An ocular technique for estimating utilization of karoo bushes

Abstract

A subjective technique for estimating utilization of karoo bushes is evaluated and guidelines for its use are proposed. Taking the average utilization from estimates on 30–40 bushes, 20% differences in utilization could be distinguished as significant ‐ even when different operators were used. Zero and 100% levels of utilization were judged with greater accuracy and precision than intermediate levels. However, if more than 30 bushes are taken per sample the precision and accuracy at all levels is adequate. Acceptable levels of accuracy were obtained with fewer bushes than that required for adequate precision. Using similar sample sizes the ocular‐estimation technique was more precise and more accurate than objective techniques. Furthermore, this technique was far more efficient than any of the objective techniques.

‘n Subjektiewe tegniek om die benutting van karoobossies te beraam is geëvalueer en riglyne vir die gebruik daarvan voorgestel. Met inagneming van die gemiddelde benutting van geskatte waardes vanaf 30–40 bossies, kan 20% verskille in benutting as betekenisvol onderskei word, selfs wanneer verskillende operateurs gebruik word. Nul en 100% vlakke van benutting kon noukeuriger en meer akkuraat geskat word as die vlakke tussenin. Indien daar egter minstens 30 bossies gemonster word, kan aanvaarbare noukeurigheid en akkuraatheid teen alle vlakke verwag word. Aanvaarbare vlakke van akkuraatheid is verkry met minder bossies as wat vereis word vir voldoende noukeurigheid. Met die gebruik van dieselfde grootte monsters was die okulêr‐skattingsmetode noukeuriger en akkurater as objektiewe tegnieke. Boonop was die skattingsmetode baie doeltreffender as enige van die objektiewe tegnieke.

Additional index words:

• Dwarf shrubs
• subjective estimation