Formation and seasonal occurrence of xylem embolism in Alnus cordata.

We investigated the vulnerability of xylem to embolism and the seasonal occurrence of xylem embolism in Italian alder (Alnus cordata Loisel.) by acoustic and hydraulic methods. Wood anatomy was also studied. More than eighty percent of the vessels were less than 50 mm long and no vessels were longer than 120 mm. Mean vessel diameter was 48 μm. Ultrasound acoustic emissions from root and branch segments dehydrating in air followed a similar pattern: in both tissues, emission peaks were recorded when the relative water content of the xylem was around 0.2. In branches dehydrating in air, xylem embolism increased linearly as water potential decreased. In trees in the field, more than 80 percent of hydraulic conductivity was lost in the tree crowns during winter. Recovery from winter embolism occurred mostly before bud burst. In summer, xylem embolism was low (< 30%) and acoustic emissions from roots, stem and branches of trees in the field were also low

Ultrasound emission after cycles of water stress in Picea abies

The relationships among rate of ultrasound acoustic emission (AE), xylem water potential and transpiration rate were investigated in 5-year-old potted saplings of Picea abies Karst. after cycles of water stress. Water-stressed plants displayed minimum xylem water potentials of –3.9 MPa, near-zero transpiration rates and up to 45 AE counts per minute. After rewatering, water-stressed plants no longer produced AEs. Well-watered control plants produced only a small number of ultrasonic AEs. After three cycles of water stress (lasting 24 days in total), it was estimated that about two-thirds of the functional tracheids were embolized. The concomitant reduction in hydraulic conductance was about 70%

Thinning affects water-use efficiency of hardwood saplings naturally recruited in a Pinus radiata D. Don plantation.

Plantations for timber production combine the productive to the nursery function for natural regeneration of native species. Thinning plays a crucial role in recruitment and establishment of native species, by modifying the irradiance regime beneath the canopy cover. It also promotes the secondary succession towards a more stable forest, which is a main goal in protected areas. The present study was carried in a timber plantation of Pinus radiata D. Don, located in the National Park of Cilento and Vallo di Diano (Southern Italy). The ecophysiological responses of saplings of two hardwood species, Quercus cerris L. and Fraxinus ornus L., according to two contrasting (low and high) relative irradiance (RI) regimes were analysed. Leaf and tree ring δ13C values were employed as indicators of water use efficiency (WUE) to explore plant responses to light regime. A preliminary methodological comparison between bulk wood and extracted holocellulose showed no significant differences in δ13C between the two materials. Results indicate lower δ13C values, thus suggesting a lower WUE, at higher RI regimes (corresponding to heavy thinning) for both the studied species. Furthermore, Q. cerris δ13C values are lower than those of F. ornus. These results suggest that, under the same light conditions, the mesophile Q. cerris exhibits a weaker stomatal control than the xerophile F. ornus, which keeps higher WUE. In the mesic environment studied, Q. cerris may overcome F. ornus in the long run, owing to a heavy thinning

Leakage and spillover effects of forest management on carbon storage: theoretical insights from a simple model.

Leakage (spillover) refers to the unintended negative (positive) consequences of forest carbon (C) management in one area on C storage elsewhere. For example, the local C storage benefit of less intensive harvesting in one area may be offset, partly or completely, by intensified harvesting elsewhere in order to meet global timber demand. We present the results of a theoretical study aimed at identifying the key factors determining leakage and spillover, as a prerequisite for more realistic numerical studies.We use a simple model of C storage in managed forest ecosystems and their wood products to derive approximate analytical expressions for the leakage induced by decreasing the harvesting frequency of existing forest, and the spillover induced by establishing new plantations, assuming a fixed total wood production from local and remote (non-local) forests combined.We find that leakage and spillover depend crucially on the growth rates, wood product lifetimes and woody litter decomposition rates of local and remote forests. In particular, our results reveal critical thresholds for leakage and spillover, beyond which effects of forest management on remote C storage exceed local effects. Order of magnitude estimates of leakage indicate its potential importance at global scales

Facing drought in a Mediterranean post-fire community: tissue water relations in species with different life traits.

Bulk shoot water potential, the osmotic component and the bulk modulus of elasticity were measured throughout one growing season in four species co-occurring in a post-fire Mediterranean community in southern Italy: Pinus halepensis, Phillyrea latifolia, Cistus salvifolius and Rosmarinus officinalis. A severe drought occurred throughout the measurement period. Large seasonal fluctuations have been observed for both predawn and afternoon water potential in all species. Although minimum values down to –4 MPa have been measured, plant water potential always recovered to less negative values after drought. Daily amplitude of water potential decreased with increasing plant water stress in all species. In Cistus and Rosmarinus less ability for short-term control of plant water status has been assessed. Osmotic potential at full turgor did not display clear seasonal patterns, with no consistent ranking of species by their osmotic values. In most cases, no osmotic adjustment (lowering of osmotic potentials) and no change in tissue elastic properties were observed in response to increasing summer drought and intensity of water stress

Preliminary observations on haemodynamics during physiological stress conditions following 'double-orifice' mitral valve repair

n/

A global assessment of forest surface albedo and its relationships with climate and atmospheric nitrogen deposition

We present a global assessment of the relationships between the short-wave surface albedo of forests, derived from the MODIS satellite instrument product at 0.5° spatial resolution, with simulated atmospheric nitrogen deposition rates (Ndep), and climatic variables (mean annual temperature Tm and total annual precipitation P), compiled at the same spatial resolution. The analysis was performed on the following five forest plant functional types (PFTs): evergreen needle-leaf forests (ENF); evergreen broad-leaf forests (EBF); deciduous needle-leaf forests (DNF); deciduous broad-leaf forests (DBF); and mixed-forests (MF). Generalized additive models (GAMs) were applied in the exploratory analysis to assess the functional nature of short-wave surface albedo relations to environmental variables. The analysis showed evident correlations of albedo with environmental predictors when data were pooled across PFTs: Tm and Ndep displayed a positive relationship with forest albedo, while a negative relationship was detected with P. These correlations are primarily due to surface albedo differences between conifer and broad-leaf species, and different species geographical distributions. However, the analysis performed within individual PFTs, strengthened by attempts to select ‘pure’ pixels in terms of species composition, showed significant correlations with annual precipitation and nitrogen deposition, pointing toward the potential effect of environmental variables on forest surface albedo at the ecosystem level. Overall, our global assessment emphasizes the importance of elucidating the ecological mechanisms that link environmental conditions and forest canopy properties for an improved parameterization of surface albedo in climate models

La Gestione dei trasporti in emergenza: attività, prodotti e risultati dell'esercitazione nazionale di Protezione Civile in Valtellina

L'articolo riporta l’esperienza maturata dal Laboratorio Mobilità e Trasporti del Politecnico di Milano in qualità di Centro di Competenza per la Gestione e la Sicurezza dei Trasporti per il Dipartimento di Protezione Civile Nazionale durante l’esercitazione nazionale di Protezione Civile in Valtellina. Le attività svolte, i prodotti realizzati e utilizzati ma soprattutto i risultati e l’esperienza emersi da una esercitazione temporalmente estesa e di estremo rilievo in ambito di Protezione Civile, si ritiene siano ancora estremamente attuali e utili come esempio per la gestione dei trasporti in caso di emergenze rilevanti

Stomatal conductance and leaf water potential responses to hydraulic conductance variation in Pinus pinaster seedlings

In this study, tree hydraulic conductance (K tree) was experimentally manipulated to study effects on short-term regulation of stomatal conductance (g s), net photosynthesis (A) and bulk leaf water potential (Ψleaf) in well watered 5–6 years old and 1.2 m tall maritime pine seedlings (Pinus pinaster Ait.). K tree was decreased by notching the stem and increased by progressively excising the root system and stem. Gas exchange was measured in a chamber at constant irradiance, vapour pressure deficit, leaf temperature and ambient CO2 concentration. As expected, we found a strong and positive relationship between g s and K tree (r = 0.92, P = 0.0001) and between A and K tree (r = 0.9, P = 0.0001). In contrast, however, we found that the response of Ψleaf to K tree depended on the direction of change in K tree: increases in K tree caused Ψleaf to decrease from around −1.0 to −0.6 MPa, but reductions in K tree were accompanied by homeostasis in Ψleaf (at −1 MPa). Both of these observations could be explained by an adaptative feedback loop between g s and Ψleaf, with Ψleaf prevented from declining below the cavitation threshold by stomatal closure. Our results are consistent with the hypothesis that the observed stomatal responses were mediated by leaf water status, but they also suggest that the stomatal sensitivity to water status increased dramatically as Ψleaf approached −1 MPa

The utility of MODIS-sPRI for investigating the photosynthetic light-use efficiency in a Mediterranean deciduous forest

The present study investigated the utility of Moderate Resolution Imaging Spectroradiometer (MODIS)-derived sPRI (scaled photochemical reflectance index) and its relationship to photosynthetic light-use efficiency (LUE) calculated from eddy covariance tower data. The analysis was performed over two consecutive years (2003–2004) in a Mediterranean Quercus cerris L. forest site in Italy. Temperature and rainfall conditions differed markedly over the study period, with 2003 being a notable drought year and 2004 a non-drought year. MODIS ocean bands 11 (centred at 531 nm) and 12 (centred at 551 nm) were used for calculating sPRI. LUE exhibited substantial variability within 2003 and 2004, and a moderate relationship between MODIS-sPRI and LUE was observed during the wet year, and for backscattering scenes. This demonstrated the capacity of sPRI to detect xanthophyll cycle activation by vegetation during high light conditions. However, our results show that sPRI should be used with care, particularly under severe water stress conditions, when an increased influence of confounding factors, such canopy structure, illumination, and viewing angles, is observed