The 'Cringing Conifer': Nastic Movements in Trees

By Robert Iglesias

A conifer enthusiast observes an interesting phenomenon in his garden.

The conifer, Japanese red pine (Pinus densiflora) in dry weather
The conifer, Japanese red pine (Pinus densiflora) in dry weather

It’s been some 25 years now since I planted a small, dwarf conifer labeled Pinus densiflora ‘Umbraculifera’ (Tagyoushou) in my northern New Jersey garden. Today, that mature “dwarf” has reached a height of 8 feet (244 cm), and has a round, spreading canopy measuring 9 feet (274 cm) in diameter.

Over the years, I’ve seen this type of Japanese red pine marketed under several cultivar names, including ‘Umbraculifera’, ‘Tanyosho’, ‘Tagyosho’, and Tagyoushou. Here in the U.S., ‘Tanyosho’ has become the cultivar name most commonly seen. While probably the easiest of the cultivar names to say, ‘Tanyosho’ is reputedly a rather poor transliteration of the original name in Japanese. I prefer the alternate name, ‘Tagyoushou’, since it’s closest to the original term that translates to “many trunks”.

True to its name, my Tagyoushou has a strong vertical central trunk which abruptly radiates into a funnel-shaped formation of smaller branching trunks. If left unpruned, the canopy of my tree eventually would have become an open, rounded dome. However, by carefully pruning the emerging candles each year, I’ve trained it into a classic “flat top."

I have a story to tell you about this tree.

A close-up of the needles of the Japanese red pine (Pinus densiflora) in dry weather
A close-up of the needles of the Japanese red pine (Pinus densiflora) in dry weather

Observing Needle Movements in Conifers

Early one morning, I got out a tall ladder with the intent of cleaning off the Tagyoushou’s broad table top. Strong winds had blown down a squirrel’s nest from a nearby tree and the canopy was littered with twigs and leaves. Since rain was predicted, and the sky was already darkening, I wanted to finish in advance of the approaching storm. As I set up my ladder, the rain began.

Although I knew that standing precariously on a wet, 10 foot high metal A-ladder during a rainstorm is NOT a good idea, I stubbornly climbed up and hurriedly picked off the twigs and leaves. As I was about to descend, the tree’s flat canopy in front of me abruptly appeared to droop and the needles shriveled, as though some invisible entity had just landed upon it. For a brief moment, I wondered if this was a prelude to the lightning strike I had so brazenly tempted.

But the rain at that point was a steady drizzle, and the movement I was seeing in the tree was not being caused by lightning, the impact of a hard downpour, or the wind. The movement was coming from the tree itself.

The conifer, Japanese red pine (Pinus densiflora) after rain
The conifer, Japanese red pine (Pinus densiflora) after rain

From my high vantage point on the ladder, I watched as the pine’s needles pressed against the now limp and drooping branches to which they were attached. They appeared to mimic the movement of the ribs of a wet umbrella as it’s being closed. Openings appeared in the canopy. As the rain increased in intensity, I held tightly onto the slippery ladder and carefully climbed down, impressed by the phenomenon I’d just witnessed. It almost seemed as if the tree reacted to getting wet by “cringing," much as we humans instinctively raise our shoulders while running for shelter through a hard downpour.

Once the storm had passed, the branches and their needles straightened as they dried in the sun. The openings which had appeared in the top of the flat canopy closed up. The next day, I hosed down the other conifers in the garden, but none of them duplicated this needle folding effect.

Curious as to how water triggered the close-up of needles, I searched for whatever information might be available, including our own ACS plant profiles, but did not find any mention of the subject. I thought that the effect might be associated somehow with the softening of wet twigs at the attachment of each twin-needle fascicle.

I also wondered what evolutionary purpose this would serve the tree in nature. Did the needles fold down to open the canopy, thereby allowing more rain water to reach the root zone underneath? Was there perhaps some other benefit, such as a reduced likelihood of damage from violent seasonal rains and high winds?

A close-up of the needles of the Japanese red pine (Pinus densiflora) after rain
A close-up of the needles of the Japanese red pine (Pinus densiflora) after rain

Needle Movements in Conifers

It is called “nastic movement”, caused from outside stimuli. In this case, the coming of rain increases the humidity. The pines respond by moving the needles up to tighter clusters. This result is called “turgor”. The trees are opening their stomata so as to regulate their internal moisture level.

This is part of the photosynthesis process defined in the chemical formula:
6CO2 + 6H2O --(Sunlight Energy)-> C6H12O6 + 6O2

In any case, whenever I’m out watering the garden, I always make a point of wetting down “Ol’ Tagyoushou”, just for the slightly wicked fun of watching it cringe.

Both Dennis Groh, ACS Past President, and Dr. Bert Cregg, Michigan State University, were consulted on this topic.

Photographs by Robert Iglesias.

This article was originally published in the Winter 2017 issue of Conifer Quarterly. Join the American Conifer Society to access our extensive library of conifer-related articles and connect to a nationwide group of plant lovers! Become a member for only $40 a year and get discounts with our growing list of participating nurseries in our Nursery Discount Program.

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