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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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Travel Advisory
Traveling to Mexico this spring? Here’s what to know about current advisories
Traveling to Mexico this spring? Visitors should be aware of state-specific travel advisories, as safety concerns in one region do not affect major resort areas like Cancun and Los Cabos, currently rated Level 2, which encourages increased caution. Monitoring official updates is essential for informed travel decisions amidst evolving conditions.
Last Updated on March 10, 2026 by Daily News Staff
Traveling to Mexico this spring? Here’s what to know about current advisories
(Tiffany Miller for ALG Vacations) For some travelers counting down to spring break, recent headlines about violence in parts of Mexico have sparked a new question: Should I cancel my trip? Travel advisors say they are seeing a surge in calls and emails from clients trying to determine whether developments in one region affect major resort areas elsewhere.
The questions follow several days of unrest in parts of Mexico after security operations targeting organized crime leaders prompted temporary flight disruptions and shelter-in-place guidance for U.S. government personnel in areas including Puerto Vallarta and Guadalajara. In this article, ALG Vacations explains what current travel advisories mean for spring break travelers heading to Mexico.
The U.S. State Department evaluates Mexico state by state, not as a single destination, and advisory levels vary by region. Many major beach destinations, including Cancun, Riviera Maya, Tulum and Los Cabos, are currently under a Level 2 advisory, which encourages travelers to exercise increased caution. It does not discourage travel.
Part of the confusion stems from geography. Puerto Vallarta, on the Pacific coast, is roughly 1,300 miles from Cancun and the Riviera Maya on the Caribbean side, about the distance between New York and Miami. Because advisories are assigned state by state, developments in one region do not automatically alter another.
In recent days, that uncertainty has translated into additional inquiries about whether specific resort areas are experiencing disruptions. U.S. Embassy security alerts issued this week indicate that temporary shelter-in-place guidance affecting Puerto Vallarta was lifted and that flight operations resumed. The advisory level for the Mexican state of Quintana Roo remains unchanged.
Some clients are asking about alternatives, advisors say, but many are continuing with their plans after reviewing official updates. Travel patterns often shift in response to breaking headlines, they add, before stabilizing as clearer information becomes available.
The State Department assigns travel advisories on a four-tier scale ranging from Level 1, exercise normal precautions, to Level 4, do not travel. While Level 2 encourages increased awareness, Level 3 and Level 4 carry stronger language discouraging or restricting travel.
Advisories are reviewed regularly and can be updated as conditions evolve. The State Department’s Mexico advisory page breaks down conditions by state, reflecting the country’s federal structure rather than issuing a single national designation. Travelers can also enroll in the State Department’s Smart Traveler Enrollment Program, which provides real-time security updates and allows U.S. officials to contact citizens in an emergency.
Embassy notices state that airports, hotels and tourism services in Quintana Roo are operating normally. Security conditions across Mexico vary widely by state, with some regions carrying higher advisories and others designated Level 1. Most destinations popular with U.S. travelers are currently classified as Level 2.
As spring break approaches, advisors say informed decision-making depends on reviewing the advisories assigned to a specific destination and monitoring official updates, rather than reacting to national headlines alone. Travel decisions ultimately depend on individual comfort levels, they add, but advisory levels are assigned regionally and should be evaluated accordingly.
Photo courtesy of Shutterstock
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Last Updated on March 8, 2026 by Daily News Staff
Jay L. Zagorsky, Boston University
With the Olympic torch extinguished in Paris, all eyes are turning to Los Angeles for the 2028 Olympics.
The host city has promised that the next Summer Games will be “car-free.”
For people who know Los Angeles, this seems overly optimistic. The car remains king in LA, despite growing public transit options.
When LA hosted the Games in 1932, it had an extensive public transportation system, with buses and an extensive network of electric streetcars. Today, the trolleys are long gone; riders say city buses don’t come on schedule, and bus stops are dirty. What happened?
This question fascinates me because I am a business professor who studies why society abandons and then sometimes returns to certain technologies, such as vinyl records, landline phones and metal coins. The demise of electric streetcars in Los Angeles and attempts to bring them back today vividly demonstrate the costs and challenges of such revivals. https://www.youtube.com/embed/9X78ZqGyc5o?wmode=transparent&start=0 The 2028 Olympic Games will be held in existing sports venues around Los Angeles and are expected to host 15,000 athletes and over 1 million spectators.
Riding the Red and Yellow Cars
Transportation is a critical priority in any city, but especially so in Los Angeles, which has been a sprawling metropolis from the start.
In the early 1900s, railroad magnate Henry Huntington, who owned vast tracts of land around LA, started subdividing his holdings into small plots and building homes. In order to attract buyers, he also built a trolley system that whisked residents from outlying areas to jobs and shopping downtown.
By the 1930s, Los Angeles had a vibrant public transportation network, with over 1,000 miles of electric streetcar routes, operated by two companies: Pacific Electric Railway, with its “Red Cars,” and Los Angeles Railway, with its “Yellow Cars.”
The system wasn’t perfect by any means. Many people felt that streetcars were inconvenient and also unhealthy when they were jammed with riders. Moreover, streetcars were slow because they had to share the road with automobiles. As auto usage climbed and roads became congested, travel times increased.
Nonetheless, many Angelenos rode the streetcars – especially during World War II, when gasoline was rationed and automobile plants shifted to producing military vehicles. https://www.youtube.com/embed/AwKv3_WwD4o?wmode=transparent&start=0 In 1910, Los Angeles had a widely used local rail network, with over 1,200 miles (1,930 kilometers) of track. What happened?
Demise of public transit
The end of the war marked the end of the line for streetcars. The war effort had transformed oil, tire and car companies into behemoths, and these industries needed new buyers for goods from the massive factories they had built for military production. Civilians and returning soldiers were tired of rationing and war privations, and they wanted to spend money on goods such as cars.
After years of heavy usage during the war, Los Angeles’ streetcar system needed an expensive capital upgrade. But in the mid-1940s, most of the system was sold to a company called National City Lines, which was partly owned by the carmaker General Motors, the oil companies Standard Oil of California and Phillips Petroleum, and the Firestone tire company.
These powerful forces had no incentive to maintain or improve the old electric streetcar system. National City ripped up tracks and replaced the streetcars with buses that were built by General Motors, used Firestone tires and ran on gasoline.
There is a long-running academic debate over whether self-serving corporate interests purposely killed LA’s streetcar system. Some researchers argue that the system would have died on its own, like many other streetcar networks around the world.
The controversy even spilled over into pop culture in the 1988 movie “Who Framed Roger Rabbit,” which came down firmly on the conspiracy side.
What’s undisputed is that, starting in the mid-1940s, powerful social forces transformed Los Angeles so that commuters had only two choices: drive or take a public bus. As a result, LA became so choked with traffic that it often took hours to cross the city.
In 1990, the Los Angeles Times reported that people were putting refrigerators, desks and televisions in their cars to cope with getting stuck in horrendous traffic. A swath of movies, from “Falling Down” to “Clueless” to “La La Land,” have featured the next-level challenge of driving in LA.
Traffic was also a concern when LA hosted the 1984 Summer Games, but the Games went off smoothly. Organizers convinced over 1 million people to ride buses, and they got many trucks to drive during off-peak hours. The 2028 games, however, will have roughly 50% more athletes competing, which means thousands more coaches, family, friends and spectators. So simply dusting off plans from 40 years ago won’t work.
Olympic transportation plans
Today, Los Angeles is slowly rebuilding a more robust public transportation system. In addition to buses, it now has four light-rail lines – the new name for electric streetcars – and two subways. Many follow the same routes that electric trolleys once traveled. Rebuilding this network is costing the public billions, since the old system was completely dismantled.
Three key improvements are planned for the Olympics. First, LA’s airport terminals will be connected to the rail system. Second, the Los Angeles organizing committee is planning heavily on using buses to move people. It will do this by reassigning some lanes away from cars and making them available for 3,000 more buses, which will be borrowed from other locales.
Finally, there are plans to permanently increase bicycle lanes around the city. However, one major initiative, a bike path along the Los Angeles River, is still under an environmental review that may not be completed by 2028.
Car-free for 17 days
I expect that organizers will pull off a car-free Olympics, simply by making driving and parking conditions so awful during the Games that people are forced to take public transportation to sports venues around the city. After the Games end, however, most of LA is likely to quickly revert to its car-centric ways.
As Casey Wasserman, chair of the LA 2028 organizing committee, recently put it: “The unique thing about Olympic Games is for 17 days you can fix a lot of problems when you can set the rules – for traffic, for fans, for commerce – than you do on a normal day in Los Angeles.”
This article has been updated to indicate that Los Angeles has four light-rail lines.
Jay L. Zagorsky, Associate Professor of Markets, Public Policy and Law, Boston University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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The Bridge
Celebrating International Women’s Day!
International Women’s Day is celebrated globally on March 8th to honor women’s achievements and promote gender equality, originating from a 1908 march in New York for better rights.
Last Updated on March 7, 2026 by Daily News Staff
International Women’s Day is a global celebration that honors the achievements of women and highlights the progress still to be made in the fight for gender equality. On this day, people around the world come together to recognize the amazing contributions of women everywhere and to rally for greater gender equity in all areas of life.
The origins of International Women’s Day can be traced back to 1908, when 15,000 women marched through the streets of New York City to demand better working conditions and the right to vote. Since then, the celebration has grown to be an international event, with more than 100 countries recognizing the day. The United Nations even declared March 8th as International Women’s Day in 1975, to honor the struggles of women around the world.
This year’s International Women’s Day theme is #ChooseToChallenge, meaning that everyone is encouraged to call out gender bias and inequality when they see it. We’re also encouraged to celebrate women’s achievements, support each other, and take action for equality.
It’s important to recognize the progress we’ve made in terms of gender equality, but we still have a long way to go. International Women’s Day serves as a reminder that we must continue to fight for gender equality in all areas of life. Let’s use this day to honor the contributions of women around the world, and to continue the fight for a more equitable world.
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