Detectability of the global weedHypochaeris radicatais influenced by species, environment and observer characteristics

Aims determine the detectability of a global weedy perennial weed radicata and its relationship with five common , species and environmental variables. independent observers conducted time-limited repeat surveys H. radicata during autumn in an endangered grassy boxgum ecosystem in south-east Australia. Single-species -season site-occupancy modelling was used to determine if of H. radicata was altered by five covariates, observer, height, grazing, maximum plant height and flowering state. Findings for H. radicata varied significantly with observer, litter , plant maximum height and flowering state, but not with grazing. significant observer-specific variation, there was a consistent in detectability with plant height and when plants in flower for all observers. Detectability generally decreased as height increases. Perfect or constant detection rates cannot assumed in plant surveys, even for easily recognizable plants in survey conditions. Understanding how detectability is influenced common survey variables can help improve the efficacy of monitoring programs by quantifying the extent of uncertainty inferences made from survey data, or by determining optimal survey to increase the reliability of collected data. For plants traits similar to H. radicata, surveying when most plants are maximum height or in flower, increasing search intensity when levels are high and minimizing observer-related heterogeneity potentially simple and effective ways to reduce detection errors. speculate that detection rates may be lower, more variable and additional covariates when surveying during the peak flowering season with the presence of more warm season and annual species.