Michael C. Wiemann

Measuring wood specific gravity…Correctly

The specific gravity (SG) of wood is a measure of the amount of structural material a tree species allocates to support and strength. In recent years, wood specific gravity, traditionally a foresters variable, has become the domain of ecologists exploring the universality of plant functional traits and conservationists estimating global carbon stocks. While these developments have expanded our knowledge and sample of woods, the methodologies employed to measure wood SG have not received as much scrutiny as SGs ecological importance. Here, we reiterate some of the basic principles and methods for measuring the SG of wood to clarify past practices of foresters and ecologists and to identify some of the prominent errors in recent studies and their consequences. In particular, we identify errors in (1) extracting wood samples that are not representative of tree wood, (2) differentiating wood specific gravity from wood density, (3) drying wood samples at temperatures below 100°C and the resulting moisture content complications, and (4) improperly measuring wood volumes. In addition, we introduce a new experimental technique, using applied calculus, for estimating SG when the form of radial variation is known, a method that significantly reduces the effort required to sample a trees wood.

Oligocene mammals from Ethiopia and faunal exchange between Afro-Arabia and Eurasia

Afro-Arabian mammalian communities underwent a marked transition near the Oligocene/Miocene boundary at approximately 24 million years (Myr) ago. Although it is well documented that the endemic paenungulate taxa were replaced by migrants from the Northern Hemisphere, the timing and evolutionary dynamics of this transition have long been a mystery because faunas from about 32 to 24 Myr ago are largely unknown. Here we report a late Oligocene fossil assemblage from Ethiopia, which constrains the migration to postdate 27 Myr ago, and yields new insight into the indigenous faunal dynamics that preceded this event. The fauna is composed of large paenungulate herbivores and reveals not only which earlier taxa persisted into the late Oligocene epoch but also demonstrates that one group, the Proboscidea, underwent a marked diversification. When Eurasian immigrants entered Afro-Arabia, a pattern of winners and losers among the endemics emerged: less diverse taxa such as arsinoitheres became extinct, moderately species-rich groups such as hyracoids continued into the Miocene with reduced diversity, whereas the proboscideans successfully carried their adaptive radiation out of Afro-Arabia and across the world.

FORENSIC ANALYSIS OF CITES-PROTECTED DALBERGIA TIMBER FROM THE AMERICAS

Species identification of logs, planks, and veneers is difficult because they lack the traditional descriptors such as leaves and flowers. An additional challenge is that many transnational shipments have unreliable geographic provenance. Therefore, frequently the lowest taxonomic determination is genus, which allows unscrupulous importers to evade the endangered species laws. In this study we explore whether analysis of wood using a Direct Analysis in Real Time (DART) Time-Of-Flight Mass Spectrometer (TOFMS) can assist in making unequivocal species determinations of Dalbergia. DART TOFMS spectra were collected from the heartwood of eight species of Dalbergia and six other look-alike species. In all, fourteen species comprising of 318 specimens were analyzed and the species chemical profiles were examined by statistical analysis. Dalbergia nigra (CITES Appendix I) was differentiated from D. spruceana; D. stevensonii (Appendix II) was distinguished from D. tucurensis (Appendix III), and all the look-alike timbers could be readily distinguished. Surprisingly, D. retusa (Appendix III) could not be differentiated from D. granadillo, and we postulate that they are synonymous. We conclude that DART TOFMS spectra are useful in making species identifications of American Dalbergia species, and could be a valuable tool for the traditional wood anatomist.

Identification of selected CITES-protected Araucariaceae using DART TOFMS

Determining the species source of logs and planks suspected of being Araucaria araucana (Molina) K.Koch (CITES Appendix I) using traditional wood anatomy has been difficult, because its anatomical features are not diagnostic. Additionally, anatomical studies of Araucaria angustifolia (Bertol.) Kuntze, Araucaria heterophylla (Salisb.) Franco, Agathis australis (D.Don) Lindl., and Wollemia nobilis W.G.Jones, K.D.Hill & J.M.Allen have reported that these taxa have similar and indistinguishable anatomical characters from A. araucana. Transnational shipments of illegal timber obscure their geographic provenance, and therefore identification using wood anatomy alone is insufficient in a criminal proceeding. In this study we examine the macroscopic appearance of selected members of the Araucariaceae and investigate whether analysis of heartwood chemotypes using Direct Analysis in Real Time (DART) Time-of-Flight Mass Spectrometry (TOFMS) is useful for making species determinations. DART TOFMS data were collected from 5 species (n =75 spectra). The spectra were analyzsed statistically using supervised and unsupervised classification algorithms. Results indicate that A. araucana can be distinguished from the look-alike taxa. Another statistical inference of the data suggests that Wollemia nobilis is more similar and within the same clade as Agathis australis. We conclude that DART TOFMS spectra can help in making species determination of the Araucariaceae even when the geographic provenance is unknown.

Nitrogen-fixing symbiosis inferred from stable isotope analysis of fossil tree rings from the Oligocene of Ethiopia

The acquisition of reduced nitrogen (N) is essential for plant life, and plants have developed numerous strategies and symbioses with soil microorganisms to acquire this form of N. The evolutionary history of specific symbiotic relationships of plants with soil bacteria, however, lacks evidence from the fossil record confirming these mutualistic relationships. Here we use modern plants in the N-fixing clade of rosids to develop a geochemical method to assess the presence of symbiotic relationships with N-fixing soil bacteria via δ 15 N values of tree rings. Application of this method to Oligocene tree rings confirms the symbiosis of certain arborescent legumes with N-fixing soil bacteria. The results suggest actinorhizal symbiosis for some Oligocene non-leguminous trees. The specific age, genera, and presence or absence of bacterial symbiosis of these fossil trees provide new information on genera that have maintained or lost the ability to form symbioses in the N-fixing clade. We envision that this approach, as applied to paleoecology, can lead to greater understanding of the response of plant symbioses under variations in atmospheric chemistry for N-limited ecosystems.