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A chronosequence method was used to study plant community changes over successional time in a replicated design over an interval of 56 years. Artificial earthworks (revetments) constructed in 1939 and 1968 within a military manufacturing facility have been maintained under a constant regime of regular cutting and biomass removal. Predictions of species and community level change based on models of Odum, Grime and Peet are tested. Aspect and time are shown to be the major explanatory factors determining vegetational differences between samples. Diversity was seen to be significantly lower in older communities in conflict with Odum's model of community development. Partitioning of community structure by relative abundance suggests that the direction of development is contingent on physical conditions. Change in species types from ruderal to stress tolerators is consistent with Grime's successional model but is supported only weakly and by a minority of the species present. Feet's model of competitive sorting is strongly supported at the l-3m scale but refuted at larger scales. It is apparent that older communities show a tendency towards divergence in structure. The influence of spatial factors on ecological research methods is examined and discussed and it is suggested that development of predictive community models will require a recognition of the multiple levels of community structure and the multiple scales of interactions between their components.

Forest community characteristics on six forest stands in northeastern Mississippi were investigated. Study sites included two cottonwood stands, two managed hardwood stands, and two unmanaged hardwood stands. Relationships between forest stand components and habitat characteristics were estimated. Measured forest stand characteristics included regeneration, midstory and overstory to estimate species composition and forest structure. Basal area, crown density, standing dead trees and fallen dead tree measurements were also taken in the fall of 2010. A higher amount of tree species in the cottonwood and managed hardwood stands with the unmanaged hardwood stands having the lowest number of tree species. It was also detected that the unmanaged hardwood stands contained a higher DBH of 29.0 cm than the remaining stands. Cottonwood stands had a higher tree per hectare than the other stands. The unmanaged hardwood stands also contained the largest amount of standing and fallen dead trees.

Microsite disturbances – including mounds created by burrowing mammals – increase local plant community diversity by supporting unique species assemblages. I investigated whether Richardson’s ground squirrel (Urocitellus richardsonii) mounds support unique plant assemblages within five Manitoba prairie pastures, and explored the factors contributing to the plant assemblages documented. Richardson’s ground squirrel mounds supported unique species assemblages relative to bare-ground disturbances with removal of vegetation but no soil disturbance. These detectable shifts in plant community structure on mounds appear to be attributable to mound-specific environmental conditions responsible for delaying vegetative recolonization and facilitating establishment of early-succession species. In contrast, seed bank distribution did not appear to influence species assemblages on mounds. Further investigation into site-specific changes in species distribution on Richardson’s ground squirrel mounds is needed to appreciate the role of these burrowing mammals in pastureland communities. / February 2017

Genome size (GS) is a fundamental trait influencing cellular, developmental and ecological parameters, and varies c. 2400- fold in angiosperms. This astonishing range has the potential to influence a plant's nutrient demands, since nucleic acids are amongst the most phosphate and nitrogen demanding cellular biomolecules, and hence its ability to grow and compete in environments where macronutrients are limited. Angiosperm GS are strongly skewed towards small genomes, despite the prevalence of polyploidy in the ancestry of most if not all angiosperm lineages. This thesis examines the hypothesis that large genome sizes are costly to build and maintain and that angiosperm species with large GS are constrained by nitrogen and phosphate limitation. It untangles the interactions between GS, polyploidy and competition in plant communities, and examines how herbivory and GS play a role in plant productivity, measured as above-ground biomass. The hypothesis that large GS are costly was approached by analysing: 1) plant communities growing under different macronutrient conditions at the Park Grass Experiment (Rothamsted, UK); 2) plant communities under different conditions of macronutrient limitation and insect, mollusc, and rabbit herbivory at Nash's Field in Silwood Park (UK); and, 3) Ellenberg's indicator values which represent the realised niche of a species in terms light, water, and soil fertility. Support for the hypothesis was found in all experiments. The range of analyses show that angiosperm plants with large genomes (e.g. 1C-value > 5 pg) are indeed under greater macronutrient limitation in comparison to plants with small genomes, and that it is polyploid plants with large GS which are the most competitive when macronutrient resources are plentiful. In terms of herbivory, the key finding is a highly significant negative association between GS and rabbit herbivory. A species' realised niche for soil fertility was found to show a positive association with its GS. Overall the thesis shows that angiosperm GS plays a central role in plant community composition and responses to macronutrient conditions, and potentially on higher ecosystem processes through associations at different trophic levels.

Os objetivos deste trabalho foram analisar a composição florística, a estrutura, alguns aspectos da dinâmica da regeneração de espécies nativas no sub-bosque de povoamentos comerciais de Eucalyptus spp e estudar o impacto que algumas práticas silviculturais (desbaste e corte raso) sobre a regeneração. Para isso, foram locadas 17 parcelas (0,68 ha de área amostral) em um talhão de Eucalyptus grandis (Talhão 48), na Fazenda São José do Bromado, coordenadas geográficas 23°13’30’’S e 48°34’07’’W, município de Itatinga - SP. Na avalia ção da composição e estrutura da regeneração, realizada 30 meses após o corte da primeira rotação do povoamento de eucalipto, foram plaqueados e identificados todos os indivíduos arbóreos ou arbustivos com altura superior a 1,5m. O estudo da evolução temporal da regeneração foi realizado em 2 avaliações, 30 e 45 meses após a exploração do povoamento de eucalipto, utilizando o mesmo método de análise, sendo considerado morto o indivíduo amostrado nos levantamento anterior e não localizado na avaliação seguinte. Após a segunda avaliação as parcelas foram divididas em três tratamentos, sendo: Tratamento 1 - testemunha (área amostral de 0,2ha), no qual o povoamento de eucalipto foi mantido, Tratamento 2 (área amostral de 0,24ha) no qual foi realizado o desbaste de 50% do povoamento de eucalipto e Tratamento 3 (área amostral de 0,24ha) no qual foi realizado o corte raso do eucalipto. Após a implantação dos tratamentos (46 meses após a exploração do povoamento) foram realizadas duas avaliações, a primeira 54 meses e a segunda 61 meses após a exploração da primeira rotação do povoamento de E. grandis. Foram amostrados 1900 indivíduos (104 espécies e 38 famílias) na primeira avaliação. A família de maior riqueza florística foi Myrtaceae seguida de Asteraceae, Fabaceae e Solanaceae, sendo esta última a que apresentou a maior densidade de indivíduos. As espécies de maior densidade relativa foram Solanum variabile e Matayba elaeagnoides. 76,66% dos indivíduos amostrados pertenciam a famílias que apresentaram padrão de distribuição espacial agregado. Na avaliação da dinâmica da regeneração, constatou-se que o recrutamento de novos indivíduos no sub-bosque do eucalipto no período de 30-45 meses da exploração comercial se concentrou nos grupos de espécies secundárias iniciais, secundárias tardias e espécies típicas da condição de sub-bosque. Enquanto a mortalidade se concentrou nos indivíduos pertencentes ao grupo das espécies pioneiras e das espécies não classificadas sucessionalmente. No período o índice para diversidade de Shannon (H´), apresentou crescimento de 3,48 para 3,573, e a equabilidade (J’), crescimento de 0,751 para 0,762, mostrando que houve ganho em relação a diversidade de espécies na área. No estudo do impacto que diferentes práticas silviculturais impõem a regeneração, o tratamento 1 - testemunha foi o que apresentou as menores taxas de mortalidade e o maior ingresso de espécies no período analisado. As operações de corte e remoção causaram grande impacto nos tratamentos 2 - desbaste de 50% do povoamento de E. grandis e tratamento 3 - corte raso, aumentando a taxa de mortalidade e diminuindo a taxa de recrutamento de indivíduos na regeneração. O Tratamento 2 foi o único a apresentar ganhos em diversidade (H’) em todos os levantamentos. / The objectives of this study were to analyze a floristic composition, the structure, some aspects of the dynamics of regeneration of native species in understory of commercial stands of Eucalyptus spp and to study the impact that some silvicultural practices (thinning and clear cut) have on regeneration. For this purpose, 17 samples (0.68 ha total sample area) were located in a stand of Eucalyptus grandis (Stand 48), on the São José do Bromado Farm, geographical coordinates 23°13’30’’S and 48°34’07’’W, municipal of Itatinga, Sao Paulo. In the evaluation of the composition and structure of the regeneration, done 30 months after the clear cut of the first rotation of Eucalyptus grandis, all of the individual trees up to 1.5m of height were tagged and identified. The study of the temporal evolution of regeneration was done in 2 evaluations, 30 and 45 months after the clear cut of the stand. The same method of analysis was used, being that the individual trees measured previously and not found in the second evaluation were considered dead. After the second evaluation the samples were divided into three treatments: Treatment 1- control (sample area of 0.2ha), of which the trees were maintained, Treatment 2 (sample area of 0.24ha), of which 50% thinning was done, and Treatment 3 (sample area of 0.24ha), of which clear cut was done. After the implementation of the treatments (46 months after the exploration), two evaluations were accomplished. The first at 54 months and the second at 61 months, after the exploration of the first rotation of the stand. One thousand nine hundred trees (104 species and 38 families) were sampled in the first evaluation. The largest floristic family verified was Myrtaceae followed by Asteraceae, Fabaceae and Solanaceae, the family which presented the largest density of individuals. Whereas the species with the greatest relative density were Solanum variabile and Matayba elaeagnoides. Among the individual samples, 76.66% were of the families that present a pattern of aggregate spatial distribution. In evaluating the dynamics of regeneration, it was found that the recruitment of new individuals in understory of eucalyptus during the period of 30-45 months after the commercial exploration was focused on the groups of initial secondary species, late secondary and typical species of understory. The mortality was concentrated in the group of pioneer species and non-classified species, respectively. The index period to the Shannon diversity (H’), presented growth of 3.48 to 3.573, and eqüability (J’), growth of 0.751 to 0.762, showing to have gained in relation to the diversity of species of the area. The study of the impact that different silvicultural practices have on regeneration, treatment 1- presented the least incidence of mortality and the greatest incidence of species during the analysis period. The practices of thinning and clear cut caused a great impact on treatments 2 and 3, improving the incidence of mortality and decreasing the incidence of new individuals of regeneration. Treatment 2 was the only one to present gains in diversity (H’) in all of the evaluations.

It is an unresolved paradox that non-native species are successful in novel environments whereas native species, presumably adapted to that environment, decline. This knowledge gap has persisted because third party processes in invasion ecology have been overlooked. Ungulate densities are increasing due to the eradication of predators and landscape change and I asked how herbivory and invasion might interact to cause declines of native species. In Garry oak meadows, Canada’s most endangered ecosystem, native forbs have declined relative to non-native grasses and I tested the facilitatory role of herbivory in that degradation. My investigations, novel to the field, were conducted on islands spanning the Canada-US border. Islands served as natural experimental units in a mensurative study of abundance patterns in seven plant groups and 15 focal species along gradients of herbivory, biogeography, soil depth, and human activities. Increasing ungulate densities were related to declines in abundances of native forbs, and increasing abundances of non-native annual grasses. These regional patterns were upheld by two plot-based, 2x2 factorial experiments that contrasted the fitness of native species under manipulations of herbivory and competition for light. Specifically, I showed that ungulates limited the establishment, growth, survival and reproduction of seedlings and transplanted native forbs and shrubs and that competition from non-native species had little effect. I also calculated forage selectivity indices and tested the efficacy of fencing and cutting to reduce competition, for the restoration of native community biomass. Non-native annual grasses were rarely browsed and increased with increasing ungulate density. Non-native perennial grasses declined with herbivory, however, their regional abundances were unaffected by ungulate density despite being preferentially foraged. That non-native annual and perennial grasses differed in their responses to herbivory has consequences for restoration and illustrates the challenge of developing a comprehensive theory of invasion. Reducing ungulates, necessary for the recovery of native forbs, also benefits non-native perennial grasses and therefore their removal speed recovery of Garry oak meadows. Despite advances in invasion ecology, scientists and managers are disconnected and research is rarely implemented. I conclude by proposing seven solutions to facilitate the integration of science into management.

Loss of wetland habitats across the nation is staggering and continues, especially in urbanizing areas. Thus, wetland restoration has become a priority. However, questions remain regarding system function and biotic communities. We studied a constructed floodplain wetland complex near Dallas, Texas. We sought to improve understanding of wetland ecosystem development under the influence of different approaches to wetland restoration in an urbanizing landscape. In the wetland complex, 10 constructed sloughs, approximately 70m by 15m, were designated for this study. Our experiment monitored the establishment of aquatic plant and invertebrate communities under different experimental conditions. In 5 sloughs, 5 native perennial hydrophyte species were transplanted in blocks in each slough, with the remaining 5 sloughs unplanted. Portions of each slough were caged to determine the effects of protective caging. Using 1m2 caged and neighboring uncaged areas as quadrats, we sampled vegetation and the invertebrate community over two years to determine the effects of restoration treatmentsSlough planting did not result in statistically different levels of plant cover. However, invertebrate abundance was greater in planted sloughs, and plant composition was different, comprised more of perennial species in planted sloughs than in unplanted sloughs. Caging did not have an effect on plant or invertebrate communities. However, changes due to time resulted in significant increases in plant cover and invertebrate abundance and shifts in community composition. Four of 5 transplanted species were emergent growth forms. Emergent cover and the remaining species, Potamogeton nodosus, a floating-leafed plant, accounted for invertebrate community variation. Transplanted emergent species did not fare well, though other emergent species did colonize the site, along with widespread coverage by submerged Najas guadalupensis. Potamogeton spread rapidly, colonizing unplanted sloughs, and this will likely affect community development across the site. Plant and invertebrate richness values were low, likely due to hydrological extremes and the short period of time since construction. Water level fluctuations resulted in plant communities dominated by obligate wetland plants, though drought stress took a toll on survival of plants and invertebrates in late summer. Community development and system function were dependent mostly upon time and hydrology. on the communities.

It is an unresolved paradox that non-native species are successful in novel environments whereas native species, presumably adapted to that environment, decline. This knowledge gap has persisted because third party processes in invasion ecology have been overlooked. Ungulate densities are increasing due to the eradication of predators and landscape change and I asked how herbivory and invasion might interact to cause declines of native species. In Garry oak meadows, Canada’s most endangered ecosystem, native forbs have declined relative to non-native grasses and I tested the facilitatory role of herbivory in that degradation. My investigations, novel to the field, were conducted on islands spanning the Canada-US border. Islands served as natural experimental units in a mensurative study of abundance patterns in seven plant groups and 15 focal species along gradients of herbivory, biogeography, soil depth, and human activities. Increasing ungulate densities were related to declines in abundances of native forbs, and increasing abundances of non-native annual grasses. These regional patterns were upheld by two plot-based, 2x2 factorial experiments that contrasted the fitness of native species under manipulations of herbivory and competition for light. Specifically, I showed that ungulates limited the establishment, growth, survival and reproduction of seedlings and transplanted native forbs and shrubs and that competition from non-native species had little effect. I also calculated forage selectivity indices and tested the efficacy of fencing and cutting to reduce competition, for the restoration of native community biomass. Non-native annual grasses were rarely browsed and increased with increasing ungulate density. Non-native perennial grasses declined with herbivory, however, their regional abundances were unaffected by ungulate density despite being preferentially foraged. That non-native annual and perennial grasses differed in their responses to herbivory has consequences for restoration and illustrates the challenge of developing a comprehensive theory of invasion. Reducing ungulates, necessary for the recovery of native forbs, also benefits non-native perennial grasses and therefore their removal speed recovery of Garry oak meadows. Despite advances in invasion ecology, scientists and managers are disconnected and research is rarely implemented. I conclude by proposing seven solutions to facilitate the integration of science into management.

Japanese knotweed is an invasive plant that grows in disturbed sites across Nova Scotia. This study recorded an average spring growth rate of 6cm per day until reaching a canopy height exceeding 2m in June. Knotweed stands contained on average 17 stems and 8.0kg of fresh biomass per m2. Leaf cover was significantly greater in knotweed patches versus grass and shrub habitats in riparian ecosystems. Plant diversity in knotweed patches was nil, yet invertebrate diversity and abundances were similar across habitats. Small mammal tracks were more abundant in knotweed than shrub patches, but not as much as grass plots. Two herbicides were applied at four different dates in 2011. The following year, Aminopyralid was ineffective while Imazapyr treatments successfully reduced knotweed biomass, density, height, and leaf cover. Imazapyr application is recommended at full growth (June) or flowering (August). This project provides new information on an invasive weed in eastern Canada.