A standardized sampling technique for measuring plant diversity is needed to assist in resource inventories and for monitoring long-term trends in vascular plant species richness. The widely used 'Whittaker plot' (Shmida 1984) collects species richness data at multiple spatial scales, using 1 m 2, 10 m 2, and 100 m 2 subplots within a 20 m x 50 m (1000 m 2) plot, but it has three distinct design flaws involving the shape and placement of subplots. We modified and tested a comparable sampling design (Modified-Whittaker plot) that minimizes the problems encountered in the original Whittaker design, while maintaining many of its attractive attributes. We overlaid the two sampling methods in forest and prairie vegetation types in Larimer County, Colorado, USA (n = 13 sites) and Wind Cave National Park, South Dakota, USA (n = 19 sites) and showed that the modified design often returned significantly higher (p < 0.05) species richness values in the 1 m 2, 10 m 2, and 100 m 2 subplots. For all plots, except seven ecotone plots, there was a significant difference (p < 0.001) between the Whittaker plot and the Modified-Whittaker plot when estimating the total number of species in the 1000 m 2 plots based on linear regressions of the subplot data: the Whittaker plot method, on average, underestimated plant species richness by 34%. Species-area relationships, using the Modified-Whittaker design, conformed better to published semilog relationships, explaining, on average, 92% of the variation. Using the original Whittaker design, the semilog species-area relationships were not as strong, explaining only 83% of the variation, on average. The Modified-Whittaker plot design may allow for better estimates of mean species cover, analysis of plant diversity patterns at multiple spatial scales, and trend analysis from monitoring a series of strategically-placed, long-term plots.

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Commercial shipping is the primary pathway of introduction for aquatic nonindigenous species (NIS), mainly through the mechanisms of ballast water and biofouling. In response to this threat, regulatory programs have been established across the globe to regulate and monitor commercial merchant and passenger vessels to assess compliance with local requirements to reduce the likelihood of NIS introductions. Resource limitations often determine the inspection efforts applied by these regulatory agencies to reduce NIS introductions. We present a simple and adaptable model that prioritizes vessel arrivals for inspection using proxies for potential propagule pressure (PPP), namely a ships’ wetted surface area as a proxy for the likelihood of biofouling-mediated PPP and ballast water discharge volume as a proxy for ballast water-mediated PPP. We used a California-specific dataset of vessels that arrived at California ports between 2015 and 2018 to test the proposed model and demonstrate how a finite set of inspection resources can be applied to target vessels with the greatest PPP. The proposed tool is adaptable by jurisdiction, scalable to different segments of the vessel population, adjustable based on the vector of interest, and versatile because it allows combined or separate analyses of the PPP components. The approach can be adopted in any jurisdiction across the globe, especially jurisdictions without access to, or authority to collect, risk profiling data or direct measurements for all incoming vessel arrivals.

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