Investigations into free tropospheric new particle formation in the central Canadian arctic during the winter/spring transition as part of TOPSE

In this paper, we investigate the role of in situ new particle production in the central Canadian sub-Arctic and Arctic as part of the TOPSE experiment. Airborne measurements conducted primarily in the free troposphere were made from 50° to 90°W longitude and 60° to 85°N latitude during the period from February to May 2000. Data pertinent to this paper include 3–4 nm diameter (Dp) particles, ultrafine condensation nuclei (Dp \u3e 3 nm), fine particles (0.2 \u3c Dp \u3c 3 μm), and the possible nucleation precursor, sulfuric acid, and its precursor, sulfur dioxide. For data averaged over this period, most species showed little evidence for a latitudinal trend. Fine aerosol number concentrations, however, showed a slight increase with latitude. The evolution of various species concentrations over the period of the study show that fine particles also had a consistent temporal trend, increasing at all altitudes from February to May, whereas sulfur dioxide at the surface tended to peak in late March. Ultrafine condensation nuclei and 3–4 nm particles showed no temporal trends. Little evidence for in situ new particle production was observed during the study, except for one atypical event where SO2concentrations were 3.5 ppbv, 2 orders of magnitude higher than typical levels. This paper cannot address the question of whether the observed condensation nuclei were produced in situ by a low particle production rate or transported from lower latitudes

Complementary resource use by tree species in a rain forest tree plantation

Mixed-species tree plantations, composed of high-value native rain forest timbers, are potential forestry systems for the subtropics and tropics that can provide ecological and production benefits. Choices of rain forest tree species for mixtures are generally based on the concept that assemblages of fast-growing and light-demanding species are less productive than assemblages of species with different shade tolerances. We examined the hypothesis that mixtures of two fast-growing species compete for resources, while mixtures of shade-tolerant and shade-intolerant species are complementary. Ecophysiological characteristics of young trees were determined and analyzed with a physiology-based canopy model (MAESTRA) to test species interactions. Contrary to predictions, there was evidence for complementary interactions between two fast-growing species with respect to nutrient uptake, nutrient use efficiency, and nutrient cycling. Fast-growing Elaeocarpus angustifolius had maximum demand for soil nutrients in summer, the most efficient internal recycling of N, and low P use efficiency at the leaf and whole-plant level and produced a large amount of nutrient-rich litter. In contrast, fast-growing Grevillea robusta had maximum demand for soil nutrients in spring and highest leaf nutrient use efficiency for N and P and produced low-nutrient litter. Thus, mixtures of fast-growing G. robusta and E. angustifolius or G. robusta and slow-growing, shade-tolerant Castanospermum australe may have similar or even greater productivity than monocultures, as light requirement is just one of several factors affecting performance of mixed-species plantations. We conclude that the knowledge gained here will be useful for designing large-scale experimental mixtures and commercial forestry systems in subtropical Australia and elsewhere

Tropolone Content of Increment Cores as an Indicator of Decay Resistance in Western Redcedar

The high decay resistance of western redeedar (Thuja plicata Donn) is due to the presence of toxic extractives, called tropolones, in the heartwood. Therefore, tropolone content may be used as an indicator of decay resistance. With increment core-sized samples of western redcedar heartwood, we used gas chromatography to measure tropolone content and soil block tests to assess decay resistance. Results showed that decay resistance was extremely variable at low tropolone levels, but was uniformly high at tropolone levels of 0.25% or greater. Analyzing tropolone content of western redeedar increment cores is a useful way to assess decay resistance of standing trees

Interpreting genotype-by-environment interaction for biomass production in hybrid poplars under short-rotation coppice in Mediterranean environments

Understanding genotype × environment interaction (GEI) is crucial to optimize the deployment of clonal material to field conditions in short‐rotation coppice poplar plantations. Hybrid poplars are grown for biomass production under a wide range of climatic and edaphic conditions, but their adaptive performance in Mediterranean areas remains poorly characterized. In this work, site regression (SREG) and factorial regression mixed models are combined to gain insight into the nature and causes underlying GEI for biomass production of hybrid poplar clones. SREG addresses the issue of clonal recommendation in multi‐environment trials through a biplot representation that visually identifies superior genotypes. Factorial regression, alternatively, involves a description of clonal reaction to the environment in terms of physical variables that directly affect productivity. Initially, SREG aided in identifying cross‐over interactions that often involved hybrids of different taxonomic background. Factorial regression then selected latitude, mean temperature of the vegetative period (MTVP) and soil sand content as main site factors responsible for differential clonal adaptation. Genotypic responses depended strongly on taxonomic background: P. deltoides Bartr. ex Marsh. × P. nigra L. clones showed an overall positive sensitivity to increased MTVP and negative sensitivity to increased sand content, whereas the opposite occurred for P. trichocarpa Torr. & Gray × P. deltoides clones; the three‐cross hybrid [(P. deltoides × P. trichocarpa) × P. nigra] often displayed an intermediate performance. This information can contribute toward the identification and biological understanding of adaptive characteristics relevant for poplar breeding in Mediterranean conditions and facilitate clonal recommendation at eco‐regional level.This research was funded by MINECO (Spain) throughout the project RTA2008-00025-C02-01 and RTA2011-00006-00-00. We also acknowledge the collaboration of project AGL2009-11006. We would like to thank the public company SOMACYL for hosting one of the experimental plots. We are also grateful to Juan Pablo de la Iglesia and Ana Parras for their technical support throughout the experiment

Effectiveness and Cost Effectiveness of Expanding Harm Reduction and Antiretroviral Therapy in a Mixed HIV Epidemic: A Modeling Analysis for Ukraine

A cost-effectiveness study by Sabina Alistar and colleagues evaluates the effectiveness and cost effectiveness of different levels of investment in methadone, ART, or both, in the mixed HIV epidemic in Ukraine