Tuatara: Volume 22, Issue 1, February 1976
PART I — VEGETATION AND SOILS IN SOUTHERN PATAGONIA AND TIERRA DEL FUEGO
VEGETATION AND SOILS IN SOUTHERN PATAGONIA AND TIERRA DEL FUEGO
Fig. 1: Map of southern Chile and Argentina showing vegetation zones. The zone N. betuloides and N. antarctica is dominated exclusively by N. antarctica in eastward and drier regions. The unshaded areas to the east are tussock grassland and low shrubland; from Godley (1960) with his permission. Keys to localities mentioned in text: 1 Agua Fresca; 2 Bahia Morris; 3 Cabo San Isidro; 4 Cordillera Chilena; 5 Cutter Cove; 6 Estancia El Condor; 7 Faro Evangalistas; 8 Fiordo Parry; 9 Isla Capitan Aracena; 10 Lago El Parillar; 11 Parque Nacional Lapataia; 12 Estancia Maria Cristina; 13 North boundary Magallanes Province, Chile; 14 Pecket Harbour; 15 Peninsula de Brunswick; 16 Primera Angostura; 17 Puerto Natales; 18 Punta Arenas; 19 Punta Dungenes; 20 Rio Caleta; 21 Rio Gallegos; 22 Rio Rubens; 23 Ushuaia.
Patagonia, in Chile and Argentina, is the country where a horse can be ridden, in tussock and open deciduous forests. Floristically, Cabrera (1958) shows that the main semi-arid vegetation types of Patagonia stretch from 32°S. at high altitudes near the Andes, reach the coast at 44° S., and then occupy land from the Andes to the Atlantic coast down to latitude 54° S. in Tierra del Fuego. A cross-section of South America, from about 40° S. to 54° S., is, topographically, a larger version of the cross-section: Westland - Southern Alps - Canterbury Plains. But in South America there is a more extensive history of vulcanism, both in the main axis and on the Patagonian Plateau. Lying, as the area does, athwart the ‘Roaring Forties’ and ‘Furious Fifties’, it experiences the same west to east moisture gradient as the New Zealand miniature counterpart; but south-easterly precipitation seems rare south of 44°. In contrast to the relatively humid New Zealand east coast plains, there are the semi-desert conditions found right to the east coast of Patagonia.
In the region of the Straits of Magellan (Fig. 1), visited by the author during research on Nothofagus antarctica in 1971-72, the climate / vegetation pattern from west to east (Fig. 2) is: Cold super-humid conditions allow only ombrogenous peat vegetation, the Magellanic Moorland, a climatic effect on vegetation compounded by the westward distribution of compact diorites (Godley, 1960). Eastward from this most extreme zone, in slightly less cloudy and hence warmer summers, forest patches of the evergreen Nothofagus betuloides appear. These forests are on more favourable sites of easily drained soil parent material within a mosaic of Sphagnum bogs on locally poorly drained sites.
With decrease in precipitation summer temperatures rise slightly and the forest becomes continuous. At about 600 mm annual precipitation forest composition changes to dominance by the deciduous, erect N. pumilio. At 400 mm precipitation this tree is in turn replaced by the multi-stemmed low N. antarctica, and around 300 mm precipitation this low forest gives way to shrubby tussock grassland of Festuca. As the chain of the Andes swings around from a north-south to west-east alignment into Tierra del Fuego, the precipitation and vegetation pattern follows the same trend.
This vegetation pattern has been known since Darwin's time from accounts of passing expeditions. Godley (1960) and di Castri (1968) present well documented recent accounts. Soil relations in the wetter zones are described by Holdgate (1961), and by O'Connor et al. (1965) in the drier zones.
Ecology of the Main Vegetation Types in the Straits of Magellan Region
Climate and the Vegetation Pattern
The climatic data on Table 3 are extracted from official records for Chile (also filed at the New Zealand Meteorological Service, Agroclimatology Section, Wellington).
The west to east precipitation gradient across the Magellanic region is at lower levels than New Zealand's 7,000 mm to 400 mm from Fiordland to Central Otago, but the more southern latitude, and consequent reduced evaporation, produce similar effects on the vegetation pattern. Not shown on Table 3 is the fact that monthly precipitation is virtually regular in all regions. Summer mean temperatures show a parallel trend to the reduced cloudiness along the west-east precipitation gradient. The ranges from mean maxima of warmest month to mean minima of coldest month follow a trend from extreme oceanicity to mild continentality; annual means reflect a similar trend.
Relative humidities show a general decrease from west to east, but are still high; the moisture lack of the grassland areas is more a function of wind evaporation than of heat-induced low humidities.
Precipitation may fall as snow at any season; but local reports are that in winter snow cover is neither deep nor long-lasting at sea level. Ré (1945) shows that only about 10% of total precipitation fell as snow at Punta Arenas over a 10-year period. In the drier regions, windblown snow freezes in winter and, thawing, produces surface floods in spring and this release of moisture is an important reserve of water for plant growth in summer.
Climatic data show relationships with vegetational distribution, particularly in the west to east gradient (Fig. 2) of vegetation types. Notable also is the depression of treeline in the N. betuloides forests of higher precipitation and heavy cloud, a similar situation to that on the western flanks of New Zealand mountains. In southern South America an upward extension of woody growth above the treeline is a zone of Nothofagus antarctica as a prostrate shrub, reaching at times 100 m above the last stunted N. betuloides. This Nothofagus shrubland occupies the situation of a mixed subalpine scrub of New Zealand (Compositae, Epacridaceae, etc.). However, N. antarctica also forms a subalpine scrub zone on both flanks of the Andes, to latitude 35°, at the northern end of Nothofagus forests.
Apparently not only climate but geology has an effect on this vegetation: This zone, vegetated by Marsippospermum and Schoenus, Donatia, Astelia, Orebolus and Gaimardia, is indicative of poor drainage, an effect of high precipitation, low evaporation, a hydric effect aggravated by the impermeable substrate. Godley (1960) demonstrates the coincidence of the ecotone between Magellanic Moorland and evergreen Nothofagus forest with the geological contact between the compact upper Cretaceous Andean diorite and more permeable metamorphics and sedimentaries to the east. Further, he believes that the absence, in the far west, of forest, and its sparsity further inland in the Magellanic Moorland zone, is due rather to substrate effects than to temperature. However, mean summer temperatures (December-February) at Evangalistas (52° S.), where vegetation is virtually treeless, is 8.6° C., well below the 10.5° C. limit associated with forest growth (Wardle, 1965); such temperature is comparable with Campbell Island, at a similar latitude.
Lack of meteorological stations in the Straits of Magellan, eastward until Cabo San Isidro, prevents determination of climate relations along the transition from Magellanic moorland to evergreen forest. However, at Cabo San Isidro, well within this forest zone, mean summer temperature is still only 8.9° C., but mean maxima for the same period is 12.4° C. Within the transition zone Pisano (1970, 1972) has described soil/vegetation relations in detail. He finds that the patches of evergreen beech forest of Nothofagus betuloides are associated with more fractured rock, and are on steeper slopes; more compact rock and gentler slopes do not permit adequate drainage. Substrate impermeability coupled with precipitation, estimated at 1,750 mm, allow only the growth of Sphagnum peat and associated mire vegetation. Young (1972) reports from Isla Desolación (52° 31′ S., 74° 31′ W.) dwarf forest of N. betuloides, in ravines sheltered from wind. These forests appear to show a distribution related to adequate drainage and shelter on this most exposed western coast.
Nothofagus betuloides Forest (Figs. 3, 4)
Fig. 3: Nothofagus betuloides forest 25 m high with Drimys winteri understorey. Rio Caleta, Magallanes, Chile. Altitude 50 m.
Photo: D. R. McQueen
In relation to precipitation it is analogous to N. menziesii (cf. Wardle, 1967). N. betuloides, in the Straits of Magellan area, forms continuous forest in a precipitation range from about 600 mm up to about 1,750 mm to the west of Brunswick Peninsula (72° 30′ W.). As precipitation increases, and secondarily as soil parent material becomes dominated by compact diorite, the forest becomes more fragmentary, in a mosaic of mire vegetation.
the westward are seen around the Primera Angostura (72° 15′ W.).
Fig. 4: A Marsippospermum/Sphagnum terrace bog in Nothofagus betluloides forest; small trees of the same species on bog hummocks in foreground. Rio Caleta, Magallanes, Chile. Altitude 50 m.
Photo: D. R. McQueen
Under slightly lower precipitation, an estimated 800-1,000 mm at Cutter Cove, Pisano (1970) reports pure N. betuloides forest to sea level; but only on steeper, well drained slopes with fractured rock as soil parent material; otherwise the vegetation is treeless.
At the wetter end of its range (Bahia Morris, Isla Capitan Aracena) Pisano (1972) estimates a precipitation of 1,750 mm. Here N. betuloides forest is established only on colluvium giving free drainage; on the compact crystalline substrate, trees are absent.
The association of N. betuloides with high precipitation and humidity is reflected in the physiognomy of the N. betuloides forests: bryophyte and Hymenophyllum cover is dense on ground and fallen logs, although not swathing the trunks as does similar epiphytic cover page 51 on N. menziesii under superhumid conditions in New Zealand. The logs and standing dead branches are ‘soggy’ in decomposition and frequently blue stained inside, as are those of N. menziesii.
A stand on a well drained site of 20° slope examined in detail by the author (January 1972) at Rio Caleta, Seno Otway, had the following composition:
|Height||Estimated % Cover|
|Nothofagus betuloides (in flower)||30 m||80|
|Drimys winteri (in flower)||16-30 m||20|
|Lebetanthus myrsinoides (in flower)||25-50 cm||5|
|Berberis ilicifolia||50 cm - 1 m||5|
|Fuchsia magellanica||25-50 cm||5|
|Uncinia lechleri||5-25 cm||10|
|Maytenus magellanica||5-25 cm||5|
|Asplenium davalloides||5-25 cm||1|
|Blechnum pennamarina||< 10 cm||5|
|Hymenophyllum secundum||< 5 cm||20|
|H. peltatum||< 5 cm||20|
|Bryophytes||< 5 cm||20|
The soil profile was silt, colluviated with schist stones: 2 cm litter/10 cm humus, medium reddish brown/20 cm leached sandy silt, light grey with 20% ferric mottles 20 cm silt loam, light grey with 25% ferric mottles.
The mottling by translocated iron presented a very similar profile to those developed under N. menziesii on loessic colluvia of the Tararua Mountains of New Zealand under 3,800 mm of rain at 600-800 m altitude.
N. betuloides seems tolerant of moderately poor drainage—and can grow on deep peats (> 2 m); for instance on a ‘pakihi’ type terrace seen near the stand just described. However, the scattered trees are only 1-2 m high and growing always on hummocks, where drainage is adequate. Such behaviour contrasts with the growth of N. antarctica on deep peats in the N. pumilio zone.
In precipitation of 800 mm and higher it appears that the greater cloud cover and lowered temperatures produce a lowering of treeline of N. betuloides equivalent to that on western flanks of New Zealand mountains. ‘Mountain scrub’ is described by Pisano (1970) only from one area: Cutter Cove. On well drained soils this scrub includes Embothrium coccineum, Berberis ilicifolia, Baccharis magellanica. At the other two localities, Fiordo Parry and Isla Capitan Aracena (Pisano, 1972, 1973), the forest gives way at the treeline directly to subantarctic cushion vegetation including Bolax borei and B. gummifera, Donatia fascicularis, Phyllachne uliginosa, Caltha dionaefolia, Drapetes muscosus and Astelia pumila and occasional prostrate Nothofagus antarctica.
In all three areas mentioned above Pisano records N. antarctica as a prostrate shrub above the N. betuloides treeline, but the upper page 52 limit of N. antarctica is specified only at Fiordo Parry, at 400 m — that is, 100 m above the uppermost N. betuloides. At Cutter Cove N. antarctica is recorded as a small tree in the ‘mountain scrub’, at the other two areas as a prostrate shrub on better drained slopes in the Bolax cushion vegetation.
Similar conditions were observed by the author above the N. pumilio treeline at 600 m on Cerro Condor (Parque Nacional Lapataia) and at 650 m on the mountains above Punta Arenas. There, on slopes over 10° the N. antarctica shrubland was dense and up to 2 m high, but was prostrate and scattered in the Bolax cushions on gentler slopes. Dense, tall N. antarctica scrub was observed from the sea on southward slopes of Peninsula Brunswick, extending over a depth of 100-150 m down to the N. betuloides forest.
Stunted, isolated stands of N. antarctica were found by Young (1972) at ‘about 500m’ on Isla Desolacion, above equally isolated patches of dwarf forest of N. betuloides. The subalpine scrub belt on N. antarctica is here fragmented by exposure to wind, and by the very limited edaphic suitability of the westernmost parts of the Magellanic area.
In comparing treeline conditions in the N. betuloides zone with those of the N. menziesii forests of wetter mountains of New Zealand it can be seen that only in one case in the Magellan Straits area has there been described a mixed shrubland equivalent to New Zealand subalpine scrub of cloudier depressed treeline conditions. In other cases N. betuloides krummholz gives way directly to the subalpine cushion vegetation, with N. antarctica as a shrub only on better drained sites.
It appears here that in the far south and right through its range to 35° S. N. antarctica is playing alone the role of the mixture of species which form subalpine scrub in New Zealand. In its relationship to the taxa of the forest below timberline the subalpine ecology of N. antarctica is close to that of Pinus uncinata var. mugho of the European Alps and the French Massif Central. The Arctic equivalent in Norway and more humid Sweden is a change from forest of Pinus silvestris to tall (2-3 m) scrub of Betula tortulosa, which in turn gives way to a lower scrub of Salix spp. of 40-60 cm high.
N. betuloides appears to reproduce exclusively by seed and according to Sra. N. Goodall, of Ushuaia (pers. comm.) has produced seed there annually in the last five years. Summer conditions there in 1968-69 and 1969-70 were apparently milder than usual, and it is possible that the trees were showing similar reaction to warmer than usual summer temperatures, as does Nothofagus in New Zealand.
Utilisation and Land Use
N. betuloides can grow to 25-30 m height with 10-15 m of clear trunk with diameters of up to 75 cm (b.h.). It is milled in the few page 53 regions where road access exists in the zone of its distribution. The wood is not durable, but superficially similar to the more durable N. pumilio, and apparently advantage is taken on this to market a mixture of both species. Little of the high precipitation area occupied by N. betuloides is farmed and the only exploitation of the zone is by random logging of Pilgerodendron uviferum trees in the wetter, westward area, and only in areas accessible by sea. Much of the area both of N. betuloides and of Magellanic moorland in Chile is now incorporated in national parks (Pisano, 1973).
Conifers and Magellanic Forests
Conifers in the Magellanic area are represented only by the tree Pilgerodendron uviferum, generally on moderately poorly drained soils, and at low altitudes in the N. betuloides forest zone. It is notably absent from the Fiordo Parry area (Pisano, 1971) which appears to have a cooler climate than other western areas described by him. In the more eastern forests of N. betuloides on Peninsula Brunswick and in N. pumilio forests of even drier and more extreme climates there are no conifers.
The prostrate Dacrydium funckii of bogs further north is also apparently absent from the Magellan Straits area and Tierra del Fuego. Only in the extreme north-west of Magallanes Province (49° S.) does Podocarpus nubigena appear (Pisano, 1973). It is found in forests dominated by N. betuloides and accompanied by Weinmannia trichosperma, Tepualia stipularis and Lomatia ferruginea. Temperature conditions are evidently more favourable than further south as the estimated 2,000-6,000 mm of rain still permits forest growth. The family combination is far more familiar to New Zealanders, and puts into contrast the combination of the familiar Nothofagus with the unfamiliar Berberis, Maytenus, etc., associants of more southern forests. Other conifers play an increasing role in Chile and Argentina, north of 48°. Godley (1960) and Schmithusen (1960) give accounts of their distribution in Chile and Cabrera (1958), of their extension into Argentina.
The diminution southwards of a coniferous component with increasing cold, and then its final disappearance eastwards in the lower rainfall forest climates is a character not found in the present New Zealand vegetation. However, certain fossil pollen floras of the penultimate glaciation in the Wellington area show very low quantities of conifers (McQueen, 1973) but abundant beech pollen; suggesting that climates of this epoch could have found their equivalent at 52° - 55° S.
Nothofagus pumilio Forests (Fig. 5)
Fig. 5: Sub-alpine Nothofagus pumilio forest 15-20 m high, Parque Nacional Lapataia, Tierra del Fuego, Argentina. Altitude 450 m.
Photo: D. R. McQueen
N. pumilio fits well with generalised theories of deciduous tress being those of more extreme climates. Climate data from Punta Arenas (Table 3 show slightly wider extremes than stations in the zone o the evergreen N. betuloides; extremes amplified by the dessication of the constant, strong westerly winds in summer.
In stands on freely drained soils, and from 0-600 m altitude near the coast, and 0-700 m inland, N. pumilioforms dense pure stands of trees varying from 30 m height in sheltered positions is 15 m on exposed plateaus, with diameters (b.h.) from 1 m down to 30 cm in canopy trees. Undergrowth on a moderately leached soil at 200 m, near Lago El Parillar, Chile (200 m alt.), is sparse of:
|Berberis ilicifolia||1 m||20|
|Pernettya mucronata||50 cm||15|
|Maytenus disticha||50 cm||15|
|Rubus geoides||10 cm||10|
|Blechnum pennamarina||5 cm||5|
On a moister nutrient accumulation site a herb cover is encountered, as at 200 m in the Parque Nacional Lapataia:
|Osmorhiza depauperata||30 cm||50|
|Cystopteris fragilis||30 cm||30|
|Cordonorchis lessonii||10 cm||10|
|Macraecaenium gracilis||5 cm||5|
|Dryopsis glechamoides||5 cm||5|
|Viola magellanica||2 cm||5|
The soil forming characters of N. pumilio in the South Patagonia climate are indicative of an acid raw humus regime. Raw humus under N. pumilio can be up to 15 cm deep, with pH 4; field evidence of leaching and podsolisation is frequent, despite Holdgate's (1961) reservations on these processes.
Altitude and increasing humidity at higher altitude may be associated with the formation of true podsols under N. pumilio. For instance at 400 m on the Cordillera Chilena, inland from the Straits of Magellan, there was no visible iron translocation under N. pumilio on well drained soils; there were ground water podsols only in poorly drained depressions. At 600 m in the same region, a 20 cm thick iron pan had formed in a leached sand beneath N. pumilio.
Likewise, near Punta Arenas, at seal level, profiles under N. pumilio showed only yellow brown, diffuse iron in the soil, but at 400 m altitude at Lago El Parillar, podsolisation was continuous, with 10-20 cm of bleached sand overlying a 2-3 cm thick iron pan.
This second pair of soil comparisons was near the Magellan Straits; temperatures there are noticeably lower than in regions to the north, so that the treeline of N. pumilio near Punta Arenas is at 600 m, while on the Cordillera Chilena it is about 700 m. The raising of temperature zonation is thus reflected in an effect on podsolisation. But complicating the problems of podsolisation in Magellanes is the question of soil parent material. Volcanics are not mapped in recent geological maps of Magellanes, but the whole of South Patagonia is mapped as ‘under the influence of volcanic ash’ (Valdés, 1969). It is known in New Zealand that podsolisation is rapid on acidic tephra soils, so possibly in Chile the same acceleration has occurred. The usual soil parent material in eastern Magellanes Province is a sandy silt (? loess + tephra) of 0-60 cm depth, dependent on topography, overlying till, and soils formed from this combination, at lower altitudes, under N. pumilio were similar to New Zealand's yellow-brown podsolic soils.
N. pumilio is less tolerant of poor drainage than N. betuloides. Within the main zone of distribution of N. pumilio between 400 mm and 600 mm of precipitation Nothofagus antarctica is the species occupying intrazonal sites of waterlogged and peaty soils. The physical characters of a sequence of soils overlying a compact Tertiary page 56 mudstone, from a slightly stunted stand of N. pumilio on mineral soil through to a peat of > 2 m depth, showed that, when aeration porosity of the soil of the rooting zone was below 18%, N. pumilio was replaced by N. antarctica.
In the deciduous N. pumilio forests the bryophyte-Hymenophyllaceaemat is absent, and the rate of deadwood decomposition is very slow and ‘dry’, so much so that a fire can be easly kindled under any weather condition in South Patagonia N. pumilio forests. In this respect the map of distribution of Indian tribes (Goodall, 1970) shows that the land dwellers, Tehuelche (Ona and Haush), occupied the N. pumilio and drier zones to the east; avoiding the N. betuloides forest: in such a climate these tribes were dependent on good fires. This character of ‘dry’ decomposition does not seem to be an inherent character of the wood of N. pumilio: further north at latitude 40°, near S.C. de Bariloche (Argentina), N. pumilio wood near the timberline was decomposing damp, with the blue fungal stain frequent in N. menziesii wood and N. solandri var. cliffortioides wood under higher rainfall conditions.
Despite the different leaf form and seasonality some equivalence can be found between forests of N. pumilio and N. solandri var. cliffortioides. They are both of lower rainfall areas: 600-800 mm at sea level in southern Chile and Argentina at latitude 50°-55°; and down to about 1,000 mm on normally drained (not excessively dry soils) in New Zealand. Both the South American and New Zealand trees ascend to the treeline. The forest floor under N. pumilio is frequently herbaceous, especially on nutrient accumulating lower slopes, and lacks ferns larger than Blechnum pennamarina. N. solandri var. cliffortioides forests may have a similar herbaceous floor vegetation in lower rainfall areas, especially when browsing mammals have destroyed the shrub and fern layers. Cattle, horses and guanaco inhabit most southern Chilean forests, so that the similar floor vegetation may be a common character of animal treatment.
N. pumilio regenerates well under its own shade, only by seed, but their survival seems jeopardised by bush grazing of cattle. Regeneration by seeding after logging is equally good, possibly due to the ‘creaming’ selection of only the millable trees, and the leaving of malformed trees wich act as seed trees.
Forest Utilisation and Land Use
Most construction of houses in Magellanic Chile is based on N. pumilio; straight logs down to 50 cm b.h. and 6 m length are felled; selecting from straightness. The sight of sawn logs leaving the bush across the tray of truck indicates the small sizes taken; but these logs could be up to 250 years old. The use of floorboards 5 cm wide also page 57 indicates intense utilisation of logs. There appeared to be little attempt at silviculture of this regeneration after logging and, indeed, it was reported that blanking with Pinus silvestris was being encouraged in cut-over land. Much millable forest of N. pumilio is on privately owned land, as backblocks of sheep farms, and the more usual policy after felling is burning and seeding of grass on ash. Pisano (1973) points out that the lower altitude areas of N. pumilio forest, coinciding with a climate of reasonable agricultural potential, has been considerably reduced. This deforestation, often unaccompanied by milling, has resulted in log-strewn landscapes sadly reminiscent of New Zealand's attempts at clearing beyond the limits of practical agriculture. Possibly the extreme is in the Parque Nacional de Torres del Paine, formerly a sheep station. Here the approach to the Southern Ice Sheet of Patagonia is a day-long tramp through skeletons of N. pumilio, burnt to the edge of the ice sheet and up to the timberline. Few extensive areas of N. pumilio forests are included in national parks although some small forest reserves include stands of this species (Pisano, 1973).
The establishment of pasture of Dactylis glomerata on these old forest soils is at first very successful, as the burning has mobilised nutrients locked in the humus. However, fertility appears to drop rapidly and pasture invasion by Aceana spp. and Baccharis magellanica (a Raoulia-like plant) is frequent.
Fertiliser is not easily available in Chilean Patagonia; all transport from the north is by sea. Reports of experimental fertilisation with N, P or K are discouraging. Response on one farm at 400 m was obtained only from sheep daggings which encouraged grass growth and raised the pH after three years by one unit.
Pasture organic matter, as in the forest, decomposes slowly in the cold, and effectively dry, windy climate: the relative humidity at Punta Arenas is around 70% during the growing season, November-March. This lack of decomposition of organic matter is probably a factor in lack of response to mineral fertiliser.
It is a generally held opinion in Magallanes Province that it is only the cold that inhibits organic matter decomposition by micro-organisms: but forest floor litter decomposition in the wetter N. betuloides forest appears similar to that in cool, humid N. menziesii forests in New Zealand.
Ploughing in of an artificial pasture of Dactylis glomerata or of native tussock in the semi-arid zone produces the same appearance, one year after, of a straw covered piece of land, the grass bases and leaves having not decomposed.
Fig. 6: Degradation sequence; bare gravel — Empetrum nigrum — Festuca — Chiliotrichum diffusum — Nothofagus antarctica; foreground to background. Estancia Maria Cristina, Magallanes, Chile. Altitude 250 m.
Photo: D. R. McQueen
Nothofagus antarctica Forests and Shrublands (Figs. 6-9)
Nothofagus antarctica (nirre) is a small tree reaching 15 m only, or shrub, frequently multi-stemmed, and coppices centrifugally by death of central stems. It also produces root suckers in soil conditions from the wettest to the driest. The foliage is deciduous, appearing in late November, and falling in April, in the far south. The leaves are small, < 2 cm and toothed. Flowering was observed in summer 1971-72; the preceding summer had been abnormally warm; it is not known if such flowering is regular.
This species is of wider ecological tolerance than any other South American Nothofagus. It was chosen for this reason as the subject of a detailed study of its soil and climate tolerance, and the account below is extracted from current research, using quantitative methods of subaerial growth and productivity measurement, and quantitative soil physical parameters. Godley (1960), Dimitri (1962), Clarke (1964) and Pisano (1973) are among authors who have described in general terms its ecology and distribution in its range, from sea level to 650 m at 55° S., to a 200-300 deep zone at 2,000 m, at 35° S.page 59
It grows in southern Patagonia in four sites: 1. semi-arid regions; 2. hydromorphic soils; 3. subalpine shrubland; 4. temperature inversion basins.
Ecotypes may exist appropriate to each site; there is little if any morphological variation; Wardle reports (1971) that seed of Argentinian timberline provenance grown at sea level in New Zealand has produced persistently prostrate saplings after three years growth and (pers. comm.) is still prostrate after five years.
1. In the driest wooded zones in southern Patagonia it is the only tree in a precipitation range from about 400 mm annually (east of Punta Arenas) to about 300 mm further to the east. Auer (1951, 1966) produced evidence of recent climatic deterioration by lowered precipitation, based on heavy mortality in stands of N. antarctica in the drier wooded areas of Tierra del Fuego and Patagonia. With such a drought tolerance N. antarctica has an important role to play in conservation on the fohn-swept areas east of the Andes and their extension into Tierra del Fuego.
Fig. 7: Nothofagus antarctica, 4 m high, on a dry site in semi arid country. Estancia Maria Cristina, Magallanes, Chile. Altitude 200 m.
Photo: D. R. McQueen
Fig. 8: Nothofagus antarctica, 1-2 m high, on peat at least 3 m deep. Lago El Parillar, Magallanes, Chile. Altitude 250 m.
Photo: D. R. McQueen
The following sequence shows the relation of depth of friable soil to vegetation cover.
|Depth Friable Soil||Vegetation|
|1 m||Dense healthy N. antarctica low forest (4 m high)|
|50 cm||Sparse, unhealthy N. antarctica low forest (3-5 m high) heavily parasitised by Myzondendron with floor invasion by shrubs of Chiliotrichum diffusum|
|20 - 30 cm||Dense Chiliotrichum diffusum scrub|
|10 - 20 cm||Festuca tussock grassland|
|< 10 - 0 cm||Empetrum nigrum heathland on gravelly clay|
In this sequence, only the two N. antarctica sites were studied in detail and considerable differences in moisture storage were demonstrated there. Not only was the total moisture storage higher in the deeper profile, but the soil held more moisture per unit volume.
Fig. 9: Nothofagus antarctica, 1 m high, as sub-alpine scrub on better drained sites in Bolax-Azorella cushion fellfield. The background range shows the N. pumilio timberline, at 650 m; darker patches above are of N. antarctica scrub. Parque Nacional Lapataia, Tierra del Fuego, Argentina. Altitude 680 m.
Photo: D. R. McQueen
2. A second type of site already documented in some edaphic detail (Holdgate, 1961) is on hydromorphic soils in areas of climate supporting forests of taller species of Nothofagus on better drained soils. Current detailed studies of soil aeration show that on a shallow peat (20 cm) radial growth rates of N. antarctica were equal to those on a well drained valley bottom site in semi-arid country. The trees on shallow peat were 3 m high; on 80 cm of peat, growth was stunted to 1 m high.
3. Also reported by several authors, including Schmithusen (1960), Dimitri (1962) and Pisano (1970, 1971, 1972) is the occurrence of N. antarctica in subalpine shrubland zone, throughout its latitudinal range. In a situation studied in detail by the present author, erect page 62 N. pumilio forest gave way at 600 m to a narrow zone (30 m) of krummholz of the same species. At 650 m, on slopes of 10° or greater, there was a dense 1.5 m high shrubland of N. pumilio : N. antarctica at a 1 : 4 proportion in cover. The two species were growing with stems running downslope for 2-3 m, then ascending. Radial growth of N. antarctica, at 1.8 mm/year, exceeded that of N. pumilio at 1 mm/year.
On a poorly drained area of 1° slope at 650 m altitude, N. antarctica grew as scattered shrubs, 30 cm high, with radial growth of ca. 0.5 mm/yr. The accompanying cushion vegetation of Bolax gummifera, Azorella lycopodioides and Empetrum nigrum accounted for 90% of the ground cover. Here N. antarctica was showing its tolerance, not only of above treeline conditions, but of impeded drainage.
4. The last type of site is extensive, and is occupied by forests of N. antarctica in well drained valley bottoms. Such zones are extensive between Rio Rubens and Puerto Natales (it is probable that Kalela, 1941, took his ‘Rio Rubens’ growth rate samples from such sites) and to the north of Puerto Natales. The hills around carry dense N. pumilio forest, and a probable reason for the change of pattern to N. antarctica is associable with cold air drainage.
The valley bottom forests of N. antarctica include some of the highest N. antarctica (15 m high, 80 cm diameter) seen in Southern Patagonia; however, almost without exception the upper third of the trees was dead; no reason was established, but the uniformity of the kill line suggests climatic accident, such as an abnormal freezing wind in spring.
Growth Rates of N. Antarctica
Studies at present under way indicate that N. antarctica in Southern Patagonia is a slow growing tree: the highest increment recorded by Kalela at Agua Fresca, south-west of Punta Arenas in ca. 500 mm of precipitation, is 1.18 mm/yr radial growth. In more arid areas of Maria Christina, north-east of Punta Arenas, studied by the present writer, 1.50 mm/yr was recorded in a favourable valley bottom site in ca 330 mm annual precipitation. Such growth rates are equalled in shallow peat (see above) and only exceeded above the treeline, where 1.80 mm/yr was recorded, but there height growth was very limited. The over-all effects of subantarctic cold temperatures, especially of summer, are seen in all these growth figures.
Despite the slow growth of N. antarctica its reproductive capacity, by seeding, coppicing and root suckering, contribute to a colonising aggressiveness and persistence under disturbed conditions, especially in the semi-arid zone. Add to these reproductive features a wide ecological tolerance, and it is difficult to equate its ecology with any New Zealand Nothofagus.page 63
These features distinguish it from N. solandri. The latter will grow in lowest precipitation experienced by Nothofagus; it will occupy shallow peats, but not over 30cm (Elder, 1965). It will form a krummholz (Wardle, 1970) at treeline, but will not form a distinct scrub zone above treeline. N. solandri will tolerate, to a limited extent, cold air drainage basins, but certainly not of the extremity of those occupied by N. antarctica.
Utilisation and Land Use
Nothofagus antarctica is used only as firewood, although sawlogs have been obtained from larger stands in Tierra del Fuego (Bridge, 1948). The wood appears durable; but almost always shows heartrot inside the first 50 growth rings.
Its main use should be as a shelter. and soil stabilising tree. All attempts at exotic establishment with Pinus, Cupressus macrocarpa, Salix and Populus are successful in the semi-arid zone only if permanent artificial windbreaks are erected.
These notes are taken partly from a visit to the sheep station, Condor Estancia, near Cabo Virgenes, in Santa Cruz Province, Argentina, close to the easternmost extent of Southern Patagonia at the Straits of Magellan. Precipitation here is about 250 mm annually and the area all within climax grassland. The frequent snow in winter is not generally deep, but freezing conditions until November imply a concentration of moisture availability at the beginning of the growing seasons.
The vegetation of the estancia, which occupies the whole southeastern corner of Argentinian Patagonia from Rio Gallegos to Punta Virgenes, shows a regional pattern, probably related to precipitation differences. To the south, along the Straits of Magellan, the shrub Chiliotrichum diffusum is more abundant in the grassland. According to Sr. E. G. Blake, the manager, rain is more frequent along the straits that flank the estancia.
To the east, Empetrum nigrum is more common. This species, associated with gravelly soils further west, is in lower precipitation areas associated with shallow soils or with gravels. Its eastern occurrence at El Condor suggests greater soil degradation in pre-settlement times, probably in consequence of great frequency of fire.
The tussock grasslands, dominated by Festuca gracillima on drier ground and F. pallescens in hollows, have a floor cover of very different botanical character from New Zealand's low tussock grasslands.page 64
For instance, Pisano (1973) lists, from Chilean tussock grassland:
- Calceolaria biflora
- C. darwinii
- Perezia recurvata
- Armeria elongata var. chilensis
- Primula farinsoa var. magellanica
- Aster vahlii
- Valeriana carnosa
It is only when one adds the cosmopolitan genera in the form of:
- Viola maculata
- V. reichei
- Oxalis enneaphylla
that any generic resemblance with New Zealand can be recognised.
Under acid conditions, and impeded drainage, invasion of these grasslands by Azorella reminds one of the closeness of the circumantarctic element.
The management of this vegetation for sheep grazing presents some features and problems very different from similar looking tussock country in New Zealand.
The Festuca tussocks are palatable at all stages, unlike Festuca novae-zelandiae; and there appears to be a higher proportion of palatable plants, especially stoloniferous grasses on the floor of the tussock vegetation. With this natural advantage, burning, as was practised in New Zealand until recently, is not used as a management technique for tussock grasslands in Argentina or Chile. In an unimproved state good tussock grassland in Southern Patagoria can carry three or four Corriedale sheep per hectare.
Pasture improvement techniques are still at a rudimentary stage; partly because of the difficulty of getting response from fertilisers, and from the persistent failure of clovers. It must be added that it was only in 1971 that I.N.T.A., the Argentinian agricultural research organisation, established its first permanent field officer at Rio Gallegos. Until then the nearest advisory office was at S.C. de Barriloche, thirty-six hours by road!
The pasture improvement technique developed by Sr. Blake consists of ploughing the tussock in and seeding with Dactylis glomerata, Phleum pratense and Lolium perenne (cocksfoot, timothy and ryegrass). Of these, cocksfoot is the most successful. It takes up to four years for a continuous grass cover to establish: consequently weed invasion is high, particularly by dandelion. Another technique used with Empetrum nigrum heath is the shallow ploughing and turning over of the humic turf developed by this heath. If left fallow for a year, then seeded, the artificial pasture establishes well; if not seeded, the heathland is replaced in a few years by good growth of Festuca tussock. Relevant to this are results of O'Connor et al. (1965) whose experiments show that both NH4 and NO3 nitrate were lower page 65 under Empetrum nigrum than under tussock grassland. They report slow growth of pasture after normal ploughing of Empetrum and it appears that Sr. Blake's practice of exposing the shallow humic turf is encouraging mineralisation of a raw humus. Deeper ploughing of Empetrum, which is always in shallow gravelly soils in this region, only exposes a less fertile, often gravelly layer, and buries the humic turf below reach of grass seedlings' roots.
There is, obviously, much need for basic research on the soils of the grasslands. I say basic, because a considerable number of Patagonian farmers have contact with New Zealand to the extent of studying at Massey or Lincoln. All too often their empirical experimentation at home, based on far more temperate New Zealand conditions, has failed in Patagonia.
Further, O'Connor et al. (1965) postulate phosphate deficiency and aluminium toxicity. Argentinians believe that sulphur deficiency may be chronic in the area. R. Schaeffer (pers. comm.) believes that the whole cycle of organic matter decomoposition is very slow in cold and dry climates. But as yet very little continuing work has been carried out in Southern Patagonia to find the chemical and physical bases of soil fertility.
A final comment: considering the climatic conditions of a frozen-up winter and a three to four months growing season it is truly surprising to see that the natural grasslands can produce such large, healthy sheep. Possibly it will be better to leave the palatable tussock and enrich by oversowing of pasture grasses, with application as fertiliser of what elements are actually lacking, rather than attempting complete conversion to swards of introduced grasses.
I should like to express my gratitude to all those who helped my field work in Chile and Argentinian Tierra de Fuego: Sr. M. Martinic B, Director of the Instituto de la Patagonia; Sr. E. Pisano V., Assistant Director and Botanist at the same institute; Dr. F. Schlegel S., Director of the Instituto de la Silvicultura y Reafforestacion, Universidad Austral de Chile; Sra. N. R. P. de Goodall of Ushuaia; Dr. D. M. Moore of the University of Reading; M. J. Pigier of Punta Arenas and the Schlumberger Geophysical Company, both in Chile and Argentina; Sr. H. MacLeay of Punta Arenas; Sr. G. Blake of Rio Gallegos; and my wife, Pamela, for enduring patience as a field assistant.
This account forms part of a research project supported by:
Victoria University of Wellington Refresher Leave Grant, and Internal Research Committee Grant
New Zealand University Grants Committee, Research Grant Bourse de Stage du Gouvernment Francais
|* Genus common to South America and New Zealand|
|† Species common to South America and New Zealand|
|Armeria elongata var. chilensis||Caryophyllaceae|
|* Asplendium davalloides||Polypodiaceae|
|* Astelia pumila||Liliaceae|
|† Blechnum pennamarina||Polypodiaceae|
|* Caltha dionaefolia||Ranunculaceae|
|† Cystopteris fragilis||Polypodiaceae|
|* Dacrydium fonckii||Podocarpaceae|
|* Donatia fascicularis||Stylidiaceae|
|* Drapetes muscosus||Thymelaceae|
|* Festuca gracillima||Gramineae|
|* Festuca novae-zelandiae||Gramineae|
|* Festuca pallescens||Gramineae|
|* Fuchsia excorticata||Onagraceae|
|* Fuchsia magellanica||Onagraceae|
|* Gunnera magellanica||Haloragaceae|
|† Hymenophyllum peltatum||Hymenophyllaceae|
|* H. secundum||Hymenophyllaceae|
|* Oxalis enneaphylla||Oxalidaceae|
|* Pernettya mucronata||Ericaceae|
|* Phyllachne uliginosa||Stylidiaceae|
|Primula farinosa var. magellanica||Primulaceae|
|* Rubus geoides||Rosaceae|
|* Schoenus||Cyperaceaepage 67|
|* Uncinia lechleri||Cyperaceae|
|* Viola maculata||Violaceae|
|* V. magellanica||Violaceae|
|* V. reichei||Violaceae|
|* Weinmannia trichosperma||Cunoniaceae|
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