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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!

Trillium Trivia

By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester

 

Western trillium (Trillium ovatum) flowers are a major attraction at Tryon Creek State Natural Area (TCSNA).  I’ve already written three Naturalist Notes about this plant.  In the process I’ve accumulated a host of materials that didn’t fit too well with any of those previous notes; the time has come to share them.

 

How big do trilliums grow?

From May 4 through May 6, 2016, I conducted a survey of trilliums that were growing more than 10 feet from any trail.  The areas I surveyed were near the Equestrian and North Horse Loop Trails in the northern part of the park, Center, Big Fir and Old Main Trails in the central part of the park, and Iron Mountain Trail in the southern part of the park.  For each triple-leafed trillium I encountered I measured the distance from the ground to the attachment point of the triple “leaves.”  I also noted whether or not each plant was flowering.  The results are shown below.

 

Photo 1

 

Ten inches is about the height where the plants shift from non-flowering to flowering, although a couple of very short plants flowered, and a few fairly tall ones didn’t.

 

What happens to the trillium’s flowers and seed pods?

Ideally, the flowers are pollinated, the seed pods (or capsules) mature, then open and release their seeds into the forest.  Of course there are other possibilities.  Deer, it has been reported, sometimes eat the flowers.  The contents of the maturing seed pod are very nutritious, and researchers have reported that both deer and mice sometimes eat the seed pods.

To assess this, I conducted surveys in two different years.  The first survey was conducted between June 23 and 28, 2015.  Two groups of trilliums were surveyed.  “Trailside trilliums” were those growing within 10 feet of the trail.  “Mid-forest trilliums” were those growing more than 10 feet from the trail.  It should be noted that at this time the seed pods are well along the path to maturity.  The plants were placed in three categories: a) capsule intact, b) pedicel only, meaning the plant had flowered, but the flower/seed capsule was missing, and c) did not flower, as indicated by having no pedicel or capsule.  Illustrations of each class are below:

 

Photo 2

Capsule intact

 

Photo 3

Pedicel only

 

 

Photo 4

Did not flower

                           

 

The results are shown below:

 

Photo 5

Plants within 10 feet of trail

 

Photo 6

Plants more than 10 feet from trail

 

A statistical analysis (Note to nerds:  I used the Chi-squared test.) clearly shows that a significantly higher percentage of the trailside plants flowered compared to plants growing more than 10 feet from the trail.  The cause of this difference cannot be determined by this study.  The other statistically significant difference between these two groups is that a higher percentage of the “mid-forest” trilliums only had a pedicel (“flower stalk”), which means that either the flower or the seedpod was removed.  Animals likely ate these seed pods or flowers.  Perhaps the deer are more comfortable eating in the middle of the forest than trailside.

In 2016 I undertook a second trillium survey, this one was conducted May 4 through May 6, at a time when the last of the trillium petals had just recently fallen off the plants.  This time, however, the “trailside plants” I tallied were within 3 feet of the trail.  The “off-trail plants” were growing more than 10 feet from a trail.  At this time the seed capsules were small and immature.  The results are shown below:

 

Photo 7

Off-trail plants

                                                         

Photo 8

Trailside on Cedar, Red Fox and Middle Creek Trails

 

Photo 9

Trailside on Old Main           

 

Once again, the percentage of plants flowering was statistically significantly higher in the trailside plants compared to plants growing “off-trail”.  A slightly smaller percentage of the flowers/seed-capsules had been eaten than in the previous study, probably because there was a shorter period of time for the animals to eat them, or perhaps, being smaller, they were of less interest to the animals.  The one thing that clearly stood out in the data is that the percentage of reproductive structures missing was significantly higher along Old Main Trail than along the other trails.  (Geek note:  Statistically, there is less than a 1 in 10,000 probability that the higher percentage of missing capsules observed along Old Main was due to chance.)  The fact that Old Main is one of the most heavily traveled trails makes it tempting to speculate that people were picking these flowers, as shown in the picture below, but this study cannot prove that.

 

Photo 10

Freshly plucked trillium flower lying on the trail.

An alternative explanation for the empty pedicels is that the flower was defective and the defective bloom was aborted.  I recently saw a single dysfunctional bloom in the forest.  It appears that the plant started to produce a functional flower, but something bad happened along the way, as in the example below, where you have what appears to be an attempt at a flower, but no actual petals.

 

Photo 11

“Failed” flower on a trillium plant.

 

Does it really take 7 years for a trillium to recover after the flower is picked?

Many people believe that if you pick a trillium it will be 7 years before the plant flowers again.  I unexpectedly got a chance to test that theory when someone picked 6 trillium flowers on a plot of trilliums I had been studying for 5 years.  I concluded these had been picked, because the remaining stems did not exhibit the type of cut associated with animal browsing.  One of the stems from which the flower had been picked is shown below:

Photo 12

Stem from which trillium was picked.

 

Although very unhappy, I decided to capitalize on the tragedy.  (“When life hands you a lemon, make lemonade!”)  I carefully documented the exact location of the trilliums.  Based on the location of the six flowers, it appeared that all of them were twin stems, arising from a total of only three rhizomes (rhizomes are like a flower bulb).

In April 2017, one year after the tragedy, I surveyed the site again.  I went to the site and measured the location of the trilliums.  Based on their location, 2 flowering stems were within ½” of the location of the flowering stems that were decapitated last year.  Thus I concluded that only 2 out of the 3 effected rhizomes produced flowering stalks again this year.  However, whereas last year they were twin-stalked, this year they only had one stalk each.  At the location of the third picked trillium, there was nothing.  Scientists have determined that some years a trillium will occasionally just take a rest, and not produce an above ground stem.  So that is what this one did, OR it died.  I don’t know which.  Either way, for at least two of the plants, the “7 year” myth is debunked.

 

Does anything eat trilliums?   

Deer are commonly reported to eat trilliums.  But it turns out that isn’t the whole story.  This spring I ran across one of our slimy forest friends deeply engrossed with a trillium.  Note that this is not our native banana slug (Ariolimax columbianus) but appears to be one of the non-native species.

Photo 13

Slug in a trillium flower

 

You’ll notice that considerable chunks of the trillium petals are also missing, and these may only have been the prelude to the slug’s full scale attack on the heart of the trillium flower.

 

What pollinates trilliums?

Most of the plants we hear about are pollinated by bees, like our Pacific waterleaf (Hydrophyllum tenuipes), or by the wind, like Douglas-fir (Pseudotsuga menziesii).  Trilliums are a little different.  A study of Trillium ovatum in southern Oregon determined that pollinators included several species of beetles, honey bees, bumble bees, crab spiders and geometrid moths1.  Since the trillium doesn’t produce nectar, at least some of these creatures are here to eat the pollen, and they spread the pollen as an unintended side effect.

 

Photo 14

Pollen-coated insect in a trillium flower

Photo 15

Pollen-carrying stinkbug in trillium flower

Photo 16

Unidentified insects (the “brown things”) converging on a trillium flower

 

 

The lesson…

The forest is endlessly fascinating, when a person just stops to observe.  Looking back on my old trillium photos, I now see lots of the “little brown bugs” deep down in the bloom.  How could I have missed that so often?  When you’re out in our forest, stop for a minute and look around.  I think you’ll be amazed, as I was, at how many interesting things are out there.

_____________________________

1Jules, Erik S. and Beverly J. Rathcke.  1999.  Mechanisms of Reduced Trillium Recruitment along Edges of Old-Growth Forest Fragments.  Conservation Biology 13:784-793.

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.

 

photo-1

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.

 

photo-2-and-3-combined

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

 

 

photo-4-and-5

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.

 

photo-6-and-7

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!

 

photo-8-and-9

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.

 

photo-10-and-11

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.

 

photo-12-and-13

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.
 

photo-14

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.

___________

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.

 

 

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