Diacrhronic analysis of the Maremma laziale (Latium) for the conservation of the natural and cultural landscapes

Abstract

Land Cover Changes (LCCs) are mainly due to human induced land use changes and they are among the major drivers of landscape transformations, especially in the Mediterranean area. They represent one of the five factors, called drivers, causing biodiversity change. The process of LCCs began with agriculture and human settlements on natural landscapes, driving sometimes the creation of characteristic cultural landscapes. Climate change is currently another mayor global concern, since it could have heavy impacts on living beings, included humans. Projected impacts encompass a broad range of effects: the evolution of new plant communities, shifts in the spatial distribution of tree species and loss in agricultural yield. The selected study area, located in the Province of Rome (Latium, central Italy), presents a typical Mediterranean landscape and it is typified by particular geographical, morphological, vegetation and historical features and thus it may represent a paradigmatic case study to analyze land use/cover and climatic changes over time. The study area covers a total surface of 556 Km2 and it constitutes a wide part of the coastal and internal plains of Northern Latium. That area has a great historical relevance, being inhabited since Etruscan and Roman periods (e.g., the UNESCO site of Cerveteri and other archaeological sites), and it shows relevant naturalistic and vegetation values. However, extensive drainage works in the lower Maremma Laziale caused fragmentation or loss of wetlands (ponds, coastal and forest marshes) and fostered urban expansion and tourist activities. Deforestation caused by agriculture expansion was more extensive in the fertile and easily accessible areas of the coasts, plains and lower hills. The aim of this research project is to increase data on and analyze changes in the vegetation landscape that occurred along the coastal and semi-coastal areas of Northern Latium over the last century, for the conservation of their Natural and Cultural Landscapes. The objectives of this research are: - to create an integrate informative geo-database summarizing biological and environmental features of the coastal and semi-coastal areas of Northern Latium; - to identify and describe the main natural and cultural landscapes of the area; - to investigate and analyze the main transformations of the area and driving factors. First of all, a dataset on past and present vegetation diversity was built using data obtained by an extensive bibliographic research. A database was set and implemented, through 180 new vegetation plots, aimed at defining the distribution of plant communities (from 1951 to 2011), using the computer package TURBOVEG 2.87 (the most widespread database program for storing phytosociological data in Europe). In this process it was tested and it is proposed a methodology to improve the quality of georeferenced vegetation data. A total of 538 relevés were analyzed as regards the different system of locating used in the study area by different researchers over time. The most common location name indicates areas of variable size and shape (rivers, mountains, or man-made structures), but sometimes it was simply reported the municipal area of the relevè station. Although data were collected mainly starting from 2000, only for very recent data (7%) spatial explicit information (geographical coordinates) are available. Moreover, only 20% of spatially-explicit records report the accuracy of coordinates, elevation, slope and exposure. In order to interpret the present landscape and to understand the dynamic in progress, a hierarchical landscape classification was used. It allowed to locate the main land facets of the study area and the main typologies of potential natural vegetation related to them. Using this classification it was possible to defined one land region, ten land systems and many environmentally homogenous land facets. It was possible to recognize 53 plant communities and to define their likely succession position (in the context of vegetation series). Among them, 10 potential natural vegetation units were defined. LCCs were assessed in four steps at two different scale: low resolution (1:100.000) (1960, 1990, 2000, 2006) and high resolution (1:25.000) (1949, 1974, 1999, 2005) by analyzing diachronically the distribution of 12 land cover categories obtained from digital land cover maps. LCCs were analyzed using GIS tools and multi-way data analyses. During the analyzed period two main land use changes (LUCs) were assessed: the surface of forests and cultivated areas has decreased over the whole investigated period and especially between 1960 and 1990. Whereas, the surface of urban areas has dramatically increased, in relation to demographic density increase. LUCs occurred mainly along the coast and on plains, with a less extent to inland areas and hills. The analysis of climatic data was carried out considering a long time period (1951-2007) of mean monthly data of rainfall and temperature measured at 18 gauging stations, within and close to the study area. Climatic data were analyzed using geostatistical methods (kriging) and descriptive statistics (moving average, bioclimatic indexes and graphs) for the definition of bioclimatic features. Vegetation map was obtained from the Province of Rome and overlaid with climate trend maps. Rainfall has decreased starting from 1980s while temperature has increased, even if not with a uniform trend. The spatialization of bio-climatic indexes showed a shift from Mesomediterranean to Thermomediterranean bioclimate. Local climatic trends are likely to impact specific plant communities (especially mesophilous forests, endangered shrubland-pastures associations, some termophilous oak wood and relict associations of meadows) in the study area, thus affecting the whole system. The environmental dynamics, observed in the study area, are taken as a paradigmatic example for other Mediterranean areas characterized by similar landscape and morphological features. This study can provide series of data and guidelines to understand the ongoing environmental changes and their impacts, to interpret the landscapes and to hypothesize their future dynamics, to provide an effective scientific template for environmental management.