First off, thanks to Tamara and all the readers of My Botanical Garden who have been visiting and posting comments. It has been a pleasure being able to cross pollinating between blogs and to hear from some new readers! Today – the last installment in the three-part series on the vegetation of Tierra del Fuego.
Darwin’s diary remains quiet today, but in the January/February section of this Zoological Notebook he has quite a bit to say about the dominant vegetation of the other major ecosystem of southwestern Tierra del Fuego – the Magellanic moorlands (I love that name – I think it is my new favorite place).
Again, let me turn the floor over to Darwin to set the stage:
“In every part of the country which I have seen, the land is covered by a thick bed of peat.— It is universal in the mountains, above the limits [of] the Beech; & everywhere, excepting in the very thickest parts of the woods it abounds.— The beech often grows out of it & hence great quantities of timber must annually be imbedded.— It flourishes It increases most on the sides of hills & is I think of great thickness: the only section I saw varied from 6 to 12 feet. In more level sites the surface is broken up by numberless pools, which have an artificial appearance, as if dug for the sake of peat.— These are often close to each other & yet of different levels, showing how impervious the peat is when acted on by water.— At the bottom of these shallow pools there is a quantity of brown flocculent matter in which Confervæ flourish & very little moss.” (Zoological Notebook)
If you recall from a couple of days ago, the moorlands are one of the four main biogeographic regions of Tierra del Fuego. They tend to dominate the southwestern coast, growing in areas that have high rainfall (coming in off the Pacific). In these regions, the high winds, lower temperatures, and poorly drained soils make it more difficult of the Southern beech to take hold, so the water-loving “peat moss” quickly takes over. Tierra del Fuego is actually just the southern margin of these Magellanic moorlands – they extend all they up to 42°S latitude. (By the way – Confervae are a type of blue-green algae. For more info see It’s not Easy Being Blue-Green.)
Alas a good picture of the Magellanic moorlands is hard to find, but here is a similar peat bog from eastern Canada (from Wikipedia Commons)
I am again reminded of my time in southeast Alaska where very similar “peat lands” are called muskegs. I can recall crossing muskegs trying to get from place to place. The journey was a combination of comfort (it was like walking on a soft carpet) and hidden obstacles. More than once I had to skirt large pools of standing water or navigate a maze of wet spots. Once I stepped in just the wrong place and suddenly found myself waste-deep in peat – a lesson not soon forgotten.
In both localities the peat tends to thrive on landscapes that were covered with glacial ice up until about 10,000 years ago. Not only did the glaciers leave a clean slate, but they also left behind sheets of glacial till – a poorly-sorted, clay-rich sediment that is like concrete. (If you live in a recently glaciated region and like to garden, you know what I am talking about.) This till is quite impermeable, and results in a lot of standing water that makes it impossible for trees to take hold (their roots would drown). However, the little plant that dominates these moorlands – sphagnum, aka peat moss – is right at home in these wet conditions. As years pass, new sphagnum grows on the old, and layer upon layer of peat can slowly accumulate into massive deposits. (Darwin notes peat that is a few meters deep, though I have seen it reach 5 meters or so in some locations.) The stagnant water in the bogs tends to promote anaerobic conditions. This lack of oxygen, taken in conjunction with the acidic waters, creates an environment where decay is slow or virtually non-existent. Hence, the mummified human remains that have been found in peat bogs thousands of years after their deaths.
Here is Darwin’s description of the keystone species of the moorlands – sphagnum:
“The great agent which forms the peat is a small plant with thick leaves & of a bright green colour — The plant grows on itself; the lower leaves die, but yet remain attached to the tap root.— this latter penetrates in a living state to the depth of a foot or two.— & from the surface to the bottom the succession of leaves can be traced from their perfect state to one almost entirely disorganized.” (Zoological Notebook)
Sphagnum megellanicum from Chile (from Wikipedia Commons)
Sphagnum is, in fact, a type of moss (as are all the members of the Bryophyta phylum). Mosses have no vascular system (“tubes” to carry water throughout the plant), hence they have no roots. Water is absorbed directly through the leaves. That is why they need to stay moist. (I should know – my lawn, which is largely in shade, is a virtually moss farm.) Many mosses have adaptations for storing water during dry times. For example, sphagnum actually has the ability to absorb tremendous amounts of water – over 25x its own weight in some species.
Peat moss is actually an important resource for humans, and in many parts of the world it is being extracted at an unsustainable pace. Peat accumulates very slowly, but it is rapidly minded today and used as a supplement for potting and gardening soils. The peat carries nutrients, helps provide more open structure for soils and also absorbs and holds water – the perfect material for soil augmentation. Alas – not the perfect solution for the peat bogs themselves. Fortunately (for now at least) the Magellanic moorlands of Tierra del Fuego are still remote enough prevent major extraction of the peat. So for the moment they remain mostly intact, but that may be changing. (Protection of peat bogs may also become more common, as they are also can store a significant amount of carbon.) For more information, check out this 10-min ute video from Wetlands International titled “Tierra del Fuego Peatlands and Climate Change”:
Although he does not provide too much detail, Darwin also comments a little on the other plants growing with the peat moss:
“This above plant is eminently social, few others grow with it: some small creeping ligneous plants bearing berrys; another in its form, habits & colour strikingly resembling the Europæan heaths; & a third equally resembling our rush; It would appear to be necessary under similar circumstances, the landscape should possess the same form & tints.” (Zoological Notebook)
The taxonomy of sphagnum (note that there are only a handful of species in the entire Sphagnopsida Class – of the three hundred or so, all but three are in the Genus Sphagnum):
Tomorrow (February 12) is Darwin’s birthday –get out your party hats! (RJV)