Category Archives: Plants & Wildlife
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.
By Deborah Hill, Park Ranger
What have you eaten today that comes from a plant’s fruit? Perhaps you’ve eaten a blueberry, orange, almond, or bell pepper? Are you enjoying the feel of wearing a cotton t-shirt, jeans or sweatshirt? None of these foods or items would be possible without pollinators, (yes, cotton can self-pollinate, but produces more cotton when pollinated by bees).
When we think of pollinators, we usually think of the honey bee. The honey bee (genus Apis) is a social bee that was brought to the Americas by European colonists in the 1600s. Although scientists found a fossilized honey bee in Nevada, it is thought to belong to an extinct species of honey bee. What was pollinating all the plants in North America before the arrival of the honey bee? All the native pollinators of course! Native pollinators are essential to the success of native plants and wildlife, and we can help them survive and thrive.
What is a pollinator?
A pollinator is an animal that moves pollen from the anther (male part) of one flower to the style (female part) of another flower. This cross-pollination fertilizes plants so it can reproduce through seeds. In addition to seed production being important to the plant, many species of wildlife are dependent on those seeds and fruits, and so are humans.
Who are pollinators?
There is a wide variety of animal pollinators including insects (bees, wasps, flies, beetles, butterflies, and moths), birds and bats, among others. Oregon bats are insectivorous (feed on insects) and aren’t pollinators. However, in other parts of the world they are essential pollinators.
Below are a few of our local native pollinators.
What do pollinators do for us?
According to the Xerces Society, a nonprofit organization focused on invertebrate conservation, pollinators are responsible for the reproduction of over 66% of our food crops, and for 85% of flowering plants worldwide. Without pollinators, our food source would be down to wind pollinated grains and meat from animals that feed on wind pollinated plants such as grass. Not only would animals that depend on animal pollinated plants through seeds and fruit suffer, the plant themselves would no longer reproduce. This is of course, a doomsday-type scenario, but it is helpful to entertain this idea to understand just how important pollinators are.
History was made March 2017 when the rusty patched bumblebee was given protection under the Endangered Species Act. It is the first bee to make the list. The US Fish and Wildlife Service can now develop and implement a plan to support this species in making a recovery.
How Can we Help Native Pollinators?
There are simple things we can do with our yards to support native pollinators.
- Plant a variety of native flowering plants: native pollinators prefer native plants.
- Have a variety flower colors: different pollinators are attracted to different colors.
- Have a variety of flower shapes: Pollinators have different shaped mouthparts: hummingbird vs. hoverfly.
- Clump flowers together: clumps of one species are more desirable than scattered plants.
- Have a diversity of plants to flower all season: pollinators are active at different points in the season.
- Create nest sites for pollinators: native bees need a safe place to nest.
- Avoid pesticides.
The next time you are enjoying the results of our hard working pollinators, whether it is a strawberry from a honeybee pollinated plant, or a huckleberry from a native pollinator, take some time to recognize the pollinators that made it happen. Look at the flowers around you and notice who is visiting them and making pollination happen.
Attracting Native Pollinators: Protecting North America’s Bees and Butterflies by the Xerces Society. 2011
Selecting Plants for Pollinators: Pacific Lowland Mixed Forest Province http://www.pollinator.org/PDFs/PacificLowlandrx8.pdf
The Xerces Society. http://xerces.org