Appalachian temperate rainforest

Temperate rainforest in the Appalachian Mountains

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Appalachian temperate rainforest

The Appalachian Trail traverses the dense, moss-covered spruce-fir understory near the summit of Old Black in the Great Smoky Mountains of Tennessee.

Areas in Appalachia that meet the climatic criteria of a temperate rainforest[a]

Ecology
Realm| Nearctic
Biome| Temperate broadleaf and mixed forests
Bird species| >240[4]
Mammal species| 68[5]
Geography
Country| United States
Elevation| Up to 6,684 feet (2,037 m)
Climate type| Oceanic climate (Cfb) and humid continental (Dfb)[6]

The Appalachian temperate rainforest or Appalachian cloud forest is located in the southern Appalachian Mountains of the eastern United States and is among the most biodiverse temperate regions in the world.[5][7] Centered primarily around Southern Appalachian spruce–fir forests between southwestern Virginia and southwestern North Carolina, it has a cool, mild climate with highly variable temperature and precipitation patterns linked to elevation.[8][9] The temperate rainforest as a whole has a mean annual temperature near 7 °C (45 °F) and annual precipitation exceeding 140 centimeters (55 in), though the highest peaks can reach more than 200 centimeters (79 in) and are frequently shrouded in fog.[8][10]

Due to variable microclimates across different elevations, the rainforest is able to support both southern and northern species, including some which were forced south during the Last Ice Age.[5][7][11] Dominated by evergreen spruce and fir forests at higher elevations and deciduous cove forests at lower elevations, the ecosystem contains thousands of plant species, including epiphytes, orchids, and numerous mosses and ferns.[12][13][14][15] It is also home to many animals and fungi, including endangered and endemic species, reaching the highest diversities of mushrooms, salamanders, land snails, and millipedes in the world.[5][7]

Humans have shaped the rainforest environment for the last 12,000 years through activities such as hunting and agriculture.[16] These impacts grew following European colonization, which brought about significant changes, including the decline of native populations, land use alterations, and the introduction of non-native species.[16] By the 1880s, industrialization reached the region, leaving the forest devastated by mining, logging and the introduction of destructive invasive species, examples being chestnut blight and the balsam woolly adelgid.[16][17][18][19] Conservation efforts such as the establishment of national forests and parks have helped preserve the ecosystem, however, it continues to face ongoing threats such as wildfire and climate change.[19][20][21]

## Climate

[edit]

The Appalachian temperate rainforest has a cool and mild climate and meets the criteria of temperate rainforests identified by Alaback.[1] Temperature and precipitation are extremely variable with elevation, with rainforest conditions usually but not always concentrated around spruce–fir forests at higher elevations.[2][22] These spruce–fir forests have an annual mean temperature of 6.5 °C (43.7 °F) and a growing season mean (May–September) of 13.5 °C (56.3 °F), though this is likely somewhat cooler than the average across the entire rainforest ecosystem.[2] It has annual precipitation above 140 centimetres (55 in), a cool summer, typical transient snow in winter, mean annual temperature near 7 °C (45 °F), and summer rainfall is above 10% of overall precipitation, classifying it as a perhumid temperate rainforest.[1][2]

Annual precipitation varies significantly within the mountainous terrain, with the highest precipitation in southwest North Carolina and the lowest near Asheville and in northeast Tennessee.[23] High altitudes hosting spruce-fir forest receive than 2,000 millimeters (79 in) of precipitation while large swaths of lower elevation rainforest receive more than 1,525 millimeters (60 in).[8][10] This pattern is primarily influenced by upslope and downslope flow of southerly winds.[23] The orographic effect causes rainfall when moist air originating in the Gulf of Mexico and western Atlantic Ocean is forced upwards by the mountains.[23][24] Winter and spring months see a gradient precipitation pattern, with higher rainfall concentrated in the south.[23] Weak upslope air flow in summer brings more precipitation to the highest elevations, while autumn is typically driest with occasional intense rainfall from tropical systems.[23]

Persistent fog covers the Smokies, sometimes called a cloud forest.

In addition to the increased precipitation from orographic lift, cloud cover keeps the rate of water loss low due to minimal evapotranspiration.[8] High elevation forests are immersed in clouds on 65% of growth-season days, leading some sources to describe the temperate rainforest as a cloud forest.[8] Water intercepted by clouds accounts for 25% to 50% of annual precipitation, which is a high rate.[2][8] For comparison, in the boreal rainforests of Eastern Canada, fog contributes only 5 to 8% of annual precipitation.[2] According to a tentative classification advocated by DellaSala, Alaback, Spribille, Wehrden, and Nauman in 2011, high-elevation temperate rainforest regions in Central Appalachia could be interpreted as "a southerly extension of Appalachian boreal rainforests from Eastern Canada", although this interpretation requires further study.[2]

See also: Great Smoky Mountains § Climate, and Southern Appalachian spruce–fir forest § Climate

## Ecology

[edit]

High precipitation levels, moderate year-round temperatures, and diverse terrain enable a wide range of species to survive.[5][7][11] The rainforest is more biodiverse than any temperate region of similar size in the world, with over 19,000 species identified in Great Smoky Mountains National Park alone.[5][7] However, scientists estimate the real number of species may be as high as 100,000 or more.[5] It is also home to many threatened, endangered, and endemic species, including plants, fungi, arthropods, fish, mammals, mollusks, and amphibians.[5][25][26]

### Flora

[edit]

Darker evergreen spruce and fir forests dominate the cooler and wetter mountaintops while lighter deciduous trees are prevalent at lower elevations, a common pattern across the entire rainforest.

Red spruce and Fraser fir are dominant canopy trees in high mountain areas. In higher elevations (over 1,980 meters or 6,500 feet), Fraser fir is dominant; in middle elevations (1,675 to 1,890 meters or 5,495 to 6,201 feet) red spruce and Fraser fir grow together; and in lower elevation (1,370 to 1,650 meters or 4,490 to 5,410 feet) red spruce is dominant.[12] Yellow birch, mountain ash, mountain maple, younger spruce and fir and shrubs like raspberry, blackberry, hobblebush, southern mountain cranberries, red elderberry, minniebush, and southern bush honeysuckle make up the understory.[12][13][27] Below the spruce-fir forest, at around 1,200 meters (3,900 ft), forest composition shifts in favor of deciduous trees such as American beech, maple, birch, and oak.[13] American rhododendron is the dominant understory shrub throughout the deciduous layer but is only occasionally present in spruce-fir forests.[28][29] Eastern skunk cabbage and common juniper are northern species that remained in this region after glaciers retreated.[7]

In addition to over 100 species of native trees, 1,400 other flowering plants and 500 moss and fern species call the rainforest home.[5][7] These include a diverse array of wildflowers and dozens of fungi-reliant orchid species.[14][30] The rainforest's high humidity supports epiphytic plant species at greater height and diversity than elsewhere in the eastern United States.[15] A wide range of mosses, ferns, and liverworts have been identified as high as 140 feet (43 m) above the forest floor.[15] These include common epiphytes like resurrection fern, the endemic liverwort Bazzania nudicaulis, and some species that are solely terrestrial in the rest of their range including Appalachian rockcap fern, rose moss, and narrow-fruited crisp-moss.[15][31] Lianas are also prevalent, especially in deciduous forest, with Virginia creeper, poison ivy, and various grapevines being the most common.[29]

### Fauna

[edit]

With 30 identified species, the rainforest is home to the highest diversity of salamanders in the world.[7] Several of these species are endemic to the region, including the black mountain salamander, southern dusky salamander, red-cheeked salamander, and Cheat Mountain salamander.[32] Many species of salamander in this area do not have lungs, so they breathe through their skin, so the wet environment of rotten trees and moist leaves is conducive for their survival.[5][7]

The red-cheeked salamander is one of many species of salamander endemic to the Appalachian temperate rainforest.

Larger animals include the American black bear, white-tailed deer, wild turkey, and groundhog.[7][33] However, many large species once lived in the area but were extirpated by land-use and hunting changes brought about by European colonization.[25] These include bison, elk, mountain lion, gray wolf, red wolf, fisher, river otter, peregrine falcon, and several species of fish.[25] Northern species including the Carolina northern flying squirrel, American red squirrel, and saw-whet owl are relics of the Last Ice Age that survive in the area because of the cool climate.[7][32] Animal diversity in the rainforest is not only limited to vertebrates, however. Mollusks and millipedes reach their highest levels of biodiversity in the region, with about 150 species of land snails and 230 species of millipedes documented thus far, though species estimates for both are much higher.[5][7] It is also home to 460 arachnid species including the endangered spruce-fir moss spider, which lives nowhere else in the world.[5][7]

### Funga

[edit]

The wet montane environment supports one of the world's highest diversities of fungi including lichens, sac fungi, molds, and mushrooms.[5][7][34] In total, over 2,300 species have been identified in the area and scientists estimate the actual number may be as high as 20,000.[5][7] Of the species discovered thus far, 800 (40%) are lichens.[34]

## History

[edit]

The southern Appalachians were left uncovered by glaciation during the Last Ice Age.

The Appalachian Mountains began to form 460 million years ago with the collision of tectonic plates, and finished their uplift around 230 million years ago.[11] During the Last Ice Age, ice covered much of northern North America, but the southern Appalachians remained ice-free.[7] This uncovered area acted as a refuge for species that were forced southward. After the ice receded, some species spread back north, but many stayed in the southern Appalachians.[7] Because temperature declines with increased elevation, the varying topography of the mountains forms microclimates that mimic both northern and southern latitudes.[5] This has combined with a relatively stable year-round climate to enable northern and southern species to live in close proximity each other, lending the rainforest its high biodiversity.[5][7]

### Pre-colonial

[edit]

Around 12,000 years ago, Paleo-Indians first settled in the Southern Appalachians, crafting stone projectile points from local materials, indicating their long-term inhabitance.[16] However, evidence for residential activities in the highlands are absent prior to about 7,500 BCE, though the archaeological record does indicate hunting, flintworking, butchering, hideworking, and woodworking in the region.[16] Throughout the Archaic period, Paleo-Indians adopted more advanced technologies such as textiles, basketry, and the atlatl and transitioned from hunter-gatherer activities towards an increasing reliance on fishing and the emergence of agriculture in lowlands. Human activities increased the dispersal of edible plants, including trees, shrubs, grasses, and lianas.[16]

Cultural developments accelerated with the adoption of agriculture in the highlands in the Middle Woodland period, delayed relative to the lowlands by rugged terrain, low population, limited fertile soil, and a shorter growing season.[16] As intensive plant husbandry expanded through the introduction of corn, beans, pumpkin, squash, and tobacco by around 1000 CE, it fostered more complex societies centered around permanent villages in Appalachian river valleys.[16] Meanwhile, human activity shaped the surrounding landscape into a patchwork of towns, farmsteads, fields, and primary forests for hunting and gathering.[16]

### Colonial

[edit]

Following European arrival in the region, native populations faced rapid decline due to both European intrusions and Old World diseases, leading to the disruption and collapse of many American Indian societies.[16] European trade and exploration had further impacts, such as the introduction of iron tools, exotic plants and animals, and increasing conflicts between American Indians and Europeans. Due to depopulation, many abandoned fields were reclaimed by secondary forests.[16] When restrictions on westward European settlement were lifted following the American Revolution, European migration increased and Euro-American communities began to grow.[16] However, the resistance of American Indian groups like the Chickamauga Cherokee delayed expansion into much of the rainforested region until 1790.[16]

Roads were quickly built, and by the early 1800s the US had full control of the region.[16] While valleys were farmed intensively, land use changed little in high-elevations, though European livestock were introduced.[16] Similarly, most industry remained agricultural prior to the 1880s, though some logging and small-scale gold and copper mining began.[16][19] During this period, bounties on predators drove them to near-extinction, bison and elk were extirpated, and trapping decimated fur-yielding species.[16] Moreover, the vast majority of the Cherokee Nation were forced to move from their traditional homeland to Oklahoma during the Trail of Tears.[35] However, about 9,000 members of the tribe continue to live inside the Qualla Boundary, which lies within the rainforest biome.[16][35]

Harvested logs being loaded onto railroad flatcars in Polk County, Tennessee in 1912

By the 1880s, Appalachia's natural resources had drawn the attention of industrialist Civil War veterans and vacationers from the North, buying up land and dramatically expanding the nascent railway system.[16][19] While Appalachia is famous for its coal, mica mining was far more dominant in rainforested areas, and logging remained generally confined to the valleys along significant rail lines.[16] However, as outside investors bought up growing tracts of land and Appalachia's railroad system matured, increasing swathes of forest were cleared.[16][19] By the 1900s and 1910s, even the spruce-fir forests of Mount Mitchell—the highest peak in the Appalachian Mountains—had begun being logged.[16][19]

A wooded stream in Joyce Kilmer Memorial Forest, part of the Nantahala National Forest

The early 1900s were devastating for the rainforest landscape. Wolves, beavers, and mountain lions vanished; bear, turkey, and deer populations plummeted; and exotic invasives like chestnut blight, wild boar, and rainbow trout were introduced.[16] Contemporaneously, devastating flooding of the Monongahela and Ohio Rivers in 1907 was attributed to clearing of upstream watersheds.[16][19][20] Encouraged by these factors and the Appalachian National Park Association (founded in 1899), Congress passed the Weeks Act in 1911 to enable the purchase of Federal lands in the Eastern United States.[16][19][20] Beginning with the creation of the Pisgah National Forest in 1916, much of the rainforest area is now conserved.[36] These areas include Great Smoky Mountains National Park, the Daniel Boone National Forest, the Monongahela National Forest, Jefferson National Forest, Pisgah National Forest, Nantahala National Forest, Chattahoochee National Forest, and Cherokee National Forest. State parks incorporating Appalachian temperate rainforest include Breaks Interstate Park, Grandfather Mountain State Park, and Gorges State Park.

## Threats

[edit]

### Fire

[edit]

The 2016 Chimney Tops 2 Fire burns on a mountainside near Gatlinburg, Tennessee.

Wildfires are a natural ecological process that has occurred within the Appalachian temperate rainforest for millennia.[37] However, fire suppression instituted after European colonization has created two significant issues in the region: a higher risk of "catastrophic wildfires", and declines in the abundance of disturbance-dependent species like Table Mountain pine and woodpeckers.[37][38] After the 2016 Great Smoky Mountains wildfires, the National Park Service put increased effort into controlled burns "to invigorate a species or ecosystem that benefits from fire" and "reduce heavy accumulations of dead wood and brush which under drought conditions could produce catastrophic wildfires that threaten human life and valuable property."[37] Natural wildfire is most frequent during the rainforest's warm summers, when lightning is common.[37][38]

### Pollution and climate change

[edit]

High peaks in the temperate rainforest have some of the highest air pollution of any region in the Eastern United States, with a 1999 study finding sulfate and nitrate deposition 6–20 times higher than lower elevation sites.[39][40] This is primarily due to pollutants from cars and coal plants settling in Appalachian valleys, trapped by the high mountain ridges.[39] However, because this pollution is overwhelmingly deposited through acid fog, it is the wettest (highest) areas that receive the most pollution.[39][41] This deposition often has a pH below 4.0 and sometimes below 3.0, having significant impacts on tree cation concentrations, potentially leading to dangerous nutrient deficiencies.[39][41]

Similarly, anthropogenic climate change will have numerous and varied impacts in the rainforest, which may be difficult to predict. These impacts will likely be felt in the relict high elevation spruce-fir forests that heavily rely on cold temperatures and near-constant fog.[8] Any change in cloud patterns or height could significantly disrupt the cloud-based deposition this forest type relies on for up to 50% of their water budget, forcing them upslope until extirpation.[8][21] However, it has been hypothesized that higher elevations may be more resistant to climactic change.[21] Similarly, climate change is predicted to increase the rate of wildfires and place more stress on existing forests, leading them more susceptible to current threats.[21]

### Invasive species

[edit]

A ghost forest of dead fraser fir stands in Mount Mitchell State Park, North Carolina.

Invasive species pose a significant risk to the landscape of the Appalachian temperate rainforest, with two major introduction events in living memory. First, the chestnut blight emerged in Appalachia in the early 20th century, decimating American chestnut trees, a dominant species in the region.[18] Originally a fungal pathogen introduced from Asia, the blight quickly spread, wiping out vast populations of mature chestnuts and dramatically altering the composition of forests across the Eastern US.[18] While the trees once made up as much as 25% of hardwood forest stands, the American chestnut is now critically endangered and largely extirpated from its natural range.[18]

Similarly, the balsam woolly adelgid was introduced from Europe in the 20th century and devastated fraser fir stands on the rainforest's mountaintops. First discovered on Mount Mitchell in 1957, it quickly spread to all fir populations.[17] Fir mortality in Appalachia rose one-hundred-sixtyfold by 1970, eventually killing two-thirds of adult trees.[17][18] Initial efforts to control the adelgid largely failed, complicating repopulation efforts.[18] Though there are signs of recovery in recent years—such as Clingmans Dome having three times more adult trees in 2020 than in the 1980s[18]—these threats to the forest are not independent and scientists warn climate change may lead to another adelgid outbreak. "If we were to have a period of warm winters and hot, dry summers, the trees will be stressed, I wouldn’t be surprised to see a resurgence of balsam woolly adelgid," says Kristine Johnson, supervisory forester at the Great Smoky Mountains National Park.[18]

## See also

[edit]

* Appalachian-Blue Ridge forests
* Southern Appalachian spruce–fir forest
* Cove (Appalachian Mountains) § Cove forest

## Notes

[edit]

1. ^ Areas in green on the map exhibit high annual rainfall (at least 1400 mm), cool year-round temperatures (4 to 12°C average) wet summers (at least 10% of total precipitation occurring during the summer months), and moderate July temperatures (dark green less than 16°C, medium green less than 18°C, light green less than 20°C). While only the darkest green meets Alaback's original 1991 definition of a temperate rainforest,[1] the July temperature limits of this definition have since been broadened by a 2011 book by DellaSala, Alaback, and others.[2] Map created in ArcGIS Pro using open-access historical climate data at 30 arcsecond resolution.[3]

## References

[edit]

1. ^ a b c Paul B. Alaback (1991). "Comparative ecology of temperate rainforests of the americas along analogous climatic gradients" (PDF). Revista Chilena de Historia Natural. 64: 399–413.
2. ^ a b c d e f g DellaSala, Dominick A. Temperate and Boreal Rainforests of the World: Ecology and Conservation. Washington, DC: Island, 2011. Print.
3. ^ "Historical Climate Data". WorldClim. Retrieved January 7, 2024.
4. ^ "Great Smoky Mountains Birds". National Park Service. Retrieved February 23, 2024.
5. ^ a b c d e f g h i j k l m n o p "Great Smoky Mountains Nature & Science". National Park Service. Retrieved February 23, 2024.
6. ^ H. E. Beck; T. R. McVicar; N. Vergopolan; A. Berg; N. J. Lutsko; A. Dufour; Z. Zeng; X. Jiang; A. I. J. M. van Dijk; D. G. Miralles (2023). "High-resolution (1 km) Köppen-Geiger maps for 1901–2099 based on constrained CMIP6 projections". National Weather Digest. 10 (1). Scientific Data: 724. Bibcode:2023NatSD..10..724B. doi:10.1038/s41597-023-02549-6. PMC 10593765. PMID 37872197.
7. ^ a b c d e f g h i j k l m n o p q r "Biodiversity of Highlands". Highlands Biological Station. 14 December 2021. Retrieved February 22, 2024.
8. ^ a b c d e f g h "Leaf Gas Exchange of Understory Spruce–fir Saplings in Relict Cloud Forests, Southern Appalachian Mountains, USA." Reinhardt, Keith, and William K. Smith. Tree Physiology 28 (2007): 113-22.
9. ^ "Weather". Great Smoky Mountains National Park. Retrieved November 2, 2023.
10. ^ a b David M. Gaffin; David G. Hotz (2000). "A Precipitation and Flood Climatology with Synoptic Features of Heavy Rainfall across the Southern Appalachian Mountains" (PDF). National Weather Digest. 24 (3): 3–15.
11. ^ a b c "Geologic Provinces of the United States: Appalachian Highlands Province." Archived 2013-03-11 at the Wayback Machine USGS Geology in the Parks. N.p., 13 Jan. 2004. Web. 1 Oct. 2013.
12. ^ a b c Creed, I. F., D. L. Morrison, and N. S. Nicholas. "., Is Coarse Woody Debris a Net Sink or Source of Nitrogen in the Red Spruce – Fraser Fir Forest of the Southern Appalachians, U.S.A.?" National Research Council Canada 24 (2004): 716-27. Print.
13. ^ a b c "Land of the Great Forests". National Park Service. Retrieved February 23, 2024.
14. ^ a b Bentley, Stanley L. Native Orchids of the Southern Appalachians. Chapel Hill, NC: University of North Carolina Press, 2000. Print.
15. ^ a b c d Harold W. Keller; Paul G. Davidson; Christopher H. Haufler; Damon B. Lesmeister (2003). "Polypodium appalachianum: An Unusual Tree Canopy Epiphyte in the Great Smoky Mountains National Park". American Fern Journal. 93 (1). American Fern Society: 36–41. doi:10.1640/0002-8444(2003)093[0036:PAAUTC]2.0.CO;2.
16. ^ a b c d e f g h i j k l m n o p q r s t u v w x y "The Southern Appalachians: A History of the Landscape" (PDF). USDA Forest Service. May 1998. Retrieved February 20, 2024.
17. ^ a b c "Fraser Fir." US Forest Service. Donald E. Beck, n.d. Web. 6 Feb. 2024.
18. ^ a b c d e f g h "Earth Day: After decades of devastation, a comeback for WNC forests." Citizen Times. Anne McDarris, 22 Apr. 2020. Web. 6 Feb. 2024.
19. ^ a b c d e f g h "Conservation Movement Comes to the Southern Mountains". National Park Service History. February 1, 2008. Retrieved February 20, 2024.
20. ^ a b c "Celebrating a Century of Conservation: The Weeks Act Turns 100" (PDF). USDA Forest Service. March 17, 2011. Retrieved February 20, 2024.
21. ^ a b c d "Proceedings from the Conference on the Ecology and Management of High-Elevation Forests in the Central and Southern Appalachian Mountains." US Forest Service. n.a., 14–15 May. 2009. Web. 6 Feb. 2024.
22. ^ "Weather". Great Smoky Mountains National Park. Retrieved November 2, 2023.
23. ^ a b c d e "Drought in the Southern Appalachian temperate rainforest? Part 1." Coweeta Listening Project. N.p., 8 Oct. 2012. Web. 1 Oct. 2013.
24. ^ David M. Gaffin (2012). Southern Appalachian Weather. New York: Vantage Press, 146 pages, ISBN 0-53316-528-8.
25. ^ a b c "Great Smoky Mountains Threatened and Endangered Species". National Park Service. Retrieved February 23, 2024.
26. ^ "Paravitrea andrewsae High Mountain Supercoil". NatureServe Explorer. Retrieved January 12, 2024.
27. ^ C. E. Tewksbury; H. Van Miegroet (August 1, 2007). "Soil organic carbon dynamics along a climatic gradient in a southern Appalachian spruce–fir forest". Canadian Journal of Forest Research. 37 (7). Canadian Science Publishing: 1161–1172. doi:10.1139/X06-317.
28. ^ "Terrestrial Habitats of Virginia" (PDF). Conservation Gateway. Retrieved January 11, 2024.
29. ^ a b Stupka, Arthur. Trees, Shrubs, and Woody Vines of Great Smoky Mountains National Park. Knoxville, TN: University of Tennessee Press, 1964. Print.
30. ^ "Common Orchids in the Smokies". National Park Service. Retrieved January 11, 2024.
31. ^ "Bazzania nudicaulis a liverwort". NatureServe Explorer. Retrieved January 11, 2024.
32. ^ a b "Appalachian & Mixed Mesophytic Forests." WWF. WWF, n.d. Web. 1 Oct. 2013.
33. ^ "Great Smoky Mountains Animals". National Park Service. Retrieved February 23, 2024.
34. ^ a b "Great Smoky Mountains Disptaches_Lichens". National Park Service. Retrieved February 23, 2024.
35. ^ a b "Cherokee History in the North Carolina Mountains and Beyond". Blue Ridge National Heritage Area. October 16, 2013. Retrieved November 1, 2023.
36. ^ "Pisgah & Its History". Pisgah Conservancy. Archived from the original on November 29, 2023. Retrieved November 1, 2023.
37. ^ a b c d "Wildland Fire." National Park Service. GSMNP, n.d. Web. 6 Feb. 2024.
38. ^ a b "Drivers and ecological impacts of a wildfire outbreak in the southern Appalachian Mountains after decades of fire exclusion." US Forest Service. Matthew J. Reilly, Steven P. Norman, Joseph J. O'Brien, E. Louise. Loudermilk, n.d. Web. 6 Feb. 2024.
39. ^ a b c d "Acid Rain and Air Quality in the Appalachians." US Forest Service. Coweeta Listening Project, 16 Sep. 2011. Web. 6 Feb. 2024.
40. ^ Ralph E. Baumgarder Jr.; Selma S. Isil; Thomas F. Lavery; Christopher M. Rogers; Volker A. Mohnen (2003). "Estimates of cloud water deposition at Mountain Acid Deposition Program sites in the Appalachian Mountains". Journal of the Air & Waste Management Association. 53 (3). Air & Waste Management Association: 291–308. Bibcode:2003JAWMA..53..291B. doi:10.1080/10473289.2003.10466153.
41. ^ a b J. D. Joslin; C. McDuffie; P. F. Brewer (1998). "Acidic Cloud Water and Cation Loss from Red Spruce Foliage" (PDF). Water, Air, and Soil Pollution. 39 (3–4). Kluwer Academic Publishers: 355–363. doi:10.1007/BF00279480.

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