1,721,039 research outputs found
Impact of climate change on Mediterranean forests: acclimation or vulnerability? Geophysical Research Abstracts 10 07154.
No full textSilvaCuore: a web-application to monitor the health status of Italian forests
Full text linkIn the current context of climate change, this paper provides a brief overview of climate-vegetation interactions in the Mediterranean basin, where global warming and aridification trends are predicted to intensify. Rising temperatures coupled with extreme drought events have notable impacts on forest ecosystems, triggering dieback and mortality phenomena worldwide. The health status of forest vegetation may be assessed by either ground surveys or remote sensing. Several investigations of declining oak forests in the Apennine region have shown that the drought vulnerability of Mediterranean oaks is dependent on differences in access to deep soil water pools, which can be related to differences in rooting depth, tree size and growth rate. Forest dieback is widely reported in Italy, but the extent and overall distribution of this phenomenon have not yet been well defined. Thus, understanding the future dynamics of forest stands has several key objectives: inventorying declining forest stands to gain insight into the phenomenon and create a national-level database; locating these stands to allow monitoring of their evolution over time; and monitoring to allow planning of mitigation measures, as well as recovery and adaptation strategies. This background led to the implementation of SilvaCuore, the first web application designed in Italy to report forest health status. Silvacuore is a web application developed with the aim of improving the link between citizens and the scientific community by contributing to the development of a valuable scientific database. The direct involvement of citizens in forest preservation offers an interesting perspective because the innovative use of technology can tap into citizens’ growing enthusiasm for environmental topics. Thus, SilvaCuore may be viewed from a dual perspective as a resource for the scientific community and as a unique opportunity for citizens to take an active role in research activities (Citizen Science project)
Variation in the access to deep soil water pools explains tree-to-tree differences in drought-triggered dieback of Mediterranean oaks
Full text linkIndividual differences in the access to deep soil water pools may explain the differential damage among coexisting, conspecific trees as a consequence of drought-induced dieback. We addressed this issue by comparing the responses to a severe drought of three Mediterranean oak species with different drought tolerance, Quercus pubescens L. and Quercus frainetto Ten., mainly thriving at xeric and mesic sites, respectively, and Quercus cerris L., which dominates at intermediate sites. For each species, we compared coexisting declining (D) and non-declining (ND) trees. The stable isotope composition (δ2H, δ18O) of xylem and soil water was used to infer a differential use of soil water sources. We also measured tree size and radial growth to quantify the long-term divergence of wood production between D and ND trees and non-structural carbohydrates (NSCs) in sapwood to evaluate if D trees presented lower NSC values. The ND trees had access to deeper soil water than D trees except in Q. frainetto, as indicated by significantly more depleted xylem water values. However, a strong δ2H offset between soil and xylem water isotopes observed in peak summer could suggest that both tree types were not physiologically active under extreme drought conditions. Alternative processes causing deuterium fractionation, however, could not be ruled out. Tree height and recent (last 15-25 years) growth rates in all species studied were lower in D than in ND trees by 22 and 44%, respectively. Lastly, there was not a consistent pattern of NSC sapwood concentration; in Q. pubescens, it was higher in ND trees while in Q. frainetto, the D trees were the ones exhibiting the higher NSC concentration. We conclude that the vulnerability to drought among conspecific Mediterranean oaks depends on the differential access to deep soil water pools, which may be related to differences in rooting depth, tree size and growth rate
A Novel Simplified Protocol for Pre-Processing Whole Wood Samples for Stable Isotope Analysis in Tree Rings
No full textIn the context of climate change, the stable isotope analysis of tree rings may play a crucial role in deciphering the eco-physiological mechanisms underlying forest decline and dieback phenomena. However, this technique is often considered expensive, time-consuming, and with several methodological constraints. Specifically, milling and transferring the material from jars to vials during the different steps of sample preparation involve risk of contamination among samples and loss of sample material. When dealing with declining trees (i.e., trees affected by loss of vitality with strong percentage of defoliation and reduction in growth) and trees subjected to extreme events or negative pointer years (characterized by extremely narrow ring) the sample preparation is particularly difficult because of scarce amount of wood material. In such a case, pooling rings from several years to achieve the minimum weight of wood is often necessary, thus losing information at the annual resolution. In order to overcome such limitations, we developed a novel protocol for quick and accurate whole-wood pre-processing, testing it on oak tree rings of different widths taken from living trees. The main novelty introduced by our protocol was freezing tree-ring samples at −80 °C and milling multiple samples at a time by using a 24-tube plate. The results showed that our novel simplified protocol significantly reduced the pre-processing time with respect to the standard protocol (12 vs. 284 sec/sample), while achieving the same wood particle size, limiting the loss of wood material and reducing the risk of contamination among samples
Growth patterns of Pinus sylvestris across Europe. A functional analysis using the HYDRALL model
No full textDrought and heat waves, cues for an adaptive silviculture
Full text linkWe propose some ideas for an adaptive silviculture in the Mediterranean biogeographic
region that could assist in shaping forests which are less vulnerable
to extreme climatic events, such as those drought and heat waves that are
expected to be more intense and frequent in the future. We discuss about silvicultural
approaches that would aim to: regulate competition and densitydependent
effects; enhance functional diversity; increase the complexity of
forest communities. These approaches are especially advisable in the Mediterranean
region, which is a hotspot for climate change and where forests have
been exploited for many centuries and are only recently taking advantage of a
recovery phase
Correction: Xylem Functional Traits as Indicators of Health in Mediterranean Forests (Current Forestry Reports, (2020), 6, 3, (220-236), 10.1007/s40725-020-00124-5)
No full textThe original version of this article unfortunately contained a mistake. The figures previously used are the old version and some symbols in the figure captions were displayed incorrectly. Final versions of figures with their captions are provided here. The original article has been corrected. (Figure presented.)
Xylem Functional Traits as Indicators of Health in Mediterranean Forests
Full text linkPurpose of Review: We conducted a literature survey and meta-analysis to assess, in Mediterranean forests impacted by drought, the role of xylem functional traits as indicators of tree health, and their potential to adjust over a range of climatic conditions to support tree performance and survival. We aimed also to depict the geographic variability of xylem functional traits among Mediterranean forest trees as a tool for regional scale-oriented vulnerability assessment. Recent Findings: Associations were investigated among xylem functional traits, hydraulic safety, and whole plant drought resistance for tree species in Mediterranean-type climates. Variable data were available from a number of study cases of Mediterranean forest communities impacted by intense drought, wherein tree growth and xylem functional traits were investigated along with tree decline and dieback episodes. Variable data were available from a number of studies that analyzed xylem trait adjustments to climatic conditions at different temporal scales. Summary: We observed differing growth patterns and xylem conduit area responses in healthy and unhealthy trees and we sketched hydraulic strategies that may fit observed patterns. Overall, a clear role of xylem conduit size as stand-alone tree health indicator did not emerge. We showed that xylem traits may adjust along different temporal scales and may support the performance and health of Mediterranean tree species over a range of climatic conditions. We outlined substantial geographic variability in xylem traits across the Mediterranean region, suggesting patchy responses to increasing drought. Knowledge gaps and needed lines of research are highlighted
Stomatal conductance and leaf water potential responses to hydraulic resistance variation in Pinus pinaster seedlings
No full textIn 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 (Psi(leaf)) 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 Psi(leaf) to K-tree depended on the direction of change in K-tree: increases in K-tree caused Psi(leaf) to decrease from around -1.0 to -0.6 MPa, but reductions in K-tree were accompanied by homeostasis in Psi(leaf) (at -1 MPa). Both of these observations could be explained by an adaptative feedback loop between g(s) and Psi(leaf), with Psi(leaf) 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 Psi(leaf) approached -1 MPa
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