Which sampling method involves measuring stationary species within a marked square for biodiversity assessment?

Quadrat sampling is a method used in biodiversity assessments where researchers measure and record stationary species within a defined square area, known as a quadrat. This technique allows for systematic sampling of specified portions of an ecosystem to estimate the abundance and distribution of various organisms, particularly plants or sessile animals.

In this method, the researcher lays out one or more quadrats of a standardized size in the study area, which can help quantify species richness and density. By examining the species present in multiple quadrats, researchers can draw conclusions about the biodiversity and health of the ecosystem being studied. This method is particularly effective for studying habitats like grasslands, forests, and other ecosystems where organisms are often found in fixed locations.

Other sampling methods listed, such as transect sampling, involve a linear approach and are used to assess changes across a gradient rather than within a defined area. Netting and canopy fogging are techniques primarily used for capturing mobile organisms, which does not align with the assessment of stationary species within a marked square.