259,835 research outputs found
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NITROGEN CAN LIMIT OVERSTORY TREE GROWTH FOLLOWING EXTREME STAND DENSITY INCREASE IN A PONDEROSA PINE FOREST
No full textExtreme stand density increases have occurred in ponderosa pine forests throughout the western U.S. since the early 20th Century, with adverse implications for growth, physiological functioning, and mortality risk. Identifying primary stressors on large, old overstory trees in dense forests can informmanagement decisions to promote resilience and survival. We tested the impact of stand density increase on overstory tree-ring growth, and the relative influence of water and nitrogen, in an old-growth ponderosa pine forest in northern New Mexico subject to variable density increase. We measured annual tree-ring growth and carbon discrimination in trees before stand density increased, in a climatically-similar period post-density increase, and in recent transition to drought. We expected density-driven water stress to drive reduced tree-ring growth in overstory trees in dense stands. We found reduced growth and higher mortality in dense stands, but nitrogen rather than water constrained growth, as determined by carbon isotope discrimination in tree rings, leaf nitrogen concentration, and soil nitrogen supply. In dense stands, less available nitrogen limited photosynthetic rate, leading to reduced assimilation of intracellular C-13 and higher discrimination with low tree-ring growth and a reduced relationship with climate. This unexpected result illustrates that a variety of limiting factors can influence forest dynamics, as density-driven nitrogen limitation interacts with water stress to influence tree growth and physiological functioning.US Forest Service, Collaborative Forest Restoration Program (CFRP); US Forest Service, Rocky Mountain Research Station [02-DG-11031000-001, 00-JV-11221615]; Joint Fire Science Program [99-1-3-08]; New Mexico Forest and Woodlands Restoration Institute; US Department of Energy Global Change Education Program; Department of Energy-Office of Biological and Environmental ResearchThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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Tree-Rings and Sunspot Numbers
No full textTree-ring series that record climatic variation have long been of interest for study of possible effects of solar variability on terrestrial phenomena. Spectral analysis, harmonic dial analysis, digital filtering, cross-correlation and principal component analysis were used separately and in combination in an attempt to detect relationships between the annual Wolf sunspot numbers and ring-width indices, primarily from western North America. The results show no evidence of significant, consistent relationships between tree-ring data and sunspot numbers.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
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¹⁴C Bomb Effect in Tree Rings of Tropical and Subtropical Species of Brazil
No full textAtmospheric 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.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring Research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
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Selecting and Characterizing Tree-Ring Chronologies for Dendroclimatic Analysis
No full textA widely spaced grid of tree-ring chronologies most suitable for dendroclimatic analysis of western North America is selected objectively on the basis of 1) numbers in the sample, length in years, and site locations, 2) statistical characteristics of the chronologies, and 3) correlation of chronologies with those on neighboring sites. The chronology statistics are then analyzed to characterize the quality of the selected set. The procedures used in this study are recommended for future climatic analysis to assure objectivity in the selection of quality tree-ring data and to allow comparisons of the statistics for new chronologies to the established data sets.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
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Density of Tree-Ring Grids in Western North America
No full textThe separating distance over which tree-ring chronologies are significantly correlated is investigated. Any chronology occuring within a radius of 161 km of another is estimated to contain at least half of the common variance occurring at zero separating distance. The separating distance of 161 km is used to calculate the number of nonoverlapping chronology equivalents present within the 40 -, 65 -, and 89-chronology western North American grids. The density of chronologies is calculated for these three grids in various ways. The results give conservative density estimates of five, seven, and eight sites per Mkm² for the three different tree-ring grids.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
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Frequency-Dependent Relationships Between Tree-Ring Series Along an Ecological Gradient and Some Dendroclimatic Implications
No full textBristlecone pines were sampled at four sites ranging from the arid lower forest border to the upper treeline in the Snake Range of eastern Nevada. Maximum ring-width response to environmental variation is found at the upper and lower forest limits. Ring-width index series from individual trees, as well as the mean site chronologies, were compared by cross-correlation analysis and principal component analysis, combined with digital filtering to emphasize variations in different frequency ranges. Positive correlation exists between the high-frequency variations at all sites, but the longer term trends and fluctuations at the upper treeline are negatively correlated with fluctuations at the lower altitude sites. Cross-spectral analysis substantiates the results of cross-correlation analysis and indicates that the associated variations in the upper treeline and lower forest border chronologies are concentrated in certain frequency ranges that may have climatic significance. From examination of the climatic response functions, the negatively correlated low frequency variations are tentatively judged to be related to warm- season temperature fluctuations, whereas the positively correlated high frequency variations may be related to precipitation. Frequency-dependent relationships between tree-ring chronologies, or between tree-rings and climate should be considered in the analysis of large arrays of tree-ringThis item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
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Trackways and Tree Trunks - Dating Neolithic Oaks in the British Isles
No full textThe Midlands and South-west of England are represented by a long oak tree-ring chronology spanning approximately 4500-3900 BC (calibrated radiocarbon dates). The wood on which it is based originates in a technologically advanced trackway crossing the low-lying Somerset Levels, in a coastal submerged forest probably killed by rising sea-level, and in flood-plain oaks washed down the River Trent. Cross-matching between the growth patterns of the three groups of trees is of good quality, yet so far the chronology has failed to cross-date with the long Irish and German dated chronologies. The reasons for this, and the implications of eventual dating, are discussed.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
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Tree-Rings and Radiocarbon
No full textTree-Rings and Radiocarbon, St. Gregory High School, 8 January 1986This item is part of the Natural History Reports collection. It was digitized from a physical copy provided by the Laboratory of Tree-Ring Research at The University of Arizona. For more information about items in this collection, please contact the Lab's Curator, (520) 621-1608 or see http://ltrr.arizona.edu/collection
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Tree-Ring Chronologies from Nepal
No full textTen ring-width based chronologies from Nepal are described and the prospects for further dendroclimatic work there reviewed briefly. The initial results are encouraging, and more intensive subregional sampling is called for. All the cores examined showed distinct annual rings, and there was little evidence of double or missing rings, except juniper at some sites and in some Pinus roxburghii trees. Difficulty was encountered in dating Pinus wallichiana and Cupressus dumosa. Individual site chronologies of Cedros deodora, P. roxburghii and P. wallichiana were particularly promising, and of high elevation Abies spectabilis moderately so. Densitometric data are likely to be more useful for this species. The paucity of meteorological data in Nepal represents an obstacle to further dendroclimatic work there.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
Constructive Heuristics for the Minimum Labelling Spanning Tree Problem: a preliminary comparison
No full textThis report studies constructive heuristics for the minimum labelling spanning tree
(MLST) problem. The purpose is to find a spanning tree that uses edges that are as similar as
possible. Given an undirected labeled connected graph (i.e., with a label or color for each edge),
the minimum labeling spanning tree problem seeks a spanning tree whose edges have the smallest
possible number of distinct labels. The model can represent many real-world problems in
telecommunication networks, electric networks, and multimodal transportation networks, among
others, and the problem has been shown to be NP-complete even for complete graphs. A primary
heuristic, named the maximum vertex covering algorithm has been proposed. Several versions of
this constructive heuristic have been proposed to improve its efficiency. Here we describe the
problem, review the literature and compare some variants of this algorithm
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