Ricostruzione dei flussi di CO₂ di un ecosistema a macchia mediterranea mediante reti neurali

Nell’ultimo decennio sono state realizzate numerose reti di monitoraggio dei flussi di massa ed energia a scala regionale, che utilizzano come standard di misura la tecnica dell’Eddy Covariance. La continuità del monitoraggio dei flussi è una condizione difficilmente realizzabile a causa sia della complessità degli apparati di misura sia di alcune limitazioni di carattere modellistico: in generale dopo i controlli di congruità fisica e biologica, non più del 65% dei dati risulta utilizzabile per la costruzione dei bilanci annuali. Negli ultimi anni sono state sviluppate metodologie per la ricostruzione dei dati mancanti dei flussi di energia e materia negli ecosistemi terrestri; tuttavia, attualmente non esiste una metodologia di ricostruzione standardizzata. In questo lavoro vengono realizzati modelli basati sulle reti neurali per la ricostruzione dei flussi di CO2 in un ecosistema a macchia mediterranea; le prestazioni fornite da tali modelli vengono confrontate con quelle di altre tecniche recentemente proposte dalla comunità internazionale. I dati sono stati raccolti nel corso del biennio 1998-99 in un sito sperimentale del progetto europeo MEDEFLU situato nella Sardegna nord-occidentale. I modelli basati sulle reti neurali hanno fornito in genere prestazioni superiori rispetto agli altri metodi, con valori dell’errore quadratico medio compresi tra 0.9 e 2.9 μmol m-2 s- 1 di CO2. Questi risultati confermano le possibilità applicative delle reti neurali nella ricostruzione dei flussi provenienti da reti di monitoraggio

Una Nuova area sperimentale di lungo termine, per lo studio degli effetti dell'incremento della temperatura e del periodo di aridità in formazioni di sclerofille mediterranee

A new long-term experimental area for studying the effects of climate warming and seasonal drought on a Mediterranean shrubland community. Global changes, such as land use changes, altered atmosphere composition, and climate changes, have been altering the functioning of ecosystems with possible impacts on the degree of biodiversity. Temperature and water availability are the two main determinants of the functional processes of terrestrial ecosystems. Climatic changes could have strong effects on vulnerable ecosystems as Mediterranean shrublands/garrigue/maquis, where the growth and survival of the plants are strictly dependent on the drought and to the high summer temperature. Furthermore, other pressures, such as grazing and wildfires, occur frequently in the Mediterranean area. In order to assess the impacts of the temperature increase and precipitation reduction on Mediterranean shrublands, a new experimental area was established in Sardinia at the Porto Conte forest, Alghero (SS). A system of automatic roofs covers 6 experimental plots (20 m2), in order to simulate an increase of temperature during the night (3 plots) or to intercept the precipitations during a 2-3 months period (3 plots). Three additional plots are used as control. All the observations were conducted in other five European shrubland ecosystems, according to common protocols developed in the context of the European project VULCAN (www.vulcanproject.com). The studies of the different ecological and physiological processes are organised in working packages (Plant, Soil, Fauna, Water) and integrated in a risk assessments evaluation. The aim of this paper is to analyse the first two years of data, to demonstrate the microclimatic modifications induced by the experimental system

Soil CO₂ flux measurements in vineyard ecosystem

Many recent studies on climate change indicate the soil as a major source for atmospheric CO2. Oxidation of soil organic matter and the respiration of plant roots produce the soil CO2 and the efflux rate to the atmosphere depends on the concentration gradient and aerodynamic resistance. Knowledge of soil respiration rate from cultivated ecosystems is important for determining the role of these ecosystems in the global carbon balance. This paper presents the results from short-term measurements conducted in two Italian vineyards with different characteristics. Soil respiration rates were measured using soil chambers in an open-system configuration. Fluxes of CO2 were measured along transects between rows approximately every four hours by sealing the chambers over the collars. Higher differences were found in relation to spatial location of chambers than to time of the day. Soil tillage showed a very important influence in relation to amount of CO2 released from soil. Root distribution and activity explains the variability of soil respiration between chambers. CO2 flux was little affected by soil temperature except when the soil was wet. The observed variability indicates that correct measurements of soil CO2 efflux require an adequate number of samples and a good sample distribution