Category Archives: Plants & Wildlife
By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester
Tryon Creek State Natural Area (TCSNA) has 15 miles of hiking trails for anyone wanting to get out into a forested area and take a run or walk. You can enjoy nature at any season of the year. In certain places you can see spots where people have not done a good job of staying on the trails, and the results can be pretty stark. The photo below shows a spot along Old Main Trail where hoards of hikers have rambled off the trail to get an up-close view of the roots. The trampled area is now essentially bare of plant life. For clarification purposes, the hemlock in the picture got started long ago on top of a decaying log. The roots of the tree (yellow arrow) started growing inside the log. Many of them eventually made it down into the ground, so when the log rotted away, the roots were exposed above ground. In “exploring” this up close, lots of the people find this fascinating and climb up on top of the roots.
How much trampling can plants tolerate?
I was curious about how much trampling it takes to kill the plant life at TCSNA. After securing permission to set up a study on this question, I laid out a plan. I identified three small areas at TCSNA where waterleaf (Hydrophyllum tenuipes), a fairly common plant at the park, was virtually the only plant growing. These three areas were located some distance away from major trails to both minimize negative visual impacts on trail-walkers at the park, and to protect the plots from unplanned visitations from other people.
I then set up 6 “plots” at each of these locations. A “plot” was an area of ground of a size that could be covered by my boots when I stepped on it, as shown in the picture below. This was approximately 10” by 12”. To minimize the influence of each plot on other plots, each plot was at least 1 foot away from all other plots. This picture was not taken at an actual plot, but was taken in an area with fairly sparse waterleaf so that you could easily see my boots. An important thing to note is that there is a tiny area between my boots that did NOT get directly trampled.
The plots were set up on April 29, 2019. The individual plots were marked by white stakes with painted rings on them. The color of the rings on the stakes indicated when they were to be trampled. I visited the general areas for 15 consecutive days, and carried out the following trampling schedule:
Green Stakes = Never trampled
Blue Stakes = Trampled 1 time
Yellow Stakes = Trample 3 times (once every 5 days)
Red Stakes = Trample 5 times (once every 3 days)
Orange Stakes = Trample 15 times (once every day)
In the photos below, I have tried to make each photo large enough so that you could see the white stakes that mark the corners of the plots. This means that on the very edge of the photos are actually outside the plots that were trampled.
Results One Month After Trampling
The last trampling was conducted on May 13, 2019. One month later, on June 13, 2019, I revisited the plots to assess their status. All of the plots were selected because they were basically 100% covered with waterleaf. Photos of the plots from each of the three study areas are shown below. In each case, the point where the white stakes enter the soil mark the 4 corners of the plots. In almost all the photos, you cannot see the actual point where the stake entered the ground, but you can get a pretty fair idea of where it was.
Control Plots – Never Trampled
In general, after a month, all the control plots are fairly well covered with green waterleaf leaves. In Area 3 there was even one plant that flowered. I don’t know what created all the little holes in the leaves, but rest assured, there were many other areas in the park that exhibited this same pattern, so I’m doubtful it had anything to do with my study.
Plots Trampled 1 Time
Area 1 and 3 had some erect healthy looking leaves, even after being trampled 1 time. In Area 2, there were still some green leaves on the plot, but the stems were pretty much lying flat on the ground, not erect.
Plots Trampled 3 Times
Two of the three thrice-trampled plots still displayed a few green leaves, but compared to the controls, things were looking a little scant. In most cases, the green leaves on the plots were on stems that had been trampled down so that they now laid on the ground.
Plots Trampled 5 Times
In the 5 times trampled plot in Area 3, the red arrow marks the point where the stem emerges from the ground. This close to the corner of the plot, the stem may not have been stepped on directly at the point where it emerged from the soil. The plots in general, compared to the plots which were never stepped on, look pretty bleak.
Trample 15 Times
On the plots which were trampled 15 times, little or no waterleaf has survived.
Sometimes, the most interesting parts of a scientific study are the unexpected results. Here is a photo of an area that I walked through to get back to one of my study areas each day. This area started out as a solid bed of waterleaf. Can you figure out where I walked to get back to the study area?
So what’s the take-home lesson?
It’s pretty clear that the forest at TCSNA will get along much better if we all stay on the established trails. Is there cool stuff to see off the trail? You bet there is. But seeing it comes at a price for Nature, and we should all keep in mind this sign posted in an area that had lots of off-trail trampling:
By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester
All photos by the author unless noted.
The forest at Tryon Creek State Natural Area (TCSNA) is literally rooted in the soil. What happens below the surface of the ground is vitally important to the forest, but something which is generally hidden from us. Rarely, Mother Nature provides us with a glimpse into her underground world, and it can be very enlightening.
The Root System Revealed
In late September of 2013, a little more than 5 years ago, a tree growing by the side of the road leading up to the “Horse Lot” at TCSNA blew over during a rainy, stormy period. Seizing the opportunity, I started studying this event, with the idea of creating a series of Natural Notes possibly stretching over many years.
When the tree blew over, the root system was revealed. Photos taken within 2 or 3 days of the blowdown are shown below.
After the tree fell over, for at least a couple of days afterwards, there was a pool of water covering the clay layer exposed when the tree had fallen over. It turns out that the soil under this tree, just like most of the soil at TCSNA, has only about a 2 to 3 foot layer of soil suitable for growing plants, underlain by a thick layer of clay. This clay is very resistant to water flow and root growth. For safety reasons, the Park Staff filled in this hole shortly after the tree fell over. The photo below gives an indication of the size of the root wad. The red arrows show moderate- to large-sized roots growing horizontally, not downwards, because they hit the clay layer.
— Photo by Anonymous Park Visitor
I measured the thickness of the root wad within a week of when the tree fell over. I did this by pounding a thick metal rod through the root wad, and measuring how much of the rod stuck out of the soil. A picture of this method is shown below. I pushed the rod through the root at 4 different locations, both 2 and 3 feet on either side of the trunk of the downed tree. On average, the thickness of the root wad was 24-1/2 inches.
As you can see, there are no roots growing straight down out of the root mass. The clay layer beneath this tree was not hospitable.
The Aging Root Wad
Five years after the tree blew down, I returned to the site, and measured the thickness of the root wad again, in the same way I had measured it when the tree first fell down. In the 5 years since it fell over, the soil on the root wad was 4.9 inches thinner than it was when it first fell down. Based on other trees that have fallen over in the forest, like this one along the Maple Ridge Trail shown below, I anticipate that sooner or later, all the soil will be washed off the skeletal root system.
An Underground Dam
These root systems all raise questions about the depth of the “plant friendly” soil, which in much of the park, seems to be pretty shallow. In many cases of fallen trees, the soil which is exposed is substantially clay. Clay of course is resistant to water flow. Just how resistant? I collected a sample of clay from the root system of a tree that had recently fallen at TCSNA.
At home, I drilled holes in the bottom of a plastic cup, as shown below. Water flowed easily through the holes as you can see in the picture below.
For my test, I put about 1/3 of an inch of clay into the pot, and gently pressed it down into the pot. Then I filled the pot with water. There was some tiny amount of water that flowed through the holes but not much. I let the pot sit with water in it for a couple of days. Then I once again filled the pot with water and let it sit inside of a plastic tray. I sat the pot on two pencil stubs to keep the bottom of the pot up off the tray, so water could easily run out of the holes. This is illustrated below. I left out the plastic tray in order that you could see the rest of the set-up more easily.
In the course of 20 hours, not a single drop of water leaked out of the cup. The clay used in this demonstration is clay that is found underground throughout much of TCSNA.
The nearly impenetrable layer of clay found at TCSNA means that the forest we love is dependent on approximately the top two feet of soil. To put this in perspective, when leading hikes for students at the Park, I will oftentimes ask them this question: What would they think if I went to Washington Square and dumped 2 feet of dirt on top of the asphalt parking lot, and declared that I was going to start growing a forest there? Almost always the kids will say something like “You are crazy!” But in fact, that is essentially the situation we have here at the Park.
The photo below shows me with a cardboard box the same height (24.5”) as the depth of soil supporting the trees at TCSNA. This is the depth of soil I would pour onto the parking lot in order to create a forest at Washington Square Mall like that at TCSNA.
The thin layer of soil supporting the forest at TCSNA is one reason that the trees need to shelter each other if they are going to resist being blown down by the wind. They really do constitute a “Forest Community.”
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.