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A comparison of distance sampling methods in Saxaul (Halloxylon ammodendron (C.A. Mey Bunge) shrub-lands

Kiani B., Fallah A., Tabari M., Hosseini S. M., In Parizi M.-H.

Polish Journal of Ecology

2013

Vol. 61, nr 2

207--219

The primarily goal of plot-less sampling methods is to reduce costs and rapid survey of plant communities. First full inventory was conducted in two 30-ha sites of Saxaul populations geo-morphologically different. In first site (site I), population had random pattern while in second site (site II) clumped pattern was observed. Crown diameters and spatial situation of all trees were recorded using distance and azimuth. Data were transferred to computer and stem map was generated with ArcGIS Software. Distance sampling methods include point-centred quarter method (PCQ), joint-point method (JP), Random pairs method (RP), T-Square method (T-Sq) and Quartered neighbour methods beside fixed area plot (FAP), n-tree and variable area transect (VAT) methods were conducted on generated stem maps. A time study was done aiding indices determined in field works. In site I, point centred quarter estimator with measurements to the second closest individual in each quadrant had the lowest relative bias (RBIAS) in estimating density followed by 3-tree and closest individual methods. In clumped pattern (site II), variable area transect method with measurements to the 4th and 5th closest individuals in each transect brought the best results. The most time consuming methods after fixed area plot, were point centred quarter estimators while methods considering measurement to the closest individual were rapid. Considering RBIAS and Time together, VAT method was the best sampling method in clumped pattern followed by point centred quarter estimator with measurements to the second closest individual in each quadrant and closest individual estimators. In random pattern, point centred quarter estimator with measurements to the second closest individual in each quadrant was the best method followed by 3-treeandclosest individualestimators. But for estimating cover per unit area N-tree methods performed well. As in this site, VAT method located in 4th grade, and due to simplicity of field works related to this method, in the case that the investigator would not be able to clearly define spatial pattern of the population, this method can be recommended as well.

Transportation needs of entrepreneurs in Wroclaw agglomeration - study results

Yedes Y., Chelbi A., Rezg N.

Logistics and Transport

2011

Vol. 12, No. 1

89-100

This paper deals with the integrated supply chain management problem in the context of a single vendor-single buyer system for which the production unit is assumed to randomly shift from an in-control to an out-of-control state. Two different strategies, integrating production, shipment and maintenance policies, are proposed and compared to satisfy the buyers order at a minimum integrated total cost rate. The first strategy is based on a classical production policy for which the buyer's order of size nQ is manufactured continuously and shipped by lots of size Q. The second strategy suggests that the same buyer's order should be produced and shipped separately by equal sized lots Q. For both strate- gies, a corrective or preventive maintenance action is performed at the end of each production cycle, depending on the state of the production unit, and a new setup is carried out. The total integrated average cost per time unit is consid- ered as the performance criterion allowing choosing the best policy for any given situation.