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  • 1
    Online Resource
    Online Resource
    Low gains in ecosystem carbon with woody plant encroachment in a South African savanna
    Cambridge University Press (CUP) ; 2013
    In:  Journal of Tropical Ecology Vol. 29, No. 1 ( 2013-01), p. 49-60
    Details
    In: Journal of Tropical Ecology, Cambridge University Press (CUP), Vol. 29, No. 1 ( 2013-01), p. 49-60
    Abstract: Total ecosystem carbon storage has frequently been found to increase with woody encroachment in savannas. However the loss of grass roots associated with woody encroachment can lead to a decrease in below-ground carbon storage which is not compensated for by an increase in above-ground carbon. To investigate how the extent of total woody cover affected ecosystem carbon, soil and above-ground carbon storage along eight thicket–savanna and five forest–grassland boundaries were measured. To investigate whether changes in soil carbon concentrations were related to the percentage of C4 (grass) roots to total roots and root quantity and quality, we measured fine-root biomass, root C : N ratios, root N, and % C4 roots at three different depths across thicket patches of different ages (n = 189). Forests contained significantly more carbon than adjacent grasslands in both above-ground carbon (mean difference 12.1 kg m −2 ) and in the top 100 cm of the soil (mean difference 4.54 kg m −2 ). Thickets contained significantly more above-ground carbon than adjacent savannas (3.33 kg m −2 ) but no significant differences in soil carbon were evident. Total fine-root biomass appeared to be more important than root quality (root C : N) in determining soil carbon concentrations during the encroachment process (i.e. in thicket of different ages). Similarly for thickets, the % C4 roots had no significant effect on soil carbon concentrations. In conclusion, thicket invading into open savanna vegetation did not lead to significant gains in ecosystem carbon at this study site. Significant gains were only evident in mature forest, suggesting that the process may take place very slowly.
    Type of Medium: Online Resource
    ISSN: 0266-4674 , 1469-7831
    URL: Article
    DOI: 10.1017/S0266467412000697
    RVK:
    WA 15000
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2013
    detail.hit.zdb_id: 1466679-0
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  • 2
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    Ants, fire, and bark traits affect how African savanna trees recover following damage
    Wiley ; 2019
    In:  Biotropica Vol. 51, No. 5 ( 2019-09), p. 682-691
    Details
    In: Biotropica, Wiley, Vol. 51, No. 5 ( 2019-09), p. 682-691
    Abstract: Bark damage resulting from elephant feeding is common in African savanna trees with subsequent interactions with fire, insects, and other pathogens often resulting in tree mortality. Yet, surprisingly little is known about how savanna trees respond to bark damage. We addressed this by investigating how the inner bark of marula ( Sclerocarya birrea ), a widespread tree species favoured by elephants, recovers after bark damage. We used a long‐term fire experiment in the Kruger National Park to measure bark recovery with and without fire. At 24 months post‐damage, mean wound closure was 98, 92, and 72%, respectively, in annual and biennial burns and fire‐exclusion treatments. Fire exclusion resulted in higher rates of ant colonization of bark wounds, and such ant colonization resulted in significantly lower bark recovery. We also investigated how ten common savanna tree species respond to bark damage and tested for relationships between bark damage, bark recovery, and bark traits while accounting for phylogeny. We found phylogenetic signal in bark dry matter content, bark N and bark P, but not in bark thickness. Bark recovery and damage was highest in species which had thick moist inner bark and low wood densities (Anacardiaceae), intermediate in species which had moderate inner bark thickness and wood densities (Fabaceae) and lowest in species which had thin inner bark and high wood densities (Combretaceae). Elephants prefer species with thick, moist inner bark, traits that also appear to result in faster recovery rates.
    Type of Medium: Online Resource
    ISSN: 0006-3606 , 1744-7429
    URL: Issue
    URL: Article
    DOI: 10.1111/btp.v51.5
    DOI: 10.1111/btp.12683
    RVK:
    WA 15000
    Language: English
    Publisher: Wiley
    Publication Date: 2019
    detail.hit.zdb_id: 2052061-X
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  • 3
    Online Resource
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    Defence strategies in African savanna trees
    Springer Science and Business Media LLC ; 2018
    In:  Oecologia Vol. 187, No. 3 ( 2018-7), p. 797-809
    Details
    In: Oecologia, Springer Science and Business Media LLC, Vol. 187, No. 3 ( 2018-7), p. 797-809
    Type of Medium: Online Resource
    ISSN: 0029-8549 , 1432-1939
    URL: Article
    DOI: 10.1007/s00442-018-4165-8
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2018
    detail.hit.zdb_id: 1462019-4
    detail.hit.zdb_id: 123369-5
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  • 4
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    Browser impacts in Mapungubwe National Park, South Africa: Should we be worried?
    AOSIS ; 2016
    In:  Koedoe Vol. 58, No. 1 ( 2016-03-31)
    Details
    In: Koedoe, AOSIS, Vol. 58, No. 1 ( 2016-03-31)
    Abstract: This study explores the impact of browsers on vegetation types within the Mapungubwe National Park and specifically whether rocky outcrops or ridges in the park serve as refugia from browsers, particularly elephants. We sampled 80 transects at 20 sites and recorded 1740 plants comprising 65 species. We found that a high proportion ( 〉 80%) of the woody vegetation sampled indicated browser utilisation. Although certain woody species (e.g. Albizia harveyi, Boscia albitrunca, Lannea schweinfurthii) appeared to be preferred by browsers, browsing levels were relatively high among all woody species. High levels of browsing by herbivores other than elephants suggest that they have a significant impact on the park’s vegetation. We did not find that rocky ridges acted as refugia to browsers, but instead found that vegetation in rocky ridges was more severely impacted by browsers than vegetation in flat areas, despite vegetation being more accessible in flat areas. If elephant numbers continue to increase at the current rate (e.g. elephant numbers doubled between 2007 and 2010), we predict that some of the heavily utilised species will become locally rare over time.Conservation implications: High levels of browsing by both elephant and smaller herbivores contribute to significant impacts on vegetation away from rivers in Mapungubwe National Park. Without management interventions that address both types of impact, structural and species diversity are bound to decrease over the short to medium term.
    Type of Medium: Online Resource
    ISSN: 2071-0771 , 0075-6458
    URL: Article
    DOI: 10.4102/koedoe.v58i1.1347
    Language: Unknown
    Publisher: AOSIS
    Publication Date: 2016
    detail.hit.zdb_id: 2413347-4
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  • 5
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    Grasses continue to trump trees at soil carbon sequestration following herbivore exclusion in a semiarid African savanna
    Wiley ; 2020
    In:  Ecology Vol. 101, No. 5 ( 2020-05)
    Details
    In: Ecology, Wiley, Vol. 101, No. 5 ( 2020-05)
    Abstract: Although studies have shown that mammalian herbivores often limit aboveground carbon storage in savannas, their effects on belowground soil carbon storage remain unclear. Using three sets of long‐term, large herbivore exclosures with paired controls, we asked how almost two decades of herbivore removal from a semiarid savanna in Laikipia, Kenya affected aboveground (woody and grass) and belowground soil carbon sequestration, and determined the major source (C 3 vs. C 4 ) of belowground carbon sequestered in soils with and without herbivores present. Large herbivore exclusion, which included a diverse community of grazers, browsers, and mixed‐feeding ungulates, resulted in significant increases in grass cover (~22%), woody basal area (~8 m 2 /ha), and woody canopy cover (31%), translating to a ~8.5 t/ha increase in aboveground carbon over two decades. Herbivore exclusion also led to a 54% increase (20.5 t/ha) in total soil carbon to 30‐cm depth, with ~71% of this derived from C 4 grasses (vs. ~76% with herbivores present) despite substantial increases in woody cover. We attribute this continued high contribution of C 4 grasses to soil C sequestration to the reduced offtake of grass biomass with herbivore exclusion together with the facilitative influence of open sparse woody canopies (e.g., Acacia spp.) on grass cover and productivity in this semiarid system.
    Type of Medium: Online Resource
    ISSN: 0012-9658 , 1939-9170
    URL: Issue
    URL: Article
    DOI: 10.1002/ecy.v101.5
    DOI: 10.1002/ecy.3008
    RVK:
    WA 15000
    Language: English
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 1797-8
    detail.hit.zdb_id: 2010140-5
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  • 6
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    〈i〉Virgilia divaricata〈/i〉 may facilitate forest expansion in the afrotemperate forests of the southern Cape, South Africa
    AOSIS ; 2013
    In:  Koedoe Vol. 55, No. 1 ( 2013-02-20)
    Details
    In: Koedoe, AOSIS, Vol. 55, No. 1 ( 2013-02-20)
    Abstract: Virgilia divaricata is a fast-growing nitrogen-fixing tree species often found on the margins of forest in the southern Cape of South Africa and is particularly abundant after fire. However, V. divaricatamay invade fynbos even in the absence of fire and it has been described as a forest precursor. We investigated whether V. divaricata enriches soil fertility after its invasion into fynbos areas adjacent to forests. We measured soil organic carbon and soil nutrients at four sites. At each site, three vegetation types (forest, V. divaricata and fynbos) were examined on the same soil type and at the same elevation. Our results showed that, on average, soils taken from V. divaricata stands had higher nitrogen and phosphorus values than the adjacent fynbos soils, with either lower or similar values to the adjacent forest soils. Higher soil fertility under V. divaricata, together with their shading effect, may create conditions favourable for shade-loving forest species dependent on an efficient nutrient cycle in the topsoil layers, and less favourable for shade-hating fynbos species, which are generally adapted to low soil fertility. We suggest that the restoration of the nutrient cycle found in association with forest may be accelerated under V. divaricata compared with other forest precursor species, which has important consequences for the use of V. divaricata in ecosystem restoration.Conservation implications: Alien plantations in the Outeniqua Mountains are being phased out and the areas are being incorporated into the Garden Route National Park. Fynbos areas are increasingly being invaded by forest and thicket species owing to fire suppression in lower-lying areas. An improved understanding of the fynbos–forest boundary dynamics will aid in efficient management and restoration of these ecosystems.
    Type of Medium: Online Resource
    ISSN: 2071-0771 , 0075-6458
    URL: Article
    DOI: 10.4102/koedoe.v55i1.1128
    Language: Unknown
    Publisher: AOSIS
    Publication Date: 2013
    detail.hit.zdb_id: 2413347-4
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  • 7
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    What do ecologists miss by not digging deep enough? Insights and methodological guidelines for assessing soil fertility status in ecological studies
    Elsevier BV ; 2013
    In:  Acta Oecologica Vol. 51 ( 2013-8), p. 17-27
    Details
    In: Acta Oecologica, Elsevier BV, Vol. 51 ( 2013-8), p. 17-27
    Type of Medium: Online Resource
    ISSN: 1146-609X
    URL: Article
    DOI: 10.1016/j.actao.2013.05.007
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2013
    detail.hit.zdb_id: 2003658-9
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  • 8
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    Leaf traits of African woody savanna species across climate and soil fertility gradients: evidence for conservative versus acquisitive resource‐use strategies
    Wiley ; 2016
    In:  Journal of Ecology Vol. 104, No. 5 ( 2016-09), p. 1357-1369
    Details
    In: Journal of Ecology, Wiley, Vol. 104, No. 5 ( 2016-09), p. 1357-1369
    Abstract: Establishing trade‐offs among traits and the degree to which they covary along environmental gradients has become a key focal point in the effort to develop community ecology into a predictive science. While there is evidence for these relationships across global data sets, they are often too broad in scale and do not consider the particularities of local to regional species pools. This decreases their usefulness for developing predictive models at scales relevant for conservation and management. We tested for trade‐offs between traits and relationships with environmental gradients in trees and shrubs sampled across southern African savannas and explored evidence for acquisitive versus conservative resource‐use strategies using a phylogenetically explicit approach. We found a distinct trade‐off between two major poles of specialization indicative of acquisitive (high leaf nitrogen concentration, leaf phosphorus concentration, leaf N:P, specific leaf area and average leaf area) and conservative resource‐use strategies (high leaf carbon to nitrogen ratios (C:N), tensile strength and leaf dry matter content). Although we found that trait variance and species occurrence were constrained by phylogeny, phylogenetically informed analyses did not contradict non‐phylogenetic analyses, strengthening relationships in most cases. The high intrasite trait variability and weak relationships with soils and climate may in part be explained by the high levels of deciduousness and disturbance (i.e. fire and herbivory) inherent in African savannas. Synthesis . The relationships between traits and between traits and environmental gradients were far weaker than, and often contradictory to, broad‐scale studies that compare these relationships across biomes and growth forms, cautioning against making generalizations about relationships at specific sites based on broad‐scale analyses.
    Type of Medium: Online Resource
    ISSN: 0022-0477 , 1365-2745
    URL: Issue
    URL: Article
    DOI: 10.1111/jec.2016.104.issue-5
    DOI: 10.1111/1365-2745.12598
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 3023-5
    detail.hit.zdb_id: 2004136-6
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  • 9
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    Online Resource
    A thorny issue: Woody plant defence and growth in an East African savanna
    Wiley ; 2019
    In:  Journal of Ecology Vol. 107, No. 4 ( 2019-07), p. 1839-1851
    Details
    In: Journal of Ecology, Wiley, Vol. 107, No. 4 ( 2019-07), p. 1839-1851
    Abstract: Recent work suggests that savanna woody plant species utilise two different strategies based on their defences against herbivory; a low nutrient/high chemical defence strategy and a nutrition paired with mostly architectural defences strategy. The concept that chemical and structural defences can augment each other and do not necessarily trade‐off has emanated from this work. In this study, we examine woody plant defence strategies, how these respond to herbivore removal and how they affect plant growth in an East African savanna. At three paired long‐term exclosure sites with high browser and mixed‐feeder densities at Mpala Ranch, Kenya, we investigated: (a) whether defences employed by the dominant fine‐ and broad‐leaved woody savanna species form defence strategies and if these align with previously proposed strategies, (b) how nine key plant defence traits respond to herbivore removal and (c) how effective the different defence strategies are at protecting against intense herbivory (by measuring plant growth with and without herbivores present). We identified three defence strategies. We found a group (a) with high N, short spines and high N‐free secondary metabolites, a group (b) with high N, long spines and low N‐free secondary metabolites and a group (c) with moderate N, no spines and low N‐free secondary metabolites (most likely defended by unmeasured chemical defences). Structural defences (spine length, branching) were generally found to be induced by herbivory, leaf available N increased or did not respond, and N‐free secondary metabolites decreased or did not respond to herbivory. Species with long spines combined with increased “caginess” (dense canopy architecture arising from complex arrangement of numerous woody and spiny axis categories) of branches, maintained the highest growth under intense browsing, compared to species with short spines and high N‐free secondary metabolites and species with no spines and low N‐free secondary metabolites. Synthesis . At our study site, structural traits (i.e. spines, increased caginess) were the most inducible and effective defences against intense mammalian herbivory. We propose that high levels of variability in the way that nutrient and defence traits combine may contribute to the coexistence of closely related species comprising savanna woody communities.
    Type of Medium: Online Resource
    ISSN: 0022-0477 , 1365-2745
    URL: Issue
    URL: Article
    DOI: 10.1111/jec.2019.107.issue-4
    DOI: 10.1111/1365-2745.13140
    Language: English
    Publisher: Wiley
    Publication Date: 2019
    detail.hit.zdb_id: 3023-5
    detail.hit.zdb_id: 2004136-6
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  • 10
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    Online Resource
    First woody cover vegetation map of Kruger National Park in 1939–1944: Evidence from historical black and white aerial photography
    Elsevier BV ; 2024
    In:  Ecological Informatics Vol. 81 ( 2024-07), p. 102590-
    Details
    In: Ecological Informatics, Elsevier BV, Vol. 81 ( 2024-07), p. 102590-
    Type of Medium: Online Resource
    ISSN: 1574-9541
    URL: Article
    DOI: 10.1016/j.ecoinf.2024.102590
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2024
    detail.hit.zdb_id: 2218079-5
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