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

Performance Prediction of Durum Wheat Genotypes in Response to Drought and Heat in Climate Change Conditions

With an approach combining crop modelling and biotechnology to assess the performance of three durum wheat cultivars (Creso, Duilio, Simeto) in a climate change context, weather and agronomic datasets over the period 1973–2004 from two sites, Benatzu and Ussana (Southern Sardinia, Itay), were used and the model responses were interpreted considering the role of DREB genes in the genotype performance with a focus on drought conditions. The CERES-Wheat crop model was calibrated and validated for grain yield, earliness and kernel weight. Forty-eight synthetic scenarios were used: 6 scenarios with increasing maximum air temperature; 6 scenarios with decreasing rainfall; 36 scenarios combining increasing temperature and decreasing rainfall. The simulated effects on yields, anthesis and kernel weights resulted in yield reduction, increasing kernel weight, and shortened growth duration in both sites. Creso (late cultivar) was the most sensitive to simulated climate conditions. Simeto and Duilio (early cultivars) showed lower simulated yield reductions and a larger anticipation of anthesis date. Observed data showed the same responses for the three cultivars in both sites. The CERES-Wheat model proved to be effective in representing reality and can be used in crop breeding programs with a molecular approach aiming at developing molecular markers for the resistance to drought stress

An Improved model for determining degree-day values from daily temperature data

Although using hourly weather data offers the greatest accuracy for estimating growing degree-day values, daily maximum and minimum temperature data are often used to estimate these values by approximating the diurnal temperature trends. This paper presents a new empirical model for estimating the hourly mean temperature. The model describes the diurnal variation using a sine function from the minimum temperature at sunrise until the maximum temperature is reached, another sine function from the maximum temperature until sunset, and a square-root function from then until sunrise the next morning. The model was developed and calibrated using several years of hourly data obtained from five automated weather stations located in California and representing a wide range of climate conditions. The model was tested against an additional data-set at each location. The temperature model gave good results, the root-mean-square error being less than 2.0 °C for most years and locations. The comparison with published models from the literature showed that the model was superior to the other methods. Hourly temperatures from the model were used to calculate degree-day values. A comparison between degree-day estimates determined from the model and those obtained other selected methods is presented. The results showed that the model had the best accuracy in general regardless of the season

Analysis of phenological behaviour of some Mediterranean shrub species in responses to warming and drought conditions

Phenology is potentially a powerful tool for monitoring the response of plant and animal to climate change. In fact, phenological observations are a valuable source of information for investigating the relationship between climate and weather variation and plant and animal development (Kramer et al., 2000, Ahas et al., 2002, Menzel et al., 2003). The objectives of this paper are (1) to develop a detailed phenological scale, using the extended BBCH-scale system, for describing phenological behaviour of Mediterranean species growing in a Mediterranean-type climate, and (2) to evaluate the sensitivity of some Mediterranean species to climatic manipulations

An Improved model for estimating degree days

Although using hourly data offers the greatest accuracy for estimating growing degree days, daily maximum and minimum temperature data are often used to estimate degree days by approximating the diurnal temperature trends. In this paper, an empirical model (TM model), recently developed for estimating hourly mean temperature, is used to calculate degree-day values. The TM model describes the diurnal variation using a sine function from minimum temperature at sunrise until reaching maximum temperature, another sine function from maximum temperature until sunset, and a square root function from then until sunrise the next morning. Degree day estimates from the TM model were compared with values obtained from single triangle (ST) method. The results showed that the TM model was superior to the ST method. The differences between observed phenological stage occurrence and predicted date from the TM model were always less than 13 days for bud break and flowering, and 10 days for harvest

Temperature data for phenological models

In an arid environment, the effect of evaporation on energy balance can affect air temperature recordings and greatly impact on degree-day calculations. This is an important consideration when choosing a site or climate data for phenological models. To our knowledge, there is no literature showing the effect of the underlying surface and its fetch around a weather station on degree-day accumulations. In this paper, we present data to show that this is a serious consideration, and it can lead to dubious models. Microscale measurements of temperature and energy balance are presented to explain why the differences occur. For example, the effect of fetch of irrigated grass and wetting of bare soil around a weather station on diurnal temperature are reported. A 43-day experiment showed that temperature measured on the upwind edge of an irrigated grass area averaged 4% higher than temperatures recorded 200 m inside the grass field. When the single-triangle method was used with a 10°C threshold and starting on May 19, the station on the upwind edge recorded 900 degree-days on June 28, whereas the interior station recorded 900 degree-days on July 1. Clearly, a difference in fetch can lead to big errors for large degree-day accumulations. Immediately after wetting, the temperature over a wet soil surface was similar to that measured over grass. However, the temperature over the soil increased more than that over the grass as the soil surface dried. Therefore, the observed difference between temperatures measured over bare soil and those over grass increases with longer periods between wettings. In most arid locations, measuring temperature over irrigated grass gives a lower mean annual temperature, resulting in lower annual cumulative degree-day values. This was verified by comparing measurements over grass with those over bare soil at several weather stations in a range of climates. To eliminate the effect of rainfall frequency, using temperature data collected only over irrigated grass, is recommended for long-term assessment of climate change effects on degree-day accumulation. In high evaporative conditions, a fetch of at least 100 m of grass is recommended. Our results clearly indicate that weather stations sited over bare soil have consistently higher degree-day accumulations. Therefore, especially in arid environments, phenology models based on temperature collected over bare soil are not transferable to those based on temperature recorded over irrigated grass. At a minimum, all degree-day-based phenology models reported in the literature should clearly describe the weather station site

Mediterranean shrubland growth responses to warming and drought conditions

Evergreen sclerophyll shrubland is a prominent feature of Mediterranean Basin. Elevated temperatures and extended drought period are predicted to have a large influence on the functioning of natural and semi-natural environments both directly and through interactions with land management and pollutant loading (Larcher, 2000; Llorens et al., 2003). Climatic changes may have particular strong effects on vulnerable ecosystems, which are already subjected to other stresses such as elevated N deposition, intensive grazing or the risk of fire (Sala et al., 1998). An experimental manipulation of climatic conditions at field scale was conducted employing a newly developed "night-time warming" technique and an automated covering system to extend summer drought (Beier et al., 2002). The objective of this study was to test how a future extended drought period and an increase in temperature could affect plant response in terms of plant cover and biomass, plant growth and reproductive effort. In this paper preliminary results obtained during the two first years of experiment (2002 and 2003) are shown

Chilling and forcing model to predict bud-burst of crop and forest species

Dormancy is commonly separated into a rest period, when the buds remain dormant due to growth-arresting physiological conditions, and a quiescent period, when the buds remain dormant due to unfavourable environmental conditions. A sequential model predicting the number of days during dormancy based on accumulation of chill days during rest and anti-chill days during quiescence is described. Chill days and anti-chill days are calculated using the single triangle method to estimate degree days relative to a threshold temperature. The temperature threshold for calculating the chill and anti-chill days and the chilling requirement to determine when rest is broken are found by trial and error to minimize the root mean square error of predicted and observed bud-burst dates. Using several years of weather and phenological data for cherry, pear, kiwifruit and olive orchards and nine forest species from locations in Sardinia, Italy, the Chill days model performed better than four classical chill unit models and two chilling hour models. The classical chill unit and chilling hour models failed to predict bud-burst in some years depending on the species and climate, whereas the Chill days model always gave good results. The classical chill unit and chilling hour models start to accumulate chilling when temperatures fall below the threshold in autumn, whereas the Chill days model begins to accumulate chilling at a phenological stage (i.e. leaf fall or harvest). Moreover, the classical chill unit and chilling hour models do not separate dormancy into rest and quiescent periods. These factors may partially explain the better performance of the Chill days model. When compared with the null model (using the mean calendar date), the Chill days model gave better results except for the cherry trees and four of the forest species

Using CERES-Wheat to simulate durum wheat production and phenology in Southern Sardinia, Italy

Durum wheat is a crop of great economic relevance for Mediterranean regions, especially in developing countries. A decreasing trend in durum production is expected in the near future because of several factors, in particular environmental constraints due to climate change and variability. The aim of this work was to test the predictive performance of CERES-Wheat model, implemented in DSSAT software systems, under Mediterranean climate condition and soil types of Southern Sardinia, Italy. CERES-Wheat model was calibrated for three durum wheat Italian varieties (Creso, Duilio, and Simeto) using a 30-year data set (1974–2004) and a trial and error iterative procedure. Then, the model was validated and evaluated using several statistics. The model showed a quite good performance in predicting grain yield and anthesis date, with errors comparable with those reported by other studies conducted on bread and durum wheat. Predictions of grain weight and grain number did not match very well observations, confirming the difficulties of CERES-Wheat in estimating grain yield components. The results of this study suggest the need of specific field experiments and further model evaluations and improvements to better understand model simulation results of grain yield components of durum wheat