Nutrient Vectors and Riparian Processing: A Review with Special Reference to African Semiarid Savanna Ecosystems

Jacobs, Shayne M.; Bechtold, J. Scott; Biggs, Harry; Grimm, Nancy B.; Lorentz, Simon; McClain, Michael E.; Naiman, Robert J.; Perakis, Steven S.; Pinay, Gilles; Scholes, Mary

doi:10.1007/s10021-007-9092-1

Cited by 75 publications

(61 citation statements)

References 133 publications

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“…Water and nutrients are locally more abundant in lowland areas, giving rise to betterquality forage compared with the adjacent upland areas (28,30,31). This topographic effect is obvious in the lowland basalt substrate treatment habitat, even when protected from herbivores for only half as long as the upland habitat (22 vs. 41 years) ( Table S1).…”

Section: Resultsmentioning

confidence: 92%

Large-scale impacts of herbivores on the structural diversity of African savannas

Asner

Levick

Kennedy-Bowdoin

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

249

229

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African savannas are undergoing management intensification, and decision makers are increasingly challenged to balance the needs of large herbivore populations with the maintenance of vegetation and ecosystem diversity. Ensuring the sustainability of Africa's natural protected areas requires information on the efficacy of management decisions at large spatial scales, but often neither experimental treatments nor large-scale responses are available for analysis. Using a new airborne remote sensing system, we mapped the threedimensional (3-D) structure of vegetation at a spatial resolution of 56 cm throughout 1640 ha of savanna after 6-, 22-, 35-, and 41-year exclusions of herbivores, as well as in unprotected areas, across Kruger National Park in South Africa. Areas in which herbivores were excluded over the short term (6 years) contained 38%-80% less bare ground compared with those that were exposed to mammalian herbivory. In the longer-term (> 22 years), the 3-D structure of woody vegetation differed significantly between protected and accessible landscapes, with up to 11-fold greater woody canopy cover in the areas without herbivores. Our maps revealed 2 scales of ecosystem response to herbivore consumption, one broadly mediated by geologic substrate and the other mediated by hillslope-scale variation in soil nutrient availability and moisture conditions. Our results are the first to quantitatively illustrate the extent to which herbivores can affect the 3-D structural diversity of vegetation across large savanna landscapes.ecological sustainability ͉ ecosystem heterogeneity ͉ Kruger National Park ͉ park management ͉ protected areas ͉ South Africa ͉ vegetation structure

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Section: Resultsmentioning

confidence: 92%

Large-scale impacts of herbivores on the structural diversity of African savannas

Asner

Levick

Kennedy-Bowdoin

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

249

229

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“…Thus, mound-associated species Allophylus africanus, Boscia salicifolia, Capparis tomentosa, Ficus natalensis, Maerua angolensis, and Ximenia americana, some of which are preferred forage, are able to provide a consistent supply of leaves for browsers. 'Evergreeness' has associations with enriched, moist soils (Cornelissen et al 2003;Jacobs et al 2007), but also with leaf strength and chemical defences (and thus protection from herbivores). Indeed, a few moundassociated species such as Euclea divinorum, Ochna pulchra, and Parinari curatellifolia tend to be avoided, even as the majority are preferentially targeted.…”

Section: Interpreting Diversity Indicesmentioning

confidence: 99%

Termite mounds mitigate against 50 years of herbivore-induced reduction of functional diversity of savanna woody plants

et al. 2015

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Context Spatially heterogeneous habitats often promote woody plant species and functional diversity (FD). Ungulate herbivory can have the opposite effect. Across the globe, the type and intensity of herbivory is changing, as domestic livestock replace wild ungulates, which are increasingly confined to protected areas. Despite recognition of the importance of FD for ecosystem functioning, the interactive effect of soilrelated fine-scale heterogeneity and larger-scale ungulate herbivory on woody plant FD is little-known.Objectives In miombo woodland of Zimbabwe, we investigated (1) how bottom-up fine-scale heterogeneity created by Macrotermes termitaria interacts with top-down effects of herbivore foraging-guilds on woody plant FD; and (2) whether browsing combined with grazing impacts FD more than grazing alone. Methods The three different herbivore treatments (grazing, combined browsing-and-grazing, and exclusion) had been maintained for 50 years. We surveyed 10 termite mound-matrix plots within three sites per treatment. We assessed woody plant traits and FD across treatments (herbivore feeding-guild) and position (mound or woodland-matrix), and interactive effects between these. Results Woody plant FD was greater on mounds, and lowest overall with browsing-and-grazing. Specific traits were associated with position (e.g. palatability was greater for mounds), and treatment (e.g. spinescence increased with grazing). Conclusions Long-term enclosure of ungulate herbivores (browsing-and-grazing, and grazing alone) decreased woody FD, but this was mitigated by termitaria. The novel finding is that at regional scales, mounds can enhance woody plant FD despite the impacts of herbivory. At broader scales encompassing the miombo system, potential exists for mounds to stabilise woody plant FD from livestock-induced impacts.

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“…This is, however, not the case for riparian nutrient dynamics, which remain poorly studied in African river systems (Jacobs et al, 2007). Riparian areas are wellestablished buffers in the N and P cycle.…”

Section: Introductionmentioning

confidence: 99%

Nitrogen, phosphorus and silicon in riparian ecosystems along the Berg River (South Africa): The effect of increasing human land use

Struyf¹,

Bal²,

Backx³

et al. 2012

WSA

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The Berg River is one of the main rivers in the Cape Region; it is essential for the local economy and ecology, as it supplies water to agriculture and industries, provides drinking water for the greater Cape Town region, and supports rich aquatic ecosystems. The Berg River is impacted by both diffuse pollution from agricultural run-off and point-source pollution from urban and industrial wastewater. Construction of a dam on the headwaters of the Berg River in 2007 has changed the hydrology of the upper catchment. Pelagic nutrient dynamics in the Berg River are well documented. The opposite is however true for riparian nutrient dynamics. We studied changes in riparian nutrient storage over a gradient in elevation (a proxy for flooding frequency and drought) and human influence (the Berg River dam and lateral nutrient and pollutant input). Our results show that nutrient concentrations in the riparian sediments reflect nutrient concentrations in the river. N concentrations in the sediment increased up to 1 000%, while P concentrations rose up to 200% with increasing human influence. For biogenic Si, we found generally low concentrations throughout the whole gradient sampled (all < 0.5 mg BSi g -1 sediment). Sediments closer to the river appear to have more efficient recycling and export of nutrients into the river. Overall, we conclude that the observed patterns indicate the necessity of incorporating nutrient status and management of riparian habitats in the Berg River monitoring strategy.

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Nutrient Vectors and Riparian Processing: A Review with Special Reference to African Semiarid Savanna Ecosystems

Cited by 75 publications

References 133 publications

Large-scale impacts of herbivores on the structural diversity of African savannas

Large-scale impacts of herbivores on the structural diversity of African savannas

Termite mounds mitigate against 50 years of herbivore-induced reduction of functional diversity of savanna woody plants

Nitrogen, phosphorus and silicon in riparian ecosystems along the Berg River (South Africa): The effect of increasing human land use

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