Disturbance as a factor in breaking dormancy and enhancing invasiveness of African grasses in a Neotropical Savanna

Gorgone‐Barbosa, Elizabeth; Pivello, Vânia Regina; Baeza, M. Jaime; Fidelis, Alessandra

doi:10.1590/0102-33062015abb0317

Cited by 33 publications

(25 citation statements)

References 39 publications

(40 reference statements)

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“…underground storage organs) to survive repeated aboveground disturbances, apparently at the cost of colonisation potential (Silcock & Scattini, ; Veldman et al ., ; Silveira et al ., ), grasslands on former agricultural land fail to recover their characteristic plant communities even after many decades (Kirkman et al ., ; Brudvig et al ., ; Vieira et al ., ). Whereas recolonisation of characteristic old‐growth grassland species is extremely limited in secondary grasslands (Silcock & Scattini, ; Ilunga wa Ilunga et al ., ; Veldman et al ., ; Silveira et al ., ), many non‐native invasive and native weedy species are rapid colonisers of post‐agricultural grasslands due to their higher germination and better ability to establish in disturbed environments (Brudvig et al ., ; Gorgone‐Barbosa et al ., ). These weedy species can limit the establishment of desired old‐growth grassland species (Zaloumis, ; Gorgone‐Barbosa, ; Le Stradic et al ., ), posing a huge hurdle to restoration (see also Section II.6).…”

Section: Resiliencementioning

confidence: 97%

“…Urochloa brizantha ) can reduce ecosystem flammability relative to native‐dominated grasslands, but this can depend on the fire season (Gorgone‐Barbosa et al ., ). Although fire can be effective at controlling fire‐sensitive invasive species (Stevens & Beckage, ; te Beest et al ., ), fire can also promote invasive species that evolved with frequent fires ( Imperata cylindrica ; Lippincott, ) or indirectly promote invasive species by opening recruitment sites, suitable for germination ( Urochloa brizantha and Urochloa decumbens ; Gorgone‐Barbosa et al ., , b ). The fire ecology of invasive species should therefore be carefully considered as part of fire management (Gorgone‐Barbosa, ) in tropical grassland restoration.…”

Section: Restorationmentioning

confidence: 99%

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Resilience and restoration of tropical and subtropical grasslands, savannas, and grassy woodlands

et al. 2018

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Despite growing recognition of the conservation values of grassy biomes, our understanding of how to maintain and restore biodiverse tropical grasslands (including savannas and open‐canopy grassy woodlands) remains limited. To incorporate grasslands into large‐scale restoration efforts, we synthesised existing ecological knowledge of tropical grassland resilience and approaches to plant community restoration. Tropical grassland plant communities are resilient to, and often dependent on, the endogenous disturbances with which they evolved – frequent fires and native megafaunal herbivory. In stark contrast, tropical grasslands are extremely vulnerable to human‐caused exogenous disturbances, particularly those that alter soils and destroy belowground biomass (e.g. tillage agriculture, surface mining); tropical grassland restoration after severe soil disturbances is expensive and rarely achieves management targets. Where grasslands have been degraded by altered disturbance regimes (e.g. fire exclusion), exotic plant invasions, or afforestation, restoration efforts can recreate vegetation structure (i.e. historical tree density and herbaceous ground cover), but species‐diverse plant communities, including endemic species, are slow to recover. Complicating plant‐community restoration efforts, many tropical grassland species, particularly those that invest in underground storage organs, are difficult to propagate and re‐establish. To guide restoration decisions, we draw on the old‐growth grassland concept, the novel ecosystem concept, and theory regarding tree cover along resource gradients in savannas to propose a conceptual framework that classifies tropical grasslands into three broad ecosystem states. These states are: (1) old‐growth grasslands (i.e. ancient, biodiverse grassy ecosystems), where management should focus on the maintenance of disturbance regimes; (2) hybrid grasslands, where restoration should emphasise a return towards the old‐growth state; and (3) novel ecosystems, where the magnitude of environmental change (i.e. a shift to an alternative ecosystem state) or the socioecological context preclude a return to historical conditions.

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Section: Resiliencementioning

confidence: 97%

Section: Restorationmentioning

confidence: 99%

Resilience and restoration of tropical and subtropical grasslands, savannas, and grassy woodlands

et al. 2018

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“…There are likely several mechanisms by which fire increased cheatgrass invasion by more than an order of magnitude in our experimental plots (Figure ). It is likely that the most important was the loss of the native plant community, which can create biotic resistance to invasion through competition for space and soil resources (Chambers et al, ; Melgoza et al, ; Prevey et al ) and lead to more ideal germination conditions for invasion (Gorgone‐Barbosa, Pivello, Baeza, & Fidelis, ). Fire also causes physical disruption of soil crusts, which are known to inhibit the germination success of invasive grasses (Kaltenecker, Wicklow‐Howard, & Pellant, ) and results in nutrient pulses that promote invasive grass growth (Esque et al, ).…”

Section: Discussionmentioning

confidence: 99%

Loss of biotic resistance and high propagule pressure promote invasive grass‐fire cycles

Clair

Bishop

2019

Journal of Ecology

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The spread of invasive grasses across Earth are modifying fire cycles resulting in state changes in arid ecosystems. Disturbance, biotic resistance of native biological communities and propagule pressure, are likely the important factors influencing the spread of invasive grasses and their influence on changing fire regimes. Over a 5‐year period (2011–2016), we tested how the potential loss of biotic resistance of native plant and native rodent communities related to fire and rodent exclusion treatments, in concert with increased propagule pressure affected the establishment of Bromus tectorum L. (cheatgrass) and the spread of secondary fires. Our study results suggest that native plant and native rodent communities contribute to biotic resistance against cheatgrass invasion and that fire and high propagule pressure act to diminish biotic resistance by native communities. Five years into the study, cheatgrass establishment was 11‐fold greater in burned plots than in unburned plots (with native plant communities still intact), 2.4‐fold greater in rodent exclusion plots than rodent access plots and 1.8‐fold greater with increased propagule pressure. At the start of the experiment in 2011 cheatgrass was present in the experimental blocks but at very low density (<1 plant/m2). However, by 2016, burned‐rodent excluded plots were fully invaded (1625 stems/m2). High propagule pressure released cheatgrass from biotic resistance of rodent communities in post‐fire conditions but had minimal effects on the biotic resistance of native plant communities in unburned plots. Fire in combination with either rodent exclusion or high cheatgrass propagule pressure produced higher density cheatgrass stands that were positively correlated with the spread of secondary fires that are characteristic of invasive grass‐fire cycles. Synthesis. Loss of native plant cover or reduction in rodent populations due to fire, extreme climatic events or disease outbreaks, which are increasing with human activity, may provide windows of opportunity for invasive grasses to escape biotic resistance and reinforce invasive grass‐fire cycles.

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“…For example, invasion of Cerrado neotropical savanna by the grass Urochloa brizantha alters frequency and intensity of natural fires, which in turn benefits the invaders U. brizantha and Urochloa decumbens , i.e. creates positive feedbacks that aggravate the problem (Gorgone‐Barbosa, Pivello, Baeza, & Fidelis, ; Gorgone‐Barbosa et al., ). Moreover, eradication treatments normally create conditions for a new invasion by the same or another exotic species (D'Antonio & Meyerson, ; Davis, Grime, & Thompson, ).…”

Section: Introductionmentioning

confidence: 99%

Controlling the invaderUrochloa decumbens: Subsidies for ecological restoration in subtropical Campos grassland

Thomas

Schüler

Boavista

et al. 2018

Applied Vegetation Science

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Questions:Restoration of grassy biomes is currently of large importance, and controlling invasive grasses is often key to restoring these ecosystems in the tropics and subtropics. We combined different ecological restoration techniques to evaluate potential to control the invasive grass Urochloa decumbens and restore plant species composition. Specific questions were: (a) are herbicide application and topsoil removal efficient to control U. decumbens cover and allow native species establishment; and (b) are hay transfer and sowing native grass species efficient to reintroduce native species and increase their cover? Location: Campos grasslands, southern Brazil. Methods: We combined the follow restoration techniques: (a) herbicide application or topsoil removal to control the invasive species, and (b) hay transfer or sowing of native grasses to reintroduce native species. We assessed and compared native plant species richness, vegetation cover, native species cover, U. decumbens cover and other exotic species cover in 2016 and 2017.Results: Herbicide application reduced invasive species cover more than topsoil removal, even though both were effective. The decrease of U. decumbens cover led to an increase in native species cover and native species richness. Hay transfer and sowing native grasses did not produce satisfactory results for native species reintroduction. Native species richness and U. decumbens cover increased from 2016 to 2017. Conclusion:Herbicide application was a better option to control U. decumbens and to allow recovery of native species. However, use of herbicides in restoration is controversial, and more detailed studies on impacts are necessary. Environmental filters appear to be a major cause for failure of hay transfer and seeding species. Recovery of the native plant community is a great challenge in invaded subtropical grasslands, and additional management actions and time are necessary to increase the establishment of native species.

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Disturbance as a factor in breaking dormancy and enhancing invasiveness of African grasses in a Neotropical Savanna

Cited by 33 publications

References 39 publications

Resilience and restoration of tropical and subtropical grasslands, savannas, and grassy woodlands

Resilience and restoration of tropical and subtropical grasslands, savannas, and grassy woodlands

Loss of biotic resistance and high propagule pressure promote invasive grass‐fire cycles

Controlling the invaderUrochloa decumbens: Subsidies for ecological restoration in subtropical Campos grassland

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