Impacts of global atmospheric change on tropical forests.
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Atmosphere↗
Biomedical subjects
Timothy R Baker
Publications and source records attributed to Timothy R Baker.
Regional and phylogenetic variation of wood density across 2456 Neotropical tree species.
Wood density is a crucial variable in carbon accounting programs of both secondary and old-growth tropical forests. It also is the best single descriptor of wood: it correlates with numerous morphological, mechanical, physiological, and ecological properties. To explore the extent to which wood density could be estimated for rare or poorly censused taxa, and possible sources of variation in this trait, we analyzed regional, taxonomic, and phylogenetic variation in wood density among 2456 tree species from Central and South America. Wood density varied over more than one order of magnitude across species, with an overall mean of 0.645 g/cm3. Our geographical analysis showed significant decreases in wood density with increasing altitude and significant differences among low-altitude geographical regions: wet forests of Central America and western Amazonia have significantly lower mean wood density than dry forests of Central and South America, eastern and central Amazonian forests, and the Atlantic forests of Brazil; and eastern Amazonian forests have lower wood densities than the dry forests and the Atlantic forest. A nested analysis of variance showed that 74% of the species-level wood density variation was explained at the genus level, 34% at the Angiosperm Phylogeny Group (APG) family level, and 19% at the APG order level. This indicates that genus-level means give reliable approximations of values of species, except in a few hypervariable genera. We also studied which evolutionary shifts in wood density occurred in the phylogeny of seed plants using a composite phylogenetic tree. Major changes were observed at deep nodes (Eurosid 1), and also in more recent divergences (for instance in the Rhamnoids, Simaroubaceae, and Anacardiaceae). Our unprecedented wood density data set yields consistent guidelines for estimating wood densities when species-level information is lacking and should significantly reduce error in Central and South American carbon accounting programs.
Altitude↗
Narrow-bore sample trapping and chromatography combined with quadrupole/time-of-flight mass spectrometry for ultra-sensitive identification of in vivo and in vitro metabolites.
The identification of in vitro and in vivo metabolites is vital to the discovery and development of new pharmaceutical therapies. Analytical strategies to identify metabolites at different stages of this process vary, but all involve the use of liquid chromatography separations combined with detection via mass spectrometry (HPLC/MS). Reported here is the use of narrow-bore column (0.5-1.0 mm i.d.) trapping of metabolites, followed by back-flushing onto a matching analytical column. Separated metabolites were then identified using quadrupole time-of-flight mass spectrometry (MS) and tandem MS. Metabolites in human plasma and from low-level in vitro incubations, that were not identified using standard HPLC/MS approaches, were characterized using the instrumental configuration described here.
Chromatography, High Pressure Liquid↗
On-line solid phase extraction using the Prospekt-2 coupled with a liquid chromatography/tandem mass spectrometer for the determination of dextromethorphan, dextrorphan and guaifenesin in human plasma.
An on-line liquid chromatography/tandem mass spectrometry (LC-MS/MS) procedure, using the Prospekt- 2 system, was developed and used for the determination of the levels of the active ingredients of cough/cold medications in human plasma matrix. The experimental configuration allows direct plasma injection by performing on- line solid phase extraction (SPE) on small cartridge columns prior to elution of the analyte(s) onto the analytical column and subsequent MS/MS detection. The quantitative analysis of three analytes with differing polarities, dextromethorphan (DEX), dextrorphan (DET) and guaifenesin (GG) in human plasma presented a significant challenge. Using stable-isotope-labeled internal standards for each analyte, the Prospekt-2 on-line methodology was evaluated for sensitivity, suppression, accuracy, precision, linearity, analyst time, analysis time, cost, carryover and ease of use. The lower limit of quantitation for the on-line SPE procedure for DEX, DET and GG was 0.05, 0.05 and 5.0 ng mL(-1), respectively, using a 0.1 mL sample volume. The linear range for DEX and DET was 0.05-50 ng mL(-1) and was 5-5,000 ng mL(-1) for GG. Accuracy and precision data for five different levels of QC samples were collected over three separate days. Accuracy ranged from 90% to 112% for all three analytes, while the precision, as measured by the %RSD, ranged from 1.5% to 16.0%
Antitussive Agents↗
Increasing biomass in Amazonian forest plots.
A previous study by Phillips et al. of changes in the biomass of permanent sample plots in Amazonian forests was used to infer the presence of a regional carbon sink. However, these results generated a vigorous debate about sampling and methodological issues. Therefore we present a new analysis of biomass change in old-growth Amazonian forest plots using updated inventory data. We find that across 59 sites, the above-ground dry biomass in trees that are more than 10 cm in diameter (AGB) has increased since plot establishment by 1.22 +/- 0.43 Mg per hectare per year (ha(-1) yr(-1), where 1 ha = 10(4) m2), or 0.98 +/- 0.38 Mg ha(-1) yr(-1) if individual plot values are weighted by the number of hectare years of monitoring. This significant increase is neither confounded by spatial or temporal variation in wood specific gravity, nor dependent on the allometric equation used to estimate AGB. The conclusion is also robust to uncertainty about diameter measurements for problematic trees: for 34 plots in western Amazon forests a significant increase in AGB is found even with a conservative assumption of zero growth for all trees where diameter measurements were made using optical methods and/or growth rates needed to be estimated following fieldwork. Overall, our results suggest a slightly greater rate of net stand-level change than was reported by Phillips et al. Considering the spatial and temporal scale of sampling and associated studies showing increases in forest growth and stem turnover, the results presented here suggest that the total biomass of these plots has on average increased and that there has been a regional-scale carbon sink in old-growth Amazonian forests during the previous two decades.
Biomass↗
Increasing dominance of large lianas in Amazonian forests.
Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium, but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass, possibly in response to the increasing atmospheric concentrations of carbon dioxide. However, it is unclear whether the recent increase in tree biomass has been accompanied by a shift in community composition. Such changes could reduce or enhance the carbon storage potential of old-growth forests in the long term. Here we show that non-fragmented Amazon forests are experiencing a concerted increase in the density, basal area and mean size of woody climbing plants (lianas). Over the last two decades of the twentieth century the dominance of large lianas relative to trees has increased by 1.7-4.6% a year. Lianas enhance tree mortality and suppress tree growth, so their rapid increase implies that the tropical terrestrial carbon sink may shut down sooner than current models suggest. Predictions of future tropical carbon fluxes will need to account for the changing composition and dynamics of supposedly undisturbed forests.
Analysis of Variance↗