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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Rangeland Resources & Systems Research » Research » Publications at this Location » Publication #381644

Research Project: Adaptive Grazing Management and Decision Support to Enhance Ecosystem Services in the Western Great Plains

Location: Rangeland Resources & Systems Research

Title: Large herbivores suppress liana infestation in an African savanna

item COVERDALE, T - Princeton University
item O'CONNELL, R - Princeton University
item HUTCHINSON, M - Princeton University
item SAVAGIAN, A - Princeton University
item KARTZINEL, T - Brown University
item PALMER, T - University Of Florida
item GOHEEN, J - University Of Wyoming
item Augustine, David
item SANKARAN, M - Leeds University
item TARRITA, C - Princeton University
item PRINGLE, R - Princeton University

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2021
Publication Date: 9/27/2021
Citation: Coverdale, T.C., O'Connell, R., Hutchinson, M.C., Savagian, A., Kartzinel, T.R., Palmer, T.M., Goheen, J.R., Augustine, D.J., Sankaran, M., Tarrita, C.E., Pringle, R.M. 2021. Large herbivores suppress liana infestation in an African savanna. Proceedings of the National Academy of Sciences (PNAS). 118(4). Article e2101676118.

Interpretive Summary: Rangelands in Africa typically support a combination of livestock and native large herbivores. While there is concern that native large herbivores often compete with livestock, these native species can often affect the rangeland in ways that are beneficial to livestock and other wildlife, because they can suppress the proliferation of certain unpalatable or aggressively growing plant species. We used two long-term exclosure experiments in an East African rangeland (central Kenya) to examine how native large herbivores affect the abundance of certain species of lianas (vines that grow into shrubs and trees). Exclusion of native browsing species, especially elephants, let to these vines aggressively growing over the canopies of most native shrubs and trees, (increasing in cover by 30-fold) suppressing their growth. Browsing livestock do not eat these vines, so replacement of native wildlife with domestic species could fundamentally alter the plant composition of these rangelands.

Technical Abstract: African savannas are the last stronghold of diverse large-mammal communities, and a major focus of savanna ecology is to understand how these animals shape the relative abundance of trees and grasses. Yet savannas support diverse plant life-forms, and human-induced changes in large-herbivore assemblages—declining wild populations and their displacement by livestock—may cause unexpected shifts in plant community composition. We investigated how herbivory affects the prevalence of lianas (woody vines) and their impact on trees in an East African savanna. Although scarce (<2% of tree canopy area) and defended by toxic latex, the dominant liana, Cynanchum viminale (Apocynaceae), was eaten by 15 wild large-herbivore species and rapidly consumed by browsers in experimental cafeteria trials. In contrast, lianas were rarely eaten by domesticated ungulates. When herbivores were experimentally excluded for periods of 8 and 17 years (simulating extirpation), liana abundance increased >30-fold (with up to 75% of trees infested), and piecemeal exclusion of different-sized herbivores showed functional complementarity among size classes in suppressing lianas. Liana infestation reduced tree growth and reproduction, but lianas were quickly cleared from trees following removal of 18-year-old exclosure fences (simulating rewilding). A simple model of liana contagion showed that, without large herbivores, the long-term equilibrium could be either endemic (liana-tree coexistence) or an all-liana alternative stable state. We conclude that ongoing declines of wild large-herbivore populations will disrupt the structure and functioning of many African savannas in ways that have received little attention and that may not be mitigated by the replacement of wildlife with livestock.