Interaction between agro-ecosystems and natural grasslands: stone graining and loss of natural ecosystems
Contributors: Valeria Tomaselli, Giuseppe Veronico (CNR-IBBR); Palma Blonda, Cristina Tarantino (CNR-IIA); Carmela Marangi, Fasma Diele (CNR-IIA)
Natural dry grasslands (pseudo-steppes with grasses and annuals species of the Thero-Brachypodietea) and scrubland on calcareous substrates are habitats that tipically characterize the Alta Murgia National Park. Natural areas are alternated with semi-natural pastures, mainly grazed by sheeps, and wide cereal crops that characterize the arid and bare Murgia land; two main habitats (according to the Annex I of 92/43 EEC Directive) characterize this site: "Pseudo-steppe with grasses and annuals of the Thero-Brachypodietea" (6220*), which includes thermo-Mediterranean xerophile annual grasslands rich in therophytes of calcareous, oligotrophic soils, with inclusions of some perennial communities (belong to classes Poetea bulbosae, Lygeo-Stipetea) and "Eastern sub-mediterranean dry grasslands (Scorzoneretalia villosae)" (62A0), this habitat incorporates sub-Mediterranean xeric grasslands with perennial important species of interest with endemic, rare species (Festuco-Brometea class). These habitats provide several ecosystem services that refer to the biodiversity maintenance (pollination, animals and plants refuge function, etc.) and to support ecotourism, education, and research. Murgia natural landscape is closely linked with man presence that is expressed by crops, in particular cereals, and livestock breeding, in particular ovine. Good agricultural practices mainly supply food but also create manifold benefits for associated agro-biodiversity (ecological niches, habitat heterogeneity in rural landscape, health crops, etc.).
The regional Authority, in charge for compliance to the Habitat directive, is most concerned of the degradation of such natural habitats (loss, fragmentation, quality depletion), particularly in connection to the conservation of some raptors species (globally threatened and priority species according to the Bird Directive).
In recent decades the area, which is characterized by the presence of unique highly diverse ecosystems and also of endemic and threatened species, has been undergoing an awfully accelerated process of habitat fragmentation and contamination both within and at its borders by a number of combined pressures. Among these:
- the Common Agricultural Policy (CAP), which drove transformation of natural grasslands and semi-natural pastures into agricultural (cereal crops) areas by stone (rock) graining (clearance). In this process rocks are crumbled through by mechanical means and are mixed with soil, with the aim of creating a substrate suitable for crops. Among the secondary effects, it induces soil erosion and sediment deposition and contamination in aquifer;
- the illegal waste and toxic mud dumping on areas subject to conversion from natural to landfills causing heavy metal contamination of soils and aquifer systems;
- the increasing of traditional legal and illegal mining;
- the expansion of wind farms.
All these factors of risks cause a alteration of the delicate balance of natural habitats, and indirectly have an impact also on the entire crop production cycles and livestock; as a consequence, the most important ecosystem services have been compromised, not only agriculture for human well-being, such as provision of crop products and dairy products (i.e. milk, cheese, etc.), but also a big fallout on the entire grassland ecosystem in terms of habitat fragmentation and biodiversity loss. Pedological studies have showed that the structural characteristics of soil have worsened in the last decades, organic matter percentage has decreased, whilst the fine inert particles increased. This means that, during heavy rains, part of these soils tend to slide down from the slopes and to accumulate in depressions, where anthropic artefacts are often present. The amount of ground that flows down also increases when plowing is made along the lines of maximum slope (known locally as "rittochino" plowing ).
The crop type influence level and severity of the erosion process: cereal crops, very common in Alta Murgia and covering the soil surface for several months per year, raise the vulnerability of the sites subject to rock clearance in terms of soil loss, especially during the most extreme weather events.
Rock clearance affects also the anthropic landscape; in facts ancient structures such as dry stone walls, beaten roads, rural tracks, wells, water and snow stone tanks, etc. and other rural artefacts are been "grounded" by unscrupulous farmers to give place to few square meters of naked land for agricultural purposes.
Illegal dumping (toxic sludge, special hospital waste, leather waste products, ferrous scraps, etc.) causes water and soil poisoning with serious consequences for the agricultural sector: wide areas become no longer cultivable; high percentages of chrome, copper, zinc and cadmium poison the soil. Overall pollution causes a decrease of agricultural yield (dairy products, vegetables, cereals, etc.), a quality decline of Murgia typical products and a field's abandonment.
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