Soils harbor a huge diversity of microorganisms, which are dominated by bacteria and fungi. These soil microorganisms, collectively termed as the soil microbiome, are major contributors to soil biodiversity and play essential roles in soil functions (e.g. soil fertility and plant nutrition, organic matter degradation and nutrient cycling, and soil formation). Therefore, many studies in recent decades have explored soil microbial diversity in order to unravel driving forces of its variations. Hence, this thesis reports on spatial and temporal variations of the soil microbiome in response to site specificities, i.e. local climate as well as soil physico-chemistry, and host tree parameters. To avoid effects of intraspecific genetic variations, the pedunculate oak clone DF159 (Quercus robur L.) generated by the project TrophinOak-PhytOakmeter of the Soil Ecology Department at the Helmholtz Centre for Environmental Research (UFZ) was used as phytometer system. In the PhytOakmeter project of which this thesis is a part, saplings regenerated from microcuttings of DF159 were out-planted in grassland, forest and urban field sites in Central Germany and along a European North-South transect. The overall goal of the project is to analyze how the clone adapts to and performs under different regional climatic contexts and changing environment conditions. Pedunculate oak was chosen as a model tree species because it is engaged in highly complex and diverse multitrophic interactions, including soil microorganisms. Q. robur displays an endogenous rhythmic growth with alternating growing flushes in shoot and root, which can be repeated two to four times along a vegetation period. These alternating flushes have been shown to impact on variations of biological activities in soil zones close to the tree roots. Based on the above-described background, the current PhD study investigated changes in the soil microbial communities associated to the pedunculate oak phytometer outplanted in grassland sites at two different spatial scales: (1) the local scale by comparing the soil microbiomes associated to the phytometer in sites located within a close geographic space of Central Germany with similar climatic conditions; and (2) continental scale by making a similar comparison among sites along a European North-South transect, which encompasses a wide range of climatic and soil physico-chemical conditions. Moreover, temporal scale was considered, whereby the variability of the microbiomes intra-annually along a vegetation period was analyzed. Soil samples were taken not only in the tree root zone (RZ), i.e. soil zone containing living roots of the tree, but also in the tree root-free zone (RFZ), i.e. soil zone out of reach of any tree roots, but within the same field plot, to access also the local microbial pools. The analyses used a PCR-based Illumina MiSeq amplicon sequencing approach targeting bacteria and fungi, to assess their diversity, community structure and functionality after assignment of their OTUs to functional groups. In addition to Chapter 1, which introduces the whole work of this PhD research, the findings are presented within Chapters 2-4, of which two studies were already published in international peer-reviewed journals, while another study was published as a conference paper. The thesis is closed by the synopsis Chapter 5 that integrates discussion of all the publication chapters together with an outlook section. Chapter 2 “Tree root zone microbiome: exploring the magnitude of environmental conditions and host tree impact” published in Frontiers in Microbiology investigates the relative contribution of abiotic environmental and host tree parameters among four sites characterized by homogeneous climatic conditions in Central Germany, two years after the tree out-plant. We first compared at each field site the composition of the bacterial and fungal communities between the RZ of the oak clone, called PhytOakmeter in this chapter, and the tree RFZ. The chapter further evaluates the diversity and structure of the microbial communities within the tree RZ among the sites. The results revealed different microbial compositions between the tree RZ and RFZ, whereby the tree RZ-associated microbiome included numerous ectomycorrhizal fungi of the genera Hebeloma, Exophiala, Scleroderma, Tomentella, Trichophaea, and Tuber. This quick recruitment of specific beneficial microbial taxa from the local microbial pool seems to be among the tree strategies to acclimate to local site conditions. However, the overall tree contribution to shape soil microbial communities was lower than the impact of abiotic environmental parameters. The results revealed also a similar level of microbial diversity within the tree RZ among the sites for both the bacteria and fungi, an outcome attributed to the homogeneous climatic conditions within the sites and the common genetic identity of the host trees. In contrast, structure of the microbial communities was site-specific. Chapter 3 “Balance between geographic, soil, and host tree parameters to shape soil microbiomes associated to clonal oak varies across soil zones along a European North-South transect” published in Environmental Microbiology, also examines the relative impact of geographic, soil physico-chemical, and pedunculate oak clone parameters on the variability of the soil microbiome, but at a larger spatial scale from Lapinjärvi (Finland) to Bordeaux (Southwestern France), which is characterized by a broad range of geographic and soil physico-chemical conditions. In addition to the tree RFZ total microbiome and the tree RZ total microbiome, this chapter introduces a new sub-microbiome called tree RZ affine microbiome. The latter was defined as a subset of the RZ bacteria and fungi, significantly enriched in this zone compared to the tree RFZ. The results demonstrated an interplay among abiotic environmental and host tree parameters in shaping bacterial and fungal communities of the tree RZ along the European transect. These parameters showed a descending order of magnitude of their impact on the tree RZ total microbiome: geographic > soil physico-chemical > host tree parameters. However, for the variability of the RZ affine microbiome alone, the impact of the abiotic environmental parameters decreased, while the tree influence was strongly increased, particularly for fungi. Another important result was the highest proportion of the tree RZ affine microbial OTUs shared among all four sites, which was here designated as the tree “core” microbiome. These bacteria and fungi with significant affinity to the host tree, and shared by all the sites because of their ability to cope with diverging environmental conditions across the transect, may be playing a crucial role in supporting the wide distribution of Q. robur across Europe. Interestingly, we found no members of the RZ affine microbiome to be exclusive of only one particular site. Chapter 4 “Temporal changes and alternating host tree root and shoot growth affect soil microbiomes” published in Proceedings as conference paper after “The 1st International Electronic Conference on Microbiology”, considers a temporal scale, and here the variability of the tree RZ and RFZ total microbiomes was analyzed along a vegetation period in two sites of Central Germany. The soil was sampled at different time points coinciding with the tree alternating root and shoot growth, and the fall senescence that concludes the vegetation period. The results show a directional change over time along a vegetation period for the bacterial communities. However, the fungal communities did not show such temporal changes; they rather displayed a fine spatial scale partitioning closely linked to host plant individuals. In addition to the effect of temporal succession, deeper analyses of the generated data set will enable us to specify the impact of the alternating root and shoot growth characteristic of the tree endogenous rhythmic growth in the near future. These further analyses will include for example zooming in the tree RZ affine microbiome and in individual microbial functional groups. The results presented in this thesis evidence the quick impact of pedunculate oak tree clone on the soil microbiome within a two-year time span after the tree out-plant. Also, to different extents, geographic, soil physico-chemical, and host tree concurrently shape the soil bacterial and fungal communities. This thesis shows different spatial and temporal responses to the abiotic environmental and tree parameters between the soil bacterial and fungal communities. The use of tree clonal phytometer to study the tree-related parameters on soil microbiomes was proved to be a promising tool, to unravel the hierarchy of different abiotic and biotic factors in shaping the soil microbiome associated to long live trees. Finally, this work represents a first step toward establishing a long term monitoring of the dynamics of soil microbiomes associated to trees, as a strategy to unravel how these microorganisms participate to the long term acclimation of these long live plants to diverse and changing environments.

This study investigates the impact of arrival order and seed traits on plant community assembly and biodiversity in a grassland ecosystem in northern Sweden. A field experiment was conducted using 20 different grassland species, with germination pre-tests in the greenhouse and sowing experiments in the field. Seed mass and germination speed were selected seed traits to provide insights into the competitive ability and early life history strategies of the sown species. In the field study, four arrival order treatments with both slow- and fast-germinating species were performed on 70 m2 plots. After three years, the aboveground biomass of the established species was harvested and analyzed, revealing that species arriving second exhibited significantly lower biomass compared to those arriving first. Our results thereby suggest that arrival order has a significant impact on the productivity of species in grassland ecosystems. Priority effect strength (PES) was assessed using two different equations, with results indicating no significant relationship between PES and seed mass or germination speed. Biodiversity analysis revealed that plots with simultaneous late arrival had significantly lower Shannon diversity indices compared to arrival earlier in the season. These findings suggest that arrival order significantly influences plant productivity, while the effect on biodiversity in grassland ecosystems is less clear. Further, seed traits such as mass and germination speed may not play a significant role in determining the strength of priority effects during community assembly.

This problem consists of classifying the four major pastures of the McKamy ranch into McConnell's four categories, by means of examinations based on these qualities and characteristics.

Research in grassland ecosystems worldwide has highlighted the crucial role many burrowing herbivore mammals provide as so-called “ecosystem engineers”. Many of these examples come from North America and have mostly been focused on Prairie Dogs (Cynomys sp.), which, due to their burrowing and grazing activities, are considered as a species of high ecological importance. Multiple studies have shown that their loss reduces grassland ecosystem functions and that their activities increase plant, arthropod, bird and mammal biodiversity, grassland heterogeneity, provide benefits to cattle, among many other key ecological roles. However, prairie dog species are distributed throughout multiple landscapes in North America, and most of the studies have been on mixed prairie grasslands. It is therefore not surprising that, when comparing the effects of different prairie dog species across ecoregions, the role of prairie dogs is not as clear and results vary, depending on spatial context, type of grasslands, climate and environmental conditions. Yet, grasslands are considered as some of the most highly threatened ecosystems, having high rates of conversion, desertification and biodiversity loss. Therefore, it is imperative to understand the effects prairie dog species have on the ecosystem. In this thesis, I focus on the Mexican prairie dog (C. mexicanus), a species in drastic decline due to habitat loss, caused by agriculture, overgrazing, human settlement, fragmentation, diseases (e.g. plague) and past eradication programs. C. mexicanus is considered endangered by the IUCN red list of threatened species and The Convention of International Trade in Endangered Species of Wild Fauna and Flora. It is also endemic to the Grassland Priority Conservation Area (GPCA) of El Tokio, located in Northeast Mexico within the Chihuahuan desert ecoregion and designated as a GPCA by the Commission for Environmental Cooperation (a cooperation between Canada, U.S. and Mexico) in 2009. Grasslands within GPCA El Tokio are highly fragmented as a result of many years of intense agricultural practices and other anthropogenic activities and around 90% of the original grasslands have been lost. However, it is considered an area of ecological importance due to its unique vegetation and edaphic associations, as well as being a key habitat for migratory birds. Up until now, very few studies have explored the role C. mexicanus has on plant taxonomical diversity and soil properties. Moreover, no studies focusing on prairie dogs have looked into the effect the species has on plant functional diversity or soil properties. Furthermore, GPCA El Tokio is a data-scarce area. Therefore, at this point, basic information and system understanding are urgently needed in order to identify which conservation efforts are most promising and which specific sites these efforts should focus on. Understanding the influence of prairie dog disturbance on vegetation parameters (taxonomic and functional), soil properties and their interaction with environmental conditions through time, will increase knowledge on the risks and vulnerability of grasslands, promoting solutions that can support grassland management. Furthermore, there is a clear gap in the literature about the varying effects of prairie dogs depending on different grassland types and environmental conditions. To study such conditions, I first classified and controlled for factors that could influence prairie dog ecosystem engineering effects addressing the following two general questions: (1) Which grassland types are present in GPCA El Tokio? (2) Do the different grassland types present in GPCA El Tokio influence prairie dog colony sizes and burrow density? When influencing factors were confirmed, I then assess the effects of prairie dog disturbance on vegetation and soil to answer the following questions: (3) Are there clear distinctions across GPCA El Tokio grassland environmental variables? (4) Do the different grassland types present in GPCA El Tokio influence prairie dog colony sizes and burrow density? To do so I selected a representative sample of sites covering the varying environmental conditions present in GPCA El Tokio grasslands, a data-driven clustering approach was used. Once clusters were defined, average burrow density was estimated from remote sensing imagery. To study vegetation measures I first, sampled plant species (92 species and 28 families and 6 traits) to obtain taxonomical and functional diversity measures, and obtained variables related to nutrient availability, carbon and climate regulation, and water regulation and purification. To study the effects on soil a total of 11 soil properties were obtained (382 samples were analyzed). Field work was done during the wet season and repeated during the dry season to obtain season variations of all measures. Soil measures were further obtained at depths of 0-10cm and 10 to 20cm. Results from the study classify GPCA El Tokio into 8 different grassland types with 4 clusters being the most dominant, named Agriculture, Arid, Calcareous, Mountain. I found agricultural grasslands had significantly lower colony sizes compared to calcareous grasslands when outliers were considered, but no differences when outliers were removed and burrow density varied depending on the grassland type, with mountain grasslands having a significantly lower burrow density compared to agricultural and calcareous grasslands. Regarding the effects of prairie dogs on vegetation and soil my findings suggest that functional metrics and community weighted mean (CWM) analyses responded to interactions between prairie dog disturbance, grassland type and season, whilst species diversity and cover measures were less sensitive to the role of prairie dog disturbance. I found weak evidence that prairie dog disturbance has a negative effect on vegetation structure, except for minimal effects on C4 and graminoid cover, but which depended mainly on season. Grassland type and season explained most of the effects on plant functional and taxonomic diversity as well as CWM traits. In the case of soil properties WOP grasslands tended to have higher nutrient availability than WP grasslands. However, mounds played a key role within WP grasslands. Mounds reduce compaction and increase nutrient levels of soil organic carbon, nitrogen, potassium, magnesium, and phosphorus. Such an effect was particularly present in calcareous and arid grasslands, and in many cases the effect was enhanced under wet conditions. In general, the effect of disturbance on soil property changes was dependent on environmental conditions. Overall, my study shows evidence that grassland type and season have a stronger effect than prairie dog disturbance on the vegetation of this short-grass, water-restricted grassland ecosystem.:3 TABLE OF CONTENTS Declaration of conformity 2 1 Acknowledgments 3 2 Extended Summary 5 4 List of Figures 11 5 List of Tables 13 1 Introduction 1 1.1 Importance of grasslands 1 1.2 Grassland conservation and ecosystem engineers 2 1.3 Prairie dogs: ecosystem engineers of grasslands in North America 3 1.4 Distribution of prairie dogs across North American grasslands 6 1.5 Current threats and conservation of the Mexican prairie dog C. mexicanus 7 1.6 Research questions, aims and objectives 9 2 Scientific background 13 2.1 Differences in grassland definitions and classifications 13 2.2 Dryland biases in grassland research 13 2.3 Research gaps on C. mexicanus 15 2.4 Functional diversity and disturbance 16 2.5 Soil complexity and limited research 17 3 Study Area: Grassland Priority Conservation Area of El Tokio 19 3.1 General overview 19 3.2 Bioregions, geology, topography and soils 20 3.3 Climate 23 3.4 Ecoregions, Land cover and Biodiversity 24 3.5 Anthropogenic activities and environmental issues 28 4 Assessing and classifying factors that could influence prairie dog ecosystem engineering effects 31 4.1 Data-driven identification of grassland types 33 4.1.1 Introduction 33 4.1.2 Methods 33 4.1.3 Results 36 4.1.4 Discussion and conclusion 39 4.2 C. mexicanus colony trends and differences across grassland types 41 4.2.1 Introduction 41 4.2.2 Methods 42 4.2.3 Results 48 4.2.4 Discussion and conclusion 52 5 Prairie dog disturbance effects on vegetation and soil across different grassland types and seasons 55 5.1 General methodology 57 5.1.1 Selection of grassland locations 57 5.1.2 Defining study sites and plots 58 5.1.3 Vegetation and soil sampling design 59 5.2 The effect of C. mexicanus on taxonomical and functional diversity across different seasons and grassland types 61 5.2.1 Introduction 61 5.2.2 Methods 63 5.2.3 Results 65 5.2.4 Discussion and conclusion 72 5.3 Soil property responses to the presence of C. mexicanus and its mounds across different grassland types, seasons and depths 77 5.3.1 Introduction 77 5.3.2 Methods 78 5.3.3 Results 81 5.3.4 Discussion and conclusion 88 6 Synthesis 95 6.1 Key findings 95 6.2 Management and Conservation opportunities 97 6.2.1 Designing management plans to suit existing environmental conditions 97 6.2.2 Functional diversity: an opportunity to identify patterns of vegetation across environmental conditions and scales. 98 6.3 Future research 99 6.3.1 Exploration of spatial and temporal effects 99 6.3.2 Mechanistic understanding of disturbance dynamics 100 6.3.3 A need for plant and soil ecological data 101 7 References 103 8 Appendix 131 8.1 Appendix 1. Prairie dog research reference list 132 8.2 Appendix 2. List of individual colonies with areas and other relevant information 140 8.3 Appendix 3. Historical and present colony data. 142 8.4 Appendix 4. Correlation results 144 8.5 Appendix 5. Top 3 models 146 8.6 Appendix 6. Species list per grassland type. 151 8.7 Appendix 7. Correspondence analysis (CA) for each grassland 154 8.8 Appendix 8. Post-hoc results 155 8.9 Appendix 9. Top 3 dominant species. 157 8.10 Appendix 10. HPD credible interval and ROPE. 159

No Brasil, foram introduzidas diversas espécies de Pinus e a espécie P. elliottii Engelm apresenta o comportamento invasor em unidades de conservação de Cerrado, no estado de São Paulo. O objetivo deste estudo foi comparar P. elliottii com outras duas espécies do mesmo gênero, P. caribaea Moret e P. oocarpa Shiede ex Schltdl, através de: viabilidade e germinabilidade das sementes, em laboratório; sobrevivência das plântulas logo após a germinação e acompanhamento de seu crescimento em estufa; germinabilidade em fisionomias campestres; e chuva de sementes dentro de talhões. Para P. elliottii, também foi verificada a distância de dispersão das sementes. As sementes utilizadas nos testes em laboratório foram coletadas em Águas de Santa Bárbara (Estação Ecológica de Santa Bárbara - EEcSB; Floresta de Águas de Santa Bárbara - FASB) e Itirapina (Estação Experimental de Itirapina - EExI). Primeiramente, as sementes foram colocadas em água para separação das sementes cheias das vazias (flutuabilidade). Em seguida, as sementes cheias foram testadas quanto à viabilidade por meio de sal de tetrazólio e quanto à germinabilidade. As sementes germinadas foram acompanhadas até os cotilédones ficarem visíveis e uma parte destas teve o crescimento acompanhado até a 24ª semana. A germinabilidade em fisionomias campestres foi realizada apenas na EEcSB, onde as sementes das três espécies foram semeadas em diferentes graus de umidade do solo. Coletores de sementes foram instalados dentro dos talhões de Pinus spp., tanto na EEcSB-FASB como na EExI, para quantificar a chuva de sementes. A distância de dispersão das sementes de P. elliottii foi avaliada apenas na EEcSB, durante o período de maior dispersão de sementes (março a maio), e teve como classes de distâncias em relação ao talhão: 10, 30, 60, 100, 150 e 250 m. Os resultados dos testes em laboratório mostraram que P. caribaea e P. elliottii apresentam as maiores proporções de sementes cheias (>70%) e P. oocarpa e P. elliottii, as maiores taxas de viabilidade (>90%) e germinabilidade (>90%). Dentre as sementes germinadas das três espécies, mais de 90% desenvolveram-se até o aparecimento dos cotilédones. Quanto ao crescimento, P. caribaea e P. oocarpa apresentaram maior vigor em relação a P. elliottii. Em campo, as três espécies apresentaram, de maneira similar, baixíssima porcentagem de germinação (<1,5% do total semeado), preferencialmente em solos mais úmidos. A chuva de sementes de P. elliottii dentro de talhões foi muito maior (pelo menos o dobro) em comparação com as outras duas espécies. A distância de dispersão das sementes de P. elliottii foi maior nos primeiros 30 m, mas chegou até os 150 m. Portanto, P. caribaea e P. oocarpa apresentaram condições de se tornarem invasores pela viabilidade de suas sementes, vigor de crescimento e germinação em campo, mas o fator determinante para o sucesso na invasão P. elliottii é, provavelmente, a pressão de propágulos, maior do que as outras duas espécies, causada pela sua alta produção de sementes e intenso plantio. / Several pine species of the genus Pinus have been introduced in Brazil, and P. elliottii Engelm is presently considered an invasive species in the Brazilian savanna (Cerrado) in São Paulo State. The aim of this study was to compare P. elliottii with two other Pinus species, P. caribaea Moret and P. oocarpa Shiede ex Schltdl according to: seed viability and germinability, in laboratory; survival of seedlings soon after germination and their growth, in greenhouse; germination at field conditions; and seed rain inside the plantation. The distance of seed distance dispersal was also verified for P. elliottii. The seeds for the laboratory tests were collected in Águas de Santa Bárbara (Santa Barbara Ecological Station - EEcSB; Águas de Santa Bárbara Forest - FASB) and Itirapina (Itirapina Experimental Station - EExI). First, the seeds were placed in water to separate the full from the empty seeds (flutuability). Then full seeds were tested by viability (tetrazolium) and germinability. Germinated seeds were monitored until the cotyledons were visible and some of those were monitored up the 24th week to verify their growth rate. In the EEcSB, seeds of the three species were sown at different levels of soil moisture to observe the germination in the field. In order to quantify the species seed rain seed collectors were installed inside the Pinus spp. stands, in both EEcSB-FASB and EExI. The distance of P. elliottii seed spread was evaluated only at the EEcSB, during the greater period of seed dispersion (March to May), at the distances of 10, 30, 60, 100, 150 and 250 m from the planted areas. The results of laboratory tests showed that P. caribaea and P. elliottii have the highest proportions of full seeds (> 70%) and P. oocarpa and P. elliottii, the highest viability (> 90%) and germination rates (> 90%). Among the germinated seeds of the three species more than 90% developed to seedling stage. Concerning seedling growth, P. caribaea and P. oocarpa showed greater vigor than P. elliottii. In the field, the three species showed similar and very low germination rates (<1.5% of the total sown), preferably in more humid soils. The seed rain of P. elliottii inside the plantation stand was much higher (at least twice) compared to the other two species. The dispersal distance of P. elliottii seeds was higher in the first 30 m, but reached 150 m. The results show that P. caribaea and P. oocarpa are able to become invaders due to their high values of seed viability and germination, and vigor growth, however, the determining factor for the invasive success of P. elliottii is probably its higher propagule pressure, caused by several human mediated introductions, and high production of seeds.

In the canyon grasslands of Garden Creek Ranch Preserve in Idaho, where the threatened plant Silene spaldingii occurs and invasion by the exotic species Centaurea solstitialis and Bromus tectorum is proceeding rapidly, I examined environmental and community patterns of site invasion, and evaluated the apparent influence of invasion on Silene population vigor. In addition, two separate lightning fires at the preserve presented the opportunity to examine the short-term influence of late-season fire on this species and its associated bunchgrass plant community. I found that Silene-supporting sites most often invaded by exotics were on relatively gentle slopes that received more incident radiation. This pattern may relate, in part, to light requirements of Centaurea solstitialis. Invaded sites were also typically at higher elevations, which may indicate they were moister and therefore more productive. The plant communities in invaded Silene-supporting sites were similar to plant communities in uninvaded sites, although invaded sites tended to have greater legume and exotic annual grass cover. Exotic species invasion did not appear to influence negatively the vigor of Silene populations, as indicated by similar plant height and comparable levels of flowering, fruit and seed set in invaded and uninvaded populations. The similarity in Silene vigor between invaded and uninvaded sites may reflect a moderating influence of site productivity in invaded populations, or may indicate that mature Silene plants and the exotic species partition space or resources differently, potentially reducing competition between them. However, Silene recruitment may be limited by competition from weeds; my data did not allow a rigorous test of this possibility. Fire apparently decreased cover of Festuca idahoensis and increased cover of Lupinus sericeus in the first year after burning, while cover of Pseudoroegneria spicata, exotic grasses, and most other forb species did not differ between burned and unburned areas. Silene cover and abundance within populations were similar before and after fire. Burning did not appear to influence levels of flowering, change the number of flowers or capsules produced per stem, or alter the number of seeds per capsule. Burning decreased plant size slightly, and decreased the proportion of flowers that matured to seed-filled capsules. Silene and the plant communities that support this species appear well suited to late season fire, however the response to burning in other seasons or at higher frequencies remains unknown in this study area. / Graduation date: 2003

The effects of fire and mechanical clearing were investigated for their potential in assisting with the eradication of Chromolaena odorata (previously Eupatorium odoratum). The study was divided into two focus areas, the first focused on mechanical clearing of dense stands of C. odorata on three sites and the second focused on the long term influences of a single burn on C. odorata plants in the different size categories. For mechanical clearing, two key issues were investigated; namely whether this type of clearing procedure was effective in dense C. odorata stands and whether rehabilitation was necessary in these cleared areas. The study was conducted from July 2002 to June 2004. The area was subject to a severe drought throughout the duration of the study. The severe drought had a large influence on the result in both focus areas. A bulldozer was found to be a very effective at clearing dense C. odorata stands. Results from the mechanical clearing study showed that there was still a large viable grass seed population in the areas that had been covered by a dense stand of C. odorata plants for over three years. Thus, indigenous plants were able to re-colonize the area after removal of C. odorata without human intervention, even thought the area was experiencing a severe drought. The density of C. odorata seedlings emerging in the cleared areas was far lower than expected. The C. odorata density in the permanent plots, for seedlings that germinated in the first season after clearing (SeptemberOctober 2002), was only 0.25,0.03 and 0.72 per 5 m2 in the three sites respectively by the end of the study in June 2004. For the C. odorata seedlings that germinated in the second season (September-October 2003) the density was, 0.5, 0.56 and 1.06 per 5 m2 in the three sites respectively by the end of the study in June 2004. It was suspected that the drought influenced seed germination. Unfortunately the number of C. odorata seedlings was so low, that no significant relationship could be found between grass and C. odorata seedling density. By the end of the study the grass fuel mass in all the rehabilitated sites was already over 3000 kg ha-1, even though the area was experiencing a severe drought. This grass fuel load, when burnt, will assist land managers in controlling C. odorata plants, especially seedlings. Very few other alien invasive plant species emerged in the cleared areas. At the Mhlosinga site, Senna pendula made up less than one percent of the herbaceous species composition and only a single Ricinus communis plant was recorded. No alien plant species were recorded on the other two sites. Results from the burning trials revealed that plants in all the size categories were affected by fire. Greater fuel masses and fire intensities were required to kill larger C. odorata plants relative to smaller ones. Fire was found to be very effective at eliminating small and medium size C. odorata plants. Fire applied as a once off treatment had a significant long-term effect on the C. odorata population. The following fuel loads were required to achieve 80% mortality in this 11 study: for small plants a fuel load of over 4000 kg ha-I, for medium plants a fuel load over 4200 kg ha-I and for large plants a fuel load over 4600 kg ha-I. Little difference could be detected between a head or a back burn, as both fire types had their own advantages and disadvantages. Although some of the C. odorata plants in the burnt plots had not perished by the time of the first investigation, following the burn (February 2003), by the time of the second investigation (June 2004), many of these plants had eventually succumbed. These results highlighted the fact that plants which are damaged by fire were more likely to persish during an extended droughts period, than plants which were not subjected to fire. Results from the control plots, in the burning trials, for medium and large plants showed dramatic increases in density over time. Tagged individuals from the control plots did reveal that some of the medium and large plants did die during the drought, although the amount was negligible when compared to the number of new plants growing into the new size categories. A large proportion of the small plants in the control plots also survived the drought with many of them even growing into the medium category. The difference between the control plots and the burnt plots was obvious and significant, especially once the fuel mass exceeded 3783 kg ha-I. Results from this study show that fire can be used as a very effective tool in assisting land managers to control C. odorata in open savanna bushveld. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

Long-term trends in rangeland sward dynamics (species composition, structure, productivity) were examined on three trials established between 1989 and 1996 at Kokstad Research Station in the Highland Sourveld, while animal performance (average daily gain and gain per hectare) was examined on two of the trials. The region enjoys moderate rainfall of 782mm per annum, with hilly topography, and soil depths ranging from >1m to <20cm. The first trial was labelled the simulation trial, as it simulated a four-paddock rotational grazing system, in which animals spent two weeks in each of three paddocks while the fourth was rested for the entire season. The rested paddock was rotated each year. The trial tested two stocking rates (0.5 and 1.0 AU.ha-1) at five ratios of cattle to sheep, ranging from cattle only to sheep only. The trial was unreplicated, and was established in 1989 on flat topography with deep soils. The second trial (labelled the flat two-paddock trial) was established in 1992 adjacent to the simulation trial. The trial examined two stocking rates of sheep weaners (0.5 and 1.0 AU.ha-1 seasonally) in a continuous grazing two-paddock system, in which one paddock of each treatment was burned and grazed continuously while the second paddock was rested, to be burned and grazed in the following season. The trial was replicated twice. The third trial (labelled the steep two-paddock trial) mimicked the grazing system of the flat trial, but was located on a steep (c. 20%) West-facing slope with shallow soils. The trial incorporated two additional treatments: an intermediate stocking rate of 0.7 AU.ha-1 and an ungrazed treatment. Species composition of the sward was recorded biennially on all trials using the nearest plant-point technique with between 200 and 800 points per paddock. Sward standing crop was measured in the rested seasons of the simulation trial and at the beginning, middle and end of each season in one paddock of each two-paddock treatment of the two-paddock trials. In the two-paddock trials, sward standing crop was measured within and outside permanently placed exclosure cages. Animals were weighed fortnightly. The response of species to grazing pressure or animal type was mediated by soil depth and slope, as well as the grazing system. Tristachya leucothrix declined on all grazed treatments. The ungrazed treatments remained relatively stable over ten years. On the low stocking rate treatments of the steep trial, unpalatable species increased, but so did Themeda triandra. The heavily grazed treatment of the steep trial was surprisingly stable, with little significant change in relative abundance of key species other than an increase in the unpalatable Alloteropsis semialata and decline in T. leucothrix. The medium stocking rate treatment on the steep trial showed significant shifts in relative abundance of key species, with declines in T. triandra and T. leucothrix and increases in A. semialata and the unpalatable wiregrass D. filifolius. These trends were not repeated on the flat trial, however, with T. triandra and A. semialata increasing and all other key species declining or remaining stable. On the simulation trial, species responded largely unpredictably with species abundances often fluctuating considerably over time. Microchloa caffra and A. semialata increased substantially in both the low and high stocking rate sheep-only treatments, with a concurrent decline in T. triandra in the high stocking rate but not the low. Changes in composition over time, as measured by Euclidean distance, showed that shallow soils, high stocking rates and a high proportion of sheep caused greater shifts in species composition over time than deep soils, low stocking rates or more cattle. Three treatments, the sheep-only treatments on the simulation trial and the high stocking rate on the steep trial, showed an initial rapid shift in composition over about 6 years, before stabilising in subsequent seasons. The flat trial showed no substantial shift in composition over time. This general pattern of change was confirmed by Non-Metric Multidimensional Scaling. On the simulation trial, total standing crop was influenced by stocking rate and by the proportion of sheep in most seasons. On the two-paddock trials, increasing stocking rate significantly reduced sward vigour, and vigour declined over time. Stocking rate reduced total standing crop on both trials at the end of the 2004/05 seasons and the crop of unpalatable species on the steep trial. Total palatable plants were unaffected by stocking rate on both trials. The classic Jones-Sandland model of animal performance as influenced solely by stocking rate was not supported. Sheep performance was influenced by stocking rate and the interaction of stocking rate and seasonal rainfall. There was no difference in average daily gain between treatments over time, and hence cumulative animal production per hectare increased with increasing stocking rate. Animal performance was possibly influenced by many factors beyond the scope of this study, including the effect of predator attacks on surviving animals, and resource availability such as shade and shelter and high-production patches in some paddocks and not others. Scale effects on ecology are being increasingly investigated and a meta-analysis of this type shows that, even in one research farm, slight differences in management and environment can have significant effects on plant and animal responses to grazing. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

A series of trials and investigations were implemented to address concerns surrounding the dynamics of the fire-climax wooded/edaphic grasslands within the iSimangaliso Wetland Park, northern KwaZulu-Natal, South Africa. The research problem surrounded inadequate historical evaluations of changes in vegetation structure, grasslands progressing to a woody dominated composition, and increases in Helichrysum kraussii (Curry bush). These were addressed as follows: Firstly, the recovery of vegetation in response to different periods of fire exclusion in different communities along a topographical gradient of a coastal dune area, was assessed over a two year period. Secondly, the regeneration after wildfire of the persistent, stress tolerant shrub H. kraussii, was studied on different catenal positions with differing fire exclusion periods and with and without defoliation of surrounding plant biomass in the coastal edaphic grasslands north of Manzengwenya, South Africa. Thirdly, aerial photography from 1937, 1975, and 2000 was georectified, digitised and analysed using a Geographic Information System to examine broad vegetation changes in response to different management regimes for a site on the Eastern Shores of Lake St Lucia and a site within the Tewate Wilderness Area. In the absence of fire, the coastal edaphic grasslands progressed to a closed canopied scrub forest within six years. An increase in fire exclusion period resulted in a decrease in species abundance, an increase in woody height, and a decrease in plant density. Richness increased initially but declined marginally with increased fire exclusion period. Higher lying east and west facing sites had a better veld condition index compared with bottom sites and had an increased response (vigour) to defoliation but were far more likely to succeed through to woody scrub forest. Woody plant biomass vigour was greater for west facing sites. Ordination of species composition across sites in response to fire exclusion and catenal position revealed greater similarities within exclusion periods than between. Bottom sites were more similar with similarity decreasing for east and west facing sites. Fire exclusion resulted in an initial increase in woody species and a subsequent increase in herbaceous species. iii Growth response of H. kraussii was unaffected by catenal position and fire exclusion period, whereas defoliation of surrounding grass tended to increase in size (P<0.05). Density and height for this species however increased with increasing fire exclusion. An increase in soil moisture negatively affected H. kraussii growth indicating susceptibility to high water tables. The number of other woody species establishing beneath H. kraussii may be due to changes in the transmission of light through the canopy where an increase in canopy diameter resulted in an increase of photosynthetically active radiation at the soil surface. The effects of fire on landscape change were investigated for the Eastern Shores and Tewate Wilderness Area, iSimangaliso Wetland Park, South Africa using aerial photography. Changes to historical disturbance regimes largely through active exclusion of fire resulted in the majority of the higher lying coastal grasslands changing to savanna scrub or closed canopied forest within 63 years on the Eastern Shores. The degree of fragmentation of these grasslands was greatly reduced within the Tewate Wilderness Area where disturbance regimes included greater frequencies of fire. Hygrophilous grasslands remained largely unaffected by woody encroachment but did not preclude woody species establishment indicating possible susceptibility during long drier periods. Frequent fires result in the maintained distribution of the higher grasslands. This vegetation type is a system which becomes resilient in response to fire, whereas in the absence of fire readily progresses to Dune Forest. The coastal grasslands above the high water table are therefore highly unstable and transformed easily in the absence of regular disturbance. It would appear that a threshold of approximately six years exists, after which substantial management intervention may be required to reverse the succession back to grassland. The growth of H. kraussii was unaffected by fire and remained persistent irrespective of fire exclusion period. An ability to attain size (height and canopy diameter) was limited with increased soil moisture but density was reduced through regular burning. Frequent fires are necessary to reduce density of H. kraussii and reduce the competitive advantage gained with age. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

The main objective of this thesis was to assess the influence of methods and intensity of use on phytosociological evolution and biodiversity of grasslands. This work includes grasslands in terms of their distribution, different ways of management and use. An important goal of this work was to evaluate the incidence of plant species in grassland lying in selected localities of the Czech Budejovice, Slavošovice and Radostice. The next section was set calculation and maintenance of the water and nutrient regime on the site fallow and statistical processing of data at the sites.Based on the findings were prepared tables and graphs that confirm and in some cases disconfirm occurrence of plant species with different modes of grassland management (mowing, grazing, fallow).