Eastern USA Temperate Rainforests

[Alex High]

Hello all,

Since my trip to the Great Smoky Mountains a couple years ago, which is located in the Appalachian Temperate Rainforest (https://en.wikipedia.org/wiki/Appalachian_temperate_rainforest), I have become fascinated with temperate rainforests (https://en.wikipedia.org/wiki/Temperate_rainforest) and the fact that we have one here in the Eastern U.S. And I have recently been doing some research to try to determine the boundaries of the Appalachian Temperate Rainforest and see what other parts of the Eastern U.S. qualify for temperate rainforest designation.  This is what Wikipedia says are the criteria for a temperate rainforest:

For temperate rainforests of North America, Alaback's definition^[1] is widely recognized:^[2]

• Annual precipitation over 140 cm (55 in) (KJ)
• Mean annual temperature is between 4 and 12 °C (39 and 54 °F)

 

I have seen various other sources, and generally it is agreed that a temperate rainforest (which often receives less rainfall than tropical rainforests) must receive 55-60 or more inches of rain per year. It seems that is really the main requirement. What makes a temperate rainforest isn't very well defined and there are varying definitions, however, unlike cloud forests, there does not seem to be a fog/cloud cover requirement, although that often comes with the high rainfall. I have seen some sources cite evenly distributed precipitation across the year as a criterion, but the Pacific Temperate Rainforest, the largest temperate rainforest on Earth, receives far less rainfall in summer than winter (similar to the Mediterranean climate it borders to the south), and relies on fog drip in summer to keep the soil moist and provide water to plants. So if the rainfall requirement is the main requirement to be considered a temperate rainforest, then there are a number of places in the East that fall within that category. I remember reading that there were patches of temperate rainforest throughout the Appalachians up into New England, and I know there is a temperate rainforest in Atlantic Canada. You can tell when you're in a temperate rainforest in the Eastern U.S. by the abundance of understory plants (Rhododendron, mountain laurel, ferns, mosses, etc.) and lush canopy often mixed deciduous and evergreen. The forests where I live near D.C., which average about 40 inches of rain per year, are open, entirely deciduous, and the forest floor is often bare. In the western part of Maryland and parts of West Virginia, some of which average 55-60+ inches of rain, the environment looks much like the Smokies, yet I've never seen them included in any description of the Appalachian rainforest. Pickens, West Virginia, for example, averages 66 inches of rainfall per year. Is that not a temperate rainforest? I was in the Appalachian highlands in WV this summer and it was much cooler than D.C. and had fog/clouds during part or all of each day, much like the Smokies. There are plenty of other places, from the mountains of Arkansas and Alabama up to Maine, that meet the rainfall requirement for temperate rainforest. Mt. Washington in New Hampshire, for example, receives 91 inches of rain a year, which far exceeds the requirement, however the extreme winter temperatures may mean it's not considered temperate. If it's not temperate would it be a boreal rainforest? It seems much of the Atlantic Canada's rainforests and the Inland North America temperate rainforest (https://en.wikipedia.org/wiki/North_American_inland_temperate_rainforest) wouldn't be considered "temperate" because of their cold winters. Is it possible to have a rainforest in a boreal climate? I know there are rainforests in parts of Siberia as well so it seems it is possible. I will continue to research and try to determine which areas of the East are temperate rainforests, it's something that really interests me. Let me know your thoughts!

Map of Appalachian Temperate Rainforest as it's often shown:

Average precipitation across the U.S.

[flplantguy]

I fantasize about having a home up there.  People grow dawn redwoods in that area too, so it fits the description for them to thrive at least.  Who knows what else will grow well there, maybe a monkey puzzle tree?

[Alex High]

9 hours ago, flplantguy said:

I fantasize about having a home up there.  People grow dawn redwoods in that area too, so it fits the description for them to thrive at least.  Who knows what else will grow well there, maybe a monkey puzzle tree?

It's such a gorgeous area, so different from the deciduous forests where I live. There are definitely lots of dawn redwoods there, monkey puzzles should be growable as well. There are some hardy palms (Trachys, Sabals, and needles) in some of the towns around the Smokies too.

[RedRabbit]

I like that area a lot along the NC/SC boarder that qualifies as a rain forest. I visited last year and it’s really nice with all the waterfalls. However, it isn’t very similar to the Hoh Rainforest which gets very very mossy as you approach the coast.

[Alex High]

9 hours ago, RedRabbit said:

I like that area a lot along the NC/SC boarder that qualifies as a rain forest. I visited last year and it’s really nice with all the waterfalls. However, it isn’t very similar to the Hoh Rainforest which gets very very mossy as you approach the coast.

Yeah I've visited the Smokies on the Tennessee-NC border and it's also rainforest, so beautiful there, waterfalls everywhere, mixed deciduous-evergreen, lots of Rhododendron, mountain laurel, and so lush. Yeah most of the temperate rainforest there isn't as mossy as the Hoh and other rainforests on the Pacific Coast, but at the highest elevations of the Appalachian Temperate Rainforest, where there is over 100 inches of rain in some places, there is the southern Appalachian spruce-fir forest, where the forest becomes dominated by red spruce and Fraser fir, and the forest floor is covered in moss:

[Aceraceae]

Mount Washington would be a boreal snow forest, tundra or sky island as it has more snow than rain and is treeless both due to the alpine climate but also the lack of soil on the summit cone and its extremely high winds. 

[Alex High]

On 10/14/2023 at 11:49 AM, Aceraceae said:

Mount Washington would be a boreal snow forest, tundra or sky island as it has more snow than rain and is treeless both due to the alpine climate but also the lack of soil on the summit cone and its extremely high winds. 

Yeah now that I've researched more, that area is definitely not rainforest, nor is it temperate by any means, even if it gets a ton of precipitation, much of it is snow, accompanied by brutal bone-chilling cold and crazy winds. However, there are also "temperate rainforests" in Southern Siberia and the Russian Far East, where it frequently gets below 0 Fahrenheit in winter (https://en.wikipedia.org/wiki/Southern_Siberian_rainforest) (https://en.wikipedia.org/wiki/Temperate_rainforests_of_the_Russian_Far_East). I would think the frigid winter temperatures would make those areas boreal and not temperate, so I was a bit confused by that. It's interesting you mention the soil component, that wasn't something I really thought of when defining temperate rainforests, but it's a very important factor. I recently watched 2 great YouTube videos on temperate rainforests by the YouTuber Atlas Pro. He made the first one 2 year ago and the second one he just made just a few days ago. In the recent video he went exploring the Catskill Mountains in New York to determine if they are temperate rainforest, and came to the conclusion that they are not. Some of the higher peaks meet the precipitation threshold, but he said that the soil there was too rocky and poor and did not retain enough moisture to support a lush understory, which is a key component of temperate rainforests. The poor soil is a result of past glaciation, something that did not happen in southern Appalachia, so that still leaves parts of West Virginia and other Appalachian areas with high rainfall open to potentially being temperate rainforests, as they have rich soil and are super lush with a dense understory.

 

[Ethan212]

Did you ever do further research on this? I am from Charleston, WV and deeply interested in the possibility of the southern appalachian rainforest's range expanding as the climate warms and the gulf stream dumps more humidity over the southeastern US.

I reached the same conclusions about that area of West Virginia with the same data you used here. I've planned a trip to Holly River State Park during the rainiest month to check out the condition of the forest and the climate there. This forest receives around 60-65 inches of rain a year and straddles the temperate/continental climate zones. However, it also receives a lot of snow, averaging 75 inches a year.

 

[Aceraceae]

Even some of the northeast mountains, PA up to New England and the Adirondacks have decent soil and moss-covered ground, if that is the benchmark. Charleston and other lowland WV are zone 7, and have the coldest month above 32, it's 35 in January for the Yeager airport located high above the city, so using the basic 2 C/3.5 F temp drop equation per 300m/1000ft of elevation, many of the mountains there up to near 1 km or 3,000ft high would still be above 27 F in the coldest month, using the bonus Koppen -3 C isotherm for the temperate C upgrade vs D hemiboreal biome. Like the mid south, cold snaps are often brief, with no more sub 0 F (-20 C) dips than those far east old world continental 'temperate rainforests', and snow and ice pack don't last for months. 

[Alex High]

On 5/10/2024 at 12:14 AM, Ethan212 said:

Did you ever do further research on this? I am from Charleston, WV and deeply interested in the possibility of the southern appalachian rainforest's range expanding as the climate warms and the gulf stream dumps more humidity over the southeastern US.

I reached the same conclusions about that area of West Virginia with the same data you used here. I've planned a trip to Holly River State Park during the rainiest month to check out the condition of the forest and the climate there. This forest receives around 60-65 inches of rain a year and straddles the temperate/continental climate zones. However, it also receives a lot of snow, averaging 75 inches a year.

 

I haven't been able to find much more info, and all the research I do only leads me to more questions. It seems a lot of it at this point is not super well defined and the qualifications for temperate rainforest are subjective, although with some common characteristics. For example, the area around Eureka, California is, as far as I'm aware, temperate rainforest. The forest of redwoods and mixed conifers there is super lush with a thick undergrowth of ferns and other vegetation, yet it receives only 40 inches of rain in some places. And the Seattle area, which gets similar amounts, is not a temperate rainforest. Both have a high number of rainy days (usually a light rain for many days per month), so that helps keep the soil moist for longer and fosters dense plant growth. Both also have fog, which is another big aspect that can lead to additional "rainfall equivalent" from fog drip, something not often considered. That likely applies in West Virginia, which gets a lot of fog in the mountains. It well seems that under current, albeit vague, qualifications, areas of West Virginia like you describe and the mountains of northern Alabama and other, milder places with lots of rain and fog in the southern Appalachians qualify as temperate rainforests. It even seems some areas of Western Maryland (my state) could qualify, at least by rainfall totals and temperature. And yeah looking at pictures and having been to some of the wetter areas of WV myself, it definitely looks and feels a lot like the temperate rainforest of the Smokies, much lusher and with more undergrowth than the open temperate forests of the coastal plain and Piedmont where I live. I am super interested in this subject, and await further clarifications from those who specialize in this subject and common observers like myself. Please keep us apprized as to what you find, I look forward to hearing/seeing what discoveries lie ahead. As far as the snow, the southern Appalachian spruce-fir forest is considered temperate rainforest (sometimes cited as the only area of temperate rainforest in that region, excluding the lower elevation forests) and it receives more than 75 inches of snowfall at the upper elevations. Winter temperature and snowfall is another thing that seems not well defined for temperate rainforests. Glad to see someone else has an interest in this subject, thanks and keep us posted!

[Alex High]

An exciting update! Someone made a more detailed map of the Appalachian temperate rainforest. Still doesn't look extensive enough, but it includes a large area of central West Virginia, right around Holly River State Park. This map, like every other one I've seen, leaves out areas that others include, but it seems that at least the areas shown can be pretty reliably called temperate rainforest. The detailed mapping criteria are explained below, from the Wikipedia article:

https://en.wikipedia.org/wiki/Appalachian_temperate_rainforest

[Aceraceae]

^^ not a minute too soon. 

On 5/10/2024 at 12:14 AM, Ethan212 said:

This forest receives around 60-65 inches of rain a year and straddles the temperate/continental climate zones. However, it also receives a lot of snow, averaging 75 inches a year.

 

2 hours ago, Alex High said:

As far as the snow, the southern Appalachian spruce-fir forest is considered temperate rainforest (sometimes cited as the only area of temperate rainforest in that region, excluding the lower elevation forests) and it receives more than 75 inches of snowfall at the upper elevations. Winter temperature and snowfall is another thing that seems not well defined for temperate rainforests.

 

Good news. 

The general Wikipedia synopsis says that zone 6 and Dfb (vs Cfb) qualify, and there's no stipulation that 20% or any percent of the precipitation can't be snow. This opens up huge swaths of WV and northeastern mountain ranges. Remember that 75 inches of snow is way less than 40 inches of rain, since even wet snow is much drier and less dense. For the colder northeastern mountains, even the snowiest peaks with over 200 inches of snow (equal to 15 to 35 inches of rain), but with at least 40 more inches of rain in the summer, would have 'more rain than snow' moisture per year. 

[Aceraceae]

3 minutes ago, Alex High said:

This map, like every other one I've seen, leaves out areas that others include, but it seems that at least the areas shown can be pretty reliably called temperate rainforest. The detailed mapping criteria are explained below, from the Wikipedia article:

If anything the very cold mean annual temp given of 12 C or 55 F max, is what excludes the warmer places, and might leave a void of rainforests between temperate and tropical, which at a minimum have that Koppen 18 C or 64 F coldest month minimum, which translates to an annual temp well over 21 C or 70 F. 

The coldest mean annual temp of 4 C (39 F) would include very cold areas such as the Adirondack mountains of New York up to almost 5,000 ft, aka the highest peaks there, and would include the eastern US' coldest mountain, Mount Washington NH up to about 4,000 ft or 1200 meters. 

[Alex High]

1 minute ago, Aceraceae said:

If anything the very cold mean annual temp given of 12 C or 55 F max, is what excludes the warmer places, and might leave a void of rainforests between temperate and tropical, which at a minimum have that Koppen 18 C or 64 F coldest month minimum, which translates to an annual temp well over 21 C or 70 F. 

The coldest mean annual temp of 4 C (39 F) would include very cold areas such as the Adirondack mountains of New York up to almost 5,000 ft, aka the highest peaks there, and would include the eastern US' coldest mountain, Mount Washington NH up to about 4,000 ft or 1200 meters. 

Very interesting, thanks for sharing! I wonder too about subtropical rainforests, for they must exist, but I never see them mentioned (areas of Louisiana, Florida could qualify). So much is subjective, after all it's merely a made up distinction, but I do find it fascinating and believe there's merit to it if we can nail down one, relatively concrete set of criteria to use globally for temperate rainforests (with exceptions, such as less rainfall can be supplemented by ample fog/fog drip). Yeah some definitions seem to say that the temperature change should be minimal throughout the year, like the coastal PNW, yet Siberia has a temperate rainforest. So minimums don't seem as important as maximums, which is odd, given that if most of the year is mild with a hot summer it seems to lend itself more to a temperate climate than mild summers and very cold winters, which is more boreal. Some count Siberia as boreal rainforest, which I guess could apply for Mt. Washington and very snowy areas with severe winters. If boreal rainforests exist then subtropical rainforests must too. So many questions remain unanswered, I will keep digging and researching. More study and clarification is needed.

[Aceraceae]

11 minutes ago, Aceraceae said:

the very cold mean annual temp given of 12 C or 55 F max, is what excludes the warmer places, and might leave a void of rainforests between temperate and tropical,

There is already an oblique name for these subtropical rainforests, they are known as 'laurel forests' after a plant family and common leaf shape found in them. 

^^ Florida wouldn't likely have any since even the panhandle with highest precip is so warm in summer, has higher seasonal variation, not just in temperature, but in PET or potential evapotranspiration vs rainfall, as invoked by the other climate classification system known as Holdridge life zones. \

Yet even so, tiny parts of SE Florida have a 'tropical rainforest climate', requiring only a paltry 2.4" of rain in the coldest month, even though the soil type and ground cover there is far from textbook rainforest. This Koppen definition seems too threadbare since it's more of a generalization that doesn't account for geography.