When the agricultural revolution took place, the biodiversity decreased and during the last century more than 90 % of the area of species-rich grasslands has been lost. Fragmentation has occurred with the area lost and insects, e.g. butterflies, suffer because of this. I investigated the impact that surrounding landscapes have on vegetation in species-rich grasslands, by using data from NILS and land use land cover data. I used the area of grassland, forest, water and arable land at radii from 100 m to 40000 m. All landscape structures showed a significant effect on the species density, but at different ranges. Arable and forest were both positive at large radii. Water had a negative effect at short ranges but positive at large ranges. The same was shown for grassland, and that is likely explained by grassland making up a very small proportion of the total area. In conclusion, species density in species-rich grasslands can partly be explained by the surrounding landscape. These results have implication for reserve selection, monitoring and restoration.

In this study, I investigated the interaction between two megaherbivores, the African elephant and white rhinoceros, that has the potential to impact grazing lawns of which white rhino are the creators and maintainers and elephants are potentially the modifiers. I hypothesized that as elephants browse, they discard a variety of coarse woody debris onto the ground; should this woody debris (of varying amounts and sizes) fall onto grazing lawns, white rhino either move them, consume grass around the woody debris or abandon the lawn entirely. If high levels of woody debris are deposited here, grazing by white rhino is likely to be prevented, at which time I predicted that mesoherbivores would have a competitive advantage in accessing forage that white rhino cannot. I examined the mechanistic links between different levels of elephant-deposited woody debris and grass response at a point scale and feeding patch spatial scale of grazing lawns in an African savanna. In addition, I assessed the response of mesoherbivores in terms of vigilance behaviour with increasing levels of predation risk posed by increasing levels of woody debris. I present the first evidence of an indirect effect of elephant on white rhino foraging behaviour. I demonstrate how increasing levels of woody debris lead to a decreasing probability of foraging by white rhino. I also demonstrate how the probability of foraging by mesoherbivores increases as the amount of forage increases. However, since this study took place during a severe drought where resources are extremely limited, I was unable to properly separate the effects of elephant-deposited woody debris from the severe lack of rainfall on grass response and subsequently herbivore foraging behaviour. Due possibly to the drought, mesoherbivores responded less or not at all to risk factors such as woody debris therefore woody debris was not a predictor of vigilance behaviour in my study. This study contributes to our understanding of how the impacts of elephants, as ecosystem engineers, have cascading effects on savanna ecosystems. My study showed that elephant impact mediates the foraging behaviour of white rhino during a drought. However, under average rainfall periods, my original hypothesized effect of the indirect impacts of elephants on white rhino foraging and grazing lawn dynamics could still hold. This key hypothesis that I was unable to test under ‘normal’ conditions due to the drought is still valid and functionally important for understanding the ecosystem processes driving grazing lawn formation, persistence and composition in African savannas where elephants and white rhinos coexist.

A l’heure où l’on cherche à optimiser les services éco-systémiques fournis par les prairies, une meilleure compréhension du fonctionnement des systèmes racinaires apparait comme nécessaire. Nous avons donc décidé de caractériser les stratégies d’espèces issues des familles des Fabaceae et Poaceae prairiales par la mesure de traits fonctionnels racinaires. Le principal résultat de ce travail est la mise en évidence de plusieurs axes majeurs de différentiation des stratégies racinaires et de leurs relations avec les exigences écologiques des espèces. Le plus important est le compromis entre stratégies de capture et de conservation des ressources. Les espèces à stratégie de capture sont mieux adaptées aux milieux peu stressants notamment pour l’eau, mais sont peu impactées par le manque de phosphore, ce sont aussi des compétitrices efficaces. Bien que les plantes à stratégie de conservation soient mieux à même de se développer dans des milieux continentaux, elles sont plus impactées que les autres par la présence de compétiteurs et le manque de phosphore. Le type de relations existant entre les stratégies aériennes et racinaires apparait aussi comme un marqueur de l’adaptation des plantes aux stress. L’étude du système racinaire est donc un moyen efficace de prédire le comportement des espèces de plantes prairiales face à des contraintes abiotiques et biotiques. Cela ouvre des perspectives particulièrement intéressantes notamment pour la construction de mélanges d’espèces mieux adaptées à leurs environnements. / In order to optimise grassland ecosystem services we need to improve our understanding of root system functioning. As a result, we decided to characterise strategies of species coming from grassland’ Fabaceae and Poaceae families, by root functional traits measurement. The main result of this work is the establishment of several axes of root strategies differentiation. The main axis is the trade-off between resources capture and conservation strategies. Species with capture strategies appear to be adapted to non-water stressful habitat and are barely impacted by phosphorus shortage; they also happen to be strong competitors. On the opposite, species with conservation strategies are adapted to water stressful continental climates, but are strongly impacted by phosphorus shortage and happen to be weak competitors. The kind of relation between above-ground and below-ground strategies also appears to be a marker of the plants adaptation to stress. We showed that the root system study is a good way to predict grassland species comportment to face abiotic and biotic constraints. The present work widens interesting perspectives for the sowing of mixed grassland species better adapted to their environments.

Made available in DSpace on 2016-01-26T18:56:30Z (GMT). No. of bitstreams: 1 Claudia Jaqueline Tome Yamamoto.pdf: 505271 bytes, checksum: a4b307bb1c1ddbf57c541f4407f9581a (MD5) Previous issue date: 2014-04-04 / Whereas it is necessary to obtain higher pastures productivity to prevent new areas occupation, agriculture maintenance and sustainability, even in Brazil and in the world, the increasing demand for water use efficiency in agriculture and use of acid soils associated with aluminium. The aim of this study was to evaluate the changes in germination and in the early seedlings development and some biochemical parameters in Urochloa brizantha cultivars subjected to stresses caused by free aluminum toxicity. The treatments were resulting from the combination of six cultivars (Marandú, BRS Piatã, MG4, MG5, Xaraés and Basilisk), with five levels of aluminium toxicity (0; 1; 2; 4 and 8 mmolc Al³+ dm³) obtained using aluminium trichloride solutions (0; 0.3996; 0.7992; 1.5984 and 3.1968 AlCl3 (g. L-¹)) in random design with four replicates. At the preliminary evaluations lots were selected with almost the same seed initial physiological quality (moisture content, germination and viability). During first trial, the selected lots were submitted to germination in simulated stress condition in laboratory quantifying germination considering root protrusion or normal seedling, shoot and root length and dry mass. At the second trial, the evaluations were done at the seventh day after seedling transfer to stress conditions, measuring length and dry mass of shoot and root relative growth-rate and biochemical determinations: membrane stability index (MSI), superoxide dismutase activity (SOD), proline, total antioxidants (DAT) and malondialdehyde amount (MDA). At the seedling studied period, up to 14 days after sowing, the most aluminium tolerant cultivar maintain root growth in that conditions, while the most susceptible one reduced root growth and developed proportionally more shoot, once the growth is done with reserves mobilization from seed tissue. The first trial methodology shows that the initial seed quality interferes in the evaluation and the Al+3 increasing levels were harmful to germination. The MG5 cultivar presented longer and heavier seedlings without stress and following 1 mmolc. dm-3 de Al³+ presented decreasing measurements, showing low stress tolerance. The Basilisk cultivar is not the more tolerant considering germination results, but its development, principally of the root, is lower affected with Al³+levels increasing. The second trial methodology, once do not include the germination period and its influence, achieve cultivar differences clearer. The cultivars, Xaraés (dry mass of shoot relative growth-rate), MG4 and MG5 (length of shoot relative growth-rate), was superior only at the non-stress situation, with more development at control (0) up to 1 mmolc. dm-3 de Al³+ level. The Basilisk cultivar is more tolerant accumulating root dry mass even in high Al³+ levels, while the Marandu cultivar do the same up to 4 mmolc. dm-3 de Al³+. The biochemical analyses, Proline amount, SOD and DAT was not related with Al3+ toxicity, but MSI e MDA was promising. / Considerando obter maior produtividade de pastagens para evitar a ocupação de novas áreas, a manutenção e a sustentabilidade do setor agropecuário, tanto no Brasil como no mundo, o aumento da eficiência de uso da água na agricultura e a utilização de solos ácidos associados ao alumínio, o objetivo deste trabalho foi avaliar as mudanças na germinação, no desenvolvimento inicial das plântulas e em alguns parâmetros bioquímicos em cultivares de Urochloa brizantha submetidos a estresses causados pela toxidez de alumínio livre. Os tratamentos foram resultantes da combinação de seis cultivares (Marandú, BRS Piatã, MG4, MG5, Xaraés e Basilisk), com cinco níveis de toxidez de alumínio (0; 1; 2; 4 e 8 mmolc Al³+ dm³) obtidos com soluções de tricloreto de alumínio (0;0,3996; 0,7992; 1,5984 e 3,1968 AlCl3(g.L-¹)) em delineamento inteiramente casualizado com quatro repetições. Nas avaliações preliminares foram selecionados lotes com aproximadamente mesma qualidade fisiológica inicial das sementes (grau de umidade, germinação e viabilidade). No ensaio 1, os lotes selecionados foram submetidos à germinação em condições de estresse simulado em laboratório analisando-se germinação por protrusão de raiz e por plântula normal, comprimento e massa seca de parte aérea e raiz. No ensaio 2, a avaliação foi realizada no sétimo dia, após a transferência das plântulas para a condição de estresse, medindo-se a taxa de crescimento relativo do comprimento e massa de parte aérea e raiz e realizada também as análises bioquímicas: índice de estabilidade da membrana (IEM), atividade de superóxido dismutase (SOD), determinação de prolina, de antioxidantes totais (DAT) e de malondealdeído (MDA). Na fase de desenvolvimento estudada, até 14 dias após semeadura, o cultivar mais tolerante ao alumínio consegue manter crescimento de raiz na condição de estresse, enquanto o mais suscetível reduz o crescimento radicular e desenvolve proporcionalmente mais parte aérea, uma vez que o crescimento ocorre com base na mobilização de reservas dos tecidos da semente. A metodologia utilizada no ensaio 1 indicou que a qualidade inicial de semente interfere na avaliação e que os níveis crescentes de Al+3 são danosos a germinação. O cultivar MG5 apresenta plântulas com maior comprimento e massa na condição sem estresse e a partir da dose 1 mmolc. dm-3 de Al³+ apresenta maior declínio nas determinações, indicando baixa tolerância ao estresse. O cultivar Basilisk não é o mais tolerante em função da germinação, mas seu desenvolvimento, principalmente de raiz, é menos afetado com o aumento das doses de Al³+. A metodologia utilizada no ensaio 2, por não envolver a germinação e portanto não sofrer interferência desse evento, conseguiu evidenciar mais claramente as diferenças entre os cultivares. Os cultivares, Xaraés (taxa de crescimento relativo de massa seca de parte aérea), MG5 e MG4 (taxa de crescimento relativo de comprimento de parte aérea), se destacam apenas na situação sem estresse, com maiores desenvolvimentos no controle (0) até o nível 1 mmolc. dm-3 de Al³+. O cultivar Basilisk é o mais tolerante conseguindo acumular massa seca na raiz mesmo nas doses de Al³+ mais elevadas, enquanto o cultivar Marandu consegue fazer o mesmo até o nível 4 mmolc. dm-3 de Al³+. Diante das determinações bioquímicas, Prolina, SOD e DAT não são indicadoras da toxidez de Al3+, porém, IEM e MDA foram mais promissoras.

Made available in DSpace on 2016-07-18T17:51:13Z (GMT). No. of bitstreams: 1 Claudia Jaqueline Tome Yamamoto.pdf: 505271 bytes, checksum: a4b307bb1c1ddbf57c541f4407f9581a (MD5) Previous issue date: 2014-04-04 / Whereas it is necessary to obtain higher pastures productivity to prevent new areas occupation, agriculture maintenance and sustainability, even in Brazil and in the world, the increasing demand for water use efficiency in agriculture and use of acid soils associated with aluminium. The aim of this study was to evaluate the changes in germination and in the early seedlings development and some biochemical parameters in Urochloa brizantha cultivars subjected to stresses caused by free aluminum toxicity. The treatments were resulting from the combination of six cultivars (Marandú, BRS Piatã, MG4, MG5, Xaraés and Basilisk), with five levels of aluminium toxicity (0; 1; 2; 4 and 8 mmolc Al³+ dm³) obtained using aluminium trichloride solutions (0; 0.3996; 0.7992; 1.5984 and 3.1968 AlCl3 (g. L-¹)) in random design with four replicates. At the preliminary evaluations lots were selected with almost the same seed initial physiological quality (moisture content, germination and viability). During first trial, the selected lots were submitted to germination in simulated stress condition in laboratory quantifying germination considering root protrusion or normal seedling, shoot and root length and dry mass. At the second trial, the evaluations were done at the seventh day after seedling transfer to stress conditions, measuring length and dry mass of shoot and root relative growth-rate and biochemical determinations: membrane stability index (MSI), superoxide dismutase activity (SOD), proline, total antioxidants (DAT) and malondialdehyde amount (MDA). At the seedling studied period, up to 14 days after sowing, the most aluminium tolerant cultivar maintain root growth in that conditions, while the most susceptible one reduced root growth and developed proportionally more shoot, once the growth is done with reserves mobilization from seed tissue. The first trial methodology shows that the initial seed quality interferes in the evaluation and the Al+3 increasing levels were harmful to germination. The MG5 cultivar presented longer and heavier seedlings without stress and following 1 mmolc. dm-3 de Al³+ presented decreasing measurements, showing low stress tolerance. The Basilisk cultivar is not the more tolerant considering germination results, but its development, principally of the root, is lower affected with Al³+levels increasing. The second trial methodology, once do not include the germination period and its influence, achieve cultivar differences clearer. The cultivars, Xaraés (dry mass of shoot relative growth-rate), MG4 and MG5 (length of shoot relative growth-rate), was superior only at the non-stress situation, with more development at control (0) up to 1 mmolc. dm-3 de Al³+ level. The Basilisk cultivar is more tolerant accumulating root dry mass even in high Al³+ levels, while the Marandu cultivar do the same up to 4 mmolc. dm-3 de Al³+. The biochemical analyses, Proline amount, SOD and DAT was not related with Al3+ toxicity, but MSI e MDA was promising. / Considerando obter maior produtividade de pastagens para evitar a ocupação de novas áreas, a manutenção e a sustentabilidade do setor agropecuário, tanto no Brasil como no mundo, o aumento da eficiência de uso da água na agricultura e a utilização de solos ácidos associados ao alumínio, o objetivo deste trabalho foi avaliar as mudanças na germinação, no desenvolvimento inicial das plântulas e em alguns parâmetros bioquímicos em cultivares de Urochloa brizantha submetidos a estresses causados pela toxidez de alumínio livre. Os tratamentos foram resultantes da combinação de seis cultivares (Marandú, BRS Piatã, MG4, MG5, Xaraés e Basilisk), com cinco níveis de toxidez de alumínio (0; 1; 2; 4 e 8 mmolc Al³+ dm³) obtidos com soluções de tricloreto de alumínio (0;0,3996; 0,7992; 1,5984 e 3,1968 AlCl3(g.L-¹)) em delineamento inteiramente casualizado com quatro repetições. Nas avaliações preliminares foram selecionados lotes com aproximadamente mesma qualidade fisiológica inicial das sementes (grau de umidade, germinação e viabilidade). No ensaio 1, os lotes selecionados foram submetidos à germinação em condições de estresse simulado em laboratório analisando-se germinação por protrusão de raiz e por plântula normal, comprimento e massa seca de parte aérea e raiz. No ensaio 2, a avaliação foi realizada no sétimo dia, após a transferência das plântulas para a condição de estresse, medindo-se a taxa de crescimento relativo do comprimento e massa de parte aérea e raiz e realizada também as análises bioquímicas: índice de estabilidade da membrana (IEM), atividade de superóxido dismutase (SOD), determinação de prolina, de antioxidantes totais (DAT) e de malondealdeído (MDA). Na fase de desenvolvimento estudada, até 14 dias após semeadura, o cultivar mais tolerante ao alumínio consegue manter crescimento de raiz na condição de estresse, enquanto o mais suscetível reduz o crescimento radicular e desenvolve proporcionalmente mais parte aérea, uma vez que o crescimento ocorre com base na mobilização de reservas dos tecidos da semente. A metodologia utilizada no ensaio 1 indicou que a qualidade inicial de semente interfere na avaliação e que os níveis crescentes de Al+3 são danosos a germinação. O cultivar MG5 apresenta plântulas com maior comprimento e massa na condição sem estresse e a partir da dose 1 mmolc. dm-3 de Al³+ apresenta maior declínio nas determinações, indicando baixa tolerância ao estresse. O cultivar Basilisk não é o mais tolerante em função da germinação, mas seu desenvolvimento, principalmente de raiz, é menos afetado com o aumento das doses de Al³+. A metodologia utilizada no ensaio 2, por não envolver a germinação e portanto não sofrer interferência desse evento, conseguiu evidenciar mais claramente as diferenças entre os cultivares. Os cultivares, Xaraés (taxa de crescimento relativo de massa seca de parte aérea), MG5 e MG4 (taxa de crescimento relativo de comprimento de parte aérea), se destacam apenas na situação sem estresse, com maiores desenvolvimentos no controle (0) até o nível 1 mmolc. dm-3 de Al³+. O cultivar Basilisk é o mais tolerante conseguindo acumular massa seca na raiz mesmo nas doses de Al³+ mais elevadas, enquanto o cultivar Marandu consegue fazer o mesmo até o nível 4 mmolc. dm-3 de Al³+. Diante das determinações bioquímicas, Prolina, SOD e DAT não são indicadoras da toxidez de Al3+, porém, IEM e MDA foram mais promissoras.

Habitat type has been suggested to be a major factor contributing to differencesin plant trait distribution of grassland habitats. Land use changes in agricultural landscapes have affected the available habitats and the dispersal ability of plants, which may effect plant trait diversity of agricultural landscapes. Little is also known about the effects of landscape openness on plant trait diversity. This study analysed differences in plant traits between different semi-natural grassland habitats in agricultural landscapes in four different regions in Sweden: Skåne, Södermanland, Gävleborg, and Norrbotten. The following research questions were used: (1) How does landscape openness (the amount of open andarable land found in a landscape) affect plant trait values collected from a new database in semi-natural grassland habitats in agricultural landscapes? (2) How does the type of habitat affect plant trait values in semi-natural grassland habitats in agricultural landscapes? (3) How does geographical location in Sweden affect plant trait values in semi-natural grassland habitats in agricultural landscapes? Overall 12 landscapes in each region were surveyed for plant data using 20 sample plots in each landscape. Trait values for biodiversity relevance, nectar production, nitrogen, phosphorus, grazing/mowing, soil disturbance, longevity, pollinator dependence, and seed dispenser were assigned for each plant species based on an external database, and average trait values were calculated for each of the studied traits in each sample. Kruskal-Wallis test andANOVA were performed on average trait values to identify differences between each habitat types and regions. Besides the effect of habitat type, the effect of openness in the landscape on the chosen traits was analysed with Spearman’s and Pearson’s correlations. The results revealed differences between habitat types in almost all studied traits: grazed habitats had plants with higher biodiversity relevance but lower nectar production. Differences were also found between the southern and northern regions. More open landscapes had plants with higher biodiversity relevance as well as higher tolerance for both nitrogen and phosphorus. Less open landscapes had higher tolerance for grazing/mowing and higher nectar production. The results of this study therefore support earlier findings of the importance of habitat in plant trait distribution of grassland habitats.

In depth studies of the vegetation of large parts of southern Africa, including detailed maps and descriptions of vegetation units are mainly limited to small areas. Meanwhile, various agricultural practises have led to destruction or deterioration of the quality of natural grassland ecosystems. The agricultural sector in developed and rapidly developing areas of southern Africa is confronted with problems like veld deterioration and the loss of natural areas that effectively contribute to the depopulation of rural areas. The necessity to identify, classify and describe the vegetation types and communities within the Grassland Biome was stressed by Mentis and Huntley (1982). The aim of the Grassland Biome Project is to integrate knowledge. comprehension and expertise, which will enable scientists to forecast the results of the available options of grassland management programmes. The phytosociological classification of northwestern KwaZulu-Natal forms part of this project. Known previous vegetation studies of this area were conducted on a large scale and a considerable time ago, which underlines the necessity for a more comprehensive and phytosociologically refined investigation of this area. The study area lies in the northern part of KwaZulu-Natal and comprises the Drakensberg mountains and slopes in the west and undulating plains and bushveld valleys in the east and south. Relevés were compiled in 526 stratified random sample plots over an area of 9300 km2, comprising the northwestern part of KwaZulu-Natal. The vegetation was classified by means of TWINSP AN and Braun-Blanquet procedures. A phytosociological investigation of this vegetation revealed great variation in floristic composition. Further refinement of the data disclosed five major vegetation types containing nine plant communities. The topography and geology of the study area contributes greatly to the diversity of the vegetation, but poor agricultural practises have caused deterioration of the vegetation. / Dissertation (MSc)--University of Pretoria, 1998. / Plant Science / unrestricted

MSc (Zoology) / Department of Zoology / The adverse ecological effects of landscape modification by humans are well known and continue to be studied. Habitat disturbances arising from such modifications result in various levels of biodiversity loss. Amongst mammals, large carnivores are usually the first to disappear, leaving a gap in the trophic pyramid. However, ecologically adaptive small carnivores, free from the effects of intraguild predation can readily fill this gap (i.e. mesopredator release). In highly productive disturbed habitats, small mammals may thrive, reaching densities that can support an abundant and diverse suite of small carnivores. After frequent sightings of serval (Leptailurus serval) on the highly disturbed Sasol Synfuels Operations property, three camera trap surveys were conducted between 2014 and 2015 to study its ecology. The resulting data was subsequently used to study the site’s small carnivores. Multispecies occupancy modelling was used to determine detection (p) and occupancy (ψ) probabilities and estimate species richness across the study area. Site-specific covariates were then modelled against abundance values to identify any correlations. Out of 23 small carnivore species predicted to occur on the site, 11 were detected. Spatially, estimated species richness was highest in disturbed habitats, while it was slightly lower in Grassland possibly due to undersampling. Detection and occupancy probabilities were low (except for serval), with interspecies variations. It is suspected that this is the result of survey bias towards serval. The only covariate showing any significant effect was livestock presence, negatively affecting serval occupancy. Estimated species richness was used as a proxy to identify high- or low-predation areas. Within these areas, three vegetation treatments were selected (low, medium and high cover). Small mammal foraging behaviour under varying predation pressures within these treatments was then studied using the giving-up density (GUD) framework. Differences in GUDs were examined using generalised linear mixed models (GLMM). Small mammal trapping in the study area showed that four-striped grass mouse (Rhabdomys sp.; diurnal) and multimammate mouse (Mastomys sp.; nocturnal) were dominant. Nocturnal GUDs were lower than diurnal, which is interesting as four-striped grass mice are more abundant than multimammate mice. This indicates that density alone does not influence GUDs. Additionally, no significant difference in GUDs was observed between predation and vegetation treatments. I suggest that observed GUDs are linked to individual or combined impacts of interspecific differences in foraging behaviour, metabolic requirements or temporal variations in perceived predation pressure. GUDs also varied between surveys, being lower in mid- compared to early winter. This might be attributable to decreased availability of food and greater metabolic requirements in mid-winter. The results show that modified landscapes (such as the study site) can contribute to biodiversity conservation, especially of small carnivores, the adaptability of which allows them to flourish in disturbed habitats. Under favourable conditions, ecologically flexible small mammal species seem to be unaffected by the risks associated with an abundance of small carnivores. While the processes governing the dynamics of predator and prey communities in disturbed systems are not entirely clear, the conservation potential of such areas cannot be ignored and deserves more attention from researchers. / NRF

No description available.

Ecosystems provide important functioning and services, like biomass for bioenergy production or storage of atmospheric carbon. Two examples of such ecosystems are temperate grasslands and tropical forests. Both vegetation are rich of various species, whereby each of the respective ecosystem benefits from its species-richness concerning their functioning, i.e. productivity. In this thesis both vegetation are in the focus of the investigations. In the first chapter, a review of existing grassland and vegetation models provides an overview of important aspects, which have to be considered for modelling temperate grasslands in the context of biomass production. Based on the review, new conceptual modelling approaches for temperate grasslands are proposed. In the third chapter, derived from the suggested concept, the process-oriented and individual-based grassland model Grassmind is presented. In the fourth chapter, the model Grassmind is used in order to parameterize and simulate the annual dynamics of a typical Central European grass species. Grassmind is able to reproduce the structure and dynamics of a temperate grass species. With reference to the parameterized grass species, a simulation study using defined species groups is performed in order to investigate on the effect of the richness of species groups on aboveground productivity. We do not observe a significant positive effect of species group richness on productivity, which is explained by limitations of using the parameterized grass species as a reference. In the fifth chapter, comprehensive investigations are carried out on the example of stem size distributions in forests concerning their statistical analyses, i.e. by using maximum likelihood estimation. The effects of uncertainties, i.e. binning of measured stem sizes or random measurement errors, are examined in detail. Uncertainties bias the analyses of maximum likelihood estimations. It is shown, that the use of modified likelihood functions, which include either binning or measurement errors, reduce these biases to a large extent. For both studies, i.e. modelling of temperate grasslands and analysing stem size distributions of forests, the presented investigations are discussed and possible examinations are suggested for future research in the last chapter.