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Deeper Roots (deeper + root)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Ecohydrology of a semi-arid forest: partitioning among water balance components and its implications for predicted precipitation changes

ECOHYDROLOGY, Issue 2 2010
Naama Raz Yaseef
Abstract The distribution of precipitation inputs into different hydrological components of water-limited forest ecosystems determines water availability to trees and consequently forest productivity. We constructed a complete hydrological budget of a semi-arid pine forest (285 mm annual precipitation) by directly measuring its main components: precipitation (P), soil water content, evapotranspiration (ET, eddy covariance), tree transpiration (sap flux), soil evaporation (soil chambers), and intercepted precipitation (calculated). Our results indicated that on average for the 4-year study period, ET accounted for 94% of P, varying between 100% when P < 250 mm and 85% when P > 300 mm (with indications for losses to subsurface flow and soil moisture storage in wetter years). Direct measurements of the components of the ET flux demonstrated that both transpiration and soil evaporation were significant in this dry forest (45% and 36% of ET, respectively). Comparison between ecosystem ET (eddy covariance measurements) and the sum of its measured components showed good agreement on annual scales, but up to 30% discrepancies (in both directions) on shorter timescales. The pulsed storm pattern, characteristics of semi-arid climates, was sufficient to maintain the topsoil layer wet during the whole wet season. Only less often and intensive storms resulted in infiltration to the root zone, increasing water availability for uptake by deeper roots. Our results indicate that climate change predictions that link reduced precipitation with increased storm intensity may have a smaller effect on water availability to forest ecosystems than reduced precipitation alone, which could help forests' survival and maintain productivity even under drier conditions. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Below-ground competition between trees and grasses may overwhelm the facilitative effects of hydraulic lift

ECOLOGY LETTERS, Issue 8 2004
F. Ludwig
Abstract Under large East African Acacia trees, which were known to show hydraulic lift, we experimentally tested whether tree roots facilitate grass production or compete with grasses for below-ground resources. Prevention of tree,grass interactions through root trenching led to increased soil water content indicating that trees took up more water from the topsoil than they exuded via hydraulic lift. Biomass was higher in trenched plots compared to controls probably because of reduced competition for water. Stable isotope analyses of plant and source water showed that grasses which competed with trees used a greater proportion of deep water compared with grasses in trenched plots. Grasses therefore used hydraulically lifted water provided by trees, or took up deep soil water directly by growing deeper roots when competition with trees occurred. We conclude that any facilitative effect of hydraulic lift for neighbouring species may easily be overwhelmed by water competition in (semi-) arid regions. [source]

Innovation and technological knowledge in the Upper Paleolithic of Northern Eurasia

EVOLUTIONARY ANTHROPOLOGY, Issue 5 2005
John F. Hoffecker
Abstract The technology of modern humans is unique in the animal kingdom with respect to its complexity and capacity for innovation. Evidence of technological complexity and creativity in the archeological record is broadly coincident with and presumably related to traces of creativity in art, music, ritual, and other forms of symbolism. The pattern of modern human technology is part of a larger package of behavior (sometimes referred to as "behavioral modernity") that emerges with the appearance of industries in Eurasia classified as Upper Paleolithic, but has deeper roots in the African Middle Stone Age.1,5. [source]

Understanding the Unilateralist Turn in U.S. Foreign Policy

FOREIGN POLICY ANALYSIS, Issue 2 2005
David Skidmore
How should we explain the recent unilateralist turn in U.S. foreign policy? Some accounts treat growing American unilateralism as a passing aberration attributable to the neoconservative ideology of the Bush administration. This paper, by contrast, traces U.S. unilateralism to the structural effects, at home and abroad, of the end of the Cold War. Internationally, the removal of the Soviet threat has undermined the "institutional bargain" that once guided relations between the U.S. and its major allies. Absent Cold War imperatives, the U.S. is less willing to provide collective goods through strong international institutions and other states are less likely to defer to U.S. demands for special privileges that exempt the U.S. from normal multilateral constraints. Domestically, the end of the Cold War has weakened the ability of presidents to resist the appeals of powerful veto players whose interests are threatened by multilateral commitments. These factors suggest that American unilateralism may have deeper roots and more staying power than many expect. [source]