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L. We (l + we)
Selected AbstractsTemporal dynamics and spatial variability in the enhancement of canopy leaf area under elevated atmospheric CO2GLOBAL CHANGE BIOLOGY, Issue 12 2007HEATHER R. McCARTHY Abstract Increased canopy leaf area (L) may lead to higher forest productivity and alter processes such as species dynamics and ecosystem mass and energy fluxes. Few CO2 enrichment studies have been conducted in closed canopy forests and none have shown a sustained enhancement of L. We reconstructed 8 years (1996,2003) of L at Duke's Free Air CO2 Enrichment experiment to determine the effects of elevated atmospheric CO2 concentration ([CO2]) on L before and after canopy closure in a pine forest with a hardwood component, focusing on interactions with temporal variation in water availability and spatial variation in nitrogen (N) supply. The dynamics of L were reconstructed using data on leaf litterfall mass and specific leaf area for hardwoods, and needle litterfall mass and specific leaf area combined with needle elongation rates, and fascicle and shoot counts for pines. The dynamics of pine L production and senescence were unaffected by elevated [CO2], although L senescence for hardwoods was slowed. Elevated [CO2] enhanced pine L and the total canopy L (combined pine and hardwood species; P<0.050); on average, enhancement following canopy closure was ,16% and 14% respectively. However, variation in pine L and its response to elevated [CO2] was not random. Each year pine L under ambient and elevated [CO2] was spatially correlated to the variability in site nitrogen availability (e.g. r2=0.94 and 0.87 in 2001, when L was highest before declining due to droughts and storms), with the [CO2]-induced enhancement increasing with N (P=0.061). Incorporating data on N beyond the range of native fertility, achieved through N fertilization, indicated that pine L had reached the site maximum under elevated [CO2] where native N was highest. Thus closed canopy pine forests may be able to increase leaf area under elevated [CO2] in moderate fertility sites, but are unable to respond to [CO2] in both infertile sites (insufficient resources) and sites having high levels of fertility (maximum utilization of resources). The total canopy L, representing the combined L of pine and hardwood species, was constant across the N gradient under both ambient and elevated [CO2], generating a constant enhancement of canopy L. Thus, in mixed species stands, L of canopy hardwoods which developed on lower fertility sites (,3 g N inputs m,2 yr,1) may be sufficiently enhanced under elevated [CO2] to compensate for the lack of response in pine L, and generate an appreciable response of total canopy L (,14%). [source] Habitat differentiation within the large-carnivore community of Norway's multiple-use landscapesJOURNAL OF APPLIED ECOLOGY, Issue 5 2008Roel May Summary 1The re-establishment of large carnivores in Norway has led to increased conflicts and the adoption of regional zoning for these predators. When planning the future distribution of large carnivores, it is important to consider details of their potential habitat tolerances and strength of inter-specific differentiation. We studied differentiation in habitat and kill sites within the large-carnivore community of south-eastern Norway. 2We compared habitat selection of the brown bear Ursus arctos L., Eurasian lynx Lynx lynx L., wolf Canis lupus L. and wolverine Gulo gulo L., based on radio-tracking data. Differences in kill site locations were explored using locations of documented predator-killed sheep Ovis aries L. We modelled each species' selection for, and differentiation in, habitat and kill sites on a landscape scale using resource selection functions and multinomial logistic regression. Based on projected probability of occurrence maps, we estimated continuous patches of habitat within the study area. 3Although bears, lynx, wolves and wolverines had overlapping distributions, we found a clear differentiation for all four species in both habitat and kill sites. The presence of bears, wolves and lynx was generally associated with rugged, forested areas at lower elevations, whereas wolverines selected rugged terrain at higher elevations. Some degree of sympatry was possible in over 40% of the study area, although only 1·5% could hold all four large carnivores together. 4Synthesis and applications. A geographically differentiated management policy has been adopted in Norway, aimed at conserving viable populations of large carnivores while minimizing the potential for conflicts. Sympatry of all four carnivores will be most successful if regional zones are established of adequate size spanning an elevational gradient. High prey densities, low carnivore densities, low dietary overlap and scavenging opportunities have most probably led to reduced competitive exclusion. Although regional sympatry enhances the conservation of an intact guild of large carnivores, it may well increase conflict levels and resistance to carnivore conservation locally. [source] The bi-criteria doubly weighted center-median path problem on a treeNETWORKS: AN INTERNATIONAL JOURNAL, Issue 4 2006J. Puerto Abstract Given a tree network T with n nodes, let ,,L be the subset of all discrete paths whose length is bounded above by a prespecified value L. We consider the location of a path-shaped facility P , ,,L, where customers are represented by the nodes of the tree. We use a bi-criteria model to represent the total transportation cost of the customers to the facility. Each node is associated with a pair of nonnegative weights: the center-weight and the median-weight. In this doubly weighted model, a path P is assigned a pair of values (MAX(P),SUM(P)), which are, respectively, the maximum center-weighted distance and the sum of the median-weighted distances from P to the nodes of the tree. Viewing ,,L and the planar set {(MAX(P),SUM(P)) : P , ,,L} as the decision space and the bi-criteria or outcome space respectively, we focus on finding all the nondominated points of the bi-criteria space. We prove that there are at most 2n nondominated outcomes, even though the total number of efficient paths can be ,(n2), and they can all be generated in O(n log n) optimal time. We apply this result to solve the cent-dian model, whose objective is a convex combination of the weighted center and weighted median functions. We also solve the restricted models, where the goal is to minimize one of the two functions MAX or SUM, subject to an upper bound on the other one, both with and without a constraint on the length of the path. All these problems are solved in linear time, once the set of nondominated outcomes has been obtained, which in turn, results in an overall complexity of O(n log n). The latter bounds improve upon the best known results by a factor of O(log n). © 2006 Wiley Periodicals, Inc. NETWORKS, Vol. 47(4), 237,247 2006 [source] Comparison of carbon monoxide (CO) single breath pulmonary diffusing capacity with non-rebreathing, open-circuit CO pulmonary diffusing capacity in healthy childrenPEDIATRIC PULMONOLOGY, Issue 11 2006Oscar E. Suman PhD Abstract Introduction The standard technique for assessing pulmonary diffusing capacity of the lungs (DL) for carbon monoxide (CO) is the single breath (SB) technique. SB_DLco in children can be problematic because it requires a vital capacity >1.5 L. We have developed an open-circuit technique (OC), which uses the wash-in of CO over a series of 8,10 normal breaths that does not require rebreathing. In this study, we compared the SB_DLco against the OC_DLco. Methods Nineteen healthy children between 7 and 18 years performed SB_DLco and OC_DLco tests. The mean SB_DLco was significantly larger than the mean OC_DLco. The mean difference OC_DLco minus SB_ DLco was: ,2.92,±,4.21 ml/min/mm,Hg, though the difference was negatively correlated with the mean of the two (r,=,0.73). The lower mean OC_DLco was in part due to lower lung volume (as measured by alveolar volume (VA)) during the maneuver. In both groups there was a positive correlation between VA and DLco, and the mean VA was ,2.17,±,1.07 L lower using OC compared to SB. The difference was again negatively correlated with the mean (r,=,0.82). The mean OC minus SB difference in DLco/VA was: 6.06,±,1.98 ml/min/mm,Hg/L, though this difference was positively correlated with the mean, r,=,0.76. Conclusions We found a good correlation between both techniques for DLco, VA, and DLco/VA. The OC offers the advantage of minimal subject cooperation, and may be preferable to use in children. Pediatr Pulmonol. 2006, 41:1095,1102. © 2006 Wiley-Liss, Inc. [source] Subclinical aspirin sensitivity in subjects with nasal polyposisCLINICAL OTOLARYNGOLOGY, Issue 6 2003J.W.W. Killen Subclinical aspirin sensitivity in subjects with nasal polyposis It is unclear whether subclinical airway responses to aspirin occur in subjects with nasal polyps and/or asthma without overt sensitivity. Sixty-three subjects without known aspirin sensitivity (13 controls, 17 nasal polyps alone, 15 nasal polyps and asthma and 18 asthma alone) inhaled increasing concentrations of nebulized lysine aspirin. Forced expiratory volume in 1 s (FEV1), symptoms and other potential markers of an airway response were measured. Four subjects (one polyps alone, one asthma alone, two with both) had a positive response to lysine aspirin predefined as symptoms plus a >10% fall in FEV1 from baseline. However, there was no evidence of a general subclinical response in any of the subject groups: mean (95% CI) change in FEV1; control 0.07 (,0.02,0.16) L, nasal polyps alone ,0.05 (,0.16,0.05) L, nasal polyps with asthma ,0.03 (,0.10,0.04) L, asthma alone ,0.03 (,0.09,0.03) L. We concluded that in the absence of a suggestive clinical history, only a small proportion of patients with nasal polyposis are likely to be sensitive to aspirin. There is no evidence of general subclinical sensitivity to aspirin in subjects with nasal polyps and no relevant history. [source] | |||||||||||||