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Sic Transit Gloria Mundi

By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester

 

The forest at Tryon Creek State Natural Area (TCSNA) contains marvelous plants that we can enjoy at different seasons for different reasons.  They range from the beautiful trillium (Trillium ovatum) blossoms in the early spring to the bright red leaves of the vine maple (Acer circinatum) in the fall.  But these individual displays of beauty are transitory, as are the plants themselves.  This is summed up in the Latin title of this note which means: “thus passes the glory of the world.”1

 

I started a phenology study in mid-2013.  This involved, for the most part, identifying and tagging specific individual plants and monitoring their developmental stages each year.  These stages were things like when I could first see the veins on the new leaves, and the first time I found open flowers on the plant.  Now, just five years later, I am surprised at how many of those individual plants I was following have died in that short timeframe.

 

Plants are Persistent 

As we realize, plants are persistent.  In the photo below, you see the result of a very old injury to the trunk of a Douglas-fir (Pseudotsuga menziesii) growing at TCSNA.  Long ago, the upright shoot of this tree was damaged or killed, and several side branches competed to take over the role of “leader.”  The branches marked with red arrows lost the race to become leader and are now dead.  The branch indicated by the blue arrow won, and became the leader so successfully, that it looks almost like it was always the leader.  Several branches that were lower down the tree when the top was lost are marked with green arrows, and they remained horizontal.

 

Photo 1

Douglas-fir near Old Main Trail that recovered after losing its leader.

 

Another example of a persistent plant is this mature black cottonwood (Populus trichocarpa) located alongside the Old Main Trail.  Normally, mature black cottonwoods don’t have little branches popping out along the main trunk.  However in this case, the reason can be seen in the wet dark seepage at the base of the tree.  This tree appears to be infected with some microorganism (Fungus? Bacteria?) which is excreting a smelly fluid out of a crack in the tree.  When Ranger Deb and I bored into the tree, the heartwood was definitely wet and smelly, evidence that it was decaying.  In these cases, the tree doesn’t do such a good job of controlling the sprouting of the buds on the tree trunk.

 

Photo 2

Basal sprouts on a cottonwood, and leakage (red arrow) from the diseased tree.

 

Finally this Douglas-fir near Old Main Trail, which still has many green needles, sports numerous fungal fruiting bodies which indicate it is heavily decayed.

 

Photo 3

Bracket fungus on a live Douglas-fir near Old Main Trail.

 

Plants are persistent, but…

Sometimes the trees have problems from which they never recover.  The red alder (Alnus rubra) pictured below probably just aged out.  Estimates of what constitutes “old age” for an alder varies from 60 years to a maximum of 100 years.  Red alder is a species that likes full sun light and most frequently gets started on disturbed sites.  So no surprise that we would find one this size dead.

 

Photo 4

Dead alder at Tryon Creek State Natural Area; Trunk view (l) and crown view (r).

 

A little more surprising is the dead western redcedar (Thuja plicata) pictured below.

 

Photo 5

Me (left) and dead western redcedar (right) near North Horse Loop Trail.

 

This species is very shade tolerant, and under normal circumstances commonly lives several hundred years.  So why is this relatively young tree dead?  My best guess is based on the fact that this was found on the uphill side of the trail.  Trails often serve as unintentional “dams” to the normal flow of underground water (great example:  Old Main Trail near the Nature Center).  A couple of years ago we had an extraordinarily rain-soaked winter season and I hypothesize that this cedar got “drowned out.”  Yes, cedar frequently grows in wet-ish areas, but there is a limit to everything.

 

Individuals from several shrub species have recently died as well.  This red elderberry (Sambucus racemosa) located just off the Old Main Trail (pictured below) is the plant that began my awareness of this topic and thus this whole article.  This plant died before the recent winter with heavy rains.  It was the first plant which was part of my multi-year phenology study that died.  Additional walks around the park revealed many other dead elderberries.  Again, it appears to be a fairly short-lived plant.

 

Photo 6

Dead red elderberry (see red arrows) near Old Main Trail.

 

Photo 7

Stem of 11-year-old, 2 cm diameter, dead red elderberry with large pith (red arrows) in center.

 

Perhaps the most dramatic die-off I’ve witnessed occurred near the upper section of the Red Fox Trail.  Last year I noticed that many of the Indian plums (Oemleria cerasiformis) seemed to turn yellow and lose their leaves a little earlier than normal.  This year, a relatively large number of them never leafed out.  I laid out a 1/20 acre plot (a circle with a radius of 26.3 feet) and counted all of the Indian plum stems.  I also measured their diameters at ground level.  To the best of my ability, if I was able to determine that multiple stems were part of a single plant, I only measured the largest stem.  Important confession:  I chose an area with a very high density of dead stems.  The results are summarized below:

 

Photo 8

 

Photo 9

Numerous dead Indian plums (marked by circled orange flags) near the Red Fox Trail.

 

In some cases these plants were quite large, both in height and diameter.  I laid one of the stems on the sidewalk near the top of the Red Fox Trail to make it easy to see.

 

Photo 10

Dead Indian plum stem 3.3 meters (about 11 feet) tall.

 

I selected a few of the larger Indian plums, and counted the annual rings at the base of the stem.  They were between 15 and 19 years old.

 

As a final example, I’ve also noticed this year a number of dead salmonberry (Rubus spectabilis) in the forest.  I don’t think this is the result of some climatic fluke or disease, because there are also a very large number of healthy salmonberries in every area where I’ve see a dead one.  One example of a dead salmonberry is pictured below:

 

Photo 11

Dead salmonberry plant 2.1 meters (about 7 feet) tall.

 

Below is a cross-section of stem from a dead salmonberry.  Note the relatively large whitish pith in the center.

 

Photo 12

Cross section of five-year-old dead salmonberry stem 2 cm diameter (about ¾ inch)

 

 

And let’s not forget the animals

Sometimes animals play important roles in the life of plants.  A couple of years ago, beavers decided that a lot of the young cedar trees near Obie’s Bridge were ready to eat, and went in for the harvest.  The results were evident by the number of chewed off stumps, like the one seen below.

 

Photo 13

Beaver-chewed western redcedar stump near Old Main Trail.

 

 

“This too shall pass”2

The forest we see today is not the forest we will see tomorrow.  Barring huge environment shifts, the major trend that we should expect is that much of our uplands forest will evolve to a predominantly redcedar-hemlock forest type.  Douglas-firs will be relegated to a tiny role.  Red alders may persist in some of the bottomlands near the creek.  This of course will bring some shifts in the animals that inhabit our forest as well.  It will be different, but still just as fascinating as it is today!

 

_____________

1Documentation on the web indicates this phrase was used as early as 1409 during the installation of the Pope.

2According to Wikipedia, this is an ancient Persian expression that worked its way into the English language sometime in the 1800s.

 

 

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Phenology in the Forest

By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester

In the forest, like much of life, timing is everything!  It’s why most animals have their young in the spring or early summer when food is abundant.  It’s why most plants don’t bloom in December, when there’s a good chance that their flowers would be killed by a subsequent frost.  The study of the timing of different biological events is called “phenology.”

 

What’s a Phenology Study?

A phenology study involves identifying when different organisms enter different stages of their life, or behave in particular ways.  My phenology study focuses largely on plants.  Plant phenology frequently involves studying the behavior of selected individuals over the course of several years.  Some “events” in a plant’s life that can easily be tracked are, for example, when the veins on the new leaves are first visible (aka, bud break), or the first time you can see the sex organs inside of a flower.

I started the phenology study at Tryon Creek State Natural Area (TCSNA) early in 2013.  For this study I tracked ten different species growing along 4 different trails at the park; Red Fox, Old Main, Cedar/West Horse Loop (referenced here as “Cedar”) and Middle Creek/Big Fir (referenced here as “Middle Creek”).  For perennial species with above ground parts, I tagged the plants and followed them each year.  For annual plants, or those species arising from underground organs, I identified a given patch of ground and studied plants at that location.  As time went by, I started including observations on a few other species like a delightful patch of bleeding hearts (Dicentra formosa), and some spittlebug nymphs (suborder: Auchenorrhyncha).

I made observations on a weekly basis, with a few exceptions caused by vacations, and extreme weather conditions.  For a couple of reasons, mostly related to “learning curve” issues, I starting collecting useable data in 2013 part way through the growing season.

One of the challenges in conducting a phenology study is the issue of when you should report the results.  In this case, the differences I observed between 2016 and 2017 are dramatic enough that it is time to provide you with a report.  This probably won’t be my last phenology report, “God willing and the creek don’t rise” (to use an old expression).

 

The Drivers of Plant Development

Plant development is driven by several factors, key among them being day-length, temperature and moisture availability.  When it comes to spring budburst in our area of the world, temperatures probably are the primary driver.

The temperature plays two important, and quite different, roles in bud break.  The plant needs to hold off on bud break until the threat of a killing frost is past.  Thus most perennial plants in our area have a “chilling requirement.”  This means that the buds have to experience a certain amount of chilling before they can start growing.  Secondly, the buds have a “forcing requirement” which is a certain amount of warm temperatures to get the buds growing after the chilling requirement has been met.  As anyone who has ever walked through the forest in the spring knows, these requirements vary dramatically between different species of plants.  If the plants receive less than the normal amount of chilling curing the winter, they will need a greater amount of warm “forcing” in the spring.  Although it is clear from the diagram that there is at least some minimal amount of chilling needed to ensure that the buds will eventually open.

The diagram below shows the generalized nature of the relationship of chilling and forcing for both Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla).  While the curves have a basically similar shape, it is apparent that with low levels of chilling, the hemlock will break bud first, but with large amounts of chilling, the Douglas-fir will break bud first.

Chilling and forcing requirements of Douglas-fir and western hemlock1photo 1

            Photo 2

 

In reviewing these bud break results, please be aware that there is very little agreement on the exact temperature that separates the “chilling” and “forcing” functions.  I believe most scientists would think 50 degrees is little bit too high, but to be blunt, this is the base I used because it is the best database to I have available.  As you can see in the chart below, there have been dramatic differences between years in the number of growing degree days in the first three months of the year, primarily that 2017 has a much cooler spring.

 

Photo 3

Week

photo 4

*Data from the Aurora Airport, approximately 15 miles from TCSNA.

 

So What Happened?

Presenting even a summary of all the data I collected would be a sure cure for insomnia, so I’ve picked out a couple of examples from the study which are fairly typical of the general trends.  The first example is to look at the behavior of the Pacific waterleaf (Hydrophyllum tenuipes).  This is a plant that has underground roots, stems and buds.

The graph below shows the results for the years 2015 through 2017.  On average, the appearance of the first leaves in spring 2017 was delayed an average of 2.5 weeks from the first appearance of leaves in the prior two years.  (And yes, the absence of data for the week of Feb 11, 2015 is unfortunate!)  The date of first flowering in 2017 was on average 3.0 weeks later than first flowering in 2016.   The primary lesson here is that both budburst and flowering in 2017 was much delayed compared to the two prior years.  Interestingly, the average date of when the last leaves died was nearly identical in 2016 (33.0 weeks) and 2017 (33.75 weeks).

 

Photo 5

Development of Pacific waterleaf on four trails between 2015 and 2017

 

Similarly, the leafing out of the vine maple (Acer circinatum) was also delayed about 3 weeks in 2017, as seen in the chart below.  For the vine maple, so few of the plants I followed produced flowers on a regular basis that the data is probably not worth presenting, although what data there is follows the same general pattern as the Indian plum above.

 

Photo 6

Leafing Out and Leaf Retention Times for Vine Maple

 

photo 7

Growing Degree Days (50o degree base) for 4 Years

 

At first glance, these lines all look fairly similar.  However, looking at Week 20, for example, the number of growing degree days in 2016 is about double the number for that same date in 2017.  This is a huge difference!

The final set of plant data that I will include here is for snowberry (Symphoricarpos albus), a reasonably common, but not abundant shrub at TCSNA.  Here again, both the budburst and flowering of these plants is three to five weeks later in 2017 compared to 2016, as seen in the graphs below:

 

Photo 8

 

And it’s not just plants

 Below is a chart of the sightings for two years of spittlebugs.  In the beginning of 2016, if there were no spittlebugs seen, I just left the space on my datasheet blank.  Midway through that year, I recognized the folly of that approach, and started making a clear record showing that no spittlebugs were seen.  My notes on the March 2016 spittlebug indicate that it was just one individual bug, and a small one at that.  Sometimes Mother Nature will show off one specimen of something way out of season, but that probably doesn’t really mean the season has started.  No matter what you think about the March 2016 outlier, it is abundantly clear that the spittle bug, like many of its botanical associates, was late in 2017 by at least three weeks.

 

Photo 9

 

The Connection to Global Warming

As documented here in the differences between the various years, the organisms in the forest are sensitive to environmental temperatures.  This will be very important as we consider global warming, and what we should do about it.  I love the fact that Mother Nature provided us with a great example of the fact that the trend of global warming is not a straight linear process, but will have some hiccups like 2017.  By the way, the early readings from this year (2018) show that some plants are starting growth way earlier than they did in 2017.  But that’s grist for another note at least a year away.  A fascinating aspect to this, which we may be many years away from experiencing, is that almost all woody plants require a certain amount of chilling before they break bud.  If global warming ever gets to the point where the winter temperatures are not adequate to chill the buds, already completed research tells us bud break will be significantly delayed.  Then we could have real problems.  But for now, enjoy the forest that we have!

 

1Harrington, Connie and Peter Gould.  2016.  Rise and Shine: How Do Northwest Trees Know

When Winter Is Over?  Science Findings, Issue 183.  USDA Pacific Northwest Research Station.

“When Autumn Leaves Start to Fall”…or Not!

By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester

It’s a sure sign of autumn at Tryon Creek State Natural Area (TCSNA) when the leaves start to fall.  However, the time of leaf fall can vary dramatically between species.  I became aware of this during the past 5 years of my phenology study.  This phenology study involves visiting more than 60 specific selected plants at TCSNA every week to ten days throughout the year.  I make notes on the stage of development of each plant on each visit.  For example, I note stages of development like “buds open enough to see leaf veins”, “flower’s stamens visible” or (in the autumn) “last leaf has fallen.”  This year, for example, every one of the vine maples (Acer circinatum) in the study had lost all their leaves by November 22nd.  In contrast, several thimbleberries (Rubus parviflorus) still had numerous green leaves as late as December 13th.  This is a difference in leaf fall between species of more than 3 weeks.  Sometimes the difference in the date of leaf fall varies dramatically even on the same plant.

This year I found numerous examples of extra-long leaf retention in several plants.  These plants appear to have differences in time of leaf fall for one of two different reasons.

 

Adventitious Buds

Adventitious buds are buds that form from normal plant tissues.  Oftentimes they arise from the cambium, the layer of soft, actively dividing cells just under the bark of woody plants.  Normally the cambium cells just differentiate into either bark or woody stem cells.  Most plants, like Douglas-fir (Pseudotsuga menziesii) and bigleaf maple (Acer macrophyllum), recognize that the energy they need for growth is coming from the sun up above.  Their secret to success is growing tall, where they can reach above most plants, and bask in the full sunlight.  To do this, these plants want to direct as much energy as possible into the shoots that are growing straight up towards the sun.  The apices of these plants “control” the growth of side buds and shoots by producing a chemical named auxin.  The chemical structure of auxin is shown below.

 

Photo 1

The chemical structure of auxin

 

This auxin is produced at the tip of the dominant stems.  As the auxin is transmitted down the stem, the message that this chemical delivers to the lower buds is “don’t grow” and “don’t develop new buds” depending upon the exact circumstances.  When the top of the tree, or the tip of a branch, is killed or broken off, the auxin no longer flows down the stems, and eager lower buds start to grow out.  In some cases, brand new buds are formed along the stem, and take off like a rocket!

One of my favorite examples of this at TCSNA is found on a Pacific yew (Taxus brevifolia) tree along the Cedar Trail.  The tree blew over during a storm and the trunk lay across the trail, although some roots were still in the ground.  On January 22, 2017 I cut off the trunk to allow the trail to be more accessible.  But the big news was months later.  All along the remaining trunk, brand new little yew branches were growing out, no longer inhibited by the top of the tree, as shown in the picture below.

 

Photo 2

Me sawing off the top of a yew tree which feel across Cedar Trail. Note the trunk is bare of sprouts.

 

Photo 3

Same yew trunk on August 10th showing new sprouts

 

Another example started last spring when a trail maintenance crew cut the top off a lot of shrubs along the Red Fox trail.  This produced results similar to what happened on the Pacific yew.  One of the plants they cut back was the hazel (Corylus spp.) shown below.  The black arrow is pointing to a stem which has lost all of its leaves, and in fact, almost all of the plant has lost its leaves.    In contrast, the purple arrow points to one of the two stems on the plant which is still holding onto its leaves.

 

Photo 4

Hazel (Corylus spp.) bush on November 29, 2017

 

So what’s the difference?  Note the blue and red circles in the picture.  The blue circle shows where a major stem of the plant was cut off by the trail maintenance crew between May 30 and June 6.  On this particular plant, the leaves had started growing about March 8 and were approximately 2 inches long at the time the bush was trimmed back.  The removal of this main stem liberated buds on the lower parts of the stem.  These liberated buds began to grow (note purple arrow and red circle).  So these adventitious shoots and their leaves were much younger than the shoots and leaves of the other parts of the plant.  These young leaves stayed on the plant much longer than the “normal” leaves.

Two other examples of this phenomena are shown below.  The first is a red huckleberry (Vaccinium parvifolium) which was also pruned off (note red arrow).         

 

Photo 5

Adventitious shoots on a red huckleberry near Red Fox Trail.

 

 

 

Photo 6

Normal shoots on a red huckleberry near Red Fox Trail.

 

 

 

The final example is an Indian plum (Oemleria cerasiformis) plant.  Here the branch tip appears to have been randomly broken off, rather than cut off, but the end result is the same.  All the leaves on this plant, except some leaves on the small shoot shown in the left picture had fallen off by September 28th.  The fact that this one leaf is still green and healthy 10 weeks after all the “normal” leaves had fallen off the plant is astounding.

 

 

Photo 7

Leaf on an adventitious shoot on December 13th on an Indian plum growing near Cedar Trail.

 

Photo 8

Leaf on a normal shoot on December 6th on the same Indian plum as above, growing near Cedar Trail.

 

 

Buds:  Preformed or Neoformed?

The second reason that some leaves might hang on longer than others is due to when the leaves are formed.  For example, in overwintering Douglas-fir buds, each of the needles that will appear the following growing season is already formed.  You can see these “baby needles” as little whitish bumps (red arrow) in the picture below after all the bud scales (blue arrows) have been cut off.

 

 

Photo 9

Dormant Douglas-fir bud after removing the protective scales.

 

 

In contrast to these “pre-formed” buds, some plants have a different (“neoformed”) growth strategy.  In these plants, new leaves (“primordia”) will be initiated during the spring and summer as long as growing conditions are favorable.  These primordia will immediately start to develop into leaves.  Thus on one plant, there will be leaves of vastly different ages.  Not surprisingly, the older leaves will drop off before the younger ones.  One example of this at TCSNA is the red elderberry (Sambucus acemose).  I took the pictures below of one plant on December 6, 2017 at TCSNA.

 

 

Photo 10

Buds. but no leaves on lower branches on a red elderberry along Cedar Trail.

 

Photo 11

Healthy leaves on the upper branches of a red elderberry along Cedar Trail.

 

 

This continual development of new leaves is illustrated in the chart below of the length of 3 different leaves throughout the growing season, until somehow the plant’s stem was severed.

 

Photo 12

Leaf length of the 7th, 8th, and 9th leaves on a red elderberry stem.

 

 

Photo 13

Tip of red elderberry stem (in winter) which is dead beyond the pair of red-brown buds

 

 

The elderberries’ strategy is successful although when the end of the growing season comes, the youngest segment of the twig hasn’t had a chance to produce viable buds, and the twig beyond the last pair of viable buds just dies.

 

There’s more than one road to success

Mother Nature has produced many species of plants, which use a variety of strategies to achieve success.  Two of the strategies involve leaf and shoot development.  As illustrated above, the first strategy involves focusing the plant’s energy on the development of just a few leading shoots and suppressing the others.  However, Mother Nature knows that bad things happen, and if those leading shoots are killed or injured, tissue lower down on the plant can create branches that will take over and keep the plant alive.  The second strategy involves having a stem that just keeps elongating and producing new leaves as long as the weather is good.  Both strategies have been successful, and add more interest to our forest.

 –All photos by Bruce Rottink

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