The Environmental Journal of Southern Appalachia
Wednesday, 29 March 2023 12:01

From soil to sky: Will the misty microclimates of the Smokies prevail in a warming world?

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IMG 7863With the help of GPS coordinates and survey flags, Jordan Stark is able to deploy and locate the exact off-trail placement of soil moisture sensors she placed in Great Smoky Mountains National Park as part of her graduate research at Syracuse University.  Elan Young/Hellbender Press

Foundational ecology moves from before times to nowadays in the Smokies

GATLINBURG — In the Middle Ages, salamanders were thought to come from fire. A log set on the hearth would send them scurrying out of the rotten wood, startling those who had gathered around for warmth. We now know that salamanders, of course, come from water — even the European fire salamander with its flame-like yellow markings.

Over the last 20 years of getting my boots soggy in Great Smoky Mountains National Park, I know these creatures to thrive in the clean, shallow streams and trickles of this temperate rainforest, where annual precipitation is higher than anywhere in the U.S. save for the Pacific Northwest.

One way to become acquainted with the park is through the water that veins through the hills and is transmuted into vapor that floats on the air in misty silence. After a rain, you can slake your thirst from the pools formed in the creases of broad rhododendron leaves. Sit by a shallow, fishless stream for long enough and you might spot the quick movement of a salamander tail, maybe a flash of orange or brown, or notice a tiny black amphibian face peeking out from behind a smooth stone in the creek.

During the last ice age, the ancestors of today’s salamanders found refuge from glaciers in what is now the southern Appalachian Mountains. These are among earth’s oldest ranges dating back to the Precambrian era — that first geologic time period when vertebrates were a mere glimmer on the evolutionary horizon. Of the 760 living salamander species, about one-third live in North America. Southern Appalachia is the global epicenter of salamander biogenetic diversity, often touted as the salamander capital of the world. The region is home to 78 species; 31 of them, including a new subspecies, recently discovered, live in the national park. 

In March 2020, as Covid was on the approach, I literally bumped elbows with Jordan Stark — a greeting in lieu of shaking hands. She was staying in a mountain research cabin across from where two friends and I were holed up in a writing retreat, periodically disrupting our writerly zone of non-distraction to check for “viral” news. So when I arranged to meet Stark more than a year later to report on a story about climate change on a muggy July day, it seemed almost too perfect an example of trail magic to recognize her from that weekend in “the before times.” 

As wildfire smoke blew in yellowing skies from forests on fire to the west, we set out on a journey, not in search of salamanders, but rather for the last eight of the soil moisture sensors she had painstakingly tucked under leaf litter in different habitats in the park. This was for her graduate research at Syracuse University, where she studied under Professor Jason Fridley, who has been conducting ecology studies in the Smokies for over 15 years. (Fridley has since moved to Clemson University, where he is a professor in the Department of Biological Sciences.)

Soil moisture data might sound dry, but salamander biologists are among those most interested in it. Changes to the microclimate will not affect all the plant and animal species the same way and, as bioindicators, salamanders are uniquely sensitive to disruptions in the ecosystem and are of unique interest to science. First, there’s the oft-cited fact that they can regenerate their tails and limbs. Also, some adult salamanders are lungless, breathing entirely through their delicate skin, yet research has not been able to explain how their skin can co-exist with deadly fungi and other microorganisms in the forest.

Stark and I hiked up a mountain during the most humid month of the year, talking about her research with Professor Fridley until we were short of breath and shiny with sweat. As a hiker and resident of the foothills of the Smokies, I was seeking to understand how climate change will impact the biodiversity here, as well as the humans like my friends and neighbors who depend on one of the 45 watersheds that make up the park.

Quantifying the forest

As a hiker, I never felt much interest in counting anything while exploring the woods unless it was miles to go or miles I’d come. But the national park is a living laboratory where researchers like Fridley rely on meticulously captured data, in his case to make predictions using microscale climate models. In the Smokies, macroscale data is collected above the tree canopy and microscale data is captured below it. Both are needed to  understand climate impacts with any precision. 

The foundational ecology research of the Smokies was published 66 years ago by R.H. Whittaker in a densely written 80-page monograph using only direct observation. Perhaps a bit like Whittaker, hikers in the Smokies can directly observe what ecologists have long understood: in complex, mountainous terrains, the local climate and species richness have sharp variations within a small area. 

Take the near-complete changeover in types of plants and animals from a cove-hardwood forest to the spruce-fir forest, for example. The area might only be a third of a mile long as the crow flies, but it can contain entirely different habitats and species compositions. All this rich variation and biodiversity beneath the canopy is one reason the park is an ideal place for collecting microclimate data — so much life depends on it, and there is still so much to learn.

Where macroscale data helps us understand a big picture, such as the mean temperature in a square kilometer, it has limitations in mountainous areas where the elevation within a square kilometer might contain both peak and valley. The data captured above the canopy simply can’t tell us about the gradations happening below it. Macroscale data also depends on high-tech instruments to be able to communicate with satellites, whereas the microscale data that Fridley and Stark collected was simple by design: sensors on a circuit board with wires encased in PVC and powered by a watch battery. It’s about as inexpensive as technology gets but requires trudging through the terrain to put them in randomly selected locations and hiking back out when the study is done. In the meantime, some may have become chew toys for bears. 

The connection between climate and plant species distributions is a foundational concept in ecology, but building on this understanding is of increasing importance in a warming world. Plants and trees offer not only refuge from direct sunlight and shade soil from evaporation, but they also cool the air as they drink in as much as hundreds of liters of water per day. 

In fact, research has found that a single tree has the same cooling capacity in a day as two average residential central air-conditioning units. 

What’s already understood about the relationship between plant species and climate is mostly because of large-scale macroclimate research (think regions, countries and continents). However, you need only visit the park’s high elevations in summer to see how the local climate of the Smokies varies greatly from the rest of the region. For example, an ambitious hiker can go from the hot and humid southern Piedmont all the way up to the cool, foggy spruce-fir forests resembling the boreal forests of Canada in a single day — at least ecologically speaking.

These high-elevation southern Appalachian spruce-fir forests are already rare islands resulting from the last ice age, and now they are among the most vulnerable ecosystems to changes in the climate.

Although ecologists agree that the microclimate will impact the distribution of plant species with climate change, there is still a need for data that demonstrates how. Stark says that plants will adapt to climate change, but how they will do so remains largely speculative, partly because some plant species are dispersed by wind and some have to wait for the right animal to come along and drop the seed. 

“For 70 years, people have been saying that there are patterns related to the fine-scale variations in a microclimate,” she says. “The really fine scale is always much harder for ecologists. There’s also a lot of chance involved. Why is a pine growing here versus there? Well, that’s where the seed fell.”

Under a wet blanket 

Hiking under the forest canopy during a summer squall can produce the peculiar situation of hearing the pitter-patter of heavy drops on the leaves above but barely getting hit with any of the refreshing rain. This is what I think of when Stark explains that the forest canopy above us acts like a warm, wet blanket, making the understory a wholly different climate than what lies just above the thick layer of trees.

First spelled by the North Carolina legislature “Smoaky” in 1789 and then corrected to “Smoky” on a map in 1804, the name Smoky Mountains is thought to harken back to the Cherokee word for these mountains —“Shaconage” — which means “place of blue smoke.” The plumes of white mist and fog lingering amid the damp treetops after a rain would make for obvious inspiration for mountains with the name Smoky in them. However, rather than the mystical fog streaming from the mountains, the name smoky comes from the same phenomenon that inspired the line “dreamy haze of impalpable mist” that writer and explorer Horace Kephart penned, which describes a scientific phenomenon.

This dreamy haze undulating through the expansive layers upon layers of mountain ridges is part of the water cycle made visible by the density of trees and terrain. As water travels to the earth, it moves through vegetation. Trees release 95 percent of the water they take up, which travels through the pores in leaves back into the atmosphere as water vapor. A single large oak tree can transpire 40,000 gallons of water in a given year, but this process is usually invisible. 

However, in the park’s 800 square miles, crowded from ridge to valley with trees (almost 95 percent is forested), fountains of water vapor and natural volatile organic compounds emanate from their leaves to scatter blue and indigo light from the spectrum across the mountainous folds. On the way to becoming new clouds and rainfall, these tiny aerosols first hover amid the mountains to create the iconic blue-tinged landscape of the Smokies. The moisture from transpiration is an invaluable part of the unique microclimate that supports more biodiversity than any other national park in the U.S.

Stark explains that under the wet blanket of the canopy, there’s much less variation in temperature than above it, where the air gets well-mixed with the surrounding atmosphere. When thermal radiation is released from trees and rocks, it gets trapped by the canopy, and there’s less wind in the understory to disperse the heat. The physics of it makes sense as I trudge further up the mountain, getting sweatier with every step. Thoughts of being huddled in my zero-degree sleeping bag in the chill of a spring or fall night are too distant in this heat.

Scientists don’t yet know whether we’ll continue to have this warm, wet blanket effect that proliferates plant growth because they don’t yet know if the forest canopy will stay intact as the planet warms. So much of the future of the Smokies depends on whether the park will stay foggy as regional temperatures rise and whether the high elevations will continue to have the protective cover of clouds. 

Fridley and Stark’s now-published research focuses on how plant species will move under different warming scenarios. The term they use for the warm, wet blanket effect is buffering, which refers to all the dampening effects of the forest that are responsible for temperature variation, including forest canopy structure and local terrain. This buffering effect is strongest on the hottest days and in the hottest climates. Therefore, it comes as no surprise that research suggests that the forest canopy, especially in high elevations, could very well limit the speed of warming experienced by the plants and animals under the protective canopy layer. 

Cryptic hope

Salamanders are so plentiful in the park that if we could magically put all of them together on a giant scale, the lump would weigh three times more than all 65 species of mammals in the park combined, from bears, deer and elk on down to the smallest — the secretive pygmy shrew.

The body types of some stand out as warnings, which is one reason they exist in all manner of stripe, dot and color combinations — nature’s protection from being digested by someone higher up the food chain. Take, for instance, the black-chinned salamanders’ candy-coated red or the chartreuse yellow spots of the aptly named spotted salamander that is dotted as if with bright paint splotches. Seeing one of these would be a rare treat, since it spends its life underground, emerging only to lay its eggs in the natal pond where it came from.

Then there’s the hellbender, or snot otter, along with a slew of other common names used for the brown bottom-dweller that spends its life in the cold, clean water and can grow up to three-feet long, including its eel-like tail. Hikers don’t often have splash encounters with this elusive, near-threatened species because of the depth of water they need to thrive in. In contrast, there’s the two-inch pygmy salamander camouflaged with multi-hued brown markings bearing a name befitting one of the smallest salamander species in the world. Its home in the high elevations is of particular threat because of rising temperatures.

If the earth manages to retain buffered areas as the planet warms, then the species distribution models created with Fridley and Stark’s microclimate data could help identify locations where sensitive species of salamanders might prevail despite unsuitably hot regional climates. Fridley and Stark term this cryptic refugia. (The singular refugium is an area where a species survives even after its extinction in the surrounding area.)

Among the most important findings from their research is a higher stability of mid-elevation species, particularly near streams, which are buffered from heat. Significantly, the model predicts that there will be less change in species composition at high elevations, which could signal pockets of resilience. Pockets of hope. 

No crystal ball for climate

The rivers in the Smokies pour forth an incomprehensibly large supply of wild, fresh water — evidence of high rainfall, which is one of the four contributing factors to the rich biodiversity here. (The others are elevation, varied topography and the last ice age.) Although there are many threats to species within the park, mainly from industrialization outside it, the Smokies provide a stark contrast to other mountains in Appalachia that have been strip-mined for coal, killing all life in the wake. 

Over 20,000 species live in the lush, moist environment of the Smokies. Scientists think that 40-60,000 may yet be discovered. Some of these species may be able to adapt to a warmer climate, but whether the more vulnerable creatures like salamanders will be able to withstand hotter temperatures is doubtful. Some may be able to tolerate warmer air and soil or be able to migrate northward. Those in the higher elevations can’t migrate because they are on ecological islands, so their survival depends on the survival of the highly specialized microclimates they already inhabit. 

While the evergreens of these high-elevation spruce-fir forests face threats from pollution, acid rain and invasive insects, historical monthly growth records show troubling signs for tree species that lose their leaves. For example, warmer March weather causes trees to put out leaves, but cold snaps as late as May can kill new growth and stress trees as they work harder to replace them. 

More intense periods of rain and drought also stresses trees and in some forests, tree growth is stunted, unable to grow to their full height. Overall, science can’t yet tell what the long-term impacts of all this stress will be on the forests that make up the park. Nonetheless, the forests are the only link between fresh water on the ground and water in the air. 

Like many people, I simply cannot imagine the Smoky Mountains without its iconic mists. As climate change became of greater concern to me, I wondered whether the park would be able to retain its character under warmer conditions and worried how the changes might impact my child and his generations’ future too. My walk with Stark was as much one through the complexities of science as through the forest. I was not prepared for the fact that science can’t yet tell what will happen to the precious microclimate here, nor what the rippling effects will be on our water supply and temperatures. 

But climate models don’t predict exact futures. Instead, they offer glimpses of multiple possible futures, helping us to take informed action now. Just as the largest and smallest organisms in an ecosystem help us understand the whole, so too can macro- and microscale climate data work together to give a clearer picture of the threats that a local environment faces.

How species (including humans) might adapt is still speculative, with so much dependent on local, regional and global policies and a speedy energy transition. But taken seriously, these models might be the closest we can get to a crystal ball for climate — if we wait too long to act.

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Last modified on Friday, 07 April 2023 16:15