Assessment of Commonly Used Sampling and Measurements Techniques as Related to Natural Rangeland Management

Abstract

This study was conducted in “El Baja” area near "Habeela" village, which is located in El Duim locality, in semi-arid zone White Nile State, in August 2007. The objective of this study was to assess the different commonly used vegetation measurements as related to range management objectives. Sampling based on locating eight transects randomly in a plot area of 1x1km. Four of these transects were 100m long, while the other four was 50m long. Two quadrate sizes (1x1m and 0.5x1m) were used. In each, transect both quadrate sizes were used at 10m and 20m intervals in transects length 50m and 100m respectively, five from each size alternately, to yield ten quadrate readings in each transects. All measurements attributes were taken along transects and across the two quadrate sizes. The main results of this study indicated that, the loop readings tend to overestimate plant cover compared with the quadrate based estimation method. Since, rangelands here are dominated by herbaceous cover compared with grasslands of subtropical areas. There are no differences that can affect the cover assessment among the two quadrate sizes and transect lengths, which make cover percentages less sensitive to size and transect lengths if sufficient number of samples were taken. The long transects (100m) overcome the effect of patchy occurrence of some species while the short transects (50m) may fit in relatively homogenous range area. For plant composition short length transect (50m) showed higher readings compared with longer transects (100m) as a result of patchy existence of some species The study also concluded that, frequency found to be less sensitive for quadrate size within the same transects length. In general, quadrate size is less sensitive compared with transect lengths. Plant density is less affected by both transect lengths and quadrate sizes as it express number of individual plants existing rather than types of species. The differences between the actual weighing and estimation in the weight estimation method of biomass or range productivity assessment found to be within a percentage of 17%. This percentage could be accepted in an intensive range measurements activity and not expected to affect decision for carrying capacity in the management of natural rangeland. Further, estimation method found to be more suitable method to assess the range productivity, provided that ranger will develop more experience in this respect if it become a common practice for biomass assessment. The study recommended that the long transects (100m) or even longer can be used in the rangelands inventories, to avoid the overestimation in readings when we were using the loop method for vegetation composition, and to avoid patchy existence of some species. Weight estimation method for biomass assessment found to be more practical, less destructive, time saving and less costly if used, provided that more experience will be gained by users with more practicing in this respect.