Costantino Sirca

Assessing temporal variation of primary and ecosystem production in two Mediterranean forests using a modified 3-PG model

ContextForest ecosystem carbon uptake is heavily affected by increasing drought in the Mediterranean region.AimsThe objectives of this study were to assess the capacity of a modified 3-PG model to capture temporal variation in gross primary productivity (GPP), and ecosystem net carbon uptake (NEE) in two Mediterranean forest types.MethodsThe model was upgraded from a monthly (3-PG) to a daily time step (3-PGday), and a soil water balance routine was included to better represent soil water availability. The model was evaluated against seasonal GPP and NEE dynamics from eddy covariance measurements.ResultsSimulated and measured soil water content values were congruent throughout the study period for both forest types. 3-PGday effectively described the following: GPP and NEE seasonal patterns; the transition of forest ecosystems from carbon sink to carbon source; however, the model overestimated diurnal ecosystem respiration values and failed to predict ecosystem respiration peaks.ConclusionsThe model served as a rather effective tool to represent seasonal variation in gross primary productivity, and ecosystem net carbon uptake under Mediterranean drought-prone conditions. However, its semi-empirical nature and the simplicity inherent in the original model formulation are obstacles preventing the model working well for short-term daily predictions.

Estimating daily forest carbon fluxes using a combination of ground and remotely sensed data

Several studies have demonstrated that Monteiths approach can efficiently predict forest gross primary production (GPP), while the modeling of net ecosystem production (NEP) is more critical, requiring the additional simulation of forest respirations. The NEP of different forest ecosystems in Italy was currently simulated by the use of a remote sensing driven parametric model (modified C-Fix) and a biogeochemical model (BIOME-BGC). The outputs of the two models, which simulate forests in quasi-equilibrium conditions, are combined to estimate the carbon fluxes of actual conditions using information regarding the existing woody biomass. The estimates derived from the methodology have been tested against daily reference GPP and NEP data collected through the eddy correlation technique at five study sites in Italy. The first test concerned the theoretical validity of the simulation approach at both annual and daily time scales and was performed using optimal model drivers (i.e., collected or calibrated over the site measurements). Next, the test was repeated to assess the operational applicability of the methodology, which was driven by spatially extended data sets (i.e., data derived from existing wall-to-wall digital maps). A good estimation accuracy was generally obtained for GPP and NEP when using optimal model drivers. The use of spatially extended data sets worsens the accuracy to a varying degree, which is properly characterized. The model drivers with the most influence on the flux modeling strategy are, in increasing order of importance, forest type, soil features, meteorology, and forest woody biomass (growing stock volume).

Pollen emission from olive trees and concentrations of airborne pollen in an urban area of North Sardinia

In this study the seasonal and daily variations in olive airborne pollen concentrations were measured in the atmosphere of Sassari (Italy) and the olive pollen emission was monitored in the countryside during the flowering period in 1995 and 1996, in order to detect the patterns of change in the atmosphere. The intensity and the timing of pollination was also studied in relation to phenological stages occurrence. In addition, the influence of the main meteorological parameters on pollen emission and airborne pollen dispersal in the city was assessed. Airborne pollen reached its highest concentration a few days before the peak of pollen emission in 1995 but several days after it in 1996 (6 days). Analysis of hourly concentrations shows that the maximum emission and dispersion recorded during the observation period occurred in the middle of the day. Significant regressions were found between hourly temperature and air humidity values and hourly pollen concentrations recorded in the olive grove for almost every day studied, indicating a negative correlation between humidity and pollen concentration and a positive correlation between pollen concentration and temperature. On the other hand, no significant correlation was observed between the meteorological parameters and pollen concentration recorded in the urban area.

A wildfire risk oriented GIS tool for mapping Rural-Urban Interfaces

The Rural−Urban Interfaces (RUI, synonym of WUI, Wildland−Urban Interface) are conceptually defined as areas where houses and burnable vegetation are in contact or intermingled. Raising concerns related to wildfire occurrence in the RUI areas of Europe have been recognized. In this paper we describe a methodology, implemented in an easy-to-use tool, which gives a fire risk oriented RUI definition and which is capable of mapping such surfaces. The tool, called RUImap, contains three mapping options and, using easily obtainable input data, offers the possibility to customize most of the parameters used in the mapping process. RUImap has been tested in Sardinia (Italy), the second largest island of the Mediterranean Basin. The methodology and the tool can help to overcome difficulties of most of the users to go from the theoretical RUI definition to data and statistics on these areas.

Assessment of Myrtus communis L. water status and water requirements

Myrtle ( Myrtus communis L.) is a naturally occurring, highly drought-tolerant, evergreen shrub or small tree that is widely distributed within the Mediterranean basin. It is classified as an aromatic species because of the essential oil compounds of the leaves and fruits. Myrtle is commercially used for liquor production and perfume, and the harvest comes mainly from wild plants. Currently, there is insufficient wild-plant production to meet the demand for myrtle leaves and berries which has led to increasing interest to cultivate the plants to increase production. To assess the water requirements and water use efficiency, research was conducted on the ecophysiological responses of commercially grown myrtle plants to different soil-moisture conditions using stem water potential measurements. Data were collected in an eight-year-old myrtle orchard located near Alghero (Italy) during two consecutive summers. Plants showed higher values of net photosynthesis and water use efficiency under moderate stress than in well watered conditions. Severe stress symptoms appeared only with low soil moisture content. These results showed that optimal myrtle production will likely occur using regulated deficit irrigation. Crop evapotranspiration was determined using the surface renewal method, and the crop coefficient (K c ), relative to short-canopy standardized reference evapotranspiration (ET o ) ranged between 0.7 and 1.2.