The thesis reports comparison of soil seed bank with actual vegetation in alluvial sites of the upper stream of Lužnice river in respect to three biotopes. The study focuses on two different methods of soil seed bank investigation and aims to reveal the applicability of macrofossil analysis for palaeoecological records and its interpretation.

A herbivoria em pastagens naturais apresenta papel de destaque no direcionamento das dinâmicas vegetacionais, determinando modificações na estrutura da vegetação, nos padrões de biodiversidade e na produtividade do sistema. Essas alterações, que de modo geral contribuem para a sustentabilidade dos ecossistemas em níveis moderados de intensidade de pastejo, podem dar origem a processos de degradação ambiental quando a lotação animal utilizada é superior à capacidade de suporte das pastagens. O objetivo do presente trabalho foi avaliar a capacidade de recuperação dos padrões de diversidade, composição botânica, biomassa de forragem, altura do pasto, interceptação luminosa e do banco de sementes de uma pastagem natural degradada por sobrepastejo, por meio do diferimento, tomando como base uma área de referência. Três tratamentos baseados em exclusões estacionais do pastejo (Diferimento de Primavera, Diferimento de Outono e Pastoreio Contínuo) com três repetições foram aplicados simultaneamente em áreas manejadas por um longo período com duas intensidades de pastejo: severa e moderada (utilizada como área de referência). A pastagem manejada com pastejo severo apresentou rápida alteração na composição botânica e nos padrões de diversidade em resposta ao diferimento. Depois de dois anos de exclusões temporárias do pastejo, a composição botânica da vegetação estabelecida e do banco de sementes dessa área sofreu alterações nos grupos funcionais de gramíneas na direção das espécies características da comunidade vegetal sob pastejo moderado. Também foram verificados importantes incrementos na biomassa de forragem, altura e interceptação luminosa. A comunidade vegetal sob pastejo moderado apresentou maior equilíbrio entre diferentes grupos funcionais de plantas, especialmente entre espécies com hábitos de crescimento prostrado e cespitoso. Essa condição favoreceu o aparecimento de estrutura espacial na distribuição das espécies de plantas, maior diversidade, riqueza e melhores condições estruturais do pasto. O diferimento realizado na moderada intensidade de pastejo proporcionou dominância de espécies cespitosas, determinando decréscimo na diversidade e riqueza de plantas. As épocas de diferimento apresentaram padrões de resposta semelhantes dentro de cada intensidade de pastejo, com magnitude superior para o diferimento de primavera. Os resultados revelam a importância do diferimento do pastejo como uma ferramenta para a recuperação de pastagens degradadas por sobrepastejo. / The herbivory on natural grasslands has a prominent role in driving vegetation dynamics, determining changes in vegetation structure, biodiversity patterns and primary and secondary productivity. These changes, which generally contribute to the ecosystems sustainability at moderate grazing intensities, can cause environmental degradation when the stocking rate used is higher than the pasture carrying capacity. The objective of this study was to evaluate the efficiency of temporary grazing exclusion to restore diversity, botanical composition, forage biomass, sward height, light interception and soil seed bank from a natural grassland degraded by overgrazing based on a reference area. Three treatments based on seasonal grazing exclusions (spring deferment, autumn deferment and continuous stocking) with three replications were applied simultaneously in areas managed for a long period with two grazing intensities: severe and moderate (used as reference area). The pasture managed under severe grazing showed a rapid change in botanical composition and diversity patterns in response to grazing exclusions. After two years of temporary grazing exclusions, grass functional groups of the established vegetation and soil seed bank from overgrazed pasture changed toward the characteristic species of plant community under moderate grazing. We also verified significant increases in forage biomass, sward height and light interception. The plant community under moderate grazing intensity showed better balance between different functional groups of plants, especially among species with prostrate and cespitose growth habits. This condition favored the spatial structure of appearance in the distribution of plant species, greater diversity, species richness and better structural pasture conditions. The grazing exclusion in moderate intensity grazing provided dominance tussock species, determining decrease in the diversity and richness of plants. The deferment periods showed similar response patterns within each grazing intensity with higher magnitude for spring deferment. These results reveal the importance of grazing exclusion as a tool for the recovery of degraded pastures by overgrazing.

A herbivoria em pastagens naturais apresenta papel de destaque no direcionamento das dinâmicas vegetacionais, determinando modificações na estrutura da vegetação, nos padrões de biodiversidade e na produtividade do sistema. Essas alterações, que de modo geral contribuem para a sustentabilidade dos ecossistemas em níveis moderados de intensidade de pastejo, podem dar origem a processos de degradação ambiental quando a lotação animal utilizada é superior à capacidade de suporte das pastagens. O objetivo do presente trabalho foi avaliar a capacidade de recuperação dos padrões de diversidade, composição botânica, biomassa de forragem, altura do pasto, interceptação luminosa e do banco de sementes de uma pastagem natural degradada por sobrepastejo, por meio do diferimento, tomando como base uma área de referência. Três tratamentos baseados em exclusões estacionais do pastejo (Diferimento de Primavera, Diferimento de Outono e Pastoreio Contínuo) com três repetições foram aplicados simultaneamente em áreas manejadas por um longo período com duas intensidades de pastejo: severa e moderada (utilizada como área de referência). A pastagem manejada com pastejo severo apresentou rápida alteração na composição botânica e nos padrões de diversidade em resposta ao diferimento. Depois de dois anos de exclusões temporárias do pastejo, a composição botânica da vegetação estabelecida e do banco de sementes dessa área sofreu alterações nos grupos funcionais de gramíneas na direção das espécies características da comunidade vegetal sob pastejo moderado. Também foram verificados importantes incrementos na biomassa de forragem, altura e interceptação luminosa. A comunidade vegetal sob pastejo moderado apresentou maior equilíbrio entre diferentes grupos funcionais de plantas, especialmente entre espécies com hábitos de crescimento prostrado e cespitoso. Essa condição favoreceu o aparecimento de estrutura espacial na distribuição das espécies de plantas, maior diversidade, riqueza e melhores condições estruturais do pasto. O diferimento realizado na moderada intensidade de pastejo proporcionou dominância de espécies cespitosas, determinando decréscimo na diversidade e riqueza de plantas. As épocas de diferimento apresentaram padrões de resposta semelhantes dentro de cada intensidade de pastejo, com magnitude superior para o diferimento de primavera. Os resultados revelam a importância do diferimento do pastejo como uma ferramenta para a recuperação de pastagens degradadas por sobrepastejo. / The herbivory on natural grasslands has a prominent role in driving vegetation dynamics, determining changes in vegetation structure, biodiversity patterns and primary and secondary productivity. These changes, which generally contribute to the ecosystems sustainability at moderate grazing intensities, can cause environmental degradation when the stocking rate used is higher than the pasture carrying capacity. The objective of this study was to evaluate the efficiency of temporary grazing exclusion to restore diversity, botanical composition, forage biomass, sward height, light interception and soil seed bank from a natural grassland degraded by overgrazing based on a reference area. Three treatments based on seasonal grazing exclusions (spring deferment, autumn deferment and continuous stocking) with three replications were applied simultaneously in areas managed for a long period with two grazing intensities: severe and moderate (used as reference area). The pasture managed under severe grazing showed a rapid change in botanical composition and diversity patterns in response to grazing exclusions. After two years of temporary grazing exclusions, grass functional groups of the established vegetation and soil seed bank from overgrazed pasture changed toward the characteristic species of plant community under moderate grazing. We also verified significant increases in forage biomass, sward height and light interception. The plant community under moderate grazing intensity showed better balance between different functional groups of plants, especially among species with prostrate and cespitose growth habits. This condition favored the spatial structure of appearance in the distribution of plant species, greater diversity, species richness and better structural pasture conditions. The grazing exclusion in moderate intensity grazing provided dominance tussock species, determining decrease in the diversity and richness of plants. The deferment periods showed similar response patterns within each grazing intensity with higher magnitude for spring deferment. These results reveal the importance of grazing exclusion as a tool for the recovery of degraded pastures by overgrazing.

A herbivoria em pastagens naturais apresenta papel de destaque no direcionamento das dinâmicas vegetacionais, determinando modificações na estrutura da vegetação, nos padrões de biodiversidade e na produtividade do sistema. Essas alterações, que de modo geral contribuem para a sustentabilidade dos ecossistemas em níveis moderados de intensidade de pastejo, podem dar origem a processos de degradação ambiental quando a lotação animal utilizada é superior à capacidade de suporte das pastagens. O objetivo do presente trabalho foi avaliar a capacidade de recuperação dos padrões de diversidade, composição botânica, biomassa de forragem, altura do pasto, interceptação luminosa e do banco de sementes de uma pastagem natural degradada por sobrepastejo, por meio do diferimento, tomando como base uma área de referência. Três tratamentos baseados em exclusões estacionais do pastejo (Diferimento de Primavera, Diferimento de Outono e Pastoreio Contínuo) com três repetições foram aplicados simultaneamente em áreas manejadas por um longo período com duas intensidades de pastejo: severa e moderada (utilizada como área de referência). A pastagem manejada com pastejo severo apresentou rápida alteração na composição botânica e nos padrões de diversidade em resposta ao diferimento. Depois de dois anos de exclusões temporárias do pastejo, a composição botânica da vegetação estabelecida e do banco de sementes dessa área sofreu alterações nos grupos funcionais de gramíneas na direção das espécies características da comunidade vegetal sob pastejo moderado. Também foram verificados importantes incrementos na biomassa de forragem, altura e interceptação luminosa. A comunidade vegetal sob pastejo moderado apresentou maior equilíbrio entre diferentes grupos funcionais de plantas, especialmente entre espécies com hábitos de crescimento prostrado e cespitoso. Essa condição favoreceu o aparecimento de estrutura espacial na distribuição das espécies de plantas, maior diversidade, riqueza e melhores condições estruturais do pasto. O diferimento realizado na moderada intensidade de pastejo proporcionou dominância de espécies cespitosas, determinando decréscimo na diversidade e riqueza de plantas. As épocas de diferimento apresentaram padrões de resposta semelhantes dentro de cada intensidade de pastejo, com magnitude superior para o diferimento de primavera. Os resultados revelam a importância do diferimento do pastejo como uma ferramenta para a recuperação de pastagens degradadas por sobrepastejo. / The herbivory on natural grasslands has a prominent role in driving vegetation dynamics, determining changes in vegetation structure, biodiversity patterns and primary and secondary productivity. These changes, which generally contribute to the ecosystems sustainability at moderate grazing intensities, can cause environmental degradation when the stocking rate used is higher than the pasture carrying capacity. The objective of this study was to evaluate the efficiency of temporary grazing exclusion to restore diversity, botanical composition, forage biomass, sward height, light interception and soil seed bank from a natural grassland degraded by overgrazing based on a reference area. Three treatments based on seasonal grazing exclusions (spring deferment, autumn deferment and continuous stocking) with three replications were applied simultaneously in areas managed for a long period with two grazing intensities: severe and moderate (used as reference area). The pasture managed under severe grazing showed a rapid change in botanical composition and diversity patterns in response to grazing exclusions. After two years of temporary grazing exclusions, grass functional groups of the established vegetation and soil seed bank from overgrazed pasture changed toward the characteristic species of plant community under moderate grazing. We also verified significant increases in forage biomass, sward height and light interception. The plant community under moderate grazing intensity showed better balance between different functional groups of plants, especially among species with prostrate and cespitose growth habits. This condition favored the spatial structure of appearance in the distribution of plant species, greater diversity, species richness and better structural pasture conditions. The grazing exclusion in moderate intensity grazing provided dominance tussock species, determining decrease in the diversity and richness of plants. The deferment periods showed similar response patterns within each grazing intensity with higher magnitude for spring deferment. These results reveal the importance of grazing exclusion as a tool for the recovery of degraded pastures by overgrazing.

Please read the abstract in the section 00front of this document / Thesis (PhD (Botany))--University of Pretoria, 2007. / Plant Science / unrestricted

Includes bibliographies. / The unique vegetation in the lowlands of the fynbos biome is threatened by alien Acacia encroachment. The seed bank dynamics of the two most widespread invaders in the region, Acacia saligma and A. cyclops, was studied to elucidate those factors contributing most to their invasive success. This information was then used to assist in developing optimal control methods. On the basis of information available prior to this study, it was predicted that both species would have large, persistent seed banks in the so.il, and that seed bank processes would provide the - key to invasive success: namely, high seed longevity and heat-stimulated germination. Seed banks were monitored for several years following clearing of the parent stand, using either sites sampled in an earlier study, or sites providing chronosequences of clearing dates. Concurrently, a demographic study of the species' seed banks, including processes from seed rain through to seedling emergence and survival, was done in dense Acacia stands and in fynbos vegetation. Acacia saligma seed banks conformed to predictions, being large and persistent owing to high percentage viability and water-impermeable dormancy. Seed banks accumulate rapidly under dense stands and are "disturbance-coupled" as they have potentially high longevity unless stimulated to germinate by fire. Although A. cyclops seed banks also may be large and long-lived, they display variable percentage viability and dormancy, with the majority of a seed cohort surviving less than a year. Acacia cyclops seed banks do not respond to heat treatment and appear to be "disturbance-uncoupled".

Biodiversity is declining faster than at any other time in the Earth's history, driven mostly by land use change and degradation. Overberg Renosterveld, some of the most species diverse mediterranean type shrublands, are no exception with about 95% of their original extent lost to agriculture. Historically, large herds of indigenous grazing mammals roamed these landscapes. Today the Overberg's agricultural lands are fragmented by land cover change and divided by fences. In the contemporary landscape animals, largely domestic livestock, and plant resources are closely coupled, and overgrazing of remaining renosterveld fragments a significant threat, with potential to cause irreversible damage. The Conservation of Agricultural Resources Act (CARA) (Act 43 of 1983) states that farmers must not exceed the grazing capacity of the veld unless it is protected against deterioration and destruction, and that any land that is degraded or denuded must be effectively restored or reclaimed. Despite this legislation, there is little empirical research on the impacts of livestock grazing on renosterveld, as well as on restoration of overgrazed areas. It was the aim of this thesis to contribute to this gap in understanding. The thesis assessed the role of grazing by different livestock types, namely cattle and sheep, on biodiversity, the soil seed bank, and the restoration potential of renosterveld vegetation from resting the veld. The effect of livestock grazing by sheep and cattle on plant species richness and diversity and growth form diversity was assessed using Modified Whittaker plots and presented in Chapter 3. It was hypothesised that livestock grazing by cattle would have less effect on species richness and diversity and growth form diversity than sheep grazing and that both cattle and sheep grazing would lead to a reduction in species richness and diversity in comparison to renosterveld sites with a treatment of no grazing. Thirty sites where either no grazing has taken place or that have been grazed by cattle or sheep were selected with sites being evenly distributed between Eastern, Central and Western Rûens Shale Renosterveld. At each of the thirty sites, vegetation data were collected from a series of nested subplots of ten 1 m2 , two 10 m2 and one 100 m2 subplots nested within a 1 000 m2 plot. One soil sample was also collected from each 1 000 m2 plot to a depth of 10 cm for nutrient analysis. Findings revealed that sites grazed by sheep had significantly lower plant species richness (median richness = 29 species, mean Shannon-Weiner = 3.39) and diversity when compared to sites with a treatment of no grazing (median richness = 49 species, mean Shannon Weiner = 3.83). Sites with a treatment of no grazing had significantly higher richness of geophyte species (mean = 14.7) than sites grazed by cattle (mean = 7.0) and sheep (mean = 7.1) during the study. The results obtained were in line with the hypothesis that livestock grazing by sheep resulted in a reduction in species richness and diversity and vegetation cover in Overberg Renosterveld in comparison to sites where no grazing has taken place. Sites with a treatment of no grazing showed higher species richness and vegetation cover of non-succulent shrubs, annual forbs and perennial forbs than sites grazed by sheep. It was concluded that livestock grazing of Overberg Renosterveld by sheep needs to be done with care. This can be done by adopting a passive adaptive management approach. Here one set of management protocols can be developed and implemented and through science-based monitoring to inform management, these can be adapted as needed based on the key findings. Chapter 4 investigated ecosystem resilience and the restoration potential of Overberg Renosterveld through an exploration of its soil seed bank as a source for potential recovery. A glasshouse germination experiment investigated the effect of livestock grazing by cattle and by sheep in comparison with a grazing treatment of no grazing on the soil seed bank in Overberg Renosterveld, as well as the similarity between the standing vegetation and the soil seed bank. It was hypothesised that cattle and sheep grazing would reduce species richness, species diversity and growth form diversity in the soil seed bank in comparison with sites with a treatment of no grazing. Soil samples were collected from 30 sites that were also used in Chapter 3. The soil was then spread on top of a 6 cm layer of compost in seed trays, and smoke treated to enhance germination. Seedlings were assigned to growth form categories including forbs, geophytes, annuals, graminoids, succulent shrubs and nonsucculent shrubs and then identified to family, genus or species level. The results of the soil seed bank study were correlated with the vegetation results from Chapter 3 to examine the relationship between the standing vegetation and the soil seed bank. A total of 48% of taxa in the standing vegetation had seed present in the germinable seed bank. However, there were no differences in species richness, species diversity or number of individuals between grazing treatments. The results indicated that livestock grazing has a far less significant impact on the composition, species diversity and growth form diversity of the soil seed bank in Overberg Renosterveld than hypothesised. Instead, the results showed that there was a well-developed seed bank comprising mainly indigenous species with a variety of different growth forms including palatable grasses and shrubs. This indicates that Overberg Renosterveld vegetation has high restoration potential. Chapter 5 showed results on the effects of livestock grazing by cattle and sheep over time on plant species richness, diversity and growth form diversity in comparison with sites protected from grazing. Following collection of a baseline dataset, four years of follow up data were collected. A total of 22 fenced plots across Western, Central and Eastern Rûens Shale Renosterveld had a baseline dataset collected prior to being monitored on an annual basis over four years in grazed/ungrazed paired plots. Results on vegetation recovery from the fenced exclosures showed a significant increase in plant cover over time at sites that were not grazed. Mean species richness increased from 20.6 species to 25.4 species at sites with no grazing. Mean vegetation cover increased from 71% at T0 (the baseline time step) to 120% at T4 (the final time step) at the end of the study. Sites grazed by sheep had a decrease in vegetation cover over time each year from T0 to T4 from 75% to 50%. Results from a linear mixed model revealed that species richness between grazing treatments was significantly different at all time steps in the study. However, the significant differences were primarily due to comparisons between grazed sites and sites with a treatment of no grazing. Therefore, livestock grazing by sheep has a significant effect on renosterveld vegetation over time. Findings from this component of the study indicates that Overberg Renosterveld degraded by continuous heavy grazing has significant passive restoration potential by fencing renosterveld patches to facilitate more effective grazing management. Most of the renosterveld of the Overberg has been lost through habitat transformation for agriculture, and the future of that which remains is uncertain. This thesis affirms concerns around the impact of livestock grazing and shows the importance of improved ecological understanding around grazing management. Grazing by sheep was shown to cause greater impacts on renosterveld than other domestic livestock studied and is therefore a threat to renosterveld. These findings warrant closer attention to management practices around sheep grazing. However, the state of renosterveld soil seed banks offer considerable hope. Findings revealed a diverse indigenous seed bank, showing that renosterveld degraded by overgrazing has high restoration potential. Furthermore, fencing renosterveld to exclude livestock improves species richness and diversity over time. These findings highlight the need for caution when grazing renosterveld. However, where the damage has been done, the potential for recovery is high. Harnessing the soil seed bank in combination with excluding livestock grazing by fencing are effective tools in this critically endangered vegetation for achieving restoration and conservation goals.

The encroachment of rangelands by woody plants causes an imbalance in the grass:bush ratio leading to decline in ecosystem services including grazing capacity, biodiversity, and water yield. This study assessed the historical changes in woody cover, and the effects of bush clearing on water loss, atmospheric carbon uptake, herbaceous vegetation, and soil seed bank (SSB) dynamics. The study was conducted at Makapanstad (Radi and Maseding) and Kgomokgomo rangelands, North-West Province, South Africa. Landsat imagery was used to assess woody cover over 34 years (1984 - 2018) in a total area of 16 397 ha. Evapotranspiration (ET) and gross primary productivity (GPP) were assessed in cleared sites and their adjacent uncleared sites from 2013 to 2018. Woody plant densities, herbaceous composition, ground cover and biomass production were assessed in 24, 5×5-m plots distributed equally in three 2500-m2 bush-encroached blocks in each rangeland in February 2016. Three samples for soil nutrient analysis were collected 20-cm deep in each plot. Thereafter, half (1250-m2) of each block was mechanically cleared to make three replicates of cleared and uncleared microsites. Post-treatment survey of vegetation was conducted in February 2017. SSB was assessed for samples collected in April 2016 before bush clearing and in August, October and December 2016, and April and August 2017 in paired microsites. In 1984, herbaceous cover (humid + arid grasslands) dominated, accounting for 36% of the total area followed by woody cover (shrublands + bushlands) and unvegetated cover (bare soils + abandoned croplands), with respective proportions of 33 and 31%. There were substantial land cover changes over time, with shrub cover increasing linearly (r2 = 0.94, p < 0.05) at a rate of 0.26% year-1, increasing the total woody cover (TWC) to 38% in 2018. Cropland abandonment was the main driver of increase in shrub cover in the study area. Herbaceous cover declined with increase in TWC (r2 = 0.69), whereas bare soil cover increased (r2 = 0.70) with TWC over time. The main encroachers were Vachellia tenuispina at Radi, Vachellia tortilis at Maseding and Dichrostachys cinerea and V. tortilis at Kgomokgomo. Most of the woody species correlated with total N and clay content (r = 0.96; p < 0.05) in black vertic clay soils of Radi and Maseding, whereas non-leguminous species correlated with total N and C:N in the red-yellow apedal soils of Kgomokgomo. ET and GPP varied interannually in all rangelands and both declined significantly (p < 0.05) after bush clearing at Radi and Kgomokgomo but not at Maseding. ET increased with GPP in cleared (r2 = 0.50-0.59) and uncleared sites (r2 = 0.82-0.93) at Radi and they showed a strong relationship (r2 >0.70) in both sites at Maseding and Kgomokgomo. ET ranged from 0.26-0.46 and 0.48-0.97 Kg H2O m-2 day-1 in cleared and uncleared sites, respectively, at Radi and from 0.44-0.98 and 0.63-1.24 Kg H2O m-2 day-1 at Kgomokgomo. Total SSB densities (constituted mostly by early successional species) increased significantly (p < 0.05) to 2470, 1872 and 693 seeds m-2 at Radi, Maseding and Kgomokgomo, respectively, in cleared microsites in August 2017. Similarly, biomass production (BP) and basal cover (BC) were highest in cleared relative to uncleared microsites. Overall, increase in woody cover reduced herbaceous cover and this calls for bush control in the studied rangelands. The decline in ET after bush clearing suggested that bush clearing could be used to increase rangeland water yield. Increased SSB densities, BP and BC indicated that bush clearing facilitates passive restoration. / Thesis (PhD (Pasture Science))--University of Pretoria, 2020. / Agricultural Research Council / National Research Foundation / Plant Production and Soil Science / PhD (Pasture Science) / Unrestricted

San Joaquin wooly-threads (Monolopia congdonii; Asteraceae) is a federally-listed, endangered annual plant species from the desert areas of the San Joaquin Valley. Its limited range puts it at risk of extinction if the climate changes in such a way as to hinder its growth and reproduction. The primary aims of the study were to 1) determine how long-lived the seeds of the M. congdonii are, a key determinant of survival of desert annual plant populations through long droughts and 2) determine how severely hotter, drier conditions impact the ability of emerged plants to grow and reproduce. Secondarily, I aimed to test two hypotheses 1) is seed longevity within the genus Monolopia correlated with habitat aridity? 2) do species’ geographic range limits represent their climatic tolerances? In testing the viability of seeds of Monolopia species collected from herbarium specimens and old field collections, I did not find evidence for the predicted pattern of seed longevity. Though, idiosyncrasies in the data suggest possible issues with the longevity of M. congdonii seeds that are collected prematurely and warrant further investigation to develop best practices for seed collections of this species. To test the climatic tolerance of M. congdonii and the relationship between geographic range and climatic tolerance, I grew several desert annual species under three manipulated water treatments. And while, M. congdonii failed to germinate, the other species showed variable tolerance for the drought treatments but this variability was seemingly unrelated to the species’ geographic range. Importantly, Monolopia lanceolata, a close relative of M. congdonii did not show exceptional vulnerability to the drought-stress conditions relative to other co-occuring species. Taken together, the results of this study enable better informed population viability analyses with the end goal of allowing recovery efforts to succeed.

No description available.