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Millennium-aged trees are rare in natural forests. Here we present an 1184-year-long tree-ring width chronology from living juniper trees in the Biru area on the southeastern Tibetan Plateau. Growth-climate response analysis shows that the Biru chronology is significantly and positively correlated with late-spring (May-June) Standardized Precipitation Evaporation Index (SPEI) (r = 0.67, n = 53, p < 0.01). The tree-ring chronology explains 44.5% of the total variance of SPEI during the period AD 1957–2010. Reconstruction of May-June SPEI shows that there was a two-century-long megadrought during the late 13th to late 15th Centuries, and a seven-decade-long megadrought during AD 1630s to 1690s. Comparisons with other moisture records in the region suggest that the two-century megadrought identified in our reconstruction might be a widespread phenomenon most likely reflecting a stage of reduced Southwest Asian Summer Monsoon. Our results provide new evidence on the megadrought events on the Tibetan Plateau for the last millennium.
This paper documents a pilot study investigating the potential use of pinyon pine (Pinus monophylla Torr. & Frem) growing in the White Mountains of eastern California for climate reconstructions. The single-leaf pinyon pine from this study exhibit a significant and stable relationship with annual (August–July) precipitation over the instrumental record (r = 0.69). This relationship is stronger than that of the lower forest border bristlecone pine (Pinus longaeva) growing nearby. Spatially, the climate-growth relationship remains strong beyond this localized region, extending over Southern California. Although pinyon pine is not as long lived as the bristlecone pine, these results indicate that the strength of the climate-growth relationship makes this species valuable in developing climate reconstructions in the future. Additionally, the presence of persistent remnant wood at all sampling sites offers an opportunity to extend pinyon records further back in time. Furthermore, the close proximity of pinyon pine to bristlecone pine at these sites presents the possibility of developing multi-species reconstructions using both species.
In trees experiencing stress prior to death, growth may be partially or totally suppressed, or may occur only in the upper part of the boles. This may induce inaccuracies when retrospectively crossdating dead trees. In this study, we investigated the occurrence and range of time lags between year of last ring production (YOLRP) in crossdated discs collected at the base, at breast height (BrH), and in the upper part (UP) of the boles of 145 snags and logs of four boreal species. We also assessed the influence of tree age and growth prior to death. When comparing YOLRP in the upper and lower part of trees, more than half the time lags departed from zero. Mean lags ranged from 0.6 to 4.6 years according to species, with lags up to 14 years. Negative time lags, i.e. ring production occurring in the lower part of boles while it has stopped in the upper part, were also observed in up to 26% of cases. We suggest that when reconstructing fine patterns of mortality where accuracy must be optimized, sampling entire discs at BrH should be considered, as well as sampling a disc in the UP when sampling old or slowly declining trees.
Maple syrup is a regional, non-timber forest product in the United States that depends upon healthy, mature sugar maple (Acer saccharum Marshall). We examined whether tapping for maple syrup altered the dendroclimatic response of sugar maple. Ring width indices from two sites (tapped and reference) in central Pennsylvania were correlated with regional temperature, precipitation, and Palmer Drought Severity Index (PDSI). Both sites had significant correlations between summer and fall PDSI and radial growth. Spring PDSI was significantly correlated with growth at the reference site, but not at the tapped site. Both tapped and reference trees experienced below-average growth during years with dry spring conditions (PSDI < 0), but tapped trees had a higher percentage of years (27%) with below-average growth during years with moist spring conditions (PDSI > 0) compared to reference trees (15%). These results indicate that tapping for maple syrup may have altered the dendroclimatic response of sugar maple to moisture availability during the spring months.
Few tree-ring based fire-history studies have been completed in pine ecosystems of the Southeastern Coastal Plain, in part because of difficulties in finding old fire-scarred material. We propose specialized field methods that improve the likelihood of locating fire scars in dead trees (i.e. stumps, snags, and logs). Classic fire-history field methods developed in the southwestern United States involve targeting only trees with evidence of repeated external scarring, but we have found this approach to be less effective in our region given that trees without any external scarring may contain an abundance of buried scars. The buried scars occur primarily near the ground surface and can be sampled by collecting full cross-sections from the bases of old dead trees. We hope our insights foster further fire-history research in the Southeastern Coastal Plain.
In recent years, a millennia-long oak tree-ring width chronology, consisting of 3194 samples from 387 locations, was developed in the Czech Republic. Despite the collection of such a huge dataset, the replication in the 19th Century was very low and the natural oak distribution in the Czech Republic was insufficiently covered by recent samples, especially in Western Bohemia. This study aimed to remove these weaknesses, which have limited the paleoclimatic potential of this dataset, and to determine the number of sapwood rings, which is crucial for dendrochronological dating. Therefore, new recent samples were randomly collected at numerous sawmills along the Czech-German border. The historical material was usually sampled using a Pressler borer from church belfry constructions traditionally made from oak. In total, 252 recent and 90 historical tree-ring width series were incorporated into the chronology. The newly built chronology cumulatively consists of 3536 series, which covers the continuous period of A.D. 352–2014. The resulting tree-ring width record shows robust signal strength and homogeneous coverage of the territory. We show that the number of sapwood rings is constant over time. Therefore, we recommend using an estimate of 5–24 sapwood rings for a more precise dating of historical wood findings in the Czech Republic.