Zooming in on coarse plant functional types—simulated response of savanna vegetation composition in response to aridity and grazing

Lohmann, Dirk; Guo, Tong; Tietjen, Britta

doi:10.1007/s12080-017-0356-x

Cited by 11 publications

(7 citation statements)

References 84 publications

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“…By contrast, (Confalonieri, 2014) suggested a model of plant community dynamics based on a single instance of a generic crop simulator, state variables being only simulated for the whole community. ECOHYD (Lohmann et al, 2017) is an ecohydrological model of semi-arid grasslands and savannas, able to simulate cover dynamics of a large number of PFTs, but focuses on hydrological processes and does not implement nutrient stress. In this paper, we address a general issue that could be raised in any modelling study: the appropriate choice of the level of detail of the model, i.e.…”

Section: Introductionmentioning

confidence: 99%

Modelling vegetation dynamics in managed grasslands: Responses to drivers depend on species richness

Moulin

Perasso

Gillet

2018

Ecological Modelling

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In mathematical grassland models, plant communities may be represented by a various number of state variables, describing biomass compartments of some dominant species or plant functional types. The size of the initial species pool could have consequences on the outcome of the simulated ecosystem dynamics in terms of grassland productivity, diversity, and stability. This choice could also influence the model sensitivity to forcing parameters. To address these issues, we developed a dynamic grassland model, DYNAGRAM, designed to simulate seasonal changes in both aboveground biomass production and species composition of managed permanent grasslands under various soil, climate and management conditions. We compared simulation results from alternative instances of DYNAGRAM that only differ by the identity and number of state variables describing the green biomass, here plant species. We assessed the sensitivity of each instance of the model to key forcing parameters for climate, soil fertility, and defoliation disturbances, using univariate and multivariate regression trees and dynamic trees. Results of 10-year simulations under various climate, fertility and defoliation conditions showed that the final total biomass was tending to increase with the size of the species pool, while species evenness and the proportion of surviving species was tending to decrease. We found a positive correlation between the species survival ratio and the defoliation intensity, and this correlation increased with the initial species richness. The sensitivity to forcing parameters of community structure and species evenness differed markedly among alternative models, showing a progressive shift from high importance of soil fertility (fertilisation level, mineralization rate) to high importance of defoliation (mowing frequency, grazing intensity) as the size of the species pool increased. By contrast, the key drivers of total biomass production were independent of species richness and only linked to resource supply (nitrogen and water). These results highlight the need to take into account the role of species diversity to explain the behaviour of grassland models.

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Section: Introductionmentioning

confidence: 99%

Modelling vegetation dynamics in managed grasslands: Responses to drivers depend on species richness

Moulin

Perasso

Gillet

2018

Ecological Modelling

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“…Accordingly, this could explain why the dominant strategy types in the model do not correspond to the dominant local shrub species. Another reason for this could be that shrubs respond more strongly to climatic conditions than to herbivory, as previous results suggested (Lohmann et al, 2018).…”

Section: Implications Of Herbivory For Plant Diversitymentioning

confidence: 86%

“…As annual grasses (annuals) only dominate degraded systems (Archer et al, 2017; Case et al, 2020), we did not subdivide them further. We used the standard set of parameters of the meta‐PFTs from previous studies (Guo et al, 2016; Lohmann et al, 2018) as starting point for parameterizing the subtypes. The basic subtype of each meta‐PFT (hereafter called “base type”) had the same set of parameters as the original meta‐PFT.…”

Section: Methodsmentioning

confidence: 99%

“…Another limitation of many of these studies is that they only included broad vegetation categories, so called plant functional types based on broad plant functional groups (PFTs), without considering the great diversity within these groups (e.g., by implementing distinguishable subtypes) (Pappas et al, 2016). However, ecosystem responses to altered drivers cannot necessarily be adequately captured when plants are grouped into very broad types, without recognizing that plant communities respond to local environmental conditions by adapting their traits, as existing simulation studies on ecosystem responses toward grazing could show (Guo et al, 2016; Lohmann et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Browsing herbivores improve the state and functioning of savannas: A model assessment of alternative land‐use strategies

Irob

Blaum

Baldauf

et al. 2022

Ecology and Evolution

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Changing climatic conditions and unsustainable land use are major threats to savannas worldwide. Historically, many African savannas were used intensively for livestock grazing, which contributed to widespread patterns of bush encroachment across savanna systems. To reverse bush encroachment, it has been proposed to change the cattle‐dominated land use to one dominated by comparatively specialized browsers and usually native herbivores. However, the consequences for ecosystem properties and processes remain largely unclear. We used the ecohydrological, spatially explicit model EcoHyD to assess the impacts of two contrasting, herbivore land‐use strategies on a Namibian savanna: grazer‐ versus browser‐dominated herbivore communities. We varied the densities of grazers and browsers and determined the resulting composition and diversity of the plant community, total vegetation cover, soil moisture, and water use by plants. Our results showed that plant types that are less palatable to herbivores were best adapted to grazing or browsing animals in all simulated densities. Also, plant types that had a competitive advantage under limited water availability were among the dominant ones irrespective of land‐use scenario. Overall, the results were in line with our expectations: under high grazer densities, we found heavy bush encroachment and the loss of the perennial grass matrix. Importantly, regardless of the density of browsers, grass cover and plant functional diversity were significantly higher in browsing scenarios. Browsing herbivores increased grass cover, and the higher total cover in turn improved water uptake by plants overall. We concluded that, in contrast to grazing‐dominated land‐use strategies, land‐use strategies dominated by browsing herbivores, even at high herbivore densities, sustain diverse vegetation communities with high cover of perennial grasses, resulting in lower erosion risk and bolstering ecosystem services.

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“…Milchunas et al [99] also illustrated with their modelling study how moderate grazing tended to increase species richness compared to ungrazed swards (see Fox [100] for a rejection of the Intermediate Disturbance Hypothesis on theoretical and practical grounds). The model EcoHyD [101] described the cover dynamics of a large number of PFTs of semi-arid grasslands and savannas but from hydrological processes only, and with growth rate determined by just two parameters (maximum water uptake rate and water-use efficiency) rather than simulating the biogeochemistry of carbon and nutrient flows. Bittebiere et al [102] showed that the predictions of IBMs for grassland composition were highly sensitive to the formulation of competitive interactions, in part because in such models resources are considered as abstract quantities, not bound to conservative recycling.…”

Section: Models For Biodiversitymentioning

confidence: 99%

Incorporating Biodiversity into Biogeochemistry Models to Improve Prediction of Ecosystem Services in Temperate Grasslands: Review and Roadmap

et al. 2020

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Multi-species grasslands are reservoirs of biodiversity and provide multiple ecosystem services, including fodder production and carbon sequestration. The provision of these services depends on the control exerted on the biogeochemistry and plant diversity of the system by the interplay of biotic and abiotic factors, e.g., grazing or mowing intensity. Biogeochemical models incorporate a mechanistic view of the functioning of grasslands and provide a sound basis for studying the underlying processes. However, in these models, the simulation of biogeochemical cycles is generally not coupled to simulation of plant species dynamics, which leads to considerable uncertainty about the quality of predictions. Ecological models, on the other hand, do account for biodiversity with approaches adopted from plant demography, but without linking the dynamics of plant species to the biogeochemical processes occurring at the community level, and this hampers the models’ capacity to assess resilience against abiotic stresses such as drought and nutrient limitation. While setting out the state-of-the-art developments of biogeochemical and ecological modelling, we explore and highlight the role of plant diversity in the regulation of the ecosystem processes underlying the ecosystems services provided by multi-species grasslands. An extensive literature and model survey was carried out with an emphasis on technically advanced models reconciling biogeochemistry and biodiversity, which are readily applicable to managed grasslands in temperate latitudes. We propose a roadmap of promising developments in modelling.

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Zooming in on coarse plant functional types—simulated response of savanna vegetation composition in response to aridity and grazing

Cited by 11 publications

References 84 publications

Modelling vegetation dynamics in managed grasslands: Responses to drivers depend on species richness

Modelling vegetation dynamics in managed grasslands: Responses to drivers depend on species richness

Browsing herbivores improve the state and functioning of savannas: A model assessment of alternative land‐use strategies

Incorporating Biodiversity into Biogeochemistry Models to Improve Prediction of Ecosystem Services in Temperate Grasslands: Review and Roadmap

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