Human Mosaicing

Human use of land creates mosaics, and this seems the most visible human footprint associated with linear elements like roads and railways.

The human mosaic is created by the specialist attitude of man to extract resources, mainly from agriculture. A mosaic is created because land is used differently according to soil climatic factors, soil constraints or for other causes, such as distance from roads, distance from markets, etc.

The human-produced mosaics differ in general from the other types of natural mosaics by the fact that the main cause of the mosaic is not the number of individuals (like in plants and in social animals), but it is the specific use of the natural resources and their handling through agriculture or livestock rearing.

This attitude selects a piece of land with suitable attributes like water content in the soil, geological composition, aspect, distance from natural constraints.

Human mosaicing can be produced according to at least three different strategies:

1. A mosaic is created because resources are patchily distributed and we intercept them according to their spatial arrangement.

2. Or on the other hand the mosaic is created because locally we need several products and we are like central-place foragers. In this way human mosaicing shows patterns common to local human communities. So we can use the land in a patchy way, or we can transform the land in a patchily structured system. It is possible to have a mixing of both strategies. Especially across the Mediterranean basin, such models are common.

3. Finally, we can also use sample resources available in a continuous medium like the cut of a small portion of a forest and then we move to another area in a type of shifting mosaic.

The evolution of the present human mosaic can be observed at different scales. The transformation of a mosaic adapted to central-place foragers to one adapted to net foragers is evident in many regions. Such transformation has modified the spatial arrangement of the mosaics and the diversity of resources available locally. This transformation is a real revolution not only locally but also regionally. In such a way the new mosaics are less diverse locally but they may be more diverse regionally. Products must be transported for longer periods of time and over greater distances because they are delocated from the final consumers. Until the recent past, every local community had a self-organized system to produce goods and services. Every village or small city had surroundings organized in a centripetal way. All around an urban area there were cultivations, and services were provided for the main urban center. Such organization appears very conservative and a real source for local uses and strategies to use resources and to handle goods. Such centripetal organization had a strong impact on the culture, language, and administrative rules. Cultural and socio-economical processes were patchily distributed in the territory contributing to the ecological diversity of a region. In fact the local uses and strategies in resource use have allowed the persistence in a patchy way of species with a distribution greater than the socio-economical patchiness. For instance in some regions a species was strongly menaced by human use of the land, but in other regions a different use of the land allows the persistence of that species.

But the most important consequence of patchy use by humans of the resources has been the creation of an incredible variety of mosaics combining differently patches of woodlands with open field, river margins, roads, edgerow structure and network. Most of the organisms are sensitive to the spatial arrangement of habitat elements that per se are perceived as true habitats (Fig. 4.9).

Today's trend toward a full circulation of goods and services across large regions and continents has disrupted in a short time such systems, reducing the diversity in local land uses and cultural mechanisms. The era of a realized globalization seems very close. The globalization of our time is more broad and sophisticated than the partial globalization during past empires (from Roman times onward). The actual network of roads, the telephone network, and the dissemination of media (radio and

"vertical" Diversity versus "mosaic" diversity

Fig. 4.9 The figure shows the hypothesis that the pre-human environment in the Mediterranean has been substituted by a mosaic of cultivated and marginal patches. The diversity of the pre-settlement environment which we call "vertical" due mainly to the vertical complexity of the primeval forests has been substituted by a horizontal "mosaic" complexity. During this shift, which probably lasted thousands of years, many organisms became extinct while others were favored

TV) via satellites allows a full exchange of information between different parts of humanity and only broad regions still resist this openness. In this process the loss of environmental mosaics reduce the potentiality of ecological diversity to persist.

For instance, across the Mediterranean, despite 13,000 and more years of intense civilization, ecological diversity still persists. Overgrazing, fires, land reclamation, human development, and domestication have reduced but not destroyed the ecological diversity. Botanists have counted thousands of plants living in densely populated areas across the Mediterranean basin (Blondel and Aronson 1999, Rackham 1998, Grove and Rackham 2001), and in many upland areas there is livestock grazing, which allows the persistence of rare species of plants. The use of the land has been so strictly linked with the organism's strategies that often we observe real co-evolutionary processes.

It is reasonable to imagine that the diversity actually observed across the Mediterranean is the result of natural as well as human mosaicing. Such a mosaic has replaced the original more homogeneous land and the more important "vertical" diversity of nondisturbed forest covers present before human settlement (Fig. 4.10).

The mosaic created by human stewardship is not devoted to creating a mosaic per se but to extracting from the land the necessary resources, vegetable and animal biomasses. Type and composition of this mosaic greatly varies according to the agricultural practices. Every crop or any other product requires precise scaled interventions, such as ploughing, fertilization, care for the products, etc.

Fig. 4.10 Three different human-induced mechanisms responsible for the formation of mosaics: (A) Resources are patchily distributed and human activity copes such spatiality. (B) The environmental context is homogeneous and human activity creates an ex-novo patchiness to extract resources. (C) The C

environmental context is homogeneous and human use is temporary (a shifting mosaic)

These activities modify soil composition and dynamics, water cycle and nutrient flux as well as overlapping with the natural patchiness of the land, creating new spatial arrangements that in many cases are recognized as favorable habitats by organisms. In particular grazing by sheep and goats has shaped the mosaic of extensive parts across the Mediterranean. The grazing disturbance influences positively the cover of grass vegetation reducing soil erosion when compared with soil cover in dense shrublands and increases the patchiness of vegetation cover (Perevolotsky and Seligman 1998).

0 0

Post a comment