Ecosystem restoration in fire-managed savanna woodlands: Effects on biodiversity, local livelihoods and fire intensity

Abstract

Ethiopia aims to restore 15 million ha degraded forests and woodlands, but effects on the potentially contrasting goals of long-term carbon storage, biodiversity and sustainable livelihoods are unknown. To quantify the effects of grazing exclusion on vegetation and fire behaviour, we established six 30 × 30 m fenced exclosures with grazed controls, in a mesic wooded savanna. Experimental burns were done after 1.5 years. Tree seedlings were few but more common inside fences. Field layer cover and biomass increased inside fences, and grass species increased in numbers and cover. Fire intensity was higher inside fences, killing shrubs and saplings but not mature trees. Interviews confirmed that overgrazing has resulted in “cool fires”, causing shrub encroachment. High-intensity fires occurred in the 1980s after a zoonotic disease killed most livestock. Short-term increase in carbon storage through fire and grazing exclusion may lead to loss of pasture, and in the long-term increased wildfire risk.

A research agenda for the restoration of tropical and subtropical grasslands and savannas

“…Many TGB are maintained by fire (Bond 2019), suggesting that fire management may be needed for restoration (but see edaphic grasslands; Buisson et al 2019). However, understanding natural fire regimes is challenging because of entrenched anthropogenic fire regimes often preventing an accurate assessment of natural fire frequency, timing, and patterns (Archibald et al 2013; Johansson et al 2020; Fig. 11).…”

“…Unfortunately, such policies are strongly forest‐ and tree‐oriented, overestimate the potential of tree planting as a means of climate mitigation (Veldman et al 2019), and do not fully acknowledge limits linked to forest stability and important ecological and climate‐related risks (Anderegg et al 2020). The intense pressure to afforest has even been identified as a major threat to non‐forest ecosystems and human livelihoods (Fagan 2020; Johansson et al 2020; Tölgyesi et al 2020), and provides a compelling reason for establishing a detailed research agenda for the restoration of overlooked and misinterpreted open ecosystems (Temperton et al 2019), including tropical grassy biomes.…”

Effects of large mammalian herbivory, previous fire, and year of burn on fire behavior in an African savanna

“…Herbivores are often drawn to burned areas (Allred et al, 2011; Archibald et al, 2005; Klop et al, 2007; Sensenig et al, 2010; Vinton et al, 1993), to feed on nutritious flushes of fresh regrowth (Foster et al, 2015), as well as on the newly established more palatable species (Greene et al, 2012), but perhaps also for increased antipredator visibility (Eby et al, 2014). Conversely, herbivory by large mammals can decrease fuel loads (Foster et al, 2020; Porensky et al, 2018) and fire intensity (Hobbs et al, 1991, Kimuyu et al, 2014, reviewed in Johnson et al, 2018 and Foster et al, 2020), even to the extent of suppressing fire completely (Johansson et al, 2020; Kimuyu et al, 2014; Liedloff et al, 2001). This effect is strong enough that the use of livestock has been proposed as a tool to mitigate fire risk (Bailey et al, 2019; Nader et al, 2007).…”

Synergistic effects of long‐term herbivory and previous fire on fine‐scale heterogeneity of prescribed grassland burns

“…Interactions among herbaceous vegetation, woody vegetation, and consumers play out dramatically in savannas, which are defined by the coexistence of trees and grasses, and characterized by their potential for alternative states of either grass‐ or tree‐dominated vegetation reinforced by fire and herbivory (Sankaran et al 2008, Touboul et al 2018). There have been an increasing number of studies of how interactions among fire, herbivores, and vegetation in these ecosystems influence the landscape‐scale heterogeneity of tree‐grass ratios (Higgins et al 2000, Sankaran et al 2008, Holdo et al 2009, Hempson et al 2019, Johansson et al 2020) and grass fuel loads (Bielski et al 2018, Starns et al 2019). Fewer examine how these interactions affect fine‐scale landscape heterogeneity (Blackhall et al 2017), despite the assertion that spatial heterogeneity in turn engenders landscape‐level diversity (Pickett and Cadenasso 1995, Stein et al 2014) and resilience to future disturbance (Koontz et al 2019).…”

“…In addition to the separate effects of fire and grazing on fuel heterogeneity, interactions between fire and herbivory, described as “pyric herbivory,” can influence subsequent fuel loads and landscape‐scale spatial complexity (Fuhlendorf et al 2009). Intense herbivory can decrease fuel load, in turn decreasing fire temperatures and continuity, even to the extent of suppressing fire completely (Liedloff et al 2001, Kimuyu et al 2014, Johansson et al 2020). Herbivores often preferentially forage within burned areas, although different herbivore groups may use burned areas differently (Klop et al 2007, Sensenig et al 2010, Allred et al 2011).…”