Sunday, February 07, 2016

Peach Mortality

Weather: Jémez are so marbled with snow they look like limestone. Temperatures remained at least five degrees colder than normal in the mornings. Rained Monday night with snow in the air Wednesday.

What’s still green: Juniper, other evergreens; leaves on yuccas, grape hyacinth, garlic, vinca, hollyhock, winecup mallow, pink evening primrose, snapdragon, anthemis, golden hairy asters, most low or buried; June, pampas, and cheat grasses.

What’s blue-green or gray: Leaves on Apache plumes, four-winged saltbushes, pinks.

What’s red or purple: Stems on roses, young peaches, sandbar willows; leaves on coral beard tongues, alfilerillo, purple asters.

What’s yellow or brown: Arborvitae, stems of weeping willows.

What’s blooming inside: Zonal geraniums.

Animal sightings: Rabbits, small birds.

Weekly update: I’ve always been told the life expectancy of Prunus persica is 15 to 20 years, and my peach tree is now 18 years ago. The bark has begun to split, and aphids attacked a couple years ago.

I’ve been wondering when it will die, and why. All I could learn on the web were the likely causes of mortality, which were nematode infestations, peach borers, and consequences of split bark. I didn’t learn much about the inherent life cycle of the tree itself.

That information is equivalent to being told the life expectancy for men is 46 years and for women 48 because that’s what it was in 1900. In 1950 it was 71 years for women and 66 years for men. What changed wasn’t something inherent in the species but the ability of doctors and governmental agencies to control the spread of infectious diseases.

Now, with more people living beyond retirement age, medical researchers are studying the effects of aging, and more important, what constitutes aging, or senescence. One important factor is the hormonal changes that divide a woman’s reproductive years into childhood, maturity, and post-menopause. Equivalent changes occur in men’s bodies but aren’t as visible.

The known botanical hormones follow annual cycles, with some encouraging growth in spring, and others preparing plants to survive the winter. As Oliver Rackham made clear, the above ground portions of all trees die every year and are rebuilt from the roots each spring. So why, if a tree has survived its initial exposures to drought and heat and cold and wet, would it die?

I got one hint from a group of Chinese anthropologists who quoted one study that said the "modern peach loses considerable productivity after 10-15 years," and another that indicated "early Chinese records report that productivity declined in years 7-8."

There are, no doubt, as many factors affecting peach fertility as there are influencing human life expectancies. Climate has changed in the thousands of years of peach domestication in China, and so has the species. The differences might also have been as simple as differences in fertilization methods and subsequent soil depletion rates.

Still, when a group in India asked orchard growers about the economics of growing peaches in Punjab and Uttrakhand they discovered incomes declined after 17 years. The horticulturalists saw no returns for the first four years after they planted trees, then earned 22,927 in year five. That increased to 31,790 in year eight and to 42,838 in year eleven. Income dropped to 31,793 in orchards that were 18 years old, fell to 21,443 in year 22 and 13,633 in year 25.

The three researchers didn’t provide their currency unit. They also wrote about orchard ages, not average ages of trees within those orchards. Thus, incomes may have been higher in older orchards because new trees had been planted when ones died. Even so, their data suggested age phases existed.

I wonder if decreases in fertility in peaches covary with decreases in the abilities of plants to survive stress caused by insects, bacteria and weather, the way age and flexibility seem to in humans.

Christina Wells and Desmond Layne found trees produced new fine roots at least three times a year, with "a significant flush occurring immediately after harvest." The plants they observed were four- to six-years old and in their first years of fruiting. Do trees grown barren have the same spurt?

Wells and another team found the age of fine roots had less effect on their life spans than "seasonal factors." In Italy, a team led by Elena Baldi found the roots "born later in the summer lived longer than those born in the spring." That in part is because "root numbers declined in the fall and remained low over winter" according to Wells’ group.

Age was important when it meant roots were larger or reached lower depths in the soil. In addition, with time, roots become more fibrous and brown. Wells’ group suggested that made them less attractive to pests and better able to handle drought. But age for them was relative to the roots themselves, and not to the parent trees.

So, I really know no more about the metabolism of my tree than when I started, because researchers aren’t interested in what happens to commercially important plants when they no longer are productive. After all, Lal Singh Gangwar’s team recommended growers replace their old orchards when their maintenance costs were greater than their gross profits.

Baldi, E., M. Toselli, D. M. Eissenstat, B. Marangoni, and Peter Millard. "Organic Fertilization Leads to Increased Peach Root Production and Lifespan," Tree Physiology 30:1373-1382:2010.

Faber, Joseph F. and Alice H. Wade. Life Tables for the United States: 1900-2050, 1983.

Gangwar, L. S., Dinesh Singh, and Goutam Mandal. "Economic Evaluation of Peach Cultivation in North Indian Plains," Agricultural Economics Research Review 21:123-129:2008.

Rackham, Oliver. See post for 19 October 2014.

Wells, Christina and Desmond Layne. "Irrigation Effects on Fine Root Dynamics in Peach (Prunus persica)," HortScience, July 2005.

_____, D. Michael Glenn, and David M. Eissenstat. "Changes in the Risk of Fine-root Mortality with Age: a Case Study in Peach, Prunus persica (Rosaceae)," American Journal of Botany 89:79-87:2002.

Zheng, Yunfei, Gary W. Crawford, and Xugao Chen. "Archaeological Evidence for Peach (Prunus persica) Cultivation and Domestication in China," Plos One, 5 September 2014.

1. Replacement peach trees, planted 19 May 2012.

2. Tree of left the next year, 19 June 2013.

3. Earliest picture I have of the main peach, 6 August 2006.

4. The worst thing that happened to my peach was a Russian olive hid in the middle, forcing its branches outward, 4 May 2012. After the olive was cut down, the tree was invaded by aphids in 2013 and the bark began splitting.

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