This article originally appeared on Grist, and it is part of Climate Desk’s collaboration.
Nicholas Dietschler, a researcher in New York’s Catskill Mountains is standing before an eastern hemlock seedling. It’s June 1, and it’s warm. It is looking a bit gloomy. The lower branches of the evergreen are dead and brittle. The limbs on its upper branches are becoming bald. Dietschler scans the tree for stubby, aching needles. He quickly finds what he is looking for. The spindly branches of the sapling are covered by tiny, woolly white bumps about the size and shape of sesame seeds. Dietschler moves his thumb over the bumps. He holds up an orange-streaked finger and says “Blood.” They’re still alive.
The ground is covered with a blue cooler, which has been filled with perfectly stacked plastic vials. Dietschler looks at the cooler and says “I just signed up for the next five years to work on this.” Dietschler will likely be the last person to see this hemlock, along with many others in the northeastern United States.
The tiny bumps are the egg sacs of a destructive insect called the woolly adelgid, which caught a ride with Japanese goods bound for America in the early 20th century and has been wreaking havoc on the nation’s Eastern forests ever since. Aphid-like insects sucking sap from hemlock branches, decimating trees. They can also reproduce sexually and are all females, making them formidable enemies. The woolly adelgid is being assisted by climate change in their quest to dominate the Northeast’s hemlocks. It has been spreading northward into more colder regions. It’s already rampaged through the southern Appalachian Mountains, leaving a trail of millions of devastated hemlocks on its way north. The adelgid could spread unchecked to the Northeast, and hemlocks may disappear completely.
Survival of an animal species is dependent on its ability to survive, and that outcome may depend on what the blue cooler contains.
Invasive species are difficult to contain in the absence of climate change. They’ve also become more difficult to control as the country has become warmer in winter and is becoming more temperate. This allows pests to reach previously unreachable areas. Invasive tree bugs, and other blights, are increasing in the United States. Dutch elm diseases, which is spread by the voracious and destructive elm bark mitetle, are threatening hundreds of thousands of American elms. Butternut canker disease has infected the white walnut. Beeches are falling ill with beech bark and beech leaf disease. The emerald oak borer, an iridescent green insect has decimated ash trees. Sudden oak death, a pathogen, is coming for oak trees. The woolly adelgid is ravaging hemlocks.
The US cannot afford to lose trees. By photosynthesis, the nation’s forests are able to absorb 9 percent carbon from its existing carbon-emitting trees. The carbon dioxide in wood slowly releases into the atmosphere when trees are killed. Only 15 pests other than the woolly adelgid threaten forests in excess of 40%. Already, the biomass lost to invasives every year releases emissions similar in magnitude to the emissions produced by trees killed in wildfires–the carbon equivalent of the tailpipe emissions produced by 5 million cars on the road each year.
The popularity of “natural” climate solutions, which use landscapes to store carbon dioxide to combat global warming, is increasing. The United States is not the only country investing millions in planting trees. In the US, members of Congress want to plant 100 billion new trees. However, their plans do not take into consideration exotic species. The rising tide of pests is not certain. It’s unlikely that the new trees or existing trees will be able withstand it. Our Hail Mary climate solution could become part of the problem if the climate changes force trees across the country to emit carbon dioxide rather than sequester it.
Dietschler is probably standing before a single hemlock. At the top of the mountain, however, is a beautiful grove of old-growth, healthy hemlocks that grow from the forest floor. They have thick canopies that are bushy and thick, unaffected by pests or saws over hundreds of years. It is striking to see the difference in these hemlocks from those of lower elevation. It’s like walking into a cathedral when you enter the healthy grove. Even on summer days, it’s dark and quiet.
Dietschler, gazing uphill, says that the reason we are releasing here was because of this stand up there. The blue cooler contains a few hundred live silver flies. The flies will feed on the woolly-adelgids in infested trees and stop the spread of this invasive insect. This battle between fly and adelgid is an example of the future fights against invasive species. In normal climate conditions, non-native pests can be difficult to control. Scientists can save our trees from the invasives that have been accelerated by climate change. If they don’t, the Northeast will suffer a lot.
In the early 1900s, ships carrying plants laden with woolly adelgid arrived in America from southern Japan. The adelgid quickly established a stronghold on the continent. However, it was only discovered in Virginia in the 1950s. The adelgid soon became a problem in other states. The bugs moved fast, sucking the juice out of hemlock twigs and killing trees up and down the Eastern seaboard–young, old, big, and small–in as little as four years. Invading the Catskill Mountains 10 years later, they hopped Long Island Sound during the 1980s. The Northeast’s winter cold temperatures limited the pest’s reach for a while. Adelgid can’t withstand temperatures below 0 degrees Fahrenheit for very long. Warm winters make the Northeast more attractive to invading species, as there is a lot of hemlock forest. The woolly adelgid has become a widespread pest. More than half of America’s Eastern forests are infested with it–almost every state in the Eastern seaboard.
Mark Whitmore is the head of New York State Hemlock Initiative. This state-funded laboratory, which works with Cornell University’s Department of Environmental Conservation, said that “it basically killed untold million of trees on the East Coast.” Dietschler is also employed by the Hemlock Initiative, which organizes the release and care for the adelgid eating flies. It’s like a wild sci-fi scenario, but right here at our door. The problem will only get worse with warmer winter temperatures.
This is exactly what occurred last winter. The East Coast’s high winter temperatures led to very low rates of mortality among the adelgid population. This resulted in an explosion of pests during the summer. Grist was told by David Orwig (a senior ecologist from Harvard Forest), that pests are “all over the place in great abundance.” The warming winters only exacerbate this problem. No question.”
If the US can’t afford to lose its trees, the Northeast really can’t afford to lose its hemlocks. Researchers from Harvard Forest wrote that “no other Eastern tree species exerts such an extensive and profound impact on the environment, other organisms and ourselves,” in a 2014 book titled Hemlock, A Forest Giant at the Edge. According to the book, losing the hemlock is similar to “losing an conductor and music producer.”
Many different types of trees are part of deciduous forests. They lose their leaves each winter, including oak, birch and ash as well as maple, poplar, and ash. If an ash tree is lost from a deciduous wood, it may be because the emerald Ash borer has killed it off. Other leafy trees will crowd out this destruction. One type dominates hemlock forests. The hemlocks grow in large, unruly stands of uniform green which are lively 365 days per year. There is not much left after the hemlock leaves a hemlock wood.
Hemlocks can be considered a foundation species. This means that they are crucial in the structuring of ecological communities. They provide deep shade, which is their greatest contribution. Only 1% of sunlight reaching the forest floor reaches a hemlock canopy. Because the trees have feathered branches, they slope to the ground rather than up towards the sun. This creates a dense dome. The temperature below this tent may be up to 10°F colder than outside at the tree’s top and 5-10 degrees at its base.
The tent helps keep snow from the ground in winter. The tent keeps snow off the ground by keeping deer safe around the circumferences of the hemlock branches. In the hemlock’s top canopies, barred owls and ruffed grouse nest. Its green branches are home to snowshoe hares. Porcupines love to chew on the bark’s tannin-rich texture. As the sun shines down on the snow, melting ice and snow elsewhere in the spring, the hemlock retains circles of snow around their trunks. This slows the leaching into the nearby creeks and streams, keeping them cool. These cooling infusions with icy water are vital for Brook trout, as well as many other species of salamanders, frogs, toads, and fly.
Even though they may not know, humans do it too. Hemlocks use water more conservatively than hardwood tree species because their dense branches create moist and cool microclimates. Orwig, a Harvard Forest ecologist, stated that hemlocks that have been replaced by hardwoods that require more water have the potential to dry streams. Those streams are used for swimming, fishing, and recreation–a major part of the Northeast’s regional identity. Hemlocks offer the same aesthetic and financial benefits as humans, no matter their location. A study that looked at hemlock decline in central Connecticut and Massachusetts over the course of five years in nine counties found an accompanying decline in property values of $105 million.
Whitmore from Cornell stated that most people only see hemlocks in a green light. But if you dig deeper, you’ll see the ecosystem functions that hemlocks play in cooling the environment and creating the climate.
Hemlocks can be beneficial for both the wildlife and people who live near them. Hemlocks are also excellent at trapping carbon dioxide.
Hemlocks can sequester approximately 12 metric tons of carbon dioxide per two and a half acres, according to a 2002 study that compared the hemlock to other tree species. This is more than what the study found for oak and ponderosa trees. The woolly adelgid might transform hemlocks, which are carbon sinks, into carbon sources. This was already happening in Harvard Forest in 2014. The hemlock stands started producing carbon, instead of sequestering it. Researchers found this out in the Harvard Forest. “The forest can behave as a source of carbon with the loss of the hemlock,” Orwig, who helped document that shift from sink to source in a 2020 study, said.
A prior Harvard study showed that the woolly adelgid could take an 8 percent bite out of Northeastern forests’ carbon sequestering capabilities between 2000 and 2040. However, this study, along with others, predicts that hardwood trees, including an opportunistic black birch, will replace dying and dead hemlock. This trend has been observed in Northeast woods. The Harvard study predicts that black birches would capture 12 percent less carbon over the 2040 period than the hemlocks. Audrey Barker Plotkin is the Harvard Forest’s senior scientist and has been studying the effects of invasives in hemlocks for years.
She stated that if hemlock is lost and carbon uptake decreases for 40 years or more, then this is the right time to do everything we can to reduce carbon loss. This timeframe is crucial if we are to win the battle against climate change.
Other scientists also question whether black birch is a better choice than hemlock in terms of carbon storage. An analysis of soil carbon and trees found that hemlocks aged 80 to 90 years old stored 6.8 times as much soil carbon than blackbirches the same age. The study found that the net carbon release from woolly adelgids could be as high as 4.5 tonnes per approximately two-and-a-half acres of hemlock forests being replaced with black birch.
Then, if you stop and think about it, how would we feel if all our hemlocks were gone? This gives you an absurdly large number,” Danielle Ignace (an assistant professor of ecology and lead author of the soil carbon study) said. The extent of the imminent carbon hole caused by the loss of eastern hemlock remains a mystery. However, Ignace’s research does have one important takeaway. She stated that “our work suggests it will be decades before we understand the consequences of losing eastern hemlocks.”
In the early 2000s, researchers had pinned their hopes of saving the eastern hemlock on a black beetle from the Pacific Northwest called Laricobius nigrinus. Previous attempts at keeping the woolly-adelgid away using predator beetles, which were from East Asia, had been unsuccessful because they are difficult to breed and have a hard time with East Coast winters. It seemed more resilient than the black beetle. US Forest Service used limited funds to release thousands in South Carolina forests.
It seemed to work for a while. It laid eggs in woolly-adelgid ovisacs and the larvae consumed the woolly-adelgid eggs. Up to 90% of woolly adelgid was consumed by the larvae. Over time it was clear that the larvae couldn’t consume enough adelgid to keep up with the pest. The woolly adelgid has two generations each year. One is a winter and one is a spring. Although the beetle consumed the winter generations of the adelgid, it was still able to recover completely from the spring.
Researchers and states had to do something, even though they were reluctant to acknowledge that black beetles, which was the biocontrol system they spent so much time raising and then releasing, didn’t work. Whitmore of the New York State Hemlock Initiative said, “This isn’t a field where people put a lot money at you.” Whitmore was also focusing on black beetles, but realized privately that resources were scarce.
Whitmore then attended the Annapolis meeting on invasive species in 2014. Darrell Ross was a professor at Oregon State University’s entomology department at that time. He had conducted an analysis of all of the woolly adelgid predators in the Pacific Northwest, and he thought that the labs in attendance were missing something big: silver flies, the only other bugs in the Pacific Northwest other than the black beetle that researchers are sure only eat woolly adelgid. Because they are difficult to capture and breed, the flies have been ignored for many years. They are just as common on the West Coast as the black beetles, but they also feed on the spring crop of woolly Adelgid.
Whitmore recalled that Darrell had a kind of bee in his bonnet. He was puzzled about why everybody was getting so excited about the Laricobius honeybeetle, when everyone else was ignoring silver flies. He had an unpleasant confrontation with the group but it was enough to get my attention.
Whitmore was clear after that meeting. Release of both silver flies as well as black beetles in a group is the key to saving the hemlocks. This will allow them to attack both generations. Andrew Cuomo (the governor of New York) would give Whitmore funding to open his Cornell lab. Whitmore was able to get the lab up and running once he had done so. He said, “That was what allowed me to really get started.” His lab published its first silver fly, 740, in May 2017. It was released at just four New York locations over three days. Whitmore recalls the experience as a “whirlwind adventure.” Cornell has now released 25,239 fly at 33 locations.
It may be some time before researchers find evidence that the beetles and flies are keeping the adelgid at bay. The New York State Hemlock Initiative so far has shown that the flies are capable of surviving year after year. However, there is not sufficient data yet to determine if the flies have survived and are eating spring-generation woolly adelgids in the wild. Whitmore’s laboratory and other smaller scale initiatives that rear these predators will not know for certain if they have succeeded until years. States with eastern hemlock have the option to spray select trees with insecticides that will kill the adelgid. This is a costly and ineffective way to address the issue on an individual species level. Long-term and cost-effective solutions to East’s pest problems are only available through flies or beetles.
Orwig hasn’t been involved in the New York State Hemlock Initiative efforts. Researchers found in the 1990s evidence that predators from East Asia were not surviving East Coast winters. Orwig remains cautiously positive that silver flies will fill this critical niche. He said that there is a greater chance of success. Biocontrol is still a possibility.
Orwig pointed out that silver flies and beetles can only work if there is enough funding to keep them alive and released. He said that there are limited resources.
New York has been generous in its funding for hemlocks. In 2020, the state’s Department of Environmental Conservation agreed to give the New York State Hemlock Initiative $1 million over two years. Grist was informed by Bryan Ellis, New York State Department of Environmental Conservation forester. We’re sort of throwing the kitchen sink at it.”
But the adelgid isn’t the only invasive threatening native flora in the state, which has earmarked more than $13 million for invasive prevention and control activities in its 2021 budget. New York Department of Environmental Conservation also fights multiple invasives. They are responsible for removing giant hogweed, the Asian longhorned beetle, and the spotted lantern fly. Ellis stated, “You cannot focus on one.” Ellis said, “There are many priorities and we’re trying to get them all.”
Researchers estimate biological invasions will increase by 20 to 30 percent by midcentury, in large part because of climate change. According to the study, these invasive species will have major effects on biodiversity worldwide.
Although a biological invasion is possible, it’s not likely to happen on this ridge in Catskill Mountains. Everything here is tranquil and peaceful. The branches of large and wizened Hemlocks are home to birds that rustle. An oak tree is lifted by a gentle breeze. Below, the Pantherkill Creek gurgles. Dietschler pulls a vial from the cooler, and then pops its lid. The lid is flipped upside down and Dietschler places it on a sickly hemlock sapling. He then nudges the silverflies free, who are lethargic from their three hour trip to Cornell’s lab. Each predator is no larger than a pinhead and comes to his senses. They’re gone in a flash and are now hanging on the understory.
Dietschler softly says, as he watches them leave. “I believe there’s hope.”
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Publited Sat, 14 August 2021 at 12:36.42 +0000