Academic literature on the topic 'Revegetation potential'

Thesis (MSc)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: A common topographical feature of the Nama-Karoo are mesas, commonly known as "platkoppies" , that provide an interesting source of landscape heterogeneity to an otherwise flat landscape. Although these isolated mesas are geologically and edaphically distinct from the surrounding flats, many species are shared between these habitats. These include palatable species such as Themeda triandra. A question asked by the broad umbrella project under which this project falls was: to what extent do mesas provide refuges for palatable species that are under pressure from heavy overstocking on the surrounding flats? A study on the regeneration potential of T triandra on and off the Tafelberg Mesa in the Middelburg district of the Eastern Cape, South Africa, was undertaken within the context of a broader umbrella project "Restoration of degraded Nama-Karoo: role of conservation islands". The Nama-Karoo has had centuries of heavy commercial livestock production and it is considered to have been transformed from a relatively (by arid ecosystems) productive system to one dominated by shrubs and somewhat less productive species. Themeda triandra is one of the preferred grass species for livestock production. Although T. triandra is a preferred grass species, relatively, little is known about its ability to produce viable seed and the establishment of seedlings particularly in restoration and rehabilitation programmes. This study examines the pattern of seed production and seedling survival, seed dispersal, seed germination, and the morphological and ecophysiological variability of T. triandra, a species with great potential for restoration of degraded Nama-Karoo sites, particularly those in the Eastern Cape. Themeda triandra was found to be one of the dominant species on summit of the Tafelberg Mesa. In comparison, it occurred in small isolated populations on the flats surrounding the mesa. The flats and slopes are grazed more intensely by domestic livestock than the summit of the mesa. This is due to the inaccessibility to livestock due to a steeper topography and the lack of water at the higher altitudes. Annual seed production of T. triandra per plant and per m2 was highest for the populations on the flats despite these populations being grazed most intensively. Rainfall had an effect on annual seed production, which was monitored over two years. Rainfall increased from less than 20mm in November 1999 to 125, 110, 50 and 135mm in December 1999, January 2000, February 2000 and March 2000 respectively. With the increased rainfall prior to the May 2000 sampling period, more seeds were produced per plant and per m2 for the flats and slopes habitats of the Tafelberg Mesa. The opposite trend occurred on the summit of the mesa, where seed production actually decreased. This could be attributed to increased competition or to lower grazing intensities. Increase in rainfall also had a positive effect on the cover of other grasses (excluding T. triandra) and T. triandra itself. Despite higher levels of seed production in populations of T. triandra on the flats, seedling survival was clearly low whereas seedlings on the slopes and summit had significantly higher seedling survivorship. This negative impact could be explained due to the trampling effect of domestic herbivores. The results of a seed dispersal experiment clearly suggest that the seed dispersal distance of T. triandra to "safe" microsites is short distance (majority of seeds disperse up to 60cm) and that the dispersal agent is wind. Microsites for re-establishment was found to be open or rocky sites. In a controlled experiment, seed emergence of T. triandra indicated that optimal sowing depths varied with soil type. Maximum germination was achieved at sowing depth 2cm and 3cm in soil collected from the flats surrounding the Tafelberg Mesa. The soil texture of the flats was found to be more sandy loam clay. The flats had slightly higher content (%) of stone, clay, silt and sand compared to the soils collected from the summit and slopes. Themeda triandra is clearly not limited in its expansion onto the flats in the Middelburg district due to soil conditions at the germination/recruitment phase. This study also revealed that T. triandra germinates best under summer conditions when the probability of rainfall is at its highest. Results with T. triandra seed did not convincingly suggest that smoke water is of adaptive significance to boost germination in restoration attempts in the Middelburg district of the Eastern Cape. In a controlled greenhouse experiment, individuals of T. triandra taken from the summit of Tafelberg Mesa showed no differences in photosynthesis, stomatal conductance or transpiration rates to individuals occurring on the flatland areas surrounding the mesa. Themeda triandra appears to be relatively adaptable to a range of temperature conditions. These findings suggest that there should be no problem using seed from mesa summits in restoration programmes on the surrounding flats. This study revealed no conclusive evidence, indicating that the populations on the summit of the mesa were a source of T. triandra seed for the flats surrounding the Tafelberg Mesa. However, this two year long investigation found that T. triandra has the potential to be used in restoration and rehabilitation programmes. If released from grazing pressures, and assuming favourable climatic conditions, the density of T. triandra on the flats can be increased and can be used as a suitable species for the restoration of heavily degraded patches in the Nama-Karoo Region.
AFRIKAANSE OPSOMMING: OnAlgemene topografiese kenmerk van die Nama-Karoo is mesas, plaaslik bekend as "platkoppies", wat Oninteressante bron van landskap ongelyksoortigheid voorsien aan On andersins vlakte landskap. Alhoewel hierdie geisoleerde mesas geologies en biofisies verskillend is van die omliggende vlaktes, word baie plant spesies gedeel tussen hierdie habitats. Hierdie sluit in smaaklike spesies soos Themeda triandra. OnVraag gevra deur die groter restorasieekologieprojek waaronder hierdie navorsingsprojek resorteer was: tot watter mate dien mesas as ° n hawe aan vreetbare spesies wat onder druk is van swaar oorbeweiding in die omliggende vlaktes? OnStudie van die regenerasie potensiaal van T. triandra op-en-vanaf die Tafelberg Mesa in die Middelburg distrik van die Oos-Kaap, Suid-Afrika, was onderneem binne die verband van die wyer herstelekologieprojek "Herstel van oorbeweide Nama-Karoo weiveld: die rol van bewaringseilande". Die Nama-Karoo was vir honderde jare al blootgestel aan swaar kommersiële lewende hawe produksie en is klaarblyklik verander van ° n relatiewe produktiewe sisteem na 'n ekosisteem gedomineerd deur struike en enigsins minder produktiewe spesies. Alhoewel dit ° n verkiesde grasspesie is bo ander inheemse grasse as weigras, is min bekend oor die fertiliteit van T. triandra sade of oor die vestiging van saailinge, veral in veldrehabilitasie programme. Hierdie studie ondersoek die patrone van saadproduksie, saadverspreiding, saadontkieming, en die morfologiese en ekofisiologiese veranderlikheid van T. triandra, ° n spesie met groot potensiaal vir die herstel van oorbeweide Nama-Karoo terriene van veral die Oos-Kaap. Themeda triandra was een van die dominante spesies op die kruin van die Tafelberg Mesa. Dit kom voor in klein geïsoleerde populasies op die uitgestrekte vlaktes rondom die mesa. Die vlaktes en hange van die mesa word op groot skaaloorbewei deur lewende hawe in vergelyking met op die kruin van die mesa. Dit is te wyte aan die onbereikbaarheid van die mesa vanweë Onsteiler topografie, asook die gebrek aan standhoudende water op die mesa's self. Jaarlikse saad produksie van T. triandra per plant en per m2 was die hoogste vir die populasies op die vlaktes, ten spyte daarvan dat hierdie populasies intensief bewei word. Reënval het 'n effek op jaarlikse saad produksie gehad wat oor twee jaar gekontroleer was. Met die vermeerdering van reënval voor die Mei 2000 proeftydperk, was meer sade geproduseer per plant en per m2 op die vlaktes en hange van die Tafelberg Mesa. Die teenoorgestelde patroon het voor gekom op die kruin van die mesa, waar saadproduksie afgeneem het. Laasgenoemde kan toegeskryf word aan die toename in kompetisie. Toename in reënval het ook 'n positiewe effek gehad op die bedekking van T. triandra self sowel as van ander grasse. Ten spyte van hoër vlakke van saadproduksie, is saailing oorlewing in T. triandra populasies op die vlaktes duidelik negatief terwyl saailinge op die hange en kruin 'n betekenisvolle hoër saailing oorlewingsskap gehad het. Die negatiewe impak kan verduidelik word deur die vertrappings-effek van lewende hawe. Die resultate van die saadvespreidingeksperiment toon dat die saadverspreiding afstand van T. triandra na 'veilige' mikroterreine kort is (die meerderheid van die sade is tot minder as 60cm versprei). Wind is die verspreidingsagent. Dit is gevind dat oop of klipperige terreine gunstige mikroterreine vir hervestiging van T. triandra is. In die gekontroleerde-eksperiment het saadverskyning van T. triandra aangedui dat die optimale saai-diepte wissel met grondsoort. Maksimum ontkieming is behaal by saaidiepte van 2cm en 3cm in die grond versamel in die vlaktes rondom die Tafelberg Mesa. Die grondtekstuur op die vlaktes is 'n sanderige leem-klei. Die vlaktes het effens hoër persentasies klip, klei, slik en sand vergelyke met die grond versamelop die kruin en hange. Themeda triandra is duidelik nie as gevolg van grondtoestande beperk in sy uitbreiding op vlaktes in die Middelburg distrik by die ontkieming/werwing fase. Gondtoestande tydens die ontkiemingsfase is duidelik niw beperkend op die gigthede van T. triandra op die vlaktes nie. Hierdie studie maak bekend dat T. triandra die beste ontkiem onder somer toestande wanneer die waarskynlikheid van reënval op sy hoogste is. Rookwater het geen effect op die ontkiemingspotensiaal van T. triandra in die Middelburg streek van die Oos-Kaap nie. Pogings om T. triandra saad se ontkieming met rookwaterekstrak te bevorder was onsuksesvol. In die gekontroleerde eksperiment het individue van T. triandra op die kruin van Tafelberg Mesa geen verskil getoon in fotosintese, huidmondjie begeleiding en transpirasie tempo nie in vergelyking met individue wat voorkom op die vlaktes rondom die mesa. Themeda triandra blyk relatief aanpasbaar te wees aan 'n wye reeks van temperatuur toestande. Hierdie bevindings dui aan dat daar geen probleem hoef te wees om sade van die kruin van die mesa te gebruik in hervestigig-programme in die omliggende vlaktes nie. Hierdie studie verskaf geen bewyse wat aandui dat die T. triandra bevolkings op die kruin van die mesa as Onbron van saad vir die vlaktes rondom die Tafelberg Mesa dien nie. Hierdie twee-jaar ondersoek vind dat T. triandra 'n potensiaal het om gebruik te word in herstel en rehabilitasie programme. As dit aan ligter weidingsruk onderwerp is en gunstige klimaatstoestande heers, kan T. triandra hervestig word op die vlaktes en gebruik word as Onplantspesie om erg beskadigde areas in die Nama-Karoo streek te herstel.

This thesis is a comparative study of the life history strategies, and in particular seed germination requirements, in Australian species of the halophyte plant genus Frankenia L. (Frankeniaceae). Frankenia is a cosmopolitan genus that occurs in Mediterranean, semi-arid, and arid regions on distinctive soil types – commonly on saline, sodic or gypseous soils – in habitats such as coastal cliffs, and on the margins of salt lakes, salt-pans and saltmarshes (Summerhayes 1930; Barnsley 1982). The plants are small shrubs or cushion-bushes with pink, white or pale purple flowers, and salt-encrusted recurved leaves. This project investigates germination requirements for Frankenia in relation to seed age, light requirements, temperature preferences, salinity tolerance, and soil characteristics. It also explores two divergent reproductive strategies – notably seed packaging strategies – in relation to environmental variables. Within the 46 currently recognized endemic Australia species, some species have a few ovules per flower and produce only a few larger seeds per fruit, while other species have many ovules per flower and produce many small seeds per fruit. Large-seededness is thought to increase the probability of successful seedling establishment in drought and salt-stressed environments. As both larger- and smaller-seeded species of Frankenia co-occur in close geographical proximity, hypotheses regarding the advantages of large-seededness in stress environments can be tested. By restricting the analysis of seed mass variation to similar habitats and within a single plant genus, it is possible to test ecological correlates that would otherwise be masked by the strong effects of habitat differences and phylogenetic constraints. Overall, larger-seeded Frankenia species were demonstrated to be advantageous for rapid germination after transitory water availability, and for providing resources to seedlings if resources became limiting before their successful establishment. Smaller-seeded species delayed germination until both soil-water availability and cooler temperatures persisted over a longer time period, improving chances of successful establishment for the more slowly growing seedlings that are more reliant on their surroundings for resources. This study produces information on the seed and seedling biology of many Australian species of Frankenia including several that are of conservation significance, e.g. F. crispa with its isolated populations, and the rare and endangered F. plicata. This information is important for the development of conservation management plans for these and other arid zone, halophyte species. In addition, the results of this study are of practical significance in determining the suitability of Frankenia for inclusion in salinity remediation and mine-site rehabilitation projects, and for promoting Frankenia as a drought and salt tolerant garden plant.

Thesis (MScConsEcol(Conservation Ecology and Entomology)--University of Stellenbosch, 2007.
Riparian areas are highly complex systems with varying levels of disturbance that are highly susceptible to invasion by alien plants. Once invaded, riparian areas play a major role in the dispersal and spread of invasive alien plants (IAPs) through the river system and, in some cases, to neighbouring landscapes. Riparian areas have therefore been prioritized by many alien clearing initiatives in South Africa. Current practice for the restoration of cleared areas is minimal and relies mainly on the un-aided recovery of native species from residual individuals and soil stored seed banks. Little research, however, has been done on the effectiveness of this approach or the extent to which riparian seed banks contribute towards community restoration. This study is part of a national research initiative (Targets for Ecosystem Repair in Riparian Ecosystems in Fynbos, Grassland and Savanna Biomes) funded by Department of Water Affairs and Forestry, in collaboration with Working for Water, The Centre for Invasion Biology and the Universities of Cape Town, Stellenbosch, Rhodes and Witwatersrand. The initiative undertook to investigate different restoration techniques on various invaded sites for their cost-effectiveness, efficiency, practicality and conservation integrity. This study has three aims. The first is to determine the composition of seed banks in un-invaded riparian areas within the fynbos biome to be used as a benchmark for future research, restoration grading and other management requirements. The second aim is to determine the composition of seed banks in heavily invaded riparian areas, and thus to assess the impact of invasion on the integrity of the seed banks. The third aim is to evaluate the restoration potential of riparian seed banks following the clearing of invasive alien plants (IAPs). Study sites were selected within four river systems in the south-western part of the Western Cape Province in South Africa: the Berg, Eerste, Molenaars and Wit Rivers. Plots were selected in both invaded (>75% IAP canopy cover; considered “closed” alien stands) and un-invaded (also termed reference, with <25% IAP canopy cover) sections of the river. Replicate plots were established along varying gradients of elevation (mountain stream and foothill) and moisture regimes (dry, wet and transitional bank zones). Soil samples were collected together with above-ground vegetation surveys and comparisons were made. Results from this study confirm those of previous studies that seed banks offer little reference to current aboveground vegetation, but rather offer insight into past vegetation history as well as future vegetation assemblages. Worldwide, many of the species that characteristically form seed banks are early successional species. A community study was done for the seed bank based on the species that germinated and were identifiable at termination of the project (6 months after initiation). Three clusters of species could be identified. One group comprised 32 generalist species that occurred in both reference and invaded sections of the rivers. A second group comprised 39 species associated with invaded sites, and a third group of 40 species that was associated with reference sites. A few sub-community groups were found within both the “reference” and “invaded” community groups which were assumed to be habitat specific. Most species were “pioneer” or relatively-short lived, early-successional species which play a vital role in the initial post-disturbance vegetation cover, and facilitate establishment of later successional species. Seed banks are notoriously variable over space and time, and floristic representation is often biased as a result of differences among species in seed production, dispersal and longevity in the soil. The general consensus is that seeds have an irregular, clustered spatial distribution that is dictated by both biological and environmental factors. Within river systems, the irregular clustering can be exceptionally skewed with the influence of pockets of high sediment deposition along the bank. Environmental factors that were found to significantly skew germination results were the presence of fire, as well as the extent and intensity of invasion (duration and cover). The high level of diversity and abundance in reference Berg River mountain stream seed banks was perceived to be a direct result of a moderate fire frequency (between 8-15 years) and the relatively natural state of the vegetation (i.e. very little invasion). Also, diversity and richness of indigenous species from the Wit and Molenaars Rivers were substantially higher in the invaded samples than the reference samples, probably because both river systems have a long history of invasion and other anthropogenic disturbances which would have an effect on the samples from “reference” sections (i.e. even a 25% presence of IAPs seems adequate enough to alter the composition of the seed bank). Correspondence analyses showed that species had clear affinities towards different levels of “key” riparian environmental variables (fire, invasion and anthropogenic disturbance). Most species were associated with moderate levels of fire frequency, invasion history, and anthropogenic disturbance. Comparisons of seed bank species assemblages between the lateral and longitudinal variables of the rivers offered insights into the habitat requirements of certain fynbos and riparian species. Most significant were the results from bank zone comparisons which showed distinct species groupings along the different moisture bands. As could be expected, riparian species were best represented within the wet bank zones and fynbos species within the dry bank zone, while species characteristic of both zones occurred in the transitional zone, making this seed bank zone the richest in species. Mountain stream sections were richer and more diverse than foothill sections over both invaded and reference samples. This is hypothesised to be linked to lower levels of anthropogenic disturbance experienced in the mountain stream sections. The impact of invasion on the riparian seed bank was most clearly shown through the correspondence analyses for the 20 most frequently occurring species. The seed bank assembly patterns were clearly defined by the state of the river (reference or invaded). Interestingly, this pattern was evident at all three spatial scales; landscape (rivers), reach (mountain stream and foothill sections) and habitat (dry, wet and transitional zones). The reference seed bank assemblage was more tightly grouped, implying that the species were more closely associated with each other and less variable than those of the invaded seed bank assemblages. The species groupings within the invaded seed banks were influenced by variables such as reach and zone, whereas the reference seed bank assemblages seem relatively unaffected by these variables. This implies that the presence of invasive alien plants creates additional variation within the seed bank which alters the natural groupings. At a broad scale, the invaded seed banks were less species rich. This means that not only will the resulting seedling community be harder to predict, but it will also have fewer species. However although generally lower in species richness, the seed banks from almost all invaded rivers interestingly showed a higher diversity of indigenous species than their reference counterparts. This is very promising in terms of rehabilitation of post-cleared riparian sites, but more information is needed to understand the seed bank composition and determine how sustainable the seed banks are for rehabilitation in the long-term. All invaded sections had fewer herbaceous perennial species but more herbaceous annual species. Graminoids made up 50% or more of the seed bank regardless of state (reference or invaded), while woody species (shrubs/shrublets) were generally more prevalent in the reference samples. These results imply that following the removal of invasive alien plants, the vegetation to regenerate from the seed bank is likely to comprise of short-lived, herbaceous species that are not necessarily an accurate reflection of the indigenous riparian community. It is however important to note that this study investigated only the species that were able to germinate over the study period (6 month germination period). Many riparian species may not have been represented because they are either late germinators or may not be present in the soil seed bank at all. In order to gain a holistic understanding of riparian community recruitment, it is recommended that seed bank studies such as this one be included in a more broad scale, long term investigation which takes into account various reproductive strategies used by riparian species. Research of this nature is in its infancy worldwide and there are many challenges involved in measuring diversity and change in these systems. However, within the scope of this study, I suggest that these results shed light on previously unanswered and important questions regarding the ecology of seed banks in the riparian ecosystems of the Western Cape.

The objectives of this research were to 1) evaluate the establishment and peak standing crop of Berber Orchardgrass (Dactylis glomerata var. "Berber"), Palestine Orchardgrass (Dactylis glomerata var. "Palestine"), and Sheep Fescue (Festuca ovina var. "Covar") ; 2) to assess establishment and production changes resulting from environmental gradients (elevation, slope, aspect, soil texture, precipitation, and resident annual community) across the foothill landscape; 3) develop a mathematical model that predicts site potential for restoration; and 4) evaluate the utility of Geographic Information Systems for creation and analysis of spatial data which identify site production potential. Sixteen sites were chosen which reflect the general character of the foothill rangelands in southwestern Oregon. A Randomized Complete Block design was used to select treatment arrangement on each site. Seeded treatments received both chemical (Glyphosate, Hoelon, and 2,4-D) and mechanical (residue removal) disturbance. Test species were seeded into three replications at each site. Each replication also included a non-treatment control. Standing crop data for test species and resident exotics were collected after three growing seasons. Berber orchardgrass did not establish at most sites and where establishment did take place production was less than 132 kgDM/ha. Palestine orchardgrass established on on a majority of the study sites and produced most aboveground phytomass at mid-elevations where coarser soil textures and deeper soil depths were common. Sheep fescue was the most successful of the three test species and did best on low elevation high clay sites. There was significantly (P=0.001) more phytomass produced by annual exotics on seeded plots than on undisturbed controls at most sites. Both Palestine orchardgrass and sheep fescue treatments significantly suppressed the annual exotics when compared to the Berber treatments. Generally, "Covar" sheep fescue can establish and successfully compete with exotics on heavier textured soils at low elevations. "Palestine orchardgrass is adapted to mid-elevation coarser soils.
Graduation date: 1995