by
Asbjørn Moen
During the seven day IMCG excursion to Tierra del Fuego in November 2005,
we visited, according to my notebook, 21 mire localities (cf. the field guide,
Urciuolo & Iturraspe 2005). Here I will give some short comments on the
variation in mire types and plant cover. But first some comments on biogeographical
research and the regional variation.
A series of individual scientists and expeditions
have worked in Tierra del Fuego and produced a voluminous literature. Certainly most famous are the
expeditions of Charles Darwin. There has also been a long Nordic research tradition
in the area, including Finnish and Swedish expeditions, e.g. led by Nordenskjöld,
Skottsberg, Auer and Tuhkanen. In the extensive bibliography of geographical,
geological and botanical publications dealing with Tierra del Fuego, Tuhkanen et
al. (1990) listed ca. 900 titles, including more than 150 by Nordic researchers.
A main reason for this Nordic interest is obviously that Tierra del Fuego is one of very
few land areas of the Southern Hemisphere where environmental conditions are
comparable with those in NW Europe.
Regional
variation in the vegetation
Regional variation in plant cover is a response
to climate, and vegetation zones and sections are two main types of regional
variation that often have been distinguished and mapped in the Fennoscandian
tradition (e.g. in Moen 1999).
Vegetation zones
display variations from equator to the poles and from lowland to upland, and
are linked with the demands of the plants for warmth during the growing season.
In Tierra del Fuego,
as a parallel to the Fennoscandian system (e.g. Tuhkanen 1992), the lower antiboreal
zone (parallel to southern boreal of NW Europe) dominates the lowlands near
Ushuaia. At higher altitudes, a middle antiboreal (parallel to middle boreal)
zones occurs from 150-200
m a.s.l. up to 300-400 m a.s.l. (altitudinal
limits after Tuhkanen, 1992 and my own observations). Then an upper antiboreal
zone (parallel to northern boreal) is found up to the climatic forest limit
at about 550-650 m a.s.l. In the
Central Cordillera area, the forest limit reaches up to 750 m a.s.l. (Tuhkanen
et al. 1990). In the mountainous areas of Tierra del Fuego, the forest limit
(with Nothofagus antarctica
and N. pumilio) is usually distinct against the upper alpine
areas. Further south, middle antiboreal zone occurs in the lowlands on the islands
south of Tierra del Fuego. The Antarctic
zone (parallel to Arctic zone) covers the Antarctic continent (cf. map in Tuhkanen
1992).
Vegetation sections display
the variation between coast and inland areas and are tied to differences from
oceanic to continental climates. The most oceanic sections (highly oceanic,
O3) have a climate with high humidity (precipitation up to more than 3000
mm in western part of Tierra del Fuego) and small differences between
summer and winter temperatures. This is followed by the sections: markedly
oceanic (O2), slightly oceanic (O1) and indifferent (OC),
all of which occur in Tierra del Fuego. In this system, the continental sections (C1-3) have an increasing
aridity (less than 400 mm of precipitation
in north-eastern part of Tierra del Fuego),
and larger differences between winter and summer temperatures than the more
oceanic sections. Clearly different to the situation in NW Europe, where the
most continental areas have very cold winters, in the lowlands of Tierra del
Fuego the winters are rather mild. Limits between the sections were not drawn
for Tierra del Fuego, but the southwest
areas certainly belong to O3, and the north-eastern areas to a continental section.
See further Tuhkanen (1992) who separates the sections in two parts: sectors
on the basis of thermic conditions (e.g. the differences between the warmest
and coldest month), and provinces, on the basis of humidity-aridity (e.g.
measured as the amount of precipitation). The variation is especially large
with respect to the provinces.
By combining zones and sections, it can
be concluded that Tierra del Fuego has a very large regional variation in the vegetation. Tuhkanen (1992),
in his “cube model”, mapped the climatic-phytogeographical regions of Tierra del Fuego, and he argued
for an inter-hemispherically uniform system of regions. There are only few and
very limited areas with climatic-phytogeographical regions corresponding to
Tierra del Fuego elsewhere. Such
areas can be found in the lowlands of the northern part of north-western Europe
(e.g. in central Norway), on the southern and south-western coast of Alaska,
on islands of New Zealand and some other southern islands; and in some mountains,
e.g. in Scotland, New Zealand and in the Patagonian Andes.
There are great differences in the natural
flora and vegetation between these separated areas, but in natural types (e.g.
in mire types) many common features can be detected.
Comments to mire types and vegetation
Based on literature (e.g. Roivainen 1954,
Tuhkanen et al. 1990), three main mire regions can be distinguished in the Fuegan
lowlands: “Steppenmoore” in the dry (north-eastern) region; Sphagnum magellanicum
raised bogs in the central area, and “Polstermoore” in the rainy (western)
region. In addition there is a sloping fen region in uplands.
During the excursions we saw a great variety
of mire types: raised bogs, blanket bogs, sloping fens, and different types
of flat fens, and spring mires. The very well developed raised bogs and the
large, intact mire landscapes at the Moat area, including the typical hard cushions
(lawn) communities (“Polstermoore”), were most impressive.
Raised bogs
are bog massifs that are distinctly domed. In Tierra del Fuego we visited some
very well developed, typical raised bogs, with a mire expanse (including string
hummocks and elongated hollows), mire margin (dominated by drier, shrub-dominated
communities) surrounded by a lagg or a soak (minerotrophic sites functioning
as drainage systems for the minerogenic water). The most typical and well developed
raised bog system we visited, in the Andorra valley, included three large mire massifs of eccentric raised bogs.
Well developed massifs of raised bogs were also seen in other localities, e.g.
at Rio Pio mire and some more localities in the Tierra del Fuego National Park, and in Tierra Mayor Valley. The “raising”
of some of the bogs is amazing, e.g. for the largest massif at Andorra,
a steep slope of more than 5 m height along the
whole margin to the north, hundreds of meters long. The raised bogs often have
more than 10 m of peat. Sphagnum magellanicum is the totally dominant species
of the raised bogs, both in present-day hollows and hummocks, and in the peat.
Less than 10 species of vascular plants were found in the ombrotrophic vegetation
of raised bogs. The differentiation between hollows and hummocks is not distinct
as the dominant bottom-layer species is the same. However, Sphagnum falcatulum
(S. cuspidatum coll.) is dominant in small areas of some wet hollows. Studies
in the Andorra mires (personal information by Hans Joosten) indicate that the following
species, additional to S. falcatulum are more common in hollows than
hummocks: Carex magellanica, Pernettya pumila and Tetroncium magellanicum.
A preference for hummocks was found for Empetrum rubrum, Nothofagus antarctica
and Marsippospermum grandiflorum.
Rather few species occur both in Tierra del Fuego and Fennoscandia,
but the strangest situation in Fuegan bog vegetation, compared to NW Europe,
is the very few Sphagnum species, and the near total dominance of Sphagnum
magellanicum. In minerotrophic mires, Sphagnum fimbriatum is the
only additional species which is common.
Raised bogs are found in the lowlands, mainly
in the lower antiboreal vegetation zone, and in the lower part of the middle
antiboreal zone. This parallels the situation in Fennoscandia, where raised
bogs mainly occur in the southern boreal zone or below.
Blanket bogs
are bog massifs that cover the landscape like a blanket, covering mounds and
sloping areas. The blanket bogs have a very restricted distribution in the world,
only occurring in the most oceanic sections (mainly O3) of boreal/antiboreal
and nemoral/temperate zones.
We saw blanket bogs in the Moat area; a
typical oceanic area with high precipitation. In this area, lawn communities
dominated by compact cushion species covered large areas, making the communities
very distinct and strange. Most common is Astelia pumila, covering large
areas, or in a mosaic with other cushion-forming species, e.g. Donatia
fascicularis (making very compact and hard cushions, often with diameter
of ca. 20 cm), Azorella spp. and Bolax spp. Such communities of cushion-plants
are described to be the most frequent mire communities in the western islands,
receiving more than 2000 mm of precipitation (Pisano 1983). So, further to the west (in Chile; not
visited by IMCG) such vegetation seems to be common.
Fens are
minerogenic mires and found wherever mires occur. Of special interest in Tierra
del Fuego were the sloping fens and the
rich fen vegetation.
We visited very well developed sloping fens
in a locality close to Paso Garibaldi (ca. 430 m a.s.l.), and in the uplands of the Moat area. Sloping fens with a
slope of more than 10 degrees of slope and at least 1m of peat occur in these
humid areas. Fens with thin peat occur on slopes of more than 20 degrees.
The well developed sloping fens mainly occur
in upper boreal/antiboreal and alpine vegetation zones, in areas with high humidity,
mainly the most oceanic sections.
In about half of the mire localities we
registered rich fen vegetation. At Fagnano mire we visited large fen areas dominated
by extremely rich fen vegetation. These species-rich communities are most easily
characterized by the bryophyte flora. And a majority of the bryophyte species,
or vicarious species in the bottom layer also occur in Fennoscandian rich fens;
e.g. species of the genera: Aneura, Brachythecium, Bryum, Campylium, Cratoneuron,
Drepanocladus, Lophozia, Mnium coll., Philonotis, Riccardia and
Preisia.
We also visited mires with springs, e.g.
a number of strong, eustatic springs in Tierra Major Valley; with species/genera
typical for spring vegetation, e.g.: Cardamine, Epilobium, Cratoneuron,
Drepano-cladus, Philonotis and Scapania.
Protection plan
Valuable mires are already protected in
the Tierra del Fuego National Park (e.g. the Rio Pipo and Lapataia mires). The large mire landscapes
(mires in mosaic with Nothofagus forests and lakes/brooks) of the Peninsula
Mitre certainly have the largest international protection value, however. Also
the yet unprotected raised bog systems in the Andorra valley belong to the most valuable mire systems. In addition, the
Hambre mires, mires in the Carbajal - Tierra Mayor Valley and Fagnano
mires are among the mires with a high conservation value. Also some other smaller
mire systems, e.g. in more continental areas (flat fens, of types like Maria
Bethy Fen) and many others should be protected.
We visited mires used by the peat industry,
and mires are today a threatened nature type in Tierra del Fuego. There is an
urgent need for a protection plan to protect these most valuable mire systems
of the Southern Hemisphere (cf. Blanco & Balze 2004).
References
Blanco, D.I. &
Balze, V.M. de la. (Eds.). 2004. Los Turbales de la Patagonia. – Wetlands International 19: 1-149.
Moen, A. 1999. National
atlas of Norway: Vegetation. – Norwegian Mapping Authority,
Hønefoss. 199 p.
Pisano, E. 1983.
The Magellanic tundra complex. Chapter 10. – Ecosystems of the World 4 B: 295-329.
Roivainen, H. 1954. Studien über die Moore Feuerlands. – Ann. Bot. Soc.
„Vanamo“ 28 2: 1-205.
Tuhkanen, S. 1992.
The climate of Tierra
del Fuego from a
vegetation geographical point of view and its ecoclimatic counterparts elsewhere.
– Acta Bot. Fennica 145: 1-64.
Tuhkanen, S., Kuokka,
I., Hyvönen, J., Stenroos, S. & Niemelä, J. 1990. Tierra del Fuego as a
target for biogeographical research in the past and present. – Anales del Instituto
de la Patagonia, Serie Ciencias Naturales 19-2: 1-107.
Urciuolo, A. & Iturraspe, R. 2005. IMCG
mires and peatlands. Field symposium Tierra del Fuego 2005. Field guide. – [IMCG],
66 pp. (mimeogr.).