Optimal method to determine density of the scarce vegetation in dry desert: variable area transect (VAT) applied to saxaul (Haloxylon ammodenderon) community

The assessment of the density and cover of very scarce vegetation in dry habitats may create methodological problems. The variable area transect method (VAT ) is a potential labour-saving sampling method and an alternative to plot (quadrate) method. It allows for density estimation without the time-consuming studies associated with other plot-less density estimators. We used the method in a natural shrubland of Saxaul (Haloxylon ammodenderon C.A.M) to define optimum parameters include transect width and individual’s number to which, distance is measured. Three transect widths were chosen, 10-m, 15-m and 20-m and distances to the 3rd, 4th and 5th individual. Transect width affected the estimation, a 20-m width transect had the least relative bias (–0.5%), and a 10-m width sampling had the greatest bias (–20%). However, all methods underestimated the plant density. The most accurate estimation was with the 3rd plant distance and 20-m transect. As the VAT method is more efficient per unit effort in the field than the quadrate methods, it can be recommended for rapid assessment of desert communities density (like saxaul) especially when plants are dispersed at random.