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Trees ‘remember’ wetter times − never having known abundant rain could buffer today’s young forests against climate change
In a changing climate, trees exhibit “legacy effects” from past droughts or wet periods. Young trees, adapted to arid conditions, offer hope for future forest resilience amidst escalating climate challenges globally.
Alana Chin, Cal Poly Humboldt ; Janneke Hille Ris Lambers, Swiss Federal Institute of Technology Zurich, and Marcus Schaub, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL)
What does the future hold for forests in a warmer, drier world? Over the past 25 years, trees have been dying due to effects of climate change around the world. In Africa, Asia, North America, South America and Europe, drought stress amplified by heat is killing trees that have survived for centuries.
Old trees may have grown through entire millennia that were wetter than the past 20 years. We are scientists who study forest dynamics, plant ecology and plant physiology. In a recent study, we found that trees can remember times when water was plentiful and that this memory continues to shape their growth for many years after wet phases end.
This research makes us optimistic that young trees of today, which have never known 20th-century rainfall, have not shaped their structure around water abundance and thus may be better equipped to survive in a chronically dry world.
What if we water the forest?
This study built on nearly 20 years of forest research in response to early warning signs of forest loss in the 1990s in the dry Rhône River Valley of the Swiss Alps. At that time, scientists observed that Scots pine trees that had stood for around 100 years were declining and dying. They wondered whether drought or other climate factors were driving this loss.
To tackle this question, researchers at the Swiss Federal Institute for Forest, Snow and Landscape Research designed an ecological experiment. To understand the impacts of drought, they would irrigate a mature forest, doubling natural summertime rainfall, and then compare how these water-rich trees fared in comparison with those receiving only natural precipitation.
The Pfynwald experiment, launched in 2003, has shown that trees survived at higher rates in irrigated plots. After 17 years of irrigation, the team found that irrigation didn’t just help trees survive dry phases – it also increased their growth rates. https://www.youtube.com/embed/OA7A-xWhDeo?wmode=transparent&start=0 Tree physiologist Leonie Schönbeck conducts research at Pfynwald, a natural reserve in southern Switzerland, to learn how trees take up and store energy and use their reserves to recover from drought.
Legacy effects are forests’ memories
Trees experiencing drought alter their leaves, wood and roots in ways that prime them for continued dry conditions. Wood under drought might have smaller cells that are less vulnerable to future damage, and roots might increase relative to leaf area. These structural changes persist after the drought has passed and continue to influence the tree’s growth and ability to tolerate stress for many years.
Known as “legacy effects,” these lingering post-drought impacts represent an ecological memory of past climatic conditions at the tree and forest level. Knowing that trees hold a persistent memory of past dry phases, researchers wondered whether they might also show structural changes in response to past wet periods.
Eleven years after summertime irrigation started in Pfynwald, scientists stopped irrigating half of each plot in 2013 to address this question. The formerly irrigated trees, which at this point were about 120 years old, had experienced a lasting period of irrigation – but now those times of plenty were over.
Would the trees remember? A decade later, we found out.
Trees, trains and particle accelerators
On an early March morning in 2023, two of us (Alana Chin and Marcus Schaub) met at Pfynwald to collect very fresh leaf and twig samples so that we and colleagues could look inside to search for signs of lasting effects of past water richness.
At the site, we climbed canopy access towers to collect newly grown treetop leaves and twigs from control trees that had never been irrigated; trees that had been irrigated every summer since 2003; and formerly irrigated trees that had not received irrigation water since 2013.
We took our samples to the Swiss Light Source, an intensely powerful synchrotron – a type of particle accelerator that produces the world’s most intense beams of light. This facility is the home of the TOMCAT, an extremely high-resolution X-ray that allowed us to look inside our leaves and twigs without disturbing their structure.
Scanning our samples took all night, but when we stumbled out of the building, we had images capturing every cell in exquisite detail.
The memory of water
We found that the new leaves of once-irrigated trees were different from both continually watered trees and never-watered control trees. Leaves carry out photosynthesis that fuels a tree’s survival and growth. Inside them, we could see the legacy of past water abundance, written in the size, shape and arrangement of cells.
Reading this cellular signature, we observed that, at the expense of structures promoting productivity, formerly irrigated trees showed every sign of chronic water stress – even more so than never-irrigated trees. In their anatomy, we saw why these trees that had it easy for 11 wet years were now growing slowly.
Every cell in a leaf comes with a trade-off. Trees must balance investments in rapid photosynthesis with others that promote leaf survival. Rather than building the cells used to harvest sunlight and ship sugar to the rest of the tree, leaves on the trees that had been irrigated showed every indication of drought stress we could think to measure.
After receiving extra water for an 11-year stretch and then losing it, the trees were producing new, tiny leaves that invested mostly in their own survival. The leaves were structured to protect themselves from insects and drought and to store water reserves. Compared with leaves on trees that had never known irrigation, these looked as though they were in the middle of the drought of the century.
While this memory of water might seem negative, it likely once helped trees “learn” from past conditions to survive in variable environments. The formerly irrigated trees did not know that humans had played a trick on them. Like trees experiencing climate change, they had no way of knowing that the water was not coming back.
When trees experience a drought event, recovery can mean reaching a “new normal” state, in which they are prepared to survive the next drought, with smaller, less vulnerable cells and increased energy reserves to ‘save up’ for future dry periods. They may have deeper roots or a smaller pool of leaves to support, helping them prepare for an unstable environment.
We wanted to know whether the same was true of trees that had experienced water abundance. Were they waiting in distress for the water to return?
Hard times may make tough trees
In some temperate forests, like the ones we studied in Switzerland, old trees once knew levels of water abundance that now are gone, thanks to climate change. That past abundance may have locked into place structural and epigenetic changes in the trees that are mismatched to today’s drier world. If this is true, then some of today’s devastating global tree mortality events may be, in part, due to the legacy effects of past water abundance.
In most of the world’s temperate forests, however, the current cohort of young forest trees – those sprouting in the past 15 to 20 years – has managed to establish itself under conditions that once would have been considered chronic drought. Those young trees, which have survived an endless dry period, will form the forests of the future.
In all, our observations in Pfynwald have provided us some room for hope that young trees currently taking their place in many forests worldwide may be better prepared to cope with the world as humans have shaped it. Climate shifts in recent decades have primed them for hard times, without the lingering memory of water.
Alana Chin, Assistant Professor of Plant Physiology, Cal Poly Humboldt ; Janneke Hille Ris Lambers, Professor of Environmental Systems Science, Swiss Federal Institute of Technology Zurich, and Marcus Schaub, Group Leader, Forest Dynamics and Ecophysiology, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL)
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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The Bridge
Harriet Tubman led military raids during the Civil War as well as her better-known slave rescues
Harriet Tubman, renowned for her vital role in the Underground Railroad, also served as a Civil War spy and leader, fighting for freedom and equality despite enduring systemic racism and discrimination.
Kate Clifford Larson, Brandeis University
Harriet Tubman was barely 5 feet tall and didn’t have a dime to her name.
What she did have was a deep faith and powerful passion for justice that was fueled by a network of Black and white abolitionists determined to end slavery in America.
“I had reasoned this out in my mind,” Tubman once told an interviewer. “There was one of two things I had a right to, liberty, or death. If I could not have one, I would have the other; for no man should take me alive.”
Though Tubman is most famous for her successes along the Underground Railroad, her activities as a Civil War spy are less well known.
As a biographer of Tubman, I think this is a shame. Her devotion to America and its promise of freedom endured despite suffering decades of enslavement and second class citizenship.
It is only in modern times that her life is receiving the renown it deserves, most notably her likeness appearing on a US$20 bill in 2030. The Harriet Tubman $20 bill will replace the current one featuring a portrait of U.S. President Andrew Jackson.
In another recognition, Tubman was accepted in June 2021 to the United States Army Military Intelligence Corps Hall of Fame at Fort Huachuca, Arizona. She is one of 278 members, 17 of whom are women, honored for their special operations leadership and intelligence work.
Though traditional accolades escaped Tubman for most of her life, she did achieve an honor usually reserved for white officers on the Civil War battlefield.
After she led a successful raid of a Confederate outpost in South Carolina that saw 750 Black people rescued from slavery, a white commanding officer fetched a pitcher of water for Tubman as she remained seated at a table.
A different education
Believed to have been born in March 1822 in Dorchester County, Maryland, Tubman was named Araminta by her enslaved parents, Rit and Ben Ross.
“Minty” was the fifth of nine Ross children. She was frequently separated from her family by her white enslaver, Edward Brodess, who started leasing her to white neighbors when she was just 6 years old.
At their hands, she endured physical abuse, harsh labor, poor nutrition and intense loneliness.
As I learned during my research into Tubman’s life, her education did not happen in a traditional classroom, but instead was crafted from the dirt. She learned to read the natural world – forests and fields, rivers and marshes, the clouds and stars.
She learned to walk silently across fields and through the woods at night with no lights to guide her. She foraged for food and learned a botanist’s and chemist’s knowledge of edible and poisonous plants – and those most useful for ingredients in medical treatments.
She could not swim, and that forced her to learn the ways of rivers and streams – their depths, currents and traps.
She studied people, learned their habits, watched their movements – all without being noticed. Most important, she also figured out how to distinguish character. Her survival depended on her ability to remember every detail.
After a brain injury left her with recurring seizures, she was still able to work at jobs often reserved for men. She toiled on the shipping docks and learned the secret communication and transportation networks of Black mariners.
Known as Black Jacks, these men traveled throughout the Chesapeake Bay and the Atlantic seaboard. With them, she studied the night sky and the placement and movement of the constellations.
She used all those skills to navigate on the water and land.
“… and I prayed to God,” she told one friend, “to make me strong and able to fight, and that’s what I’ve always prayed for ever since.”
Tubman was clear on her mission. “I should fight for my liberty,” she told an admirer, “as long as my strength lasted.”
The Moses of the Underground Railroad
In the fall of 1849, when she was about to be sold away from her family and free husband John Tubman, she fled Maryland to freedom in Philadelphia.
Between 1850 and 1860, she returned to the Eastern Shore of Maryland about 13 times and successfully rescued nearly 70 friends and family members, all of whom were enslaved. It was an extraordinary feat given the perils of the 1850 Slave Fugitive Act, which enabled anyone to capture and return any Black man or woman, regardless of legal status, to slavery.
Those leadership qualities and survival skills earned her the nickname “Moses” because of her work on the Underground Railroad, the interracial network of abolitionists who enabled Black people to escape from slavery in the South to freedom in the North and Canada.
As a result, she attracted influential abolitionists and politicians who were struck by her courage and resolve – men like William Lloyd Garrison, John Brown and Frederick Douglass. Susan B. Anthony, one of the world’s leading activists for women’s equal rights, also knew of Tubman, as did abolitionist Lucretia Mott and women’s rights activist Amy Post.
“I was the conductor of the Underground Railroad for eight years,” Tubman once said. “and I can say what most conductors can’t say; I never ran my train off the track and I never lost a passenger.”
Battlefield soldier
When the Civil War started in the spring of 1861, Tubman put aside her fight against slavery to conduct combat as a soldier and spy for the United States Army. She offered her services to a powerful politician.
Known for his campaign to form the all-Black 54th and 55th regiments, Massachusetts Gov. John Andrew admired Tubman and thought she would be a great intelligence asset for the Union forces.
He arranged for her to go to Beaufort, South Carolina, to work with Army officers in charge of the recently captured Hilton Head District.
There, she provided nursing care to soldiers and hundreds of newly liberated people who crowded Union camps. Tubman’s skill curing soldiers stricken by a variety of diseases became legendary.
But it was her military service of spying and scouting behind Confederate lines that earned her the highest praise.
She recruited eight men and together they skillfully infiltrated enemy territory. Tubman made contact with local enslaved people who secretly shared their knowledge of Confederate movements and plans.
Wary of white Union soldiers, many local African Americans trusted and respected Tubman.
According to George Garrison, a second lieutenant with the 55th Massachusetts Regiment, Tubman secured “more intelligence from them than anybody else.”
In early June 1863, she became the first woman in U.S. history to command an armed military raid when she guided Col. James Montgomery and his 2nd South Carolina Colored Volunteers Regiment along the Combahee River.
While there, they routed Confederate outposts, destroyed stores of cotton, food and weapons – and liberated over 750 enslaved people.
The Union victory was widely celebrated. Newspapers from Boston to Wisconsin reported on the river assault by Montgomery and his Black regiment, noting Tubman’s important role as the “Black she Moses … who led the raid, and under whose inspiration it was originated and conducted.”
Ten days after the successful attack, radical abolitionist and soldier Francis Jackson Merriam witnessed Maj. Gen. David Hunter, commander of the Hilton Head district, “go and fetch a pitcher of water and stand waiting with it in his hand while a black woman drank, as if he had been one of his own servants.”
In that letter to Gov. Andrew, Merriam added, “that woman was Harriet Tubman.”
Lifelong struggle
Despite earning commendations as a valuable scout and soldier, Tubman still faced the racism and sexism of America after the Civil War.
When she sought payment for her service as a spy, the U.S. Congress denied her claim. It paid the eight Black male scouts, but not her.
Unlike the Union officers who knew her, the congressmen did not believe – they could not imagine – that she had served her country like the men under her command, because she was a woman.
Gen. Rufus Saxton wrote that he bore “witness to the value of her services… She was employed in the Hospitals and as a spy [and] made many a raid inside the enemy’s lines displaying remarkable courage, zeal and fidelity.”
Thirty years later, in 1899, Congress awarded her a pension for her service as a Civil War nurse, but not as a soldier spy.
When she died from pneumonia on March 10, 1913, she was believed to have been 91 years old and had been fighting for gender equality and the right to vote as a free Black woman for more than 50 years after her work during the Civil War.
Surrounded by friends and family, the deeply religious Tubman showed one last sign of leadership, telling them: “I go to prepare a place for you.”
Kate Clifford Larson, Professor of History, Brandeis University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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health and wellness
Rural Americans don’t live as long as those in cities − new research
Rural Americans, especially men, face shorter life expectancies compared to urban dwellers due to higher rates of chronic conditions and limited healthcare access. Education disparities significantly contribute to these health inequities, influencing lifestyle choices and economic stability.
Elizabeth Currid-Halkett, University of Southern California; Bryan Tysinger, University of Southern California, and Jack Chapel, University of Southern California
Rural Americans – particularly men – are expected to live significantly shorter, less healthy lives than their urban counterparts, according to our research, recently published in the Journal of Rural Health.
We found that a 60-year-old man living in a rural area is expected on average to live two fewer years than an urban man. For women, the rural-urban gap is six months.
A key reason is worse rates among rural people for smoking, obesity and chronic conditions such as high blood pressure and heart disease. These conditions are condemning millions to disability and shortened lives.
What’s more, these same people live in areas where medical care is evaporating. Living in rural areas, with their relatively sparse populations, often means a shortage of doctors, longer travel distances for medical care and inadequate investments in public health, driven partly by declines in economic opportunities.
Our team arrived at these findings by using a simulation called the Future Elderly Model. With that, we were able to simulate the future life course of Americans currently age 60 living in either an urban or rural area.
The model is based on relationships observed in 20 years of data from the Health and Retirement Study, an ongoing survey that follows people from age 51 through the rest of their lives. Specifically, the model showed how long these Americans might live, the expected quality of their future years, and how certain changes in lifestyle would affect the results.
We describe the conditions that drive our results as “diseases of despair,” building off the landmark work of pioneering researchers who coined the now widely used term “deaths of despair.” They documented rising mortality among Americans without a college degree and related these deaths to declines in social and economic prospects.
The main causes of deaths of despair – drug overdoses, liver disease and suicide – have also been called “diseases of despair.” But the conditions we study, such as heart disease, could similarly be influenced by social and economic prospects. And they can profoundly reduce quality of life.
We also found that if rural education levels were as high as in urban areas, this would eliminate almost half of the rural-urban life-expectancy gap. Our data shows 65% of urban 60-year-olds were educated beyond high school, compared with 53% of rural residents the same age.
One possible reason for the difference is that getting a bachelor’s degree may make a person more able or willing to follow scientific recommendations – and more likely to work out for 150 minutes a week or eat their veggies as their doctor advises them to. https://www.youtube.com/embed/_WzwHJbAGVc?wmode=transparent&start=0 Rural communities are increasingly hampered by their lack of access to health care.
Why it matters
The gap between urban and rural health outcomes has widened over recent decades. Yet the problem goes beyond disparities between urban and rural health: It also splits down some of the party lines and social divides that separate U.S. citizens, such as education and lifestyle.
Scholarship on the decline of rural America suggests that people living outside larger cities are resentful of the economic forces that may have eroded their economic power. The interplay between these forces and the health conditions we study are less appreciated.
Economic circumstances can contribute to health outcomes. For example, increased stress and sedentary lifestyle due to joblessness can contribute to chronic health issues such as cardiovascular disease. Declines in economic prospects due to automation and trade liberalization are linked to increases in mortality.
But health can also have a strong influence on economic outcomes. Hospitalizations cause high medical costs, loss of work and earnings, and increases in bankruptcy. The onset of chronic disease and disability can lead to long-lasting declines in income. Even health events experienced early in childhood can have economic consequences decades later.
In tandem, these health and economic trends might reinforce each other and help fuel inequality between rural and urban areas that produces a profoundly different quality of life.
What still isn’t known
It should be noted that our results, like many studies, are describing outcomes on average; the rural population is not a monolith. In fact, some of the most physically active and healthy people we know live in rural areas.
Just how much your location affects your health is an ongoing area of research. But as researchers begin to understand more, we can come up with strategies to promote health among all Americans, regardless of where they live.
The Research Brief is a short take on interesting academic work.
Elizabeth Currid-Halkett, James Irvine Chair in Urban and Regional Planning and Professor of Public Policy, University of Southern California; Bryan Tysinger, Assistant Professor of Health Policy and Management, University of Southern California, and Jack Chapel, Postdoctoral Scholar in Economics, University of Southern California
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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