1,720,999 research outputs found
Forb ecology research in dry African savannas: Knowledge, gaps, and future perspectives
Full text linkSavannas 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
Herbaceous biomass species diversity relationships in nutrient hotspots of a semi-arid African riparian ecosystem
No full textThe hump-back relationship between species diversity and productivity predicts highest species richness at
intermediate levels of biomass, and low species numbers in least and most productive habitats. Sodic patches of
semi-arid savannas are considered ‘nutrient hotspots’ by producing high-quality forage. The impact of biomass
reduction (due to overgrazing) and accumulation (in the absence of herbivores) on herbaceous species richness
and diversity is still unknown for these hotspots. We tested the relationship between biomass and herbaceous
species richness/diversity in savanna sodic sites across varying biomass levels obtained through different
herbivore exclosures. LOWESS and quadratic regression analyses revealed a unimodal species richness/
diversity–biomass relationship for biomass <2 500 kg ha−1. Species richness and diversity in the sodic zone peaked
at 1 300 kg ha−1, followed by a steady decline. At biomass levels exceeding 2 500 kg ha−1, i.e. where herbivores
have been excluded for 10 years, the decline in species richness and diversity stabilised. Despite many debates
surrounding unimodal relationships and the intermediate disturbance hypothesis, this study confirmed a peak
in species richness and diversity at intermediate biomass levels in a herbivory-adapted ecosystem. Herbivores
drive ecosystem heterogeneity and enhance herbaceous species richness and diversity by keeping biomass at
intermediate levels (i.e. <2 500 kg ha−1 for this sodic site
The vegetation and floristics of the Letaba exclosures, Kruger National Park, South Africa
No full texthttp://dx.doi.org/10.4102/koedoe.v52i1.777http://www.scielo.org.za/scielo.php?pid=S0075-64582010000100004&script=sci_arttex
The vegetation and floristics of the Nkhuhlu Exclosures, Kruger National Park
Full text linkThe need to conduct research on the impact of elephant on the environment prompted the construction of exclosures along two of the most important rivers in the Kruger National Park. Scientific research on these exclosures along the Sabie and Letaba rivers addresses how patterns of spatial and temporal heterogeneity of the riparian zone are affected by fire, flood and herbivory. To further assist this research programme, a vegetation survey was conducted at the Nkhuhlu exclosure site along the Sabie River to classify and map the vegetation of the area. This will provide baseline data to assess future changes in vegetation and floristic patterns due to small-scale environmental factors created by the presence/absence of herbivory and fire. Phytosociological data were analysed to identify plant communities and subsequent mapping units. Five plant communities, ten sub-communities and four variants were recognised and described in relation to prevailing soil forms. Differences in species richness, diversity and community structure of the plant communities are clearly articulated
The impact of herbivore exclusion on forb diversity: comparing species and functional responses during a drought
No full textRainfall and herbivory shape savannah herbaceous communities, but these disturbances are being altered globally. To assess potential consequences of such alterations, we evaluated herbivore effects on species and functional diversity during an episodic drought in a sodic savannah using data collected from long‐term herbivore exclosures in the Kruger National Park, South Africa. Herbaceous life forms are rarely acknowledged as distinct functional entities. Moreover, the functional ecology of forbs remains elusive. Here, we present disturbances–responses by forbs separately from grasses. We hypothesised that combinations of intense utilisation and drought would be associated with low diversity and high dominance at species and functional levels for both life forms. Contrary to our hypothesis, low forb and grass diversity was associated with long‐term herbivore exclusion, which exceeded expected undesirable effects of intense utilisation and drought. Grasses responded less sensitively, suggesting that forbs respond dynamically to changes in herbivore assemblage when these alterations are combined with drought. Consistent with patterns in savannah systems, forbs contributed significantly to species and functional trait diversity. High forb diversity is suggested to enhance resilience of this nutrient‐rich ecosystem against declines in its functioning when subjected to drought and alterations in herbivor
Herbaceous species diversity patterns across various treatments of herbivory and fire along the sodic zone of the Nkuhlu exclosures, Kruger National Park
Full text linkUnderstanding relationships between large herbivores and plant species diversity in dynamic riparian zones is critical to biodiversity conservation. The Nkuhlu exclosures in the Kruger National Park (KNP) provided opportunity to investigate spatial heterogeneity patterns within riparian zones, as well as how these patterns are affected by fire and herbivory. A monitoring project was initiated to answer questions about the dynamics of the herbaceous layer and was aimed at determining, (1) whether there exists meaningful variance in herbaceous plant species richness and diversity across different treatments in the ecologically sensitive sodic zone and (2) whether an increase in herbaceous biomass, an artefact of herbivory and fire exclusion, suppresses herbaceous plant species diversity and richness. Herbaceous vegetation was sampled in two 1 m2 circular sub-plots in the eastern and western corners of 81 fixed plots. The biomass of each plot was estimated with a disc pasture meter (DPM) diagonally with the plot. DPM-readings were converted to kg/ha, according to the latest conversions for the Lowveld Savanna. Species richness and biomass showed significant variance across treatments, whereas no significant variation in herbaceous species diversity was perceived. Combined treatment of fire absence and herbivore presence contributed to higher forb species richness in the sodic zone. Biomass is significantly higher in fully fenced areas where herbivores are excluded, as opposed to the open and partially fenced areas. Although no significant variation was recorded for diversity across treatments, lowest diversity was recorded in the absence of all herbivores, especially in combination with fire treatment. Therefore herbivores are essential in sustaining herbaceous plant species richness in the sodic zone, whilst no significant results were found with regard to their effect on species diversity. Although statistically non-significant, fire seems to suppress species richness.Conservation implications: This study could be used as framework to advance and develop science-based management strategies for, at least, the sodic zones of the KNP. Research in these exclosures will create better understanding of these landscapes, benefit ecosystem conservation planning of national parks and also provide valuable long-term information on key ecological processes.</p
Myth-busting tropical grassy biome restoration
No full textThe historical focus in research and policy on forest restoration and temperate ecosystems has created misunderstandings for the restoration of tropical and subtropical old‐growth grassy biomes (TGB). Such misconceptions have detrimental consequences for biodiversity, ecosystem services, and human livelihoods in woodlands, savannas, and grasslands worldwide. Here, we demystify TGB restoration myths to promote a positive agenda to increase the likelihood of success of ambitious landscape‐scale restoration goals of nonforest ecosystems. The 10 TGB restoration myths are: (1) grasslands originate from degraded forests, (2) tree cover is a reliable indicator of habitat quality, (3) planting trees is always good for biodiversity and ecosystem services, (4) grasslands are biodiversity‐poor and provide few ecosystem services, (5) enhancing plant nutrition is needed in restoration, (6) disturbance is detrimental, (7) techniques used to restore temperate grasslands also work for TGB, (8) grasslands represent early stages of forest succession, (9) grassland restoration is only about grasses, and (10) grassland restoration is fast. By demystifying TGB restoration, we hope that policymakers, scientists, and restorationists come to understand and embrace the value of these ecosystems and are motivated to establish policies, standards, indicators, and techniques that enhance the success of TGB restoration. We must abandon misperceptions and misunderstandings of TGB ecology that result in ill‐conceived policies and build an informed and compelling global ecosystem restoration agenda that maintains and improves the well‐being of all inhabitants of grassy biome
Manganese tolerance of Aloe greatheadii Schönland var. davyana (Schönland) Glen & D.S.Hardy (Asphodelaceae: Alooideae) on Ultramafic-Peralkaline Outcrops, South Africa
No full textVery little is known about the relations between aloes and soil metals, despite evidence that aloes often form dense populations on metalliferous soils. This study targeted eight rock outcrops where aloes dominated the vegetation to determine whether these succulents have a preference for soils rich in heavy metals and whether they accumulate any of these metals in their leaf tissue. Soil analyses suggested that densely populated rock outcrops are rarely characterised by high concentrations of heavy metals. Analyses of leaf material revealed no metal hyperaccumulators, with most species acting as excluders of most metals. The only metals to be reflected in leaf material to some degree across populations were copper (mean of 4 µg g-1), iron (mean of 208 µg g-1), manganese (mean of 342 µg g-1) and zinc (mean of 31 µg g-1)(all values are based on leaf dry weight). Aloe greatheadii plants from the ultramafic-peralkaline Koedoesfontein Complex in the Vredefort Dome contained the highest concentrations of Mn (558 µg g-1) and were subjected to further sampling across four geological substrates to determine the limits of its accumulation ability (mean of 855 µg g-1 on wehrlite). This aloe was found to be non-hyperaccumulating, but tolerant to elevated Mn concentrations in its tissue. The uptake of Mn from the soil was not so much influenced by soil available Mn, but rather by decreasing pH, and increasing electric conductivity and soil potassiu
Characterisation of the woody assemblages of Zululand coastal thornveld along the Nseleni river
Full text linkA classification of the woody component of the riparian vegetation of Zululand coastal thornveld is analysed using the height classes of different woody species as an indication of age. A total of 43 randomly stratified plots was selected using aerial photographs to include all the different plant communities in this rare and endemic vegetation type. A floristic survey of the woody component was conducted within each sample plot. Species data recorded included tree cover and tree richness. Environmental data recorded included altitude, soil type, soil chemistry, aspect and slope. The data set was analysed with TWINSPAN and four woody-plant assemblages were identified. An ordination using CANOCO was applied to examine the relationships between species distribution and associated environmental gradients. Changes in the species composition of woody assemblages occurred along an environmental gradient determined by soil properties and past land use
- …
