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Plants’ essential services and climate change

By FRANCES LAMBERTS

When the rains stay away and they are water-starved, trees become stressed, vulnerable to insect attacks and other maladies, and may die. In an international bestseller book, “The hidden life of trees,” German forester Peter Wohlleben observes that after a couple of weeks of high temperatures and no rain, forests usually begin to suffer, and “extreme droughts bring many trees to the brink of death.”

In our months-long drought last year, rainfall was nearly a foot below its yearly average, and 20 inches below in the Chattanooga area. There, many shallow wells ceased to bring up water and “forests and fields (were) drying to a crisp,” as the Times Free Press reported. Incident to climate change, last year’s drought was the third to afflict Tennessee since the turn of the century.

In March, in the journal Science Advances, a hydrology research team from Purdue University and, separately, Urs Willmann in Die Zeit, reported on a region in Africa where a unique dwarf tree and other vegetation must make due with “non-rainfall water” to survive. In the Unesco World-Heritage Namib Desert, the life-essential water resource also has been dwindling under climate change.

Dry periods there can last for decades. Because an Antarctic cold-water stream prevents cloud formation along the coast, the desert receives almost no rain and is considered one of the driest of the world’s “drylands.” These, the researchers say, are zones where precipitation is “considerably less” than what their plants give back to the atmosphere through evaporation.

The Welwitschia tree is known only from this region. Adapting itself to the desert’s harsh conditions, it lets its upward-growth bud die after the stem reaches some three or four foot height and has grown two broad, strap-like, leathery leaves. These lie on the ground, continually growing in length and becoming “torn to ribbons” in the desert sand. A cone-bearing tree and its nectar and pollen nourishing insects, Welwitschia reaches an average lifespan of 400 to over 1,000 years; the largest specimens are thought to be 2,000 years old.

Morning dew and thick blankets of fog which nightly envelope the sand dunes are the principal source of water for all life forms there. Over millions of years, this desert’s plants and animals evolved growth forms and behavior that lets them sustain their lives and future. Welwitschia opens its leaf pores during the night to “drink,” beetles stand rear-end up on the dunes to “harvest” water from the fogs.

By far, most of the water present in the fogs, the researchers found, comes through the plants recycling it from deep in the ground. But with up to 20 percent less humidity and hotter sands under global warming, the area covered by the nightly fogs is shrinking and, already, some fog-harvesting beetles are disappearing.

In Tennessee as across the globe, trees and other plants are the primary food providers for all “higher” life. Not just the Namib desert’s beetles but our own, humans’ future will be at risk if the causes of climate change are not addressed.