جستجوی مقالات مرتبط با کلیدواژه « double sampling » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Proper range management needs an accurate and updated method of rangelands production measurement. In range production measurements, selecting an accurate and low-cost method is very important. In the present study, three estimation methods including Adelaide technique, and double sampling using the 20 and 30% of vegetation cover were compared with clipping and weighing method (as control) in two shrub species of Halocnemum strobilaceum (Pall.) Bieb and Halostachys caspica C. A. Mey (in May 2017). In each vegetation area, two 300m length transects with 100m distance randomly were placed. Data were collected from 15 quadrates 4m2 along each transect systematically. In each plot, the vegetation cover and yield of two species were estimated and harvested. Data were analyzed regarding variance for each species and means comparison was done using Duncan method. Regression analysis was performed for each method between the estimated and actual clipping rates. The result showed that in H. strobilaceum, there were no significant differences between both double sampling with 20% and 30% and control. But higher estimation was obtained by Adelaide method than control. For H. caspica, there was no significant difference between both Adelaide and double sampling 30% with control. But the yield estimation of double sampling 20% was significantly higher than control. Also, the regression relationship was well matched to the data. It was concluded that the double sampling method was more suitable for H. strobilaceum species due to its symmetrical diameter of the canopy. The Adelaide method was recommended for H. caspica, which has separate foliage.

To find an accurate and rapid method of estimating herbage crop, Double Sampling (DS), Comparative Yield (CY), and clipping and weighing (CW) methods were applied to a summer rangeland in North-eastern Alborz Mountains, Iran. The method was called SMFY (Simulation Model of Forage Yield) to emphasize the statistical aspects of simulated model. In representative stands five 1-m2 reference plots were chosen to represent the ranges of standing crop. Using a systematic-random design, 180 1-m2 plots were ranked against the reference plots for CY, visually estimated for DS, and subsequently, all of them were Clipped and Weighed (CW). After clipping and weighing 5 reference plots with 6 replications for CY and estimating and clipping 37 plots for DS, regression lines were plotted between the estimated, ranked, and clipped plots. This study was conducted during 2011-13. There was high correlation (0.90-0.99) for DS and CY, so the estimated and ranked data were corrected based on the regression equations. There were strong linear relationships between the corrected and clipped data for the DS and CY methodswhich confirmed the suitability of both methods against the CW, so all of 180 estimated plots were corrected and were compared by ANOVA. The non-significant F for CY, DS, and CW confirmed the high efficiency of DS and CY, so based on the estimated production, grazing capacity of study area was calculated. Preferring one of these methods depends on further research in time and cost efficiency of DS and CY. Available DM of 389.75 kg/ha support 6.5 AUM per ha and for the grazing period of 4 months, each hectare of this rangeland can carry on 1.62 AU per ha. The current stocking rate of study area is about 0.82 AU per hectare which was suitable based on carrying capacity of study area.

Today, in the rangeland management science and determination of range capacity, accurate and true information about range production is crucial. In fact, range production is considered as a basis for range management. The aim of this study was to compare different methods for the estimation of forage production with four sampling methods in the rangelands of Kurdistan province, Iran. The sampling methods were Adelaide technique, double sampling, estimating method, clipping and weighting method (control). A two-way analysis of variance was made to compare the methods and vegetation types. The estimating methods and plant vegetation types were considered as treatments and blocks, respectively. The results showed that Adelaide method had no significant difference with control method and was selected as the best method for estimating the plant production in the rangelands of study area with dominant shrub plants. A significant difference was obtained between control and estimation methods. Therefore, this method had lower accuracy for estimating the production of range plants. The results showed that the composition of range plants was an effective factor on the accuracy of estimating methods and also paying attention to ecosystem variability was an important key to achieve a suitable method in order to estimate the range production. A significant difference was obtained between double sampling method and clipping and weighting method (control). It was due to various plant combinations of the study area. Therefore, the double sampling had lower efficiency than clipping and weighting method to estimate various plant species such as grasses, shrub and herbaceous plants.