Valmore C. LaMarche

Paleoclimatic Inferences from Long Tree-Ring Records Intersite comparison shows climatic anomalies that may be linked to features of the general circulation

Tree-ring data contribute to a better understanding of the nature of past climatic variations. Annual ring records several thousand years long can be constructed for a few areas, but interpretation of them requires the development of new approaches. For example, a single record of average ring width in the upper tree line environment provides a guide to past temperature fluctuations. However, comparison of this record with another, that of the arid lower forest border, from the same area permits characterization of associated precipitation and temperature anomalies that may, in turn, be linked to features of the general circulation. Other approaches that promise to be very fruitful include study of the variation of ring-width statistics through time, investigation of the physical and chemical properties of wood, and combined multivariate analysis of data for a variety of paleoclimatic indicators.

Increasing atmospheric carbon dioxide: tree ring evidence for growth enhancement in natural vegetation

A response of plant growth to increased atmospheric carbon dioxide, which has been anticipated from laboratory data, may now have been detected in the annual rings of subalpine conifers growing in the western United States. Experimental evidence shows that carbon dioxide can be an important limiting factor in the growth of plants in this high-altitude environment. The greatly increased tree growth rates observed since the mid-l9th century exceed those expected from climatic trends but are consistent in magnitude with global trends in carbon dioxide, especially in recent decades. If correctly interpreted, these findings have important implications for climate studies involving tree ring observations and for models of the global carbon dioxide budget.

Tree ring evidence for chronic insect suppression of productivity in subalpine eucalyptus.

Experimental reduction of insect grazing pressures suggests that longterm, continuous feeding by phytophagous insects has severely depressed growth and productivity of subalpine Eucalyptus trees (measured by annual ring growth) for at least 25 years.

ANOMALY PATTERNS OF CLIMATE OVER THE WESTERN UNITED STATES, 1700–1930, DERIVED FROM PRINCIPAL COMPONENT ANALYSIS OF TREE-RING DATA

Abstract Major anomaly patterns of annual tree-ring growth in “drought-sensitive” trees of the Western United States, 1931–1962, seem to reflect corresponding patterns in monthly precipitation amounts, which in turn may be related to circulation anomalies. The three most important anomaly patterns that dominated the 1931–1962 period were also prominent in the tree-growth data during the preceding period 1700–1930. These patterns can thus be expected to maintain their importance during at least the immediate future. Time series of eigenvector amplitudes show how the relative importance of the anomaly patterns changes through time. These can be studied for properties lending possible forecasting value and may provide important insight into the past behavior of the atmospheric circulation over the Western United States.

A climatically responsive tree-ring record from Widdringtonia cedarbergensis, Cape Province, South Africa

The use of dated tree-ring series to reconstruct past climate has received much attention in recent years1,2. The development of long and climatically responsive chronologies in many areas of the Southern Hemisphere is an important step towards better understanding past environments in these areas3,4, but little dendrochronologically related work of any sort has been done on the African continent5–11, and most of this has consisted primarily of ring counts to estimate ages. We report here on the development and climatic interpretation of the first dated annual ring-width index chronology from Africa south of the Sahara.

Evaluation of Effects on Trees of Past Movements on the San Andreas Fault, Northern California

Fault movement accompanied by surface rupture can fracture, twist, or tilt trees that grow on the surface break of the fault. Trees growing near, but not on, the fault may be felled or topped as a result of ground motion. Changes in growth rate of trees may relate to hydrologic and topographic changes or from “release effects” caused by death of neighboring trees. Many other causes such as landslides, wind, and fire can produce similar effects and must be considered when using trees to date past movements on the San Andreas fault. The effects of tilting of trees growing on surface ruptures seem to provide the least ambiguous evidence of past movement on the fault, but few ancient trees that record multiple movements in the past were found. A redwood tree near Fort Ross was tilted between 1400 A.D. and 1650 A.D.; tilting is tentatively attributed to movement on the San Andreas fault. The same tree also records two other tilts, and in 1906 the base of the tree was fractured by faulting. In contrast, a redwood tree possibly 500 to 600 yrs old in Woodside grows only 10 ft (3 m) from the 1906 surface rupture and yet no effects in growth rate or tilt record the event.