Serena Marras

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).

Urban metabolism and climate change: A planning support system

Patterns of urban development influence flows of material and energy within urban settlements and exchanges with its surrounding. In recent years the quantitative estimation of the components of the so-called urban metabolism has increasingly attracted the attention of researchers from different fields. To contribute to this effort we developed a modelling framework for estimating the carbon exchanges together with sensible and latent heat fluxes and air temperature in relation to alternative land-use scenarios. The framework bundles three components: (i) a Cellular Automata model for the simulation of the urban land-use dynamics; (ii) a transportation model for estimating the variation of the transportation network load and (iii) the Advanced Canopy-Atmosphere-Soil Algorithm (ACASA) model tightly coupled with the mesoscale weather forecasting model WRF. We present and discuss the results of an example application on the City of Florence.

The Role of Vineyards in the Carbon Balance Throughout Italy

A common belief is that agricultural fields cannot be net carbon sinks, but perennial tree crops, growing a permanent woody structure with a life cycle of decades could act as carbon sink. Vineyards are good candidates to test this hypothesis, because they are often grown with limited soil cultivation and produce plenty of woody pruning material that can be left on the ground. Three Eddy Covariance sites were established in different vineyards, along a north-south transect, in Italy, to study the role of vine cultivation in the carbon balance of the Italian penisula. The year 2009 was chosen as a reference year for the three sites, in order to compare carbon budget estimates in areas characterized by different meteorological, pedological and geomorphological conditions. In the three sites a carbon sink ranging between 814 (Negrisia site) and 89 (Serdiana site) g C m−2 y−1 was measured. Both climate (water availability and PAR) and management (in particular the presence of permanent grass cover) have a strong impact on the carbon balance of the ecosystems. Even if it can be argued that this sink may be only temporary and the built-up can be substantially disrupted at the end of the vineyard life cycle, these results show that there is a concrete possibility of storing carbon in agricultural soils. Proper practices can be defined to preserve this storage at best, greatly contributing to the global carbon budget.

Towards a planning decision support system for low-carbon urban development

The flows of carbon and energy produced by urbanized areas represent one of the aspects of urban sustainability that can have an important impact on climate change. For this reason, in recent years the quantitative estimation of the so-called urban metabolism components has increasingly attracted the attention of researchers from different fields. On the other hand, it has been well recognized that the structure and design of future urban development can significantly affect the flows of material and energy exchanged by an urban area with its surroundings. In this context, the paper discusses a software framework able to estimate the carbon exchanges accounting for alternative scenarios which can influence urban development. The modelling system is based on four main components: (i) a Cellular Automata model for the simulation of the urban land-use dynamics; (ii) a transportation model, able to estimate the variation of the transportation network load and (iii) the ACASA (Advanced Canopy-Atmosphere-Soil Algorithm) model which was tightly coupled with the (iv) mesoscale weather model WRF for the estimation of the relevant urban metabolism components. An in-progress application to the city of Florence is presented and discussed.

Using energy balance data for assessing evapotranspiration and crop coefficients in a Mediterranean vineyard

Improving water use efficiency is a key element of water management in irrigated viticulture, especially in arid or semi-arid areas. In this study, the micrometeorological technique “Eddy Covariance” was used to directly quantify the crop evapotranspiration (ET) and to analyze the complex relationships between evapotranspiration, energy fluxes, and meteorological conditions. Both observed Direct measurements (DIR) of latent heat flux (LE) and observed from the residual of the energy balance (REB) equation were used for crop evapotranspiration calculations. Observed crop coefficients (Kcms) were then determined using the standardized reference evapotranspiration (ETo) equation for short canopies. In addition, linear approximations from observations were used to model the seasonal trend lines for crop coefficients and Kcs values were parameterized by first identifying the beginning and end of each growth stage. The modeled Kcs values were used to predict daily ET from ETo measurements and compared with values from literature. The daily observed DIR ET values (ETdo) were lower than REB ET (ETro) during periods with precipitation, but they were similar during dry periods, which implies that energy balance closure is better when the surface is drier. Comparisons between modeled ET and crop ET estimated using Kc values from best agreement was observed between the modeled REB and FAO 56 and the local Kc values provided by the Regional Agency ARPAS showed good agreement with observed ET (from DIR and REB data) than the FAO 56 ones. The study confirmed that the availability of locally driven Kc could be relevant to quantify the crop water requirement and represents the starting point for a sustainable management of water resources.

The Role of Managed Forest Ecosystems: A Modeling Based Approach

Regional approaches to estimate the carbon budget of Italian forest ecosystems using Process-Based Models (PBMs), have been applied by several national institutions and researchers. Gross and net primary productivity (GPP and NPP) have been estimated through the PBMs simulations of carbon, water, and elemental cycles driven by remotely sensed data set and ancillary data. In particular the results of the GPP and NPP estimations provided by the implementation of two hybrid models are presented. The first modeling approach, based on the integration of two widely used models (C-fix and BIOME-BGC), has been applied to simulate monthly GPP and NPP values of all Italian forests for the decade 1999–2008. The approach, driven by remotely sensed SPOT-VEGETATION ten-day Normalized Difference Vegetation Index (NDVI) images and meteorological data, provided a NPP map of Italian forests reaching maximum values of about 900 g C m−2 year−1. The second modeling approach is based on the implementation of a modified version of the 3-PG model running on a daily time step to produce daily estimates of GPP and NPP. The model is driven by MODIS remotely sensed vegetation indexes and meteorological data, and parameterized for specific soil and land cover characteristics. Average annual GPP and NPP maps of Italian forests and average annual values for different forest types according to Corine Land Cover 2000 classification are reported.

Trying to Link Vegetation Units with Biomass Data: The Case Study of Italian Shrublands

Although their carbon stock is relevant in assessing the baseline for the negotiation of future agreements with respect to carbon balance, there still are few available studies concerning the biomass and the net ecosystem exchange capacity of Mediterranean shrublands. In this chapter a preliminary overview on the biomass values concerning Italian shrubland communities and/or their dominant/characteristic woody species is provided. Many useful data on above- and belowground biomass issued from investigations carried out in other Mediterranean countries and concerning plant communities, which share the same ecological, floristic and structural traits of Italian shrublands. A preliminary finding of this research is the uneven degree of knowledge concerning the different non-forest woody communities. For example, there is still no literature on the biomass of some 2/3 of all the considered phytosociological units. Besides, both the above and the below-ground biomass of many Mediterranean shrubs show a very wide range of variation as they are strongly influenced by progressive succession processes and by the nature, the intensity and the frequency of disturbance factors. Thus, direct measuring of these values for each vegetation unit and dominant woody species should be encouraged and intensified. Monitoring activities concerning biomass increase are recommended as well: as a matter of fact, at present reference data on this topic are so limited and variable that it is not possible to confidently estimate the annual growth of shrubland communities.

Urban CO2 Planning: A Decision Support System

Patterns of urban development affect flows of material and energy within urban settlements and exchanges with their surroundings. In recent years the quantitative estimation of the components of the so-called urban metabolism has increasingly attracted the attention of researchers from different fields. To contribute to this effort we developed a modelling framework for estimating carbon exchanges in relation to alternative land-use scenarios. The framework bundles three components: (1) a Cellular Automata model for the simulation of the urban land-use dynamics; (2) a transportation model for estimating the variation of the transportation network load and (3) the Advanced Canopy-Atmosphere-Soil Algorithm (ACASA) model tightly coupled with the mesoscale weather forecasting model WRF. We present and discuss the results of an example application on the City of Florence.

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.