Boreal mixedwood forest stands are comprised of a mixture of small canopy patches of varying dominance by conifer (mostly white spruce (Picea glauca (Moench) Voss)) and broadleaf (mostly trembling aspen (Populus tremuloides Michx.) trees. The purpose of this work was to extend our understanding of the patterns and causes of variation in understory vascular plant communities in unmanaged, mature boreal mixedwood forests. First, I assessed variation in understory community composition in relation to canopy patch type (conifer, mixed conifer-broadleaf, broadleaf, gaps) within mixedwood stands. The mosaic of canopy patches leads to different micro-habitat conditions for understory species, allowing for communities that include both early and late successional species and contributing to greater understory diversity. This study suggests that the mosaic of small canopy patches within mixed forest stands resembles a microcosm of the boreal mixedwood landscape, across which understory community composition varies with canopy composition at the stand scale. Second, I investigated the hierarchical organization of understory diversity in relation to the heterogeneous mosaic of canopy patch types through additive partitioning of diversity. The largest proportion of species richness was due to turnover among patches within patch type while individual patches had higher evenness. The mosaic of canopy patch types within mixedwood forests likely plays a crucial role in maintaining the hierarchical levels at which understory diversity is maximized. Third, I examined interactions among understory plant species by investigating the effect of shrub removal on biomass, composition and diversity of herbs using a 3-yr removal study in a natural understory community. There is asymmetric competition for light between erect shrub and herb species but herb response to erect shrub removal was species-specific. Plant interactions play an important role in structuring boreal understory communities. Finally, I explored the relative influence of space, environmental variables, and their joint effects, on understory composition and richness. The environmental variation caused by small canopy patches and biotic processes, such as species interactions, converge at the fine scale to create a spatially patchy structure in understory communities in boreal mixedwood forests. Modifications in the natural mixture of small canopy patches could disrupt the spatial and environmental structures that shape understory composition and diversity patterns. / Forest Biology & Management

Boreal mixedwood forest stands are comprised of a mixture of small canopy patches of varying dominance by conifer (mostly white spruce (Picea glauca (Moench) Voss)) and broadleaf (mostly trembling aspen (Populus tremuloides Michx.) trees. The purpose of this work was to extend our understanding of the patterns and causes of variation in understory vascular plant communities in unmanaged, mature boreal mixedwood forests. First, I assessed variation in understory community composition in relation to canopy patch type (conifer, mixed conifer-broadleaf, broadleaf, gaps) within mixedwood stands. The mosaic of canopy patches leads to different micro-habitat conditions for understory species, allowing for communities that include both early and late successional species and contributing to greater understory diversity. This study suggests that the mosaic of small canopy patches within mixed forest stands resembles a microcosm of the boreal mixedwood landscape, across which understory community composition varies with canopy composition at the stand scale. Second, I investigated the hierarchical organization of understory diversity in relation to the heterogeneous mosaic of canopy patch types through additive partitioning of diversity. The largest proportion of species richness was due to turnover among patches within patch type while individual patches had higher evenness. The mosaic of canopy patch types within mixedwood forests likely plays a crucial role in maintaining the hierarchical levels at which understory diversity is maximized. Third, I examined interactions among understory plant species by investigating the effect of shrub removal on biomass, composition and diversity of herbs using a 3-yr removal study in a natural understory community. There is asymmetric competition for light between erect shrub and herb species but herb response to erect shrub removal was species-specific. Plant interactions play an important role in structuring boreal understory communities. Finally, I explored the relative influence of space, environmental variables, and their joint effects, on understory composition and richness. The environmental variation caused by small canopy patches and biotic processes, such as species interactions, converge at the fine scale to create a spatially patchy structure in understory communities in boreal mixedwood forests. Modifications in the natural mixture of small canopy patches could disrupt the spatial and environmental structures that shape understory composition and diversity patterns. / Forest Biology & Management

Thesis (M.S.)--West Virginia University, 1999. / Title from document title page. "July 31, 1998." Document formatted into pages; contains viii, 108 p. : ill. (some col.), map. Includes abstract. Includes bibliographical references.

Thesis (M.S.)--Southern Oregon University, 2007 / Computer printout. Includes bibliographical references (leaves 49-53). Also available via Internet as PDF file through Southern Oregon Digital Archives: http://soda.sou.edu. Search Bioregion Collection.

No description available.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Nutrient cycling and energy transformation processes fuel plant productivity and are directly related to ecosystem diversity. The preservation of diversity has thus been identified as a way to improve the sustainability of agroecosystems. It also follows that agroforestry systems (AFS) are recommended since they maintain high plant diversity, increase carbon and nutrient stocks and promote emergy efficiency. Agroforestry systems represent an alternative to traditional agricultural systems, which are responsible for large losses of diversity and environmental degradation in Brazilâs semiarid northeast. It is assumed that the greater plant diversity in AFS yields greater productivity, improves soil nutrient inputs, and increases carbon and nutrient stocks as well as energy efficiency. We evaluated a model agroforestry production system consisting of three areas: agrosilvopastoral, silvopastoral and preserved caatinga vegetation (CAT). Also, data was taken from a traditional management system including an area under cropping and two areas under fallow for six and nine years. The objectives of this work were to assess whether AFS remain similar to preserved vegetation and whether fallow periods restore land to its initial condition, in terms of: (i) the species composition and community structure of herbaceous and tree/shrub strata; (ii) plant diversity and biomass production; (iii) carbon and nutrient stocks in standing vegetation, litter and the soil and (iv) emergy flux transformations. We found that species composition and plant productivity were similar in the AFS and preserved caatinga, however in AFS the structure of the plant community was modified and diversity indices were reduced. Soil carbon and nutrient stocks in AFS were similar to those in CAT, but stocks in standing biomass and litter were lower. Overall, the AFS performed better in terms of emergy, due to more efficient energy use, a lesser environmental impact and greater renewability. The fallow periods following traditional cropping allowed the species composition, productivity and carbon and nutrient stocks in soil and litter to recover. However, areas under fallow differed from CAT in terms of tree community structure, with a greater number of individuals and species. Tree species found in fallow areas reach smaller sizes than under CAT. Therefore total biomass and carbon and nutrient stocks were lesser under fallow than CAT. Agroforestry systems managed in an integrated fashion represent great potential for sustainability, since they provide agricultural, pastoral and wood products while maintaining vegetation structure characteristics which allow constant fluxes of energy and nutrient cycling, as occurs under preserved vegetation. / Os processos de ciclagem de nutrientes e transformaÃÃes energÃticas impulsionam a produtividade e estÃo diretamente relacionados com a diversidade dos ecossistemas. Assim, tem-se priorizado a manutenÃÃo da diversidade em Ãreas agrÃcolas para a conduÃÃo de agroecossistemas mais sustentÃveis. Neste sentido, os sistemas agroflorestais (SAFs) sÃo recomendados por manter elevados nÃveis de diversidade vegetal, aumentar os estoques de carbono e nutrientes e promover eficiÃncia nas transformaÃÃes energÃticas. Os SAFs sÃo indicados para substituÃr os sistemas agrÃcolas tradicionais responsÃveis por grande perda de diversidade e degradaÃÃo ambiental na regiÃo semiÃrida nordestina. Espera-se que nos SAFs, a maior diversidade vegetal proporcione maior produtividade, maior retorno de nutrientes ao solo, maiores estoques de carbono e nutrientes e melhor eficiÃncia emergÃtica. Um modelo de produÃÃo agroflorestal composto de trÃs Ãreas foi avaliado: agrossilvipastoril (ASP), silvipastoril (SP) e caatinga conservada (CAT); e um sistema de manejo tradicional, composto de uma Ãrea em cultivo (AG), e duas Ãreas em pousio de seis (P6) e nove (P9) anos. Este trabalho objetivou verificar se os SAFs mantÃm-se semelhantes a vegetaÃÃo conservada e se os perÃodos de pousio retornam as Ãreas a sua condiÃÃo inicial, quanto a: (1) composiÃÃo florÃstica e estrutura da comunidade dos componentes herbÃceos e arbÃreo/arbustivo; (2) diversidade e produÃÃo de biomassa; (3) estoques de carbono e nutrientes presentes nas plantas, serrapilheira e solo e (4) transformaÃÃes dos fluxos emergÃticos. Verificou-se que as Ãreas sob SAFs apresentam composiÃÃo florÃstica e produtividade semelhante a caatinga conservada, porÃm este manejo provoca modificaÃÃes estruturais na comunidade vegetal e reduÃÃo nos Ãndices de diversidade. Os estoques de carbono e nutrientes nos SAFs sÃo semelhantes a CAT no compartimento solo, porÃm foram inferiores nas plantas e na serrapilheira. Contudo, o modelo agroflorestal apresenta melhor desempenho emergÃtico devido sua melhor eficiÃncia na utilizaÃÃo de energia, menor impacto ambiental e maior renovabilidade. Durante os perÃodos de pousio adotados apÃs o cultivo tradicional as Ãreas se recuperaram em relaÃÃo a composiÃÃo florÃstica, a produtividade e os estoques de carbono e nutrientes no solo e na serrapilheira. Entretanto, apresentaram modificaÃÃes quanto a estrutura da comunidade arbÃrea, com maior nÃmero de indivÃduos e espÃcies, sendo estes de menor porte e assim, menor biomassa total e menor estoques de carbono e nutrientes. Os sistemas de produÃÃo agroflorestal utilizados de forma integrada apresentam grande potencial de sustentabilidade, por proporcionarem a produÃÃo agrÃcola, pastoril e madeireira, mantendo diversas caracterÃsticas estruturais da vegetaÃÃo que permitem um fluxo de energia e uma ciclagem de nutrientes constante, assim como em Ãreas conservadas.

M.Sc. (Aquatic Health) / The relationships between water quality variables and phytoplankton diversity in the Hartbeespoort Dam were assessed spatially and temporally from February 2011 to March 2012 to evaluate the effects of the water quality variables on cyanobacterial bloom (Microcystis aeruginosa) hence aquatic macrophytes growth (Eichhornia crassipes) in the dam. Variables measured using standard methods included; temperature, pH, electrical conductivity, total suspended solids, dissolved oxygen, nitrate, nitrite, total phosphorous , ammonium, trace metals, chlorophyll-a and the phytoplankton community. The physical parameters ranged between: temperature (11.8-28 oC), electrical conductivity (282-796 ƒÊS/cm), dissolved oxygen (0.33-32.2 mg/L), pH (6.95-9.91) and total suspended solids (2-372 mg/L). Chemical variables ranged between; total phosphorous (0.02-3.5 mg/L), nitrate (0.03-21.2 mg/L), nitrite (0.02-0.48 mg/L) and ammonium (0.01-1.58 mg/L), chlorophyll-a (0.13-8693 ƒÊg/L), and exceed the TWQR values of the South African Water Quality Guidelines for aquatic ecosystem health health. Metal concentrations in water had the following decreasing order; macro elements: potassium > calcium >sodium > magnesium. Microelements: iron >zinc > aluminium > copper > nickel > manganese > chromium> selenium > lead > silver > arsenic > cadmium. Iron had the highest concentration among microelement of 631.62 ƒÊg/L and potassium the highest concentration amongst macro element of 34.49 mg/L. Six Different algal divisions were found in the dam with cyanophyta (cyanobacteria) been the most dominant group (95 %) and M.aeruginosa the most dominant species (69 %). The current study revealed an increase in physical parameters, chlorophyll-a and phytoplankton community and a decrease in chemical parameters in the summer months. An inverse relationship was observed in the winter months at all sites. One-way ANOVA showed a significant differences for physical variables (p <0.05) between months, with no significant differences noted (p > 0.05) between sites and between depths. Chemical variables however, showed a significant differences between months, sites and between depths (p <0.05). A 2-tailed Pearson correlation revealed negative correlations between temperatures and phosphorus, ammonia, nitrate, nitrite, electrical conductivity and iron (r=-0.298;-0.232;-0.099;-0.461;-0.441;-0.260) respectively and positive correlations between temperatures and chlorophyll-a and pH (r= 0.240; 0.609 ;) respectively (p <0.05; p <0.01). Canonical discriminant functions analysis revealed similarities and dissimilarities in water quality variables temporally and spatially with eigenvalues of 84.6 % and 59.1 % respectively. There was an adverse impact of the physico-chemical variables on the phytoplankton community, therefore aquatic macrophytes growth in the dam. The current study revealed that temperature, pH, phosphorous, nitrate and probably iron, copper, zinc and selenium may have contributed to the hypertrophic state of the dam, hence cyanobacterial bloom and growth of aquatic macrophytes.

Please read the abstract in the section, 00front, of this document / Thesis (PhD (Botany))--University of Pretoria, 2006. / Plant Science / unrestricted

The aim of this study is to gain a predictive understanding of the patterns and determinants of plant biodiversity in temperate, mesic grasslands of South Africa with a primary focus on the geographical area of the Eastern Cape. From a review of the literature on hypotheses explaining diversity (Chapter 2) it was possible to formulate a number of hypotheses that could be tested to explain species richness patterns in Eastern Cape grasslands. This thesis is organised so that each main chapter deals with a specific body of theory concerning the explanation of diversity patterns. A detailed description of the study area is provided (Chapter 3), including environmental variation and a description of major vegetation patterns. A summary is provided of grassland plant community patterns, as determined by phytosociological studies in the study area. A multivariate analysis of environmental variables was undertaken to determine which variables contributed the most towards explaining environmental variation in the study area and to determine whether any variables co-vary, a possible problem for any multivariate analysis in later chapters. Altitude produced one of the strongest gradients in the study area. There were a number of variables that were correlated with altitude, most notably temperature. Rainfall co-varied partially with altitude, but there was also a strong rainfall gradient perpendicular to the altitude gradient. A description of species richness, diversity and evenness patterns at the plot scale within different grassland plant communities of the Eastern Cape is provided in Chapter 4. To determine whether the environment acts differently on different growth forms, the contribution to species richness by different major growth forms is analysed. Furthermore, since the majority of literature attempts to explain diversity in terms of environmental factors, it was necessary to analyse the relationship between species richness and various environmental variables. The results indicate that there is high variation in species richness both within and among grassland communities. Forbs make the most significant contribution to overall species richness per 100 m2, followed by grasses. Variance in richness of all species together is not significantly related to environmental variables in mesic grasslands, but is significantly related to environmental variables in semi-arid grasslands. The result of greatest interest from this chapter is the fact that richness amongst different life-forms in the same place is explained by different environmental factors, indicating that the environmental factors that affect coexistence of species have a different effect on different life-forms. A classification of all the species of the dataset into plant functional types using a multivariate approach based on functional traits was conducted (Chapter 5). The grass species were classified into 16 functional types and the forbs into 14 functional types. The functional type classification provided the opportunity for undertaking analyses to develop an understanding of 8 the contribution by niche differentiation towards promoting species richness (Chapter 6). The results provide evidence of niche differentiation in the grasslands of the study area and also that niche differentiation promotes species richness in the grasslands of the study area. It was found that higher rainfall grasslands are less structured by niche differentiation than semi-arid grasslands. A regional / historical analysis is undertaken (Chapter 7) to investigate the relationship between the regional species pool and local richness, and the relationship between local richness and phytochorological diversity. Regional richness appears to have little effect in promoting local richness in grassland plant communities of the study area except at sites where there is high local richness. This provides an indication that regional richness only promotes local richness in the absence of local limiting factors. Phytochorological diversity promotes local richness, but mostly through diversity amongst species with narrow distribution ranges. Some theories ascertain that seasonal uncertainty may provide opportunities to species that would otherwise be outcompeted and thereby promote local richness. The degree to which seasonal uncertainty and seasonality promote local richness in the Eastern Cape grasslands was therefore investigated (Chapter 8). A weak relationship exists between these variables and local species richness in grassland communities of the study area, indicating that they do not promote niche differentiation to a significant degree in the study area. It is clear that in the grasslands of the Eastern Cape, environmental limiting factors are more important in semi-arid grasslands and species interactions are more important in mesic grasslands for structuring plant communities (Chapter 9, Discussion). Regional processes do not appear to be important in structuring local communities, but the analysis undertaken in this study shows that they may be significant when factors operating at the other two levels are overcome (species interactions and environmental limiting factors.

Characterization studies on the genetic diversity among cultivated cowpea (Vigna unguiculata (L.) varieties are valuable tools to optimize the use of available genetic resources by farmers, local communities, researchers and breeders. Eight cowpea (Vigna unguiculata (L.) genotypes ( Vegetable cowpea, Ivory grey, Okhalweni, Fahari, Fahari dark, 97K-1069-8, IT93K-73h, and 129-3) were subjected to molecular, morphological and agronomical characterization. DNA amplification fingerprinting markers were used to evaluate the genetic diversity among the eight genotypes. Nine random arbitrary primers were used to screen the eight genotypes to assess their ability to reveal polymorphisms in cowpea, and seven of them were selected for use in characterizing the total sample. A total of 43 bands were generated which are all polymorphic. On the average, the primers generated a total of 6.1 polymorphic bands. The resulting data-matrix included 43 analysed bands with a total of 344 characters. Neighbour joining analysis was used to generate the dendrogram, clustering the genotypes into two groups at an agglomerate coefficient of 0.30 irrespective of their geographical origins. The results also showed the presence of significant differences in morphological and quality traits among the genotypes. Fahari yielded the highest concentration of crude protein (46.51 mg/mg dry leaf) while Vegetable cowpea yielded the lowest (24.41 mg/mg dry leaf). The influence of manure was also found to be effective by increasing the crude protein content of the genotypes as shown by Fahari dark with an average of 53.53 mg/mg dry leaf as opposed to 39.85 mg/mg dry leaf without manure application. Although some small clusters grouped accessions of the same growth habits, a general lack of agreement between clustering and morphological features was observed. It can therefore be concluded that the significant differences between the molecular genetic analysis using DAF-PCR markers, morphologic characters and yield traits can be important tools to identify and discriminates the different cowpea genotypes.