Bald cypress (Taxodium distichum) is known to respond to increases in precipitation with increased radial growth even when rooted in continuously saturated sediments where water is not a growth-limiting factor. Measurements of δ¹⁸O, Cl⁻, ³H and hydraulic head in surface water and shallow groundwater in an oxbow lake-wetland in northern Mississippi show that rapid downward flow of surface water into the root zone is initiated only after precipitation-induced increases in surface water depth exceed a threshold value. Rapid flow of surface water through the root zone has the potential to introduce oxygen to sediments that would otherwise be anoxic, facilitating nutrient uptake and growth. Climatic reconstruction using tree rings from bald cypress in this environment appears possible because increases in precipitation generally correlate well with increases in water level, which in turn enhances the delivery of oxygenated water to the roots.

A 155-point US grid of tree-ring reconstructed summer (JJA; Cook et al. 1996) averaged Palmer Drought Severity Index (PDSI) was used to document the history and investigate the external forcing of growingseason climate anomalies for the period 1700 to 1978. Statistical analysis software was used to composite years temporally by computing averages for the years of known dates of major potential climate-forcing events. A geographic information system (GIS) was used to display the composites as well as individual years. The forcing factors investigated were the 22-year Hale solar magnetic cycle, major El Niño (warm) and La Niña (cold) events based on the Southern Oscillation Index (SOI), and large magnitude low latitude volcanic eruptions. Positive and negative moisture anomalies appear around Iowa in the alternate 11-year sunspot cycles that make up the Hale solar magnetic cycle. Experimentation with the grouping of years in the Hale cycle composites led to unexplained spatial shifts of the moisture anomalies in the same region. The El Niño episodes usually show positive (wet) PDSI anomalies in the Southwest from California to Texas, while La Niña events usually have drought in the same area, with some inconsistent signals in the north central Plains and the Northwest. The eastern and northern US were unaffected by the Southern Oscillation, although the summer season reconstructed PDSI may have missed the SOI variation, which is primarily a winter signal. The three largest tropical volcanic eruptions since 1800 failed to follow a consistent pattern, but the 1815 eruption of Tambora in Indonesia was followed by a very strong positive growth anomaly in the Southwest in 1816 and 1817. Important regional studies with the winter-spring season could be done with this network of tree-ring chronologies and observed monthly PDSI data.

The International Tree-Ring Data Bank (ITRDB) is an invaluable resource, providing access to a massive and growing cache of tree-ring data. Oxygen, carbon, nitrogen and hydrogen isotope treering studies, which have provided valuable climatic and ecological information, have proliferated for decades so an ITRDB expansion to include isotopic data would likewise benefit the scientific community. An international tree-ring isotope databank (ITRIDB) would: (1) allow development of transfer functions from extended isotopic data sets, (2) provide abundant tree-ring isotopic data for meta-analysis, and (3) encourage isotopic network studies. A Europe network already exists, but the international data bank proposed here would constitute a de facto global network. Associated information to be incorporated into the database includes not only the customary ITRDB entries, but also elements peculiar to isotope chronologies. As with the current ITRDB, submission of data would be voluntary and as such it will be crucial to have the support of the tree-ring isotope community to contribute existing and forthcoming isotope series. The plan is to institute this isotope database in 2010, administered by the National Climatic Data Center.

Sixty individual ring-width series of oak (Quercus robur L.) from six sites in the northwestern Iberian Peninsula, ranging from 50 to 120 years, were grouped using hierarchical cluster analysis with different types of distance measures. Euclidean distances as well as other linkage distances based on statistics used to crossdate tree-ring series (Gleichläufigkeit and coefficient of correlation with its corresponding t-value) were compared. In addition, a new distance measure based on a corrected inversion of the Student’s t is proposed in the present paper, which takes into consideration the number of years used for series comparison. The Euclidean distances, commonly used in ecological analyses, inefficiently identified homogeneous units of trees based on their ring-width patterns. Among crossdating statistics, the correlation coefficient was more effective than Gleichläufigkeit, but the most satisfactory results were obtained when 1/t was used as distance measure. Finally, these methods of cluster analysis have been implemented into a computer program for future use of the dendrochronological community.

Increment cores are invaluable for assessing tree attributes such as inside bark diameter, radial growth, and sapwood area. However, because trees accrue growth and sapwood unevenly around their pith, tree attributes derived from one increment core may not provide sufficient precision for forest management/research activities. To assess the variability in a tree’s inside bark radius, sapwood radius, and 10-year radial growth estimated by tree cores, two increment cores at 90 degree angles were collected from ponderosa pine (Pinus ponderosa) trees in eastern Montana (n = 2,156). Paired core measurements varied substantially with 13% mean difference for inside bark radius, 19% mean difference for sapwood radius, and 23% mean difference for estimates of radial increment. Furthermore, decreasing crown ratio, decreasing diameter, and increasing site slope were all found to increase differences in estimates derived from paired cores. Whether for management or research purposes, the number of cores that should collected per tree depend on a stand’s susceptibility to reaction wood, required measurement precision, and budgetary constraints.

We apply a combination of suppression and release criteria to reconstruct the disturbance history of a ponderosa pine – Douglas-fir stand in central Idaho. In this stand, disturbance, likely fire, induced growth releases in some trees, and sudden, severe suppressions in others. To characterize growth release following disturbance, we developed boundary-line release criteria for Douglas-fir and ponderosa pine. Suppression criteria were applied to identify disturbances defined as a growth reduction of more than 1.8 standard deviations sustained for a minimum of five years. To prevent confusing a true release event with growth increases associated with recovery from suppression, release events were not tallied for at least fifteen years following a suppression event. Release and suppression events were combined to create a disturbance chronology characterized by a high frequency of disturbance between 1820 and 1920. This period of disturbance likely reflects post-European settlement land uses such as grazing and logging as well as an increase in fire frequency. Fire suppression in the latter part of the 20th Century likely explains the decrease in disturbance after 1940. We believe that a combination of release as well as suppression criteria best describes the disturbance history of this stand.

Recent research has challenged the long-standing hypothesis that forests in the Upper Midwest of the United States developed during wetter periods and retreated during dry periods. We explored this debate by examining patterns of tree establishment on an oak savanna in east-central Minnesota within the context of variable moisture availability and fire suppression. We used superposed epoch analyses (SEA) to evaluate the mean moisture conditions for a 21-year window surrounding tree establishment dates. Before effective fire suppression (1809–1939), 24 of 42 trees with pith dates (62%) grew to 30-cm height during dry years (Palmer Drought Severity Index < -1), versus only 5 of 42 (12%) that established in wet years (PDSI > 1). Significantly more trees established during dry periods (negative PDSI values) than would be expected with the proportion of wet-to-dry years (x²= 10.738, df = 1, p-value = 0.001). Twenty of the complete sample of 74 trees with pith dates (27%) established during drought in the 1930s. We hypothesize that dry conditions limited plant productivity, which in turn decreased competition between grasses and tree seedlings and reduced rates of accumulation of fine fuels, enabling seedlings to grow tall enough to resist subsequent fires. We recommend SEA as a methodological approach to compare historical climate conditions with the timing of regeneration success in other regions of forest expansion.

February-April (FMA) temperature at Foping (1879-1989) and July-August (JA) precipitation at Xian (1895–1988) have been reconstructed using total ring width (TRW) and maximum latewood density (MXD) from trees in the Qinling Mountains, at the northern limit of the East Asian monsoon, in central China. The Xian JA precipitation reconstruction, albeit short, represents the first well-replicated, crossdated dendroclimatic reconstruction of summer monsoon precipitation for this region. Reconstructed Xian precipitation shows significant positive relationships with historical evidence from the region. The key feature of the precipitation reconstruction is prolonged summer drought during the late 1920s and early 1930s. The Foping reconstruction displays warmer-than-average FMA temperatures during this time period. These exploratory reconstructions, along with a previous reconstruction from Huashan, demonstrate the complexity of attempting dendroclimatic reconstructions from this region. Our results indicate that further attempts to locate long-lived conifers from here can result in an extended well-calibrated and verified reconstruction of summer monsoon precipitation.