Can Human DNA Help Guide Reforestation?

Early shock damages trees for life, as it did for survivors like Audrey Hepburn.

Posted Apr 13, 2019

 Patricia Prijatel
One of our Ponderosa pine seedlings
Source: Patricia Prijatel

This spring, we will again plant seedlings on our 35 acres in the southern Colorado Rockies. It’s been nearly six years since the East Peak Fire of 2013 incinerated much of our forest, and we’ve planted more than a thousand trees to replace the burned hulls that now pockmark our hillsides. We’ve tried a variety of evergreens and broad-leaf trees, and the Douglas firs and ponderosa pines have grown the best. The largest, a fir, is now almost five feet tall, a bit gorgeous.

We’re looking for evidence of why some trees grow better than others in this new landscape and for guidance on what to do next.

Our mountain is getting hotter with each summer, and drought is persistent, results of climate change.  According to the Natural Resources Defense Council, the American West is warming at a rate 70 percent higher than the rest of the world, with an average increase in temperature of 1.7 degrees in the four years from 2003 to 2007. Every year since 1998 has been hotter than the previous one, with all the hottest years recorded since 1880 occurring since 2005.

But we’re committed to helping rebuild our forest for reasons profound and petty: We want our grandchildren to enjoy a planet similar to the one we knew and we know that healthy forests help create healthy people and a healthy planet. Plus, we want our beauty back.

Forests play a significant role in helping cool the planet, reducing carbon and pollutants from the air. They are one of the most natural solutions to climate change—and their destruction is one of its causes. Plus, they are giant anti-anxiety medications, calming us naturally with no side effects.

We also know we are making only small progress on our land, but that is clearly better than no progress. We’ve pored through forestry materials and may have found some direction in a field that helped me understand my two bouts of triple-negative breast cancer: epigenetics.

Trees and the Climate

In the United States, tree species are slowly moving north and west, so logic holds that if we want to plant something that can withstand a warming planet, we should consider varieties that have traditionally grown in areas south and east of us, which would likely mean pinons and junipers, the trees of the high desert.  Yet, what to make of the health of our firs and pines, trees that have grown on this mountainside for hundreds of years? Perhaps, like humans, they have evolved in response to their environment.

This latter theory gets some support from the science of epigenetics, which has been studied in humans but which, researchers now say, might help us understand how other species, such as trees, prepare to weather a changing climate. 

What Is Epigenetics?

Epigenetics is a process in which our DNA expression changes because of factors such as stress, the environment, age, and lifestyle. Our underlying DNA sequence remains the same—we can still use it to see if we are actually related to the Rockefellers—but the way those genes are read is altered, as is the way they react to one another.

Grammarians and psychologists might understand this in passive-versus-active terms. That is, the underlying DNA is passive, while the epigenetic changes are active, influencing the way cells within the genes communicate. Epigenetic changes in humans can result in diseases such as cancer and can affect how cancer progresses and the degree to which it becomes a risk for subsequent generations. Most important in terms of cancer is that epigenetic factors can be reversible—both by drugs and by changing some of what influenced the cancer to begin with—such as quitting smoking to avoid lung cancer.

Why am I the only one among my five siblings to get cancer? Partially because of the environment in which I grew. I was born in December, a month full of colds and sicknesses. The others were born in spring and summer. Who knows what viruses my mother faced in pregnancy? As an adult, my diet, exercise, stress level, and exposure to environmental toxins influenced the cells in my body to develop cancer. I gained weight in the decade before I was diagnosed, and obesity is a clear risk factor for breast cancer. That’s a shorthand picture of epigenetics. Did I pass it on to my children? I hope not, as my worst lifestyle impulses hit long after they were born, but I’ve had less control over toxins in the water and air, nor my mother’s sniffles.

Epigenetic Research

Perhaps the most widely quoted study of epigenetics was conducted during the Dutch famine between 1944 and 1945, which found that children born of mothers deprived of food had increased rates of schizophrenia, coronary heart disease, and obesity compared to those not affected by the famine. That is, the mothers were starved, and the children faced both psychological and physical harm because of it. These were not trivial changes; these were DNA-level alterations. Audrey Hepburn may be the most famous survivor of the famine. She suffered from anemia and respiratory illness for her entire life and her waif-thin body could have been the result of childhood starvation.

A recent study in Indonesia discovered that children who were exposed to smoke from forest fires while in the womb were significantly shorter—1.7 inches by age 17—than those whose mothers had breathed healthier air. Researchers followed the children since 1997 when fires that had been intentionally set to clear land for palm oil plantations burned out of control.

Depending on who you ask, epigenetics either contradicts or complements Darwin’s theory of natural selection, which maintains that species thrive and evolve because of their inherent strengths and die because of inherent weaknesses. Nature chooses the strongest to survive, and too bad for the rest.

But according to epigenetics, species adapt based on external, not internal, forces. The environment in which an individual plant or human grows determines the challenges it faces, how it evolves based on those challenges, and how those changes are passed on to subsequent generations.  This answers some of the question left open by Darwin’s theories—such as why one identical twin gets cancer and the other doesn’t and why some diseases, such as cancer, have increased in frequency in modern decades.

It also explains how Scott Kelly's DNA changed after six months aboard the International Space Station, as compared to his earthbound identical twin, Mark Kelly. 

Patricia Prijatel
A 5-year-old Douglas fir
Source: Patricia Prijatel

Epigenetics and Our Forest

As some of the largest organisms on the planet, trees also have epigenetic activity. When a tree is planted, its seed contains epigenetic memory related to conditions at the time of planting.  This memory helps it withstand changes in temperatures from season to season and tells it when to bud.

This is a sequence horticulturists and foresters know well. But what hasn’t been clear until recent research is how that sequence can vary based on whether that seed was planted during a warm, cold, dry or wet conditions. Research on Spruce trees in Norway demonstrated that the trees’ ability to live through brutal winters—with temperatures as low as 200 degrees below zero—is part of their genetic makeup that can evolve based on what happens in their embryonic stage.  Trees planted in warmer temperatures may bud at different times or be able to withstand climate variations related to heat and drought.

In short, if conditions warm, younger trees might be able to survive because of changes embedded in them when they were seeds. And they will pass this along in their seeds, changing the species along the way.

The fact that we planted our pine and fir seedlings in drought conditions may mean they can handle the increasingly hot and dry summers, which is leading to the loss of forests through disease, insect infestation, and wildfires.  

And today’s trees may also be different internally from their ancestors. Researchers in Munich found that trees have consistently begun growing faster. More importantly, they are lighter, with a lower volume of wood, than in old growth forests. The causes include temperature increases related to climate change that results in a longer vegetation period, plus added nitrogen from commercial and agricultural sources. Sadly, this means that newer trees are less resilient to the risks they face and are more likely to burn quickly or to break in heavy winds or snows.

But the epigenetic study of forests is in its infancy, with much more work needed before we can make any plans or conclusions based on it. In short, as we plant our trees, we’re looking to the future with hope rather than with scientific proof.

We’ve ordered 30 seedlings—ponderosa pines and Douglas firs—from the Colorado State Forest Service to plant this spring as part of our little amateur experiment. We’re going with what worked in the recent post-fire past. We realize that this piece of our past is a sad predictor of our future: more heat, more drought, more tree loss, more fire danger.

Is that epigenetic philosophy? Only the recent past is the predictor of our future? Could be.

Our forest is such a little drop in the global bucket, and I’m not sure we can do this, or that we know what we are doing, but we have to at least try. We need all the forests we can get.

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