Herbaceous biomass–species diversity relationships in nutrient hotspots of a semi-arid African riparian ecosystem

South African Journal of Botany

Scogings

2015

a b s t r a c tEcological models to explain savanna heterogeneity and functioning weakly represent herbaceous forbs, which inevitably created knowledge gaps regarding the diversity and ecology of forbs. Forbs constitute over 70% of semi-arid savanna species richness. The aim of this study was therefore to (i) identify forb species that potentially form part of herbivore diet, and (ii) determine forb browsing intensity across a granitic savanna catenal sequence. Localized contrasts between nutrient-poor dystrophic uplands and nutrient-rich eutrophic bottomlands led us to predict that bottomlands would host forb assemblages dominated by browsed species. Forbs contributed to 78% of the total herbaceous layer species richness, of which 43% were browsed at varying intensities along the catenal sequence. Each topographic zone hosted a unique assemblage of browsed forbs, although browsing intensity was highest in the sodic bottomlands. Some browsed forbs formed prostrate, stoloniferous covers on the bottomlands, creating a lawn type dominated by forbs. Results presented here are the first to identify browsed forb species and to illustrate the turnover in browsing intensity of forbs across a semi-arid savanna catenal sequence. Our results add weight to the need to include herbaceous forbs in savanna management models to better understand savanna resource ecology and heterogeneity.

Section: Discussionmentioning

confidence: 97%

Section: Sampling Designmentioning

confidence: 99%

Browsing intensity of herbaceous forbs across a semi-arid savanna catenal sequence

South African Journal of Botany

Scogings

2015

“…For some studies, only grasses are reported on species level while forbs remain lumped under “all remaining herbaceous plants” (Fynn & O'Connor, ; Young, Palmer, & Gadd, ). Furthermore, it is quite common that forbs are lumped with grasses to calculate herbaceous biomass, cover, or dry matter production (Van Coller & Siebert, ; Knoop & Walker, ; Smit & Prins, ; Treydte, Baumgartner, Heitkönig, Grant, & Getz, ) or to measure species richness and diversity (Angassa, ; Van Coller et al, ; Porensky, Wittman, Riginos, & Young, ). Accordingly, there is much scientific uncertainty about how forbs are affected by biotic and abiotic drivers at the species and community level, and how this relates to global environmental problems, especially climate‐ and land‐use change (Zerbo, Bernhardt‐Römermann, Ouédraogo, Hahn, & Thiombiano, , ).…”

Section: Introductionmentioning

confidence: 99%

Forb ecology research in dry African savannas: Knowledge, gaps, and future perspectives

Dreber

2019

Ecology and Evolution

Self Cite

Savannas are commonly described as a vegetation type with a grass layer interspersed with a discontinuous tree or shrub layer. On the contrary, forbs, a plant life form that can include any nongraminoid herbaceous vascular plant, are poorly represented in definitions of savannas worldwide. While forbs have been acknowledged as a diverse component of the herbaceous layer in savanna ecosystems and valued for the ecosystem services and functions they provide, they have not been the primary focus in most savanna vegetation studies. We performed a systematic review of scientific literature to establish the extent to which forbs are implicitly or explicitly considered as a discrete vegetation component in savanna research. The overall aims were to summarize knowledge on forb ecology, identify knowledge gaps, and derive new perspectives for savanna research and management with a special focus on arid and semiarid ecosystems in Africa. We synthesize and discuss our findings in the context of different overarching research themes: (a) functional organization and spatial patterning, (b) land degradation and range management, (c) conservation and reserve management, (d) resource use and forage patterning, and (e) germination and recruitment. Our results revealed biases in published research with respect to study origin (country coverage in Africa), climate (more semiarid than arid systems), spatial scale (more local than landscape scale), the level at which responses or resource potential was analyzed (primarily plant functional groups rather than species), and the focus on interactions between life forms (rather seldom between forbs and grasses and/or trees). We conclude that the understanding of African savanna community responses to drivers of global environmental change requires knowledge beyond interactions between trees and grasses only and beyond the plant functional group level. Despite multifaceted evidence of our current understanding of forbs in dry savannas, there appear to be knowledge gaps, specifically in linking drivers of environmental change to forb community responses. We therefore propose that more attention be given to forbs as an additional ecologically important plant life form in the conventional tree–grass paradigm of savannas.

“…Cattle may even suppress forb cover through forb forage preferences towards the end of a dry season (Young et al 2005;Odadi et al 2007;Kimuyu et al 2017). Despite significant contributions to ecosystem goods and services, both annual and perennial forbs are often perceived negatively by land managers, because of their association with savanna land degradation (Siebert and Dreber 2019) and dominance over grasses under particular environmental conditions, such as on nutrient-rich soils (Reich et al 2003;Van Coller and Siebert 2015), when grazing pressure is moderate to high (Scholes 1987;Hejcmanová et al 2010;Cowley et al 2014) or after drought events (Fynn and O'Connor 2000;Buitenwerf et al 2011).…”

mentioning

confidence: 99%

Forb community responses to an extensive drought in two contrasting land-use types of a semi-arid Lowveld savanna

African Journal of Range & Forage Science

Klem

Coller

2020

Projected increases in the frequency and severity of drought events are expected to impose changes in the ecology of native forb communities in semi-arid ecosystems. We examined the state of forb communities during, and directly after an extreme drought event across two contrasting land-use types, which included a protected area (high diversity of free roaming wild herbivores) and communal rangeland (long history of intensive cattle grazing) in a semi-arid Lowveld savanna of the Gazankulu area, South Africa. Forb floristic data were collected towards the end of the drought and repeated after the drought release a few months later. Forb community composition was significantly different among land-use types. Community changes were not induced by annual forb emergence alone, but through species-specific dominance shifts, which differed among land-use types. Forb richness, diversity and biomass were equally low at both land-use types and increased significantly after the drought release, although the magnitude of response was much stronger in the protected area, whereas drought contributed to a directional change in the protected area with a complete post-drought turnover in both annual and perennial forb species, much less variability was observed in the communal rangeland, which may suggest long-term effects imposed by land-use history.