Three eastern hemlock (Tsuga canadensis (L.) Carr.) and three chestnut oak (Quercus prinus L.) ring-width chronologies were constructed from old-and second-growth stands in the Black Rock Forest in Cornwall. New York, the first developed for the highlands of southeastern New York State. The longest hemlock chronology extends from 1780-1992 and the longest oak chronology from 1806-1994. The oldest trees sampled had minimum ages of 275 and 300 years for hemlock and chestnut oak, respectively. The tree-ring chronologies were compared to monthly temperature and precipitation data from nearby West Point, NY for the 1850s-1990s and to Palmer Drought Severity Indices for 1911-1990. The chronologies provide forest growth information for the period prior to the initiation of meteorological measurements, begun in 1824 at West Point. Black Rock Forest eastern hemlock growth correlates positively with current July and prior September precipitation, with February-March temperature and with prior September Palmer Drought Severity Indices. It correlates negatively with prior June temperature. Black Rock Forest chestnut oak growth correlates positively with current June-July and prior September and December precipitation, with January temperature, and with prior September-October and current June-July Palmer Drought Severity Indices. It correlates negatively with current June-July temperature. The Black Rock Forest tree-ring records and analyses yield useful information for climate reconstruction and for assessing the potential impact of anthropogenic change (e.g. CO₂-induced climate effects, CO₂ and N fertilization, acid deposition, changes in soil chemistry due to atmospheric pollution).

A 280-year old white oak chronology was developed for south-central Virginia to verify the timber harvesting and construction dates of a cabin located on the Reynolds Homestead Research Center. A plaque on the cabin stated that the logs were harvested in 1814. However, the outer rings of the logs dated to 1875 and 1876. From the land-use history of the area, the cabin was most likely constructed to house tenant farmers after the Civil War. Most of the periods of below average growth identified in the 280-year chronology were related to drought events. Correlations between the radial growth of the white oak with temperature and precipitation data from a local weather station were examined. Precipitation had more influence on radial growth than temperature, and significant correlations (p = 0.05) existed between radial growth and precipitation from the previous September, the current April, and the current June.

No description available.

Fifty-three ring-width chronologies have been developed from open-grown, low-elevation stands of Pseudotsuga menziesii (Douglas-fir) and Pinar ponderosa (ponderosa pine) in the southern Canadian Cordillera. These chronologies will be used to develop precipitation reconstructions for the region. The sites are unevenly distributed across the interior valleys from east of the Coast Ranges to the Canadian Rockies and from the Canada-U.S. border to the northern limits of both species. The chronologies range from 123-691 years (mean = 383 years) and, on average, have a strong within-chronology common signal (Expressed Population Signal > 0.85) with as few as eight trees. A Rotated Principal Components Analysis (RPCA) identified three regions within which annual ring-width chronologies covary similarly. A preliminary assessment of regional chronologies and patterns of extreme narrow and wide marker rings demonstrates that common growth variations exist in the chronology network that are probably precipitation related. Both the RPCA and marker ring analyses suggest distinctive regional patterns of growth on both interannual and longer timescales that vary through time and are possibly linked to persistent large scale climatic anomalies.

Atmospheric nuclear tests in the early 1960s introduced large amounts of radiocarbon into the atmosphere, which resulted in an increase of tropospheric ¹⁴CO₂ concentration by nearly 100% during the years 1964-1965. The bomb-produced ¹⁴C was then gradually incorporated within the global carbon cycle. The history of ¹⁴C concentration in the troposphere is preserved within annual growth layers of trees and can be reconstructed for those areas where direct measurements of 14C in the atmosphere were not performed. The paper presents results of ¹⁴C activity measurements in tree rings of tropical and subtropical species from Brazil, for the period 1945-1997. We investigated two species ( Araucaria angustifolia and Parkia sp.) growing at three sites covering the latitudinal band between 7 °S and 24 °S. The results indicate that the maximum ¹⁴C activity in the Southern Hemisphere occurred in 1965, with the Δ¹⁴C values reaching around 700%. Significant differences in Δ¹⁴C were recorded among the studied sites for the period of maximal ¹⁴C levels in the atmosphere, with the highest level observed at the tropical site and lowest in the subtropical zone. This reflects the dynamics of interhemispheric transport of ¹⁴C during the years of high spatial and temporal gradients of this isotope in the atmosphere.

No description available.

COFECHA is a computer program that assesses the quality of crossdating and measurement accuracy of tree-ring series. Written by Richard L. Holmes in 1982, the program has evolved into one of the most important and widely used in dendrochronology. It is important to note that COFECHA does not perform all the necessary steps in crossdating. Rather, the program is a tool that helps the dendrochronologist assess the quality of crossdating and measurement accuracy. The ultimate decision whether or not a tree-ring series is successfully crossdated must lie with the dendrochronologist and not with the software. Therefore, the program is most useful after initial crossdating is accomplished using visual or graphical techniques (such as skeleton plots), and the rings have been measured. The proper use of COFECHA adds a high degree of confidence that tree-ring samples have been crossdated correctly and measured accurately, ensuring that the environmental signal is maximized. In this paper, I describe the use of COFECHA through all necessary steps, and discuss the meaning of the initial questions posed at program start-up, the various options available in the main menu, the various sections of the output from COFECHA, and interpretation of the diagnostics of crossdating and measurement accuracy. I demonstrate methods used to help crossdate undated series, and offer tips on taking full advantage of the various options available in the program.

No description available.

No description available.

No description available.