Climate extremes, such as abnormally dry and wet conditions, generate abrupt shifts in tree growth, a situation which is expected to increase under predicted climate conditions. Thus, it is crucial ...to understand factors determining short‐ and long‐term tree performance in response to higher frequency and intensity of climate extremes.
We evaluated how three successive droughts and wet years influenced short‐ and long‐term growth of six dominant Iberian tree species. Within species variation in growth response to repeated dry and wet years was evaluated as a function of individual traits related to resource and water use (diameter at breast height DBH, wood density WD and specific leaf area SLA) and tree‐to‐tree competition across climatically contrasted populations. Furthermore, we assessed how short‐term accumulated impacts of the repeated dry and wet years influenced long‐term growth performance.
All species showed strong short‐term growth decreases and enhancements due to repeated dry and wet years. However, patterns of accumulated growth decreases (AcGD) and enhancements (AcGE) across climatically contrasting populations were species‐specific. Furthermore, individual trait data were weakly associated with either AcGD or AcGE and the few relevant associations were found for conifers. Intraspecific variations in tree growth responses to repeated climates extremes were large, and not explained by intraspecific variability in SLA and WD. Accumulated impacts of repeated dry and wet years were related to long‐term growth trends, showing how the recurrence of climate extremes can determine growth trajectories. The relationships of AcGD and AcGE with long‐term growth trends were more common in conifers species.
Synthesis. Repeated climate extremes do not only cause short‐term growth reductions and enhancements but also determine long‐term tree growth trajectories. This result shows how repeated droughts can lead to growth decline. Conifers were more susceptible to the accumulated effects of extreme weather events indicating that in the future, more intense and frequent climate extremes will alter growth performance in forests dominated by these species.
Repeated climate extremes do not only cause short‐term growth reductions and enhancements but also determine long‐term tree growth trajectories. This result shows how repeated droughts can lead to growth decline. Conifers were more susceptible to the accumulated effects of extreme weather events indicating that in the future, more intense and frequent climate extremes will alter growth performance in forests dominated by these species.
Proactive silviculture treatments (e.g., thinning) may increase C sequestration contributing to climate change mitigation, although, there are still questions about this effect in Mediterranean pine ...forests. The aim of this research was to quantify the storage of biomass and soil organic carbon in Pinus forests along a climatic gradient from North to South of the Iberian Peninsula. Nine experimental Pinus spp trials were selected along a latitudinal gradient from the pre-Pyrenees to southern Spain. At each location, a homogeneous area was used as the operational scale, and three thinning intensity treatments: unthinned or control (C), intermediate thinning (LT, removal of 30–40% of the initial basal area) and heavy thinning (HT, removal of 50–60%) were conducted. Growth per unit area (e.g., expressed as basal area increment-BAI), biomass, and Soil Organic Carbon (SOC) were measured as well as three sets of environmental variables (climate, soil water availability and soil chemical and physical characteristics). One-way ANOVA and Structural Equation Modelling (SEM) were used to study the effect of thinning and environmental variables on C sequestration. Biomass and growth per unit area were higher in the control than in the thinning treatments, although differences were only significant for P. halepensis. Radial growth recovered after thinning in all species, but it was faster in the HT treatments. Soil organic carbon (SOC10, 0–10 cm depth) was higher in the HT treatments for P. halepensis and P. sylvestris, but not for P. nigra. SEM showed that Pinus stands of the studied species were beneficed by HT thinning, recovering their growth quickly. The resulting model explained 72% of the variation in SOC10 content, and 89% of the variation in silvicultural condition (basal area and density) after thinning. SOC10 was better related to climate than to silvicultural treatments. On the other hand, soil chemical and physical characteristics did not show significant influence over SOC10- Soil water availability was the latent variable with the highest influence over SOC10. This work is a new contribution that shows the need for forest managers to integrate silviculture and C sequestration in Mediterranean pine plantations.
Adaptive forest management (AFM) is an urgent need because of the uncertainty regarding how changes in the climate will affect the structure, composition and function of forests during the next ...decades. Current research initiatives for the long-term monitoring of impacts of silviculture are scattered and not integrated into research networks, with the consequent losses of opportunities and capacity for action. To increase the scientific and practical impacts of these experiences, it is necessary to establish logical frameworks that harmonize the information and help us to define the most appropriate treatments. In this context, a number of research groups in Spain have produced research achievements and know-how during the last decades that can allow for the improvement in AFM. These groups address the issue of AFM from different fields, such as ecophysiology, ecohydrology and forest ecology, thus resulting in valuable but dispersed expertise. The main objective of this work is to introduce a comprehensive strategy aimed to study the implementation of AFM in Spain. As a first step, a network of 34 experimental sites managed by 14 different research groups is proposed and justified. As a second step, the most important AFM impacts on Mediterranean pines, as one of the most extended natural and planted forest types in Spain, are presented. Finally, open questions dealing with key aspects when attempting to implement an AFM framework are discussed. This study is expected to contribute to better outlining the procedures and steps needed to implement regional frameworks for AFM.
Thinning influence on litterfall chemical composition (N, P, K, Ca and Mg) was studied for 30 months in two contrasting
Pinus sylvestris L. stands in the western Pyrenees mountain range (Northern ...Spain): Aspurz (625
m.a.s.l, high productivity, Mediterranean climate) and Garde (1335
m.a.s.l, low productivity, continental climate). Two different thinning intensities were carried out by removing 20% and 30% of pre-thinning basal area. In accordance with site quality differences between sites N, K, Ca and Mg total soil returns via litterfall were significantly higher in Aspurz than in Garde. However, P, K, Ca and Mg concentrations were higher in Garde and N higher in Aspurz. Changes in nutrient concentrations over time varied depending on litterfall fractions, showing a variety of patterns; seasonal (N, P, K) or erratic patterns (Ca, Mg) in Aspurz, and seasonal (N, P), biannual (Ca, Mg) or erratic (K) patterns in Garde. In addition to these patterns, differences in nutrient concentrations between years were found in needle litter in Aspurz but not in Garde. Nitrogen returns to forest floor via litterfall were more constant in Aspurz but followed a pulse dynamics in Garde, with the opposite for P, due to important returns from the miscellaneous fraction in the Mediterranean site. Thinning reduced nutrient returns via litterfall in both sites, but significant differences were found only in summer. These results suggest that Aspurz (Mediterranean stand) is more sensitive in the short-term to human intervention than Garde (continental stand) and therefore site-specific forest management plans should be used within more general region-wide plans in order to ensure sustainability of forests.
Needle chemical composition was measured, and nutrient resorption, nutrient-use efficiency (NUE), and other indexes were estimated for 24 months in two contrasting natural Pinus sylvestris L. forests ...in the western Pyrenees in Spain. For each location (Aspurz, 650 m elevation, 7% slope; Garde, 1335 m elevation, 40% slope), there were three reference plots (P0), three plots with 20% of the basal area removed (P20), and three with 30% of the basal area removed (P30). Needle P, Ca, and Mg concentrations were higher in Garde, but N concentration was higher for Aspurz, without differences for K. Nutrient-resorption efficiency of P was higher in Aspurz, of Mg higher in Garde, and there were no differences between sites in N and K. Nutrient-resorption proficiency was significantly higher in the site with lower soil nutrient availability, i.e., for P, Ca, and Mg in Aspurz, but N in Garde (no differences in K); this may be an indicator of nutrient conservation strategy. Annual nutrient productivity (A) was higher for all nutrients in Aspurz, whereas the mean residence time (MRT) was higher in Garde in all nutrients but P. NUE was significantly higher in Garde for all nutrients but P, which was more efficiently used in Aspurz. In both sites, N, P, and K concentrations were higher in the 2002 cohort, Ca in the 2000 cohort, and maximum Mg was found in the 2001 cohort. Thinning caused a reduction of Mg concentration in the 2001 cohort in Aspurz, an increase of Ca resorption proficiency in Aspurz and Mg resorption at both sites, and reduction of P, K, and Mg nutrient response efficiency (NRE) in Garde. Thinning may have caused an increase of the C:Mg ratio through facilitating the development of more biosynthesis apparatus in a more illuminated canopy, but it seemed not to affect resorption in a significant way. Changes in NRE in Garde after thinning show that forest management can affect how trees use nutrients. Our results indicate that the strategy to optimize NUE is different in each stand. In Aspurz (a Mediterranean ecosystem), pine trees carried out resorption more efficiently, while in Garde (a continental forest), trees used nutrients for longer periods of time and reduced their efficiency in using the available soil nutrients after reduced competition by thinning.
Litterfall production was studied for 30 months in two contrasting
Pinus sylvestris L. stands in the western Pyrenees managed under two low thinning intensities: Aspurz (625
m a.s.l., Mediterranean ...climate) and Garde (1335
m a.s.l., continental climate). Nine 0.12
ha plots per site were set up with three treatments three times repeated: removal of 0% (not thinned, P0), 20% (P20) and 30% (P30) of initial basal area. Total litterfall was significantly higher in Aspurz (5533
kg
ha
−1
year
−1) than in Garde (3986
kg
ha
−1
year
−1). Maximum annual needle fall values were in September (Aspurz) or October (Aspurz and Garde), and second order peaks were in June or July at both sites. In both sites, cones and other pine organs (e.g., seeds, inflorescences) showed the same seasonal patterns, while bark and branches, affected by sporadic occurrence of storms or snowfalls, followed no clear pattern. Low thinning effects were site-dependent (e.g., needles; Aspurz, P0
>
(P20
=
P30); Garde, P0
>
P20
>
P30) due to between site differences in stand structure. Thus, more dominant and codominant trees (i.e., high litterfall producers) were felled in P30 than in P20 in Garde relative to Aspurz. Needle fall in Aspurz showed unique significant positive correlations with days of dryness and moisture deficit, probably reflecting its Mediterranean climate. However, relative to Aspurz, Garde exhibited significant retarded responses of total litterfall and needle fall to changes in air temperature, soil temperature and soil moisture suggesting in part that Garde's needles are more resistant to climatic stress. Furthermore, litterfall was better predicted in Aspurz than in Garde, partly due to the greater influence of sporadic windstorms and snowstorms in Garde. It appears that in these Pyrenean
P. sylvestris stands, site-dependent climatic variables have an important control on litterfall. At the local scale, however, stand structure influences effects of thinning on litterfall.
Forest harvesting may interfere with long-term ecosystem structure and function and different harvesting methods will differ in their effects on soil fertility (e.g. whole-tree harvesting versus stem ...removal). In the case of thinning, effects of thinning intensity, rotation length and site quality must be assessed in order to formulate sustainable management practices. Assessment of the relative impact of these practices is difficult, however, given the long temporal scales involved. In this study, we implement a process-based model of nutrient cycling to evaluate temporal changes in ecosystem nutrient dynamics of managed and non-managed forest stands. The model was specifically designed to asses differences between two contrasting site-quality
Pinus sylvestris L. stands in the western Pyrenees (Navarre, Spain) managed under two thinning intensities. The model describes the main nutrient fluxes in the stand: litterfall, decomposition, retranslocation, root uptake and management type, and it was parameterized and verified with 3 years of field data. After model verification we examined the effects of thinning intensity, thinning frequency and harvesting method (whole-tree versus stem removal) on potential nutrient losses. The results suggest that in this heterogeneous region, sustainability of forestry practices is strongly site dependent. N and P were particularly sensitive to overexploitation and in no case could whole-tree removal be recommended as it may have a strong negative effect on nutrient reserves. In relation to previous nutrient cycling models, our model offers a satisfactory compromise between simplicity, biological realism and predictability, and it proved to be a useful tool to predict short-term changes in nutrient reserves as well as to evaluate possible negative effects of applying current thinning prescriptions on long-term sustainability of managed forests in the western Pyrenees.
FR171456 is a natural product with cholesterol-lowering properties in animal models, but its molecular target is unknown, which hinders further drug development. Here we show that FR171456 ...specifically targets the sterol-4-alpha-carboxylate-3-dehydrogenase (Saccharomyces cerevisiae--Erg26p, Homo sapiens--NSDHL (NAD(P) dependent steroid dehydrogenase-like)), an essential enzyme in the ergosterol/cholesterol biosynthesis pathway. FR171456 significantly alters the levels of cholesterol pathway intermediates in human and yeast cells. Genome-wide yeast haploinsufficiency profiling experiments highlight the erg26/ERG26 strain, and multiple mutations in ERG26 confer resistance to FR171456 in growth and enzyme assays. Some of these ERG26 mutations likely alter Erg26 binding to FR171456, based on a model of Erg26. Finally, we show that FR171456 inhibits an artificial Hepatitis C viral replicon, and has broad antifungal activity, suggesting potential additional utility as an anti-infective. The discovery of the target and binding site of FR171456 within the target will aid further development of this compound.
Genetic analysis of selected genome regions of hepatitis A virus (HAV) suggested that distinct genotypes of HAV could be found in different geographical regions. At least seven HAV genotypes have ...been identified all over the world, including four human genotypes (I, II, III, and VII) and three simian strains (IV, V, and VI). Phylogenetic analysis using full-length VP1 sequences revealed that human strain 9F94 has a close genetic relation with strain SLF-88 (sub-genotype VII). Nevertheless, the same analysis using full-length VP2 or VP3 sequences revealed that strain 9F94 has a close genetic relation with strain MBB (sub-genotype IB). To test the possibility of genetic recombination, phylogenetic studies were carried out, revealing that a crossing over had taken place in the VP1 capsid protein. These findings indicate that capsid-recombination can play a significant role in shaping the genetic diversity of HAV and, as such, can have important implications for its evolution, biology, and control.
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