Angelo Nolè

Hydraulic adjustment of Scots pine across Europe.

* The variability of branch-level hydraulic properties was assessed across 12 Scots pine populations covering a wide range of environmental conditions, including some of the southernmost populations of the species. The aims were to relate this variability to differences in climate, and to study the potential tradeoffs between traits. * Traits measured included wood density, radial growth, xylem anatomy, sapwood- and leaf-specific hydraulic conductivity (K(S) and K(L)), vulnerability to embolism, leaf-to-sapwood area ratio (A(L) : A(S)), needle carbon isotope discrimination (Delta13C) and nitrogen content, and specific leaf area. * Between-population variability was high for most of the hydraulic traits studied, but it was directly associated with climate dryness (defined as a combination of atmospheric moisture demand and availability) only for A(L) : A(S), K(L) and Delta13C. Shoot radial growth and A(L) : A(S) declined with stand development, which is consistent with a strategy to avoid exceedingly low water potentials as tree size increases. In addition, we did not find evidence at the intraspecific level of some associations between hydraulic traits that have been commonly reported across species. * The adjustment of Scots pines hydraulic system to local climatic conditions occurred primarily through modifications of A(L) : A(S) and direct stomatal control, whereas intraspecific variation in vulnerability to embolism and leaf physiology appears to be limited.

Physiological and structural changes in response to altered precipitation regimes in a Mediterranean macchia ecosystem

Significant decrease in precipitation up to 15–20% has been observed in the Mediterranean area in the last two decades as a consequence of climate change. To simulate an analogous scenario, the precipitation regime was altered in replicated experimental plots in a Mediterranean macchia dominated by Arbutus unedo L. species. Two different levels of soil water content (SWC) were obtained during the summer: a mean value of 7% was obtained in water-depleted (D) plots by a partial (−20%) rain exclusion treatment using rain gutters; while a mean value of 14% in SWC was obtained in watered (W) plots supplying water by a sprinkler net. The physiological and structural changes were investigated over the course of two consecutive years by measurement of water potential, gas exchange leaf carbon isotopes, leaf pigments and growth. Apart from short-term responses, mainly related to the elastic response of stomatal conductance to soil water, a more long-lasting and significant acclimation to water availability was observed as a result of the increase in hydraulic resistance in the soil–plant continuum, which persisted even after the return to full water availability during the fall and winter. This response involved the permanent down-regulation of stomatal conductance and photosynthesis, accumulation of photo-protective pigments, as well as a reduction in shoot growth, leaf area index and an increase in shoot-bearing flowers in D plots. This acclimation response prevented the onset of any run-away damage thereby reducing the forest vulnerability to drought. Furthermore, the imposed drought induced a slight increase or no change in intrinsic water-use efficiency (WUEint), as a result of the parallel increase in stomatal and non-stomatal limitations; conversely integrated WUE (i.e., estimated from leaf carbon isotopes) was not affected by drought.

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.

Shaping the role of 'fast' and 'slow' drivers of change in forest-shrubland socio-ecological systems

The temporal speeds and spatial scales at which ecosystem processes operate are often at odds with the scale and speed at which natural resources such as soil, water and vegetation are managed those. Scale mismatches often occur as a result of the time-lag between policy development, implementation and observable changes in natural capital in particular. In this study, we analyse some of the transformations that can occur in complex forest-shrubland socio-ecological systems undergoing biophysical and socioeconomic change. We use a Multiway Factor Analysis (MFA) applied to a representative set of variables to assess changes in components of natural, economic and social capitals over time. Our results indicate similarities among variables and spatial units (i.e. municipalities) which allows us to rank the variables used to describe the SES according to their rapidity of change. The novelty of the proposed framework lies in the fact that the assessment of rapidity-to-change, based on the MFA, takes into account the multivariate relationships among the systems variables, identifying the net rate of change for the whole system, and the relative impact that individual variables exert on the system itself. The aim of this study was to assess the influence of fast and slow variables on the evolution of socio-economic systems based on simplified multivariate procedures applicable to vastly different socio-economic contexts and conditions. This study also contributes to quantitative analysis methods for long-established socio-ecological systems, which may help in designing more effective, and sustainable land management strategies in environmentally sensitive areas.

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.