Asymmetric effects of hydroclimate extremes on eastern US tree growth: Implications on current demographic shifts and climate variability.

Forests around the world are experiencing changes due to climate variability and human land use. How these changes interact and influence the vulnerability of forests are not well understood. In the eastern United States, well-documented anthropogenic disturbances and land-use decisions, such as logging and fire suppression, have influenced forest species assemblages, leading to a demographic shift from forests dominated by xeric species to those dominated by mesic species. Contemporarily, the climate has changed and is expected to continue to warm and produce higher evaporative demand, imposing stronger drought stress on forest communities. Here, we use an extensive network of tree-ring records from common hardwood species across ~100 sites and ~1300 trees in the eastern United States to examine the magnitude of growth response to both wet and dry climate extremes. We find that growth reductions during drought exceed the positive growth response to pluvials. Mesic species such as Liriodendron tulipifera and Acer saccharum, which are becoming more dominant, are more sensitive to drought than more xeric species, such as oaks (Quercus) and hickory (Carya), especially at moderate and extreme drought intensities. Although more extreme droughts produce a larger annual growth reduction, mild droughts resulted in the largest cumulative growth decreases due to their higher frequency. When using global climate model projections, all scenarios show drought frequency increasing substantially (3-9 times more likely) by 2100. Thus, the ongoing demographic shift toward more mesic species in the eastern United States combined with drier conditions results in larger drought-induced growth declines, suggesting that drought will have an even larger impact on aboveground carbon uptake in the future in the eastern United States.

Old forests and old carbon: A case study on the stand dynamics and longevity of aboveground carbon.

Most information on the ecology of oak-dominated forests in Europe comes from forests altered for centuries because remnants of old-growth forests are rare. Disturbance and recruitment regimes in old-growth forests provide information on forest dynamics and their effects on long-term carbon storage. In an old-growth Quercus petraea forest in northwestern Spain, we inventoried three plots and extracted cores from 166 live and dead trees across canopy classes (DBH ≥ 5 cm). We reconstructed disturbance dynamics for the last 500 years from tree-ring widths. We also reconstructed past dynamics of above ground biomass (AGB) and recent AGB accumulation rates at stand level using allometric equations. From these data, we present a new tree-ring-based approach to estimate the age of carbon stored in AGB. The oldest tree was at least 568 years, making it the oldest known precisely-dated oak to date and one of the oldest broadleaved trees in the Northern Hemisphere. All plots contained trees over 400 years old. The disturbance regime was dominated by small, frequent releases with just a few more intense disturbances that affected ≤20% of trees. Oak recruitment was variable but rather continuous for 500 years. Carbon turnover times ranged between 153 and 229 years and mean carbon ages between 108 and 167 years. Over 50% of AGB (150 Mg·ha-1) persisted ≥100 years and up to 21% of AGB (77 Mg·ha-1) ≥300 years. Low disturbance rates and low productivity maintained current canopy oak dominance. Absence of management or stand-replacing disturbances over the last 500 years resulted in high forest stability, long carbon turnover times and long mean carbon ages. Observed dynamics and the absence of shade-tolerant species suggest that oak dominance could continue in the future. Our estimations of long-term carbon storage at centennial scales in unmanaged old-growth forests highlights the importance of management and natural disturbances for the global carbon cycle.

Synergistic abiotic and biotic stressors explain widespread decline of Pinus pinaster in a mixed forest.

Global change potentially increases forest vulnerability. Different abiotic and biotic factors may interact to cause forest decline and accelerated tree mortality. We studied a mixed Mediterranean continental forest where Pinus pinaster Ait. (maritime pine) shows widespread decline to analyse the role of different abiotic and biotic factors on health status and growth dynamics both at the individual and plot levels. We also analysed stand composition and regeneration of tree species to check whether there is a change in species dominance. Fungal pathogens were seldom present and we detected no pervasive fungi or insect infestation and no presence of pathogens like Heterobasidion or Phytophthora. Infection of hemiparasite plants like Viscum album L. (mistletoe) can reduce leaf area and its abundance is generally considered an expression of host decline. Yet, the existence among declining trees of high defoliation levels without mistletoe, but not vice versa, suggests that defoliation in response to some abiotic stressor could be a predisposing factor preceding mistletoe infection. Compared to healthy trees, declining and dead trees exhibited higher defoliation rates, smaller needles and lower recent growth with steeper negative trends. Dead and declining trees showed similar negative growth trends since the early 1990s droughts, which we interpreted as early warning signals anticipating mortality of currently declining trees in the near future. Mortality of maritime pine extending across all size classes, the lower presence of this species in the smallest size classes and its lack of regeneration suggest it is potentially losing its current dominance and being replaced by other co-occurring, more drought-tolerant species. Our results unravelled that maritime pine decline seems to be mainly driven by a combination of predisposing and inciting abiotic factors (microenvironment and drought stress) and biotic factors (mistletoe). The absence of widespread fungal pathogens suggests that they may have a minor role on pine decline acting only eventually as contributing factors. Although there could be other interrelations among factors or other biotic agents at play, our results strongly suggest that water stress plays a major role in the decline process of the dominant species on an ecosystem with strong land-use legacies.

Analysis of macrolide antibiotics in water by magnetic solid-phase extraction and liquid chromatography-tandem mass spectrometry.

Macrolides are one of the most commonly used families of antibiotics employed in human and veterinary treatment. These compounds are considered emerging contaminants with potential ecological and human health risks that could be present in surface water. This paper describes the development and application of a simple and efficient extraction procedure for the determination of tilmicosin; erythromycin, tylosin and erythromycin-H2O from water samples. Sample extraction was carried out using magnetic solid-phase extraction using oleate functionalized magnetic nanoparticles followed by LC-MS/MS analysis. The effects of several parameters on the extraction efficiency of MLs from water were evaluated. The recovery results obtained were >84% for most of the compounds, except for erytromycin. The LOD and LOQ values ranged from 11.5 to 26ngL-1 and from 34 to 77ngL-1, respectively. The selected method was applied to monitor these contaminants in water samples from different sources. Tilmicosin and tylosin were not detected in any of the samples, but erythromycin and erythromycin-H2O were found in 50% of the surface water samples at levels from

Rapid multiresidue determination of bisphenol analogues in soil with on-line derivatization.

Bisphenol analogues are compounds extensively used which have been potentially linked to adverse health effects. Nevertheless, few studies reported the analysis of compounds, other than bisphenol A, in environmental solid samples and none in soil samples. In this study, a rapid and sensitive analytical method is presented for the simultaneous determination of 13 bisphenols in soil samples. The method combines ultrasonic-assisted extraction of samples placed in small columns and GC-MS/MS analysis. Manual and on-line derivatizations were compared and results showed that significant higher chromatographic responses were achieved with on-line derivatization. Different parameters such as the quantity of derivatization agent, the extraction solvent, or the extraction time were assayed. The detection limits for all target bisphenols ranged from 0.04 to 0.27 ng g-1, for BPC and BPA, respectively. Analysis of spiked soil samples gave satisfactory recovery results, from 70 to 111%, for all the compounds. Finally, the validated method was applied to soil samples from several Spanish areas, and 3 of the 13 target bisphenols (BPAF, BPF, and BPA) were detected, although only BPF and BPA could be quantified with levels up to 127 ng g-1. Graphical abstract Schematic diagram of the developed method for the determination of bisphenol analogues.