Tree-grass competition for soil water in arid and semiarid savannas: The role of rainfall intermittency

D’Onofrio, Donatella; Baudena, Mara; D’Andrea, Fabio; Rietkerk, Max; Provenzale, A.

doi:10.1002/2014wr015515

Cited by 48 publications

(34 citation statements)

References 83 publications

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“…podocarpa neither changed the general pattern of the Stipagrostis biomass–rainfall relationship nor affected the grasses dormancy state, but had an immediate and considerable negative impact on the productivity of Stipagrostis tussocks. This reduced growth of Stipagrostis on Crotalaria -affected sites was not compensated for by higher rainfall, indicating rather a competition for below- or above-ground resources such as nitrogen [12,49] or light [50,51] instead of the expected competition for water, as suggested by other studies [49,52]. Further, the reduced productivity obviously weakens the affected tussocks and reduces their ability to survive through the dry season [53], which explains the dramatically decreasing tussock density on Crotalaria -affected sites.…”

Section: Discussionmentioning

confidence: 76%

Herbaceous Legume Encroachment Reduces Grass Productivity and Density in Arid Rangelands

et al. 2016

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Worldwide savannas and arid grasslands are mainly used for livestock grazing, providing livelihood to over a billion people. While normally dominated by perennial C4 grasses, these rangelands are increasingly affected by the massive spread of native, mainly woody legumes. The consequences are often a repression of grass cover and productivity, leading to a reduced carrying capacity. While such encroachment by woody plants has been extensively researched, studies on similar processes involving herbaceous species are rare. We studied the impact of a sustained and massive spread of the native herbaceous legume Crotalaria podocarpa in Namibia’s escarpment region on the locally dominant fodder grasses Stipagrostis ciliata and Stipagrostis uniplumis. We measured tussock densities, biomass production of individual tussocks and tussock dormancy state of Stipagrostis on ten 10 m x 10 m plots affected and ten similarly-sized plots unaffected by C. podocarpa over eight consecutive years and under different seasonal rainfalls and estimated the potential relative productivity of the land. We found the percentage of active Stipagrostis tussocks and the biomass production of individual tussocks to increase asymptotically with higher seasonal rainfall reaching a maximum around 300 mm while the land’s relative productivity under average local rainfall conditions reached only 40% of its potential. Crotalaria podocarpa encroachment had no effect on the proportion of productive grass tussocks, but reduced he productivity of individual Stipagrostis tussocks by a third. This effect of C. podocarpa on grass productivity was immediate and direct and was not compensated for by above-average rainfall. Besides this immediate effect, over time, the density of grass tussocks declined by more than 50% in areas encroached by C. podocarpa further and lastingly reducing the lands carrying capacity. The effects of C. podocarpa on grass productivity hereby resemble those of woody encroachers. Therefore, against the background of global change, the spread of herbaceous legumes and the underlying patterns needs to be further investigated to develop adequate counter measures for a sustainable land use.

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Section: Discussionmentioning

confidence: 76%

Herbaceous Legume Encroachment Reduces Grass Productivity and Density in Arid Rangelands

et al. 2016

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“…due to the space-for-time substitution) with a Monte Carlo approach (MC) (Jakoby et al, 2014;D'Onofrio et al, 2015). For this, the old-field-cal was repeated taking into account the uncertainties in the data (e.g.…”

Section: Parameter Estimationmentioning

confidence: 99%

Increased aridity drives post‐fire recovery of Mediterranean forests towards open shrublands

et al. 2019

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Summary Recent observations suggest that repeated fires could drive Mediterranean forests to shrublands, hosting flammable vegetation that regrows quickly after fire. This feedback supposedly favours shrubland persistence and may be strengthened in the future by predicted increased aridity. An assessment was made of how fires and aridity in combination modulated the dynamics of Mediterranean ecosystems and whether the feedback could be strong enough to maintain shrubland as an alternative stable state to forest. A model was developed for vegetation dynamics, including stochastic fires and different plant fire‐responses. Parameters were calibrated using observational data from a period up to 100 yr ago, from 77 sites with and without fires in Southeast Spain and Southern France. The forest state was resilient to the separate impact of fires and increased aridity. However, water stress could convert forests into open shrublands by hampering post‐fire recovery, with a possible tipping point at intermediate aridity. Projected increases in aridity may reduce the resilience of Mediterranean forests against fires and drive post‐fire ecosystem dynamics toward open shrubland. The main effect of increased aridity is the limitation of post‐fire recovery. Including plant fire‐responses is thus fundamental when modelling the fate of Mediterranean‐type vegetation under climate‐change scenarios.

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“…In tropical savannascharacterized by the coexistence of a continuous C 4 grass layer with a discontinuous tree canopy (Scholes & Archer, 1997;Ratnam et al, 2011) the frequency and intensity of rainfall probably influence the relative dominance of trees and grasses, which differ markedly in their responses to variable soil moisture (Holdo, 2013;D'Onofrio et al, 2015;Xu et al, 2015). However, while the few studies that have examined this phenomenon agree that intra-annual rainfall variability affects savanna vegetation, they disagree fundamentally about whether less frequent, more intense rainfall promotes or reduces tree cover, a key ecosystem property in these systems.…”

Section: Introductionmentioning

confidence: 99%

Soil texture mediates tree responses to rainfall intensity in African savannas

Case

Staver

2018

New Phytologist

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Rainfall variability is a major determinant of soil moisture, but its influence on vegetation structure has been challenging to generalize. This presents a major source of uncertainty in predicting vegetation responses to potentially widespread shifts in rainfall frequency and intensity. In savannas, where trees and grasses coexist, conflicting lines of evidence have suggested, variously, that tree cover can either increase or decrease in response to less frequent, more intense rainfall. Here, we use remote sensing products and continent-wide soil maps for sub-Saharan Africa to analyze how soil texture and fire mediate the response of savanna tree cover to rainfall climatology. Tree cover increased with mean wet-season rainfall and decreased with fire frequency, consistent with previous analyses. However, responses to rainfall intensity varied: tree cover dramatically decreased with rainfall intensity on clayey soils, at high rainfall, and with rainfall spread over longer wet seasons; conversely, on sandy soils, at low rainfall, and with shorter wet seasons, tree cover instead increased with rainfall intensity. Tree cover responses to rainfall climatology depend on soil texture, accounting for substantial variation in tree cover across African savannas. Differences in underlying soils may lead to divergent responses of savannas to global change.

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Tree-grass competition for soil water in arid and semiarid savannas: The role of rainfall intermittency

Cited by 48 publications

References 83 publications

Herbaceous Legume Encroachment Reduces Grass Productivity and Density in Arid Rangelands

Herbaceous Legume Encroachment Reduces Grass Productivity and Density in Arid Rangelands

Increased aridity drives post‐fire recovery of Mediterranean forests towards open shrublands

Soil texture mediates tree responses to rainfall intensity in African savannas

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