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English Ivy: Forest Invader

By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester

 Photo 1

This Naturalist Note is dedicated to Phil Hamilton who passed away on June 12.  Phil devoted more than 24,000 volunteer hours helping make Tryon Creek State Natural Area the wonderful place it is today.  He played many leadership and resource roles, but is perhaps best known as the ‘King of the Ivy Pullers.’  He not only pulled a lot of ivy himself, but led hundreds of groups of ivy pullers out into the park.  Every time I went out with him, he told me something brand new about the forest that I did not know before.  He was a great role model, and helped many people get started on the track of volunteering at Tryon Creek.  I, and I’m sure many others, will remember this dedicated, knowledgeable and hard-working man forever.  Thank you Phil!

 

 

If there was a vote on the most despised plant at Tryon Creek State Natural Area (TCSNA), ivy would win hands down.  This aggressive, invasive plant outcompetes and displaces many native plants.  In an area near the Red Fox Trail where the ivy completely covered the forest floor, I removed and measured the ivy in a three-foot by three-foot plot.  In that plot there were 285.8 linear feet of the ivy vine.  (Yes, it was really thick, in multiple layers!)  If (and thankfully, it doesn’t) this density of ivy covered all of TCSNA there would be enough ivy to wrap around the earth at the equator more than 6 times!

Photo 2

Ivy harvested from a 3 ft. x 3 ft. area of forest floor.

 

 

Ivy’s habit of climbing up tree trunks makes it difficult to ignore.  Not surprisingly, ivy has many special features that make it so successful.

Photo 3

Ivy growing up a tree trunk near the Red Fox Trail.

 

 

Ivy:  The ingenious climber

Ivy needs sunlight to grow.  How does a plant get close to the sun?  Most trees, like our Douglas-fir (Pseudotsuga menziesii) develop a thick trunk that lifts their leaves up toward the sun.  Building the thick stem takes a lot of resources.  A study in western Washington showed that for 47-year-old Douglas-fir, 87% of the above ground biomass was in the trunk of the tree.  The major purpose of the tree trunk is to get the needles up into the sunlight where they can photosynthesize.  The ivy developed the habit of just climbing the tree trunks that were already there.  It saved itself all the energy required to develop a self-supporting stem.

 

I pulled down an ivy vine that was growing up the side of a tree.  The diameter of the ivy’s stem at ground level was 3/4 of an inch.  Twenty-one feet up the tree, it was not much smaller, as you can see below:

Photo 4

Cross section of a single ivy stem at ground level (left) and twenty-one feet high (right).

 

Since ivy doesn’t need a thick stem to hold itself erect, it uses its energy to grow taller.

In contrast, a western redcedar (Thuja plicata) only 10 feet tall growing along Old Main Trail had a basal diameter of 1.59 inches.  The redcedar needs this thick stem to hold itself up, while the ivy doesn’t.

Photo 5

Stem diameter a base of 21+ foot tall ivy and 10 foot tall western redceadar.

 

 

Not that ivy vines don’t grow large, especially when two or more vines merge together.

Photo 6

Cross section of a large ivy vine with red arrows marking the pith (“center”) of the three original vines.

 

Ivy only had to develop a method of holding onto the tree.  Voilà!  The aerial rootlet, which adheres to the tree’s bark:

Photo 7

Ivy stem (blue arrow) with aerial rootlets (red arrows) clasping the tree bark.

 

Using these aerial rootlets, the ivy manages to climb up the trunk of trees into the light without having to expend the energy to develop a big, supportive stem.

 

Creating a Home for Others

While we rarely envision ivy as a benevolent plant, other organisms may have a different view.  As you can see in the photo below, sometimes the mass of ivy stems creeping up a tree is part of a community complex most frequently involving moss or licorice fern (Polypodium glycyrrhiza).  While removing ivy from a tree near the Red Fox Trail, I collected the sample (in cross section) shown below.  It is a combination of primarily ivy and licorice fern, with a hint of moss.

Photo 8

Mat of ivy stems and roots mixed with licorice fern stems (red arrows) and roots from trunk of red alder.

 

The mass of roots, stems and miscellaneous dirt measured about 7 cm (~2-1/2 inches) thick.

 

How much water might this hold?  I cut a 2-1/2” by 3-1/4” sample from the tree.  I soaked it overnight in water.  I weighed the wet sample and then let it air dry completely and weighed it again.  I calculated that a square foot of this material would hold slightly more than 2-1/4 quarts of water.  This is a mixed blessing.  While some of this is a nice reservoir of water for the licorice fern growing in this mass, it is also a significant weight burden for the tree.

 

To find out how much water might be stored in the mass of ivy roots and licorice fern, I did some calculations.  I measured the diameter of the trunk of a large fallen alder tree near the Middle Creek Trail at 10 foot intervals, up to 63 feet above ground, where it started branching out.   Based on this data, I calculated the surface area of the tree trunk.  If the entire surface of this tree trunk were covered like the sample above, the ivy/moss/licorice fern could potentially contain up to 1,520 lbs. of water.  That’s three-quarters of a ton of water.  Yikes!

 

Ivy:  It’s Tough

Every species of plant contains nutritious chemicals like sugar, cellulose and dozens of others.  This naturally attracts other species that don’t have the ability to capture solar energy to sustain themselves.  One of the keys to a plant’s survival is to protect itself from these organisms, which range from molds and insects, all the way to humans.  In the picture below, you can see the surviving remnants of leaves on one of TCSNA’s common shrubs.

Photo 9

Damaged leaves on dull Oregon grape (Mahonia nervosa)

 

To find out how effective ivy is in protecting itself, I conducted a survey in the fall of 2016.  I examined the leaves of three species of plants, and counted the number of leaves (or leaflets) that were damaged.  To minimize the possible effects of humans, I examined sites more than 10 feet from a trail.  (Confession: I don’t actually know what caused the damage; it might have been insects, diseases, a hailstorm or whatever.)  For each species, I examined leaves in two different places (for example, near Red Fox Trail and near Old Main Trail), to get an “average” value.

The results are presented below:

                                 Number of                  Total leaves           Percent of

Species                damaged leaves               examined           leaves damaged

Red Alder                   181                                  199                          90.0%

Oregon grape            375                                  559                          67.1%

Ivy                                  93                                  279                          33.3%

 

Ivy has less leaf damage, whatever the cause, than either the red alder or the Oregon grape.  Good for the ivy!

 

Ivy is a Persistent Grower

Every plant has a growing season, and for ivy, it’s long.  To determine how long into the fall/winter this plant might grow, I measured the growth of an individual ivy stem along the Red Fox Trail.  The data shows that ivy continues growing quite late in the year.

Photo 10

In contrast to the ivy, on September 28, one of the Indian plum (Oemleria cerasiformis) plants I was monitoring in that area was completely bare of leaves, while the other Indian plum in that area had dropped about 98% of its leaves.

 

Ivy’s Secret Strategy

One of ivy’s secret strategies is that virtually every place along the stem where there is a leaf, there is the potential to grow roots.  That is seen in the photo below:

Photo 11

Ivy roots developed at every node on this stem.

 

Should the stem of this ivy plant be broken, no sweat!  Every part of the stem has its own root system and can stay alive.  This is in contrast to most woody plants which only produce roots at a single point in the plant.

 

English Ivy really isn’t that bad (a tidbit for geeks!)

It turns out that much, if not most, of the ivy that we have at the park really isn’t English ivy (Hedera helix); it’s Irish ivy (Hedera hibernica).  Not that the other plants care!

 

The key reliable morphological feature that discriminates between the two species are the miniature hairs that grow in clusters on the plant.  The Irish ivy hairs are in small clusters lying flat on the plant’s surface, while English ivy hairs are in larger clusters and stand erect.  The microphotographs below of plants collected at TCSNA shows the difference.

Photo 12

Left: Flat “hairs” on Irish ivy; Right: Erect “hair” clusters on English ivy.

 

To further complicate things, hybrids of English and Irish ivy have been discovered and….  Okay, I’ll quit now!

 

The Ivies:  Green Success Stories

The ivies in the genus Hedera are very successful plants.  They can grow tall without having to use their own stem to support themselves.  When hacked into pieces, many of the pieces are able to stay alive and become a whole new plant.  They also appear more resistant to disease and predation than many of TCSNA’s other plants.  They have a longer growing season than many of our native plants.  All of this spells success for the plant, and lots of work for our ivy pullers who are trying to encourage the growth of native plants by reducing the resource competition from the ivy!

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Native American Uses of the Forest

By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester

 

For thousands of years before settlers from the eastern United States or Europe arrived in the vicinity of what is now Tryon Creek State Natural Area (TCSNA), Native Americans called this forest home. The Native Americans used resources ranging from rocks to trees to animals. However, the basis for much of the Native American life was the plant life of this area. They relied on the forest and waterways for everything; food, medicine, tools, clothes, everything!

What kinds of plants did they eat?

There were lots of plants and fruits the Native Americans ate. Some of the more tasty items were the berries from the forest, like the salal (Gaultheria shallon) berries. Pictured below are the plant and berries. I’ve planted salal in my front yard, and they are delicious on my morning cereal!

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Salal plant, with salal berries in the inset at lower left

 

Another food the Native Americans sometimes ate were the berries of the Oregon grape (Mahonia nervosa). In the photo below, the blue-colored berries are almost ready to eat, while the greenish ones have a way to go before they are ripe.

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Oregon grape berries starting to ripen

 

I’ve tasted Oregon grape berries too. My taste buds’ response was, o-o-o-o-kay! I think they’re about half way between yummy and yucky. According to ethnobotanists, people who study how different groups of people use plants, the Native Americans would sometimes mash the fruits of the salal and Oregon grape together. In this way, they had a greater total quantity of food, which still tasted “kind of” good.

 

Another category of food plants is represented by the skunk cabbage (Lysichitum americanus) pictured below. This plant has a large underground tuber (note: potatoes are also tubers). Unfortunately, the skunk cabbage tuber tastes awful. It had to be specially prepared to become even edible. Ethnobotanists refer to this as a “starvation food” meaning that you only ate it when the alternative was starvation. If you’ve ever smelled a skunk cabbage in the spring, you understand why it wouldn’t necessarily pop into your mind as a good food item!

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Skunk cabbage plant and flower

What kind of medicine is in the forest?

For the Native Americans, the forest was their drugstore. Just one of the many medicinal plants used by some Native Americans was the licorice fern (Polypodium glycyrrhiza). The pictures below show the licorice fern growing on the side of a tree at TCSNA and the second photo shows a cleaned-up licorice fern plant that was growing on a branch that was blown down during a windstorm. The rhizome can be thought of as a perennial stem, while the leaves come and go with the seasons.

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Licorice fern growing on a tree trunk

 

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Licorice fern after removing the surrounding moss

 

The Native Americans cleaned up the rhizome of the licorice fern and chewed it as a cough and sore throat remedy. Once when I was not at TCSNA, I cleaned up a licorice fern rhizome and chewed it a bit. It does taste faintly like licorice. Within 30 seconds of starting to chew the rhizome, I got a tingle right in the back of my throat. Although I was perfectly healthy at the time, the fern was definitely affecting me. It would have been interesting to see the effect if I’d had a cold or sore throat.

 

What kind of tools did they find in the forest?

One of the tools the Native Americans found in the forest was the horsetail (Equisetum spp.), pictured below. This primitive plant contains a lot of silica crystals. Silica is the most common material found in sand. The Native Americans used this as a “natural sandpaper” for finishing their wooden tools. The effectiveness of this tool can be demonstrated by using it to polish a penny.

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Equisetum and polishing a penny with Equisetum

 

The effectiveness of polishing is shown in the “before and after” photos below.

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Two unpolished pennies (left)        Far right polished for 2 min. with Equisetum.

 

What kind of clothes did they make from forest plants?

The western redcedar tree (Thuja plicata) had many uses. To give just one example, its bark is very fibrous. With careful harvesting and care it can be used to produce everything from rope to clothes. Pictured below is a cedar bark rain hat. These were widely made and used by the Native Americans on the Pacific coast. According to some sources, they would sometimes treat this hat with pitch to make it even more water repellent.

 

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Native American cedar bark rain hat

 

But of all the clothing that the Native Americans made from forest plants, the one that always intrigued me was that they used moss for baby diapers. I wondered how well those would work. Strictly as a public service, I decided to run an experiment and find out.

You personally tested moss as diapers? Seriously?

Before your imagination runs wild (it may already be too late), let me explain. I took samples of five water-absorbing things:

  • A major brand of modern disposable diaper
  • A sponge
  • A pile of moss
  • A traditional cloth diaper
  • A bunch of paper towels

 

I weighed each item dry, making sure I had between 60 grams and 90 grams of each material (this is about 2 to 3 ounces). I then soaked each item (separately) in water completely covering the test material with water for 15 minutes. Then I put each material on a sheet of screen to drain. When the drops of water falling out of the material were 10 or more seconds apart, I considered the material to be completely drained. I then weighed each item wet. I calculated “absorbency” by dividing the weight of water absorbed by the dry weight of the material.

 

The results are displayed in the chart below.

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Modern diapers with their SAP (Super Absorbent Polymer) ingredient can absorb more than 80 times their weight in liquid! But let’s cut to the chase. I was fascinated to see that moss, the key ingredient in the Native American diaper could absorb 7.4 times its dry weight in water. In contrast, a classic 100% cotton, all-cloth diaper can only absorb 3.5 times its own dry weight in water. So the Native Americans were using the superior diapering material! Wow!

 

At home in the forest!

To the Native Americans, the forest was their home, their grocery store, their pharmacy, their hardware store, their everything! They adapted to their environment to meet all their needs.

 

Looking Back and Ahead

Weather and Climate: Looking Back and Ahead

By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester

 

Talk about a double whammy! The Portland area, including Tryon Creek State Natural Area (TCSNA), has set an all-time record for December rainfall, and the 2015 United Nations Climate Change Conference has just wrapped up in Paris! Lots of people are thinking about the weather and climate now!

The growth, survival and distribution of the plants at Tryon Creek State Natural Area (TCSNA) are affected by a host of factors. These factors include climate and weather, but also things like soil chemistry, soil depth, the steepness of the slope the plant is growing on, and soil moisture holding capacity. Probably the two most important weather variables are temperature and rain fall. Most of the discussion around climate change has to do with increases in the mean annual temperatures. This is a good place to start, but perhaps inadequate to explain all the changes we might see.

 

So how might climate change effect our forest?

Climate change might affect TCSNA in many ways, for example, altering the species composition of the forest. I am in my third year of monitoring the growth and development of a variety of plants in my phenology study at TCSNA. In my monitoring I visit the same plants every week to ten days and record their status. Perhaps looking at some of the results might provide a peek into the future. One of the species that I am monitoring is Pacific waterleaf (Hydrophyllum tenuipes). As the waterleaf tends to form dense clumps, I am monitoring approximately a 3-foot diameter circle of plants at each of four separate areas, rather than just trying to track a single stalk.

Pacific waterleaf is a perennial plant, which sends new shoots up every year from rhizomes. Think of rhizomes as “underground stems”. The above ground shoots die back in the “off season” and only the roots and rhizomes persist from year to year. At TCSNA waterleaf is generally from 40 to 60 cm (16 – 24”) tall at maturity. These shoots die back sometime in the summer, generally after they have produced a crop of seeds.

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Pacific waterleaf near Red Fox Trail

 

Reviewing the phenological records, the last two years have seen a lot of variability in the behavior of the Pacific waterleaf at TCSNA. The chart below indicates the presence or absence of waterleaf leaves at each of the four monitoring sites on a weekly basis.

Weekly Presence/Absence of Pacific Waterleaf at Four Locations at TCSNA over Two Years

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Key:  Yellow = Waterleaf Absent; Green = Waterleaf Present;

Week 1 = first week in January, Week 26 = end of June, Week 52 = last week of December

The late-winter through early-summer growth is the time when the waterleaf is making the vast majority of its sugar to support the plant, AND when the plant is producing seeds. The second emergence of leaves is around weeks 40 to 45 (roughly October thru early November). This “second leafing out” produces leaves that tend to be fairly small and I’ve never seen this second leafing produce flowers, much less seeds. And, as you notice, there is a certain amount of “now you see it, now you don’t” with this second leafing out. In at least some cases, the second leafing out leaves are eliminated by a serious frost.

It is interesting to note that on the Middle Creek Trail, there is never a “second leafing out.” The major difference between the Middle Creek waterleaf patch, and all the others is that the Middle Creek patch is on a significant slope, and is more exposed to direct sunlight. All the other patches are on flatter sites. Thus, it may dry out sooner than the other patches, and not have the late-season water it needs for a second set of leaves.

Why are these years so different?

  • One thing that you can see immediately is that the green bar (indicating the presence of waterleaf plants) consistently ends earlier in 2015 than in 2014 for any given site. In 2015 the leaves disappeared on average 7 weeks earlier than in in 2014. This is a significant amount of time.
  • The seeds of the waterleaf mature approximately in mid-June, so in both cases the plants survived long enough to produce seeds, and nothing more. It is likely that the leaves which persist after seed production are producing sugars to help support the plant for the next growing season.

What could have caused that difference?

The contrasts in weather between 2014 and 2015 are dramatic. I think the weather data probably goes a long way in explaining this year-to-year behavioral difference.

First let’s look at the (Portland) air temperatures maximum and minimum for the years. In each chart, the highest average minimum or maximum air temperature is highlighted in color. Where the temperature for any month was more than 5° F higher than any other year, it is highlighted in red.

Average Daily Minimum Air Temperature – Portland

(In °F; higher year highlighted red)

Month 2014 2015
January 35.1 37
February 34.6 41.5
March 40.2 42
April 44.7 42.6
May 51.3 51.5
June 53.9 57.9
July 59.8 61.1
August 61.4 60.5
September 56.5 53.1
October 52.1 51.2
November 40.7 38.5
December 39.1

 

You can easily see that for most of the spring and early summer months, the minimum temperatures were higher in 2015 than in 2014. But that’s just the start. The next chart tells us even more.

Average Daily Maximum Air Temperature – Portland

(In °F; higher year highlighted in red)

Month 2014 2015
January 47.7 49.9
February 46 56.8
March 58 62.8
April 62.6 62.9
May 71.1 70.7
June 73.4 82.7
July 83.8 86.7
August 84.8 84.3
September 78.7 75.8
October 68 69
November 51.9 52
December 49.2  

 

Again, for most of the spring and early summer months, the average maximum daily temperature was higher to dramatically higher in 2015 than in 2014. The yellow-highlighted months are more than 5°F warmer than the comparable month in 2014. The average high temperature in June 2015 was almost 10° F higher than June 2014! This higher temperature would probably cause the plants to lose more water, produce less sugar, and grow less in 2015 than they did in 2014. But the icing on the cake is yet to come. Just take a look at spring/summer rainfall data (from the PCC Sylvania rain gauge station).

February through June Rainfall

(Inches)

Year Amount
2014 22.76
2015 13.42

 

Wow! The early growing season rainfall in 2014 was nearly twice what it was in the comparable time in 2015.

The “growing season” for Pacific Waterleaf in 2015 was both hotter and drier than it was in 2014. The result was that the above ground waterleaf shoots disappeared on average 7 weeks earlier. Yikes! A seven-week difference in leaf persistence is not trivial.

 

The future!

I can’t wait to see what kind of impact this has on waterleaf in the 2016 season.

Think of all the linkages that there may be between waterleaf and the other organisms in the forest. Possibly less food for waterleaf-eating insects, less cover for mice scurrying around looking for food, fewer waterleaf seeds for food, and possibly increased soil erosion from late summer rainstorms.

This is the story of just one species of plant, but it might foretell the challenges we face if climate change continues unabated.

 

 

 

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