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Recycling the Forest: Year 2

By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester

 

Mother Nature is the world’s first, largest and best recycler!  Each year in Tryon Creek State Natural Area (TCSNA), tons of organic matter like trees, dead animals and coyote feces are recycled.  This recycled material is used by the forest to grow new trees, birds and mice, to name just a few.  If it weren’t for recycling, the surface of the earth would be covered with unimaginable amounts of dead organic matter.  In addition, it would be tough for any new organisms to grow because so many materials vital to life would be locked up in the litter.

Two years ago, I started a small study at TCSNA to determine just how fast the recycling process is in our forest.  The first year’s results were published in a Naturalist Note last fall.  To access this previous note, use this link, and then scroll to the bottom.  This second Naturalist Note takes a look at the results after two years.

 

How it works…

As indicated in the previous Naturalist Note, samples of five different kinds of fresh organic matter were collected from the ground in TCSNA in the fall of 2014.  Collecting them from the ground insured that they were naturally ready to start being recycled.  The samples included a) red alder (Alnus rubra) leaves, b)  bigleaf maple (Acer macrophyllum) leaves, c)  western redcedar (Thuja plicata) branchlets, d) Douglas-fir (Pseudotsuga menziesii) branchlets, and e) scales from a Douglas-fir cone that had been chewed apart by a squirrel.  Two samples of each thing were collected, for a total of 10 samples.

Each sample was placed inside a flat “bag” made of standard plastic window screen material.  The bags were then taken into the forest, placed down flat on the forest floor, and fastened down by inserting a nail through the corner of each screen down into the ground.

From September 2015 through September 2016, pictures were taken on a quarterly basis.  The results after two full years can be seen in the photos below.  The first photo shows the array of litter bags before I disturbed them to take the photos.  The silvery-gray bits seen in the photo are the exposed part of the screen bags.  As you can see, there were also some plants growing up through the litter bag array.

 

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Undisturbed array of litter decay bags on September 21, 2016.

 

They’ve really changed!

The rate of decay of materials from the different species varies dramatically.  Specific samples are shown below.  The first two sets of pictures show the two different red alder leaf bags.  I’ve included both sets of red alder bags to show that there is a certain amount of bag-to-bag variation in the rate of decay.  For the remainder of the species in the study, I’ve included only one of the two bags.  You may observe that due to my picking up these bags periodically for photos, the position of some of the materials in the bags has shifted a bit.

 

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Red alder leaf bag #1, left: September 11, 2014, right: September 21, 2016

 

 

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Red alder leaf bag #2, left: September 11, 2014, right: September 21, 2016

 

While most of the leaf blades are substantially degraded, some of the veins are still intact.  This is typical of many different leaf decay studies.

The following photos are of one of the bags containing bigleaf maple leaves.  Again, you can see that the leaf blades themselves are pretty well decayed, but some of the veins, and petiole (the “stem” that connects the leaf blade to the branch) are still identifiable.

 

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Bigleaf maple bag #1, left: September 11, 2014, right: September 21, 2016

 

…Or maybe not so much!

The remaining samples are all from conifers, which retain their foliage for more than a single season.  If you could feel their foliage, you could tell it was definitely tougher.  This becomes evident in the photos below.

The western redcedar foliage has not only not decayed very much, but also, many of the leaf scales are still attached to the branchlets.  I’m impressed!

 

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Western redcedar bag #2, left: September 11, 2014, right: September 21, 2016

 

Most of the Douglas-fir needles in the bag shown below have fallen off the twigs, but they still appear to be largely intact.  Detailed scientific studies suggest that while there has probably been some substantial decay inside the needles, the outer tough surface of the needle has been somewhat resistant.  One unfortunate thing with the Douglas-fir branches is that once the needles have fallen off the twig, they can easily slip through the mesh screen when they are jostled very much.  I have no doubt that some of the needles that were originally on the twig have fallen out of the bag.

 

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Douglas-fir branch bag #2, left: September 11, 2014, right: September 21, 2016

 

The final set of photos below show the tough cone scales of the Douglas-fir which appear to be only minimally changed over the course of two years on the ground.  This is not surprising, given that the cones are made tough to protect the seeds of the tree.  Also, the cones tend to have high resin content, and thus resist decay.

 

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Douglas-fir cone scales bag #2, left: September 11, 2014, right: September 21, 2016

 

Litter as fertilizer

Litter contains vital nutrients that help trees grow.  One of the advantages of relatively slow litter decay is that the litter then acts as a “slow-release fertilizer” a method of ensuring that the living plants will have ample opportunity to absorb it to assist with their growth.

But long before the nutrients trapped in the litter help the next generation of trees and shrubs grow, those nutrients help the fungus and bacteria that decay leaves grow.  And just like you, the microorganisms are more attracted to a lavish banquet than to a bowl of thin soup.  The more nutritious the litter, the faster it decays1.  For example, red alder leaves have 4 times the nitrogen content of either western redcedar or Douglas-fir foliage.  Bigleaf maple litter has more than 3 times as much phosphorus as either western redcedar or Douglas-fir.  Both red alder and bigleaf maple have more than 10 times the amount of potassium as Douglas-fir litter.  Viewed from the perspective of nutrient contents, it’s no surprise that the red alder and bigleaf maple foliage decays faster.

It was found in the mid-1970s that applying urea fertilizer containing 200 lbs of nitrogen per acre to Oregon’s Douglas-fir forests, significantly increased their growth rate.  As noted above, red alder leaves, due to the nitrogen-fixing nodules on the alder roots, contain relatively high levels of nitrogen.  The photo below shows the amounts of urea fertilizer (the typical nitrogen fertilizer for forests) and alder leaves that would be needed to provide 200 lbs/acre of nitrogen.  So the decaying leaves, especially the alder leaves, are acting as a slow release fertilizer.
 

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The box of dried alder leaves contains as much nitrogen as the small vial of white urea.

 

The dead plant parts like tree trunks, branches, leaves and even the unseen roots, are important parts of the whole cycle of life at TCSNA, as well as in other forests.  In their role as nutrient recyclers, the fungus and bacteria that decay the forest litter play a vital role in helping maintain a healthy and vigorous forest.  Recycling is an important example of how different parts of the forest work together to create the TCSNA we love so much.

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1Valachovic, Y. S., B. A. Caldwell, K. Cromack Jr., and R. P. Griffiths.  2004.  Leaf litter chemistry controls on decomposition of Pacific Northwest trees and woody shrubs.  Can. J. For. Res.  34:2131-2146.

 

 

Big Hairy Deal!

By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester

 

If you’re reading this, there’s an excellent chance that you have hair!  Well, you’re not alone!  Amazingly enough, many species of plants have “hair” too.  Technically, plant hairs are called “trichomes” and they’re different from mammalian hair in many ways.  They come in a variety of shapes and sizes, and perform many different functions.  The plants at Tryon Creek State Natural Area (TCSNA) have a variety of different kinds of trichomes.  Based on their physical properties, trichomes can protect plants from a variety of herbivores, reduce the loss of water and help spread the plant’s seeds.

 

Simple Plant Hairs     

 Let’s start out with the basic plant trichome.  These simple trichomes can be found, for example, on the petiole (“petiole” is the little stem that attaches the leaf blade to the branch) of TCSNA’s own red elderberry (Sambucus racemosa L. var. racemosa), as shown below.  These are simple, straight, unbranched hairs.

 

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Trichomes on a red elderberry petiole.

 

Plants, like most things in nature, are rarely frivolous.  If they expend the energy to produce plant hairs, those hairs most likely have a purpose.  One of the benefits of plant hairs is that they help reduce the rate of water loss from the plant.  Imagine a water molecule trying to escape from the elderberry pictured above.  The thicket of plant hairs on the stem dramatically slows down air movement right at the surface of the plant.  This mass of plant hairs is essentially a maze that the escaping water molecules have to slowly wander through before it leaves the plant.

To demonstrate this effect, I set up the following demonstration.  I took two small identical plastic tubs and completely filled them with water.  The first tub (pictured below) is totally open to the atmosphere.

 

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Open tub of water

 

For the second tub, I inserted a scrub brush, bristle side up, into the top of the tub.  The bristles of the brush created a maze similar to that created by plant hairs.  The water molecules had to move through this maze in order to escape (evaporate) from the tub of water.  And, yes, just like in plants, it did slightly reduce the open surface area of the water.

 

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Tub of water “with hairs”

 

I weighed the containers as shown before the experiment started.  After 36 hours of evaporation, I weighed the containers again.  The open container lost 39 grams of water, while the “hairy” container lost only 25 grams of water, 64% as much as the open container.

 

Get a Grip!

Some of the trichomes found in the plant world are simple, but not straight.  A good example found at TCSNA is the seed of the bedstraw (a.k.a. “cleaver”) plant (Galium spp.).  The seed, which is shown below, is covered with stiff, curved trichomes.

 

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Bedstraw seed with hook-shaped hairs

 

In case you’re wondering why the seed has these hook-shaped hairs, take a look at the picture below.

 

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Bedstraw seeds clinging to my shirt

 

The hook-shaped hairs allow the seeds to attach themselves to some innocent passing animal and hitch a ride to a new location.  Presumably they will be brushed off, or rub off somewhere after the passing human or other animal has traveled some distance and “voilà” the plant spreads itself to a new growing place.

 

En garde!

Plant hairs can defend against insects and other pests that want to eat the plants.  Sometimes, the sheer density of the hairs can serve as a deterrent to hungry herbivores.  Some insects might not be able to get through the hairs.  Some larger herbivores might just experience the hairs as “sharp pokey things” and decide to leave the plant alone.  A good example is the ultra-hairy seed of TCSNA’s bigleaf maple (Acer macrophyllum) as seen below.

 

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Seed of bigleaf maple

 

Sometimes, defensive plant hairs are a little more complicated.  One of the premier examples here at TCSNA is our beloved stinging nettle (Urtica dioica) which is pictured below.  The stinging nettle uses some of its plant hairs defensively.  The larger trichomes have a largely silica (like glass) hollow needle (blue arrow) mounted on a relatively soft green pedestal (red arrow) which contains toxins.  When some animal carelessly brushes against it, the tip of the needle breaks off and the movement of the animal against the plant bends the needle over, squeezing the toxin out of the green tissue at the base of the needle.  The toxin is thus injected into the offending animal.  The toxins in this species include histamine, acetylcholine, serotonin, and formic acid.  Typically they cause an itching sensation that for most people lasts no more than 24 hours.  Note that the stinging nettle also has much smaller hairs (yellow arrow) that are common on many plants.

 

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Stinging nettle petiole showing two types of plant trichomes.

 

While humans tend to be very sensitive to stinging nettle, apparently it isn’t 100% effective against all animals.  The banana slug (Ariolimax columbianus) pictured below crawling on stinging nettle seemed to be pretty calm and unconcerned by the trichomes.  It may be that the slug is either immune to the chemicals in the stinging nettle, or its famous slime layer is protecting it or it moves so gently that it doesn’t break the nettle’s needles!

 

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Banana slug crawling on stinging nettle near Old Main Trail.

 

“Fancy” Hairs

Human hairs are all unbranched.  This is not necessarily so for plant hairs.  The English Ivy (Hedera helix) has hairs that are branched.  The pictures below show these branched hairs from two different perspectives.

 

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Branched hairs of English ivy, top view.

 

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Branches hairs of English ivy, side view

 

Glandular Hairs

Finally, there are glandular hairs, which produce chemicals in a small gland at the tip of the hair.  One of the most interesting examples at TCSNA is the invasive plant commonly known as “herb Robert” (Geranium robertianum).  Another name for this species is “stinky geranium.”  If you ever pulled one of these plants, you’ll know why it’s called stinky geranium.  On the tips of the hairs (blue arrow) on the stem below, you can see a small red dot.  This red dot is actually a gland that produces the stinky chemical.  One of the traditional ways humans have used the chemical produced by herb Robert was to rub it on their skin to repel mosquitos.  It probably keeps insects away from the plant as well.

 

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Glandular trichomes on herb Robert with one of the glands indicated by the blue arrow.

 

A second example of glandular hairs on a plant at TCSNA is hazel (Corylus spp.)  Both of the hazel species that we have at the park have a significant number of glandular hairs, as shown in the photo below.  The chemicals are located in the brown tips of the hairs.  In both pictures below note that in addition to the glandular trichomes, the hazel also sports a large number of very small hairs on the midrib on the leaf.

 

 

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Single glandular hair of hazel

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Many glandular hairs on mid-rib of hazel leaf

 

Many interesting chemicals are produced by glandular hairs on plants.  The trichomes of the sweet wormwood plant (Artemisia annua), which is not found at TCSNA, produce the chemical “artemisinin” which is an effective drug against malaria.  And the psychoactive chemicals in marijuana (Cannabis sativa) are produced in the tips of the plant hairs of that species.

 

All in all, the hairs on plants are quite diverse, and have many functions.  As has shown here, plant hairs can slow water loss, help spread the seeds to new locations, and protect the plant from herbivores.  For the plants, the many functions of these trichomes do indeed make them a big hairy deal!

The Sun: Mother of Us All!

By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester

With the exception of a few “iron eating” bacteria described in my Naturalist Note of May 3, 2015, all life at Tryon Creek State Natural Area (TCSNA) depends upon energy from the sun. It might have to go through several steps like plants using sunlight to create carbohydrates, insects eating the plants, birds eating the insects and bigger birds eating the smaller birds, but eventually we all depend upon the sun.

 

How Much Sunlight Is There?

The amount of sunlight falling on TCSNA depends upon many things. It depends, for example, upon the season of the year, the time of day and the amount of cloudiness. An important factor for the plants includes competition from other nearby plants. So how much sunlight is there in various parts of the forest?

To find out, I took measurements at TCSNA on two totally clear days, July 13 and July 30, 2016. On July 13th, I focused on an area near the Nature Center around noon, and on July 30th, I focused on the Cedar Trail in mid-afternoon. On July 13th, the full sunlight at noon in the Equestrian Parking Lot measured 104,000 lux (lux is a standard measure of light intensity). On July 30th my 2:50 PM and 3:30 PM full sunlight readings averaged out to 101,000 lux.

Out on the trail, 3 feet above the ground, there were about 1500 lux of light on July 13th, and from 260 – 610 lux on my second day in the forest.

 

How dark is “shade”?

I plunged into the “dark side” by measuring the light level under some plants. First I checked under a dense clump of salmonberry (Rubus spectabilis). At the soil surface there were only 60 lux of light under those plants. But the champ was a cluster of young western redcedar (Thuja plicata) which let just 50 lux of light through to the soil surface. That is less than 1/20 of 1% of full sunlight. And what was growing under that clump of western redcedar? Take a look in the picture below:

 

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Almost nothing grew under this clump of western redcedar.

 

Why Don’t Plants Grow in Dim Light?

Plants use light to power the photosynthetic process to produce the carbohydrates (like sugars) they need to grow. The more light, up to a point, the more sugar. So you would think that they might grow everywhere there is any light at all. However, the flip side to photosynthesis is respiration. Respiration is the result of internal processes for cell maintenance that are vital to life. The amount of light at which the process of photosynthesis is creating the same amount of energy that the plant uses to maintain its basic functions is called the “compensation point.” At this point, the plant can stay alive, but not grow. When the light level is so low that photosynthesis falls below the respiration rate, the plant ultimately dies.

Various species of plants have different compensation points. Plants are sometimes grouped by their tolerance of shade. At TCSNA one example of an “intolerant” plant (one that can’t tolerate the shade) is our Douglas-fir (Pseudotsuga menziesii). While we have many mature Douglas-fir, the number of young ones is very small. Shade tolerant plants include both the western redcedar and western hemlock (Tsuga heterophylla).

Published standards on how many lux plants need are somewhat variable. As a general rule it appears that shade tolerant plants need at least 150 to 500 lux, while shade intolerant plants need at least 800 to 1500 lux to survive. On the high end, it appears that for all plants about 25,000 to 35,000 lux saturates the photosynthetic process.

 

Those Mysterious Sunflecks

Both days at the park I periodically encountered “sunflecks” on the trails beneath tall trees as shown in the picture below. They typically appear as circles or multiple overlapping circles.

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Sunflects on Maple Ridge Trail: Blue arrow points to a bright one, red arrow to a dim one, and the orange circle outlines a very dim one that is just barely visible.

 

The first day, the light intensity of these sunflecks typically measured between 2,500 and 9,000 lux. That is the equivalent to about 2-1/2 to 9% of full sunlight. My second day measuring sunflecks at approximately 3:00 PM, the majority were from 2,500 to 3,500 lux. So these sunflecks can provide adequate light for photosynthesis to the plants near the ground.

Sunflecks have intrigued me ever since I was delivering newspapers during a partial solar eclipse in Minneapolis, Minnesota in the early 1960s. I saw something on the side of a house that stuck with me the rest of my life. Four decades later, during the partial solar eclipse of June 10, 2002 at my home in Lake Oswego, I captured this phenomenon on film. The photo below was taken during a partial solar eclipse. This is how the sunflecks looked on the side of my house.

 

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Crescent shaped sunflecks during a partial solar eclipse.

 

Amazingly, the sunflecks were crescent-shaped, not circular. Compare the sunflecks above to the diagram below of what the sun (and moon) looked like that day during that partial eclipse (based on information from the internet).

 

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Diagram of how the sun appeared during the solar eclipse of June 10, 2002 in Portland, Oregon.

 

You will note that the sunflecks on the house seem to be flipped 180° from the sun’s actual shape in the sky. This is because of the sun’s image passing through a tiny hole in the crown of the tree. This is sometimes referred to as the “pinhole camera effect” as illustrated below using a tree instead of the sun. This effect was described by Aristotle in the 4th century BC.

 

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An image passing through a tiny hole will be flipped upside down.

 

 

Interestingly enough, your eye also does this, and the images on your retina at the back of your eye are all upside down.

Flipping the image of the actual eclipse by 180° we get the following image, which is virtually identical to the images on the side of the house. This is because the tiny spaces in the crown of the tree are acting as pinhole cameras.

 

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Image of the eclipse flipped 180 degrees by the pinhole camera effect.

 

The bottom line: the round sunflecks we see on the trail are really images of the sun.

 

Why aren’t all sunflecks the same?

Sunflecks have two different properties, size and brightness. Both of these properties are influenced by two factors. First, the size of the hole in the canopy, and second, the distance from the hole in the canopy to the ground. For a given size hole in the canopy, the closer to the ground, the smaller and brighter the sun fleck. In the picture below, the sunflecks are produced by the same size hole. Because both holes are letting the same amount of light through, the larger sunfleck doesn’t appear as bright as the small one.

 

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Sunflects produced by the same sized holes held 4 feet (left) and 4 inches (right) above the ground.

 

For holes in the canopy at the same height above the ground, the bigger the hole, the bigger the sunfleck. Both sunflecks below are produced by different size holes at the same distance above the ground. However the intensity of light in the sunflecks is the same.

 

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Sunflecks produced by different sized holes the same distance from the ground. Leftmost sunflect came through a small hole, the one on the right came from a much larger hole.

 

If you start thinking about the combination of different size holes at different distances from the ground, you can see that a vast array of different sunflecks are possible.

 So in a sense, these sunflecks on the trail are constant reminders that the sun is indeed the mother of us all.

 

 

 

 

 

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