Akira Kagawa

Stable carbon isotopes of tree rings as a tool to pinpoint the geographic origin of timber

Illegal logging is a major cause of worldwide deforestation, and demands for scientific methods to identify the geographic origin of timber are increasing. “Dendroprovenancing” is one such method, in which the origin of unknown wood is estimated by calculating correlations of the ring-width series of the unknown wood with reference trees of known geographic origins. We applied the dendroprovenancing method to carbon isotope network data of pinyon pines (Pinus edulis and Pinus monophylla) from the southwestern United States to test the efficacy of using a carbon isotope time series for provenancing wood. First, we calculated correlations (t values) between test trees temporarily assumed to be of unknown origin and reference trees from 13 surrounding sites. Then, we plotted the t values on a map. When provenancing was successful, the tested trees showed the strongest correlation with reference trees from sites close to the actual origins of the test trees, and the correlations decreased with the distance between the original sites of test and reference trees. This conical distribution of t values enabled provenancing of wood with precision of 114–304 km. Although isotope measurement is more expensive and laborious than ring-width measurement, our tests of provenancing pinyon pines in the southwestern United States showed a higher success rate with carbon isotopes.

Seasonal variations in the stable oxygen isotope ratio of wood cellulose reveal annual rings of trees in a Central Amazon terra firme forest

In Amazonian non-flooded forests with a moderate dry season, many trees do not form anatomically definite annual rings. Alternative indicators of annual rings, such as the oxygen (δ18Owc) and carbon stable isotope ratios of wood cellulose (δ13Cwc), have been proposed; however, their applicability in Amazonian forests remains unclear. We examined seasonal variations in the δ18Owc and δ13Cwc of three common species (Eschweileracoriacea, Iryantheracoriacea, and Protiumhebetatum) in Manaus, Brazil (Central Amazon). E. coriacea was also sampled in two other regions to determine the synchronicity of the isotopic signals among different regions. The annual cyclicity of δ18Owc variation was cross-checked by 14C dating. The δ18Owc showed distinct seasonal variations that matched the amplitude observed in the δ18O of precipitation, whereas seasonal δ13Cwc variations were less distinct in most cases. The δ18Owc variation patterns were similar within and between some individual trees in Manaus. However, the δ18Owc patterns of E. coriacea differed by region. The ages of some samples estimated from the δ18Owc cycles were offset from the ages estimated by 14C dating. In the case of E. coriacea, this phenomenon suggested that missing or wedging rings may occur frequently even in well-grown individuals. Successful cross-dating may be facilitated by establishing δ18Owc master chronologies at both seasonal and inter-annual scales for tree species with distinct annual rings in each region.

Inorganic elements in typical Japanese trees for woody biomass fuel

The inorganic element contents of trees were measured to evaluate the safety of using wood biomass as thermal power generation fuel. Twelve species of typical conifer trees and 17 species of typical broad-leaved trees in Japan plus 9 species of commonly imported trees were selected and analyzed for the main inorganic elements and several trace elements that are potentially harmful in combustion ash. The ash content in bark, especially in the inner bark, was higher than that in wood, but the highest concentration was in the leaves. In almost all parts of the trees, the order of inorganic element concentration was calcium ≥ potassium ≥ magnesium ≥ sulfur ≥ phosphorous. Among the trace elements, the boron content was high and the mercury content was recorded as being high in conifer bark.

Seasonal changes of δD and δ18O in tree-ring cellulose of Quercus crispula suggest a change in post-photosynthetic processes during earlywood growth

Leaf photosynthetic and post-photosynthetic processes modulate the isotope ratios of tree-ring cellulose. Post-photosynthetic processes, such as the remobilization of stored starch in early spring, are important to understanding the mechanisms of xylem formation in tree stems; however, untangling the isotope ratio signals of photosynthetic and post-photosynthetic processes imprinted on tree rings is difficult. Portions of carbon-bound hydrogen and oxygen atoms are exchanged with medium water during post-photosynthetic processes. We investigated the δD and δ18O values of tree-ring cellulose using Quercus crispula Blume trees in two different habitats to evaluate seasonal changes in the exchange rate (f-value) of hydrogen or oxygen with medium water, and examined the associations of the post-photosynthetic processes. Theoretically, if the f-value is constant, δD and δ18O would be positively correlated due to meteorological factors, while variation in the f-value will create a discrepancy and weak correlation between δD and δ18O due to the exchange of carbon-bound hydrogen and oxygen with medium water. The values of δD decreased drastically from earlywood to latewood, while those of δ18O increased to a peak and then decreased toward the latewood. The estimated seasonal f-value was high at the beginning of earlywood and decreased toward the latewood. The post-photosynthetic processes associated with changes in the f-value were the remobilization of stored starch and triose cycling during cellulose synthesis because of the shortage of photo-assimilates in early spring. Although we did not evaluate relevant physiological parameters, the seasonal pattern of δD and δ18O in tree-ring cellulose of Q. crispula was clear, suggesting that the dual isotope (δD and δ18O) approach can be used to reveal the resource allocation mechanisms underlying seasonal xylem formation.