106,959 research outputs found
Frequent burning promotes invasions of alien plants into a mesic African savanna
No full textFire is both inevitable and necessary for maintaining the structure and functioning of mesic savannas. Without disturbances such as fire and herbivory, tree cover can increase at the expense of grass cover and over time dominate mesic savannas. Consequently, repeated burning is widely used to suppress tree recruitment and control bush encroachment. However, the effect of regular burning on invasion by alien plant species is little understood. Here, vegetation data from a long-term fire experiment, which began in 1953 in a mesic Zimbabwean savanna, were used to test whether the frequency of burning promoted alien plant invasion. The fire treatments consisted of late season fires, lit at 1-, 2-, 3-, and 4-year intervals, and these regularly burnt plots were compared with unburnt plots. Results show that over half a century of frequent burning promoted the invasion by alien plants relative to areas where fire was excluded. More alien plant species became established in plots that had a higher frequency of burning. The proportion of alien species in the species assemblage was highest in the annually burnt plots followed by plots burnt biennially. Alien plant invasion was lowest in plots protected from fire but did not differ significantly between plots burnt triennially and quadrennially. Further, the abundance of five alien forbs increased significantly as the interval (in years) between fires became shorter. On average, the density of these alien forbs in annually burnt plots was at least ten times as high as the density of unburnt plots. Plant diversity was also altered by long-term burning. Total plant species richness was significantly lower in the unburnt plots compared to regularly burnt plots. These findings suggest that frequent burning of mesic savannas enhances invasion by alien plants, with short intervals between fires favouring alien forbs. Therefore, reducing the frequency of burning may be a key to minimising the risk of alien plant spread into mesic savannas, which is important because invasive plants pose a threat to native biodiversity and may alter savanna functioning
Physiological adjustments to arid and mesic environments in larks (Alaudidae)
No full textBecause deserts are characterized by low food availability, high ambient temperature extremes, and absence of drinking water, one might expect that birds that live in these conditions exhibit a lower basal metabolic rate ( BMR), reduced total evaporative water loss (TEWL), and greater ability to cope with high air temperatures than their mesic counterparts. To minimize confounding effects of phylogeny, we compared the physiological performance of four species of larks at ambient temperatures (T-a's) ranging from 0degrees to 50degreesC: hoopoe larks (Alaemon alaudipes) and Dunn's larks ( Eremalauda dunni) live in hot and dry deserts, whereas skylarks (Alauda arvensis) and woodlarks (Lullula arborea) occur in temperate mesic areas. Mass-adjusted BMR and TEWL were indistinguishable between hoopoe lark and Dunn's lark and between skylark and woodlark. When grouping the data of the two desert larks in one set and the data of the two mesic larks in another, desert larks are shown to have 43% lower BMR levels and 27% lower TEWL values than the mesic species. Their body temperatures (T-b's) were 1.1degreesC lower, and the minimal dry heat transfer coefficients ( h) were 26% below values for the mesic larks. When T a exceeded T-b, the h of hoopoe larks and Dunn's larks was high and indistinguishable from h at 40 degreesC, in contrast to the prediction that h should be decreased to minimize heat gain through conductance, convection, or radiation from the environment when T-a exceeds T-b
ENSTAR detector for eta-mesic studies
No full textWe have initiated a search for a new type of nuclear matter, the eta-mesic nucleus, using beams from the multi-GeV hadron facility, COSY at Juelich, Germany. A large acceptance scintillator detector, ENSTAR has been designed and built at BARC, Mumbai and fully assembled and tested at COSY. A test run for calibration and evaluation has been completed. In this contribution we present the design and technical details of the ENSTAR detector and how it will be used to detect protons and pions (the decay products of eta-mesic bound state). The detector is made of plastic scintillators arranged in three concentric cylindrical layers. The readout of the detectors is by means of optical fibres. The layers axe used to generate Delta E - E spectra for particle identification and total energy information of stopped particles. The granularity of the detector allows for position (theta and phi) determination making the event reconstruction kinematically complete
Canopy transpiration of Jeffrey pine in mesic and xeric microsites: O3 uptake and injury response
No full textCanopy transpiration of mature Jeffrey pine was compared in "mesic" and "xeric" microsites differing in topographical position, bole growth, and the level of drought stress experienced. Diurnal and seasonal course of canopy transpiration was monitored with thermal dissipation probes in 1999 and 2000. Mid-canopy measures of diurnal foliar stomatal conductance (gs) were taken in June and August in 1999. In early summer, there was little difference between trees in either microsite with regard to gs (55 mmol H2O m-2s-1), canopy transpiration (4.0 1 h-1), and total duration of active transpiration (12 h >0.03 1 h-1). In late summer, xeric trees had a lower daily maximum gs (by 30%), a greater reduction in whole canopy transpiration relative to the seasonal maximum (66 vs 79%), and stomata were open 2 h less per day than in mesic trees. Based on leaf-level gas exchange measurements, trees in mesic sites had an estimated 46% decrease in O3 uptake from June to August. Xeric trees had an estimated 72% decrease over the same time period. A multivariate analysis of morphological and tissue chemistry attributes in mid-canopy elucidated differences in mesic and xeric tree response. Mesic trees exhibited more O3 injury than xeric trees based on reduced foliar nitrogen content and needle retention in mid-canopy
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Spectroscopy of -mesic nuclei with WASA at GSI/FAIR
No full textWe plan to conduct an experimental search for η′-mesic nuclei in order to investigate in-medium properties of the η′ meson. A 2.5 GeV proton beam is employed to produce η′-mesic 11C nuclei with the 12C(p,d)η′⊗11C reaction. Simultaneous measurements of the forward ejected deuterons and decay protons from η′-mesic nuclei will allow us to achieve high experimental sensitivity. The experiment will be performed at GSI by making full use of the fragment separator FRS and the WASA detector system. The plan of this proposed experiment is described
Farm level cost of reducing nitrate leaching by economic instruments in Croatian farming systems
No full textCroatian farming systems have become more intensive in recent years. There is some evidence of rising NO3-N-levels in ground water. The aim of the paper is to find pos-sible ways of preventing NO3-levels to rise in Croatian farming systems and their im-plications from the viewpoint of the manager. More specifically the purpose is to 1. Determine whether Croatian farmers exceed profit maximising levels of N-fertiliser use in maize cultivation and possible influence on NO3-N-levels. 2. To estimate the marginal abatement cost (MAC) at farm level of reducing NO3-N leaching through following economic instruments: a tax on optimal N-doses, a product tax and a N-fertiliser quota, all instruments corresponding to the same abatement level. Based on N-response experiments from field trials for maize N-response curves were derived. A sample of 20 family farms was used to calculate intensity, nutrient content in manure and the prices paid for N and obtained for maize. Profit maximising doses from the field trials were compared with nutrient use on farms. An effluent production function was estimated based on experiments with NO3-N contents in lysimeter water for the same treatments as in the N-response experiments. The results indicate that farmers use higher than optimal levels of N-fertilisers, if the technology and conditions of experimental fields could be applied on the farms and if manure is accounted for. Neglecting the N-content of the manure shows close to optimal nutrient levels. At profit maximising levels the NO3-N level is approximately 14 mg NO3-N/l (62 mg NO3/l) or clearly higher that the critical level stipulated by the nitrate directive (11.3 mg NO3-N/l or 50 mg NO3/l). If the N-content in the manure is taken into account the esti-mated NO3-N/l level in groundwater is about twice higher than the critical level stipulated by the Nitrate Directive. Through any of the three instruments a 76% NO3-leaching reduction could be obtained. However, it was concluded the quota has the lowest MAC (4.08 /mg NO3-N/l or 0.92 /mg NO3/l), followed by the N-fertiliser tax (16.16 /mg NO3-N/l or 3.65 /mg NO3/l) and the product tax in third place (41.25 /mg NO3-N/l or 9.32 /mg NO3/l). Management practices that may increase yield level and correspondingly NO3-leaching in the short and long run were identified. One way to achieve a quick improvement would be a system of cross compliance stipulating a code of good agricultural practices.Farm Management,
Water sources for street trees in mesic urban environments
No full textIsotopic composition of potential water sources and water extracted from tree stems in Boston, Massachusetts, United States during August and September 2021. These are the data for the manuscript "Water sources for street trees in mesic urban environments" by Ian A. Smith, Pamela H. Templer, and Lucy R. Hutyra
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Salt intake and regulation in two passerine nectar drinkers: white-bellied sunbirds and New Holland honeyeaters
No full textAvian nectarivores face the dilemma of having to conserve salts while consuming large volumes of a dilute, electrolyte-deficient diet. This study evaluates the responses to salt solutions and the regulation of salt intake in white-bellied sunbirds (Cinnyris talatala) and New Holland honeyeaters (Phylidonyris novaehollandiae). Birds were first offered a choice of four sucrose diets, containing no salt or 25, 50 or 75 mM NaCl. The experiment was repeated using five sucrose concentrations (0.075-0.63 M) as the base solution. Both species ingested similar amounts of all diets when fed the concentrated base solutions. However, when birds had to increase their intake to obtain enough energy on the dilute sucrose diets, there was a general avoidance of the higher salt concentrations. Through this diet switching, birds maintained constant intakes of both sucrose and sodium; the latter may contribute to absorption of their sugar diets. A second, no-choice experiment was designed to elucidate the renal concentrating abilities of these two nectarivores, by feeding them 0.63 M sucrose containing 5-200 mM NaCl over a 4-h trial. In both species, cloacal fluid osmolalities increased with diet NaCl concentration, but honeyeaters tended to retain ingested Na+, while sunbirds excreted it. Comparison of Na+ and K+ concentrations in ureteral urine and cloacal fluid showed that K+, but not Na+, was reabsorbed in the lower intestine of both species. The kidneys of sunbirds and honeyeaters, like those of hummingbirds, are well suited to diluting urine; however, they also appear to concentrate urine efficiently when necessary
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