Spatial Pattern Analysis for Underground Propagules ofPotamogeton gramineusL. in Two Northern California Irrigation Canals

We sampled areas of two canals (Solano Irrigation District, California) that were dominated by Potamogeton gramineus L. The ratios of variance to mean for winter bud abundance in the Byrnes Canal indicated that winter buds were not randomly distributed. Clumping was detected at a patch size of 7.2 cm diameter in both 1985 and 1989. Applying two quadrat variance methods to data from the Weyend Canal also indicated that winter buds were clumped. The radius of the patch size was 1.65 m. Patch edges were not sharply defined, and the spaces between patches were not empty. Geostatistical analysis yielded an experimental semivariogram for winter bud abundance, using the spherical equation, with a sill of 49776, a nugget of 32378, and a range of influence of 57 m.