1. Introduction
Humans, pastures, and grazing animals are closely related factors in Mediterranean ecosystems. The dynamic coexistence of these ecosystems and human societies has determined and shaped the evolution and stability of both over several millennia [
1].
Pastoral land in the Mediterranean basin covers an estimated area of 850,000 square kilometers, mostly occupying areas characterized by unfavorable pedo-climatic and soil conditions. Their use is limited mainly to extensive systems or is bounded to specific periods of the year, when animals have low nutrient requirements [
2,
3,
4]. However, such ecosystems play a crucial role in sustaining local societies and their economies in marginal lands of the Mediterranean through livestock farming and in particular sheep husbandry [
5,
6,
7]. In these areas, low-intensity and site-specific agricultural practices, mainly based on grassland resources, have evolved, over centuries, to limit risks associated with the inter- and intra-annual climatic fluctuations and to ensure regular production [
4,
8,
9].
Traditional practices carried out in these areas are often regarded as environmentally friendly and landscape-preserving, and the lands are also considered as being of high nature value [
10,
11]. Mediterranean grassland-based systems are usually extensive, with low use of agrochemicals and irrigation, while they are utilized predominantly by small ruminants due to their high efficiency in the use of locally available feeding resources [
12,
13] as well as their adaptation to the specific environments of these areas [
14,
15]. These farming systems have proved to be resilient to frequent, but moderate, disturbances such as deforestation, periodic fires, and overgrazing, by developing strategies to optimize the production of multiple goods as well as ecosystem services [
16,
17].
The productivity of Mediterranean grazing lands is limited by physical constraints: such as climatic and soil characteristics [
9]. Their growing season ranges from 4 to 8 months, depending on precipitation (300–1000 mm/year) and timing as well as the tolerance of flora to water scarcity. Annual and interannual forage production under rainfed conditions is often highly variable, although generally low, depending on land management and soil fertility. Typically, average dry matter yields range from 0.5–1.0 t ha
−1 year
−1 in semi-natural lands found on marginal soils, to 6.0–7.0 t ha
−1 year
−1, in agriculturally improved grasslands [
18]. In semi-natural grasslands, forage is usually of low nutritional quality, often worsened by the presence of plant species with anti-nutritional properties or other traits that limit their acceptability for ruminants. Dry matter accumulation ranges between 110 kg ha
−1 day
−1, in the most favorable season (spring), down to 20 kg ha
−1 day
−1 in autumn [
19,
20]. Annual species dominate in the herbage, but most of them are also encroached by perennial species such as
Cistus ladanifer [
21],
Genista acanthoclada,
Sarcopoterium spinosum [
22],
Phlomis fruticosa [
23], etc., that can contribute to some extent to feed resources, but are of limited and unbalanced nutritional value. An increase in shrub cover leads to a decline in herbage production, as well as an overall reduction in the nutritional value of the land’s forage production [
24].
Livestock grazing impacts grazing lands’ biodiversity and in particular plant community composition, as well as quantity and quality of the herbage produced [
25], vegetation dynamics [
26], species and bio-societies variability [
27], and the landscape overall [
28]. In total, grazing activity contributes to a rich mosaic of vegetation [
29] and results in the creation and preservation of all biodiversity forms [
30,
31]. However, changes in plant community diversity, created by grazing animals, can vary with environmental conditions, including regional variation in climate [
32], the evolutionary history of grazing [
33], as well as the supply of nutrients [
34]. Although Mediterranean semi-arid pasturelands have proven to be very resilient over the ages and have managed to recover from frequent and intense disturbance events such as fires, droughts, and the constant exploitation of humans, nowadays they appear to have reached a critical point [
35].
Lesvos Island, in the eastern Mediterranean, is the third-biggest island in Greece and the seventh in the Mediterranean, occupying an area of about 163,280 hectares [
36]. Land cover varies significantly from west to east, the eastern part is covered by olive groves, while the western is characterized by phryganic vegetation and used as pastoral land. Western Lesvos is a typical semi-arid Mediterranean area with a sparse population and low development, combined with environmental sensitivity and serious problems of local degradation and desertification [
36]. Agra, a settlement in western Lesvos has a long tradition of sheep farming and during recent decades sheep farmers have shifted from traditional farming practices towards modernization, leading to intensification of production [
37]. In fact, the number of farmed sheep there increased by 297.5%, between 1961 and 2010, while the number of holdings decreased slightly by 4.9% [
38]. These changes have led to the average size of a holding increasing by 318.1% from 34.5 sheep heads up to 144.3 during the same period. These developments coincided with a shift of farming systems in the area towards importing considerable quantities of supplementary feeds, in an attempt to maintain the balance between the animals’ nutritional requirements and the available local feed resources. It is questionable though as to whether management practices, in the use of this resource, are sustainable in terms of herbage productivity, forage quality, and land maintenance. In this study, we aimed to assess the effects of sheep farming practices on the sustainability of a semi-arid Mediterranean pastoral landscape; thus we recorded several characteristics of the land, including land cover, herbaceous vegetation productivity, plant diversity, and herbaceous feed quality over two seasons. Grazing practices, pasture improvement practices, and climatic conditions were also considered. The overall outcome will serve as a guide for management practices and policies for these pastoral lands.
4. Discussion
Western Lesvos is a typical semi-arid Mediterranean area, facing socio-economic and environmental issues [
36], leading to soil degradation and desertification [
47]. According to estimations, large parts of the island are already degraded and under the process of desertification, including areas such as oak forests [
40,
48]. According to [
49], the region is a typical case of the association between several socio-economic development policies and the environmental degradation process with practices such as overgrazing and deforestation, but the degree of dependency on sheep farming for livelihoods in many remote villages is high [
38,
49].
In our approach, we investigate the relationship between grazing practices, productivity, and plant diversity not at a specific time of the season (typically in the end in most of the literature, e.g., [
50,
51,
52], but along the whole season [
53]).
This allows a detailed view of the relationship between the characteristics of the pasture and the grazing practices of the farmers. Some of the most important findings are related to the pastures and their management, including grazing within the season, plant diversity, and long-term sustainability of the system and the pastures.
In terms of the production of pastures, the results of the significant seasonal changes in biomass production suggest that the late spring growth of grazed plants produces significantly more biomass when the temperatures of the soil and air rise owing to the rapid growth of many plants [
54]. Therefore, pastures that can be left ungrazed for a short period of time during that period, have a better potential to yield biomass later in the season, although this cannot be extended over a long time due to the proximity of the dry summer. The overall productivity in the area is in the upper limits of the range suggested by the literature for semi-natural lands found on marginal soils (from 0.5–1.0 t ha
−1 year
−1) [
18], but the high heterogeneity of the productivity in our pastures suggests that those with production values lower than 0.5 t ha
−1 year
−1 are on unfavorable soils while the others are in the range of agriculturally improved grasslands, though most of the latter are former fields of arable crops not more than 30–40 years ago. The ranges suggested by the literature for daily dry matter accumulation are within the values in our pastures as well [
19,
20].
In such an area, the long history of grazing and, in general, the use of the pastures has been suggested as important in understanding current trends [
6]. The pastures we measured can be categorized into two categories: pastures that were arable fields until roughly the 1970s or 1980s when cultivation of arable plants more or less stopped on the western part of the island [
38]. These pastures are in flat areas with deeper soils and their grazing histories are short compared to the rest of the area. The rest of the pastures are on sloping land, with shallower soils and long grazing history. Our findings show that despite important variability within the categories, there are significant differences in biomass production between these types of pastures that seem to reflect these histories, but also their differences in abiotic features, notably soil depth. Nevertheless, what also comes out is that these differences in productivity are not mirrored in the plant diversity data. The lack of a significant relationship between diversity and productivity has been also found in both experimentally [
55,
56,
57] and naturally assembled Mediterranean herbaceous communities [
58]. In general, productivity is considered to explain a small portion of the overall variation in grassland plant diversity worldwide [
59,
60].
Furthermore, the findings of the recognized species show that grazing seems to be unrelated to the overall level of diversity within each season. It has to be noted though that the small surfaces used in the approach may affect the overall number of species, especially in localities within each pasture where specific species may be found (e.g., in rocky places or along streamlines). The number of species is relatively low for these types of ecosystems [
61,
62], probably related to the long-term effects of heavy grazing on many of the pastures [
63,
64]. Another plausible explanation of the patterns of herbage growth can be offered on the basis that, after several decades of high-grazing pressure, flora in the area has been adapted to the specific biotic and abiotic pressures of the area. Indeed, the ability of plants to grow, reproduce, and survive under changing environmental conditions depends on their efficiency in acclimatizing and adapting, where the first one is associated with short-term challenges as opposed to the second one [
65,
66,
67].
The nutritional composition of grazed material shows a low content of nutrients. The CP values are as low as cereal straw, but the crude fiber is somehow better than straw. However, a pattern of differences between the samplings within a year is associated with less mature herbage biomass harvested from the cages set later in the season (2nd and 3rd cage) which appear higher in CP and lower in crude fiber. This effect can also be associated with the higher presence of legumes in the 3rd cages, and their lower presence in samples from the control cages that represent plants grown very early in the season.
Overall, the approach followed here can be used for monitoring different aspects of the productivity of pastures in semi-arid and heavily grazed areas including seasonal differences and design improvement strategies.
5. Conclusions
Semi-arid areas of poor soils and intense relief have been grazed for millennia. Sustaining an important livelihood activity for local populations, while conserving pasture productivity and avoiding land degradation within climate change is a challenge that will determine socio-economic viability and environmental conservation in these areas. In this study, we analyzed pastures grazed by sheep in a semi-arid Mediterranean area, recording the land cover, herbaceous productivity, and plant diversity over the grazing season. Grazing history seems to be important and perhaps more important than seasonal grazing practices differences between pastures. This seems to suggest that the improvement and sustainability of pastures is a long-term concern and should be the result of a multi-annual plan that can provide guidance to farmers on how they have to treat their pastures. This is not easy, of course, within a climate of increasing livestock numbers and intensifying feeding practices, both in and off the pastures.
Past grazing practices that incorporated the cultivation of crops were possible and grazing after the end of the growing season and in the fallow years could provide an improvement plan that may prove more sustainable in the long term. Such policies are not incorporated into the current thinking and practice of the Common Agricultural Policy of the EU and a shift toward greater complementarity between cultivation and grazing and also towards less intensive grazing practices could provide incentives to farmers and local societies to continue a long-term and sustainable use of these pastures.