Trophic Interactions Drive Tree Establishment in the Serengeti Ecosystem

Donaldson, Jason E.; Holdø, Ricardo M.; Sarakikya, Jeremia; Anderson, T. Michael

doi:10.1002/bes2.1992

Cited by 1 publication

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“…This assumption can also be relaxed, allowing vegetation feedbacks on herbivores (Holdo et al ., 2013) and/or fire frequency (Beckage et al ., 2011; Schertzer et al ., 2015). Grazing reduces grass biomass and therefore moderates both fire effects on trees (Staver et al ., 2021; Donaldson et al ., 2022) and the intensity of tree–grass competition (Donaldson et al ., 2022). Fire occurs as a stochastic process (D'Odorico et al ., 2006), with intensity being a function of grass biomass (Higgins et al ., 2000; van Langevelde et al ., 2003).…”

Section: A Synthetic Model Of Tree–grass Coexistence and Savanna Vege...mentioning

confidence: 99%

Linking resource‐ and disturbance‐based models to explain tree–grass coexistence in savannas

Holdø

Nippert

2022

New Phytologist

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Summary Savannas cover a significant fraction of the Earth's land surface. In these ecosystems, C3 trees and C4 grasses coexist persistently, but the mechanisms explaining coexistence remain subject to debate. Different quantitative models have been proposed to explain coexistence, but these models make widely contrasting assumptions about which mechanisms are responsible for savanna persistence. Here, we show that no single existing model fully captures all key elements required to explain tree–grass coexistence across savanna rainfall gradients, but many models make important contributions. We show that recent empirical work allows us to combine many existing elements with new ideas to arrive at a synthesis that combines elements of two dominant frameworks: Walter's two‐layer model and demographic bottlenecks. We propose that functional rooting separation is necessary for coexistence and is the crux of the coexistence problem. It is both well‐supported empirically and necessary for tree persistence, given the comprehensive grass superiority for soil moisture acquisition. We argue that eventual tree dominance through shading is precluded by ecohydrological constraints in dry savannas and by fire and herbivores in wet savannas. Strong asymmetric grass–tree competition for soil moisture limits tree growth, exposing trees to persistent demographic bottlenecks.

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