No description available.

No description available.

No description available.

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Vegetation dominated by heather and bracken, two common species of the UK uplands, is often nutrient limited and heavily influenced by climate. Thus, changes in climate or nutrient availability might be expected to have pronounced effects on growth and competition between these species. Mature heather and bracken turfs, transplanted from the field into 1 x 1 by 0.5 m deep plots, were subjected to factorial experimental treatments of root competition, shoot competition, summer drought, increased nitrogen supply and increased temperature for four consecutive years. The effects of root competition on the growth of heather and bracken were as great as those caused by the environmental treatments alone. Shoot competition had little effect on the growth of the two species, and thus, competition was concluded to occur predominately for below ground resources. Heather, in the building phase, was a superior competitor to bracken due to its extremely fine and invasive root system. Heather was able to compete with and deplete water from the roots of established bracken plants. Measurement of integrated of water use efficiency () and water use by droughted heather and bracken showed that the predicted environmental change scenarios are likely to cause an increase in the intensity of competition for water. There was no evidence of competition for nitrogen, despite nitrogen clearly limiting the growth of both species. The effects of the treatments on shoot phenology, morphology, photosynthetic physiology, biomass and below ground biomass have been examined. Above ground, heather was more responsive to the treatments imposed than bracken, having greater increases in shoot growth in favourable conditions, but greater decreases in shoot growth, and greater physiological acclimation, in stressed conditions, particularly drought in combination with increased nitrogen supply. Below ground, growth of bracken was extremely responsive whilst that of heather was not. However, even when bracken below ground growth was most stimulated, by increased nitrogen supply, it was still held in check by heather.

No description available.

A thesis submitted to the Faculty of Science in fulfilment of the requirements for the degree of Doctor of Philosophy. 30 August 2016 in Johannesburg, South Africa. / The presence of Portulacaria afra affects the flow of ecosystem services from the thicket landscapes of the Eastern Cape. Degraded and intact thicket ecosystems deliver different bundles of ecosystem services, and within each bundle the services are linked non-linearly, so that land-use and management decisions which seek to increase a particular service affect the delivery of other services. One of the challenges of restoring the historically degraded thicket areas is understanding the trade-offs between various objectives, including re-establishing biodiversity and critical services such as carbon sequestration, climate regulation, water provision and forage supply. This thesis uses a variety of techniques to assess some of these trade-offs at several spatial and temporal scales. The amount, rate and nature of carbon assimilation by P. afra at a variety of spatial and temporal scales are also explored. Methods At a landscape scale stream flow data from transformed and intact catchments, near Jansenville and Bucklands respectively, are used to compare the freshwater ecosystem services provided by the presence of P. afra. Similarly, at a landscape scale, the new high resolution Multi-angle Imaging SpectroRadiometer (MISR-HR) products are used to explore the differences in the surface energy budget of intact thicket and degraded ecosystems. Two simple radiative transfer models are used to assess the radiative forcing (RF) trade-off between carbon uptake-related global cooling and albedo-related global warming. From samples and measurements taken from a field site 15 km south-west of the town of Kirkwood, radiocarbon and stable carbon isotope analysis, growth ring analysis, dendrometry, infrared thermometry, water use efficiency and eddy covariance data are used to quantify the rate of carbon assimilation by P. afra, and unpack the contribution of C3- and CAM-derived carbon to total carbon sequestration. Results Intact thicket cover results in a higher total yield of water as a fraction of rainfall, fewer extreme high flow events, and a higher volume of low-flow in comparison to landscapes thought to represent transformed former thickets. Intact thickets have a lower albedo than degraded thickets. Restoring to an intact state will result in a mean albedo decrease of 5% (absolute) which constitutes a direct radiative forcing of +0.019 pW m-2 at a global scale. This warming effect overwhelms the climate benefit derived from carbon sequestration related to P. afra growth by a factor of 1.6. The growth data suggests that P. afra produces two growth rings annually on average, with the average growth increment of 0.8mm in diameter. The multi-year and multi-source aboveground relative growth rate mean is 0.006 (±0.005 SD) g DM per g DM per year, which is mean average increment about 1.1% per year. The eddy covariance data highlighted the temporal variability in the system, measuring intact P. afra thicket vegetation as a net source of carbon to the atmosphere 0.018 gC m-2 hr-1, over the three short-duration campaigns. CAM is now understood to come in several variants. The sampled stems, averaged across all rings, had a δ13C signature of -15.8±1.0 ‰ indicative of “strong CAM” behaviour. P. afra plants in the Kirkwood locality over the past decades have derived 61% of their carbon through the CAM pathway and 39% through the C3 pathway, with substantial inter-stem variation. The soil isotope data suggests 51 - 63% C3 derived carbon, with values increasing with sampling depth. There are occasional large excursions, always in a single growth ring, towards more negative δ13C values (-19.0‰); in other words towards the C3 range. Although thought to be related to water stress, it was hard to determine a single trigger for the switching between C3 and CAM modes. This is consistent with findings for other strongly CAM plants. From the dendrometers and infrared thermometry, P. afra shows flexible stomatal behaviour on a range of timescales. For the majority of the study period the stomata were open both day and night. There is variation in stomatal closure over the year, which appears strongly seasonal, and suggests a link to the bimodal rainfall pattern experienced in the region. Using decision tree to classify the photosynthetic mode, this data suggest that the individual plants being measured are spending only 4% of the time in classical CAM mode, and the majority of the time in CAM-cycling. Conclusions Restoration of transformed thicket will improve freshwater ecosystem services associated with useful water yield, sustained supply, and flood control. It is important to include land-atmosphere feedbacks other than carbon assimilation when assessing the climate service delivered by restoration. The negative and positive radiative forcing will operate over different timelines. CAM metabolism plays an important but not exclusive role in carbon gain. Contrasting patterns between plant and soil C3 fraction may relate to allocation issues and the contribution by plants other than P. afra. The growth rates of thickets are not substantially greater than similar water-limited ecosystems. / LG2017

Pixel based and object based vegetation community classification methods were performed using 30 meter spatial resolution Landsat satellite imagery of the Arthur R. Marshall Loxahatchee National Wildlife Refuge (Refuge), a remnant of the northern Everglades. Supervised classification procedures using maximum likelihood and parallelepiped algorithms were used to produce thematic maps with the following vegetation communities : wet prairie, sawgrass, cattail, tree island, brush, aquatic/open water. Spectral data, as well as NDVI, texture and principal component data were used to produce vegetation community classification maps. The accuracy levels of the thematic maps produced were calculated and compared to one another. The pixel based approach using the parallelepiped classification algorithm on the spectral and NDVI dataset had the highest accuracy level. A generalized form of this classification using only three vegetation communities (all wet prairie, tree island/brush and aquatic/open water) was compared to a previously published classification which used 1987 SPOT imagery in order to extract information on possible vegetation community transitions that are occurring within the Refuge. Results of the study indicate that 30 meter spatial resolution may be useful for understanding broad vegetation community trends but not species level trends. Pixel based procedures provide a more accurate classification than object based procedures for this landscape when using 30 meter imagery. Lastly, since 1987 there may be a trend of tree island/brush communities replacing wet prairie communities in the northern part of the Refuge and a transition to wet prairie communities in place of tree island/brush communities in the southern portion of the Refuge. / by Dorianne M. Barone. / Thesis (M.S.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, FL : 2008 Mode of access: World Wide Web.

Floodgates were constructed in 1971 on the main creek draining Hexham Swamp, a large wetland on the floodplain of the lower Hunter River, New South Wales. Substantial changes in vegetation have occurred in Hexham Swamp subsequent to the construction of the floodgates. Previous areas of mangroves and saltmarsh have been reduced (180ha to 11ha, and 681ha to 58ha, respectively), and Phragmites australis has expanded (170ha to 1005ha). Much of the mangrove loss (ca. 130ha) was a result of clearing, and the remainder has gradually died off. The factors contributing to the dieback are likely to be a combination of drying of the soil, root competition and, at times, waterlogging. Field sampling as well as microcosm and reciprocal transplant experiments involving key species, Sarcocornia quinqueflora, Sporobolus virginicus, Paspalum vaginatum and Phragmites australis, suggest that a reduction in soil salinity has been an important factor in initiating successional change from saltmarsh to Phragmites reedswamp. The data also suggest that increased waterlogging has been an important factor in initiating vegetation change. This apparently paradoxical result (floodgates and associated drainage generally result in drying of wetlands) is likely to have resulted from occlusion of drainage lines (by sediment and reeds) and is, therefore, likely to be a condition that developed gradually. That is, the initial effect of the floodgates is expected to have been a drying of the swamp, followed over time by an increasing wetness. An examination of vegetation changes after removal of cattle from part of Hexham Swamp, suggests that grazing had little effect on species composition of vegetation or rate of expansion of Phragmites australis. However, grazing does affect vegetation structure (height and density), possibly favours some coloniser species (e.g. Sarcocornia quinqueflora) in particular environmental conditions, and possibly inhibits establishment of Phragmites australis.