Posts Tagged ‘Science’

Each garden has its own personality, distinct oddities that make it unlike any other patch of ground in the world. My current garden amuses itself by sending me a mystery vine every summer. It’s always in a different spot, it’s always something from the squash family, and it’s never the same species.

One year enormous yellow flowers turned into hard green balls which slowly resolved into pumpkins. Another year, the vine climbed around a wire bin in the shady northeast corner of my garden and by season’s end dripped with tiny jewel-like decorative gourds.

Two summers ago, as I awaited the huge sexy flowers typical of squashes and gourds, I was startled by spikes of white flowers poking out along my vine: it was a wild cucumber.

Last year, however, I could find nothing. June came and went. Maybe I missed some offering to the garden gnomes. But then, in mid-July I saw it beginning to creep along between the house and the garage. Just before the leaves dissolved into black mush this fall, I harvested two perfect acorn squash. Last night I baked them for dinner with apples and a touch of butter and brown sugar.

I had not left space for this squash (it grew into a path and we stepped over it all summer), I had not purchased the seed, I had not planted the vine, nor had I watered or weeded. The squash, all on its own, planted itself, harvested its own sunlight and extracted its share of limited rainfall. It was free in every sense of the word: no labor, no money, no planning, no time.

But, least you think that the “no free lunch” adage applies only to lunch, I have to tell you it applies to dinner too. It turns out there was a cost to my squash. It goes by the eye-glazing name of soil depletion. The squash took from the soil the nutrients it needed to grow–nutrients that will be gone from this patch of land for years to come unless someone returns them, perhaps via a handful of compost or some chicken droppings.

In the words of Lester Brown, founder of the Earth Policy Institute, “The thin layer of topsoil that covers the planet’s land surface is the foundation of civilization.” Looking back on world history is more often than not a study of soil productivity. Where soils were deep and life-giving, people flourished, when soils were over-tapped and over-grazed, civilizations fell.

Indeed, when we consider what is necessary to support life on earth, productive soil is right up there near the top of the list, close to sunshine and water.

Healthy soil is a world unto itself: a mix of minerals, organic matter, insects, bacteria, fungi, and animals, that provides both the critical nutrients plants require as well access to water and air.

Soil formation begins with a pocket of minerals such as sand, glacial grit, or lava, worn fine enough for a rugged pioneer plant to sneak in a few roots. When the plant dies it returns some of the nutrients it used as well as adding organic matter. As the soil becomes richer, more plant species are able to survive.

Insects and animals appear, contributing their droppings and eventually their bodies to the gradually deepening soils. Its a beautiful natural process, but unfortunately rather slow: a single inch of topsoil is approximately five hundred years in the making.

The planet is now losing topsoil 10-20 times faster than it is being replenished. Much of this erosion is due to farming and grazing practices that leave bare soils exposed to wind and rain.

As topsoils are washed into our waterways and blown into dust storms, so are vast quantities of carbon released. Scientists estimate that there is three times more carbon locked in soil than there is currently in the atmosphere. This carbon is released as soils are disturbed, and may contribute up to 30% to global warming.

If there were vast swaths of untapped agricultural land just waiting in the wings, none of this might be a problem. But farmland is in scarce supply in many places. A few years ago South Korea tried to purchase a 99 year lease to half of Madagascar’s arable land. South Korea and Madagascar are 6,500 miles apart.

Virtually all human food calories come from the land. Global food production has kept pace with population growth largely because of reliance on chemical fertilizers. However, overuse of fertilizer, along with many other modern farming practices eventually destroy soil structure and the soil ecosystems that maintain it. The result is that food production per acre of land is declining.

Although most people pay no attention to it, good dirt is a resource sorely in need of protection. Practices that protect soil fertility, soil structure, and retain soil carbon include low or no-till methods, leaving some of the crop behind after harvest to hold soil in place, and planting cover crops, windbreaks, and vegetative buffers along waterways.

On my quarter acre square of the planet, I try to minimize the amount of organic matter that leaves our property. We compost our food scraps, pile up our oak leaves, and allow our grass clippings to disappear back into the lawn.

The area where my acorn squash grew used to be a compacted beat up piece of grass. A few years ago I put down a thick layer of partially decomposed oak leaves to kill the grass, and topped it with pine needles swept up from Brunswick streets. The result was a lovely rusty golden path between the structures, edged with a few ferns, and other plants–and no need for mowing. It was here that my squash chose to grow, perhaps a thank you for giving something back to the soils.

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The prairie town of Lethbridge in southern Alberta sits on a high plain just to the east of the Rockies. Winds from the west scream across the mountains, depositing on the peaks whatever moisture they might contain. Lethbridge, consequently, is bone dry, averaging about 15” of precipitation annually–about the same as Tucson, Arizona.

In regions as arid as this, life revolves around rivers. The St. Mary River flows out of Glacier National Park in the mountains of northwestern Montana, across the border into southern Alberta, just south of Lethbridge.

The river supports a lush corridor of trees, a rare green oasis bustling with wildlife. Cottonwoods and willows, uniquely suited to the wet and dry cycles of river flood plains, dominate the banks and are key species, providing food, shade and shelter for innumerable plants, fish, insects, amphibians, and animals.

Not surprisingly, the St. Mary River is also critically important to the human population, serving a range of uses including irrigation, hydroelectric power, and municipal water. Fed in large part by snow melt from the mountains, the St. Mary typically runs high in spring and lower in the summer. In 1951, a dam was built on the river to allow for limited storage of spring melt water for use later in the summer, as well as to facilitate a diversion of water to the adjacent Milk River basin.

Within a few decades it became apparent that cottonwood populations downstream of the dam were collapsing. Older trees were gradually dying and younger trees were not being established. The same pattern was evident in other arid western river basins below dam installations. Kayakers were among the first to notice the decline.

What was going on? Biologists at the University of Lethbridge, lead by Stewart Rood, wondered if the altered timing of stream flows, caused by the dam, were to blame. They compared historical records of stream flow data to the age, health, and species mix of trees along the river. They retreated into greenhouses and simulated the effects of different watering regimes on seedlings.

Newly hatched cottonwood seedlings are, in fact, perfectly adapted to the vagaries of life on the banks of arid western rivers.  To deal with the natural cycle of abundant spring water followed by long dry summers, the tiny trees, some no taller than inch or two in height, unfurl a few token leaves and then sink all of their energy into growing a single hair-like tap root.  As long as the trees can keep a toe in the dropping water table, they have a good chance for survival.

The building of the dam allowed for spring water flows to be terminated abruptly, rather than gradually as used to happen in the free flowing river. In other words, once the spring flood crest passed, dam operators shut spillway gates to save water for the drier summer months, resulting in an immediate and steep drop of the water table in the flood plain. The baby trees could not keep up and quickly withered.

In the greenhouse, Rood and his colleagues found that young seedlings could generate an impressive 2.5 cm per day of new root. They proposed that stream flow be reduced gradually enough to allow the trees’ roots to keep pace with the water table. Dam operators were willing to give it a try, provided there was ample water from spring storms or winter snow melt.

Heavy rain in June of 1995 offered a perfect opportunity for a trial. The test was wildly successful. By the end of the season the river banks were covered, for the first time in decades, with vivid green carpets of new cottonwood seedlings. Similar tests in other river basins yielded the same results. Because ideal conditions for new tree establishment in wild river systems occur about once every 5-15 years, there was no problem with resource managers implementing the additional spring water flows only in years with high spring precipitation or a large winter snow-pack.

This utterly elegant solution highlights the ongoing importance of continued investigation into the basic natural sciences such as biology, hydrology, and ecology. As natural systems are under increasing pressure, it is only our intimate understanding of how they function that will let us live in harmony with them rather than destroying them.

Yet I fear that many of the skills required to be a good student of the natural world are skills that have eroded with our changing culture. The speed of a calculator, for example, may allow us to quickly find answers and perhaps produce more, yet it also distances us from a feel for numbers that comes only from hours spent cranking through problems by hand.

Many folk that used to be able to rebuild every bolt in their cars now look under the hood with bafflement. Kids that once grew up intimately connected with the woods out the back door are now, instead, teaching their parents how to use computers.

While it is absolutely true that we must train people to work in hi-tech fields, with calculators, computers, and microchips, it is equally true that we still need to nurture tinkerers, careful observers, and those people who will float down rivers and first say, “What happened to all the trees?” and then, “I have an idea…”

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