Sunday, July 31, 2016

Drought and Plant Stress

Another shower, another eight-inch of water that makes no difference, and the drought goes on.  We in Massachusetts have had four continuous months of low rainfall.  In June, at our nearest recording station, less than two inches of rain fell altogether, and only two days brought a quarter-inch or more.  July was as bad or worse, with just over two inches, and no day with even half-an-inch, never reaching more than the top-most inch-or-so of soil.   Three weeks ago the state declared a drought watch; Worcester's reservoirs are down a third or more, Brockton draws increasingly on a desalinization plant on the Taunton River to help preserve the main reservoir of Silver Lake.  Walking raises dust--even crossing the lawn--groundwater recedes, plants are stressed.  

I have watched for some time for signs of drought stress in the trees.  Trees and most shrubs are not yet in obvious trouble, but there are exceptions. 

 European buckthorn, an alien invasive, is wilting even on a drizzly, overcast day.

 Wild grape, Vitus labrusca, wilts in sunshine, but has recovered turgor in the overcast.

 Gray dogwood, Cornus racemosa, a thicket-forming shrub, is wilted all over my little wood.

 Garlic mustard, a prolific alien invasive, is suffering; but its a tough plant and will recover.

 Enchanter's nightshade, Circaea quadrisulcata (above), and especially heart-leaved aster, Aster divericatus (below) are looking poorly.

 The cucumbers in my garden have wilted nearly every day--even when watered
--but they recover out of direct sun. 

 White ash, Fraxinus americana (above), and 
ash-leaved maple, Acer negundo (below), have leaves curling with wilt.

 Of the three paper birches I saw this day, only this one was losing leaves prematurely.

The same stretch of Salisbury Brook in early May above, and mid-July below.

Like all living things, plants are critically dependent on water.  With carbon dioxide from the air, water is a raw material for photosynthesis: the building of sugar molecules (and many other compounds) using the energy in sunlight.  Photosynthesis is a trick that every other creature around you, from mushroom to man,  depends on for life: it is the ultimate source* of all our food and oxygen.  

Of the enormous amount of water consumed by plants, only a tiny fraction is "split" into hydrogen, for making sugar, and "waste" oxygen; most is used to maintain turgor pressure in soft tissues, to expand their cells as they grow, and to transport minerals upwards in the plant.  If you've ever marveled at how soft a football is when deflated, you will understand turgor pressure: just as the pressure of air can turn flabby pigskin into a nearly-rigid football, the pressure of water does the same for plants.  Typical plants first draw water into their roots by maintaining a higher concentration of dissolved substances in their root cells than are present in soil water (osmosis).  From these root cells, water is drawn upward in the tube-like vascular tissue of the stems in a kind of tug-of-war by evaporation of water from leaf cells.  (These tubes--"vessels" in flowering plants and "tracheids" in conifers-- are small enough that the attraction of water molecules for each other causes them to act as if the water were in "strands" that could be pulled upward.)  Plants are forced to lose water at high rates by their need for carbon dioxide from the air: the same pores (stomata) in leaves that allow carbon dioxide to diffuse in and oxygen to diffuse out, also allow water to evaporate from cell surfaces and difuse away.  (The evaporation of water from plant surfaces is called transpiration.)

Bad news for plants begins when water is not entering the roots quite fast enough to replace that evaporating from leaves.  Plants respond to this by closing their stomata: these pores (usually in the undersides of leaves) are flanked by banana-shaped "guard cells" that are spring-loaded to close automatically as their turgor pressure declines.  Since the closing of stomata reduces water loss, you may not see any change in the plant at this point, but the plant is feeling it.  With stomata closed, carbon dioxide  becomes scarce inside the leaf tissue, so photosynthesis declines.  Then a funny thing happens--called photorespiration--yet another fact that argues against living things being "designed".  

In the first step in building a sugar molecule by photosynthesis, an enzyme called ribulose 1,5-bisphosphate carboxylase** ("rubisco" for short) grabs a carbon dioxide molecule.  The rubisco enzyme has a peculiar trait: it has a small tendency to grab oxygen (O2) instead of CO2, probably because the enzyme has a hard time telling these compounds apart.  As long as the stomata are open, there will be a good supply of CO2 inside the leaf, so that photosynthesis usually occurs normally.  But with stomata closed and CO2 scarce, more and more often rubisco will grab oxygen and engage in photorespiration--a sort of "reverse photosynthesis" that is very wasteful of energy and creates nothing good for the plant.  In dry conditions under bright sun, it is possible for a plant to waste by photorespiration much of the sugar it already fixed.  My guess is that many even of those plants that are not visibly wilting are photorespiring*** furiously in the bright sun, and at best marking time until there is enough moisture in the soil to go back to the business of making the food our local ecosystems depend on.

Micrograph of the underside of a fern leaf, showing seven stomata.  Besides the flanking guard cells, some of the choroplasts that do the work of photosynthesis are visible as tiny green hockey pucks.

Micrograph of cross-section through a privet leaf shows different cell types (mesophyll) that do photosynthesis, the air spaces in the leaf, the vein that brings water and minerals, and stomata.

*Our understanding of another of way of making food--extracting energy by chemosynthesis from inorganic chemicals such as the hydrogen sulfide (think ocean floor "black smokers") as certain bacteria can--is still evolving.  Some believe chemosynthesis is as important a food source for life as photosynthesis, and it may well have preceded photosynthesis in life's early history.

**Rubisco is fairly slow enzyme and so plant chloroplasts need them in high concentration--making it possibly the most abundant protein on Earth, and responsible for "fixing" more than 100 billion tons of atmospheric carbon dioxide each year.

***A small fraction of plant species have solved this problem.  They have evolved a way of isolating their rubisco from the air and using a powerful added enzyme (PEP carboxylase) to scavenge CO2 even at low atmospheric concentrations to provide rubisco with a high CO2 levels even with stomata closed.  Such plants can do better in dry conditions, and also in dense stands of plants that have drawn down the CO2 concentration in the air around them.  Among these C4 plants are corn and  crabgrass.

Thursday, July 21, 2016

The Taming of the American Child

I had just finished doing some yard work today when I spotted them: berries.  Raspberries or blackberries.  LOTS of them, and many were the almost-black of peak ripeness.  I turned over a leaf--green: blackberries, then.  (Raspberry leaves are white underneath, but their berries are just as sweet.)  As I picked all I could carry, I wondered.

A brief survey
  1. When did you last pick and eat a wild berry? 
  2. When did you last see the moon?  (Did you know the moon was full on Wednesday?) 
  3. When did you last pause to listen to birds sing? 
  4. When did you last spend half an hour in your garden?  (Do you even have a garden?) 
  5. When did you  relax outdoors with a little something to eat or drink? 
  6. When did you last walk a mile or more in a wood or a park or another natural place?

I hope you have good answers!  But your children may answer these questions very differently than you do. Yesterday I listened to a radio interview with author Scott Sampson (How To Raise A Wild Child: The Art and Science of Falling In Love With Nature) who cited a statistic that scared me:  
American kids today spend only four to seven minutes a day playing outdoors.

The statistic was new to me, if not the issue--advocating that people get outdoors and experience the natural world was the reason I started this blog.  It also led me to  a few years ago to design and run an after school program designed in part to get city kids outdoors.  Even so, I hadn't imagined the situation was that bad.

Sampson sees two big consequences.  Children grow up impoverished, lacking awareness of the world around them, and are also less healthy (studies have found that spending time in nature reduces stress hormones).  Just as important--perhaps even more so--they will not develop the love of natural environments, the emotional connection, that provides the impetus to save these places.  And of course nature itself is increasingly in danger from human activities ranging from over-fishing to habitat destruction to greenhouse gas emissions.  Our very future might very well depend on the emotional connections we and our children form with the wild outdoors.  

Sampson blames many forces, including the lure of electronics, over-scheduling by busy parents who want kids supervised, and fears of media-soaked parents who see a child outdoors and unsupervised as a target in a dangerous world.  

Their parents largely grew up differently.  It was commonplace in my neighborhood to be told to shut off the TV and GO OUTDOORS.  We would be left to our own devices without supervision for hours at a time--for whole days in summer.  Was this dangerous?  Perhaps.  But not nearly as dangerous as we have come to assume today, after a generation of seeing kidnapped children's faces on milk cartons. 

Of course, some neighborhoods really aren't safe, and these present special challenges.  And the issue is, in general, not on the radar screens of less-affluent, or those from an ethnic minority.  But it needs to be.

Sampson's  solution for those of us who care about this?  Start small and manageable: get your kids outside for half an hour three times a week.  

Go to wild places--they don't need to be wilderness.  EngageNotice things--the clouds, the weather, trees, bugs.  Wonder about things: asking questions is much more important than answering questions. 

So much depends on adult attitudes that children absorb.  Are bugs yucky, or cool?  Are grass-stained knees a disaster, or something to accommodate with "play clothes?"  Does a skinned knee call for major first aid, or just some antiseptic and a bandaid?  Do you avoid rain or cold like the plague, or do you simply dress differently? 

Plant yards and cities with native plants.  Native plants attract native insects, birds, and other animals.  And don't manicure everything, for goodness' sake!

In school, space needs to be made for recess, or other outdoor time.  Though time is short in the era of standardized testing, freedom to burn a little energy might pay dividends in greater attention during regular learning.  

It may take a generation or longer to get back to a society in which "free range" parenting isn't a crime, and where boredom can be viewed as a creative force (a bored child might be forced to entertain herself!), but it is vital we do so. 

Friday, July 8, 2016

Morning on Nippenicket

Here it is July and I've only just gotten a kayak in the water!  It was a busy few months.  I decided yesterday would be a good morning (not too hot) to catch up on the happenings at a local pond.  "Lake Nippenicket" is a mile-long pond that has it all: an interesting shoreline, a couple of little islands, lots of pond plants; the southern half has waterfront properties (I like to paddle along and peer shamelessly into people's backyards), while the northern half tucks into the wilds of the great Hockomock Swamp. Most often I noodle slowly along the shoreline, pausing to look at flowers and birds.  My boat this day was Musketaquid my twelve-foot homemade skin-on-frame kayak.

 My Merlin bird ID app from the Cornell Lab of Ornithology 
pegged this bird pretty quickly as an Eastern Kingbird.

 The round flower heads of buttonbush (Cephalanthus occidentalis).

In one place the air was alive with electric blue dragonflies damselflies doing what dragonflies are meant to do.  Several pairs rested on my paddle blades--even refusing to move when I began to dip a blade in the water.  (Several shallow strokes left this pair unimpressed.)  I didn't get far until they finally decamped. 

Whoops!  I just notice these kids have their wings folded over their backs, rather than 
outstretched like an airplane: that makes them damselflies rather than the related dragonflies.  
They look like Northern Bluet damselflies (Enallagma cyathigerum).  
(Mind you, all I really know about damselflies is the name of the group!)

 They can even fly in the act of mating!

Soon after leaving the damselflies behind, the air filled now with dragonflies!  A dozen mated pairs flew about, many repeatedly dipping their abdomens in the water (likely laying eggs)--while flying in tandem!  None rested on the boat, so all I could see is that these were a medium golden-brown color. 

 I quietly chased this mama mallard and three ducklings ashore
in an effort get close enough for a picture.

I like to imagine living in these places, with their varied ways of enjoying the pond.

 White water lilies (Nymphaea odorata).  Floating leaves are nearly round.

 Yellow water lilies (Nuphar advena).  Floating leaves are more oval, and larger than white lily.
 One of the little islands.

 white water lilies line the shallows.

 Passage between the mainland and a small island was a squeeze even for a little kayak.

 The water level in the pond is a bit low for this time of year because it's been so dry.  
The water ranges over about a foot of depth.  

This was the first time I noticed the hollow in the top of the rock.  It has its own tiny ecosystem.

I paddled back a little before noon, very happy with my morning!

Wednesday, July 6, 2016

Gypsy Moths are (done) Pupating

Gypsy moth pupae in white pine, black oak, and white oak.

A few days ago I first noticed a white pine with caterpillar pupae--I counted sixteen on one small branchlet.  Today I found oaks and maples with leaves bunched and curled around many more pupae.  That means we will see a lot of adult gypsy moths--smaller brown males, and large, white flightless females--in two weeks or so.  (Probably not all the caterpillars around here pupate at the same time: my wife noticed numbers of moths flying around the high school.)  

Adult gypsy moths live only about a week, and their sole aim is to mate.  The large female will attract a male with a powerful pheromone.  (One environmentally-friendly way to combat an infestation from year to year is to decoy the males with synthetic pheromone, which is specific to this one species.)   A single female will lay perhaps five hundred eggs in a patch covered with peach-colored fuzz on tree trunks, rocks or other surfaces.  The eggs overwinter and hatch in spring.  The tiny caterpillars then disperse on silken threads like the baby spiders at the end of Charlotte's Web.

What signals the caterpillars to pupate?  Do they need to reach a certain size, or begin to run short of food, or is there a certain triggering temperature, or a certain day length?  Since the adults live such a short time, whatever the trigger is should be experienced at about the same time by all the caterpillars in one region-- anything more idiosyncratic would spread out pupation and leave early and late moths at risk of finding no one to mate with.  

What will next year bring?  I may invest in some BT (Bacillus thuringiensis) bacterial insecticide and a sprayer.  I know from experience that a little hand-pump sprayer can't reach the tops of tall trees, but it's something to try.

UPDATE: my son spotted moths laying eggs right in our yard the next day.  

 The mate for one of the females is still there.

 I wouldn't imagine white would make sense as protective coloration,
but it seems to work for these moths.  (At least until they begin laying eggs.)

 Spotted a female just emerged in a white oak.  I guess pupation is about done; lots of males fluttering about.

Saturday, July 2, 2016

What do Gypsy Moth caterpillars like to eat?

Given that most caterpillars don't travel very far from where they were born, a better question might be: "what trees do gypsy moths lay their eggs on?  I suppose, since the female moths are flightless, these might amount to the same question after all!  Only in the last week or so have the local papers been really interested in the outbreak--possibly the worst in southern New England since 1981.  Of course, now the damage is done, and caterpillars are about ready to pupate.  We will be dealing with the moths in a few weeks.  

 (I remember having, as an undergraduate, the surreal experience of hearing the patter of raindrops (really frass) in bright sunshine where no sunshine should reach: the middle of an oak forest.)  Here, at least, the damage does not compare to that of 1981.  

This witchhazel has been hit pretty hard.  This is the only individual 
of this native shrub I know nearby, so its hard to say how general the damage is.

White oak is supposed to be a caterpillar favorite, but damage seems to be moderate here.  
But this may be mere appearance: white oak can put out a new suit of leaves pretty fast

The river birches have been hit pretty hard, but are recovering.

Black oak has suffered at least as much damage as white oak, and is at least as heavily infested.

The big surprise to me: I didn't see any damage to white pines, but suddenly there are tons of caterpillar cocoons in one neighborhood tree; maybe the damage is too high up to be easily visible.

Some trees appear to have suffered little damage.  (Appearances can be misleading: sometimes a tree looks good because it is able to produce new leaves as fast as caterpillars eat them.)

What do Gypsy Moth caterpillars not like?  


They appear to have no use for white ash.  Most ashes around the neighborhood
have leaves in pristine condition.  I haven't seen caterpillars in any ash trees. 

 Pignut and shagbark hickories are also mostly in very good shape.

 Quaking aspen suffered some damage early on, but has mostly recovered.