Effectiveness of a decade of treatments to reduce invasive buffelgrass (Pennisetum ciliare)

Abstract

The invasion of non-native grasses threatens biodiversity and ecosystem function globally through competition with native plant species and increases to wildfire frequency and intensity. Management actions to reduce buffelgrass [Pennisetum ciliare (L.) Link], an invasive warm season perennial bunchgrass, are widely implemented, with chemical and mechanical treatments extending over two decades within Saguaro National Park in the Sonoran Desert of North America. We assessed how the effectiveness of treatments to reduce P. ciliare cover spanning from 2011 – 2020 were influenced by stage of invasion, treatment type and intensity, and environmental conditions. An increase in treatment effectiveness was largely explained by high initial cover of P. ciliare, an indicator of a late invasion stage and associated with high treatment intensity. Treatments had potential to be effective in patches as small as 0.3 m2P. ciliare canopy area per 400 m2 area (< 0.001% canopy cover) across treatment types and environmental gradients. Chemical treatments had higher or equal effectiveness than mechanical treatments, and greater reductions in P. ciliare were associated with shorter average years of treatment interruptions, or gaps, and to a lesser degree, total years of treatment. In many cases, P. ciliare was reduced with as little as two years of treatment, but more than 3 average years of treatment gap could result in reduced treatment effectiveness. There was generally higher treatment effectiveness on shallow slopes, north and east facing aspects, and on higher elevations within one district of the park. Our findings highlight that resource-intensive treatments in all but the smallest patches of P. ciliare have largely been effective. Further opportunities for improvement include more frequent surveillance, limiting treatment gaps to ≤ 3 years in areas of low P. ciliare cover, and comparing treated to untreated areas.

Effects of Clipping an Invasive Plant Species on the Growth of Planted Plants of Two Co-Occurring Species in a Greenhouse Study

“…Aboveground removal has long been commonly applied as the primary control measure of invasive exotic species [18][19][20]. In our experiment, the biomass of S. canadensis could be reduced by up to 90% by clipping, indicating the high effectiveness.…”

“…The low efficiency, high cost, or environmental problems limit application of traditional measures, such as clipping, mowing, or fire and herbicide application, to control invasive exotic species [18][19][20]. Evidence indicates that restoring native cover can enhance invasion resistance [16,17,31,37].…”

“…Intervention of growth of invasive exotics (mostly that of the aboveground part) with mowing or clipping, prescribed fire, and spraying herbicides are common approaches to control invasive exotics [18][19][20]. Aboveground clipping or mowing can weaken priority effects by reducing their growth vigor and competitive strength with native species [21][22][23][24][25].…”