Friday, December 23, 2016
Just a short mid-afternoon walk, mainly along the powerline right-of-way. Besides those animal signs mentioned below, I saw tracks of deer and of racoon. I was happy to see no sign of recent heavy equipment use, like that which had worried me a year ago March, and a few days earlier. The light was getting a little too low for good photos, unlike earlier winter walks.
Bird, probably tufted titmouse, brought down by a predator.
I saw signs like these in three different places.
American beech holds its leaves long after they die.
I was quite proud of myself that I walked almost a mile of the right-of-way without breaking any ice. There was little sign I had passed.
I was pleased to see that even the local 4-wheeler crowd tried to avoid the ice.
Mole? Very long snout catches my attention. Not much sign of foul play.
High tension tower was a gathering place for birds--about a thousand. Why this tower? No idea. The nearby wooden towers were empty, as were the other steel towers. Consensus? Attraction to the birds already there by chance? Food sources?
Friday, December 9, 2016
One of the few photos I have of a good part of the property before.
House and trees in late fall.
Red oak flanked by pignut hickories in late fall, in winter, and in the following spring.
Red oak and pignut hickory growth in summer.
One consequence of being on a first-name basis with neighborhood trees is noticing their absence. I have seen a number of trees cut down in the last few years, beginning with "my" big, healthy sugar maple--cut by its owner because she thought it "invasive." (Sugar maple is native; I pointed out the true invasive: her big Norway maple.) Most of these vanished trees have been nodding acquaintances, but a few, like that sugar maple, were being officially observed for Nature's Notebook; necessitating the notation"DD" beside their names in the logbook.* Now I must add more.
In a forest, dead trees often do not fall for years, and then may rot gradually to mould over decades more. One of the bizarre facts of death in an urban landscape is "disappearance without a trace": tree removal companies pride themselves on erasing all signs that a tree even existed, carrying off trunk and branches, and even grinding down the stump and sometimes even landscaping over it.
I had always been attracted by a property a few blocks from me. A large, pleasantly-unkempt yard was fronted by a tumble-down split rail fence, with brush and trees at one end, and a small yellow house at the other. An open shed at the back held old equipment and a boat trailer made of wood. The remains of an old farm stand decayed gently. A gigantic Norway spruce stood near the house. The yellow house had a peculiar shape that spoke additions; the one-car garage had a swinging door which ought to have an old car with wood-spoked wheels behind it--I don't know since I never saw the door open. The house had reached that picturesque stage of slow decay. I never saw the owner, and assumed there was an elderly couple inside, or a widow or widower. Mostly I was there for the large red oak and two pignut hickories that overhung the street. One hickory in particular I valued for the low branches that allowed me to watch the development of flowers and nuts up close.
Things began changing early this year. Contractors appeared. Trucks drove all around the Norway spruce, which soon died. (Since Norway spruce is invasive, and commonplace in the neighborhood, I did not mourn.) A new roof went on the house. The dead tree was cut down. The porch was enclosed, and the garage became a room. A new stoop was followed by a new front walk, which was landscaped and planted and mulched. They did a nice job, though it was a little surreal to see all this personal detail in a house that was unoccupied. I understand the owner had died, and the house was being rehabilitated as affordable housing. At the time, I did not wonder what that would mean.
It means the the property will be subdivided into more house lots.
A few days ago I found this out the hard way. All the trees on the property are gone; only low stumps--some two feet or more across--remain. I will count their rings. My red oak and hickories have been discharged dead. I will miss them, but I will miss even more the humpy ground, the unkempt lawn turning to woods, the shed and stand, the decayed fence, the yellow of hickories turning in fall.
Last spring the big Norway spruce was gone, and the house was being transformed.
Elliot Tree does fast, efficient, neat work, curse them.
Only stumps remain; here are some. Ages at death are roughly 96 & 100 (double trunk), 44, 100, & 50. (The last is too messy to count.)
Have you ever come upon something so changed
that it just didn't register? That was my experience here.
*Discharged Dead, a notation of British naval captains in the days of sail.
Saturday, December 3, 2016
Sixty-foot white ash (center) and white oak (right) in a strong wind on July 2, 2014, and today.
One consequence of a rooted life is that endurance is worth a lot. Regarding a tree bowed under the weight of ice following an ice storm, I have wondered at this. Some events--this year's severe drought and simultaneous gypsy moth caterpillar outbreak, for example--seem almost unsurvivable. And in our sixteen winters in this house I have seen the thermometer dip into negative temperatures many times. Yet the ash tree above that may be decades my senior has stood all that time, without shelter or escape, taking whatever chance has sent its way. And still it stands, wounded, bowed, but unbroken--the limits of its tenacious grip on life never once exceeded.
Can trees live forever?* Having no fixed size, and growing all their lives has a downside. Because they must collect sunlight to produce their food, trees grow ever upward in competition with those around them. But in a large tree the mass of trunk and branches needed to support its leaves in sunlight begins increases faster than the leaf area needed to feed all that tissue. In effect, a large tree's growth begins to slow as the needs of new wood begin to equal the food produced, and parts must begin to starve and die. Height itself can also be a problem in the tallest trees, such as redwoods: the force required to bring water upward from roots to treetop has a practical limit, beyond which taller shoots must die. Both of these problems increase susceptibility to disease and insect damage, making life tenuous. Most tree species have accepted life spans,** though it is a concept fuzzier than most animal life spans. And the longest-lived trees, such as bristle-coned pines, are often the slowest-growing. Finally, the longer a tree lives, the longer it is subjected to the slings and arrows of outrageous fortune, such as lightning or fire. Eventually something must fell it.
The "energy pyramid" shows how energy enters and moves through most ecosystems. A small fraction of the 697 Watts per square meter of sunlight that strikes the earth's surface is actually fixed in the sugar produced by photosynthesis by producers. Animals that eat plants (primary consumers) get a fraction of this, those that eat these animals (secondary cons) a fraction of that, and so on. Producers (on land, at least) will always outweigh other organisms partly because they have first crack at the energy, and so have the most.
I have always appreciated the out-sized role plants play on Earth (another reason I like them): they along with algae and cyanobacteria in the oceans are the producers for all the rest of life.*** Only they can capture sunlight and bring that energy into ecosystems where it becomes available to us consumers--everybody from germs to people. Science textbooks sometimes treat the photosynthesis that plants do as part of a "cycle" that we complement by our respiration: breaking down the food we eat back into the CO2 and water that are the raw materials from which sugars are made. This makes it seem that plants need us as much as we need them. But this is a false conceit: CO2 and water are common substances that are belched out by volcanoes as readily as by living things, while only plants make food and oxygen in any significant amounts. I tell students that we need plants very much more than they need the animals, fungi, and microbes that depend on them.
Plants define their ecosystems. A biome --the largest ecological unit, such as rainforest, or desert--is defined by its climate and vegetation. The plants of any terrestrial biome or ecosystem far outweigh all the other life in them.
One thing I like best about plants is their abundance, diversity and approachability: I don't have to go through the gymnastics that zoologists sometimes do to simply find the animals they want to study. On my walks around the neighborhood I greet the trees just the way I would neighbors on their porches, always right where they're supposed to be.
Here ends my essay, The Life of a Tree.
*An interesting side issue is that "lifespan" is a meaningless concept in organisms such as bacteria that do not necessarily ever die, or species in which the individual is hard to define. Trees such as aspens fit here: since new trees may sprout from the roots of older trees, a whole grove may consist of genetically identical individuals. (Plants were expert at cloning before it ever occurred to humans.)
**Life spans in the hundreds of years are often given for longer-lived trees such as white and black oaks, but most typically don't exceed the human life span--perhaps because time and chance happeneth to all things.
***The idea that plants & algae (photosynthesizers) are Earth's only producers is actually too broad a generalization. A wide variety of bacteria and archaea produce food using inorganic chemical energy (called chemosynthesis), rather than sunlight. For example, the life surrounding deep sea hydrothermal vents rely on bacteria that extract energy from hydrogen sulfide in hot water flowing from these vents. These bacteria support their own ecosystems in the pitch darkness at the bottom of the sea, without any reliance on light or photosynthesis. Other chemosynthetic bacteria have been discovered in even more unlikely places--including inside rock deep in mines. It remains an open question how much of Earth's life is supported not by photosynthesis, but by chemosynthesis. But an intriguing hypothesis gaining evidence is that life first arose on earth in such a place, rather than in"some warm little pond" as traditionally assumed.
Tuesday, November 29, 2016
Most animals are integrated in another important way: their growth. You (as a representative animal) grew from the cell that resulted from conception in a highly organized dance in which cells actually moved from place to place, divided (at different rates in different places and times), and differentiated into all the many tissues and organs that make up the adult human. (Just how all of this is organized and regulated is cutting-edge science today.) Then, once you had reached adult size, your cells stopped dividing. Just stopped. --with the exception, of course, of those needed to replace skin, blood cells and the like, and those triggered to divide in wound healing, and so on.
Plants do this is a very different and simpler way. Plant cells are encased in a cell wall that strengthens them, provides overall structure to the plant, and effectively fixes the individual cells in place--and is one reason plants don't move. Instead of growing everywhere, land plants grow at shoot and root tips, at regions called meristems. Cells in a meristems divide, then those that end up on the side opposite the tip differentiate into vascular tissue, fibrous tissue, cortex "filler," leaf primordia, etc., while those that are nearer the tip continue to divide, gradually leaving the differentiated stem or root cells behind as the shoot elongates.
Shoot (Coleus?) and root (onion) meristems. Tissue slices have
been stained to show individual cells and their nuclei more clearly.
One consequence of apical growth that surprises people is that the tree branch you have to duck under this year will never be any higher: its height was established when that branch was only a twig. (Those lower branches tend to die over time, though, often leaving the lower trunk bare.)
Unlike animals, most plants have no "adult size": as long as they live, trees and shrubs continue to grow. Because each year's shoot growth begins with last year's buds, to cease to grow is death.
Besides growing at tips, woody plants (trees, shrubs and vines) also grow around their circumference. A layer of tissue under the bark, a lateral meristem called vascular cambium, adds cells inward to form water-carrying xylem tissue, and outward to form sugar-carrying phloem tissue. (When you look at a piece of wood, you are looking at xylem, and the tiny holes sometimes visible in end grain are the cut ends of water-carrying tubes called xylem elements.) While xylem is long-lasting, typically carrying water for many years before finally clogging up and becoming dark-colored "heartwood", phloem is only active for a short period, eventually becoming a second kind of lateral meristem: bark cambium.
This is a good place to talk about the chemistry of animal and plant strength. We mobile animals are a peculiar mixture of delicacy and strength: our individual cells are floppy, insubstantial little blobs of Jello, but together they secrete proteins that form immensely strong fibers (mostly collagen) that make our bodies tough and strong and yet flexible. The walls of plant cells are made of a very different fiber called cellulose, which is a polymer of sugar molecules instead of a protein.
Loose cells are easily scraped off the inside of your cheek with a dull toothpick.
These are stained to show the nuclei. Notice how floppy they are!
Cells in the leaf tissue above have been soaked in a salt solution so they have wilted.
The living tissue of each cell (complete with green, disc-shaped, sugar-generating chloroplasts)
have collapsed, leaving the box-like cell walls intact. Think of severely wilted lettuce.
A cross-section through a stem shows thinner-walled cortex cells with thicker-walled cells. Producing linen begins with beating stems of flax to separate these strong vascular fibers
from the rest and spinning them into thread.
The little cellulose boxes in which plant cells live make them individually tough even as they trap the cells in place. (In fact, green plant cells are hydraulic structures: their rigidity is due to internal water pressure in exactly the same way a football's rigidity is due to air pressure.)* Animals must continually bathe their cells in a mild salt solution that prevents them from either shriveling up (too much salt) or exploding (too little). This vulnerability is the reason athletes must watch their electrolyte (salt) balance. Though plant cells may wilt with too little water (or too much salt) , these cells are immune from damage by fresh water because their cell walls are strong enough to prevent their bursting. Together, these cell walls form the fiber of countless natural products, from the cotton in our clothes, to the rope that formed the rigging of tall ships. In a form stiffened by other molecules (lignin prominent among them), this fiber becomes the wood that builds our homes. Wood, sometimes disparaged in comparison with modern materials, remains stronger for its weight than any other substance.
*I remember the first time I handled a deflated football: the pigskin is soft and flexible (like a plant cell wall). Inside it is a delicate but air-tight rubber bladder (like a cell membrane). The pigskin prevents the inflated bladder bursting just the way a cell wall prevents the plant cell membrane from bursting.