No description available.

Perennial grass vegetation dynamics of heavy grazing, moderate grazing and ungrazed treatments were analyzed during two extreme drought events: the drought of 1951 to 1956 and the drought events centered on the year 2000. Analysis of each drought event from weather records and Palmer Drought Severity Index values showed that the intensity, duration and pattern of each drought event were structurally unique. Grazing intensity was the primary driver of perennial grass species composition and community structure both during and between each drought event. Total basal area for each drought event was driven primarily by variation in precipitation pattern. Basal area per plant dynamics were significantly influenced by grazing intensity while plant density was driven by both precipitation and grazing intensity. Topo-edaphic variation significantly influenced the persistence and distribution of perennial grass species during an extreme drought event centered on the year 2000. The presence of large or abundant surface rock features facilitated the survival of perennial grasses during this drought event by creating a positive soil microenvironment. Sites with large surface rock features acted as drought refugia for perennial grass populations. Sites with abundant surface rock features had 10 times greater perennial grass basal area and 5 times greater plant density than sites with few surface rock features. Grazing intensity was the primary driver of species composition and community structure within both refugia and non-refugia sites. Grazing intensity had no effect on perennial grass basal area. However, grazed treatments had two times greater perennial grass density than non-grazed treatments. Species response to grazing intensity and surface rock cover was individualistic. Grazing response groups (intolerant, intermediate, and tolerant) separated along a gradient of surface rock cover and grazing intensity. Abundant surface rock features act as refugia for perennial grasses by facilitating their persistence during extreme drought events on the Edwards Plateau.

No description available.

Invasive species drive ecosystem changes throughout the world. Introduced grasses in dryland ecosystems have driven a grass-fire cycle that transforms ecosystems into homogenized grasslands (Brooks et al. 2004; D'Antonio & Vitousek 1992). Little is known about the spread rates of these grasses, effects on native ecosystems or how climate modulates spread, yet these uncertainties may be the difference between success and failure. Equally important is a quantitative assessment of the current states of invasion, yet mapping efforts have been lacking and remote sensing assessments have been inadequate for regional and local assessments. This research examines these uncertainties in the context of buffelgrass (Pennisetum ciliare Link (L.)), a C₄ grass introduced into the Sonoran Desert. These are presented as three distinct but related studies. The first study documents changes in diversity and dominance at 11 sites in the Sonoran Desert with respect to time since infestation by buffelgrass. Dominant and rare species alike declined rapidly following infestation, although the longer-lived shrubs showed no signs until after five years. This calls into question basic assumptions about the grass-fire cycle. The second study assesses constraints to successful operational identification of buffelgrass via remote sensing. We combined ground-based spectral measurements with cover estimates and found that Landsat TM-based classification will result in high commission/omission errors regardless of timing. We also identified several spectral characteristics that distinguish buffelgrass that are only available using hyperspectral imagery. The third study reconstructs spread of buffelgrass using historical aerial photography dating from 1979. Populations grew from small colonizing patches to 66 ha in 2008, doubling every 2-3 years since 1988. Although spread closely fit a logistic growth curve between 1989 and 2008, we found evidence that the 1980s were a period of rapid expansion. Thus, we may presently be in a period of slower spread in which treatment efforts will be more effective than the long-term average. This research documents grass-led ecosystem transformation without changes in the fire regime and constant spread rates over multiple decades. Along with suggested methods derived from our remote sensing study, this provides managers with critical information for managing buffelgrass in the long-term.

In 2003 eight peanut and cotton crop rotations were established in southeastern Virginia, 4 of which included 2 or 3 years of tall fescue or orchardgrass grown as high-value hay crops. Each crop rotation was evaluated for changes in soil quality indicators including soil carbon and nitrogen, water stable soil aggregates, plant available water content, bulk density, cone index values, and soil moisture. Cotton and peanut growth and yield were also observed to evaluate changes in crop growth associated with differences in soil quality. Soilborne plant pathogens including root-knot nematode, stubby root nematode, ring nematode, stunt nematode, and Cylindrocladium parasiticum microsclerotia were measured in the spring and fall of each year to determine differences associated with crop rotations. Water stable soil aggregates in 2007 were higher in rotations with 3 years of either perennial grass. Soil moisture tended to be the highest at depths 30 - 60 cm in the 3-year tall fescue rotation in August and September 2007. Cotton in 2006 and peanut in 2007 had higher growth and yield where the annual crop directly followed a perennial grass. Root-knot nematode tended to decrease in all rotations over time. Stubby root nematode populations tended to increase in rotations with either duration of orchardgrass. Including perennial grasses in cotton and peanut rotations has the potential to increase growth and yield as demonstrated in this research. / Master of Science

The graduation thesis is described economical valuation of production hey. There is described methods and condition of measure consumption a fuel of energetic vehicle and working set and demand of time for provide sinlge technologic operation of harvest. The measure value was used for assesment a general straight cost on the produciton of hey. In the next point is described technologic procedure of pruduction hey and structure technologic line. The one part of graueted thesis is analysis of using areas of perennial grass stands and their characteristic.

Thesis (MSc. (Pasture Science)) -- University of Limpopo, 2016 / South Africa is regarded as a semi-arid area; only 28% of the country receives more than 600 mm rainfall recorded annually. Sustainable utilization of cool season fodder grasses in summer rainfall areas to produce winter animal feed remains a major problem. Farmers are affected by a shortage of adequate, good quality herbage for livestock during winter and dry periods on commercial farms. The study aimed to evaluate and compare the production potential of six Festulolium hybrids, three Dactylis species, and five Lolium hybrids and three grass-legume mixtures in the summer rainfall area. A total of 17 cultivars were evaluated for their DM production under the treatment of different fertilizer levels on three planting dates (16 March 2011, 21 April 2011 and 4 April 2012). The study was carried out at Hygrotech Seed Company (Experimental site), Dewagensdrift in Moloto Village outside Pretoria in the Gauteng Province. Data was collected on a monthly basis from sub-plots of 1 m x 1 m (m2) in 51 plots of 1.5 m x 6 m (9 m2), with nine rows that were 10 cm apart arranged under RCBD with three replicates per cultivar. Harvested fresh samples were taken, weighed, dried at 60ºC until they reached a constant dry weight and weighed to determine DM content. A Fischer’s protected LSD at the 5 % level was performed to compare the treatment means. Over a period of three years of study, it shows that the low fertilizer level resulted in the lowest DM production, with no significant difference occurring between medium and high fertilizer levels. To achieve optimum DM production with minimum cost medium fertilizer is recommended. The cultivars responded differently to the three different planting dates. The time of planting had an effect on DM production in winter. It is recommended that Festulolium hybrids and Lolium hybrids be planted earlier (March) for better DM production in winter. / National Research Foundation (NRF)

Doctor of Philosophy / Department of Biology / David C. Hartnett / Perennial grass populations propagate vegetatively via the belowground bud bank. Climate, photosynthetic pathway, and growth form impact bud production, longevity, and dormancy; leading to alterations in bud bank and tiller dynamics. Previous research in mesic C₄-dominated tallgrass prairie revealed that a C₄ grass had greater bud longevity and differing bud bank dynamics than a C₃ species. This study examined the bud bank dynamics of rhizomatous and caespitose grasses in a more arid C₃ dominated prairie to gain insights into how bud banks differ among grass species, growth forms, and environments, and the relationship between bud bank characteristics and grass architecture and growth patterns. The bud bank and tiller dynamics of four perennial grasses in the C₃-dominated northern mixed grass prairie were examined over 15 months. The C₃ caespitose and rhizomatous grasses produced similar numbers of buds per tiller and their bud longevity was [greater than or equal to] 2 years. Tiller longevity drove the turnover within the bud bank of the dominant C₃ caespitose grasses Hesperostipa comata and Nassella viridula. Their polycyclic tillers (tillers that lived for more than one year) created multi-aged bud banks. The rhizomatous C₃ grass Pascopyrum smithii also had a multi-aged bud bank because buds were able to live longer than its annual tillers. Differences between caespitose and rhizomatous C₃ grass bud banks were driven by differences in tiller and rhizome production and spatial distribution. Responses to water availability fluctuations are likely buffered by the maintenance of polycyclic tillers in the caespitose grasses and flexible timing of annual tiller recruitment in the rhizomatous grass. The C₄ rhizomatous grass Andropogon gerardii had similar phenology to populations in its tallgrass prairie range center. Despite declines in bud production per tiller and lowered flowering probability in mixed-grass prairie, A. gerardii maintained a multi-aged bud bank and a positive population growth rate via vegetative reproduction at both the center and edge of its range. Bud bank dynamics of different growth forms and photosynthetic pathways, as they offer insight into the control of grass population dynamics and production, will enhance understanding of the mechanisms by which management practices and environmental change can alter perennial grasslands.

Thesis (PhD (Conservation Ecology and Entomology))--University of Stellenbosch, 2010. / ENGLISH SUMMARY: Climate change and biological invasions are major components of global change induced by human activity and are considered major drivers of global biodiversity decline in terrestrial ecosystems. These drivers interact synergistically and render ecosystems vulnerable to invasion by invasive alien species. Grasses are a group of invasive plants that easily respond to global changes and alter native plant community structure and ecosystem processes, such as fire frequency. To date there have been few studies that assess the ecological drivers and effects of invasive grass species on arid and semi-arid ecosystems of South Africa. Fountain grass (Pennisetum setaceum) is a widely distributed invasive alien perennial grass from North Africa and the Middle East, valued by horticulturalists worldwide. It spreads along the edges of roads on the outskirts of most towns, and is common on mine spoil in many areas throughout South Africa. Occasionally, it escapes into natural vegetation along drainage lines or after fires. This grass can be a costly problem for agriculture and biodiversity conservation as it is unpalatable and increases fire risk. Understanding its distribution and invasive dynamics will contribute to better management and control practices. The main objective of this study was to understand the ecology and invasion processes of P. setaceum across South African environmental gradients, and use it as a model to understand the synergistic relationships between biological invasions and other global change (climate and land use) scenarios. This study provides the first assessment of how P. setaceum overcomes different invasion barriers in South Africa as an emerging invader, in comparison with other parts of the world where it has already become problematic. A number of management and control options for this grass and other similar perennial grasses result from this study. Specifically, the study provides comprehensive understanding of: 1) the distribution and habitat preferences of P. setaceum in arid and semi-arid parts of South Africa, 2) environmental resources and habitat conditions that promote its invasive potential, 3) growth and reproductive performance across environmental gradients, 5) the response of an arid ecosystem to P. setaceum invasion and fire promotion, and 6) the predicted future distribution of this grass in South Africa under scenarios of climate change and spread. The study has found that road-river interchanges are ideal sites for P. setaceum growth and that these sites should be targeted for management and control of this species. P. setaceum was found to persist under diverse biome environments, which is attributed to local adaptation. Disturbance was found to be a major factor promoting fountain grass invasion into semi-natural areas away from roadsides. Major clean-ups of this grass should focus on disturbed areas, especially in the fertile parts of the fynbos region where the grass has high climatic suitability. Management and control should also focus on areas with high nutrients and extra water, as these areas facilitate growth and reproduction. The dynamics of P. setaceum invasion and spread makes it a good model for management of similar emerging invasive perennial grasses in similar ecosystems. / AFRIKAANSE OPSOMMING: Klimaatsverandering en biologiese indringing is grootskaalse komponente van mensgedrewe globale veranderinge, en kan ook gesien word as prominente drywers van die huidige afname in globale biodiversiteit van terrestriële ekosisteme. Hierdie drywers werk saam in sinergie, en laat sodoende ekosisteme kwesbaar vir indringing deur uitheemse indringerplante. Grasse is ‘n groep indringerplante wat maklik reageer ten opsigte van globale veranderinge en verander inheemse plantgemeenskapstruktuur en ekosisteem prosesse, soos byvoorbeeld veldbrand frekwensie. Tot op hede is daar wynig studies gedoen wat die ekologiese drywers en effekte van indringergras spesies in droë en semi-droë ekosisteme van Suid-Afrika assesseer. Pronkgras (Pennisetum setaceum) is ‘n wyd verspreide meerjarige uitheemse indringergras, oorspronklik vanaf Noord-Afrika en die Midde-Ooste, en word waardeer deur tuinboukundiges wêreldwyd. Dit versprei al langs padrande aan die buitewyke van meeste dorpe, en is algemeen op ou mynhope in verskeie dele van Suid-Afrika. Somtyds ontsnap hierdie gras langs dreineringskanale of na veldbrande, en beland so in die omringende natuurlike plantegroei. Hierdie gras kan ‘n duur probleem word vir landbou asook biodiversiteit bewaring omdat dit onsmaaklik is vir diere, en dit verhoog veldbrand risiko. ‘n Beter begrip van pronkgras verspreiding en indringingdinamika sal bydra tot verbeterde bestuur en kontrole praktyke. Die hoofdoel van hierdie studie was om die ekologie en indringing prosesse van P. setaceum regoor Suid-Afrikaanse omgewingsgradiente te begryp, en dit dan te gebruik as ‘n model om die sinergistiese verhoudings tussen biologiese indringing en ander globale veranderinge (klimaat en grondgebruik) te verstaan. Die studie verskaf die eerste assessering van hoe P. setaceum verskillende indringing hindernisse in Suid-Afrika oormeester as ‘n opkomende indringer, in vergelyking met ander dele van die wêreld waar dit al klaar problematies is. Hierdie studie verskaf uiteindelik ‘n aantal bestuur en kontrole opsies vir hierdie en ander soortgelyke meerjarige grasse. Die studie verskaf spesifiek ‘n deeglike verstaan van: 1) die verspreiding en habitat voorkeure van P. setaceum in droë en semi-droë areas in Suid-Afrika, 2) omgewingshulpbronne en habitat toestande wat hierdie plant se indringing potensiaal verhoog, 3) groei- en voortplantingsvertoning oor verskillende omgewingsgradiente, 4) die reaksie wat ‘n droë ekosisteem toon teenoor P. setaceum indringing en veldbrand verhoging, en 5) die toekomstige verspreiding van hierdie gras in Suid-Afrika onder voorspellings van klimaatsverandering en verspreiding. Die studie het gevind dat pad-rivier tussengange ideale liggings is vir P. setaceum vestiging, en dat hierdie liggings dus geteiken moet word vir bestuur en kontrole doeleindes. P. setaceum toon volharding onder diverse bioom omgewings, wat toegeskryf word aan plaaslike aanpassing. Daar is gevind dat versteuring ‘n groot faktor is in die verhoging van pronkgras indringing in semi-natuurlike areas weg van padskouers. Grootskaalse pronkgras uitroeiing projekte moet fokus op versteurde gebiede, veral in die vrugbare dele van die fynbos streek, waar hierdie gras hoë klimaatsgeskiktheid toon. Bestuur en kontrole programme moet ook fokus op areas met hoë nutriente inhoud en ekstra water, aangesien hierdie areas groei en voortplanting vergemaklik. Die dinamika van P. setaceum indringing en verspreiding maak dit ‘n goeie model vir die bestuur van soortgelyke opkomende meerjarige indringergrasse in soortgelyke ekosisteme.

The anthropogenic introduction of species into new ecosystems is a global phenomenon, and identifying the mechanisms by which some introduced species become dominant in their introduced ranges (i.e., invasive) is crucial to predicting, preventing, and mitigating the impacts of biological invasions. Introduced perennial C₄ grasses are invading semi-arid grassland and savanna ecosystems throughout the south-central U.S. We hypothesized that in these semi-arid ecosystems, where variable precipitation patterns strongly influence vegetation dynamics, the success of an invasive plant species may be due in part to ecophysiological traits that enable high performance in response to unpredictable water availability. We also hypothesized that increased primary productivity and decreased plant input quality associated with these grass invasions have the potential to alter ecosystem carbon and nitrogen cycling and storage by altering the ratio of inputs (productivity) to outputs (decomposition/respiration). We tested the first hypothesis by quantifying ecophysiological performance differences between an invasive C₄ grass, Bothriochloa ischaemum, and co-occurring C₃ and C₄ native grasses under wet and dry conditions in the field and under two levels of simulated precipitation frequencies in a greenhouse experiment. We tested the second hypothesis by examining whether increased primary productivity and decreased C₃:C₄ grass ratios in savanna grass-matrices associated with B. ischaemum invasion altered (1) plant input quality and thus nutrient cycling and/or (2) net ecosystem carbon uptake in invaded areas. B. ischaemum's success as an invader was not directly related to its ability to cope with precipitation variability and availability, but its ability to rapidly produce large amounts of biomass may allow it to directly out-compete native species. B. ischaemum invasion decreased plant input quality and soil nitrogen availability. B. ischaemum invasion shifted ecosystem C-uptake from being nearly year-round to occurring predominantly in the summer. Greater C-uptake during the summer and under drier conditions compensated for a shorter growing seasons in B. ischaemum-invaded areas and cumulative annual NEE was similar between invaded and native-dominated areas. We conclude that B. ischaemum's impacts on soil nitrogen availability and plant-canopy microhabitat may allow it to exclude native species from invaded areas, but that its impacts on ecosystem C sequestration may be small. / text