Plant community responses to bison reintroduction on the Northern Great Plains, United States: a test of the keystone species concept

Abstract

Keystone species restoration, or the restoration of species whose effect on an ecosystem is much greater than their abundance would suggest, is a central justification for many wildlife reintroduction projects globally. Following restoration, plains bison (Bison bison L.) have been identified as a keystone species in the tallgrass prairie ecoregion, but we know of no research to document similar effects in the mixed-grass prairie where restoration efforts are ongoing. This study addresses whether Northern Great Plains (NGP) mixed-grass prairie plant communities exhibit traits consistent with four central keystone effects documented for bison in the tallgrass prairie. We collected species composition, diversity, abundance, bare ground cover, and plant height data in three treatments: where livestock (Bos taurus L.) continuously grazed, livestock were removed for 10 years, and bison have been introduced and resident for 10 years. We observed mixed support for bison acting as keystone species in this system. Supporting the keystone role of bison, we observed higher species richness and compositional heterogeneity ( -diversity) in the bison treatment than either the livestock retention or livestock removal treatments. However, we observed comparable forb, bare ground, and plant height heterogeneity between bison-restored sites and sites where livestock were retained, contradicting reported keystone effects in other systems. Our results suggest that after 10 years of being restored, bison partially fulfill their role as a keystone species in the mixed-grass prairie, and we encourage continued long-term data collection to evaluate their influence in the NGP.

Are bison movements dependent on season and time of day? Investigating movement across two complex grasslands

“…Seasonal and diurnal rhythms are known to affect ungulate movement broadly (Johnson et al 2002, Owen‐Smith et al 2012, Owen‐Smith and Goodall 2014), but the importance of these basic and critical factors has been mostly overlooked for American bison. Therefore, as many bison reintroduction projects are ongoing across the Great Plains (Fuhlendorf et al 2018, McMillan et al 2019), addressing gaps in our fundamental understanding of bison movement has significant management and conservation value. We conducted this descriptive study asking: (1) Does bison movement probability and (2) distance change between seasons and times of day; or are they better explained by differences between the two independent herds and landscapes alone?…”

“…Since their decline in the 19th century, American bison (Bison bison L.) have become an icon for many grassland restoration and conservation organizations in North America. Many of these groups cite hypothesized keystone effects that bison may have on grassland ecosystems as a rationale for some of the reintroduction projects v www.esajournals.org that are ongoing (Fuhlendorf et al 2018, McMillan et al 2019. However, there is evidence that these effects are often confounded with management actions and may not be due to bison reintroduction alone (Allred et al 2011b, Fuhlendorf et al 2018.…”

The Sustainability of Bison Production in North America: A Scoping Review

“…Paine [32] was the first to define keystone species as those that have an extremely high impact on a given ecosystem relative to their small population. Numerous studies conclude that bison, both historically and presently, play a crucial role in the conservation of biodiversity in the Great Plains and can therefore be considered as a keystone species [13,31,33]. From this, it can be deduced that the bison can promote the biodiversity of both plants and the animals on the Great Plains to a greater extent than modern-day cattle farming [14].…”

Grassland bird diversity and abundance in the presence of native and non-native grazers

“…There is evidence that restoration of bison at small scales can lead to increased diversity in insects and plants compared with cattle grazing (Moran 2014, McMillan et al 2018, Nickell et al 2018), but patterns in birds are equivocal. Combining fire and bison restoration resulted in similar bird communities compared with cattle in one study (Greibel et al 1998), and reduced densities and diversity in another (Lueders et al 2006).…”