Detectability of species of Carex varies with abundance, morphology, and site complexity

摘要

Questions Are graminoids more poorly detected than other life forms of vascular plants in surveys? How well do observer-, species-, and site-specific variables explain variation in detection of Carex species across forests of different structure? Location Northeastern Alberta, Canada. Methods Species inventories were assessed within 50 belt transects, each 100 m in length and 2 m in width. Pseudoturnover was estimated for four life forms and all encountered species. Site-specific factors were then compared with pseudoturnover of all vascular plants and graminoids using generalized linear regression. Carex detection probabilities were compared based on morphological groups. Detection success at a site and delays in detection within a site were assessed using logistic regression with AIC used to rank a-priori hypotheses and standardized variables used to determine effect sizes of parameters related to plant detectability. Results Pseudoturnover for graminoids was similar to that for other life forms and best related to ground layer cover. Morphological groups related to differences in detection, with short, small-inflorescence Carex most poorly detected. Detection failure was best explained by species abundance and morphology, but delays were more tied to a site's vegetation structure and species abundance than to species morphology. Conclusions Surveys targeting graminoids, including species of Carex, can achieve high detection rates with high survey effort over small areas, but should consider species- and site-specific biases in detection success. Abundance is likely the most influential factor in determining detection success, and this must be accounted for when searching for low-density species. We recommend that increased effort (time, repeat observations) be applied when searching for morphologically small graminoids.