New Zealand's South Island tussock grasslands have been highly modified by human activities, including burning, grazing and introductions of exotic plants for pastoralism. Studies suggest that tussock grasslands are degraded, in that native species have declined, and exotic species have increased in both diversity and abundance. These trends are primarily thought to be related to the impacts of grazing and subsequent grazing removal. Few studies have assessed long-term changes that have occurred in tussock grasslands, and those that have are generally limited to one particular location. This thesis aimed to investigate temporal changes in community structure in tussock grasslands, and relate these changes to environmental variables and land tenure. Data were used from 90 permanently-marked vegetation transects, which were set up on 19 geographically widespread properties in areas of tussock grassland across Canterbury and Otago in the South Island of New Zealand. The transects were on land in both conservation and pastoral tenure. Each transect was 100 m, and consisted of 50 0.25 m² quadrats. The transects were measured between 1982 and 1986 (first measurement), were re-measured between 1993 and 1999 (second measurement) and again between 2005 and 2006 (third measurement). A total of 347 vascular species were observed over the 90 transects and three measurement times. Species richness declined between the first and second measurements (first time interval), and increased between the second and third measurements (second time interval), at both the small (quadrat) and large (transect) scales. Both native and exotic species declined in mean quadrat species richness during the first time interval, and then increased during the second time interval. Changes in mean quadrat species richness were similar on transects in both conservation and pastoral tenure. Multivariate analysis of species' occurrences in quadrats identified a long gradient in species composition for these 90 transects. Four key plant communities were identifed along this gradient and differed in their mean elevation: (1) Highly-modified pastoral community, (2) Short-tussock grassland community, (3) Tall-tussock grassland community, (4) Alpine mat-forming species community. A detailed investigation into temporal changes that occurred on 53 transects that occurred in short- and tall-tussock grassland communities showed that changes in species composition were not consistent over time. Transects on different properties changed in species composition by different amounts. Specifically, in ordination space, transects on two properties changed in composition significantly more than transects on one other property. The property that a transect was on also affected the way that it changed in composition, i.e. native species were more likely to have increased on transects on some properties. Transects in conservation tenure did not change in species richness or composition differently from those in pastoral tenure. Considering that many native plants in tussock grasslands are relatively slow-growing, and that these areas have been grazed and burned for more than a century, we may expect it to be some time before we can detect differences in vegetation dynamics on conservation land from that on pastoral land. The changes in the community structure of these tussock grasslands were related to a combination of environmental factors, such as soil chemistry, climate, and management factors. This study has allowed greater understanding of vegetation change in tussock grasslands, and demonstrates the importance of long-term ecological monitoring in making reliable and accurate predictions about landscape-scale changes in tussock grassland community structure.

Invasive species are an increasingly severe conservation problem that can dramatically alter native plant communities. Although ecologists have proposed many mechanisms for the dominance of invasive species, superior competitive ability is one of the longest standing hypotheses. In winter annual plant communities, germination timing affects competition among plants. I hypothesized that grass invasion has changed the costs and benefits of early and late germination, and that species with flexible germination timing would compete better with invasives. Experiments at the Bernard Field Station in Claremont, CA and germinator trials in a controlled environment were used to examine the survivorship and germination rate of three native forbs in the presence or absence of invasive grass competition. Germinator trials revealed that most Clarkia purpurea seeds germinated in fall conditions, though newer seeds had higher proportions germinate under winter conditions. Older seeds had a lower germination success, indicating a potential decrease in seed viability. In the field experiment, November germinants had higher survival rates than October germinants for Amsinckia menziesii and Phacelia distans, and both species had similar numbers of new germinants at each census. Removal of invasive grasses did not significantly affect the survival of either species, though a trend towards increased survivorship was observed in removal plots of November germinants. Taken together, these results show evidence for variation in germination timing and responses to environmental cues among native annual seeds, and also support the idea that germination timing has important consequences for survivorship, and potentially competitive interactions, with invasive grasses.

Tallgrass prairie restoration is an important conservation activity in rural areas. However, little is known about prairie restoration in urban environments. The overall objective of this study was to characterize and better understand urban prairie restoration. This was carried out through an examination of 29 restoration sites within Winnipeg, Manitoba. The results indicated that actively restored urban prairies were successful and high in diversity. Multiple attributes of the restorations were examined as indicators of success including vegetation, the propagule bank and insects. However, not all attributes delivered equivocal results. This suggests that multiple measures should be used to assess a restoration site. Anthropogenic and biophysical variables were found to influence vegetation of the restorations equally, highlighting the importance of incorporating a human component in urban ecological research. These urban restorations were seen to surpass larger rural restorations in quality; thus, efforts should be made to increase their prevalence. / February 2008

A series of land-use-land-cover-change (LULCC) based sensitivity experiments, including changes in vegetation type, fractional vegetation (FV), and soil moisture (SM), over Western Kentucky were conducted to investigate atmospheric response to land-use. The choice of land-use for this study was chosen in the context of Western Kentucky’s historical LULCC. For this study, vegetation types considered were grassland, forest, and bare soil with further variations in FV for grassland and forest at 25, 50, 75, and 100 % and systematic increases and decreases in volumetric SM of 0.05, 0.10, and 0.15 m3 m-3. To the author’s knowledge, this is the first assessment of its kind that incorporates these types of LULCC in a single study. In addition, typical anthropogenic land-use change often incorporates several types of LULCC. Moreover, this assessment provides a robust analysis of the impacts LULCC has on atmospheric processes over Western Kentucky. To simulate the importance of land-use on atmospheric processes, a well known meso-scale model developed by the National Center for Atmospheric Research (NCAR) and the Pennsylvania State University (PSU) MM5 coupled with an intermediately complex land surface model (LSM) Noah was used. The purpose of this research is to investigate the impact of multiple types of LULCC on planetary boundary layer (PBL) evolution, PBL stability, near surface 3D-wind fields, temperature, and moisture. Furthermore, it is anticipated that multiple types of LULCC will provide more insight into the complex nonlinear land-atmosphere interactions from atmospheric, air quality, and climatology perspectives. Modeling analysis revealed the importance of land-use on atmospheric processes. Changes in all three types of LULCC (land-cover, FV, and SM) altered the distribution of surface energy and moisture, PBL structure, 3D-wind fields, and PBL stability. In general, it was found that LULCC that enhanced (diminished) ET rates reduced (increased) sensible heat flux, atmospheric temperature and, and PBL heights below (above) control (CTRL). For instance, the conversion of land-cover from CTRL to grassland reduced 2 m temperature and PBL heights by 0.60 °C and 228 m respectively compared to CTRL due to an evaporative advantage (lower stomata resistance). Multiple types of land-use change were found to either offset or enhance overall modeled response to LULCC. A reduction in FV to 25 % over grassland diminished ET despite the evaporation advantage of grassland and increased 2 m temperature and PBL heights with respect to CTRL by 3.3 °C and 504 m. These results significantly altered horizontal and vertical wind fields, affecting moisture advection and the development of meso-scale circulations. Compared to CTRL, these differences were enhanced over drier soils, but muted over moist soils. Moreover, the impact of LULCC on atmosphere evolution was not only dependent on the type of LULCC, but also on the current state of other unaltered land surface features such as vegetation type, FV, and SM. Alterations to modeled PBL development, as a result of LULCC, can have important impacts on a region’s climatology and air quality. Simulated changes in typical PBL moisture and temperature through time can affect local and regional climatology. Depending on the type of LULCC, these alterations in climate may lead to localized cooling. In addition, it was further hypothesized that changes in PBL height can affect air quality. Given the capping inversion layer at the top of the PBL, changes in PBL heights can significantly affect air quality with lower (higher) PBL heights diminishing (enhancing) air quality. Moreover, this research prescribes the importance of considering LULCC in atmospheric assessments of climatology and air quality, including pollutant dispersion and trajectory modeling.

A majority of the arid grasslands in the western U.S. have been dramatically altered by anthropogenic influences resulting in degradation and desertification. Within the arid grasslands of North America a guild of burrowing herbivorous rodents that includes kangaroo rats (Dipodomys spp.) and prairie dogs (Cynomys spp.) is often considered integral to arid grassland maintenance. As part of the larger guild of burrowing herbivorous rodents, kangaroo rats are considered to be an important keystone guild whose role as ecosystem engineers and habitat modifiers complements that of prairie dogs. Together these species organize and structure arid grassland ecosystems and the biodiversity therein, by providing a mosaic of microhabitat patches, thus increasing overall heterogeneity. In an area where black-tailed prairie dogs (C. ludovicianus) were reintroduced, I used Giving-up Density (GUD) to assess the indirect effects black-tailed prairie dogs might have on the foraging patterns of resident kangaroo rats (D. spectabilis and D. merriamii). My objective was to compare and contrast kangaroo rat foraging GUD within and along the boundary of a on a recently established black-tailed prairie dog colony with that in the surrounding unmodified native habitat. This enabled assessment of whether black-tailed prairie dogs had an influence on the perceived quality of the habitat by kangaroo rats. Kangaroo rats visited off-colony feeding trays more frequently, and collected a greater mean mass of seed per tray as well. This indicates that the kangaroo rats perceived the area off the prairie dog colony as having a lower foraging cost than on the colony or along the colony edge. I conclude that from the perspective of the seed-eating kangaroo rat, the colony is not viewed as high quality habitat. What impact the reintroduction and management of one keystone species might have on another keystone species deserves additional consideration as we attempt to restore arid grassland ecosystems.

No description available.

Promotion of a predictive understanding of plant community response to various forms, frequencies and seasons of disturbance, either through the direct physical effect on biota and or indirect effect on plants, through modification of microclimate and soil attributes is currently a major goal in plant ecology. In particular, the effect of disturbance on altering the ratio between available light and nutrients and their resultant effect on growth, shoot/root allocation, and thus community composition has gained considerable recognition in connection with the mechanisms of plant succession under a popular heading "the resource ratio hypothesis of plant succession". Contemporary and long-term (>50 years) burning and mowing experiments in KwaZulu-Natal (KZN) provide important sites for investigation that in the mesic grasslands of KZN, community composition changes in response to the frequency, time and type of disturbances such as burning, mowing and veld fertilization. However, the relationship between disturbance-resource-plant traits and their interactive role in species change is virtually unknown. This study sought to improve understanding of mesic grassland dynamics in. KZN, using short-term pot and plot experiments. The principal objectives were: 1) by subjecting plants to different levels of resources viz. light, nutrients, water and cutting to determine the relative above and below-ground growth performances (biomass allocation) of species from contrasting habitat preference in KZN, which implies their relative competitive ability for limiting resources and tolerance to cutting, 2) by using a short-term (one-season period) burning and mowing experiment to determine the effect of different veld management practices on microclimate and availability of soil resources and their subsequent effect on plant growth performances, 3) testing the relative shade tolerance of representative species from contrasting habitat preferences, 4) by combining the outcomes from these experiments, to provide a general synthesis concerning species' response to disturbance/resource which further signifies species change. The hypothesis that competitive ability as a function of biomass allocation is fertility dependent was supported by a pot experiment. In low nutrient treatments short grass species that predominate infertile soils in KZN viz. Aristida funcifarmis and Themeda triandra attained double the shoot biomass, more than double root biomass, initiated more tillers and re-grew better (after cutting) than those inherently tall species that predominate fertile sites viz. Eragrostis curvula and Hyparrhenia hirta. In contrast, in high nutrient treatments, tall species attained far higher shoot biomass and grew taller in height. Interestingly, short species had a smaller shoot: root ratio than tall species, consistent with the prediction of the resource ratio hypothesis. However, no evidence was obtained suggesting that tall species were more shade tolerant than short species. A field-based shade experiment rather showed that, those species that initiate tillers below-ground viz. Aristida junciformis, Eragrostis curvula and Tristachya leucothrix were more shade tolerant than those species that initiate tillers above-ground viz. Hyparrhenia hirta and Themeda triandra. On the other hand, the effect of disturbance/resource relationship in influencing the growth (biomass production, growth rate, and basal circumference) of contrasting species was examined by conducting a short-term (one season) burning and mowing experiment. The effect of disturbance, its form and frequency through its effect on light and soil moisture was able to account for a substantial difference in species vigour, which can potentially impact community composition. Short species (Themeda triandra and Tristachya leucothrix) showed their highest biomass production and higher basal circumference enlargement in burnt summer mown sites, whereas medium to tall species (Aristida junciformis, Eragrostis curvula and Hyparrhenia hirta) were less tolerant to summer mowing. Aristidajunciformis and Eragrostis curvula appeared to be more vigorous (both in terms of above-ground biomass production and growth rate) in burnt but not mown and control treatment respectively. High biomass and litter accumulation on sites protected from disturbance appeared to have a large influence on species vigour. Species such as Aristida junciformis, Eragrostis curvula and Tristachya leucothrix had high tolerance to litter accumulation while in contrast Hyparrhenia hirta and Themeda triandra were more vulnerable. In total this study has revealed that the association of some short species e.g. Themeda triandra with the reccurrence of disturbance is mainly due to increases in light availability and lowered dominance from tall species in frequently disturbed sites rather than nutrient related. However, this study has revealed that there are some indications whereby the notion that the inverse relationship between available light and nitrogen are important driving variables in species change is an important working theory in the mesic grassveld of KZN. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

Tallgrass prairie restoration is an important conservation activity in rural areas. However, little is known about prairie restoration in urban environments. The overall objective of this study was to characterize and better understand urban prairie restoration. This was carried out through an examination of 29 restoration sites within Winnipeg, Manitoba. The results indicated that actively restored urban prairies were successful and high in diversity. Multiple attributes of the restorations were examined as indicators of success including vegetation, the propagule bank and insects. However, not all attributes delivered equivocal results. This suggests that multiple measures should be used to assess a restoration site. Anthropogenic and biophysical variables were found to influence vegetation of the restorations equally, highlighting the importance of incorporating a human component in urban ecological research. These urban restorations were seen to surpass larger rural restorations in quality; thus, efforts should be made to increase their prevalence.

Grassland fuels quickly respond to moisture changes in the environment, and successfully ignite more readily compared with other wildland fuel types. In recent years in New Zealand grasslands, wildfire ignitions have increased due to recreational activities on public conservation land. Ignition sources have included off-road vehicles, sparks from machinery, and campfires, cooking stoves, etc. This research investigated ignition thresholds for fully cured tussock (Festuca novae-zelandiae) and exotic (Agrostis capillaris) grasses, with the aim of providing a scientific basis for wildfire prevention through decision-support tools for activity controls. Five ignition sources of concern to the Department of Conservation were tested in the laboratory, and results were validated against field experiments. Experiments were innovative, and were designed to simulate ignitions from: hot exhaust systems on off-road vehicles (hot metal); sparks from vehicle exhausts (carbon emissions); grinding operations (metal sparks); smouldering debris dropped onto grass fuels from hot vehicle parts (organic embers); and ordinary cigarette lighters (open flame). Fuel moisture content (MC), and wind speed were varied, but ambient temperature and relative humidity were kept relatively constant in the laboratory. Logistic regression was used to analyse data for each ignition source, except organic embers because no ignitions occurred. Ignition thresholds were determined for a probability of ignition success of 50%, and all models were statistically significant. The thresholds are listed in terms of model accuracy for each experiment: open flame was 28% MC without wind, and 55% MC with light wind (1 m/s); metal sparks was 37% MC; hot metal, with a wind speed of 2 m/s and MC of 1%, was 398ºC hot metal temperature; and carbon emissions was 65% MC. The results represent a significant contribution to knowledge of the ignition behaviour of grassland fuels. Further research is required to verify and extend the results; but, initial findings provide a scientific basis for management, investigations of wildfire causes, and decisions around controls on recreational activities to protect highly sensitive ecosystems and natural areas from damaging wildfires.

Cattle are responsible for the deterioration of aquatic and riparian ecosystems throughout the North American prairies. Marked preference for riparian areas has resulted in vegetation loss, stream bank destabilization, changes in sediment particle size, and increased nutrient loads in the streams. A grazing experiment in Grasslands National Park of Canada manipulated the density of cattle to represent a range of grazing intensities (from no grazing to very heavy grazing, 70% forage utilization). This experiment provided the opportunity to study how streams in the semi-arid mixed-grass prairie environment respond to a range of grazing pressure. Nine experimental pastures located on previously ungrazed land within the park boundary and four located within the adjacent community pastures were created, each subjected to a specified grazing treatment. Sampling occurred in the autumn from 2007 to 2009 and included the measurement of 33 physical, chemical, and biological habitat metrics and the characterization of the aquatic invertebrate community. Linear regressions were performed to determine if the habitat variables had a significant relationship to grazing intensity (P < 0.05). Of the habitat variables, two sediment particle size categories were significantly related to grazing intensity: per cent of fine gravel (4-8 mm diameter) (P =0.003) and per cent of medium gravel (8-16 mm diameter) (P = 0.007). The only other habitat variable with a significant linear relationship to grazing intensity was the concentration of suspended carbon in the stream water (P = 0.050). Three invertebrate community metrics were focused on for their expected response to changes associated with cattle impacts: iii per cent Chironomidae (%Chiron), per cent Ephemeroptera, Odonata, and Trichoptera (%EOT), and taxa richness. There was a significant non-linear relationship between %Chiron (P = 0.005) and grazing intensity, no linear or non-linear relationship between %EOT and grazing intensity, and a non-linear trend between richness and grazing intensity (P = 0.083). A Reference Condition Approach was used to test for the effects of grazing on the invertebrate community. Multiple regression was used to create a model predicting the invertebrate community from habitat metrics. Of the three community metrics, only richness resulted in a model with acceptable predictive ability. The predicted richness values for each test site were calculated and their residuals were determined and compared to the distribution of residuals observed in the reference sites. Using this technique, I determined that 73.3% of the sites subjected to grazing deviated significantly for the reference condition and were therefore deemed to be impacted. There was no significant relationship between the test site residuals and grazing intensity. The macroinvertebrate community in this semi-arid environment is already under a lot of stress, the addition of cattle to the environment, even at low intensities, pushed the community beyond the reference condition.