Grass species richness decreases along a woody plant encroachment gradient in a semi-arid savanna grassland, South Africa

Mogashoa, Regina Etla; Dlamini, Phesheya; Gxasheka, Masibonge

doi:10.1007/s10980-020-01150-1

Cited by 29 publications

(19 citation statements)

References 81 publications

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“…C 4 graminoids typify and define tropical grassy ecosystems, and generally have high light requirements due to their morpho‐physiology, and therefore are often reduced in richness or completely lost from encroached ecosystems where disturbance is infrequent (Diaz‐Toribio et al, 2020; Peterson & Reich, 2008; Wood et al, 2020). Beyond our observations for functional groups, woody encroachment likely leads to habitat homogenisation and predominance of a single or only a few herbaceous species (Mogashoa et al, 2020; Pinheiro et al, 2016). Moreover, rare and threatened species can decline in abundance and go locally extinct (Costello et al, 2000; Pinheiro et al, 2016), while ruderals and non‐native species can increase in numbers (Lett & Knapp, 2005).…”

Section: Discussionmentioning

confidence: 48%

“…Consequently, where encroachment is a result of fire suppression, declines in forb species richness are commonly observed (Parr et al, 2012;Peterson & Reich, 2008). Both leads to habitat homogenisation and predominance of a single or only a few herbaceous species (Mogashoa et al, 2020;Pinheiro et al, 2016). Moreover, rare and threatened species can decline in abundance and go locally extinct (Costello et al, 2000;Pinheiro et al, 2016), while ruderals and non-native species can increase in numbers (Lett & Knapp, 2005).…”

Section: Discussionmentioning

confidence: 99%

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Encroachment diminishes herbaceous plant diversity in grassy ecosystems worldwide

Wieczorkowski

Lehmann

2022

Global Change Biology

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Woody encroachment is ubiquitous in grassy ecosystems worldwide, but its global impacts on the diversity of herbaceous plants that characterise and define these ecosystems remain unquantified. The pervasiveness of encroachment is relatively easily observed via remote sensing, but its impacts on plant diversity and richness below the canopy can only be observed via field‐based studies. Via a meta‐analysis of 42 field studies across tropical to temperate grassy ecosystems, we quantified how encroachment altered herbaceous species richness, and the richness of forbs, C3 graminoids and C4 graminoids. Across studies, the natural logarithm of the response ratio (lnRR) of herbaceous species richness ranged from −3.33 to 0.34 with 87% of encroached ecosystems negatively impacted. Assessment of the extent of encroachment, duration of encroachment, mean annual rainfall, latitude, and continent demonstrated that only extent of encroachment had relevance in the data (univariate model including a random effect of study explained 45.4% of variance). The global weighted mean lnRR of species richness decreased from −0.245 at <33% of woody cover increase, to −0.562 at 33%–66%, and to −0.962 at >66%. Continued encroachment results in substantial loss of herbaceous diversity at medium and high extents, with a loss of richness that is not replaced. Although all functional groups are significantly negatively impacted by encroachment, forb richness is relatively more sensitive than graminoid richness, and C4 graminoid richness relatively more than C3 graminoid richness. Although no geographic or climatic correlates had relevance in the data, encroachment as an emergent product of global change coalesces to decrease ground layer light availability, lead to loss of fire and grazers, and alter hydrology and soils. Encroachment is accelerating and grassy ecosystems require urgent attention to determine critical woody cover thresholds that facilitate diverse and resilient grassy ecosystems.

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Section: Discussionmentioning

confidence: 48%

Section: Discussionmentioning

confidence: 99%

Encroachment diminishes herbaceous plant diversity in grassy ecosystems worldwide

Wieczorkowski

Lehmann

2022

Global Change Biology

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“…However, tree's ability to alter their environment depends on their density and canopy characteristics (e.g. Mogashoa et al, 2021; Randle et al, 2018). If trees are widely spaced and solitary, have thin leaves and/or show limited lateral branching, they may not be able to alter their environment sufficiently to support a community that differs from the grassland matrix.…”

Section: Discussionmentioning

confidence: 99%

Taxonomic, functional and phylogenetic diversity peaks do not coincide along a compositional gradient in forest‐grassland mosaics

Erdős

Bátori

et al. 2022

Journal of Ecology

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“…We found that shrub encroachment drove the local extinction of 9 herb species, while another 12, 11, and 7 new species colonized meadows with 30%, 60%, and 90% shrub coverage, respectively. Previous studies have shown that shrub encroachment promotes strong environmental filtering by increasingly limiting light availability for herb growth (Mogashoa et al, 2020; Ratnam et al, 2011). However, these effects are not random.…”

Section: Discussionmentioning

confidence: 99%

“…Shrub encroachment can affect community structure and functioning by altering the microenvironment for herbaceous plant growth (Harpole & Tilman, 2007; Price & Morgan, 2010). For example, shrub canopies intercept light and reduce photosynthetically‐active radiation at the understory (Mogashoa et al, 2020). Moreover, overstory shading directly affects temperature and water evaporation at the topsoil (Aguirre et al, 2020; Brantley & Young, 2009), which are key drivers of plant growth in alpine meadows (Sun, Zhou, Liu, et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Shrub encroachment impaired the structure and functioning of alpine meadow communities on the Qinghai–Tibetan Plateau

et al. 2022

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Shrub encroachment has been rapidly occurring due to climate change, with profound ecological consequences for the alpine meadows of the Qinghai-Tibetan Plateau. Here, we conducted field surveys along a shrub coverage gradient to examine the effects of shrub encroachment on the structure and functioning of alpine meadows' plant communities. Our results showed that the overall coverage, density, aboveground biomass, species richness, and diversity of meadow community gradually declined with increasing levels of shrub encroachment, especially when shrub coverage exceeded 60%. Aboveground ecosystem multifunctionality also decreased along the shrub coverage gradient. With 90% shrub coverage, the relative importance value of the forbs functional group significantly increased while the Cyperaceae functional group showed the opposite trend: the originally dominant sedges Carex moorcroftii and Kobresia myosuroides were replaced by the forbs Androsace umbellate and Polygonum sparsipilosum. Additionally, shrub encroachment had a strong effect on nonrandom herb species extinction and colonization. At shrub coverages higher than 60%, there were 9 herb species absent and 18 new species colonizing-7 of which were only observed in meadows with 90% shrub coverage. Rare species and those with lower stature were more likely to go extinct, while taller and shadetolerant species tended to colonize areas with increasing shrub coverage. Overall, our results indicate that shrub encroachment negatively affects herbaceous community structure and functioning, which has important implications for the management of alpine meadows of the Qinghai-Tibetan Plateau under ongoing climate change.

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Grass species richness decreases along a woody plant encroachment gradient in a semi-arid savanna grassland, South Africa

Cited by 29 publications

References 81 publications

Encroachment diminishes herbaceous plant diversity in grassy ecosystems worldwide

Encroachment diminishes herbaceous plant diversity in grassy ecosystems worldwide

Taxonomic, functional and phylogenetic diversity peaks do not coincide along a compositional gradient in forest‐grassland mosaics

Shrub encroachment impaired the structure and functioning of alpine meadow communities on the Qinghai–Tibetan Plateau

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