Nothofagus obliqua (Mirb.) Oerst.

The deciduous ‘roble’ is distributed on the Argentinian side of the mountains only between 36° 50′ and 40° 15′ S (Hueck 1966). In Chile this species advances considerably further north, in its var. macrocarpa to approximately 33° S (Munoz 1968). Here it occurs between 750 and 2,200 m altitude. In the south, dow nto 41° 20′ S the main distribution of this species is in the lowlands.

Fig. 5 shows a schematic transect across the Coast Range near Valdivia. This is the only known region where all species of Nothofagus are together with the exception of N. pumilio. Here Nothofagus obliqua goes up to about 500m on the lower rainfall east face. Generally it can be considered as the dominant species of a tree association which is typical for a region of episodic summer drought. Frequent evergreen companions are Persea lingue Nees and Laurelia sempervirens Tul.

Fig. 4 shows that Nothofagus obliqua is a relatively thermophilic tree. In its ‘ideal biotopes’ the day and night temperatures were higher than in those of all other Nothofagus species. Accordingly N. obliqua is found further into the sclerophyllous woodland where conditions are close to the mediterranean climate areas of California and the Mediterranean. The ecoclimogram in Fig. 6 reflects the tolerance range of this species in respect to north-south (vertical axis) and west-east distribution (horizontal axis). These compass orientations are obviously not to be interpreted in a strictly literal sense for it is not only the geographic co-ordinates which determine the degree of increasing latitude or ‘southerness’ and continentality of a site. These orientations have been transferred to an ecological sense, because localised topography is a deciding factor. In this way flat land will show a stronger continentality than adjacent slopes; the degree of southerness of a slope will be determined by its aspect. Fig. 6 shows a certain continental tendency exhibited by Nothofagus obliqua as does Fig. 4, with a wide temperature amplitude. It has been observed that Nothofagus obliqua never goes down to the west coast, although in breaks in the Coastal Range, near Valdivia, and at Rio Tolten the species grows within a few kilometres of the sea. This species does not penetrate into the coastal belt of Aextoxicon forest. Even in open pioneer communities this light demanding species is absent near the sea. Nor does it grow on the flat foreland of Arauco that extends in the front of the coastal range between 37° 15′ and 38° 15′ S.

In the other ecoclimogram (Fig. 7) there are two parameters (temperature and saturation deficit) that are linked by a positive correlation. The higher are their values then the drier and warmer are the respective sites in summer. It must be recalled that these page 253

Fig. 4: Daily temperature cycle in summer on ‘ideal’ Nothofagus sites. 25cm above soil. n = number of sites for each species.

figures are those concerning the climate at the air layer close to the soil. However, these values at best allow indirect conclusions on the edaphic conditions of the site.

Nothofagus obliqua is considered an indicator of fertile sites in the southern part of its distribution, but in the north, N. obliqua occupies sites of shallower soils. Because there are commonly long summer droughts in the hardwood region N. obliqua has to be well adapted to this contingency. In this respect, Fig. 7 shows a certain similarity between N. obliqua and N. antarctica.

The ideal site for N. obliqua, even though relatively warm is not, however, free of frost (Table 3). For south Chilean agriculture this is an important factor because former sites of N. obliqua forest are now intensively farmed. Here summer frosts quite often cause serious damage to wheat during the flowering season.

N. obliqua prefers flat sites but not to the same extent as the next species, N. antarctica. This is true not only for the flat lands of the Central valley. For example one can find N. obliqua in the northern sector of the Coastal Range (Nahuelbuta National Park, 37° 47′ S 73° W) on high plateaus of 1,200m altitude. There its range overlaps with that of Nothofagus antarctica and Araucaria araucana C. Koch. page 254

Fig. 5: Distribution of Nothofagus at different altitudes and expositions of Cordillera Peladar (Coastal Range) 140° 10′S. Rain gauges installed in open sites. At Valdivia situated nearby 136% long term precipitation was recorded.

N. obliqua does not grow on the slopes of the Coastal Range; instead one finds N. procera (syn. N. alpina) with numerous evergreen species. In the lowlands, 1,000 m below, Nothofagus obliqua is again found and has the same type of distribution in the Tolhuaca National Park (38° 12′S 71° 48′W) in the Andes.

Nothofagus antarctica (Forst.) Oerst.

N. antarctica is also observed in the southern part of the area of distribution of N. obliqua. Only occasionally are both species found together, there being generally a sharp boundary between the two forest types, so that the transition from one to the other may take place within a few paces. In such conditions the areas occupied by N. antarctica commonly are flat valleys with shallow soils, areas called locally ‘nadis’ (Weinberger et al. 1970). Such sites are occupied by ‘Zarzales’, formations which are open and contain a high proportion of thorny shrubs, Berberis, Discaria etc. Embothrium coccineum is frequently present and shows a preference for such sites along with Nothofagus antarctica.

N. antarctica is a notable light demander and in this respect is very similar to N. obliqua. This behaviour is reflected in the high values for both species of the average temperature of the warmest half-day (Fig. 7). Sites studied are frequently open and subject to strong insolation. However, both species show quite different optima and tolerance ranges. This is expressed not only by the data in Table 3, but also in Figs. 6 and 7. This is especially the case for the ranges of high temperatures and saturation deficits; there the ecoclimagrams demonstrate noticeable divergences between the two species. The temperature environment which corrsponds to the cuneiform intercalations between the ranges of the two species (Figs. page 256

Fig. 6: Ecoclimagram for thermal factors showing general heat requirements of Nothofagus spp. and their tendency towards more oceanic or more continental climatic conditions respectively. Temperatures at 25cm above soil for 3 summer months. (See Fig. 7 for legend.)

6 and 7), is found predominantly on the eastern flank of the Andes. This zone is specifically occupied by Austrocedrus chilensis and Lomatia hirsuta.

N. antarctica sites are characterised by particularly high atmospheric saturation deficits. There the soils are usually only partially covered by vegetation. They dry out on the surface very rapidly page 257

Fig. 7: Ecoclimagram of Nothofagus spp. for microclimatic factors which influence the water regime. Number of values as for Fig. 4.

and evaporation decreases to low values. N. antarctica is the only species of the genus which tolerates conditions of the sub-Andean rain shadow steppe formation.

Nothofagus procera (Poepp. et Endl.) Oerst. (Syn. N. alpina Oerst.)

The ‘rauli’ forms almost pure stands as trees up to 40 m in height. It is distributed in mountain areas of Argentina (39° 22′ to 40° 23′S, Hueck 1966), and Chilen (35° 20′ to 40° 20′S). This page 258 summer green tree occupies an intermediate position in its temperature ecology. This does not, however, imply that it will be found together with all the other Nothofagus species.

According to Figs. 4 and 6 the continentality is approximately the same as for N. obliqua. Mixed stands are located in areas of transition between the two species but the ‘ideal’ stand of N. procera is considerably cooler than for N. obliqua. In 46 samples from stands of N. procera, N. obliqua was present in less than one third. A marked plant-sociological link exists with N. dombeyi which was present in two-thirds of the stands sampled. Coincidentally in Fig. 4 is shown a large similarity of the temperature curves of both species (N. procera and N. dombeyi).

N. procera frequently occurs with Lomatia dentata. In general the deciduous N. procera shows considerable affinity to various evergreen trees of the cool oceanic climate. This affinity goes so far that in Valdivia province, on the eastern flanks of the Coastal Range at 800-900 m this species forms mixed species — rich stands with N. nitida (Fig. 5). According to Urban (1934) N. procera appears in the province of Chiloe scattered in the evergreen forests. However, the writer did not succeed in relocating any N. procera there.

According to the ecoclomagrams, the thermal requirements of the sites of N. antarctica and N. procera overlap to a considerable extent. Nevertheless both species are not found growing together because there are other differentiating factors. N. procera is almost exclusively a tree of slope positions, on soils developed in the Andes from recent volcanic ashes. On the geologically older Coastal Ranges it is limited to deeply weathered soils, where competition pressure on these soils is very strong. The excellent ability of N. procera to succeed under such conditions is shown by the fact that it shows good regeneration in heavy shade. By contrast, it has already been emphasised that N. antarctica is light demanding.

Finally, the frequency of frosts is substantially lower in N. procera sites and is a consequence of the temperature regime of slopes occupied by this tree. The interpretation of many daily curves of temperature show that on these sites at night warm air streams flow upwards from the valleys (Fig. 4). Such air flows contribute to a marked lowering of the night cooling effect and may often result in temperature increase. This phenomenon is so marked that it remained even when the average from 62 daily temperature curves was calculated. Undoubtedly this is a mechanism which helps to reduce the number of frosts. This phenomenon is responsible for the fact that the relative humidity of the air of the ‘ideal’ sites for Nothofagus procera is approximately 90% between 4 a.m. and 8 a.m. whereas for all other Chilean Nothofagus, including Nothofagus obliqua, there is a variation in the corresponding mean values, from 95% to almost 100% relative humidity. Consequently dew is scarcer on sites of N. procera.

The occurrence in the same areas of N. procera and N. pumilio is not known to the writer. According to Fig. 6 this would not be expected.

Nothofagus pumilio (Poepp. et Endl.) Krasser

The ‘lenga’, a summer green species reaching 30 m height, forms typical tropophilic forests, according to Schimper's definition. These forests are sharply delimited from all other woodland associations plant-sociologically, and extend with particular uniformity from 35° 30′S in Chile and 36° 56′S in Argentina to the southern end of the continent. In Tierra del Fuego this species grows at sea level (Skottsberg 1916).

Fig. 4 also shows that the mean night temperatures for both N. pumilio and N. antarctica are very similar. Nevertheless even here there is a characteristic difference in the smaller variability of the temperature minima for N. pumilio sites. Consequently there is a significantly lower frequency of night frost (Table 3). From the fact that the average daily temperature for N. pumilio is generally within a lower range than that of N. antarctica (Fig. 6) it follows that the latter possesses greater plasticity. It is probable that the restriction of N. pumilio in the northern part of its area to the more moderate microclimates of slope sites, is due to the thermal limitation described above.

In this connection it is of interest to compare leaf emergence, which in Nothofagus pumilio occurs up to two weeks earlier than for N. antarctica. N. pumilio flowers and begins to open its leaves when N. antarctica is still leafless. This phenological difference, which was noted by Skottsberg (1916) is generally very marked and also indicates a better adaptation by N. antarctica.

In the southern part of its area N. pumilio also occupies valley flats and formed extensive forests; around Punta Arenas these forests are mainly destroyed by farming activities. This distribution thus raises the question of how this biotope change can be understood. Data on Table 4 and comparison with more northern stations support the following explanation:

Lonquimay at ca.40° S is in an Andean high valley in which the extensive N. antarctica low forest is physiognomically important. N. pumilio is located here only on the higher slopes. The sky is usually cloudless during the warmer part of the year. By contrast the sky of Punta Arenas is overcast at least every third day. Such cloudiness, significantly frequent at Punta Arenas, demonstrates weather conditions which prevent a strong inward or outward radiation. As a result there are considerably smaller daily temperature variations at Punta Arenas.

Moreover, northern sites of N. antarctica owe their thermal characteristics to the circumstance that they are excluded from the equalising influence of the west wind. In the south the effects of such winds are more pronounced, even inland, and for that reason there are extremely pronounced allochthonous climates (Weitschet 1970). The low number of calm days in Punta Arenas, by comparison with Lonquimay, shows that there is a permanent intensive exchange of air masses at Punta Arenas, and the formation of static cold air ponds is less probable. As a result of these conditions there are practically never any night frosts detected during the warm period of the year at Punta Arenas (at 2 m above soil). However, 1700 km to the north, at Lonquimay such frosts on an average occur every tenth summer night.

Nothofagus pumilio forms the timber line on the Andes more frequently than other species. Above is a dwarf scrub, very rich in Ericaceae. The plant-sociological link of N. pumilio forests to the evergreen forest is slight, but of special importance are Drimys winteri, Maytenus magellanica, Nothofagus betuloides in southern areas and Nothofagus dombeyi that comes from lower altitudes into the Nothofagus pumilio forests in the Andes.

Nothofagus dombeyi (Mirb.) Oerst.

The evergreen ‘coigue’ is distributed in Chile from 35° S to 47° 30′S (Skottsberg 1916) and in Argentina from 38° to 44° S (Dimitri et al. 1950). According to Fig. 4 and 6 it is a tree with its main distribution on sites of oceanic tendency. Growing to a height of up to 45 m, it reaches its optimum development in the high rainfall western slopes of the Andes mountains.

According to Hueck (1966 p. 364) it is a demanding species that needs deep and dominantly moist soils. The present author wishes to modify this opinion. In fact its ecological amplitude is considerably wider, as Nothofagus dombeyi penetrates successfully into the biotopes of all the other species considered in this paper. In the area examined no other species shows a comparable adaptability. In the region of Valdivia, with increasing altitude or on shallow soils of the lowlands there is an impoverishment of the species-rich mixed forest which gives way to almost pure N. dombeyi forest. Its relative insensitivity to cold goes so far that this species goes up to the lower part of the winter snow line zone. For example, in the National Park of Puyuehue at 900 m to 1000 m there are extensive mixed forest with N. pumilio. In the lowlands N. dombeyi penetrates into the areas of frost exposed ‘nadis’ where it is established together with N. antarctica.

The volcanoes Llaima (38° 42′S), Villarrica (39° 23′S) and Osorno (41° 06′S) lie west of the main range of the Andes in a more oceanic climate. N. dombeyi is located here as a pioneer species on lahars (the volcanic debris streams which flowed down from the volcanoes after eruptions had thawed the ice). Lahars represent extreme sites where soil formation is at an initial state. Most species are not able to establish except with the protection of scattered N. dombeyi shrubs. Such sites are essentially free of vegetation and exposed to strong insolation. Therefore high water saturation deficits are frequently observed in the air layer close to the soil. These conditions, however, usually are limited to short daily periods because such localities are open to west winds, normally starting at noon and bringing moist air masses from the Pacific Ocean.

Less frequent in South Chile are weather conditions defined by a warm dry wind locally called ‘puelche’, occurring every summer for some time. This wind advances over the Andes from the eastern grasslands and causes, on open mountain sites, an abrupt temperature page 262

Fig. 8 (upper): Temperature variation near the coast, at Valdivia (10 m alt.) and in the Andes, La Picada (840 m alt.) during an easterly ‘puelche’ wind. 27 February to 2 March 1971. (Lower): Wind direction at Valdivia. At La Picada the wind started only on the morning of the second day (28/2/71).

increase (Fig. 8). The temperature influence of this wind at the coast is considerably lowered. It is probable that within the region of evergreen forests those ‘Puelche’ weather conditions on edaphically dry sites cause a similarly effective selection pressure as does night radiation in frost hollows.

The La Picada site (Fig. 8) is one of such lahars. This site is on an open mountain saddle. The fact that N. dombeyi, usually considered as a ‘rain forest species’, regenerates well at this site shows that it is exceptionally well adapted. In fact N. dombeyi, in a comparison of 53 evergreen species, had the highest plasmatic drought resistance (Weinberger et al. 1972).

Taking into account the above mentioned results, N. dombeyi can be characterised as follows:

It is a tree with lower tolerance limits to xerothermic conditions than the summer green N. obliqua, N. antarctica and N. procera (Fig. 7). However, N. dombeyi resists considerable atmospheric and physiological saturation deficits, if they are transitory and when the overall climate of the site is oceanic. Within the more continental N. procera belts of the mountains it is generally observed that N. procera prefers the exposed slopes whereas N. dombeyi is found in the wetter more temperate mountain gorges (Fig. 5).

Nothofagus nitida (Phil.) Krasser

This evergreen tree closely resembles the preceding species, N. dombeyi and, its common name is ‘Coigue’ or ‘Coigue de Chiloe’. Its distribution starts from 40° 20′S on the Coastal Range near Valdivia (Fig. 5) southwards to 48° 30′S (Skottsberg 1916). It has not been recorded on the east of the Andes.

Although the daily temperature curves of N. dombeyi and N. nitida are similar (Fig. 4) the climatic limits of N. nitida are page 263 substantially narrower. The ecoclimagram shows that it has a more restricted ecological tolerance than the other species (Fig. 5). The tolerance range is almost completely within the amplitudes covered by N. dombeyi (Figs. 6 and 7). However, it is only occasionally that both species are found in mixed stands as they differ very markedly in their edaphic requirements. N. dombeyi grows well on the wet soils of depressions in the northern part of its area, whereas towards the south a biotope change is observed. On Chiloe Island the wet soils are occupied by extensive N. nitida forests, whilst N. dombeyi is limited to the better drained morainic soils. Further to the south N. nitida is the tree of the flat and permanently wet soils along the coast.

In further comparison of both species the wider tolerance range of N. dombeyi to daily temperature variations (Fig. 6) is essentially based on its adaptation to higher temperature maxima. The dispersion downwards of minimum values is only a little higher for N. dombeyi sites. Finally the average night temperatures for N. nitida are a little below the temperatures for the other species (Fig. 4). Thus there is only a slight difference in the amount of summer night frost (Table 3). As mentioned earlier, even moorland sites in the coastal area can be affected by a certain frost frequency. This applies to West Patagonia where N. nitida occupies flat coastal lands.

The biotopes of N. nitida are defined by permanently high air humidity. Accordingly this tree occupies the high rainfall belts of the montane Cordillera Peladar (part of the Coastal Range) (Fig. 5). In this respect N. nitida is more demanding than all other species considered (Fig. 7), and may be related to the fact that this species has a very shallow root system.

N. nitida shows strong phyto-sociological links with other forests of evergreens, particularly with Drimys winteri, Weinmannia trichosperma, Laurelia philippiana, Amomomyrtus luma and the conifer Saxegothea conspicua. N. nitida is better suited to very temperate climatic sites than N. dombeyi and is present adjacent to one of the few forest formations of south Chile where the forests lack any Nothofagus species. Such are the forests of the western flank of Coastal Range which are characterised by many trees of the Myrtaceae. Southwards of Valdivia such forests increasingly replace Aextoxicon forests (Fig. 5). However, such Nothofagus-absent forests do not penetrate the general area of the following species.

Nothofagus betuloides (Mirb.) Oerst.

The evergreen ‘Ouchpaya’ or ‘Cohue de Magallanes’ dominates coastal areas from 48° southwards. In the Valdivia region it is found only in a few isolated stands located on the highest and most windy position on the Coastal Range (Fig. 5), and inland, on the volcanoes Osorno and Calbuco. This tree does not grow tall and in the main forests of the Magellanic areas few trees are taller than 15 m.

In south Patagonia Nothofagus betuloides forms the ‘maritime forest boundary’ inland of the oceanic heath and moorland (Skottsberg 1916). Table 4 defines the climatic conditions. Evangelistas is one island on the outer coast where N. betuloides can grow only in the protected hollows. Temperature variations are very small and clear days are scarce on these coasts where there are storm winds at all times of the year. Even in summer wind speeds of over 40 km per hour occur every two days on the average. N. betuloides is well adapted to such an environment, with its compact growth and particularly small leaves.

Unfortunately there are only 11 daily measurements for 2 sites and for this reason it is only possible to estimate its ecological tolerance. Only the average values which could well define the ‘ideal site’ are represented in the ecoclimagrams (Figs. 6 and 7). The position of N. betuloides in these diagrams demonstrates that it is the equivalent in the far south to the two other evergreen species (N. nitida and N. dombeyi). On the other hand it is in the whole of its distribution in contact with stands of N. pumilio which grows on higher sites on mountains and drier sites to the eastward.

In its habit N. betuloides is very similar to stunted examples of N. dombeyi. The climatic tolerance appears similarly wide and certainly greater than that of N. nitida. However, N. betuloides does not grow on such dry sites as Nothofagus dombeyi. In the trans-Andean valley of the Rio Baker (in Aysen Province, approximately 47° 50′ S) N. nitida occurs on the coast; somewhat further inland is N. betuloides, and 60 to 70 km inland from the mouth of the river a zone of N. dombeyi commences. Skottsberg cited this succession as very remarkable. ‘It is surprising to find Nothofagus betuloides replaced by Nothofagus dombeyi inland when the opposite would be expected’ (Skottsberg 1916, p. 71).

However, according to the results of the present study the plant geographic observations of Skottsberg are quite comprehensible. It had already been noted that a warm and very dry east wind (Fig. 8) can penetrate such openings in the mountains as the Rio Baker. The average temperatures between 10 a.m. and 8 p.m. (Fig. 7) indicate that N. betuloides does not tolerate high temperture to the same extent as does N. dombeyi. The distribution in the Cordillera Peladar, where both species are represented, also shows clearly that Nothofagus dombeyi tends towards an inland climate, rather than Nothofagus betuloides.

However, in even more southern and colder regions N. betuloides substitutes completely for the other species. It is there established on edaphically favourable sites as well as to the east of the Andes (Hueck 1966).