Essential Differences

Heard a bluebird about a week ago.  There are very few phenomena which can be described indifferently as occurring at different seasons of the year, for they will occur with some essential difference.  Journal, Nov 3, 1853

Henry David Thoreau's attempt to made a detailed seasonal nature calendar was probably doomed.  After my own "years of observation," I am astonished at how variable events can be.  Not only do the early-blooming trees vary year to year by more than a month, these trees have not been varying together, but each following its own mysterious impulses.

Henry David Thoreau is well-known among modern naturalists for his close, systematic, and long-continued observation of nature in his hometown of Concord, Massachusetts.  Among his ambitions was to record the events of nature precisely enough to predict--almost on a daily basis--the flowering and fruiting of plants, arrival and departure of migrating birds, mating seasons, and other events of the season.  Although Thoreau's interests varied from year to year (one year he hatched and followed snapping turtles), he did one concentrated, conscientious "year of observation" around 1852 in which he determined to record every seasonal event.  He was building his own version of the seasonal calendars that were popular at that time.

I have been doing my own "years of observation" in my own little neighborhood over the last three years or so.  The wild swings of the last few springs have convinced me that nature is predictable only within wide limits.  Last year the warm winter brought out the early-blooming trees far earlier than the year before.  This year we had another warm winter--one of the warmest Februarys on record worldwide, and definitely the warmest ever in this region--and I looked for the same trees to bloom at about the same times as last year.  To my surprise, some bloomed earlier, but some bloomed later.  So nature is still less predictable than I'd thought. 

Silver maples began blooming April 4, 2015, but February 29, 2016 and February 23 this year!

Quaking aspens bloomed around April 10, 2015, but March 26th, 2016, and was in full bloom before March 22 this year.

 Red maples bloomed April 15, 2015, but March 11, 2016, and is just beginning to bloom as I write on March 25th.  (Males above, females below.)

But maybe it's better this way.  A predictable Nature would be a boring Nature.  In truth, the closer you look, the more Nature remains full of surprises.

Fetching the Year About

 

 

A single Red maple (Acer rubrum) from April to March.

April 1856  As I was measuring along the Marlborough road, a fine little slate-blue butterfly fluttered over the chain.  Even its feeble strength was required to fetch the year about.   --Journal  Henry David Thoreau

August 1853  I think that within the week I have heard the alder cricket,--a clearer and shriller sound from the leaves in low grounds, a clear shrilling out of a cool moist shade, an autumnal sound.  The year is in the grasp of the crickets, and they are hurling it round swiftly on its axle.  --Journal  Henry David Thoreau

Henry David Thoreau lived nearly all his life in Concord, Massachusetts.  Nearly every day, he spent hours wandering its beloved woods, fields and streams.   Besides studying the behavior of birds, turtles, and other animals, Thoreau recorded detailed observations of seasonal change over many years.¹  These he gradually compiled into a nature calendar. Thoreau believed he could find an essential difference--a distinctive essence--to each day of the year, and that, in creating his calendar, he was doing his part to "fetch the year about."  It was almost as if he, like the butterfly or the cricket, were propelling the earth in its march around the year.

I feel this ambition, but confine myself mainly to observing trees I encounter in my walks.²  In this I have at least two advantages over Thoreau: a pocket camera, and the accumulation of a century-and-a-half of evolutionary thought.³  I aim to know the approximate dates and the order in which my trees flower, leaf out, drop their seeds, etc. and also the varied "habits" of these different species.  I hope to observe for enough years to get a rough idea of the year-to-year variation in these seasonal changes.  Someday I might earn the right to say, "I have traveled a good deal" in Brockton."⁴  Already I have almost enough observations, I think, that I might be tempted--in the doldrums of early spring, say--to open my calendar a bit early, get a good grip on the universe, and try to "fetch the year about" for myself.

 The growing season begins with just a few trees (above: red, Norway, sugar and silver maples down the left margin; below: quaking aspen, river birch and alder) in mid- to late April.  (January to April across the top of the pages.  Yellow shows timing and duration of flowering, green is leaf expansion.)

 May-August. By mid-May the party has really gotten going.
Yellow is flowering, green is leaf expansion, red is fruit/seed dispersal.
The vertical bars at the bottom of the page above are precipitation.

Postscript: I intended to post this in the doldrums of late winter or early spring a year ago--a time of year when little appears to be happening in the natural world.  Instead, I was surprised to find silver maples and quaking aspen beginning to flower, and that news displaced my intended post.  (Freezing weather later on doomed these blooms.)  After this year's unusually warm February, history looks like repeating itself: the fuzzy, pussy-willow-like inner buds of quaking aspen are showing, and silver maples appear on the point of flowering.  Since freezing weather is surely still ahead, this is unfortunate; I hope it's just a coincidence to have such warm weather in mid-winter two years running.

1 His observations were detailed and thorough enough to be used by modern researchers studying the effects climate change has had on different species of plants.

2 Though I couldn't help but notice the high-pitched chittering and aerobatics of the newly-arrived chimney swifts last May 11th!

3 Thoreau read Darwin's Origin of Species shortly after it was published in 1859, and was intrigued enough to begin experiments of his own.

4"I have traveled a good deal in Concord..."  -- Walden