By Marlene Cimons
Neil Pederson's introduction to tree rings came from a "sweet and kindly" college instructor, who nevertheless was "one of the most boring professors I'd ever experienced," Pederson said. "I swore tree rings off then and there." But they kept coming back to haunt him.
As a future forest ecologist, he needed to learn more about the history of forests. So he read countless articles in graduate school extolling the importance of tree rings in unraveling a forest's past. Ultimately, "I fell in love with the beauty and wealth of information found in tree rings," he said. "Since then, tree rings have revealed to me the absolute resiliency of trees and forests. I'm hooked."
Today, he and his colleagues are using the data inherent in these ancient sources of nature to better understand the impact of climate change and carbon dynamics on forests, all the more valuable because data from long-lived trees can reach back decades, even centuries. This is far longer than modern satellite imagery, carbon dioxide measurements, and computer models, whose high-tech information gathering only stretches back about 30 years.
"What tree rings can do is enhance those records," Pederson said. "The satellite record … represents a small portion of the life of a tree, let alone the 'life' of a forest. Further, it only captures the weather 'norm' for a region and, as we are learning, climate varies over time. The weather norms or averages on your nightly weather reports are based on 30-year means. So, while satellite records are good at covering space, they might be limited in what they can tell us about forests due to shortness of these records."
Scientists sampling tulip-poplar at the Black Rock Forest in southern NY.
Neil Pederson / Harvard University
Pederson, now a senior ecologist with Harvard University's Harvard Forest, a 4,000-acre research site, along with Laia Andreu-Hayles, an associate research professor at Lamont-Doherty Earth Observatory of Columbia University, and Mathieu Levesque, research leader of the forest management group at ETH Zurich, analyzed tree rings to determine if the information they gleaned matched the accuracy of high-tech equipment. They wanted to know whether the rings could serve as a proxy for learning more about carbon storage and climate change in forests over the long-term, and found that they could.
Forests serve as important carbon "sinks," absorbing planet-heating carbon dioxide that has been released into the atmosphere by the burning of fossil fuels. But little is known about exactly how much carbon is stored in forests now, or in the past, and scientists are only in recent years learning about the past effects of climate change.
The scientists examined ring samples from two widespread species — tulip poplar (Liriodendron tulipifera) and northern red oak (Quercus rubra) — growing in three climatically different regions of the eastern U.S., then analyzed the carbon and oxygen molecules — or stable isotopes — stored in them. They compared them to estimates obtained from satellites, and found strong agreement each year, and over time. No trees were destroyed to obtain the rings, by the way. Rather, scientists remove an increment core for each sample, each slightly narrower than a pencil.
"Our study is the first to compare stable isotopes from tree rings with the latest generations of productivity estimates from satellites," Levesque said. "We took advantage of the newly developed satellite data, and this is the main novelty of our study."
Their findings appear in the journal Nature Communications.
Flower of tulip-poplar, the tallest documented tree in the eastern U.S.
Neil Pederson / Harvard University
"Tulip poplar trees, one of my favorite trees, are highly sensitive to rainfall," Pederson said. "In fact, they are considered drought deciduous. (These are plants that drop their leaves during dry or drought periods.) During the drought in 1999 in the New York City area, some tulip poplars turned yellow in August and dropped many of their leaves due to the dryness of the year. In 2005, in Kentucky, after a drought in August, the three tulip poplars I walked by every day to work started to grow new leaves in September with the return of rain. I was stunned. These observations made me think this species might be a good candidate [to study.]"
Tulip poplar is highly sensitive to the amount of water in the soil, Pederson said. Also, he added, "it is an important species for timber and ecology over a large portion of the eastern U.S. … We [also] chose the stalwart, northern red oak, because of its different physiology, importance as a species, and its value as a study species in understanding forest productivity."
Levesque agreed. "Both species are great to study," he said. "Their wide distribution in eastern North America and their sensitivity to climate make them ideal species for our research." Moreover, "annual tree rings act like a thermometer and rain gauge and record climate in a very good way," he added.
The rings, in fact, revealed that access to water was the biggest influence in annual forest growth, regardless of climate. "These broadleaf trees need moisture to grow," Andreu-Hayles said. "Some people may think that in wet regions, moisture will be not important, but our study found that even in very humid time periods, as today, these trees are still sensitive to moisture variations. The stable isotopes measured in tree rings are highly sensitive to tracking moisture."
Levesque agreed. "Moisture availability is one of the most important factors for temperate forest growth in the northeastern, southeastern and central U.S.," he said. "That does not mean more moisture [means] more growth, because too wet conditions can also be a limiting factor. By 'regardless of climate,' we simply meant that moisture was the main limiting factor for tree growth and productivity irrespective of the local climate conditions found at the study sites."
Scan of the rings and wood structure of one of the tulip-poplar samples used in the study.
Mathieu Levesque / Harvard University
This is important because climate change has ushered in an era characterized by dramatic increases in extreme weather events, including prolonged drought, heavy precipitation and flooding and dangerous heat waves, thus more information about historic climate fluctuations could be useful in projecting future climate effects on forests. Experts regard the health of forests as a critical factor in mitigating carbon pollution.
Pederson noted that droughts in the 16th and 17th centuries were believed to be far worse than those in recent centuries, but it could be that climate change — by prompting more intense precipitation in some regions — has made the earlier droughts seem severe in comparison, he said. "The important thing to remember, however, is even though it is expected to rain more in the northeastern and eastern U.S. in the future, the warming associated with climate change will increase evaporation and the drought stress on plants," Pederson said. "It is not clear what will happen."
It's possible that as parts of the world become wetter, and warming reduces the overall amount of water in the region during the summer, it will worsen droughts, he said. Or it will become so wet that a rise in warming will balance the increase in precipitation, he said. Or — if rain decreases — the increase in warming will amplify the drought stress in trees, even if it doesn't seem as if the amount of available water has changed, he said.
The researchers hope to expand their research, examining more trees and additional species, and to look further back in time. "This kind of work will be extremely important considering that the longest remote sensing data started in 1982, and trees can live centuries-long," Andreu-Hayles said.
Pederson agreed. "These kinds of studies will provide considerable insight into how these trees will respond to climate and extreme climatic events … We can learn a lot from the memories of trees," he said.
Reposted with permission from our media associate Nexus Media.
EcoWatch Daily Newsletter
By Michael Svoboda
The enduring pandemic will make conventional forms of travel difficult if not impossible this summer. As a result, many will consider virtual alternatives for their vacations, including one of the oldest forms of virtual reality – books.
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By Beth Ann Mayer
Since even moderate-intensity workouts offer a slew of benefits, walking is a good choice for people looking to stay healthy.
How to Rock Your Walk<p>Walking isn't just fun and healthy. It's accessible.</p><p>"Walking is cheap," says Dr. John Paul H. Rue, a sports medicine doctor at <a href="https://mdmercy.com/" target="_blank">Mercy Medical Center in Baltimore</a>. "You can do it anywhere at any time; [it] requires little to no special equipment and has many of the same cardio benefits as running or other more intense workouts."</p><p>Want to up your walking game? Try the tips below.</p>
Use Hand Weights<p>Cardio and strength training can go hand-in-hand when you add weights to your walk.</p><p>A <a href="https://journals.lww.com/acsm-msse/Fulltext/2019/03000/Associations_of_Resistance_Exercise_with.14.aspx" target="_blank">2019 study</a> found that weight training is good for your heart, and <a href="https://www.mayoclinicproceedings.org/article/S0025-6196(17)30167-2/abstract" target="_blank">research</a> shows it reduces the risk of developing a <a href="https://www.healthline.com/health/nutrition-metabolism-disorders" target="_blank">metabolic disorder</a> by 17 percent. People with metabolic disorders have a higher chance of being diagnosed with high cholesterol, high blood pressure, and diabetes.</p><p>Rue suggests not carrying weights for your entire walk.</p><p>"Hand weights can give you an added level of energy burning, but you have to be careful with these because carrying [them] over a long period of time or while walking could actually lead to some overuse injuries," he says.</p>
Make It a Circuit<p>As another option, consider doing a circuit. First, put a pair of dumbbells on your lawn or somewhere in your home. Walk around the block once, then stop and do some bicep curls and tricep lifts before walking around the block again.</p><p>Rue recommends <a href="https://www.healthline.com/health/exercise-fitness/running-with-weights" target="_blank">avoiding ankle weights</a> during cardio workouts, as they force you to use your quadriceps rather than hamstrings. They can also cause muscle imbalance, according to the <a href="https://www.health.harvard.edu/staying-healthy/wearable-weights-how-they-can-help-or-hurt" target="_blank">Harvard Health Letter</a>.</p>
Find a Fitness Trail<p>Strength training isn't limited to weights. You can get stronger by <a href="https://www.healthline.com/health/bodyweight-workout" target="_blank">simply using your body</a>.</p><p>Often found at parks, fitness trails are obstacle courses with equipment for pullups, pushups, rowing, and stretches to build upper and lower body strength.</p><p>Try searching "fitness trails near me" online, checking out your local parks and recreation website, or calling the municipal office to <a href="https://calisthenics-parks.com/" target="_blank">find one</a>.</p>
Recruit a Friend<p>People who workout together stay healthy together.</p><p><a href="https://bmcgeriatr.biomedcentral.com/articles/10.1186/s12877-017-0584-3" target="_blank">One study</a> showed that older adults who exercised with a group improved or maintained their functional health and enjoyed their lives more.</p><p>Enlist the help of a walking buddy with a regimen you aspire to have. If you don't know anyone in your area, apps like <a href="https://www.strava.com/" target="_blank">Strava</a> have social networking features so you can get support from fellow exercisers.</p>
Try Meditation<p>According to the <a href="https://www.nccih.nih.gov/research/statistics/nhis/2017" target="_blank">2017 National Health Interview Survey</a>, published by the National Institutes of Health, meditation is on the rise, and for good reason.</p><p>Researchers <a href="https://pubmed.ncbi.nlm.nih.gov/29616846/" target="_blank">found</a> that mind-body relaxation practices can regulate inflammation, <a href="https://www.healthline.com/health/biological-rhythms" target="_blank">circadian rhythms</a>, and <a href="https://www.healthline.com/health/glucose" target="_blank">glucose</a> metabolism, as well as lower <a href="https://www.healthline.com/health/high-blood-pressure-hypertension" target="_blank">blood pressure</a>.</p><p>"Any form of exercise can be turned into a meditation of some type, either by the surroundings you are walking in, like a park or trail, or by blocking out the outside world with music on your headphones," Rue says.</p><p>You can also play a podcast or download an app like <a href="https://www.headspace.com/headspace-meditation-app" target="_blank">Headspace</a> that has a library of guided meditations to practice while you walk.</p>
Do Fartlek Walks<p>Typically used in running, fartlek intervals alternate periods of increased and decreased speed. These are <a href="https://www.healthline.com/nutrition/benefits-of-hiit" target="_blank">high-intensity interval training (HIIT)</a> workouts, which allow exercisers to accomplish more in less time.</p><p><a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0154075" target="_blank">One study</a> showed that 10-minute interval training improved <a href="https://www.healthline.com/health/metabolic-syndrome" target="_blank">cardiometabolic</a> health, or lowered the risk of heart disease, stroke, and diabetes, just as well as working out at a continuous pace for 50 minutes.</p><p><a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0111489" target="_blank">Research</a> also shows that HIIT workouts increase muscle <a href="https://www.healthline.com/health/fast-twitch-muscles" target="_blank">oxidative</a> capacity, or the ability to use oxygen. To do a fartlek walk, try walking at an increased pace for 3 minutes, slow down for 2 minutes, and repeat.</p>
Gradually Increase Pace<p>A faster walking pace is associated with a lower risk of <a href="https://www.healthline.com/health/copd" target="_blank">chronic obstructive pulmonary disease (COPD)</a> and respiratory diseases, according to a <a href="https://pubmed.ncbi.nlm.nih.gov/30303933/" target="_blank">2019 study</a>.</p><p>Still, it's best not to go from a stroll to an Olympic-worthy power walk in a day. Instead, increase your pace gradually to prevent injury.</p><p>"Start by walking at a brisk pace for about 10 minutes per day, 3 to 5 days per week," Rue says. "Once you've done this for a few weeks, increase your time by 5 to 10 minutes per day until you get to 30 minutes."</p>
Add Stairs<p>You've likely heard that taking the stairs instead of an elevator is a way to add more movement into your daily routine. It's also a way to step up your walking. Stair climbing has been shown to <a href="https://www.sciencedirect.com/science/article/pii/S2211335519301123?via%3Dihub" target="_blank">decrease the risk of mortality</a> and can easily add a bit more challenge to your walk.</p><p>If you don't have stairs in your home, you can often find them outside a local municipal building, train station, or at a high school stadium.</p>
Is Your Walk a True Cardio Workout?<p>Not all walks are equal. A walk that's too leisurely may not provide enough burn to qualify as cardio. To see if you're getting a good workout, try to <a href="https://www.healthline.com/health/how-to-check-heart-rate" target="_blank">measure your heart rate</a> using a monitor.</p><p>"A target goal for a good walking workout heart rate is about 50 to 70 percent of your maximum heart rate," Rue says, adding that maximum heart rate is <a href="https://www.healthline.com/health/fitness-exercise/fat-burning-heart-rate" target="_blank">typically calculated</a> by 220 beats per minute minus your age.</p><p>You can also monitor how easily you can carry on a conversation while you walk to gauge your heart rate.</p><p>"If you can walk and carry on a normal conversation, that's probably a lower intensity walk," says Rue. "If you are slightly breathless but can still have a conversation, that's probably a moderate workout. If you are out of breath and can't talk normally, that's a vigorous workout."</p>
Takeaway<p>By shaking up your routine, you can add excitement to your workout and reap even more rewards than a basic walk provides. Increasing the pace and intensity of a workout will make it more effective.</p><p>Simply pick your favorite variation to add some spice to your next walk.</p>
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