the story of many coastal temperate habitats brings some to tears. In many notable cases, we lost so much before we understood these places, so we don't even know what has been wiped off the face of the planet.
There are a few rough geographic categories of the temperate rainforest, spread out over the world, with a variety of species ... a kind of coastal temperate rainforest - ification of other adjacent habitats (e.g. Knysna-Amatole is similar to the Afromontane forests).
Roughly speaking, the sun heating the air at the equator, and the lack of sun cooling the air at the poles, results in circulation cells of air rising and cooling at particular latitudes. Where air rises, it cools, and the moisture in it condenses into clouds and rain ... it dumps its water content as it cools and sinks downward once outside of the influence of the rising hot air. it's more complex than that but that's alright for now.
here's a visual representation which is helpful.
these circulation cells result in bands of wet and dry climates alternating as one moves equator --> pole.
pole <-- wet <-- dry <-- equator(wet) --> dry --> wet --> pole
look at the positions of the deserts in/near Mexico, the sahara, west asia, the gobi ... they line up horizonally very well. Between this dry desert band and the poles are where temperate rainforests may form , wet like the tropics but colder.
There are a few other elements that affect the formation of these forests. The big thing here is wetness, specifically things that make it more soggy.
Hence coastal temperate rainforests. Being near the coast can make it soggy further inland. Warm, wet air getting blown over a cold ocean can result in dense fog, e.g. Haar and Karl. Ocean currents can sweep the dregs tropical storms away from the tropics. so on.
Then existing forests can make things wetter than a non-forest (e.g. grassland) in the same location. The high amount of plant life uptakes a lot of water and then, via transpiration (plants "sweating" water to cool down + maintain the movement of xylem for nutrient transport) . That transpired water can condense and then rain down near to where it did before. so forests can "trap" rainfall in an area1, so rainforests can exist in places where one may expect it to be too dry.
so lets dig in. coastal temperate rainforests.
Im gonna give a few cool facts, and some more tragic history. I'll talk of two examples, but there are many more of these habitats. Basically every continent (not antarctica) has their own version(s). both examples below are in the West / the Global North, for a few reasons: 1) the southern hemisphere has less land especially at the right polar-adjacency, and 2) I feel the conservation focus on "exotic" forests while ignoring ecologies right on the doorstep of major imperial players (USA, UK...) allows these countries to continue as-normal while forcing other countries to "go green" in incredibly harmful ways.
so, lets go, square up.
...
Pacific temperate rainforest.
Chosen because it is massive and encompasses a diversity of species, indigenous groups, and colonial histories. it stretches along the coast from roughly South-of-San Francisco to Anchorage. like I say huge & I mean it.
Ocean circulation drives water from north to south along the coastline, so the ocean water is comparatively cold to the land in the more southern reaches.
At the southern extreme, the cold-ocean fog is what brings in the needed moisture -- this is Karl that I mentioned before. So this rainforest can cozy up against dry chaparral and fire-maintained environments, and many of the plants are fire-resistant.
This rainforest contains the largest and tallest tree species in the world ... many of which have been cut down. Decades of continued logging turns trees into pulp, and clears forests as part of a land claim (e.g. 1971 Alaska Native Claims Settlement Act) to force indigenous groups into assimilation-via-desperation. The true locations tallest and largest trees still standing are now kept secret.
As we learn more about the extant forest, the more we realize we have lost. Research from the 1990s indicates that the canopies of some of these rainforests, much like the tropical ones, host their own unique microhabitats of endemic lichens and mosses. As the tallest trees have been lost, so have their canopy habitats, and maybe many mosses and lichens that were never described to science before they were rendered extinct. Animals like the marbled murrelet that nest in the canopies are at risk.
These canopy dirt-moss-bryophyte tangles were the entire world for countless microscopic animals. Many are gone.
& the settlers danced on those graves.
to this day, tourists flock to photograph their own emulations of these dances-on-dead-trees. logging continues. the indigenous communities remain displaced.
Yet the rainforest still stands, and land regained, stewardship restored. There is hope, and maybe with time the canopy will re-entangle with new species of moss.
...
on to the second.
Atlantic / Celtic temperate rainforest.
not so long ago, most of scotland was some manner of forest. The landlocked Caledonian pine forest mingled with deciduous rainforest towards the coast. The rainforest covered ireland and wales and stretched down the west coast of england. These forests are borne of the Gulf Stream sweeping Caribbean storms northeast towards them. Oak, ash, birch, etc are common. sycamore may have been brought over by the romans and hazel from mesolithic tribes but theyre not invasive.
Much like the pacific rainforest discussed before, lichens and mosses grow on these trees and harbor tiny habitats2. I don't know if they had the kind of canopy climate comparable to the pacific -- the trees would not reach such heights, so the ground-canopy divide was smaller -- but it existed nonetheless. And even without a distinct canopy wasn't developed, moss microhabitats are extraordinary and hard-to-repair. When a slight crevice from a broken branch or scar allows a moss to gain purchase and grow, this moss becomes a textured, soft surface upon which other mosses grow ... the layers grow thicker and thicker, with species specialized to this thick-layering appearing ... and if this moss is torn off, it will not necessarily grow back3.
and so much of it is gone.
this was a rainforest.
the colonization of Ireland and the ethnic cleansing of the highlands also devastated the land. Recall the purposes of the logging before -- destroying the land forces cultures relying on it to assimilate, to urbanize.
the land has never recovered. Cultures like the highland Gaels operated more with collective ownership, and the land was stolen from these people by privatization. Private land is used to raise artificially high deer populations, with eat saplings and prevent tree regrowth; it is maintained in a deforested state to facilitate sport shooting; past and present deprivation of agency & constant taking deprive people from the means to begin the land's recovery.
many people displaced there assimilated in desperation, following the flow of people to maybe-greener pastures in America and South Africa and ... over time assisting in the logging of the pacific temperate rainforest.
...
mosses are such small things, and require such specialism to identify to the species3, that i dont know if we can conceptualize the species we've lost from these imperial devastations. but the rainforest survives, and what remains of it stands in defiance of the colonial history of the USA and the british empire.
and so we must love it, and ensure that further attempts to put it in peril are not allowed to pass !
- van der Ent, R. J., Savenije, H. H. G., Schaefli, B., Steele-Dunne, S. C. Origin and fate of atmospheric moisture over continents. Water Resources Research 46(9), 2010.
- Ellis, C. J. Ecological Indicators Oceanic and temperate rainforest climates and their epiphyte indicators in Britain. Ecological Indicators 70:125-133, 2016.
- Kimmerer, R. W. Gathering Moss: A Natural and Cultural History of Mosses. 2003.