Monday, September 7, 2015

Counting Things

I once heard it said that a scientist who didn't know what to do next would count things.  There's no telling what might turn up in the data!  But the saying needs to be taken with a grain of salt: scientists count (measure) things because quantitative (numerical) data has several advantages over qualitative data: it's more exact and less open to misinterpretation, it's open to powerful statistical analyses, and it can be applied more closely to real-world issues.  I'd guess it's been over a century since science could be done without quantitative data.

I long ago noticed that the samaras (winged seeds*) that fall from sugar maple trees often have bite marks in them.  Many of these have been eaten, leaving an empty shell.  A few minutes' research brought forth the likeliest culprit: squirrels.  The gray squirrel, far from being an acorn specialist, is actually broadly omnivorous, eating a variety of nuts and berries, buds and bark, and not passing up an undefended, nestling bird, either.  The menu specifically includes maple samaras, buds and bark.  How serious is the damage to maple reproduction?  A little half-vast science would provide a clue.

On my walks over the last few days I brought plastic bags and a sharpie marker.  Under three different trees varying distances apart I picked up fistfuls of fallen samaras and put them into labeled bags.  Under a particular tree I've been watching I collected three bags--to get an idea how much random variation there was.  Then home I went to count things. 

Science is messy!  Or it that just me?

 I saved the samaras that had at least one intact seed.  Hmm--if half of them germinate,
I only need an acre or so of land to plant them all!

Probably the hardest job doing this sort of science is deciding what to count.  For example, if I decided that every samara was either eaten (seed gone) or alive, what about those I'd seen with a bit mark that might or might not be dead? or the samaras damaged by insects? or those I simply couldn' decide on?  So first I emptied a bag on the kitchen table, pawed through it, and decided on categories.  Even, then, I can't pretend there weren't judgement calls, and my judgement may well have changed as I worked.  For this and other reasons (chiefly about my sampling method and the small number of trees I looked at), I call this "half-vast science."**  Nevertheless, I think I learned some things. 

There was variability between samples taken from under the same tree, but that was probably because of where the samples came from: the two that were alike were seeds that had fallen in the street, rather than on the lawn.  

Less than half of the seeds were intact in any sample, and it was more typically about one-quarter.  

There was very little insect damage: the enemy of sugar maple (at least here in the 'burbs) is the squirrel.  Period!***  


Oh, did I forget to mention that THE SUGAR MAPLES ARE HERE!  I noticed samaras falling from the first one in the neighborhood at the end of July, but more trees became involved and the pace really picked up in the last two weeks.  I guess we're now in the middle of it.

Sugar maples are easy to tell by their samaras.  When still joined together, samaras appear squared-off, with plump, rounded seeds.  The only other maple that might be shedding samaras right now is the common (invasive alien) Norway maple, with its nearly straight samaras with flattened seeds.

One of the sugar maples I collected samaras under.  Majestic tree!

Sugar maple samaras have plump seeds and sharply-angled wings, while Norway maples 
(few of which have yet dropped many samaras) are larger, have flat seeds, and wings nearly in line.  (Image below from

Sugar maple is uncommon in southern New England, but is commonly planted as a yard tree here in the city.  It is the same tree of northern New England forests whose sap, boiled down to about 1/40th its original volume, makes maple syrup.  In recent years it has become harder for New Englanders who "tap" the sugar maple to get enough sap to make the work profitable, since the necessary conditions (days reaching about 45 degrees F with nights well below freezing, ending with leaf bud break) have been shortened, probably by climate change.

Even if it is planted, it's nice to have native maples in our yards and by out streets. 

*Really, fruit: the actual seed is inside the samara.
**aka pretty good middle school science fair project.
***Automobiles are another danger here in the city: many samaras, acorns, etc are ground to mush beneath tires.

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