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Overgrazing This report draws on research results from projects other than DESERTLINKS.
g Description of reasons leading to overgrazing and why it is an issue in the context of desertification Author: Vasilios P. Papanastasis <vpapan@for.auth.gr> Livestock grazing is an old practice in Mediterranean Europe. It dates back to the Neolithic period when the first domesticated sheep and goats arrived in the region. Since then livestock husbandry has become a dominant human activity supporting civilizations and shaping Mediterranean ecosystems and landscapes. In discussing the factors underlying deforestation in the Mediterranean countries, Thirwood (1981) considers grazing by domestic animals among the major causes, with goats singled out for their predilection of woody forage. Also, Tsoumis (1985) considers that grazing had a major contribution to deforestation, more than agricultural clearances, with goats being the main catastrophic agents. The same views are shared by Tomaselli (1977), who in addition points out that grazing can prevent the evolution of maquis and garrigue to high forests. The convictions against goats were so strong in the middle of the past century that several countries had to take decisive measures to reduce their numbers or even eliminate them completely by subsidizing their slaughter (FAO, 1964). As a result of these views, the "Ruined Landscape" theory about Mediterranean Europe has been developed (Grove and Rackham, 2001). As a matter of fact, the blame on livestock for destroying the environment is confounded with the mismanagement applied for which the sole responsibility is with men and not the animals (Papanastasis, 1986). Rangelands of the Mediterranean region include grasslands, also known as pastures, as well as "woody" rangelands, namely dwarf shrublands (e.g. phrygana, batha, tomillares), shrublands (e.g. garrigue, maquis, matorral) and open forests (less than 40% tree canopy), also known as silvopastoral systems. According to Le Houerou (1981), these rangelands are grazed by 270 million sheep-equivalents, which include horses, mules, donkeys, cattle, camels, pigs, sheep and goats. The latter two kinds of animals are the dominant group making 75% of the entire population. All these animals graze on about 830,000 km² of rangelands corresponding to a stocking rate of about 2.2 sheep-equivalents per hectare. If we consider that the grazing capacity of Mediterranean rangelands is no more than 1 sheep-equivalent/ha/year on the average, we may conclude that these rangelands are seriously overgrazed. However, the grazing pressure is not evenly distributed all over the Mediterranean rangelands and it is certainly higher in the south than in the north Mediterranean. In Mediterranean Europe, it is also unevenly distributed with areas being highly overgrazed (e.g. lowlands, around villages) as well as undergrazed (e.g. remote areas). In discussing the reasons for overgrazing in Mediterranean rangelands, Le Houerou (1981) considers the main reason to be the Mediterranean climate itself, and more specifically the mild and rainy winters which allow grazing animals to stay outdoors not only in the summer - as happens in the temperate areas - but also in the winter, resulting in nearly year-long grazing periods. As a second reason he considers the socio-economic conditions which provide a social status to farmers having large flocks, or force farmers to raise large flocks in order to make a living. However, there are additional, very important, reasons. One such reason is the marginality of grazing areas in the Mediterranean region made up of hilly and mountainous lands with relatively shallow and rocky soils and steep slopes resulting in low productivity and grazing capacity. In dry and semi-dry areas, this problem is further aggravated by the low and erratic precipitation. Another important reason is land tenure. A large proportion of rangelands in the Mediterranean region including southern Europe are state or municipality and community-owned areas that are communally grazed by livestock of the local people (e.g. the island of Crete - Papanastasis, 1993). Under this communal system, grazing management is difficult or impossible and most often leads to overgrazing (Papanastasis, 1988). A final reason is the EU policies applied before the Agenda 2000 was implemented that subsidised the number of animals, thus encouraging farmers in Mediterranean EU countries to increase their flocks in order to receive higher levels of subsidy (Dubost, 1998; Pulina et al., 1998).
Grazing has multiple
effects on natural ecosystems. Animals defoliate vegetation and consequently
affect plant growth, plant vigour, plant reproduction, species composition,
plant cover and biomass, thus resulting in bare soil. Grazing animals
also trample the soil thus reducing bulk density and infiltration rates
and increasing overland flow. If the slopes are steep and the soils erodible
then soil erosion may result leading to desertification. This can happen,
however, only when overgrazing is applied on a continuous basis, namely
when too many animals are trying to feed on a limited supply of forage
(Dregne, 1978).
Overgrazing has a negative effect on plant diversity. Although several individual plant species are adapted to intensive grazing or seem to be favoured due to the reduction of competition (Bergmeier, 1998; Egli, 1991; Grove and Rackham, 2001; Seligman and Perevolotsky, 1994), the overall impact of overgrazing is negative, particularly in grasslands (Koukoura et al. 1998; Koutsidou and Margaris, 1998; Papanastasis, 1985; Papanastasis et al. 2002). On the contrary, moderate grazing has a beneficial effect on plant diversity (Montalvo et al., 1993; Naveh and Whittaker, 1979; Noy-Meir, 1998; Puerto et al., 1990), but undergrazing or no grazing at all may also produce negative effects (Peco et al., 1998). Undergrazed or ungrazed rangelands present the problems of abandoned lands being invaded by woody species, which increase the fire risk and result in devastating wildfires. In woody rangelands, the impact of overgrazing may not be adverse to plant diversity because the woody species can play a buffering role. This is the case with the phryganic communities, in which phryganic species, being unpalatable to animals themselves, can protect herbaceous species from overgrazing under their canopy. This buffering role however is eliminated if overgrazing is combined with wildfires (Papanastasis et al., 2002). Wildfires set by shepherds to control undesirable growth of vegetation is a common practice in several parts of Mediterranean Europe (e.g. Corsica, Sardinia, Crete, western Greece). Although Mediterranean vegetation is well adapted to fire and usually grows back after burning, it can be destroyed if burning is combined with overgrazing. Several studies have shown that the combination of wildfires and overgrazing are the main cause of rangeland degradation and desertification in the Mediterranean Europe (Arianoutsou-Faraggitaki, 1985; Aru, 1986; Margaris and Koutsidou, 1998; Pantis and Mardiris, 1992; Pantis and Margaris 1988; Papanastasis, 1977; Papanastasis et al. 1990; Vokou et al., 1986). In conclusion, overgrazing is an issue of desertification in Mediterranean Europe particularly in those areas where it is combined with pastoral wildfires g
Examples of reasons for overgrazing in European
Mediterranean areas g
Lower Inner Alentejo, Portugal The importance of cattle breeding in the area of the municipality of Mértola is well documented. Royal laws exist, dating from the medieval period, protecting the activity. In the past, sheep and pigs extensively grazed natural pastures, in a balanced use of local resources. Vast areas of the Mértola municipality provided spring grazing for flocks brought in from other regions of the country (for example the Algarve and higher Alentejo).
Now, incentives over many decades to increase cereal production have led to a significant decrease of natural pasture areas. This has resulted in the remaining areas for grazing cattle becoming more intensively used, and consequently increasingly degraded. In addition CAP incentives for sheep, pig and cattle production have led to a significant increase in numbers of animals per hectare and new methods of husbandry. Previously shepherds grazed their cattle over extensive areas, but now they stay in the same place supported by the installation of an infrastructure of fences, stables and small dams to provide drinking water. This causes a more prolonged effect on the soil from trampling and pasture exhaustion.
All these factors have contributed to more intensive and widespread land degradation in the area. It is important that attitudes towards the activity are changed and that husbandry systems are adopted that are more suited to the specific soil and climatic conditions of the area. g Psilorites
mountain, Crete (Greece) Psilorites mountain has a maximum
altitude of 2,456 m a.s.l. It is located at the middle of Crete with an
area of about 500 km², mostly lying above 600 m a.s.l. It is permanently
inhabited by about 18,000 people living in 20 village communities. The
dominant bedrock is undivided limestone and the soils are red. The climate
is sub-humid Mediterranean with wet and mild winters that become cold
in high altitudes. Vegetation is complex; it includes mostly evergreen
but also a few deciduous woody species as well as phryganic species, which
dominate the mountain. Land tenure is also complex; agricultural lands
are privately owned but forests and rangelands are state owned and the
right to graze them belongs to the local people.
As far as the soils are concerned, they were found to be very shallow (<15 cm) or shallow (15-30 cm) on most of the mountain, with about 40% of the surface area occupied by rocky outcrops (Pendarakis, 1994). They get deeper in karstic dolines, which however are limited in area, and found towards the foot of the mountain. Livestock husbandry is a traditional activity that has shaped Psilorites mountain since the Neolithic period (Lyrintzis and Papanastasis, 1995). In the last few decades, however, the number of grazing animals have been dramatically increased, mainly due to national initiatives,and, especially since 1981 (when Greece became a member of the European Union), due to EU subsidies. Based on National Statistical Data, the numbers of sheep were increased by 529% and of goats by 279%, from 1961 until 1991. These high numbers in 1991 resulted in an average stocking rate of 4.6 sheep-equivalents/ha/year (Menjli, 1994), which is at least four times higher than the grazing capacity of rangelands (Papanastasis et al., 1990), suggesting overgrazing.
In order to study the impact of overgrazing
on Psilorites mountain, air photographs taken in 1961 and 1989 were processed
and the major land use/cover types were identified and recorded for the
two periods. The results showed an increase of sparse and medium density
shrublands (mainly phryganic ecosystems) at the expense of the dense ones,
as well as of forests. This evolution indicates degradation, since fewer
shrubs suggest less woody cover to protect the soil and sustain productivity.
The impact of overgrazing was more severe when it was combined with pastoral
wildfires.
g Overview
of how the indicators inter-relate Overgrazing is management oriented but as a process it is affected by several physical and socio-economic factors as well. Assessment indicators may relate to management, vegetation and abiotic conditions as well as to social, economic and political ones.
Overgrazing is caused when the number
of animals carried in a rangeland are more than its grazing capacity,
suggesting these extra animals could be from a few to too many. As a result,
the number of animals grazing in a rangeland or the grazing intensity,
expressed as stocking rate, is a very important indicator of rangeland
degradation (Papanastasis, 1998; 2000). Due to the different way that
the various grazing animals collect the forage, their impact on vegetation
is different (Rook et al., 2004) and therefore the kind of animal species
is very important in the overgrazing process. Also, the system with which
animals graze in rangelands is important, too. For example, continuous
grazing on a year-long basis is more adverse to species composition than
a seasonal or rotational grazing system (Sternberg et al., 2000). It has
been already mentioned that combining overgrazing with wildfires can be
more detrimental than either of the two processes alone. The distribution
of available infrastructure may decide whether a rangeland will be evenly
used or not; normally the animals tend to graze more intensively near
the watering points and animal sheds than away from them (Ghossoub, 2003).
Finally, overgrazing will be avoided if alternative feed resources are
available and therefore the production system applied is affecting the
impact of grazing animals on rangelands (Papanastasis, 1990).
For vegetation, important indicators are the amount of biomass produced or left at the end of the grazing period, the plant cover (Papanastasis et al., 2003) and the species composition. Usually, when overgrazing has occurred, the pasture is filled with weeds, which are undesirable plant species to animals. Soil and climatic variables such as soil depth, slope gradient, parent material, soil erosion, rainfall (amount and distribution), and temperature are all affecting vegetation and therefore the number of animals that can be grazed on a rangeland. There is a direct relationship between the soil depth (Papanastasis, 1994) or the amount of surface rocks (Alexandris et al., 1997) and herbage production in grasslands. Also, herbage production is very much affected by rainfall and air temperature (Papanastasis, 1982). Considering socio-economic indicators, they may include EU subsidies for animal numbers, the local traditions as far as the flock size is concerned, the land tenure (private, state or communal rangelands), the alternative income that the farmers can have apart form raising livestock and the laws that dictate the use of rangelands by the farmers. All these indicators interrelate with each other and with several physical indicators (e.g. productivity of rangelands) as well as management factors (e.g. number and kind of animals, grazing system, etc). Overgrazing is related ro other issues,
particularly land abandonment and deforestation.
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