Chapter 4
GRASSLANDS OF PATAGONIA

Andrés F. Cibils and Pablo R. Borrelli

A.F. CIBILS

SUMMARY

Patagonia lies between 39° and 55°S, partly in Chile but mainly in Argentina; its extra-Andean portion is treeless semi -arid grass and shrub steppes that have been grazed by domestic livestock for a little over a century. The climate is arid to semi-arid, and cool to cold, with mean temperatures decreasing from 15.9°C in the north to 5.4°C in the south. Extra-Andean Patagonia is an area of semi-arid grass and shrub steppes; vegetation is characterized by xerophytes. Guanacos are the only large native ungulate herbivore and the region has evolved under light grazing pressure. Most vegetation has been seriously modified by sheep, particularly in the past 40-50 years, with palatable grasses being replaced by unpalatable woody plants. Private property is the main land tenure form. Human habitation probably began about 10 000 years BP, but European settlement began at the end of the nineteenth century, with commercial sheep farming. Aboriginal peoples were hunter-gatherers; private property limited their opportunity for migratory hunting. The success of early settlers encouraged more immigrants, who occupied progressively drier areas, until 1940. Sheep numbers peaked in 1952, at over 21 million head, and have since fallen to 8.5 million head. Cattle, kept at higher elevations near the Andes, are the next largest stock; herds have increased over the past 50 years. Horses and goats have decreased less dramatically than sheep. Sheep farming is almost a monoculture in the steppes. There are three kinds of farm: Large Commercial, with flocks of more than 6 000; Small and Medium farms in the drier areas, with 1 000 to 6 000 head; and Subsistence, with fewer than 1 000 sheep. Paddocks are grazed continuously, except for the high elevation (summer) ranges. Vast areas, with few paddocks, restrict the potential for controlling grazing. Guidelines for pasture management began in the 1980s, but much work has been done since on soil-plant-animal relations. Since areas are vast, Decision Support Systems (DSS) are a new frontier for range management. Development of agrotourism on sheep farms is incipient, mostly in the Andes.

Introduction

The vast area of southern Argentina and Chile between latitudes 39° and 55°S is referred to as Patagonia (Figure 4.1). Almost all of Patagonia's grazing lands are on the cool semi -arid steppes of the extra-Andean territory of southern Argentina (approximately 750 000 km²), extending into Chile around the Straits of Magellan (Paruelo, Jobbágy and Sala, 1998b; Villamil, 1997) - see Figure 4.2.

This chapter refers mainly to extra-Andean Argentinian Patagonia, an area of treeless semi -arid grass and shrub steppes that has been grazed by domestic ungulates for over a century.

Patagonia is mostly made up of sedimentary landscapes that blend with volcanic deposits from the Mesozoic and Tertiary eras, unfolding as a series of plateaus that lose elevation eastward from the Andes (Soriano, 1983). The Patagonian mesa landscape is interrupted by a series of rivers that flow from the Andes to the Atlantic, such as the Colorado, Negro, Chubut, Chico, Santa Cruz and Coyle. Irrigated floodplains in some valleys have allowed the development of agricultural oases (Table 4.1).

TABLE 4.1
Biozones of Patagonia grouped according to phytogeographical province.

NOTES: (1) Biozone codes are those of Paruelo, Jobággy and Sala, 1998.
SOURCE: Paruelo, Jobággy and Sala, 1998. Reproduced by permission of authors and editors of Ecología Austral.

Figure 4.1
Extent of grasslands in Latin America.

Description of Patagonia's climate is hampered by the low density and very uneven distribution of weather stations (40 000 km²/station) (Paruelo et al., 1998). Climate is influenced mostly by Pacific Ocean air masses forced inland by prevailing westerlies, across ocean currents that are warmer than the land masses and move towards the equator (MacArthur, 1972). The Andes stand between the moist air and the Patagonian steppes, creating an extensive rain-shadow that controls climatic patterns (Paruelo et al., 1998). There is a very steep gradient of mean annual precipitation (MAP), decreasing towards the east, from 4 000 mm at the Andes eastern foothills (at about 42°S) down to 150 mm in the central plateau 180 km east of the mountains (Soriano, 1983). Inter-annual variation in precipitation increases exponentially with decreasing rainfall, reaching coefficients of variation greater than 45 percent at the drier end of the gradient (Jobággy, Paruelo and León, 1995). The east coast is influenced by moist air from the Atlantic, with somewhat higher annual precipitation (200 to 220 mm) evenly distributed, as opposed to the winter rainfall of most of Patagonia (Paruelo et al., 1998; Soriano, 1983). The ratio of mean annual precipitation to potential evapotranspiration (MAP/PET ratio) of the steppes fluctuates between 0.45 and 0.11, with marked deficits in spring and summer (Paruelo et al., 1998). Water is the most important factor regulating primary production. Some of the variation can be associated with El Niño-La Niña cycles (Paruelo et al., 1998), but Cibils and Coughenour (2001) reported a longer-term cycle for MAP in southern Patagonia: a significant decrease in precipitation from 1930 to 1960 and a reversal of this trend (significant increase) over the subsequent thirty years in Río Gallegos.

Figure 4.2
A map of the provinces of Argentinian Patagonia (shaded area) and neighbouring provinces (Digital Cartography by Ing. Ag. Liliana González).

Mean annual temperatures range from 15.9°C in the north (Cippoletti) to 5.4°C in the far south of Tierra del Fuego (Ushuaia) (Soriano, 1983). Mean temperatures of the coldest month (July) are above the frost mark, although absolute minimum temperatures can be below -20°C (Paruelo et al., 1998). Cibils and Coughenour (2001) reported a significant increase in mean annual temperatures over the last 60 years of the twentieth century for Río Gallegos, a town with one of the longest weather records, on the steppes surrounding the Straits of Magellan. This trend is consistent with predictions of climate change from Global Circulation Models simulating enhanced atmospheric CO₂ concentration (Hulme and Sheard, 1999), but conclusions from weather station data analysis are still preliminary.

Strong, persistent westerly winds are an outstanding characteristic of Patagonia's climate. Because there is relatively little land in the Southern Hemisphere, westerlies between 40°S and 50°S gain impressive momentum, with annual intensities of between 15 and 22 km/h and frequent gusts of over 100 km/h, mostly in spring and summer (MacArthur, 1972; Paruelo et al., 1998; Soriano, 1983). Strong winds increase evaporation and can have a considerable influence on sheep performance through chill (Borrelli, unpublished data; Soriano, 1983).

Over half of Patagonia's soils are Aridisols (desert soils), with Entisols (soils with little development) and Mollisols (dark coloured, base-rich steppe soils), respectively, as the second and third most important types (del Valle, 1998). Over 70 percent of topsoil is coarse-textured, ranging from sand to sandy-loam (del Valle, 1998). Soil textures can explain a large portion of the variation in dominant plant life form (grasses vs shrubs) across the region (Noy-Meir, 1973; Sala, Lauenroth and Golluscio, 1997). Small-scale spatial heterogeneity of soils tends to increase with aridity (Ares et al., 1990); important differences in leaching and salinity occur over short distances, possibly causing soils within a taxonomic group to function differently (del Valle, 1998, and references therein). Over 90 percent of Patagonian soils are degraded to some degree, mostly because of improper land use; severe desertification affects 19 to 30 percent of the region (del Valle, 1998). Some of the most dramatic erosion processes occur in the form of sand macro-accumulations that, in the early 1970s, covered approximately 85 000 km² (Soriano, 1983). Both aerial photography and satellite imagery indicate that many of these accumulations are about 100 years old, suggesting that the rate of wind-driven erosion has been accelerated by the introduction of domestic livestock (Soriano, 1983).

Archaeological records from caves suggest that human occupation began around 11 000 BP (Borrero and McEwan, 1997). Native peoples were hunter-gatherers, although there are indications of limited agricultural activity in the north (Villamil, 1997). Bifacial stone weapons suggest that people of south Patagonia hunted guanaco (Lama guanicoe). The Mapuche tribe occupied the northern reaches, the Tehuelches the southern mainland, and the Selknam, Haush and Yámana tribes occupied Tierra del Fuego and surrounding islands (McEwan, Borrero and Prieto, 1997, and references therein). European contact with natives began early in the sixteenth century; it is thought that conquerors named the natives after Patagón, a fantastical character of the Spanish chivalric tale Primaleón (Duviols, 1997: 129-130). European settlement only began at the end of the nineteenth century, mostly from Spain and the British Isles, or companies that established sheep farms (Barbería, 1995).

Figure 4.3
Sheep population by province in Argentinian Patagonia.

SOURCE: SAGPyA, 2001.

Plate 4.1
Merino flock in Patagonia.

V.A. DEREGIBUS & M.F. GARBULSKY

There are currently over 12 000 sheep farms (family or company owned) in Patagonia, with flocks ranging from less than 1 000 to over 90 000 head (Méndez Casariego, 2000). According to the latest on-farm population census (1988) there were 75 000 people on sheep farms and irrigated valley farms. From the 1970s to present, the rural population increased in Río Negro (+44%) and Tierra del Fuego (+132%), remained fairly stable in Neuquén, and decreased in Chubut (-33%) and Santa Cruz (-44%) (Méndez Casariego, 2000). Over the same period, the on-farm population increased in Neuquén (+51%) and Río Negro (+5%) and decreased in Chubut (-28%), Santa Cruz (-41%) and Tierra del Fuego (-26%) (Méndez Casariego, 2000).

Patagonia's grasslands have only been grazed by sheep for just over a century. Sheep numbers peaked in 1952, at over 21 million, and since then numbers have been slowly shrinking, to about 8.5 million in 1999 (Méndez Casariego, 2000) (Figure 4.3). Ranchers raise unherded Merino (Plate 4.1) or Corriedale flocks in continuously-grazed large pastures, usually for wool (Soriano, 1983). Wool production is fairly insensitive to forage scarcity associated with high stocking-rates or drought, so several authors have blamed present day land degradation on the wool-oriented operations (Borrelli et al., 1997; Golluscio, Deregibus and Paruelo, 1998; Covacevich, Concha and Carter, 2000). Cattle have increased steadily over the last 50 years (Méndez Casariego, 2000) and although present numbers (836 000) are more than double those of 1952, this does not compensate for the decrease in sheep (Méndez Casariego, 2000). The numbers of horses and goats have decreased considerably, but not as dramatically as sheep. The most recent figures (1999) indicate that there are 180 000 horses and 827 000 goats - roughly half of the previous peak populations (Méndez Casariego, 2000). Goat farming is mainly in the north, such as Neuquén province, where numbers have remained fairly constant in spite of the general negative tendency (Méndez Casariego, 2000).

Guanacos are the only large native ungulate (Soriano, 1983) and although the region has generally been considered to have evolved under light grazing pressure (Milchunas, Sala and Lauenroth, 1988), pre-European numbers of guanacos may have been higher than previously thought (Lauenroth, 1998); recent counts show populations are fairly stable at approximately 500 000 (Amaya et al., 2001). The native vertebrate fauna is poor (Soriano, 1983). The lesser rhea (Pterocnemia pennata pennata) and the upland goose (Cloephaga picta) are the most conspicuous birds. The Patagonian hare (Dolichotis patagonum) and the small armadillo (Zaedyus pichyi), together with the lesser rheas, are important zoogeographical indicators (Soriano, 1983). There are significant numbers of predators, such as red foxes (Dusicyon culpaeus), grey foxes (Ducisyon griseus), pumas (Felis concolor) and skunks (Conepatus humboldtii) (Soriano, 1983). Red foxes and pumas are responsible for most predation, and lamb losses due to red fox predation can be as high as 75 to 80 percent (Manero, 2001).

Figure 4.4
Land tenure regimes in Argentinian Patagonia

(SOURCE: Adapted from Peralta, 1999)

Political system

Argentinian Patagonia has five provinces: Neuquén, Río Negro, Chubut, Santa Cruz and Tierra del Fuego (Figure 4.2). Parts of other provinces, such as Buenos Aires, La Pampa and Mendoza, are in the Patagonian environment. As a Federal Republic, each province of Argentina has an elected government. A Governor, the executive, is elected every four years. Each province has a Constitution, Legislative Power and an independent Judicial Power. Argentinian Patagonian provinces are relatively new because most of them were national territories until after the Second World War; national territories depended entirely on the central government in Buenos Aires. Irruption of dictatorships in Argentina between 1966 and 1983 prevented the exercise of democracy, so Patagonian provinces are young democratic states, in which political forces and institutions are beginning to organize and evolve.

Land tenure

Private property is the most important land tenure form, as shown in Figure 4.4 (Peralta, 1999). Permanent title deeds predominate, but legal occupation is also significant. Unfenced public lands comprise a small percentage of farms, and are locally important in Neuquén. Land tenure variation is related to the colonization process, which is summarized below.

Aboriginal distribution

There were many ethnic groups prior to colonization. Mapuches lived in the northwest, Tehuelches lived on most of the continental part of the steppe, and Onas lived on the steppes of Tierra del Fuego. All of these were “terrestrial cultures” (Borrero, 1997). Tehuelches and Onas were migratory hunters. There were also “canoe cultures”on the coasts of the Beagle Channel in Tierra del Fuego, which were reduced, absorbed or exterminated by Europeans (Martinic, 1997). Tehuelches were severely reduced and absorbed by European colonization. Fences and the concept of private property limited the opportunity for migratory hunting. As Martinic (1997) pointed out, “cultural exchange was unidirectional, from the colonists to the Indians, which affected the latter's hunting and fishing tools and customs, relationship with natural resources, social behaviour, health and very survival as people”. Survivors mostly became farm employees and in a few generations had lost most of their language and culture. There are a few reservations suitable for raising sheep and horses where Tehuelche descendants subsist.

The Mapuches were better able to maintain their culture and survive under conditions imposed by colonizing groups, and their descendants live in Neuquén, western Río Negro and northwest Chubut. More than 3 000 family groups live on public pastures raising goats and sheep (Casas, 1999). Some families have fenced or demarcated individual grazing lands, which they run as legal occupants. Many others graze on common lands, where transhumance is still practiced, from low winter ranges (invernadas) to high summer ranges (veranadas) (Casas, 1999).

Welsh colonization

In 1866 a colony of Welsh immigrants established themselves in the lower valley of the Río Chubut, close to the Atlantic coast (Mainwaring, 1983); the settlers had enormous difficulty in surviving. They made little progress until 1885, when several horsemen rode west and settled as sheep farmers in the Andes foothills. The colony did not prosper until settlers managed to develop irrigation and learn basic farming skills (Mainwaring, 1983).

First settlers

The first sheep farmers arrived in 1885 (Barbería, 1995). The government in Buenos Aires granted land concessions to settlers. After a visit of Governor Moyano to the Falkland Islands, colonization started on the most suitable land for sheep, i.e. grass steppes close to the Andes foothills and in southern Santa Cruz and northern Tierra del Fuego (Lafuente, 1981). By 1908, families and large companies occupied the most productive land. Settlers were mainly Spanish, Scottish, English, German and French. By the end of land concessions, settlers had obtained private title to their lands (Lafuente, 1981; Barbería, 1995)

Last settlers

The success of the first settlers encouraged new waves of immigrants, who occupied prtogressively drier areas until 1940, by when Patagonia was fully colonized (Barbería, 1995). In 1908, national legislation prevented liberal distribution of remaining public range (Lafuente, 1981). In an attempt to restrict the amount of land purchased by an individual, Patagonia was divided into equal-sized blocks that were assigned to settlers without considering carrying capacity (Barbería, 1985), so most settlers received a limited amount of relatively unproductive land, which thereafter was subject to high grazing pressure. Most farms are now privately owned, under legal occupation or with permanent title (Casas, 1999).

Management authorities

The responsibility of provincial government to ensure sustainable management of natural resources is recognized in Provincial Constitutions, which were mostly amended in the 1990s and clearly define this role, but legislation is either weak or not enforced. By the end of the 1980s, “desertification” was well established as a subject of discussion, but sustainable use policies have still not been achieved. There is lack of institutional development for natural resources administration at provincial and national levels (Consorcio DHV, 1999). The federal Department of Sustainable Development and Environmental Policy, which is responsible for national policies on sustainable management, carries out planning, coordination and training. A National Plan for Desertification Control was formulated in 1998, but has not been implemented due to funding constraints.

Market systems

Wool market systems

Patagonian wool is mainly exported; domestic consumption is less than 10 percent of greasy wool produced. Wool is mainly exported as tops and scoured wool. China, Italy, Germany and France have been the main customers (Argentine Wool Federation, 2001). Scouring and combing is done by multinational companies and some local industries in Trelew (Chubut), the main wool textile centre of Argentina. Sheep farms in northern and central Patagonia produce fine Merino wool, while farms in the south produce fine crossbred Corriedale -type wool (Argentine Wool Federation, 2001). Direct sales from farmers to wool processors and exporters predominate, but there are a few wool concentration and auction sale mechanisms (Peralta, 1999). In the 1980s, many wool cooperatives were created, but most collapsed due to financial problems and lack of managerial skills. Subsistence farmers with small quantities usually barter for basic goods with middlemen (Peralta, 1999).

In 1994, the government launched PROLANA, a joint wool quality programme with provincial governments, to improve shearing, handling, grading and packing, prevent contamination and improve wool appearance. By 2000, 37 percent of Patagonia's wool was processed under PROLANA procedures (SAGPyA, 2001). This Programme increased market transparency significantly by expanding farmer awareness regarding the characteristics and value of wool.

Meat marketing

Grassland -based systems produce about 10 500 tonne/year of high quality lamb and mutton (SAGPyA, 2001), which is natural, free from diseases and contaminants, with low fat content and a mild flavour, but the local markets are not sensitive to meat quality. Most lamb is exported to Europe (SAGPyA, 2001). Wool-oriented Merino farms have a low reproductive efficiency (less than 60 percent lambing) and produce few lambs. The meat production areas are southern Santa Cruz and northern Tierra del Fuego, where forage production is higher and Corriedale operations are oriented to lamb production (Borrelli et al., 1997; Méndez Casariego, 2000).

Farmers sell to local abattoirs, which supply supermarkets and retail butchers. Overseas markets were historically the most important meat buyers (Lafuente, 1981). The progressive reduction in the number of animals for slaughter caused the collapse of large (mostly foreign) companies that had operated in the region from the beginning of the twentieth century. Most lamb was marketed locally during the 1990s (SAGPyA, 2001). Recently, a farmer-owned company began processing and exporting lamb from Santa Cruz. Many farmers in this project have organic certification that allows them to enter premium market niches.

Dominant natural vegetation

Extra-Andean Patagonia is covered by treeless shrub and grass steppes that give way to dwarf-shrub semi -deserts in the drier areas of the central plateaus (Roig, 1998). Vegetation is characterized by the dominance of xerophytes, which have evolved remarkable adaptations to cope with severe water deficit (León et al., 1998). Shrubs, for example, have either very small sclerophyllous leaves with abundant glandular hairs, or leaves with thick cuticles, and often dwarf cushion growth habits. Grasses commonly have leaves with a thick cuticle, convoluted laminae and bunch growth habits, with fairly large accumulations of dead biomass (León et al., 1998). Blended in the steppe landscapes are small areas associated with rivers or permanent water sources, with more mesic plant communities comprising mostly grasses, sedges and rushes, referred to as riparian meadows (Golluscio, Deregibus and Paruelo, 1998; Roig, 1998), and, although they account for a very small proportion of the total area, they play a key role in livestock production and, in many instances, suffer most from the effects of bad land management (Golluscio, Deregibus and Paruelo, 1998).

Two phytogeographic provinces occupy all of arid and semi -arid Patagonia: the Patagonian phytogeographic province, and the Monte phytogeographic province (Cabrera, 1971). The latter occupies most of the arid west of Argentina; its southern tip enters Patagonia, occupying approximately the northern third of the region. The remaining two thirds of extra-Andean Patagonia correspond to the Patagonian phytogeographic province (Table 4.1) (Cabrera, 1971). Most classifications of natural vegetation types of have used either structural (physiognomic) characteristics of dominant plant life-forms (Cabrera, 1971; Soriano, 1983; León et al., 1998; Roig, 1998) or phytosociological approaches as the main grouping criteria (Collantes, Anchorena and Cingolani, 1999; Golluscio, León and Perelman, 1982; Boelcke, Moore and Roig, 1985). Recently, Paruelo, Jobbágy and Sala (1998b) classified the vegetation of the region on the basis of functional characteristics, using productivity -related indices derived from NOAA satellite imagery analysis (Figure 4.5 and Table 4.1). An advantage of this approach is that it provides a functional up-to-date classification of vegetation, reflecting the current state of rangelands, rather than the potential expected vegetation types typical of most structural classification maps. This section follows the grouping of biomes proposed by Paruelo et al. (1998), but endeavours to produce a synthesis of both structural and functional aspects of the vegetation of each biome.

Figure 4.5
Biozones of Patagonia, from Paruelo, Jobággy and Sala (1998).
(Reproduced with permission of the authors and the editors of Ecología Austral)

Plate 4.2
A typical Patagonian shrub steppe.

V.A. DEREGIBUS & M.F. GARBULSKY

Patagonian shrub steppes

This vegetation type (Unit Jg 11 in Figure 4.5) accounts for close to 20 percent of the semi -arid area (Paruelo, Jobbágy and Sala, 1998b) (Plate 4.2). Overall, the MAP of this area is below 200 mm; vegetation cover varies between 30 and 50 percent and annual above ground net primary productivity (ANPP) estimated from NDVI -I values (the annual integral of the Normalized Difference Vegetation Index) is 490 kg/ha/yr (León et al., 1998; Paruelo, Jobbágy and Sala, 1998b). The physiognomy of this unit is that of a bi-layered shrubland: an upper layer of shrubs circa 100 cm high, and a lower layer made up of shrubs with crown heights that rarely exceed 15-20 cm (León et al., 1998). The most conspicuous shrubs are Chuquiraga avellanedae, Lycium ameghinoi, L. chilense, Verbena ligustrina, Prosopis denudans and Colliguaya integerrima (León et al., 1998; Roig, 1998). Grasses of the genera Stipa, Festuca and Poa, such as Stipa neaei, S. speciosa, Festuca argentina and Poa ligularis, occur as a sparse understorey (León et al., 1998). Shrub steppes occur in transition areas between the grass steppes and the semi-deserts (Paruelo, Jobbágy and Sala, 1998b).

Semi-deserts and shrub steppes

Semi-deserts and shrub steppes (Units Kg 11 and Kf 11 in Figure 4.5) exhibit similar latitudinal extents; together, both variants of semi -desert cover 22 percent of the region, with plant communities of low diversity, including, on average, 19 plant species (Golluscio, León and Perelman, 1982). The MAP of much of the area is less than 150 mm. Patagonian semi-deserts are less productive than shrub steppes; ANPP calculated from NDVI -I values by Paruelo, Jobbágy and Sala (1998b) are 450 and 390 kg/ha/yr for units Kg 11 and Kf 11, respectively (Table 4.1). From a species composition standpoint, Kf 11 is the most typical and less degraded semi-desert type, in spite of being less productive (Soriano, 1983). Dwarf shrubs with cushion habits are typical of this vegetation type in the Kg 11 and Kf 11 units. Nassauvia glomerulosa, N. ulicina and Chuquiraga aurea are dominant, accompanied by others such as Chuquiraga kingii, Brachyclados caespitosus and Perezia lanigera (León et al., 1998). Grasses such as Stipa humilis, S. ibarii, S. ameghinoi and shrubs such as Chuquiraga avellanedae, Schinus polygamus and Lycium chilense are secondary species in semi-desert plant communities. Some co-dominant species occur, but only in the Kg 11 semi-deserts: dwarf shrubs such as Azorella caespitosa, Mullinum microphyllum and Frankenia sp., grasses such as Poa dusenii, P. ligularis and, less frequently, Stipa neaei, and shrubs such as Junellia tridens, which occur in clumps on paleodepressions and natural drainage networks (León et al., 1998; Roig, 1998).

Shrub-grass and grass-shrub steppes

Shrub-grass and grass-shrub steppes span almost the entire latitudinal extent of Patagonia and cover approximately 20 percent of the arid area (Units Jf 11 and Jd 12 in Figure 4.5). According to Paruelo, Jobbágy and Sala (1998b), both types have similar ANPP levels (650 kg/ha/yr), although NDVI values peak somewhat later in the growing season in grass-shrub steppes. Vegetation cover of the shrub-grass steppes is 47 percent, with plant communities that contain about 26 vascular plant species (Golluscio, León and Perelman, 1982). Adesmia campestris, Mullinum spinosum, Senecio filaginoides, Berberis heterophylla, Colleguaya integerrima, Trevoa patagonica and Schinus polygamus are the most conspicuous shrubs (León et al., 1998). The most important grasses are Stipa speciosa, S. humilis, Poa ligularis, P. lanuginosa, Festuca argentina and F. pallescens, and occur with sedges of the genus Carex (León et al., 1998). Grass -shrub steppes are a transition between the shrub steppes and grass steppes on the one hand and the grass-steppes and the Nothophagus subantarctic forest ecotone on the other (Figure 4.5) (Roig, 1998). Paruelo, Jobbágy and Sala (1998b) combine the latter (Chiliotrichum diffusum grass-shrub steppes) and the steppe-forest ecotones in southern Santa Cruz and northern Tierra del Fuego into a single biozone (unit Ha 12). Physiognomically, these are different domains; they may exhibit similar functional attributes and should be significantly more productive than the grass-shrub steppes at the opposite end of the moisture gradient. Dominant species of the grass-shrub steppes are the same as those mentioned above, except for the shrubs Junellia tridens, Nardophyllum obtusifolium, Berberis buxifolia and Chiliotrichum diffusum, and the grasses Stipa ibarii, Poa dusenii, Festuca pallescens, F. gracillima and F. pyrogea (León et al., 1998; Roig, 1998).

Grass steppes

Grass steppes (Unit Id 12 in Figure 4.5) also span the latitudinal extent of mainland Patagonia as a belt along the Andean foothills, that widens in the south, reaching the Atlantic Ocean, and giving way to the Magellanic steppes that occupy all of the area surrounding the Straits of Magellan, on the mainland and the northern tip of Tierra del Fuego (Figure 4.5) (Paruelo, Jobbágy and Sala, 1998; Cibils and Coughenour, 2001). This vegetation unit occurs in areas where MAP exceeds 250 mm. Average ANPP is about 900 kg/ha/yr according to NDVI -I-derived estimates reported by Paruelo, Jobbágy and Sala (1998). There are about 34 and 40 plant species in the sub-Andean and Magellanic steppes, respectively (Golluscio, León and Perelman, 1982; Boelcke, Moore and Roig, 1985). Vegetation cover is about 65 percent on sub-Andean grass steppes, where Festuca pallescens accounts for up to 70 percent of plant cover and occurs along with F. magellanica, F. pyrogea, Deschampsia elegantula, D. flexuosa, Phleum commutatum, Elymus patagonicus and Rytidosperma virescens (León et al., 1998). Magellanic steppes exhibit two main variants: dry steppes on the eastern portion of the mainland, and mesic grasslands in the west and southeast of the mainland and the northern region of Tierra del Fuego, where MAP exceeds 350 mm. Vegetation cover ranges from 60 to over 80 percent; the dominant plant on both variants of the Magellanic steppe is Festuca gracillima, a 25-cm-tall tussock-forming bunchgrass that is the most conspicuous life form of this ecosystem (Boelcke, Moore and Roig., 1985; Collantes, Anchorena and Cingolani, 1999). Other grass and grass-like species are associated with the tussocks, such as Poa dusenii, P. poecila, Rytidosperma virescens, Bromus setifolius, Deschampsia flexuosa, Agropyron magellanicum, Festuca magellanica, Agrostis tenuis, Carex andina, C. argentina, among others (Boelcke, Moore and Roig, 1985). Empetrum rubrum-dominated communities occur as heathland blended in the grass steppes on south-facing slopes of moraine hills on moister Magellanic steppes (Collantes, Anchorena and Cingolani, 1999).

Monte shrubland s and Monte ecotone

A third of semi -arid Patagonia is taken up by Monte vegetation units (Units Jh 11, Ig 4 and Hg 11 in Figure 4.5) (Plate 4.3), exhibiting ANPP levels ranging from 650 to 730 kg/ha/yr (Paruelo, Jobbágy and Sala, 1998b). Hg 11 scrubland is the most productive and is an ecotone between the Monte and Espinal phytogeographic provinces (Cabrera, 1971; Paruelo, Jobbágy and Sala, 1998b). Rainfall rarely exceeds 200 mm and tends to be evenly distributed throughout the year (León et al., 1998; Paruelo, Jobbágy and Sala, 1998b). The most conspicuous plant of these biomes is Larrea divaricata, which occurs with L. cuneifolia and L. nitida and other shrubs such as Prosopis alpataco and P. flexuosa and species of Lycium, Chuquiraga, Ephedra and Atriplex. Grasses such as Stipa tenuis, S. speciosa, S. neaei, Poa ligularis and P. lanuginosa make up the herbaceous stratum (León et al., 1998). For a description of units corresponding to subantarctic forests and forest ecotones, see Veblen, Hill and Read (1996) and references therein.

Plate 4.3
A shrub steppe in the Monte.

V.A. DEREGIBUS & M.F. GARBULSKY

Pastoral and agricultural systems

Sheep farming is almost a monoculture in the arid and semi -arid steppes (see Plates 4.4 and 4.5). Intensive agricultural activities such as fruit and horticultural crops are important in a few irrigated valleys, but are almost absent on sheep farms (Borrelli et al., 1997). Cattle production has become important on mountain ranges near the Andes, where sheep farming is more difficult due to the presence of forests, steep landscapes and losses to predators. There has been an important substitution of sheep for cattle in the Monte region. Agrotourism activities on sheep farms are developing, mostly in the Andes, where there are scenic lakes, mountains and glaciers (Borrelli et al., 1997; Méndez Casariego, 2000).

Plate 4.4
Sheep being driven up to summer range paddocks in the Magellan Steppe.

PABLO BORELLI

Plate 4.5
Gauchos herding a Corriedale flock on bunchgrass rangelands in southwestern Patagonia.

PABLO BORELLI

Sheep farming is extensive; each farm has, on average, three to four 5 000-ha fenced paddocks. No supplementary feeding is used. On-farm hay or silage production is insignificant and off-farm feeds are too expensive. Animals graze freely in large areas and are never housed, in spite of periodic severe winters. There is significant mortality during big snow falls (Sturzenbaum and Borrelli, 2001). Sheep are gathered three or four times each year. Drinking water comes from springs and lagoons, rivers, artificial ponds and windmill-pumped groundwater.

Patagonia is free of Bovine Spongiform Encephalopathy (BSE disease) and Foot-and-Mouth Disease (FMD) (Robles and Olaechea, 2001). Environmental conditions constrain the development of internal parasites and anthelmintics are often not necessary (Iglesias, Tapia and Alegre, 1992); no antibiotics or hormonal treatments are used. Patagonian farms supply wool and meat that can naturally reach the highest standards of quality in terms of food safety and lack of contaminants. Despite this, sheep stocks have declined continuously since the 1980s (Figure 4.4) and, under current conditions, sheep farming is unsustainable, whether in economic, ecological or social terms (Noy-Meir, 1995; Borrelli and Oliva, 1999; Pickup and Stafford-Smith, 1993). Factors contributing to this are low wool prices, small farm size, poor adoption of available technology, desertification, high winter losses, predator losses, high farmer indebtedness and lack of sustainable development policies (Borrelli et al., 1997; Consorcio DHV, 1999).

Sheep farming systems

Conditions and attributes of sheep farming in Patagonia are quite heterogeneous, in spite of the general characteristics summarized above. The main sources of variation are:

• rain and temperature gradients, which form twelve biomes that differ in rangeland vegetation, primary and secondary productivity and potential for rangeland improvement (as discussed in the natural vegetation section, above); and

• farm size, as the sustainable number of sheep that can be kept on a farm depends on the area for grazing and its carrying capacity. Because sheep products are the only source of income, flock size determines farm income.

Three kinds of farms can be recognized (Table 4.2): (1) Large commercial farms, with more than 6 000 head and which are usually derived from the first settlements and on the best pastures. (2) Small and medium commercial farms, in the drier areas, with flocks of 1 000 to 6 000; these have serious financial problems due to present wool prices. (3) Subsistence farms, with less than 1 000 sheep, mainly in northwestern Patagonia, which belong mostly to aboriginal families and graze on unfenced public lands.

TABLE 4.2.
Farm distribution by size in Argentinian Patagonia.

SOURCE: Data from Casas, 1999.

More than half of sheep farmers in Patagonia are very poor and together own less than 10 percent of total sheep (Casas, 1999; Table 4.2). Most of the other half is limited by farm size, so at present net farm income does not satisfy their economic expectations. A few companies run sheep farms that can be considered economically viable. Company farms own approximately 40 percent of the sheep. There is a marked increasing north-south farm size gradient, beginning in the northwest (Neuquén), where subsistence farms are commonest, to Tierra del Fuego, where large company-owned farms are more frequent than in any other province (Table 4.2). The combination of biozone and farm size (which is related to the kind of farm operation) gives a wide range of pastoral systems, differing in terms of objectives, productivity and sustainability.