Comparison of the Whittaker method and distance sampling software for woody vegetation at Loskop Dam Nature Reserve

Abstract

Efficient management decision-making within protected and rangeland conservation areas depends on the monitoring activities that are in place as well as the type of methods used in vegetation sampling. No single method is sufficient to achieve all sampling objectives within different vegetation areas. Sampling methods vary in terms of accuracy, precision, time and cost efficiency. In this study, distance sampling software (DSS) was compared to the Whittaker method for determining species richness, diversity and density of woody vegetation. The Whittaker method was used as a baseline to determine the overall accuracy and precision of the DSS. Sampling plots that were randomly distributed were selected in two structural habitats, namely open and closed woody vegetation. The precision of the DSS was assessed and compared to the Whitaker method using the coefficient of variation (CV). Further, the power to detect change was also assessed for both sampling methods. This study compared DSS measures of time and cost efficiency, accuracy and precision to those of Whittaker method. There was a statistically significant difference (P < 0.05) between DSS and Whittaker method when estimating the time and cost of the survey, suggesting that the Whittaker method is time efficient while DSS is cost efficient. Furthermore, there was no significant difference in terms of precision between the two methods at detecting species richness, species diversity and species density in the entire study area. Moreover, both Whittaker method and DSS showed greater power with an 80% probability of being able to detect significant change in species richness, diversity and density.

Die doeltreffende bestuursbesluitneming binne beskermde en weiveld bewaringsgebiede hang af van die moniteringsaktiwiteite wat in gereedheid is, sowel as die soort metodes wat in steekproefnemings van plante gebruik word. Geen enkelmetode is voldoende om al die steekproefnemingsdoelwitte in verskillende plantegroeigebiede te bereik nie. Steekproefnemingsmetodes verskil ten opsigte van akkuraatheid, presisie, tyd en kostedoeltreffendheid. In hierdie studie is twee metodes van plantegroei-steekproefneming vergelyk om die beste metode te vind vir die bepaling van spesierykheid, diversiteit en digtheid van houtagtige plantegroei. Die metodes wat getoets word, is die afstand-steekproefnemingsagteware (DSS) (puntopnametegniek van afstand-steekproefneming) en die Whittaker-metode. Verskillende plantegroei steekproefneming-terreine (sirkelpunte en kwadrante) – όf ewekansig όf sistematies ewekansig versprei – is gekies. Die akkuraatheid van die twee plantegroei steekproefnemingsmetodes is vergelyk in die navorsingsgebied. Die presisie van die plantegroei-steekproefnemingsmetodes is geassesseer en vergelyk as die variasiekoëffisiënt (CV). Die mag om verandering te bespeur is ook geassesseer vir albei steekproefnemingsmetodes. Verder was die Whittaker-metode na verhouding meer akkuraat as DSS met die assessering van spesierykheid. Daarteenoor was DSS meer akkuraat met die digtheidsassessering van houtagtige spesies. Die twee metodes was ewe akkuraat met die opsporing van spesiediversiteit. Boonop was daar geen beduidende verskil wat betref die presisie tussen die twee metodes in die opsporing van spesierykheid, -diversiteit en -digtheid in die algehele navorsingsgebied nie. Sowel die Whittaker-metode as DSS het ook groter mag getoon, met ’n 80%-waarskynlikheid dat ’n beduidende verandering in spesierykheid, -diversiteit en -digtheid opgespoor kan word.

Go tsaya ditshwetso go go nonofileng ga botsamaisi mo mafelong a a sireleditsweng le a tshomarelo ya naga go ikaegile mo ditiragatsong tsa peoleitlho tse di gona le mefuta ya mekgwa e e dirisiwang go tsaya disampole tsa dimela. Ga go na mofuta o le mongwe o o ka lekanang go fitlhelela maitlhomo otlhe a go tsaya disampole mo mafelong a a farologaneng a a nang le dimela. Mekgwa ya go tsaya sampole e farologana go ya ka go nepa, nako le go nna tlhotlhwatlase. Mo thutopatlisisong eno, go bapisitswe serweboleta sa go tsaya sampole ya sekgala (DSS) le mokgwa wa ga Whittaker wa go swetsa ka go nona, go anama le go kitlana ga mofuta wa dimela tsa ditlhare. Mokgwa wa ga Whittaker o dirisitswe jaaka motheo wa go swetsa ka nepo ya DSS ka kakaretso. Go tlhophilwe mafelo a a farologaneng a disampole tsa dimela tse di kitlaneng le tse di sa kitlanang a a tlhophilweng kwa ntle ga thulaganyo . Go nepa ga DSS go ne ga sekasekwa go bapisitswe le mokgwa wa Whittaker go dirisiwa rešio ya phapogo (coefficient variation (CV)). Go sekasekilwe gape maatla a go lemoga phetogo mo mekgweng ya go tlhopha sampole ka bobedi. Thutopatlisiso eno e bapisitse ditekanyetso tsa DSS tsa nako le botlhotlhwatlase le nepo le tsa mokgwa wa ga Whittaker. Go ne go na le pharologanyo e e maleba ya dipalopalo (P < 0.05) magareng ga DSS le mokgwa wa ga Whittaker fa go fopholediwa nako le ditshenyegelo tsa tshekatsheko, e leng se se tshitshinyang gore mokgwa wa ga Whittaker o boloka nako fa DSS e le tlhotlhwatlase. Mo godimo ga moo, go ne go se na pharologano e e kalo malebana le nepagalo magareng ga mekgwa e mebedi go lemoga go nona ga mefuta, dipharologano tsa mefuta le kitlano ya mefuta mo karolong yotlhe ya thutopatlisiso. Go tlaleletsa, mekgwa ya ga Whittaker le DSS mmogo e bontshitse maatla a magolwane ka kgonagalo ya 80% ya go kgona go lemoga phetogo e e bonalang mo go noneng ga mefuta ya dimela, dipharologano le kitlano.