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Owen Sholes

Living in the New England countryside

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Give Them Space

Our old science building, from the 1960s, had only one room that was easily available to students, and it sucked.  The table was too big, leaving hardly any room for chairs.  And the chairs were all rejects from elsewhere, and all were uncomfortable.  

But there were always students in that room, doing whatever they had to do, conversing with one another, bursting out to find one or more faculty, whose offices were nearby, or to go to classes, which were also nearby.  Proximity was a major reason why they used this horrible space.  So was the simple act of getting together.  Space mattered.

So when we designed our new science building (early 2000s), we wanted to include lots of student space, and the architects helped us get it.

There are expanded areas near landings and along railings, most of it close to classrooms and not far from laboratories.  The soft chairs and small tables are used throughout the day.  

We made clusters of faculty offices, and left a common area in each cluster with a table, white board, and simple, comfortable chairs.  Some areas also have a microwave and mini-fridge, which students often ask to share, hardly ever abuse, and have never stolen.

There are also dedicated study rooms with tables and comfortable chairs.  They have glass walls and lots of windows with nice views.  While we were arranging the new furniture, the students helping us suggested that we add white boards.  So we added white boards.  We prevented faculty and administrators from reserving these rooms for meetings (the person in charge of reserving rooms was kind enough to take them off the list).  Students always have priority.  Students use these rooms all the time, write on the white boards all the time, and when they are preparing for exams, write on the glass walls, too.  Yes, dry erase marker can be erased from glass.

One entrance to the building has a three-story atrium, and there are soft chairs, a few sofas, and small tables.  Sometimes events require additional tables and chairs for a conference or meal, and students love to sit at the tables before and after the event for as long as the tables are present (no, they don’t mess up any tablecloths).

Another entrance has a two-story foyer and a small, carpeted area with a two chairs.  These were the only wooden chairs we put in the building, and they are hardly ever used.  We hadn’t expected them to be used because of the high traffic so close to the entrance, so we put in these exotic-looking chairs that were visually attractive, but uninviting.  When someone brought a soft chair from another building, it was immediately used a lot.  We should have put in soft chairs from the start.

Above that entrance is a balcony near three faculty offices and a conference room.  We put in soft chairs and a small table, but students hardly ever sit there, and we still aren’t sure why.  Maybe it’s because the conference room is often available, and has a white board.  Maybe it’s because there are decent chairs in the nearby common area shared by the faculty offices.  Maybe it’s too far from the classrooms, all of which were at the other end of the building.  It’s a mystery.

The conference rooms are often used for faculty and administrative meetings, but there are plenty of times when they are empty.  That’s when students move in.  Students are particularly attentive to the presence of meetings in which food was served.  When the meetings end, students grab the leftovers.  But even without food, students know about and use the space.

One of the enclosed stairwells has windows, so we put in a nice wooden bench on one of the landings next to the window.  In fifteen years, I have seen one student on that bench.  I used it more often than the students.  Maybe if the bench had cushions, it would have been more attractive.  I certainly would have used it more myself.

Overall, even though we would change a few things about a few spaces, most of them worked as we had hoped.  And there is no doubt that students would have used more spaces if they were near the action (faculty, classrooms, traffic) and attractive (soft seating and tables).  

In short, student space matters.

And space doesn’t design itself.  We consulted students during the design process, and faculty discussed it at length (Kim Schandel, Brian Niece, Stuart Cromarty, Ed Dix, and Steve Theroux all contributed).  The architectural team at EYP, led by Heather Taylor, incorporated our wishes through their expertise, giving us the wonderful Richard and Janet Testa Science Center.  Everyone deserves a huge amount of credit for contributing to a great process that led to a great result.

Timing

Giving guidance when students are ready for it

When should professors provide guidance to their students?  We hand out the syllabus on the first day (or post it earlier) as a guide for the entire course.  But is the first day the best time for all of that guidance?  Some years ago, I stumbled upon an answer for that question: probably not.  I learned this with regard to a semester-long project I assigned to my students.

Task

I taught introductory environmental science throughout my forty-year career.  A few years in, I began asking the students to pick an article from the popular press (now, they get it from the web) and write a critique.  But I wanted them to write an informed critique, so I split the task into three parts, due at different times, and allowed them revise the whole thing after they got my comments on all three parts.  

Part one was a one-paragraph summary of the article, plus a list of the issues in the article that they would need to check.  Part two was a compilation of information, from sources other than the article, about each issue they had identified (I called this the background section).  Part three was the critique of the article, issue by issue and overall, comparing the article to what they had found from other sources (I called this the evaluation section).

Many (perhaps most) students had difficulty with one or more steps in the process.  Some picked articles that were too short, or too long, or inappropriate for the course.  Most had trouble identifying the issues.  Some had trouble gathering and organizing information from other sources.  Some had trouble using the information to evaluate the content and presentation of their chosen articles.  In my comments, section by section, I tried to steer them in productive directions.  I typed and printed my comments for each section so that they had a readable record of what they had done well, and of what they needed to revise.  I always gave them hard copies (old habits die hard), but electronic transmission would obviously work instead.

When students had problems, I also referred them to the handout I gave them on day one about the task.  Some found the handout useful, some didn’t, and some didn’t even have the handout when they needed it.  I know this because they were supposed to keep everything in a folder and hand in the folder when each part of the paper was due.  Most of them kept the handouts, and my comments, but some didn’t (using printed materials allowed me to provide replacement copies, when needed).

Timing

One semester, on the day I handed back the last set of comments on their evaluations, I also gave them a one-page schematic, based on the original two-page handout, that listed each part of the paper, what should be in it, and how it should be organized.  I told them that they could revise everything, and that the schematic was a guide for their revisions.  The classroom buzzed with comments, their voices rising and falling with the sounds of revelation.  The most common sounds I heard were, “Oh, yeah!”  They had been through the whole process of the critique once, and now they had directions for how to fix the problems.  The students immediately began asking questions, each of them about a specific part of the critique as it applied to their particular article.  Because I had read all their chosen articles and the drafts of their critiques, I could nearly always give them answers specific to their articles (the class ranged in size from 20-40 students).

Here’s my point: When the students got the guidance they needed when they needed it, the guidance was helpful.  They were about to make the revisions that would earn them an actual grade, not just more comments.  Now, things were serious.  And now (not three months earlier) they could see how to get to a successful conclusion.

The original handout was also helpful, but it had not been particularly helpful on day one because it came too soon, before they knew the problems that they would actually encounter.  Immediacy seemed to matter.

I was not always able to time my advice as well as I did for theses critiques, but I certainly tried, as did many of my faculty colleagues.  We often exchanged ideas about how to provide various types of guidance.  Sometimes, all we did was give students the same handout again, or reminded them of it, pointing out how the handout provided the information they should follow.  Sometimes, we gave them a new, shorter handout, emphasizing essential aspects of the task.  Sometimes, we would hand out or refer to the syllabus again, in whole or in part, to reinforce what the course was trying to accomplish.   Often, we were able to provide the timely guidance that at least some students seem to need.  

Conclusion

Timing matters.

How Serious Are Invasive Spongy Moths?

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The moth Lymantria dispar has been feeding on trees in parts of North America since its introduction into the continent from Eurasia in 1869.  By “feeding” I mean, “stripping every freaking leaf off” when the caterpillars are at peak abundance.  In most years, the larvae are nearly impossible to find.  But every so often (the frequency of outbreaks varies widely), there is a hoard of these hairy, irritating, munching critters, and trees in summer can be as bare as they are in winter.  Where I live in central Massachusetts, we had an outbreak in 1981, and it was unpleasant to see the trees defoliated, to listen to the rain of droppings, and to have hoards of caterpillars all over the outside of the house.  But we have had no outbreaks since, though pockets of abundance have appeared just a few miles away.  We don’t know why we have been spared.

In Eurasia, these moths also boom and crash every so often, about as frequently as they do here.  So they are behaving pretty much the same where they have existed for a very long time and where they have been present for only a century and a half.

How bad are they?

The moths continue to spread into new parts of the continent.  When moths first arrive in an area, their initial outbreak can kill a few vulnerable trees.  The percent mortality is usually in the single digits (rarely a true decimation, one out of ten).  After that, tree mortality is quite low, but not zero.  In 1981 near our house, a large hemlock tree surrounded by oaks was stripped bare and never recovered.  In contrast, clusters of hemlocks all survived because they weren’t completely defoliated.  None of the oaks and white pines died, even though they lost essentially all their leaves (the pine needles were eaten down to little stubs, but for some reason, not all the way down to the branches).  

But even if the trees weren’t killed, were they affected in other ways?  Yes.  When trees lose all or most of their leaves, their growth slows down.  How do we know?  By looking at the growth rings of the trees.  

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This is a piece of red oak that I cut for firewood in the winter of 1988-89.  I know when I cut it because of the distinctly narrow ring from 1981 when the tree was defoliated.  In 1981, the tree began to grow in the spring (the coarse cells in the inner portion of the ring) but then grew slowly or not at all until the larvae had finished eating and new leaves could form in the summer.  Counting out from 1981, the last ring is 1988 (the one just inside the bark).  I cut this tree after the growing season of 1988, but before any growth could occur in 1989.

Tree rings reveal good years and bad years of growth, and insect attack is only one of many possible causes.  Shade from other trees produce consistently narrow rings (until the tree casting the shade dies).  Drought can slow growth, especially in trees that are rooted in soils that don’t hold a lot of water.  Injury to the tree can also be a problem if it is serious.  And feeding by many species of insects, indigenous and introduced, can damage trees.

Questions

Has the arrival of Lymantria moths increased the frequency, duration and/or amount of growth reduction in oak trees?  Or are moth outbreaks just another cause of growth reduction among those already apparent in the tree ring record?

I tried to answer these questions at six sites in Pennsylvania and New Jersey where the first outbreaks of these moths were well documented by the state forestry departments.  I measured the tree rings before and after the first outbreaks, and used observations from foresters, and published records of drought severity, to determine (when possible) the cause of significant declines in growth.

Tree growth, as recorded in the width of tree rings, varies widely over time. Different trees grow at different rates for all kinds of reasons, including genetics, neighbors, soil, weather, and so on.  To reduce the individual differences among trees, space, and time, dendroecologists detrend, normalize, and average the results for dozens of trees at a site.  The result looks like this graph from site 4 in Pennsylvania.

Years of low growth

At the six sites, there were 529 site-years with at least fifteen trees present.  In 78 of those site-years (15%), growth was reduced by at least one half of a standard deviation.  

Fifty-one of the reductions were in drought years, 29 occurred during outbreaks of Lymantria (19 of which were also drought years), nine were associated with outbreaks of indigenous insects (oak leaf tier, oak leaf roller, and scale insects), and two occurred when there was evidence of fungal disease.  For eight of the growth reductions, I couldn’t find anything in the drought or forestry records that was associated with low growth.

The magnitude of growth reduction varied widely, but on average, Lymantria outbreaks caused greater reductions in growth than droughts.  The mean reduction of growth in drought years was -0.69.  When moths were present during droughts, the mean reduction in growth was -0.94.  During outbreaks when there was no drought, the mean reduction in growth was -1.20.

But the plot of these results shows something interesting.  Growth reductions usually ranged between -0.5 and -1.2 for drought only, drought plus moths, and moths only.  In five cases, growth plummeted by more than -1.5.  At their worst, Lymantria outbreaks caused the greatest reductions in tree growth over nearly a century.  On the other hand, they did so only five times between the time outbreaks began until 2006 (when my data collection ended).

Events of low growth

Reductions in growth often lasted for more than one year at a site.  Droughts and insect outbreaks might end after one growing season, or continue for several years.  Has the arrival of Lymantria moths changed these events, compared to growth reductions before they arrived?

Before there were outbreaks of Lymantria, growth reduction occurred less than once per decade at the six sites.  After moth outbreaks began, growth reduction was about twice as frequent, well over one per decade.  It is impossible to know why the frequency increased, but this invasive moth almost certainly contributed to the increase.

On average, growth reduction events lasted 1.7 years when moths were absent.  Duration increased somewhat, to 1.9 years, once moths were present at the study sites.  This difference is not statistically significant, and probably not ecologically significant.

The maximum amount of growth reduction during an event increased quite a bit once moths arrived, going from an average of -0.74 down to -1.01.  An outbreak of Lymantria moths can be a big deal for tree growth.

But so can an outbreak of the indigenous oak leafroller, Archips semiferanus.  At site three, the outbreak began in 1970 and lasted three years, reducing tree ring width to -1.62 in 1972.

After nearly every outbreak of an insect defoliator, whether invasive or indigenous, tree growth quickly shot up to values among the highest seen in the entire tree-ring record.  The trees are resilient, for whatever reason, after severe damage from herbivores.

How bad is this invasive insect

There are plenty of invasive pests that are serious problems, none worse than the chestnut blight that wiped out American chestnuts in the twentieth century.  Today, the emerald ash borer is killing lots of ash trees, and the hemlock woolly adelgid is killing lots of hemlocks.  If we can stop the spread of these introduced pests, we can save a lot of trees.

How serious is Lymantria dispar? Outbreaks of these caterpillars can kill trees, and the survivors have reduced tree growth.  Also, the frequency and intensity of growth reduction has increased since the moths arrived.  

On the other hand, outbreaks are infrequent, few trees are killed, and the surviving trees seem to bounce back readily after an outbreak.  The moths have affected tree growth, but have not radically altered our forests.

Perhaps most significant, there is nothing we can do to stop the spread of this moth.  It continues to disperse west, south and north since its release in Massachusetts over a century ago.  We will have to tolerate its presence, just as people – and forests – do across Eurasia.  We have no choice.

By the way, if you have never heard of the spongy moth, it is because it is the new name for the gypsy moth.  The old common name for Lymantria dispar is ethnically insulting, so it has been changed https://www.nytimes.com/2022/03/03/science/spongy-moth-romani.html

Life of a broken oak

Tree nine is a white oak in Rutland, Massachusetts.  I gave it that number when I was tagging trees that had lost a noticeable number of branches in an ice storm in 2008.  Tree nine lost about half of its branches, but its neighboring trees lost nearly all of theirs, so tree nine ended up growing about as much per year in the four years after the storm as it had in the three years before the storm.  More sunlight compensated for having many fewer leaves.

Tree nine has been alive for a century, producing its thickest growth rings early in its life, but its growth declined steadily throughout its life.  What happened?

The answer is simple.  Nothing.  Under constant, ideal conditions, any tree would have thick growth rings at first, with a steady decline in ring thickness throughout their lives.  That’s the natural geometry of tree growth, as reflected in growth rings.  Each year, a bigger tree makes more wood, but each year, it has to distribute that wood just inside the surface of a larger body (yes, the tree is a body).  It might not be obvious how that will affect the width of each ring, year to year, but the result, both empirical and theoretical, is a steady decline in ring width each year (if you care, the decline follows a negative exponential curve).

So tree nine, in general, followed an expected pattern of growth.  But there was also a whole lot of variation.  Conditions were not constant, often not ideal, and sometimes destructive.  Life in the forest is hard.  Yet tree nine persevered, and does so to this day.

But the damage from 2008 didn’t heal completely, and eventually the tree was weakened by invading fungi. New wood couldn’t keep up with decaying wood, at least not in one of the major branches.  In the summer of 2021, that branch broke, not completely, but more than enough to let the ends of the branch hit the ground, leaves and all.  

The base of the branch was still attached to the tree.  There was enough good wood to retain a connection between trunk and branch, and good wood is tough stuff. This is what the growth rings look like in the fallen branch:

The bark is on the left side of this portion of the tree.  The growth ring for 2021 ended just inside the bark, and began with the large cells a little to the right of the bark (the rings grow outward).  The final ring is narrow because the branch broke off sometime in the spring or summer, and the branch stopped growing.  The rings for three years after the ice storm (2008) are among the widest in this section of the fallen branch, but growth began to decline in 2012, probably because of the invasion of fungi that ultimately led to the failure of the branch in 2021.

The connection was not sufficient to sustain life in the fallen branch.  The leaves of summer all died, and the stems and buds all died with them.  The broken branch, with all the many branches stemming from it, is dead.  I will harvest as much of the wood as I can reach to dry and then burn in my stove a year from now.  I’ll leave the small twigs and branches and leaves for scavengers and decomposers.  I will leave the parts out of reach for insects and woodpeckers.

Tree nine lives on, broken, but not dead.  It still stands tall, and the surviving portions of the tree will grow.  How long will it live?  I have no idea, but I wouldn’t be surprised if it outlives me.  Oaks, even wounded ones, can easily outlive people.  Oaks give us hope.

Reference

Owen D. V. Sholes “Effects of ice storm damage on radial growth of Quercus spp.” The Journal of the Torrey Botanical Society 140(3), 364-368, (1 July 2013)

https://bioone.org/journals/the-journal-of-the-torrey-botanical-society/volume-140/issue-3/TORREY-D-13-00036.1/Effects-of-ice-storm-damage-on-radial-growth-of-Quercus/10.3159/TORREY-D-13-00036.1.short

Goldenrods: The Next Generation

Goldenrods have finished blooming in central Massachusetts.  They have also finished preparing for the future

The flowers produced seeds, one per flower, each with an embryo and a wind-catching pappus that could colonize a new location, maybe nearby, maybe far away.  The seeds hang on to the parent plant, but the time it takes for them to leave varies enormously.  Some break free quickly, and the last are still clinging to the old plant in the spring.  Their variation probably increases the chances that at least some of them will be successful.  If they all went at once, they might all get lucky – or they might all fail if there is some disaster that befalls the group.  So spread them out over time and hope that some seeds will succeed.  Of course, most will fail.  That is the way with seeds.

The also vary genetically, most (all?) of the pollen having come from other plants, some nearby, some far away.  These diverse offspring are mostly like their parents, but not identical.  Will some grow better than their parents and leave lots of offspring?  Maybe.

Goldenrods are perennial plants, sprouting up each year from tissues that have spent the winter or dry season underground.  During the growing season, they produce new roots, and new rhizomes.  The rhizomes are stems, botanically speaking, that spread underground.  They don’t spread that far in any one year, and there might not be that many of them.  But each year, if they succeed, they can take over a little more ground and make their clone a little more abundant in their habitat.  Over time, they can take over a lot of land.

Some species of goldenrods from North America become invasive weeds when introduced into other continents.  By seed and rhizome, they take hold and expand, just as they do in their original locations.  They are among the many perennial weeds that have found ways to expand vigorously.  Of course, there will be bad times and bad locations, and they will not take over the world.  But they will keep trying.

Bladderwort Boom and Bust

I posted last year about bladderwort in a pond (Utricularia is the formal name – more on that in a bit).  For several years, it bloomed like a carpet.  In some years, it was a lush carpet, and in others, thinner, but still extensive.  

This year, there were essentially no Utricularia in the pond.  Probably not zero, but nothing even hinting at a carpet of flowers.

There are lots of animals that irrupt and become conspicuously abundant. Lymantria dispar, the soon-to-be-renamed gypsy moth, is one infamous example, and there are many others.  Periodical cicadas are NOT an example – they just have a weird life cycle.  But the annual cicadas in some places are an example.  In sixteen years of field work among pinyon pines near Sunset Crater, Arizona, there were always a few cicadas around, except in one year when they were practically dripping from the trees.  The next year, they were just around, not abundant.  Why?  I have no idea.  And maybe nothing is more irruptive, and more mysteriously so, than the freshwater “jellyfish” Craspedacusta sowerbii.  I saw it in a campus pond in 1979, and never again.  It was spotted in 2020 in Walden Pond.  It appears in a pond and then vanishes, only to appear in another pond years later.  How does it do that?  Who knows?

But are there irruptive plants?  Algae blooms, sure.  But vascular plants?  The mast years of tree seeds or blooming years of desert annuals don’t qualify because they are always there, just not always reproducing or germinating.  Perhaps gentians qualify, here this year, elsewhere the next, though they rarely get superabundant.  I would not be surprised if there are truly irruptive plants, but I just don’t happen to know of any.

Except bladderwort.  Utricularia just went through a boom and bust on my neighborhood pond, and I think that’s pretty amazing.

Now I have to admit that there’s a problem: I don’t know the species of bladderwort.  It looks like the pictures of U. radiata (floating bladderwort) or U. inflata (swollen bladderwort), and I don’t have any specimens to check and confirm the identification.  Both species have floating leaves and light yellow flowers.  Both live in shallow ponds.  But swollen bladderwort is said to be invasive, and invasive species often have the ability to grow quickly.  That would be consistent with the sudden appearance of a carpet of plants on the pond.  But their rapid demise was a surprise.  So whatever species it is (I’m leaning toward U. inflata), I think it qualifies as irruptive.  

So maybe – just maybe – the concern over an invasive bladderwort might be tempered a bit if their populations are likely to collapse after a few years.  It would be helpful if we had more data, more observation of bladderwort populations over several years.  If they consistently disappear, then maybe all we have to do is wait.  That’s my hopeful hypothesis, and I look forward to learning whether I’m right.

Goldenrod Co-Stars

In northeastern North America, there are a few species of goldenrod that conspicuously inhabit old farm fields, including Canada goldenrod, tall goldenrod, rough-leaved goldenrod, giant goldenrod, and early goldenrod.  But there are many others.  In my town, gray goldenrod (Solidago nemoralis), sharp-leaved goldenrod (Solidago arguta), and downy goldenrod (Solidago puberula) are three that are more common than one might think, but just not everywhere.

I’ve mentioned these species before, and I’ve even posted pictures of S. arguta earlier in the growing season, when it was just getting going.  Sharp-leaved goldenrod is blooming now, but the only places I find it are along heavily-shaded dirt roads.  Maybe that’s why some people call it forest goldenrod.  The plants are tall, but the leaves are more widely placed on the stem than any species living in the open sun (except early goldenrod).  My guess is that they don’t have the resources to make lots of leaves, so they spread them out in hopes of catching as many sun flecks as possible during the day.  And they minimize one leaf shading another.  They don’t produce a lot of flowers, but enough that you would notice them when you drive at a speed appropriate for a poorly-graded road.

Gray goldenrod is short, maybe half the height of the species that dominate old fields.  I used six different fields in my research back in the 1970s, and in only one of them did gray goldenrod account for more than one percent of the plant cover.  In Iowa, Patricia Warner and Robert Platt found gray goldenrod on the driest soils they studied.  Massachusetts is not as dry as Iowa, but there are dry places here and there where the taller species might have trouble making a living.  Those are places where gray goldenrod can maintain a foothold.  One such place is in just a bit too steep to mow next to a field not far from one of our elementary schools.  About 50 meters from a mesic slope covered with tall and Canada goldenrod, gray goldenrod is holding forth, blooming beautifully, with only grasses to cast shadows on their leaves. 

Downy goldenrod used to be abundant behind our house when it was a field with small pine trees.  Now those pines are several meters tall, casting too much shade for sun-loving goldenrods.  Our neighbors sold off some timber about 25 years ago, and the open area by the road was another place for downy goldenrod, at least up until a few years ago.  I checked last week and the birches have grown tall, too tall, it seems, for the goldenrods.  I couldn’t find any.

But along the highway to the north, the west roadside has some downy goldenrods, and on the opposite side, with a sparsely-wooded wetland next to it, there is a thriving stand.  They tend to be taller than gray goldenrod, but shorter than Canada goldenrod.  They do best on nutrient-poor soil (reduced competition?), and many roadsides qualify for that distinction.  Good to see some, compact and bright, finishing off the summer.

If a goldenrod looks a little different from what you expect, or is in a place that seems unusual, then it is probably not one of the more common species.  These glimpses of something different are the first clue to the diversity of goldenrods.  It’s a good time of year to appreciate how many kinds there are.

Silverrods

Most goldenrods have yellow flowers, but a few species of Solidago have white petals, and at least one of those (S. bicolor) has the common name silverrod.  But perhaps we could call it platinum-rod, or palladium-rod, both metals having more of a white cast than silver.  Whichever precious metal we use for the name, the flowers are showy.  And the disk flowers are at least faintly yellow, like those in the rest of the genus (hence the species name bicolor?).  In the riot of blooming at this time of year, a little variety is just fine.

Goldenrod Pollination

Flowering plants produce seeds through the process of pollination, the release of pollen (containing sperm cells) from stamens, and the transfer of pollen to the receptive surface (stigma) of the pistil (containing egg cells).  

Flowers

Goldenrod flowers (see my earlier posts) are clustered in flower heads.  The flowers on the edge (ray flowers) have large petals and are solely female (no stamens).  When a flower head opens, the first flowers to bloom are the ray flowers, which (presumably) provide nectar as a reward for any pollinating insect, and which can receive pollen.

The disk flowers in the middle of the head are both male and female.  When the head first opens, the disk flowers are closed (see their blunt, closed ends in the photo above).

But later, the disk flowers open and the stamens thrust the anthers upward, exposing the pollen above the surface of the flower head (see photo below).

Insects

Many insects visit goldenrod flowers.  I posted a one-minute video (Twitter and Facebook) of pollinator frenzy on a couple of goldenrod inflorescences.  The video is full of wasps and bees, and goldenrods also attract beetles, ants, flies, butterflies, moths, and more.  These insects get nectar and/or pollen as a reward (and some probably nibble on the tissues of the flowers).  For some, the reward is immediate and short-term, fueling their activity during that day.  For others, the reward is long-term, as they take the pollen and/or nectar back to their nest to share (for social insects) or to provision the nest for their young when they hatch.  

Pollen is a durable, nutrient-rich food.  Nectar is almost entirely sugar and water, an energy drink.  A few species can evaporate the water to produce honey, a sugar solution so highly concentrated that it won’t spoil.   I posted about honey earlier.

Pollination

As the insects cling to and walk on the flowers, they are almost certain to pick up some sticky pollen on their bodies.  They might ignore the pollen, or try to clean it off, or eat some of it, or gather some of it to take with them, but no matter how carefully they groom themselves, some pollen grains are likely to be scattered on their bodies.  When they move on to other flowers, some of those grains will rub off on stigmas, the topmost part of the female portion of a flower.  If the pollen from plant A rubs off on a stigma of plant A, that will be a dead end.  Goldenrods are self-incompatible (they can’t fertilize their own flowers).

But pollinators on goldenrods are greedy, abundant, and highly mobile.  They will bump into each other, knock each other off of the flowers, and cause each other to fly to other flowers, some of which will be on another plant.  Or they will drink the flowers dry and fly a bit to find more flowers, sometimes on another plant.

If the pollen from plant A ends up on the stigmas of plant B, then fertilization can get going.

Fertilization

The process of fertilization in flowering plants has several steps, and some of them seem at least somewhat improbable.  But all flowering plants do it, and there are thousands of species of flowering plants.  As complex as the process seems, they make it work.

When a pollen grain contacts the stigma of a flower, the grain “germinates.”  A tube, called the pollen tube, grows from the pollen grain, and two sperm cells, both haploid, venture down the tube.

The stigma is the topmost portion of the pistil, the female portion of a flower, and the tube penetrates the stigma, the style below the stigma, and enters the ovary below the stigma.  Inside the ovaries there are ovules, each surrounded by layers of cells, and each containing an embryo sac, a small structure with eight cells or nuclei, all of which are haploid.

The pollen tube finds its way into the ovary and then into an ovule and embryo sac.  One of the sperm cells will fuse with one of the female haploid cells, the egg cell, and that fusion produces a diploid zygote, the first cell of a new plant.  The zygote begins to divide and produces an embryo, which will stop growing and become dormant within the ovule.  The ovule will eventually become a seed.  

The other sperm cell inside the embryo sac fuses with two of the female haploid nuclei to produce a triploid cell (I warned you that the process was weird), and this triploid cell divides by mitosis multiple times to produce endosperm within the seed.  Some plants have almost no endosperm (orchids), and others have a lot (coconuts).  Goldenrods have enough to serve as a nutrition source for the seed when it germinates.  Goldenrod seeds are small and light, easily blown around to places at some distance from the parent plant.  But they also have a bit of endosperm to help the new plant to grow, wherever it lands.

Each goldenrod flower has one ovary with one ovule, so each flower produces, at most, one seed.  The ovary provides a covering around the seed, which is technically a fruit, a dry fruit called an achene.  As the ovary wall dries out, small filaments remain attached to the top of each seed.  These filaments (the pappus) provide wind resistance and help the seed disperse away from the parent plant sometime in the next several months.  Most of the seeds will fail for one reason or another, but there is always a chance that some will find a place to grow once the next spring rolls around.

Sexual reproduction

This whole sequence of events is sexual reproduction: flowers attract pollinators, pollen transfer leads to fertilization, fertilization leads to seeds and dry fruits, and dry fruits blow around in the wind.  Each offspring has half of its genes from one parent and half of its genes from the other parent, and thus is genetically different from both them.  Each unique seed then has a chance to colonize new habitats.  It’s a risky business, but it has worked for an unfathomably long time.

If you feel lost in the details, take a look at the video on Twitter or Facebook.  The frenetic pollinators can’t get enough of the goldenrod flowers.  All that messing around leads to pollination, an essential part of producing another generation of goldenrods.  And there it is, right by your house, along the road, or in whatever habitat your local goldenrods occupy.  It won’t last forever, so take a look while it’s going on.  If you miss it, it will all happen again next year.  Nature is persistent.

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