Responses of Karoo plants to hail damage near Williston, Cape Province

Although hail contributes occasionally to the water budget in the Karoo, it may also cause localized, extensive damage to plants. A comparison was made between damaged and undamaged vegetation to assess the recovery of species, growth forms and palatability classes following a hail event during autumn (April 1988) in natural veld on a farm near Williston, Cape Province. Grazing stock had been withdrawn for the fourteen months between the time of the damage and the study. There was no significant long-term reduction in species diversity, growth form richness, percentage plant cover and growth form richness in the hail-damaged vegetation. There was a significantly lower cover of palatable plants in the hail-damaged area. It is concluded that the supposed long-term effects of hail damage on vegetation composition may be seriously overstated and that alleviating grazing pressure during the year following hail damage may contribute greatly to successful recovery

Severely degraded rangeland: Implications for plant diversity from a case study in Succulent Karoo, South Africa

This study aimed to quantify and understand the impact of severe land degradation on plant diversity in part of the Succulent Karoo. Although total number of species declined with heavy grazing, greater evenness resulted in an increase in species diversity. Annuals and geophytes increased while protective nurse plants were decimated and their dependent beneficiary plant species consequently became locally extinct with heavy grazing. The rich biological soil crust dominated by mosses and liverworts with light grazing gave way to brittle physical-chemical or cyanobacterial crusts after heavy grazing. Although heavy grazing can result in extreme levels of degradation in the context of agricultural rangeland use, the implications for plant diversity per se need not be as severe. There appear to be disturbance-dependent indigenous species which may become locally extinct under good rangeland conditions. Our results support the notion of two different species pools, a grazing resistant pool and a grazing beneficiary pool, where changes in grazing intensity can cause substantial changes in composition and some local extinction of species with little or sometimes even positive change in diversity. Beta diversity across the disturbance contrast substantially raised the gamma diversity and hence landscape species diversity. © 2009 Elsevier Ltd. All rights reserved.Articl

Severely degraded dunes of the southern Kalahari: Local extinction, persistence and natural re-establishment of plants

This study aimed to quantify and understand the impact of severe land degradation on plant attributes and diversity on dunes of the southern Kalahari. Heavy grazing pressure in particular resulted in a significant decline of canopy cover and species number in annual and perennial life forms; forb and graminoid growth forms; erect and prostrate habits; and leafy stem, tussock and stoloniferous architectures. However, no significant change was found in shrub and tree forms which persisted without apparent new recruitment. Under these conditions, species diversity dropped sharply and a number of species, mainly graminoids, became apparently locally extinct. The perennial shrub, Crotalaria cf. spartioides, showed the converse with a high frequency of establishing seedlings on the degraded dunes. Changes in relative dominance show that the extreme treatment favours perennial over annual, woody over graminoid and forb, erect over prostrate and leafy stem over stoloniferous and tussock. Some of these results and certain species and soil responses differ from those reported from grazing studies elsewhere, and are possibly no longer directly related to the impact of the primary grazing pressure but to the secondary effect of subsequent instability of the dunes. © 2009 Blackwell Publishing Ltd.Articl

Can heavy grazing on communal land elevate plant species richness levels in the Grassland Biome of South Africa?

A common perception, particularly in South Africa, is that heavily and continuously grazed communal land leads to degradation and loss of plant diversity when compared to commercial rangeland farming or conservation areas. We focus on whether this applies to the Grassland Biome of South Africa and whether the opposite can occur, namely, an increase in plant species richness under heavy grazing. A study of a contrast between a communal area of the former Ciskei and a neighbouring nature reserve showed that intense utilization under communal use led to a significant increase in plant species richness. However, this increase was scale-dependent with the greatest significant difference occurring at sample plot scale (50 m2) but converging at the broader scale of the whole study site. Species that increased with heavy grazing included those from arid Karroid areas as well as some from more mesic grassland and savanna areas. The contribution of beta diversity to gamma diversity across the grazing contrast was relatively low which reflects the relatively high proportion of species shared between treatments. Total plant canopy cover declined sharply with heavy grazing. In terms of plant canopy cover, grazing favoured annual over perennial plants, prostrate over erect plants, and stoloniferous over tussock plant architecture. This pattern was not supported when expressed in terms of number of species belonging to these grazing response groups or traits. © 2011 Springer Science+Business Media B.V.Article in Pres

Plant diversity consequences of a herbivore-driven biome switch from Grassland to Nama-Karoo shrub steppe in South Africa

Questions: How does heavy grazing change plant community structure, composition and species richness and diversity in an ecotone between grassland and semi-arid shrub steppe-type vegetation? Does grazing favour plants with arid affinity over those with less arid affinity? Does the grazing-induced transformation constitute a switch to the equivalent of a shrub-dominated biome? Location: Central South Africa. Methods: Using systematic scanning of SPOT 5 imagery and ground-truthing, a grazing treatment area was selected that met criteria of intensity of grazing, sampling requirements, and biogeographical position within a broad ecotonal zone. Differential vegetation responses to heavy grazing were tested for significant differences in plant traits, vegetation structure, and species diversity, richness and evenness. Gamma diversity was calculated for the whole study site, whereas, independent beta diversity was calculated across the treatments assuming the additive partitioning of diversity. In addition, the biogeographical association of grazing-induced species shifts was determined using a range of available databases. Results: Canopy cover and height of woody shrubs increased significantly with heavy grazing whereas that of graminoid plants declined. The resultant species turnover was modest, apparent extinctions of local species were minimal, species richness was maintained and species diversity was significantly enhanced. There was a significant increase in species evenness, through possible suppression of dominant species. Significant increases in species cover were those associated with mainly the Nama-Karoo biome indicating that species from more arid areas are more resistant to grazing as would be expected by the convergence model of aridity and grazing resistance. Conclusions: The significant increase in shrub cover in heavily grazed semi-arid grassland followed general global expectations. The study confirmed that the supposed former large shift of grassland to shrubby Nama-Karoo in the eastern upper Karoo can indeed be readily affected by heavy grazing. The negative connotations for biodiversity that have often been associated with intense grazing seem, in terms of the positive responses of plant species diversity in this study, to perhaps be exaggerated. The elevated species diversity with grazing of vegetation with a long evolutionary grazing history in a low resource area may require a reappraisal of the application of certain grazing hypotheses. © 2011 International Association for Vegetation Science

Impacts of high utilisation pressure on biodiversity components in Colophospermum mopane savanna

This study aimed to quantify and evaluate the effects of heavy land utilisation, mainly grazing, on plant species richness and diversity, species abundance, vegetation structure and soil characteristics in a communal area in Colophospermum mopane dominated savanna in southern Africa. The treatment was benchmarked against a relatively lightly stocked neighbouring farm. An assessment of termite richness across the contrasting land-use areas was also made. Significant differences were found mainly in plant structure, with reduced plant canopy cover and plant height on the communal land, thus transforming a woodland to a predominantly shrubland physiognomy. There was no significant effect of heavy utilisation on richness or diversity of plant or termite taxa. Species compositional shifts were reflected by significant species associations with either land-use type. Forb species formed an important component of the vegetation irrespective of grazing intensity. Cover of annual plants did not increase with heavy utilisation owing to the increase of 'weedy' annual species being counterbalanced by declining cover of palatable annual plants. Biological soil crusts were markedly less common on the communal land, which may result in an increased hydraulic conductivity of the soil. Other soil properties measured appeared to be insensitive to the intense level of land utilisation. © 2012 NISC Pty Ltd

Early post-fire plant succession in Peninsula Sandstone Fynbos: The first three years after disturbance

The early post-fire plant succession in fynbos vegetation in the Mediterranean-type climate area of South Africa was studied. Relatively little has been published on this early stage of plant succession in fynbos. Annual sampling over the first three post-fire years confirmed a steady, but relatively slow increase in plant canopy cover of shrubs and graminoids (mainly Restionaceae), whereas cover of geophytes and other herbs peaked in the first year and declined significantly, thereafter. Cover of annual plants increased each year, which may relate to the persistence of a relatively open vegetation cover by the third year. The responses of reseeder and resprouter species of the Restionaceae to the post-fire environment appeared to be habitat dependent. Cover of the reseeders increased rapidly in seep areas, but their recovery was distinctly delayed in dryland areas outside the seeps. Re-establishment of the many reseeder Erica species appeared to be delayed until the second post-fire year. Seed banks of these species were possibly negatively impacted by the fire, and required dispersal of seed from unburnt areas for recruitment. In contrast to some current generalisations, species richness appeared to increase after the fire; less certainly from the first to the second year, but more certainly from the second to the third year. Therefore, this study does not support a short-term monotonic decline in species richness after fire in fynbos. © 2011 SAAB.Articl