To determine the response of tree rings to climate, twenty cores were extracted from ten trees of Pinus pinea L. in Istanbul-Alemdag. A response function was used to characterize the relationships between tree rings and temperature and precipitation. The precipitation of the current year and the temperature at the beginning of the growing period have a significantly positive influence on the growth of the tree ring. Mean sensitivity was found to be 0.291, and it was concluded that Pinus pinea L. is a dendroclimatologically sensitive species.

Progressive tree-ring xylem cell size changes may reveal the influence of changing environment during the growing season. This study examines xylem tracheid cell growth in red pine (Pious resinosa Ait.) seedlings grown in cabinets under controlled environment, where single parameters (temperature, light, soil moisture and CO2) were varied step-wise in each chamber at ca. 30-day increments for ca. 6 months. Control and temperature treatments were replicated. Cross-sections (20 μm thick) sliced with a sliding microtome from each of four seedling stems from each cabinet were mounted on glass slides. Lumen diameters and cell-wall thickness were measured on 4 orthogonal tracheid radial files on 4 radii of each stem. Mean cell sizes were 11-17 μm among treatments and growth periods, whereas numbers of cells formed averaged 0.2-1.3 cells per day. Cell size increased throughout the experiment in most of the treatments, including one of the control treatments and those with the greatest potential to limit growth (decreasing temperature, light and soil moisture). Soil moisture was the only environmental parameter that tended to cause late declining growth, and CO, up to 500 (μmol mol⁻¹ did not appear to influence cell development. Despite a substantial range of environmental shifts in the chambers (100 μmol mol⁻¹ CO₂; 125 μEinsteins m⁻² s⁻¹ light; 8 °C temperature; 35% relative humidity; watering every day to every 5th day), the continued stem elongation and cell-size increases indicate that conditions never became significantly limiting to growth in most treatments. Although the range of environmental variability is undoubtedly much greater in most natural red pine systems, these results indicate that fairly large variations in environment during development of juvenile wood in seedlings may not leave an imprint retrievable from cell-size measurements made on the earliest rings of mature trees.

The objective of this study was to document correlations between radial growth of white oak (Quercus alba L.) at 128 sites in the eastern US and variables related to early growing season site water balance, including the ratio of actual to potential evapotranspiration (AE/PE) computed based on the procedure described by Thornthwaite and Mather (1957). White oak radial growth was strongly correlated with all measures of early growing season water balance, but was most consistently and strongly correlated with Palmer Drought Severity Index (PDI) and AE /PE ratio computed using a modified Thornthwaite-Mather model. We propose that dendroecological analyses of tree growth responses to climate based on AE /PE variables could provide empirical data useful for improving climate response algorithms in forest simulation models. This change of standard practice could also improve biological interpretations derived from such dendroecological analyses.

A new collection of tree-ring chronologies developed from trees and remnant material located in the western and central Great Plains makes an important contribution to the spatial coverage of the US tree- ring chronology network. Samples from 24 sites were collected from the west-central Great Plains, and to date, ten chronologies have been produced. When correlated with a set of 47 single-station PDSI records, the chronologies display relationships with regional spring and summer drought. The reconstruction of spring PDSI for eastern Colorado generated in this study suggests that the inclusion of Great Plains trees can improve the quality of Great Plains drought reconstructions. The eastern Colorado drought reconstruction explains 62% of the variance in the instrumental record and extends to 1552. This reconstruction provides information about the regional character of major droughts over the past four and a half centuries. Major eastern Colorado droughts include events in the 1580s, 1630s, 1660s, 1730s, and the 1930s. The late 16th century drought, noted as an especially severe drought in the southwestern US, appears in this reconstruction as only slightly more severe than other major droughts in this region.

Within the framework of the linear aggregate model of dendrochronology, the potential role of soil nutrient availability in explaining multi-decadal variation in radial growth at the tree level was studied in the central Spanish Pyrenees. Increment cores were collected from 20 mature Pinus uncinata Ram. and analyzed dendrochronologically. One ion-exchange resin capsule was buried within the root zone of each sampled tree for just over eight months. The resins were chemically extracted and measured for NH₄, NO PO₄, Ca, and K. Statistical relationships between indexed tree growth and soil nutrient availability were determined with regression analysis and bivariate plots. The single most important soil nutrient with respect to decadal-scale dendrochronological tree-growth variables in this study was N in the form NO which explained 22% of variation of trend in growth since 1950. The 20 values of NO₃ availability fell into two subgroups, one of trees with relatively higher NO₃ availability and the other with lower NO₃ availability. When the tree-growth data were grouped based on NO₃ availability, the two resultant index chronologies had different low-frequency features since 1950. Trees with low NO₃ availability have been growing as expected based on past growth, but trees with high NO availability have been growing better than expected. Measuring and analyzing soil nutrient availability at the tree level might enhance environmental applications of dendrochronological research. With soils information at this spatial scale, it is possible to distinguish between subgroups of trees within a tree-ring site and thereby construct subchronologies that differ significantly, especially for variation at the decadal scale. Subsite-chronologies may then lead to different and presumably more informative environmental interpretations relative to those based on a full-site chronology.

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Dendrochronological methods were used to date hail injuries in tree rings of six mountain pines (Pinus mugo var. uncinata) at a site in central Switzerland. Annually dated injuries (1939-1996) were in 89% of the cases attributable to years with severe regional hailstorm occurrence (1957-1996). Days with severe hailstorms were successfully dated in either the earlywood and /or latewood portions of a tree ring in a given year. Tree rings provide an alternative proxy to existing data for reconstructing past severe hailstorm occurrence.

High-resolution paleoclimatic data for West Africa are needed to provide context for contemporary climatic and ecological dynamics. Six hundred trees (22 botanical families, 43 genera and over 70 species) from semi-arid West Africa were evaluated for their suitability for dendrochronological research; specifically ring development. The samples were classified as 'potentially useful', 'problematic', or 'poor' based on the presence and distinctiveness of annual rings, ability to achieve crossdating between radii using skeleton plots on at least some samples, circuit uniformity, ring wedging, and variability of ring widths. Samples were classified as potentially useful if (a) they exhibited distinctive annual rings that could be identified and counted with little uncertainty and be independently verified by a second person with little or no error, (b) crossdating between radii could be successfully achieved, at least on some samples, (c) the rings were generally consistent throughout the stem cross section, (d) ring wedging was minimal (in the relative sense) or absent, and (e) the ring widths were variable, indicating the possibility of climatic sensitivity. Seven species, including five from the Caesalpiniaceae family (Cassia sieberiana, Cordyla pinnata, Daniella oliveri, Isoberlinia doka, Tamarindus indica), and one each from Mimosaceae (Acacia seyal) and Verbenaceae (Gmelina arborea) families, that most closely satisfied these criteria were classified as 'potentially useful'. The 'problematic' category includes those samples that satisfied some of the criteria but for which greater diligence is required to detect rings. Eight species from three families were classified in this category. Finally those samples on which ring detection appears futile given current methods and techniques were classified as 'poor'. Most of the samples classified as 'potentially useful' belong to three botanical families, Caesalpiniaceae, Mimosacae, and Verbenaceae. These results are consistent with the findings of other studies, and therefore support further investigation of the potential of West African trees for tree-ring analysis focusing on these families. Furthermore, inability to crossdate between trees and to explain several ring anatomical features underscores the pressing need for comprehensive field studies of cambial activity during the growing season, and for the identification of dormant seasons. This requirement, and other difficulties discussed suggest a need for increasing the local dendrochronological expertise in West Africa.