The guanaco (Lama guanicoe) is the largest mammal inhabiting Patagonia. Adult weight may range from 100-120 kg in males and 90-110 kg in females. The species shows a high adaptability to harsh environments, particularly to arid and semi-arid zones.
The guanaco (Lama guanicoe) is the largest mammal inhabiting the Argentine Patagonia. The distribution of this species is strongly based on its sociobiological characteristics. Family and non-reproductive groups tend to be associated with environments with food resources, water availability and escape corridors in areas of slopes and rough terrain.
Radar images present diverse types of textures in direct and/or indirect relationship with geophysical and biophysical information. Space resolution and sign-noise characteristics make these images useful for the analysis of environmental affinity of some faunal species. Our data were obtained from two ERS- 1 SAR images over Central Patagonia (Chubut Province, Argentina). The texture of the images, as a function of the degree, orientation and change rate of slope (as well as vegetation cover and physiognomy), were used to classify the landscapes of the selected areas.
High and intermediate levels of environmental affinity for guanacos were found in areas with low inter-specific competence, abundant escape corridors and volume of forage availability. Intermediate and low levels of affinity are strongly related to inter-specific competence and final stages of degradation (anthropic and natural processes). This project is a leading case in Patagonia, where remote sensing will be used to determine a priori areas of distribution of guanacos, with the aim to define policies of conservation and sustainable use for the species.
The guanaco (Lama guanicoe) is one of the wild species of the South-American camels (Fig.1). The distribution of the species ranges from high altitude to sea level. However, the highest densities of animals were described in Patagonia, particularly in the Chubut Province, Argentina.
The guanaco (Lama guanicoe) is the largest mammal inhabiting Patagonia. Adult weight may range from 100-120 kg in males and 90-110 kg in females. The species shows a high adaptability to harsh environments, particularly to arid and semi-arid zones.
The social structure is characterised by 'family groups', composed by one male and several females (4-10) with their offsprings called 'chulengos' (Fig.2). The 'non-reproductive groups', are composed by males (80%) [Fig.3] and females (20%) (de Lamo et al. 1982; Saba et al. 1995).
The offspring of the guanaco is called 'chulengo'. In the photograph, a chulengo (60 days old) is followed by his mother. The new-born will remain with the family group for about a year.
Typical composition of a 'non-reproductive group'. Usually this group occupies the periphery of the so-called 'family groups '.
Sociobiologically, the species has been classified as 'resource defense poly-gyny' (Franklin 1983) meaning that a dominant male will defend his territory against predators and other males (Fig.4). In that range, the family group will have food supplies, water and escape paths, associated with slopes and rough terrain (Fia.5).
An alpha male 'relincho' (right) chasing a younger male (left) from his territory. During the reproductive season (late spring) solo males try to mate with females belonging to a family group. The relincho spends 60% of the time chasing other males from his home range.
A family group spends most of the day foraging in areas where food and water supplies are available. Guanacos share this sort of environment with domestic sheep.
Previous studies defined that the areas where forage, water and slopes are available, would be the selected site for guanacos in the wild (Garrido et al. 1980; de Lamo 1990). Nevertheless, this hypothesis has not been quantified.
Remote sensing is an important tool to differentiate types of environments in time and space. For instance, ERS-1 offer a permanent record of the terrain configuration, using interpretation systems based on physiography. It is possible to obtain digital cartography with information such as physiographic units with higher affinity for the studied species or stratification of those landscape units based on economic interest or conservation.
The landscapes of Patagonia range lands share many features with deserts. Rainfall is low, vegetation sparse or lacking, and the land surface is exposed to processes that change mostly the status of soil, vegetation and local water resources. Especially in these arid areas, the penetration depth of the radar can be half of the wavelength. Therefore, covered morphological features not discerned by optical systems are detectable by microwave.
This contribution aims to describe and compare two selected areas in the Northeast of Central Patagonia and correlate them with guanaco's environmental affinity. This proposal is the first approach to develop a methodology where image processing will help reduce field work, and define policies for the conservation and sustainable use of the guanaco.
ERS-1 SAR image acquisition and environmental characteristics
The study sites were defined from two available ERS-1 SAR sub-scenes (Fig. 6). The acquisition dates
were: Telsen area (07.04.1992) covering 231 km2 and Valdés area (07.09.1992) with 3800 km2. Both sub-scenes belong to Central Patagonia, Chubut Province.
Location of study areas.
Telsen sub-scene is a small range of surface form and properties expressive of a lithological unit having completely undergone comparable geomorphic evolution (representative of a larger land region). The land systems of this study site aid in the reconnaissance of large areas by providing an overall view of genetic relations which helps economise effort in field sampling. Here, the climate is arid and temperate, exhibiting temperatures between 11°C and 13°C with annual precipitation generally below 200 mm. Vegetation and physiognomic characteristics may be found elsewhere (Beeskow et al. 1987). The production of the area is based on sheep husbandry, being the land of private property. Ranches have an extension of about 100 km2 with about 6.5 sheep/km2.
In the Valdés area the climate is semiarid and temperate. The mean annual precipitation varies from 200 mm (West) to 250 mm (Southeast). Rainfall is almost uniformly distributed throughout the year, May and October being the wettest months. The mean annual temperature is 12°C; wind velocity at 10 m above around level is 4.5m/s. Vegetation is that of a shrubby steppe type with different dominant species in the shrubby stratum. As in the other area, ranches produce sheep wool, but carrying capacity is to the limit with about 21 sheep/km2. On the other hand, the whole peninsula is a natural wildlife reserve under regulation of the Chubut Province.
All image enhancement steps were performed on a PC-486 DX2, using an ERDAS image processing software, as well as own-developed algorithms. To simplify processing and storage, the ERS-1 SAR image was first converted from 16 bit to 8 bit. After getting a Gaussian histogram distribution, best results were derived by using a logarithmic transformation. The next step consisted in repeating speckle reduction by adaptive filters (Frulla et al. 1995); image analysis was per formed using a division by landscape systems (Gagliardini et al. 1994). Each land system was interpreted based on the properties of the surface as a function of the complex dielectric constant and surface roughness. Defined types of texture were analysed and classified as degrees of erosion resulting from clustering unitary features coming from the terrain configuration. The delineation of the land systems from radar imagery was based on apparent relief and radar shadowing. Image texture, as a function of the degree, orientation and change rate of slope (as well as vegetation cover) was used for the integrated landscape analysis.
Land systems attributes were defined
To determine the guanacos' environmental affinity, the three land attributes were multiplied and the resulting number was ordered as a hierarchy of affinity. The values obtained were grouped in three affinity categories defined as High (1-2), Medium (3-4) and Low (5-6) .
Land degradation was classified as a percent of desertification status as severe and very severe. The weighed percent for each area was determined using the actual area of that land system from the image, multiplied by the percent of land degradation. Using this procedure, it is possible to compare land systems with different land coverage in the images. The result of this equation gives a series of values, where the largest is the area with the higher degree of anthropic and natural impact. Following the criterion used for the affinity ranking, the resulting values were grouped considering the land degradation percentage as High (>50%), Medium (50-25%) and Low (<25%).
The average grey scale or tone on the ERS-1 image is a very important characteristic in radar interpretation (especially in geologic and vegetation mapping). The degree of erosional dissection of landscapes is related to images texture, drainage density and erosional features of the terrain. Characteristics of the land system classes are presented in Figures 7 & 8. The Telsen area presents a high environmental heterogeneity, but the land system boundaries are precise and representative of an area of about 20000 km2. In the Valdés area the landscape limits are ambiguous, therefore, it was useful to work with an image covering the whole surface of the peninsula.
Land systems. Reverse image of Telsen area. Bar length=2 km.
1) Porphyritic complex peneplain (PCP) showing topographic and erosion textures from ERS- 1 image.
2) Gaiman structural terraces (GST) with differences in land use. Range condition in response to overgrazing: good range condition class (inside of the perimeter delimited), and poor to fair range condition class outside.
Land systems of the Valdés area. Bar length=7km.
1) Valdés structural terraces levelIII (VSTIII) showing active barchanoid and fixed dunes.
2) Valdés structural terraces levellV (VSTIV).
3) Valdés coastal plain (VCP).
4) Valdés marine cave (VMC).
5) Basin landforms (BL).
Texture as a discriminant factor on Sub-scenes from ERS-1 imagery is shown in Table 1. The spatial textures observed in these land systems result from complex interactions between physical, biological and social forces. Most land systems have been influenced by human land use, and the resulting landscape mosaic is a mixture of natural and human-managed patches that vary in size, shape and arrangement.
Table 1. Texture classes
Porphyritic complex peneplain (PCP) presents a great variety of textures compared to the rest of the land systems described, being the major difference related to terrain aspect and slopes. From the image, the topography shaping this landscape is enhanced based on the surface roughness. The dissected landscape defines narrow valleys and depressions with forage and temporary water available for herbivores in several states of environmental degradation.
Gaiman structural terraces (GST) present two types of texture, with vegetal cover fluctuating between 40 and 60% on a patchy structure. This landscape is flat and the available water sources are artificial (wells. tanks. etc.).
Valdés structural terraces-level III (VSTIII). The structural stripped plains constituted by 'Rodados Patagonicos' (Plio-Pleistocene age) have a wide distribution of landforms. In this landscape the wind, aided by the arid climate, is a dominant transport and deposit agent. About 50% of this land system is a grass steppe with a vegetal cover of 60-80%.
Valdés structural terraces-level IV (VSTIV). The structural plains are controlled mainly by calcareous cementation of the upper gravely banks. The pattern of texture is relatively homogeneous with small closed basins distributed on the surface.
Valdés coastal plain (VCP). This occupies the entire coastal zone of the peninsula and varies from smooth sand beaches to abrupt, active and inactive cliffs. The VCP presents few escape corridors, scarce water sources and low primary production.
Valdés marine cave (VMC). This consists of a series of NW-SE beach ridges flanked on the west by a low, inactive cliff. ERS-1 images show for this environment the dynamics of the water mass which corresponds to the evolution of the coast from the littoral drift standpoint.
Basin landforms (BL). This environment comprises three tectonic depressions according to bottom morphology. It presents few escape paths, moderate to abundant temporary natural water sources and medium primary productivity. The environmental affinity of the described land systems for guanacos is presented in Table 2. The ranking shows only six categories from the original landscapes. In other words, the affinity ranking overlaps some of the variables used to determine landscapes by using ERS-1 even under a coarse grain criteria, since it is possible, using this tool, to define more units under a finer grain criterion.
Table 2. Guanaco's environmental affinity ranking
This ranking implies that with high affinity, the environment would be appropriate for the guanacos' distribution, but it does not necessarily mean that in those environments high densities of guanacos will be found. Abundance of this species depends on several factors such as natality/mortality, migration or other natural or artificial stresses (hunting, domestic livestock, etc.). In fact, aerial surveys performed in 1995 in some of the areas presented here showed intermediate densities of guanacos in the PCP and GST land systems. Furthermore, densities lower than 0.589 guanacos/km2 were estimated for the VCP (ranked 6) land system (Baldi et al. 1997). In spite of the results found by these authors, the densities are very low compared to the densities described for the Chubut Province. Surprisingly, the estimated mean density for the Peninsula Valdés (natural reserve) is about 0.51 animals/ km2, when in other environments, densities as high as 7-8 guanacos/km2 were reported.
Since land degradation is the main ecological problem in the arid and semi-arid rangelands of Patagonia (Soriano & Movia l986), the land systems of this study, in terminal states of degradation, were categorised (Table 3). The land systems of the Telsen area refers to the landforms of a wide region and its associate habitats.
Table 3. Land degradation of land systems analysed.
Table 4 compares the relationship between the guanacos' environmental affinity and categories of degradation. The guanaco's high affinity is found only in medium- and high-degradation categories. On the other hand, the guanaco's low affinity is found only in medium-degradation categories. Intermediate affinities may be found in all of the three categories of degradation.
Table 4. Summary of land systems, guanaco affinity categories and degradation
Results from Table 4 enable us to infer about the relationship between the guanaco's environmental affinity and the process of degradation. The main variables used as diagnostic tools to analyse the results are inter-specific competence (sheep-guanaco), as well as natural and/or anthropic effects impacting the environment. Interspecific competence has been described for guanacos in different environments of southern Patagonia (Raedeke 1979).
The PCP land system presents high affinity with a high degree of desertification that may be explained by the following characteristics: low interspecific competence, abundant escape corridors and high natural degradation (more than anthropic) due to ancient landscapes (Jurassic age).
The GST landscape in a second level of environmental affinity presents a higher degree of inter-specific competence (see Fig.7 for land use) and a larger volume of forage available. Degradation is of an intermediate level, attributable to overgrazing. This feature is visualised in the texture of the radar image.
The land systems of the Peninsula Valdés area present low and intermediate affinities for guanacos and three land degradation categories. This result is a consequence of different levels of inter-specific competence and final stages of degradation (anthropic and natural processes). We cannot find a direct relationship between the guanaco's environmental affinity and the process of desertification. The facts suggest that the distribution of guanacos would be the result of the interaction between inter-species competition and processes of degradation, whether they are natural (slow) or man-made (faster). When affinity is high, the degradation process seems to be independent (with a differential temporal pattern) of guanaco distribution. When affinity is intermediate or low, the levels of environmental degradation would reduce guanacos relative density, mainly due to anthropic effects. This sort of analysis for areas other than those described above will facilitate design strategies for terrestrial or aerial sampling or population census. The procedure could be used for guanacos or other wild species for which environmental affinities are known or may be assessed. Studies of this type in other areas will help to define strategies for field work, reducing time and expenses. On the other hand, using other types of satellite sensors (Spot, Landsat, AVHRR/ NOM, etc.), it is possible to complement the studies, adding information about primary productivity in a temporal and spatial sense. These tools will facilitate defining policies concerning the sustainable use and conservation of this typical patagonian species.
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