Effect of patch size on establishment and productivity of Opuntia columbiana

Abstract

Efforts are underway to return Opuntia columbiana Griffiths (pro sp.) [fragilis × polyacantha] (Ištíš, grizzleybear pricklypear [Cactaceae]) to a mitigation area in the Columbia Basin that is now dominated by invasive species. The relationship between patch size of densely installed pads and survival along with production was examined. This study was done by installing, in separate plots, 1, 3, 6, 18, or 30 pads and replicating this 6 times. Patch size or year had no effect on percent survival, which was 77 ± 5.5% in 2019 and 67 ± 6.1% in 2020. Productivity (the number of new pads/the number of remaining installed pads) decreased with increasing patch size with an estimated maximum of 4 new pads/to the number of remaining installed pads at the 1-pad patch size dropping to 1.2 at the 29-pad patch size. Of the 348 pads installed, 232 remained, producing 574 new pads by 2020. The production of new pads of this First Foods species will be greatest when pads are installed at low density