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Rangeland management and Geomatics - an overview
Rangelands
in the context of Mediterranean land degradation
Rangelands in the Context of Mediterranean Land Degradation Since historical times, the lands of the European Mediterranean have been strongly utilised. The history of livestock grazing of cattle, sheep and goats began in early Holocene, when it replaced the precedent wild herbivores to a large extent, and has been a common and traditional practice in the Mediterranean region ever since (Papanastasis, 1998). In combination with physical factors this utilisation frequently caused degradation processes, which in some areas coincided with a substantial loss of biodiversity. Beside grazing, fire is and has always been a major factor in shaping rural landscapes in the Mediterranean area. Again, the fire phenomenon is closely related to land use and other human activities. This document provides a short introduction into some of the aspects related to rangeland management and the benefit of geomatics appraoches which are considered relevant for the GeoRange project.
Rangelands in the European Mediterranean In the Mediterranean Basin, the majority of the land surface can in fact be considered as "rangelands" or "ranges", which may be defined as "... areas of the world which by reason of physical limitations […] are unsuited to cultivation and which are a source of forage for free-roaming native and domestic animals, as well as a source of wood products, water and wildlife." (Holechek et al., 1998). This broad definition has a strong focus on parts of the world such as North America or Australia, where rangelands are large, homogeneous areas and their management is a well established science (Williams et al. 1968, Stoddartt et al., 1975). Mediterranean rangelands are much more interwoven with cultivated areas, and there is a variety of highly heterogeneous ecosystem types (Naveh, 1988). Following the small-structured character of the landscape, the ownership of land may be split into many smaller parcels, which complicates the application of management decisions. Since livestock husbandry is closely related with agriculture and agro-pastoral activities, and is strongly influenced by socio-economic changes (Gomez-Sal, 1998), there is no uniform grazing activity throughout the Mediterranean Basin, nor has it been of the same intensity over the centuries. While nowadays there are countries and regions, mainly at the northern rim of the Mediterranean Basin, where livestock population has been drastically reduced or completely eliminated, similar ecosystems are still heavily grazed in most countries of the southern rim and in the Middle East.
Land degradation in the European Mediterranean Present land degradation in Northern Mediterranean countries is partially due to dramatic land use changes that occurred during the second half of this century, and which lead in many cases to an unstable state of ecosystems under rapidly changing disturbance regimes. In particular, large areas of Mediterranean rangelands are now affected from transitional processes that cause conflicts between past and present land uses or economic and ecological priorities, i.e. between optimised productivity and ecosystem conservation. Heavy overgrazing in some parts, the accumulation of woody biomass triggered by the abandonment and undergrazing of rangelands in others, are causing substantial management problems. Either the depletion of range resources, or the increasing frequency and severity of wildfires, have become a major concern in the environmental policies all over the European Mediterranean countries, as in other regions of the world.
It is agreed that excess grazing for a long time can have negative effects on productivity and conservation of Mediterranean ecosystems, and it is considered a major cause of the destruction of Mediterranean vegetation in association with or without wildfires, ahead of agricultural clearings (Perez-Trejo, 1994). This has resulted in decisive measures taken by several countries to exclude livestock from many areas in some Mediterranean countries, such as France, Italy, former Yugoslavia or Cyprus (Thirwood, 1981). However, it has to be noted that also undergrazing may cause adverse effects, such as the disappearance of grazing-prone species or the accumulation of flammable biomass, which is one cause for the recurring wildfires in southern countries (Seligman and Perevolotsky, 1992). Also, the long history of livestock husbandry in the Mediterranean has resulted in an adaptation of the flora to grazing pressure (Rackham and Moody, 1996), and there is a growing evidence of community response to grazing that suggests that properly managed grazing at moderate to even high intensities can in certain areas be a necessary component of a conservation strategy. It may locally be considered "…. as a solution for protection of abandoned rural areas and for reducing the cost of livestock production in a highly competitive European and international market" (Papanastasis and Peter, 1998; Noy-Meir, 1998; Narjisse, 1998). Fire, as an environmental concern for forest managers in Mediterranean countries, appeared mostly in the second half of the present century, at different periods in the various countries depending on land use transformations (Moreno et al, 1998; Pausas and Vallejo, 1999). Before the outbreak of wildfires, reforestation was conceived for watershed protection, dune fixation, and wood production, in addition to its social role in promoting rural employment. After the wildfires expansion, forest management have been developing strategies for fire prevention. However, a fully integrated strategy of Mediterranean silviculture, which should incorporate the multifunctional role of forests and shrublands in agreement with the current social demands, is not yet available (Corona and Zeide, 1999). Reforestation strategies have only been slowly adapted to the new fire regime and the socio-economic context of rangeland function in the Mediterranean countries. Forest plantations are predominantly based on conifers (mostly pines) (Conacher and Sala, 1998), following the traditional reforestation strategy. The introduction of other forest species has been considered only very recently, and it is very scattered (in terms of countries and even within regions).
The need for optimised land management systems Given their spatial extension, their economic and ecological importance as well as their vulnerability to various disturbance regimes, it becomes clear that an improved management of rangeland resources, where both development and conservation/restoration objectives are considered, becomes increasingly important. However, in comparison to rangelands in other parts of the world, specific European perspectives need to be considered which account for the differences in landscape structure, ecological history and socio-economic context.
Range management in grazing areas For drafting and implementing sustainability-oriented management schemes, the evaluation of the present ecological state of Mediterranean rangelands in relation to their potential is an undisputed prerequisite. This state, which in range science is known as "range condition" expresses the health of rangelands or, in other words, the level of their productivity in relation to what it could have been if a proper management was applied . Depending on the grazing management applied, range condition may improve, stay unchanged or deteriorate, a process also known as range trend (Heady and Child, 1994; Holechek et al. 1998). Factors that affect range condition and its trend may be stocking rates, kind of animal species (e.g. sheep, goats, cattle or mixtures), rangeland type (grassland, shrubland, silviopastoral systems), land tenure, grazing systems or human interventions resulting in wildfires, infrastructural developments, range subdivision, etc. All these factors may improve or deteriorate Mediterranean rangelands depending on their intensity or complexity (Naveh and Lieberman, 1994). At the community level, range condition is evaluated with regard to conservation criteria such as biodiversity, cover, Leaf Area Index (LAI), litter and soil factors, as well as to productivity criteria such as amount, distribution, availability and forage quality of biomass. At the landscape level, it may be evaluated with diversity, dominance and patchiness including number, area, perimeter, regularity and complexity of patches (Farina, 1998).
Range management in fire-prone areas In abandoned and already degraded areas, reforestation should incorporate fire hazard considerations (Vélez, 1990), i.e. fire resistance and resilience, not only in species selection but also in the spatial configuration of reforestation projects. In addition to these fire prevention aspects, forest restoration must account for improving landscape quality (Montero and Alcanda, 1993; Ludwig and Tongway, 1995; Aronson and Le Floc'h, 1996). Some key elements to be considered in land restoration of fire-prone systems are the diversification of forest species (Vélez, 1990; de Simón et al., 1993), in addition to pines, with the utilisation of sclerophyllous resprouters (Vallejo and Alloza, 1998, Vallejo, 1999), that improve the resistance and resilience of ecosystems to wildfires. Prime options also include the delineation of forest stands to allow for fuel-breaks, taking advantage of topographic features such as ravines, or to introduce less flammable species as green firebreaks (Vélez, 1990). Fuel control measures may combine different methods, e.g. controlled grazing, chopping, grubbing (Legrand et al., 1994; Etienne et al., 1994), and designing linear fuel control structures (Vélez, 1990) such as fuel-break areas along stand perimeters and linear features (roads, water courses). Summarising, restructuring forest and range landscapes to maintain their function (e.g. production of values, watershed conservation) and resilience, requires a holistic approach for landscape management (Baskent and Yolasigmaz, 1999), which in turn can only be implemented based on sufficiently precise and differentiated information on the environment.
For defining any of these multi-functional range management scenarios, either the design of optimised grazing schemes, the protection/ enclosure of specific areas, or the re-introduction of grazing animals to reduce flammability risks in fire-prone areas, we find that the acquisition of specific and spatially differentiated information documenting the state of the ecosystem is one of the key problems. However, determining and evaluating the required parameters by ground methods is very laborious and expensive, and must necessarily be complemented and supported by approaches involving spatial information technologies.
The importance of geo-information processing
In
geo-information processing, the need for up-to-date information layers
has long been recognised and stimulated the use of remote sensing data,
which are providing a synoptic, repetitive and consistent perspective
over large areas. Remote Sensing is commonly introduced as the science
of collecting information about objects without coming into physical
contact with them (e.g., Elachi, 1987; Asrar, 1989; Schott, 1996; Schowengerdt,
1997). In Earth observation, the most important medium for transmitting
this information is electromagnetic radiation in the optical and microwave
region. The ability to draw concise conclusions with respect to land
resources and environmental change, however, depends on the capability
to assess specific surface characteristics (such as vegetation cover,
biomass, leaf area index (LAI), leaf litter, specific soil and substrate
properties). Remote sensing satellites measure the spectral properties
of surfaces; they can not measure specific resources nor land degradation
directly (e.g., Hill, 2000). The major problem associated with their
use is to interpret quantitatively a measured signal that has interacted
with remote objects in terms of properties of these objects.
While the techniques and methods to pre-process satellite images (i.e. geometric and radiometric rectification of data sets) are well described and considered largely operational (e.g., Schowengerdt, 1997), the extraction of specific object properties has only partially achieved operational status. More recently, the use of linear mixture modelling (e.g., Smith et al., 1990; Hill et al., 1995a) has resolved some of the problems to derive meaningful soil and plant parameters for natural ecosystems, but still the complex interaction of soil and plant properties may affect the significance of results. Nevertheless, several successful studies have shown that operational data interpretation algorithms can provide meaningful assessments (Graetz and Gentle, 1982; Pech et al., 1986; Graetz et al., 1988; Milham et al., 1996), in particular when long data series from earth observation satellites are used to derive a retrospective assessment of changing rangeland conditions (e.g., Hill et al., 1998). Besides using classical indicator variables (LAI, biomass, proportional cover) that can be derived from operational earth observation satellites through empirical and semi-empirical approaches (e.g., Lacaze, 1996; Hill, 2000), research is now focussing on approaches based on the inversion of analytical reflectance models (e.g., Jacquemond and Baret, 1992; Pinty et al., 1996; Atzberger, 2000; Udelhoven et al., 2000) which may open new avenues to quantitative assessments of relevant canopy parameters.
GIS and analysis of spatial patterns While the only way to obtain environmental information on a European scale is to employ remote sensing satellites, the only way to achieve their integration with other base data, to analyse and present the information derived therefrom, is by using Geographic Information Systems (Star et al., 1997). GIS has become a synonym for handling and understanding spatial information (e.g., Goodchild et al., 1996; Bonham-Carter, 1996; Burrough and Mc Donnell, 1998). Its infancy long left behind, Geographic Information Systems have made their way into ecology (Haines-Young et al., 1993; Johnston, 1998) and ecosystem and resource management (Alaric Sample, 1994; McCloy, 1995). However, environmental models require data for calibration, verification and the specification of boundary conditions. Much of this information can be derived from remote sensing, other items only from selected base data and limited field observations.
While in non-European rangelands (particularly in Australia) the use of remote sensing and GIS for rangeland monitoring has already a long tradition (Tueller, 1995; Zhou and Garner, 1990; Zhou and Milne, 1990; Pickup and Chewings, 1994;), the situation in Europe is considerably different. Despite the obvious benefits of using satellite imagery and GIS environments for the assessment and management of rangelands, only very limited or highly specific studies have been carried out for Mediterranean rangelands (Pulina et al., 1998; Legg et al., 1998). More important, so far no integrated approach has been undertaken to use geo-information processing for solving practical problems in the multi-functional management of Mediterranean rangelands.
The science and technology of gathering, analysing, interpreting, distributing and use of geographical information is frequently summarised under the term Geomatics. It is for this reason that our project, which intends to combine satellite remote sensing, spatial analysis concepts and GIS (Geographic Information Systems) technology, has been paraphrased GeoRange - Geomatics in the Assessment and Sustainable Management of Mediterranean Rangelands. It is our hypothesis that the problems described in the previous sections require an integrated approach that adequately considers the multi-functionality of Mediterranean rangelands. Based on conceptual research and specific field studies, the project aims at creating an efficient documentation, management and decision support environment, dedicated to the specific needs of rangeland ecologists, managers and conservationists who are also involved in the project. To cope with these objectives, the system must be capable to support a thorough assessment of range conditions (mainly based on data from earth observation satellites), to assist in the identification of physical and socio-economic factors driving ecosystem processes, and to efficiently support the design and implementation of multi-functional range management scenarios that can meet the requirements of local administrative authorities. Beyond the technology aspects, such a data processing and assessment environment must incorporate the expert knowledge of range ecologists and managers, as well as the expertise of specialists in landscape conservation and restoration. Beside generating specific data products and strategic perspectives derived in relation to three case studies on quite different rangeland problems (grazing optimisation, fire prevention and conservation, integrated watershed management), the GeoRange proposal finally aims at providing actual and potential end-users with a dedicated software package that includes remote sensing and GIS-related processing tools for optimising their management actions.
Aguiar,
M.R. and O. Sala, 1999, Patch structure, dynamics and implications for
the funcioning of arid ecosystems, TREE, 14 (7): 273-277. Lacaze,
B., 1996, Spectral characterisation of vegetation communities and practical
approaches to vegetation cover changes monitoring, in: Hill, J. and
D. Peter, (eds.), 1996, The Use of Remote Sensing for Land Degradation
and Desertification Monitoring in the Mediterranean Basin. State of
the Art and Future Research, Proc. of a Workshop, jointly organized
by JRC/IRSA and DGXII/D-2/D-4, Valencia, 13-15 June 1994, Valencia,
EUR 16732 EN, (Office for Official Publications of the European Communities:
Luxembourg), 149-166.
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