The heartbeat of a twig

We mammals tend to regard plants as stationary objects, inert beings that form a backdrop for the more exciting lives of those us of driven by heartbeats and nerves. Here’s some data from a twig on the sugar maple in my backyard that might call us to a more expansive view of our botanical cousins. The graph shows how the diameter of a growing twig changes over a week.

Maple graph

Measurements made by Ecomatik dendrometer

This is the pulse of the tree: one heartbeat every twenty four hours. The twig is fattest at dawn, then the twig shrinks as the water-conducting vessels, the xylem “tubes,” get pulled inward by the draw of passing water. Like a straw that collapses inward under the influence of an enthusiastic drinker, the twig shrinks and reaches its narrowest point in the early afternoon when the leaves are hemorrhaging water to the hot, thirsty sunshine. The twig then gradually swells as the sun lowers and darkness comes. The movement is slight, a few hundredths of a millimeter each day.

Note that the graph shows an upward trend. This young green twig is adding wood, growing day by day.

All around us: every twig throbbing with life.

33 thoughts on “The heartbeat of a twig

  1. Joe Mehling

    Beautiful, David – thank you. “There is grandeur in this view of life, with its several powers….from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

  2. Anonymous

    What does it do in the winter? Is there any pulse that could be measured perhaps in the roots?

    1. Anonymous

      root growth pulses with about the same periodicity- maybe even a bit quicker. but fine root hairs grow out with rain and then die back. no idea about the diameter though. any grad students out there with a shovel?

  3. Paul Lask

    Hi David, Wanted to let you know my wife and I are fans of your work. We recently recorded a demo, of which climate change is a theme. Figured I would share…

    Keep up the good work! Best, Paul

  4. Denise

    When you slow down enough to see that the plant world is populated by living beings and not merely stationary objects, the whole world seems to pop into focus. Much more beautiful.

  5. Donna Black

    “throbbing with life”. Great line and it states how I sense plants. When you see the ‘nose’ of a perennial just starting to push up through the soil in spring, you can almost see the potential energy ready to burst. Thanks for making my day…again.

  6. Jean DeSaix

    I found a link to this on the fb page of our friend Brad Williamson and have since shared it on my fb and at least 2 people who have also shared it! This is so cool and will surely be the basis of some Biology 101 questions for my future classes. Thank you for sharing this amazing phenomenon.

  7. Ralph

    I’m late to the discussion, but what a wonderful way to start the day! To be conscious of the variety of ALL the various forms of life around us! Thank you again!

  8. Pingback: Magnificent Beech | gardeningmatters

  9. kathy

    Wow! and its happening all around us….. and has been for ever so long. Its nice to know that someone else takes the time to sit back and smell (feel) the roses….well maybe the trees. thanks for sharing ……….

  10. Anonymous

    How do you control for the expansion and contraction of the twig and/or sensor due to just temperature change and not fluid content?

    1. David George Haskell Post author

      Excellent question! This has been the source of some vigorous debate in the literature. I absolutely need to run the control before the summer is done. I’m thinking of using a twig of the same age, but cut and waxed so that water flow/evaporation is minimized but temperature still varies. Interestingly, the main trunk shows very little daily variation at all (I have another sensor connected there).

    1. David George Haskell Post author

      Yes! I make no claim to any originality here: these oscillations have been studied by many physiologists. I’m delighted to have this link the the very early work. Impressive!


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