Sunday, February 11, 2018

Point of Failure

Nurse Log. Hoh Rain Forest, Olympic National Park, WA. Photo Taken 9/4/15.

Trees growing out of trees. That old, dead tree lying on the ground that supports the newer trees is called a Nurse Log, as in, it nurses the young trees until they can stand on their own. Many old trees started out as young trees growing out of old trees.

The wheel, the pulley, the inclined plane, screw, wedge, lever, these were early machines. In the beginning, they were simple, made of wood, stone, or raw metals. Today, machines are usually elaborate complexes or systems of these simple machines. An example would be a jet engine.

In a system or machine, there are points at which failure can occur. Some points are more prone to failure than others and some points are more critical than others. Some points of failure will stop the entire machine. These are called Single Points of Failure. This is an undesirable state; such a machine is highly vulnerable to total system failure. Imagine a jet engine flywheel breaking apart and slicing through the hydraulic lines while cruising at 40,000 feet.

The ideal is to create redundancies, that is, to duplicate critical functions within the machine. That way, if one function fails, a duplicate function takes over and the machine can continue to operate. That is one reason a passenger jet has multiple engines. This is important while travelling eight miles high.

It is also important on the ground. To understand this, we must consider the experience of the mythical Jedediah Clampett. According to the legend, when he discovered crude oil on his property in Limestone Tennessee, it came to the surface under its own power. A small hole punched in the ground by an errant bullet provided relief to the pressurized oil trapped underground. Why, it flowed out of the hole like water from a garden hose and the bubbling crude made old Jed a millionaire.

At that point in time, his machine for oil extraction was no more than a shovel. A shovel is a simple machine, just a wooden handle, a pin, and a blade. It acts as a wedge and lever. Each is a Single Point of Failure. One of those breaks and the tool is useless and Jed is unable to gather any oil. He tosses the handle into the woods, drops to his knees, scoops the oil with a flat rock, and gently eases back into the Stone Age.

Today, it is unusual to find an oil field that pours from the ground under artesian pressures. Most of the new oil is found at the margins of extractability: in shale, sand, offshore, deepwater. A shovel will not do. It requires an exceedingly complex machine, a myriad of pipes, valves, gauges, wires, alarms, switches, and sensors. The possible points of failure become innumerable. The Single Points of Failure also increase, requiring a complex arrangement of redundant functions. However, this increases the risk of total system failure and a calamity. In the Deepwater Horizon disaster, there were numerous points at which failure occurred - a blowout preventer, two mechanical valves, one battery, one gas alarm, a defective switch, and human oversight - all of which conspired to create a total system failure. Eleven lives were lost, 4.9 million barrels of crude poured into the Gulf of Mexico, and 52,590 tons of mangled metal settled to the bottom of the Gulf. This was just one machine. The planet is littered with millions of broken machines; in landfills, backyards, war zones, junkyards, garages, parking lots, sealed in concrete bunkers, ravines, at the bottom of the sea, tumbling in earth orbit. What to do?

A tree is a machine. A large tree functions as a water pump, oxygen generator, carbon sink, weather moderator, fog filter, windbreak, birdhouse, soil stabilizer, food source, to name a few. As with other machines, at some point, it experiences a total system failure, whether it's from drought, insects, lightning, windthrow, climate shift, fungus, landslide, overshading, hydrologic changes. Add them up and there are millions of failure points in a tree. Yet these provide opportunities for other living things. Spring ephemerals take advantage of fall leaf failure and prosper in the abundant spring sunlight. Microorganisms on forest floor take advantage of needle failure and turn them into nutrients. Campers take advantage of branch failure and roast marshmallows. Insects and birds take advantage when the whole tree fails and build apartments. Other trees take advantage of a fallen tree and drop their seeds into the rotting carcass where they germinate and thrive. Trees grow out of failed trees. This machine is designed to fail.

Fail as they may, we have searched the newspapers and it is very difficult to find accounts of massive explosions, tragic loss of life and limb, toxic chemical spill, or power grid failure associated with the death of a tree, despite millions of them occurring every year since the late Carboniferous period.

Monday, February 05, 2018

Minimum Viable Population

Distribution of Prairie fringed orchid (Platanthera praeclara) in a portion of Ransom County, ND. 
Map from a 2008 report. 
This is a federally threatened species. In a given year, there may be 10-20,000 specimens in existence, distributed across 45 counties. This is a drastic decline from pre-settlement populations, which enjoyed vast expanses of tallgrass prairie habitat. Today, that habitat is one of the rarest in North America.

While 10-20,000 plants in 45 counties may sound like a lot, it is not. Here is why: Species have what are called Minimum Viable Populations (MVP), or extinction thresholds. These are population numbers below which they spiral into extinction. Below this threshold, the effects of inbreeding, loss of genetic variability, or loss of mating opportunities are fatal to the population. They go extinct.

There have been attempts to establish a universal MVP; in the 1980's it was suggested that at least 50 individuals were needed to prevent inbreeding and 500 individuals were needed to prevent genetic drift. Genetic drift is the change in frequency of a particular gene variant, which can be devastating if that frequency is a decline or loss of frequency. Which is to say, a loss of genetic diversity, a capacity to express traits that may be needed in a given environment. This is called a shrinking gene pool. 

But those threshold numbers, while somewhat useful, are persistently impractical because reproductive rates, existing genetic diversity, and habitat requirements vary from species to species. Consider: Those of us who have been ushered into the Space Age are aware that we are now able to look back at ourselves from a distant vantage point. A nighttime view from 223 miles above the earth shows the arrangement of human populations, bright, lighted clusters of humans with dark, somewhat vacant gaps in between. This satellite view is of the middle of North America. 

As you may have noticed, the populations of Platanthera praeclara, and in fact, most other species, are arranged in a similar way. Rather than being evenly or regularly distributed across the landscape, populations are usually clustered in nodes or centers with gaps of relatively unpopulated land in between. The entire network of lights or population clusters in a given region may be likened to a metapopulation. The arrangement of clusters is largely driven by habitat suitability. For humans, that is rivers, fertile valleys, groundwater, wind protection, coffee shops, trails. 

Removing a population cluster removes their genetic material from the metapopulation. This may be insignificant if there are enough individuals remaining in the metapopulation that contain the same genetic material. But removing many more populations will increase the risk that vital genetic material is removed from the entire metapopulation. Thus, most people understand that the total number of species must be maintained at a high level. 

However, here is where the total numbers can mislead, as in 10-20,000 orchids or 370 black-footed ferrets or 25,000 Red Knots. Back to the satellite photo. Suppose the metapopulation in the photo is 20,000 people. What would happen if all of those remaining populations were cut off from one another, if you removed the corridors between populations, the roads, rivers, railroads, and air routes? The breeding population would be reduced to the population of the city, in this scenario, maybe no more than 1000 people. The population would become like the inhabitants of a walled city surrounded by siege engines. This forces consanguineous marriage, prohibits the exchange of genetic material with outside populations, creating a community much like the royal families of ancient times. Gigantic jaws, cartoon character hands, flowerpot-shaped heads. In this scenario, the effective population is not the metapopulation, it is the individual population cluster. They are restricted to their own shallow, stagnant gene pool, sluggish, in a torpor, each generation less fit than the last. As the catapults fling blighted cattle over the walls, the inhabitants of the besieged city succumb to plague, infertility, reproductive failure, and loss of mates. Extinction approaches on fused feet. 

The lesson? This teaches us that it is not enough to consider total population numbers, it is necessary to consider the access one population has to another. This means corridors - suitable habitat patches connecting populations - are essential in maintaining an MVP.

In the end, the niches are filled, the city is reinhabited, and soon there is a bustling metropolis teeming with cane toads, mongoose, brown tree snakes, Norway rats, Asian carp, feral pigs, water hyacinth, and a broad spectrum of strip malls. At the moment, humans appear to have the genetic diversity needed to adapt to these threats. In the meantime, however, the orchids, ferrets, and Knots cannot interpret aerial photography; they have no idea what approaches their city walls.

Friday, February 02, 2018

Carbon Fingerprint

Lignite Coal.
Decaying blocks of black coal along the bank of the Missouri River, McKenzie County, ND. Photo 7/15/13

This coal is from a geologic stratum called the Sentinel Butte Formation. Lignite is a soft, brownish coal with fewer calories and more moisture than other coals, making it an intermediary between peat and bituminous or anthracite coal. The Sentinel Butte Formation is from the late Paleocene Epoch in the early Cenozoic Era. This epoch began after the C-T extinction event, which marked the extinction of dinosaurs and the advent of mammals. It is old. 
It has been observed that that plains Indians did not burn much of this coal, nor did the Corps of Discovery as they sailed by these bluffs two hundred years ago. It was in 1804 that William Clark remarked that the coal was of "inferior quality." Their fuel of choice was firewood cut from the cottonwood, ash, elm, and juniper trees that were plentiful along the Missouri River. This is for good reason. The smokes of hickory, mesquite, apple, alder, cherry and other woods have long been popular flavorings in grilled foods, but we have yet to see any food products on the market that advertise "Natural Coal Smoke Flavor", nor do we expect to see any in the near future. The hapless homesteaders did make use of the lignite, perhaps out of the desperation of the times, and by 1939, at the height of the Great Depression, there were some 309 mines operating in North Dakota. But today there are only six coal mines out there and two of those produce oxidized lignite, not for burning. None for food. 
The distinction between coal smoke and wood smoke goes beyond successful backyard bar-b-ques. While coal and wood both originate as plant matter and terminate as fuel, the antiquity of the plant matter accounts for a significant difference in the chemistry of the fuel, a distinct carbon fingerprint. Here is how it works: Humans have a symbiotic relationship with plants. We produce carbon dioxide as waste matter, plants consume carbon dioxide as food. Carbon comes in about 15 sizes, called isotopes. Three are naturally found on earth: C12, C13, and C14. The latter is a radioactive isotope, unstable, formed by cosmic radiation, ultimately decaying into an isotope of Nitrogen. This is a slow deterioration; the half-life of C14 is 5,730 years.
While living, plants incorporate carbon in their tissues and the balance of carbon isotopes in their tissues reflects the balance of carbon isotopes in the atmosphere. When a plant dies, they no longer take in carbon and the carbon that remains in their tissues is fixed, set. From this point, the unstable C14 continues to decay, slowly depleting the dead tissues of C14.  
In the short term, what this means is, when a dead cottonwood limb is thrown into a campfire, and the wind shifts and casts the plume of campfire smoke over the campers, they are inhaling smoke almost fully stocked with busy, buzzing, radioactive C14 atoms. Only a few atoms have been lost to decay. However, when a chunk of Paleocene coal is thrown into a campfire, and the wind shifts and the smoke descends upon the ashen, hacking campers, they inhale a lighter, decadent smoke, one depleted of C14 atoms.
In the mid-term, the empirical evidence is there has been a dramatic increase in carbon in the earth's atmosphere. Currently, we are above 400 ppm. That's a 100% increase since the ice age and a level 25% higher than anything for the past 400,000 years. Where is all that smoke coming from?
The answer is in the chemistry of the carbon. The atmospheric carbon, while increasing in quantity, has been steadily decreasing in C14 in the past century; it is being depleted of C14. This could not be from the burning of firewood or rain forests, grassland or forest fires, or burning other plant matter of recent origin. These would produce smoke that has nearly the full stock of C14, which would not deplete the atmosphere of C14. This must be from the combustion of carbon sources that are depleted in C14. Ancient plant matter has lost its C14 through radioactive decay. Their combustion products lack C14 and thereby deplete the atmosphere of C14. This is the source of the smoke. This is what is called "fossil fuel." Coal, natural gas, petroleum. Old plant matter.
Ah, the smoking gun.
In the long-term, it is estimated that there are over one trillion tons of extractable coal reserves on earth, which would last 150 years at present consumption rates. At the same time, combustion of these reserves in that time frame would contribute to a novel set of environmental conditions on earth. As Foster (2017) states, "Humanity's fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO2 not seen since the early Eocene...If CO2 continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years."
Without precedent. At which point, all trees may be ancient plant matter, food may grill spontaneously, coal-flavored dishes may be standard fare, and visibility would be reduced to a few smoggy meters. Let us cough. This remodeled earth will have a brand new look, but with a decidedly retro feel. We will name our new home Venus.

Gavin Foster et al. Future climate forcing potentially without precedent in the last 420 million years. Nature Communication. April 2017.

M. S. Baxter and A. Walton. A Theoretical Approach to the Suess Effect. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences. Vol. 318, No. 1533 (Aug. 11, 1970), pp. 213-230