Interacting effects of grass height and herbivores on the establishment of an encroaching savanna shrub

Hagenah, Nicole; Munkert, H.; Gerhardt, Karin; Olff, Han

doi:10.1007/978-90-481-2798-6_15

Cited by 6 publications

(6 citation statements)

References 63 publications

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“…If grazing can make pasture grasses less vigorous, then they may not be able to act as a competitor against weeds such as Navua sedge. Previous studies have shown that several grasses were negatively affected by simulated grazing for survival, growth and reproduction (Hagenah et al, 2008; Mabry & Wayne, 1997). This trend was exhibited by our focal grasses in terms of reduced tiller number, biomass gained and crown diameter, with humidicola being the more negatively affected species (Figure 3).…”

Section: Discussionmentioning

confidence: 99%

Growth of the invasive Navua sedge (Cyperus aromaticus) under competitive interaction with pasture species and simulated grazing conditions: Implication for management

Shi¹,

Osunkoya²,

Soni

et al. 2022

Ecological Research

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Navua sedge (Cyperus aromaticus), a perennial monocot plant native to tropical Africa, is a major weed in pasture and cropping areas in the wet tropical regions of Australia and South Pacific countries. In grazing pasture lands, rapid growth and reproduction of unpalatable Navua sedge leads to displacement of co-occurring pasture species and depletion of livestock carrying capacity and production. Understanding the interspecific competitive ability of Navua sedge with co-occurring desirable grasses and in response to varying ecological scenarios (e.g., grazing and plant density) is critical for the management of the weed in pasture situations. In a glasshouse setting, two cooccurring pasture species-humidicola (Urochloa humidicola) and Rhodes grass (Chloris gayana) were grown with Navua sedge, in pots using a replacement series model. For each Navua sedge weed-pasture species pair, the experimental setup comprised of four ratios in two densities under simulated grazing and nongrazing conditions of the pasture grasses. Navua sedge growth and reproduction was highest when it grew as a monoculture or when cooccurring pastures were exposed to simulated grazing as this action, reduced the competitiveness of the pasture grasses. Overall and using biomass gained, tiller production and relative yield as indices of growth dynamics, Rhodes grass was more competitive against Navua sedge than humidicola in both grazed and nongrazed conditions especially under high plant density. These results suggest the potential to include competitive pastures in integrated management strategies for Navua sedge, but species selection and grazing practices may influence the effectiveness of this approach.

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Section: Discussionmentioning

confidence: 99%

Growth of the invasive Navua sedge (Cyperus aromaticus) under competitive interaction with pasture species and simulated grazing conditions: Implication for management

Shi¹,

Osunkoya²,

Soni

et al. 2022

Ecological Research

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“…Grass competition was found to be a major factor limiting tree recruitment (Ward and Esler, 2011;Grellier et al, 2012). Frequent and intense grazing may indirectly facilitate tree seedling survival by suppressing grass competition (Hagenah et al, 2009;Ward and Esler, 2011). In our study, grass clipping was performed once only and despite being watered daily, grasses did not eliminate tree saplings.…”

Section: Sapling Survivalmentioning

confidence: 97%

Herbivory effects on saplings are influenced by nutrients and grass competition in a humid South African savanna

Vadigi¹,

Ward²

2014

Perspectives in Plant Ecology, Evolution and Systematics

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“…Thus, while much of the historic woodland losses in Serengeti have been attributed to the recovery of elephant populations and subsequent loss of large trees (McNaughton 1992;Sinclair et al, 2010), our results suggest that browsing, grass, and fire in combination with low grazing intensity during the rinderpest pandemic would have severely limited seedling establishment and hence woodland recovery even after longer-term elephant losses. Invertebrates and rodents consume seedlings in other savanna systems (Goheen et al, 2004;Hagenah et al, 2009;Shaw et al, 2002) and we did not quantify their effects. Both respond negatively to the presence of ungulate herbivores, appearing to be suppressed when ungulate herbivore numbers are high (Goheen et al, 2004(Goheen et al, , 2010Keesing, 1998).…”

Section: Discussionmentioning

confidence: 99%

Fire, grazers, and browsers interact with grass competition to determine tree establishment in an African savanna

Donaldson

Holdø

Sarakikya³

et al. 2022

Ecology

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In savanna ecosystems, fire and herbivory alter the competitive relationship between trees and grasses. Mechanistically, grazing herbivores favor trees by removing grass, which reduces tree-grass competition and limits fire. Conversely, browsing herbivores consume trees and limit their recovery from fire.Herbivore feeding decisions are in turn shaped by risk-resource trade-offs that potentially determine the spatial patterns of herbivory. Identifying the dominant mechanistic pathways by which fire and herbivores control tree cover remains challenging, but is essential for understanding savanna dynamics. We used an experiment in the Serengeti ecosystem and a simple simulation driven by experimental results to address two main aims: (1) determine the importance of direct and indirect effects of grass, fire, and herbivory on seedling establishment and (2) establish whether predators determine the spatial pattern of successful seedling establishment via effects on mesoherbivore distribution. We transplanted tree seedlings into plots with a factorial combination of grass and herbivores (present/absent) across a lion-kill-risk gradient in the Serengeti, burning half of the plots near the end of the experiment. Ungrazed grass limited tree seedling survival directly via competition, indirectly via fire, and by slowing seedling growth, which drove higher seedling mortality during fires. These effects restricted seedling establishment to below 18% and, in conjunction with browsing, resulted in seedling establishment dropping below 5%. In the absence of browsing and fire, grazing drove a 7.5-fold increase in seedling establishment. Lion predation risk had no observable impact on herbivore effects on seedling establishment. The severe negative effects of grass on seedling mortality suggests that regional patterns of tree cover and fire may overestimate the role of fire in limiting tree cover, with regular fires representing a proxy for the competitive effects of grass.

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Interacting effects of grass height and herbivores on the establishment of an encroaching savanna shrub

Cited by 6 publications

References 63 publications

Growth of the invasive Navua sedge (Cyperus aromaticus) under competitive interaction with pasture species and simulated grazing conditions: Implication for management

Growth of the invasive Navua sedge (Cyperus aromaticus) under competitive interaction with pasture species and simulated grazing conditions: Implication for management

Herbivory effects on saplings are influenced by nutrients and grass competition in a humid South African savanna

Fire, grazers, and browsers interact with grass competition to determine tree establishment in an African savanna

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