Important factors to model climate change effects on evapotranspiration

Although growers have considerable control over crop production, a major concern is the anticipated increase in evapotranspiration (ET) due to global warming. ET rates, however, are also affected by radiation, humidity, wind speed, crop morphology, and crop physiology in addition to temperature. Crop ET (ETc) is commonly estimated as the product of reference ET (ET0) and a crop coefficient (Kc), and the main factors affecting Kc values are net radiation, aerodynamic resistance, and canopy resistance differences between the reference and crop surfaces. The standardized ET0 equation has fixed values for the canopy resistance (rc), and different values are likely for other crops. The rc values might also adjust with increasing CO2 and higher temperature. Aerodynamic resistance (ra) depends on atmospheric stability, wind speed, and surface roughness. The relative aerodynamic contributions of sensible heat to ET0 and ETc could change if the canopy development or the wind speed climatology are modified by global warming. In this paper, we will discuss how the ET0 and Kc values vary with microclimate and how Kc values and ET0 rates might react to global warming

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

Effetti dell'anulazione del tronco nell'olivo (Ascolana tenera)

Effects of girdling with and without removal of a bark ring in «Ascolana tenera» olive-trees, whose charac teristic is the variable yield, are reported in this study. Girdling with and without removal of a bark ring, carried out before anthesis, increased the percentage of setting of 40% the first one and of 70% the second one. The yield levels (resulted definitely low in control) resulted superior to 100% and 300%. At the same time leaf diagnostic showed (between May and October) a decrease of leaf mineral composi tion in leaves from girdled trees regarding N, Ca, Mg, P, Mg rates: in any case girdling with removal of a bark ring showed more intense effects. Considerable yield increases showed no bad influence on fruit morphology and quality

Stima evapotraspirativa dei fabbisogni irrigui nelle principali aree agricole della Sardegna

ETP calculation for three important irriguous areas of Southern (39°17' N. I), Central (39°53' N. I) and Northern (40°41' N. I) Sardinia through F.A.O. method shows too much high values with originai Blaney-Criddle equation, reduced differences with Penman (original and F.A.O.) equation, Radiation method and B.-C. F.A.O. equation respectively. The last method, believed the most suitable according to the first lisimetric measurements, estimates annual mean ETP equal to 1194 mm, 1077 mm and 1022 mm for Southern, Central and Northern Sardinia. Effective rainfall successive analysis shows they are 50% of total rainfall (in case of grasses) and they hold ETP for about 22%. Therefore seasonal irrigation requirements, calculated through F.A.O. crop coefficients, are among 841 mm, 791 mm and 706 mm concerning grasses, and 353 mm, 322 mm and 311 mm concerning olive tree, for Southern, Central and Northern Sardinia

Orientamenti per l'irrigazione del mirto

Preliminary observations on ecophysiology of Myrtus communis L. in cultural conditions are reported. Responses of plants to different moisture soil conditions were observed using the stem water potential methodology. Plants showed optimal ecophysiological behaviour under moderate stress condition. Stress symptoms appear only with very low soil moisture content. These first results show that this species requires only few water applications or regulated deficit irrigation

Incendi ed ecosistemi mediterranei: valutazione degli impatti in regime di cambiamento climatico

In Europa, in particolare nella parte meridionale, ogni anno si registrano mediamente 60.000 incendi, con una superficie complessiva percorsa dal fuoco di circa 600.000 ettari. Negli ultimi anni si è sviluppato un interessante dibattito sui fattori che guidano il regime degli incendi in queste aree. Le ricerche più recenti, supportate dalla statistica, confermano il ruolo guida del clima e della meteorologia, strettamente condizionato dall’uso del suolo e con diverse caratteristiche a seconda della regione. In condizioni di cambiamenti climatici e socioeconomici, quali quelle attuali, è logico pensare che anche il regime degli incendi subisca importanti influenze, a seguito delle modifiche del clima e dell’uso del suolo

Effects of warmer and drier climate conditions on plant composition and biomass production in a Mediterranean shrubland community

The last IPCC report predicts warmer and drier conditions for the future European climate and the Mediterranean basin could be highly sensible to future climatic change. In order to investigate how the forecast more stressing factors could affect Mediterranean shrubland ecosystems, an appropriate manipulation of the microclimate was carried out in an area covered by Mediterranean maquis aimed at extending the drought period and increasing the night-time temperature. Soil cover, plant growth, litterfall, leaf water status, and leaf nutritional status were monitored over three growing seasons. The manipulation altered the microclimate according to common scenarios, increasing mean annual night-time air temperature by about 1 °C and mean annual temperature by about 0.5 °C, and decreasing precipitation between 6-46% of the total rainfall during the growing seasons. A general increase of vegetation cover was observed in the whole community during the three years of experimentation. This positive temporal pattern was mainly observed in control and warming treatment, whereas in the drought treatment it was less evident. At species-specific level, a clear negative effect of drought treatment was observed for C. monspeliensis percentage cover. Shoot elongation was not significantly affected by the warming treatment. A significant negative effect of drought treatment was noticed in the 2001-2002 and 2002-2003 growing seasons. An increase of N and P concentrations in the drought treatment in Cistus was observed and it can be explained by the reduced shoot growth induced by the water shortage that we had observed in the same treatment. The absence of a concentration effect on the other two species could be the signal of the different behaviour with regard to a drier climate, and therefore could be a symptom of future change in species composition. We underline the need of longterm observation, because of the different responses of plants in the short and long- term conditions

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

Advanced-Canopy-Atmosphere-Soil Algorithm (ACASA model) for estimating mass and energy fluxes

There is a recognized need to improve land surface models that simulate mass and energy fluxes between terrestrial ecosystems and atmosphere. In particular, long-term land planning strategies at local and regional scales require better understanding of agricultural ecosystem capacity to exchange CO2 and water. One of the more elaborate models for flux modelling is the Advanced Canopy-Atmosphere-Soil Algorithm (ACASA) model (Pyles et al., 2000), which provides micro-scale and regional-scale fluxes. The ACASA model allows for characterization of energy and carbon fluxes. It is a higher-order closure model used to estimate fluxes and profiles of heat, water vapor, carbon and momentum within and above canopy using third-order closure equations. It also estimates turbulent profiles of velocity, temperature, humidity within and above canopy. The ACASA model estimates CO2 fluxes using a combination of Ball-Berry and Farquhar equations. In addition, the effects of water stress on stomata, transpiration and CO2 assimilation are considered. The model was mainly used over dense canopies (Pyles et al. 2000, 2003) in the past, so the aim of this work was to test the ACASA model over a sparse canopy for estimating mass and energy fluxes, comparing model output with field measurements taken over a vineyard located in Montalcino, Tuscany, Italy

Il Modello ACASA per la stima degli scambi di carbonio negli ecosistemi mediterranei

L’attività di ricerca finalizzata allo sviluppo e alla validazione di modellistica avanzata per la contabilizzazione del bilancio del carbonio nei sistemi agrari e forestali nasce da una intensa collaborazione con l’Università della California. In particolare è in fase di studio il modello ACASA (Advanced Canopy-Atmosphere-Soil Algorithm), che è attualmente uno dei modelli del tipo soil-vegetation-atmosphere transfer (SVAT) più sofisticati. ACASA contiene equazioni differenziali di terzo ordine per simulare i flussi di energia e materia nella canopy (10 strati atmosferici all’interno e 10 al di sopra), mentre il suolo è suddiviso in 15 strati. Una combinazione delle equazioni di Ball-Berry e Farquhar è utilizzata per stimare il flusso di CO2. Il modello considera gli effetti dello stress idrico sulla traspirazione e sull’assimilazione della vegetazione