Author Archives: tryoncreeknaturalist
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
It’s a sure sign of autumn at Tryon Creek State Natural Area (TCSNA) when the leaves start to fall. However, the time of leaf fall can vary dramatically between species. I became aware of this during the past 5 years of my phenology study. This phenology study involves visiting more than 60 specific selected plants at TCSNA every week to ten days throughout the year. I make notes on the stage of development of each plant on each visit. For example, I note stages of development like “buds open enough to see leaf veins”, “flower’s stamens visible” or (in the autumn) “last leaf has fallen.” This year, for example, every one of the vine maples (Acer circinatum) in the study had lost all their leaves by November 22nd. In contrast, several thimbleberries (Rubus parviflorus) still had numerous green leaves as late as December 13th. This is a difference in leaf fall between species of more than 3 weeks. Sometimes the difference in the date of leaf fall varies dramatically even on the same plant.
This year I found numerous examples of extra-long leaf retention in several plants. These plants appear to have differences in time of leaf fall for one of two different reasons.
Adventitious buds are buds that form from normal plant tissues. Oftentimes they arise from the cambium, the layer of soft, actively dividing cells just under the bark of woody plants. Normally the cambium cells just differentiate into either bark or woody stem cells. Most plants, like Douglas-fir (Pseudotsuga menziesii) and bigleaf maple (Acer macrophyllum), recognize that the energy they need for growth is coming from the sun up above. Their secret to success is growing tall, where they can reach above most plants, and bask in the full sunlight. To do this, these plants want to direct as much energy as possible into the shoots that are growing straight up towards the sun. The apices of these plants “control” the growth of side buds and shoots by producing a chemical named auxin. The chemical structure of auxin is shown below.
This auxin is produced at the tip of the dominant stems. As the auxin is transmitted down the stem, the message that this chemical delivers to the lower buds is “don’t grow” and “don’t develop new buds” depending upon the exact circumstances. When the top of the tree, or the tip of a branch, is killed or broken off, the auxin no longer flows down the stems, and eager lower buds start to grow out. In some cases, brand new buds are formed along the stem, and take off like a rocket!
One of my favorite examples of this at TCSNA is found on a Pacific yew (Taxus brevifolia) tree along the Cedar Trail. The tree blew over during a storm and the trunk lay across the trail, although some roots were still in the ground. On January 22, 2017 I cut off the trunk to allow the trail to be more accessible. But the big news was months later. All along the remaining trunk, brand new little yew branches were growing out, no longer inhibited by the top of the tree, as shown in the picture below.
Another example started last spring when a trail maintenance crew cut the top off a lot of shrubs along the Red Fox trail. This produced results similar to what happened on the Pacific yew. One of the plants they cut back was the hazel (Corylus spp.) shown below. The black arrow is pointing to a stem which has lost all of its leaves, and in fact, almost all of the plant has lost its leaves. In contrast, the purple arrow points to one of the two stems on the plant which is still holding onto its leaves.
So what’s the difference? Note the blue and red circles in the picture. The blue circle shows where a major stem of the plant was cut off by the trail maintenance crew between May 30 and June 6. On this particular plant, the leaves had started growing about March 8 and were approximately 2 inches long at the time the bush was trimmed back. The removal of this main stem liberated buds on the lower parts of the stem. These liberated buds began to grow (note purple arrow and red circle). So these adventitious shoots and their leaves were much younger than the shoots and leaves of the other parts of the plant. These young leaves stayed on the plant much longer than the “normal” leaves.
Two other examples of this phenomena are shown below. The first is a red huckleberry (Vaccinium parvifolium) which was also pruned off (note red arrow).
The final example is an Indian plum (Oemleria cerasiformis) plant. Here the branch tip appears to have been randomly broken off, rather than cut off, but the end result is the same. All the leaves on this plant, except some leaves on the small shoot shown in the left picture had fallen off by September 28th. The fact that this one leaf is still green and healthy 10 weeks after all the “normal” leaves had fallen off the plant is astounding.
Buds: Preformed or Neoformed?
The second reason that some leaves might hang on longer than others is due to when the leaves are formed. For example, in overwintering Douglas-fir buds, each of the needles that will appear the following growing season is already formed. You can see these “baby needles” as little whitish bumps (red arrow) in the picture below after all the bud scales (blue arrows) have been cut off.
In contrast to these “pre-formed” buds, some plants have a different (“neoformed”) growth strategy. In these plants, new leaves (“primordia”) will be initiated during the spring and summer as long as growing conditions are favorable. These primordia will immediately start to develop into leaves. Thus on one plant, there will be leaves of vastly different ages. Not surprisingly, the older leaves will drop off before the younger ones. One example of this at TCSNA is the red elderberry (Sambucus acemose). I took the pictures below of one plant on December 6, 2017 at TCSNA.
This continual development of new leaves is illustrated in the chart below of the length of 3 different leaves throughout the growing season, until somehow the plant’s stem was severed.
The elderberries’ strategy is successful although when the end of the growing season comes, the youngest segment of the twig hasn’t had a chance to produce viable buds, and the twig beyond the last pair of viable buds just dies.
There’s more than one road to success
Mother Nature has produced many species of plants, which use a variety of strategies to achieve success. Two of the strategies involve leaf and shoot development. As illustrated above, the first strategy involves focusing the plant’s energy on the development of just a few leading shoots and suppressing the others. However, Mother Nature knows that bad things happen, and if those leading shoots are killed or injured, tissue lower down on the plant can create branches that will take over and keep the plant alive. The second strategy involves having a stem that just keeps elongating and producing new leaves as long as the weather is good. Both strategies have been successful, and add more interest to our forest.
–All photos by Bruce Rottink
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
The plants growing at Tryon Creek State Natural Area (TCSNA) require a supply of nutrients to stay healthy and keep growing. An important part of supplying those nutrients is the decay of dead organic matter like leaves and branches. This decay process releases the chemicals in the dead leaves and branches so those nutrients can be reused by plants that are still growing.
To study this process, I collected leaves, branches or cone scales of several species of trees found at TCSNA in September 2014. I only collected fresh materials which had recently fallen to the ground. Within two days I placed these in wire mesh (screen) “envelopes” and fastened the envelopes to the ground with nails. During the first part of the study I took photographs of the envelopes on a monthly or quarterly basis, but starting in September of 2016 I switched to once-a-year monitoring. The results after one and two years have already been published in earlier Naturalist Notes.
The one-, two- and three-year end results are presented here. While I had two envelopes for each of the materials, I only selected the most photogenic envelope for inclusion in this report.
Red Alder (Alnus rubra) Leaves
Red alder is a common tree at TCSNA, and is renowned for dropping its high nitrogen leaves onto the ground while they are still green. The results from this study are seen in the photos below.
One university research project studying the decay of dead red alder leaves indicated that 93% of the nitrogen in the alder leaves was released into the soil via the decay process the first year. The same study found that 91% of the calcium and 97% of the potassium (both key nutrients) were also released during the first year of leaf decay1. This relatively rapid decay of the red alder leaves was attributed to the fact that they generally contain higher levels of nutrients than most trees, thus nourishing the decay organisms.
Western Redcedar (Thuja plicata) Branchlets
In sharp contrast to the red alder leaves, the western redcedar foliage contains lower levels of many nutrients, thus making it a somewhat less attractive food source for microorganisms. In addition, redcedar foliage and twigs contain many terpenes. Terpenes not only give the tree it’s distinctive “cedar smell,” but terpenes also have anti-fungal properties. The major terpene in western redcedar (α-thujone ) is shown below.
No wonder that the cedar is decaying a little more slowly than some of the other samples.
Bigleaf Maple (Acer macrophyllum) Leaves
With no special chemical defenses against fungi, and a fairly high nutrient content, the maple leaves are another fast decaying material.
Douglas-fir (Pseudotsuga menziesii) cone scales
These Douglas-fir cone scales were already lying on the ground at the time of collection. The cones they came from had probably been chewed apart by a squirrel looking for the nutritious seeds.
Superficially, the cone scales after three years look almost exactly like they did the day I put them in the bag. Obviously the scales are made up of a very hard material, not too much different than the wood in the main stem of the tree. Mother Nature made the cone scales very durable to protect the precious young seeds, and as a result, they are being recycled very slowly.
Again, the Douglas-fir twigs and foliage contain some terpenes similar to the terpenes found in the redcedar, and thus, they decay more slowly than the alder and maple leaves. Notwithstanding the resistance to decay, all the needles have fallen off the twigs.
The End Result
The nutrients within each of the samples used in this study will be released and then absorbed by living plants and fungus, helping the forest to grow the next generation of life. This study shows the enormous differences in the decay times of different kinds of tree litter. The softer materials, like the alder and maple leaves also have the highest nutrient content, and lowest concentration of anti-fungal chemicals. But, as the old saying goes, “All in good time!” All these nutrients will once again join living organisms, ensuring the continuation of TCSNA’s forest!
1Radwan, M. A., Constance A. Harrington and J. M. Kraft. 1984. Litterfall and nutrient returns in red alder stands in western Washington. Plant and Soil 79(3):343-351.
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
Some of the smallest, but most important predators at Tryon Creek State Natural Area (TCSNA) are our spiders. Spiders are the most voracious predators in the world, consuming far more prey than larger, more dramatic predators like owls and coyotes. It was estimated by an eminent spider scientist that the all world’s spiders together each year consume a weight of insects greater than the weight of the human population of England.1
Spiders: Voracious Predators
Spiders catch their prey in variety of ways, the most obvious being those that weave webs. Just a brief look around TCSNA reveals that we are home to many different kinds of spiders and their webs.
The Orb Weavers
The most common and recognizable group of spiders are the orb-weaving spiders, named for the shape of their webs as seen below. These webs are designed to help the spider catch flying insects for food.
After weaving the orb web, the spider will most often wait upside down in the center of the web for some hapless insect to become stuck to, and entangled in, the web. The thrashing motion of the insect trying to escape attracts the spider’s attention. I have also observed a situation where a Douglas-fir needle fell into a web and got stuck. The spider ran down and disentangled the needle and threw it down. Unfortunately it got tangled again lower in the web. The spider went down further, and repeated the process, this time the needle fell free of the web. The spider then returned to the center of the cleaned up web to continue monitoring the action.
Once the victim is in the web, the spider will rush to the insect and inject it with poison to kill it. Sometimes, as seen below, the spider will wrap up the insect for future use.
The Mat Weavers
A slightly less common type of spider is the “mat weaving” spider. I was lucky enough to be in the park on a dewy February morning which highlighted one of the better examples of a “mat” web that I have ever seen. It is a flat web suspended by strands from the overhanging branches. This particular web measured about 3 inches across. Typically, these mat webs are not sticky, and the spider is lurking very near and when an insect gets into the web, the spider rushes over and poisons it before it can escape. These kinds of webs can also be found in the crevices of large tree trunks.
The Funnel Weavers
An even less common type of web is made by “funnel weaving” spiders. The example below was found along the Middle Creek Trail. While it may not be obvious in the photo, this really is a three dimensional funnel. The spider typically waits near the bottom of the funnel.
The Dome Weavers
A fourth kind of web which you may occasionally encounter at TCSNA is the product of a dome-weaving spider. Again, these webs are not inherently “sticky” and the spider will rush towards the insect which is trying to escape the web and inject poison into it. The example shown below was near the Iron Mountain Trail, and was approximately 1 foot wide.
While it is the large spiders and their webs that attract our attention, the population of “tiny” spiders is considerable. Worldwide, more than half of all spider species are less than 2/10 of an inch long1. The spider below was living in a shrub with no obvious spider web. It is important to know that a significant number of spider species do not use webs to catch their prey. This spider MAY be among them.
Shy and Sexy Spiders
Spiders reproduce from eggs. Spiders’ sexual encounters are frequently a one-time event for the males, not because of any spider-y sense of monogamy, but because the female will oftentimes eat the male immediately after mating.
In some species the female will create a protected place to lay her eggs. Examples of this behavior can be seen by looking for folded leaves. When you consider that one small spider was able to fold over this leaf and fasten it together, it is nothing short of amazing. An example found along the Old Main Trail at TCSNA is shown below.
The underside of this folded leaf is shown below. The white areas between the leaf edges are web strands which hold the structure in place. I was able to see an adult spider inside of this “nest” but my attempts to get a good photo of her were not successful.
A less dramatic, but still interesting example is shown below in which the mom spider just rolled up part of the leaf to create her nest. She is still on guard. The empty “skin” just to her left might either be the remnants of her nutritious sex partner, a recent meal or her own recently shed exoskeleton. Just for scale, the brown thing she is standing on is a Douglas-fir needle.
Gently unfolding this leaf just a bit revealed part of her nest, and also excited a few of the newly hatched young spiders into action. The young spiders, one of which is highlighted with the red arrow in the photo below, started scurrying around as I unfolded the leaf, but none of them went very far. After I looked, the leaf rolled up again quite nicely.
The young spiders were almost unimaginably tiny. They were way outside the range of what my camera was designed to photograph. Some species of spiders are reported to eat plant material when they are young, and graduate to insect food as they mature.
Yeah for Spiders!
The spiders of TCSNA are a tremendous aid in controlling insect populations that could devour tons of plants and be much more annoying to our human visitors. While they are a lot less visible and dramatic than other predators at the park, they are likely much more important, at least in the amount of insects they consume. Next time you’re at the Park, pause for just a moment at a spider web, and thank the spider for all it does.
1Dalton, Stephen. Spiders: The Ultimate Predators. Firefly Books Ltd. 2008