Protégé<i>Ziziphus mucronata</i> (Rhamnaceae) show no negative effects of competition with the nurse tree <i>Acacia</i> (Leguminaceae), even as adults

Seymour, Colleen L.

doi:10.1111/j.1654-1103.2009.01096.x

Cited by 5 publications

(3 citation statements)

References 46 publications

(48 reference statements)

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“…Frugivores were associated with large trees, probably because juicy-fruited plants in the Kalahari tend to occur beneath large trees (Leistner 1996;Dean et al 1999), which tend to serve as establishment sites (Seymour 2009). Most avian groundfeeders in this study were also seed-eaters, and this may explain the decline in ground-feeders; seed-eaters rely largely on grass, which is progressively excluded with increasing bush thickening (Donaldson & Kelk 1970).This would also explain the decrease in groundnesting bird species with bush thickening (which tend to nest in or against grass clumps).…”

Section: Discussionmentioning

confidence: 98%

The influence of changes in habitat structure on the species composition of bird assemblages in the southern Kalahari

Seymour

Dean

2010

Austral Ecology

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Land use management practices often change habitat structure, which in turn influence diversity and the composition of floral and faunal assemblages. In the southern Kalahari, southern Africa, heavy grazing after above-average rainfall has lead to bush thickening, and widespread use of arboricides and/or removal of large trees for firewood has also impacted habitat structure. At sites near Kimberley, in South Africa, we investigated the effects of these changes on bird species richness and which aspects of habitat structure most influenced bird assemblage diversity and composition. We also investigated correlations between bird life history traits and habitat characteristics using RLQ analysis. Bird species richness and abundance were both explained by vertical habitat heterogeneity and density of woody species between the heights of 0-2 m, with bird species richness also explained by the density of woody species at heights above 6 m. Large trees within bush-thickened areas dampened the effects of bush thickening on bird assemblages by enabling certain species to persist, consistent with the idea that large trees are keystone structures. Smaller insectivorous gleaners, ball-and cup-nesters, birds with parts of their range extending into arid areas and birds with long-wavelength plumage (i.e. red, orange or yellow plumage) dominated bush-thickened habitats. Seed-eaters, burrow-and ground-nesters, bark-foragers, birds that perch and sally, or perch and swoop to the ground, were all negatively associated with bush thickening. Cavity-nesters, bark-foragers, hawkers, frugivores, birds that perch and sally and species with iridescent plumage were negatively affected by the loss of large trees. Of the common species analysed, nearly 40% of species had life history traits tied to large trees; and 68% had traits negatively associated with bush thickening and removal of large trees together, suggesting that where these changes in habitat occur simultaneously, bird diversity will be strongly affected.

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Section: Discussionmentioning

confidence: 98%

The influence of changes in habitat structure on the species composition of bird assemblages in the southern Kalahari

Seymour

Dean

2010

Austral Ecology

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“…giraffe feed on spinescent acacias; du Toit et al. ; Skinner & Chimimba ); and (3) trampling of saplings (Seif El Din & Obeid ; Seymour ).…”

Section: Discussionmentioning

confidence: 99%

Woody species composition in an African savanna: determined by centuries of termite activity but modulated by 50 years of ungulate herbivory

Seymour

Joseph

Makumbe

et al. 2016

J Vegetation Science

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Questions: Ungulate herbivory and formation of large termite mounds occur over different time scales, but both can affect plant community composition in savannas. Human-managed savanna systems are increasingly dominated by domesticated grazing herbivores. These have replaced a mix of indigenous browsers and grazers, leading to changes in plant communities such as increased bush encroachment. We compared the relative impacts of five decades of different types of ungulate herbivory (cattle grazing, browsing and grazing by wild herbivores, and exclusion of all larger herbivores) on woody plant assemblages in two habitats, namely, large termite mounds, which may be thousands of years old, and the surrounding matrix.Location: Miombo woodland savanna, Zimbabwe. Methods:To determine the influence of termite mounds and herbivory on spatial distribution and composition of woody assemblages, we compared 40 paired mound-matrix plots from the three herbivory treatments using PERMANOVA. We assessed whether mound plots were more similar to each other than matrix plots were to each other, and whether herbivory influenced similarity. We used SIMPER analysis to identify changes in abundance of indicator species for each habitat (i.e. mound or matrix). Results: Species composition differed significantly between mound and matrixand also between herbivory treatments. Woody plant assemblages on mounds were more similar to each other than woody plant assemblages in matrix plots were to each other, regardless of type of herbivory, but herbivory reduced the mound/matrix contrast. Sample location (i.e. on mound or in matrix) explained 23% of the variation in woody species composition, compared to 12% explained by herbivory. Woody plant abundance was lowest where there were both grazers and browsers.Conclusions: The influence of large termite mounds on plant assemblages was roughly double that of herbivory, which has occurred over five decades. Type of herbivory emerged as relatively influential on woody plant species composition, given that the time periods involved were short by comparison to the slow formation of termite mounds. Type of herbivory also influenced species composition and vegetation structure, with a diversity of herbivores necessary to reduce encroachment by woody species.

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“…Large leguminous trees often produce seed pods that provide valuable fodder for livestock in times of drought, and the volume of pod production is correlated with tree size (Barnes et al, 1997; Meyer et al, 2007). In addition, subcanopy sites are favorable to a suite of plant species that are functionally distinct from the surrounding matrix (Seymour, 2009). Large trees are also key to nutrient (Dean et al, 1999) and water (Dawson, 1993; Hoffmann & Jackson, 2000) availability, playing key roles in ecological networks (Seymour & Joseph, 2019).…”

Section: Introductionmentioning

confidence: 99%

Mean height increase in saplings of a keystone woody savanna species over 15 years similar to that over a single season

et al. 2022

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Woody structure, particularly that created by large trees, is crucial to savanna biodiversity pattern and process. We assessed changes in vertical and horizontal canopy over 15 years of saplings of Vachellia (Acacia) erioloba (camelthorn), a keystone species and one of the only trees to grow large in arid savanna on low rainfall areas of Kalahari sands, southern Africa. We also assessed whether the fastest growing saplings over the 2003-2004 growing season were also the fastest growing over the following 15 years. We measured height, canopy extent, and diameter of largest stem at ground level of 120 saplings of V. erioloba in November 2003, remeasuring these in March 2004. In November 2019, we were able to find 67 of these saplings, and we measured them again to assess growth between 2004 and 2019. We modeled interindividual explanatory variables for growth (i.e., measures taken in 2004 of height, diameter, number of stems, evidence of fire, and largest stem diameter). We also compared residuals of growth between 2003 and 2004 with those between 2004 and 2019, to assess whether individuals showed similar progress relative to their peers over the two periods considered. Height increase was extremely variable, but mean increase over 15 years was only 45.4 mm, similar to that measured for the 2003-2004 growing season (43.1 mm). Mean horizontal canopy showed far greater growth (mean 120.2 mm over 15 years, compared with 7.12 mm over 2003-2004) than vertical growth. Individuals that had shown the fastest increase in horizontal canopy in [2003][2004] tended to be the same individuals that grew fastest over the following 15 years, but even the highest "achievers" showed increases of only 47.2 mm and 37.5 mm year À1 in average horizontal canopy extent and height, respectively. This study demonstrates how crucial long-term studies are, particularly in arid systems.Many individuals may be trapped in the "sapling" class and could take decades to become large trees. Woody sapling growth was not cumulative, and

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ProtégéZiziphus mucronata (Rhamnaceae) show no negative effects of competition with the nurse tree Acacia (Leguminaceae), even as adults

Cited by 5 publications

References 46 publications

The influence of changes in habitat structure on the species composition of bird assemblages in the southern Kalahari

The influence of changes in habitat structure on the species composition of bird assemblages in the southern Kalahari

Woody species composition in an African savanna: determined by centuries of termite activity but modulated by 50 years of ungulate herbivory

Mean height increase in saplings of a keystone woody savanna species over 15 years similar to that over a single season

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