than they receive.
Seeds: Then and Now
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
Almost every plant at Tryon Creek State Natural Area (TCSNA) started from a seed. Back “Then”, in the mid-1800s, Socrates Hotchkiss Tryon staked his land claim at the mouth of Tryon Creek. “Then” logging started in the nearby forests. From that time until “Now” we have basically the same kinds of seeds at TCSNA.
So what has changed?
Well, the first thing is the abundance of seeds. The plant’s most important activity on a day-to-day basis is making sugar using just sunshine, water and carbon dioxide from the air. This sugar is in essence the “money” of the plant. Just like you have to budget your money, the plant has to decide where to invest its resources too. And, just like you, the plant only has so much “money.”
The plant’s options are to invest in roots, shoots, leaves or seeds. The roots are pretty important since they absorb the water and minerals the plant needs to stay alive. The leaves are important, because they make the sugar the plant lives on. And the stems are pretty important because they are what holds the leaves up in the air so they can catch some decent sunlight.
But what about the seeds?
Nature’s only measure of success is whether or not an organism leaves offspring. So the plant better invest in seeds. Well, maybe. If it is one of the few plants at TCSNA that dies at the end of each season, like our jewelweed (Impatiens capensis) it really needs to put some priority on seeds, or the family line is finished! On the other hand, if it is a perennial plant like Douglas-fir (Pseudotsuga menziesii) that might live 500 years, it doesn’t need to produce seed every year, but it can’t put it off forever.
Scientists have found that when sugar is in short supply, perennial plants will invest their sugar in leaves, stems and roots before they will invest in seeds.
Why would sugar be in short supply?
There are many reasons why a plant’s sugar supply would be low. For many plants here at TCSNA the most important issue is the amount of light the plant gets. With too little light the plant makes less sugar. With less sugar, the plant invests it in leaves, stems and roots, but not seeds. For example, you’ve probably seen salal (Gaultheria shallon) plants (see photo below) in the forest at TCSNA.
There is one patch of salal growing under a dense canopy of trees that I’ve been watching for 4 years. Struggling along in heavy shade, not once has it flowered, much less produced fruit and seeds! In contrast, the salal growing in my yard in the full sun produces abundant delicious berries every year.
The dominant trees always have lots of sunlight, but for the other plants, light is an important contrast between “Then” and “Now.” From a plant’s perspective, logging can be either good, or bad! For the straight, tall trees, it’s bad news because they are going to be cut down. But, for many (but not all) of the smaller plants and bushes like thimbleberry (Rubus parviflorus) struggling to stay alive under those big nasty, light-hogging Douglas-fir, logging means “Happy Days are Here Again!” (Assuming of course that the plant doesn’t get ripped out of the ground when a log is dragged over it.) Post-logging, the surviving plants are basking in the full sun and its leaves are pumping out sugar like crazy! With lots of sugar, there’s enough to invest in leaves, stems, roots, and lots of seeds! It was also a great time for the few trees the loggers left behind because the trees were too small, growing in inaccessible areas, or were in some way defective.
Lots of seeds back “then,” what else changed?
Logging is also an excellent way to churn up the ground, exposing mineral soil. That’s a good thing, because in the undisturbed forest, much of the ground is covered with “litter.” No, not litter like candy wrappers and dog-poop bags, but the litter of fallen leaves, small twigs, old cone scales, and such, as shown in the photo below.
Scientists know that litter can form a barrier to the successful germination and establishment of new plants, particularly for species with small seeds. In addition, this litter layer, also known as “duff”, has a tendency to dry out quite quickly, depriving new seeds and seedlings of optimum moisture conditions. For these smaller-seeded species, there is nothing like exposed mineral soil to provide the perfect place to start a new life.
What kind of seeds are there are Tryon Creek SNA?
The diversity of seeds at TCSNA is amazing. Some of the major differences are how the seeds are dispersed and the size of the seeds. These are very important decisions. The best chance for a young perennial plant is to get away from the mother plant, so it doesn’t have to compete with it. So plants have developed a wide variety of mechanisms for getting their seed spread around. Then too, the plant has to decide on seed size. Putting a lot of resources into a few large seeds would give the resulting seedlings a real leg up when they are first getting established. But on the flip side, if the plant produces very few seeds, and they just happen to land on a rock, or get eaten, too bad! Alternatively, the plant could produce millions of smaller seeds, so that at least some would surely land in favorable sites and avoid being eaten, but then they don’t have much energy with which to get started.
How do seeds get spread around?
At Tryon Creek, seeds mainly are dispersed by either the wind, or by various animals. Two good examples of wind-dispersed seeds are our black cottonwoods (Populus balsamifera ssp. trichocarpa) and our bigleaf maples (Acer macrophyllum). Although both are wind dispersed, they choose radically different ways to do that. The cottonwoods have tiny seeds with each seed sporting a large fluffy mass of fine hairs that completely obscures the actual seed (see the picture below.) This fuzz suspends them in the air as they drift around the forest. The maple has gone with a more traditional idea, having a wing (as you can see in the picture below). This wing arrangement helps the seed drift away from the parent tree.
Other plants use a different type of wing to disperse their seeds, a bird’s wings. All they have to do is produce a nice attractive fruit. The fruit attracts birds that digest the fleshy part of the fruit, and excrete the seeds at some distant location. Two examples of this from TCSNA are the western wahoo (Euonymus occidentalis) and red huckleberry (Vaccinium parvifolium), as seen in the pictures below. (In both cases, the blue lines represent a length of half a centimeter, about two tenths of an inch.)
The third, and most unusual way that plants are dispersed is used by the jewelweed that grows abundantly in the wet areas near the creek. When the jewelweed seed pods are ripe, there is hydraulic tension in the walls of the pod. When the pod is touched, or just naturally dries out, the pod “explodes.” The walls of the pod curl backwards with amazing speed and force. This sends the seeds flying through the air to a new location. Before and after photos of a seed pod are shown below.
How important is seed size?
Seed size varies a lot. The monster seed of TCSNA is the beaked hazel (Corylus cornuta var. californica). There are lots of medium sized seeds like Douglas–fir and western wahoo, while the “tiny” end of the spectrum is represented by red huckleberry. Find them all in the photos below, which are all to the same scale; the blue line represents half a centimeter (about 2 tenths of an inch).
It is interesting to note that there is no clear relationship between fruit size and seed size. Look at the vastly different sizes of the red huckleberry and western wahoo seed above. Then look back earlier in this note at the fruits of these two species. The fruits are nearly identical in size.
Clearly, seed size has little or no relationship to the ultimate size of the plant. Douglas-fir grows phenomenally larger than either beaked hazel or western wahoo, and yet the Douglas-fir has the smaller seed. Scientists in California studying seed size of over 2,500 native plant species have come to an interesting conclusion. First of all, shrubs and trees have seeds adapted to their environments in totally different ways. For shrubs, those species with the largest seeds are best adapted to areas with heavy shade and fierce competition. But for trees, the species with the largest seeds are the ones best adapted to survive on drier sites. The trees of TCSNA follow that rule quite nicely. Both black cottonwood and red alder (Alnus rubra) are commonly found in moist sites, and have relatively small seeds. Douglas-fir, with seeds dramatically larger than either of those two species, are commonly found on somewhat drier sites.
So the bottom line is that compared to the post logging “Then”, we probably “Now” have a lot fewer seeds produced by the shrubs and ground cover plants at TCSNA due to heavier shading. And especially for the smaller-seeded plants, the presence of an undisturbed litter layer is holding back the success of the seeds that are produced.
The fruits of the plants in TCSNA ripen at different times of the year. Cottonwoods shed seed in late May, Douglas-firs in July and grand firs in late August or September. On your next hike at Tryon Creek State Natural Area, keep a look out for the seeds and fruits. You’ll be amazed at the inventiveness of our plants.
Stemflow: Tiny Rivers of Life
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
[Author’s note: Following a recent Naturalist’s Note on licorice fern, several questions arose concerning which trees licorice fern grows on and why it grows there. This note helps answer those questions.]
If you’re like me, when you think about rain, you think about drops of water falling out of the clouds, hitting your face and streaking those windows you’ve just washed. That’s part of the story, but there’s an important part of rain that’s easy to miss. It’s called “stemflow.”
Stemflow is water that starts out as a falling raindrop, but on the way down it hits a leaf or a twig. Much of this intercepted water starts to move over the surface of the leaf or twig to a branch and then to the stem. At that point it becomes part of a tiny river known as stemflow.
While stemflow is only marginally interesting to humans, both the quantity and quality of the stemflow can mean life or death to epiphytes, the small plants growing on the surface of larger plants like trees. The most obvious epiphytes at Tryon Creek State Natural Area (TCSNA) are moss, lichens and licorice ferns (Polypodium glycyrrhiza).
How is stemflow different from ordinary rain?
The chemical properties of stemflow are vastly different from those of free-falling rain. One study of stemflow on bigleaf maple (Acer macrophyllum) found that stemflow had a significantly higher concentration of the plant nutrients calcium, magnesium, sulfur and nitrogen than did raindrops. These chemicals apparently came either from dust that had been deposited on the branches since the last rainfall, or they were leached by the raindrops from the bark itself. In addition, stemflow was less acidic than raindrops.
In a study of stemflow on red alder (Alnus rubra), a nitrogen-fixing species, the stemflow contained 11 times as much life-sustaining nitrogen as raindrops. In contrast to bigleaf maple, the stemflow of alder was more acidic than the raindrops. Numerous studies show that different species of trees produce stemflow with different chemical properties. It seems reasonable that the chemical differences in stemflow between species of trees would influence the amount and kinds of epiphytes growing on those species.
So how much stemflow is there on a tree trunk?
Depending upon the kind of forest, researchers have found that the amount of stemflow is generally between 1% and 5% of the total rain that falls. The amount of stemflow on a tree of a given crown size varies depending upon how the branches are attached to the trunk, and how rough the bark is.
How do tree branches effect stemflow?
Tree branches can be attached to the main trunk of a tree at many different angles. If the branches point strongly upwards (as in the red alder pictured below) any rain hitting a branch will probably run right down to the main stem. However, if the branches are attached to the trunk horizontally, like they are in the western redcedar (Thuja plicata) pictured below, if a raindrop hits the branch, it probably won’t flow to the main stem and become stemflow.
Another factor which apparently hasn’t drawn the attention of researchers, is whether or not the foliage is droopy. Two of TCSNA’s conifers have extremely droopy small twigs and foliage. You can see that in the western redcedar pictured above. Droopy foliage is also characteristic of western hemlock (Tsuga heterophylla). As you can see in the picture below, with droopy foliage, intercepted water runs off the branch tips, and never becomes stemflow.
How does bark effect stemflow?
Researchers have discovered that trees with rough bark have less stemflow than trees with smooth bark. Having rough bark increases the surface area of the tree trunk. In the diagram below, the cross sections of two hypothetical trees are superimposed, each represented by a different color. While conventional measurements would say both of these trees are of equal diameter, clearly the orange tree, with the rougher bark, has a larger surface area.
Research suggests two factors are involved here. The first factor is that before stemflow can start, all of the bark surface area will need to be wet. Trees with rougher bark need more water to get all the bark wet, so stemflow, especially with a light rain, is less. The second factor is that bark itself absorbs some water, and with a larger surface area, more water can be absorbed by the bark, resulting in less stemflow. Less stemflow means fewer epiphytes.
I recently measured the “roughness” of the bark on the Douglas-fir pictured above. The roughness made the actual surface area of the trunk 10% greater than if the bark had been smooth.
One accepted method of determining bark roughness is to wrap a string around the tree, and measure how long the string is to determine the circumference. Then a wire is wrapped around the tree at the same height, but as the wire is wrapped around the tree, it is pushed into all the cracks and crevices on the tree. It stays “pushed in” and afterwards the length of wire needed to encircle the tree is measured. The ratio of the additional length of the wire divided by the length of the string is a measure of bark roughness. The process is illustrated below.
Okay, so where does licorice fern grow?
Some believe that bigleaf maple is the only significant host of licorice fern at TCSNA, while red alder will occasionally host a few fronds. To address those beliefs, I turned to the last resort of those truly desperate humans we call “scientists,” actual (No, no, don’t say it!) data!
First, looking around TCSNA I managed to find licorice fern growing as epiphytes on living plants of the following species: bigleaf maple (of course), red alder, Pacific yew (Taxus brevifolia), Oregon ash (Fraxinum oregona), Douglas-fir (Pseudotsuga menziesii), black cottonwood (Populus balsamifera spp. trichocarpa) and vine maple (Acer circinatum).
Next, to clarify the relationship between red alder and licorice fern, I grabbed a stick about 6 feet long, and walked along Center Trail/Big Fir Trail/Middle Creek Trail as far as Beaver Bridge. Any living alders along that path that I could touch with the stick while standing on the path became a part of my sample. Of the 36 alders in my sample, licorice fern grew on 35 of them (97+ %).
Finally, to address the issue of alders supporting only a few fronds of licorice fern, I stopped at three alders with “lots” of ferns and while standing still on one side of the tree, counted visible fronds. On one tree I stopped counting at 50, the next at 75 and at the third tree I stopped counting at 150 individual fronds. Thus it appears that licorice fern and alder can get along quite well. To be fair, there were a few good-sized alders which supported only 2 or 3 fronds high up in the tree.
Your mission, should you decide to accept it….
Search for licorice fern in unusual places. Will you be the first person at TCSNA to find it on western redcedar? Can you find it growing on a rock? Or maybe you can find it someplace totally unexpected like on an old signpost along a trail. Keep your eyes open, and if you find some licorice fern in a different kind of place, post a comment below. We’ll all be smarter. As someone once said, “Our current state of knowledge only represents the point at which we’ve decided to stop asking questions.”