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Vegetation patterns and dynamics of Renosterveld at Agter-Groeneberg Conservancy, Western Cape, South AfricaWalton, Benjamin Alan 03 1900 (has links)
Thesis (MSc (Conservation Ecology and Entomology)--University of Stellenbosch, 2006. / Swartland Shale Renosterveld is restricted to fertile fine-grained soils in the winter rainfall region of
the Western Cape. Between 91% and 97% of this vegetation type is transformed, mostly due to
agriculture. Remaining fragments have an irreplaceable conservation value due to a high richness of
endemic geophytes. Information on renosterveld vegetation composition and response to
disturbance is sparse. Research occurred at three sites near Wellington: Voëlvlei Provincial Nature
Reserve (CapeNature), Elandsberg Private Nature Reserve (Elandsberg Farms (Pty.) Ltd.), and
Krantzkop munitions factory (Armscor/Somchem) forming a contiguous fragment in the Agter-
Groeneberg Conservancy. The primary research aim was to identify or ascertain patterns of plant
succession in Swartland Shale Renosterveld and associated different-aged old fields (previously
ploughed), with the interaction of grazing. The key research questions are: (1) What are the plant
communities of unploughed renosterveld and different-aged old fields which originated in habitats
of ploughed renosterveld? (2) What are the most characteristic features of the floristic and
ecological relationship between the described plant communities in terms of ecological factors
operating within the studied system? (3) Does total species and life-form group richness differ
between natural vegetation and old fields? (4) Is life-form richness influenced by ploughing and
grazing or the interaction between these disturbances? (5) Is life-form cover-abundance influenced
by ploughing and grazing or the interaction between these disturbances? (6) Does alien plant
species richness differ amongst seres, and with different levels of grazing intensity? A comparison
of life-form richness and cover-abundance of old field vegetation was made with adjacent natural
unploughed “controls”. The effects of ploughing on community structure, with the inclusion of
grazing was established. These life-form richness comparisons also occur across a gradient of
increasing large mammalian herbivore grazing intensity. Sampling was conducted in winter and
spring using nested 1000m2 relevés.
A hierarchical classification, description and floristic interpretation of renosterveld and old field
vegetation were made using TWINSPAN, SYN-TAX 2000 and CANOCO. The samples were
classified with TWINSPAN and two communities were described at the association level, namely:
Ursinia anthemoides–Cynodon dactylon Grassland Community (with two variants) and the
Pterygodio catholici–Elytropappetum rhinocerotis Shrubland Community (with two subassociations),
respectively. The vegetation data were further hierachically classified using SYNTAX
2000 which revealed similar clustering of sample objects to that resulting from classification and ordination. Following ordination of sample objects with CANOCO, select groups of species
were used to depict their response curves in relation to seral development.
Briefly it was found that the effects of grazing vs. non-grazing was more pronounced on old fields
than in unploughed vegetation. Overall total species and life-form richness was reduced by
ploughing with old fields requiring a recovery period of 30 years to resemble unploughed
vegetation.
Keywords: Swartland Shale Renosterveld, phytosociology, vegetation patterns, life-forms,
succession, disturbance, ploughing, grazing, old fields.
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Spatial patterning and demography in Strandveld succulent Karoo : implications for biodiversity managementCheney, Chad (Chad Crispian) 12 1900 (has links)
Thesis (MSc) -- University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis focuses on the effects of vegetation resting on biodiversity and community
dynamics at Rocherpan Nature Reserve (320 36'S, 180 18'E) in the semi-arid coastal strip of
the Succulent Karoo known as Strandveld. As a whole, the Succulent Karoo has an
extraordinary high level of phyto diversity with high levels of endemism. This is particularly
true for succulent shrubs belonging to the groups Mesembryanthemaceae, Crassulaceae and
Asteraceae.
The thesis begins with an investigation into effects that vegetation resting has on plant
diversity. The aim was to determine if resting affected biodiversity levels and if so, which
plant groups are affected and why. Through a numerical approach, it was determined that
with resting overall species richness remained the same. However, different plant life forms
responded to resting differently. With increased resting, abundance of succulent shrubs
decreased, while richness of annuals increased.
The second aspect under investigation was to determine how resting the vegetation affected
community dynamics. The aim was to understand how vegetation structure and interspecific
associations changed with resting and to apply these findings to known community models.
Through an autocorrelation approach, it was found that horizontal patterning of long-lived
woody species, that formed distinctive vegetation clumps, did not change with resting, while
differences were found in woody matrix species and succulent species. These changes in
structure were investigated further through a study on the demography of specific species.
Demography of woody species associated with vegetation clumps did not change with
vegetation resting, while significant changes were observed for woody matrix species and
succulent species. In longer rested vegetation, woody matrix species showed a greater range in
size class distribution (i.e. had both very large and smaller plants) with the tendency towards
larger plant sizes. Succulents on the other hand, had a smaller range in size class distribution
with a tendency towards larger plants. For all species investigated there were low seedlings
counts. It was concluded that succulent shrub populations were 'mature' and continued resting
could result in local extinction of some species due to the lack of regeneration. The overall
lack of seedlings was attributed to a saturated establishment environment. Implications for
conservation management were discussed. / AFRIKAANSE OPSOMMING: Hierdie tesis fokus op die gevolge van plantegroeirus op biodiversiteit en
gemeenskapsdinamika by die Roeherpan Natuurreservaat (320 36'S, 180 18"0) in die halfdor
kusstrook van die Sukkulente Karoo, bekend as die Sandveld. In die geheel gesien het die
Sukkulente Karoo 'n buitengewone hoë vlak plantdiversiteit met hoë vlakke endemie. Dit is
veral waar vir sukkulente struike wat tot die groepe Mesembryanthemaceae, Crassulaceae en
Asteraceae behoort.
Hierdie tesis ondersoek eerstens die gevolge wat plantegroeirus op plantdiversiteit het. Die
doel was om te bepaal of rus die biodiversiteitsvlakke beïnvloed het en indien wel, watter
plantgroepe en waarom. Deur middel van 'n numeriese benadering is bepaal dat die algehele
diversiteit, numeries gesproke, met plantegroeirus dieselfde gebly het. Verskillende
plantlewensvorme het egter verskillend gereageer. Met toenemende rus het die diversiteit van
sukkulente struike afgeneem, terwyl die diversiteit van jaarplante verhoog het.
Die tweede aspek wat ondersoek is, was om te bepaal hoe die plantegroeirus die dinamika van
die omgewingsgemeenskap beïnvloed het. Die doel was om te verstaan hoe die struktuur van
die plantegroei en die interspesifieke assosiasies verander het met rus en om dan hierdie
bevindinge toe te pas op bekende gemeenskapsmodelle. Deur middel van 'n outokorrelasiebenadering
is gevind dat die horisontale patrone van meerjarige houtagtige spesies wat in
duidelik-uitkenbare plantegroeigroeperings voorkom, nie met rus verander het nie.
Veranderinge is egter wel in die houtagtige matriksspesies en die sukkulente spesies
waargeneem. Hierdie veranderinge in struktuur is verder ondersoek deur 'n studie te maak van
die demografie van spesifieke spesies. Daar is gevind dat die demografie van houtagtige
spesies geassosieer met plantegroeigroeperings nie met plantegroeirus verander het nie, maar
beduidende veranderinge is waargeneem in die geval van houtagtige matriksspesies en
sukkulente spesies. By plantegroei wat langer gerus het, het die houtagtige matriksspesies 'n
wyer verspreiding in klasgroottes vertoon (d.i. daar was baie groot plante én kleiner plante)
met 'n gemiddelde afname in plantgrootte. Sukkulente, aan die ander kant, het 'n kleiner
verspreiding in klasgroottes vertoon met 'n neiging tot groter plante. Vir al die spesies wat
ondersoek is, was daar lae saailingtellings. As gevolg van die "volwassenheid" van die
populasies van sukkulente struike, sou voortdurende rus, weens die gebrek aan regenerasie, kon lei tot die plaaslike uitwissing van sommige spesies. Die algemene gebrek aan saailinge is
toegeskryf aan die versadigde vestigingsomgewing. Die implikasies VIr
natuurbewaringsbestuur word bespreek.
v
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A historical perspective on recent landscape transformation: integrating palaeoecological, documentary and contemporary evidence for former vegetation patterns and dynamics in the Fleurieu Peninsula, South AustraliaBickford, Sophia Anastasia. January 2001 (has links) (PDF)
Includes bibliographical references (p. 301-319). Palaeoecological records, documented historical records and remnant vegetation were investigated in order to construct a multi-scaled history of vegetation pattern and change in the Fleurieu Peninsula, South Australia over the last c. 8000 years. Aims to better understand post-European landscape transformation and address the inherently historical components of the problems of regional biodiversity loss, land sustainability and the cumulative contribution to global climatic change.
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A historical perspective on recent landscape transformation: integrating palaeoecological, documentary and contemporary evidence for former vegetation patterns and dynamics in the Fleurieu Peninsula, South Australia / Sophia Anastasia Bickford.Bickford, Sophia Anastasia January 2001 (has links)
Includes bibliographical references (p. 301-319). / xx, 319, [30] leaves : ill. (some col.), maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Palaeoecological records, documented historical records and remnant vegetation were investigated in order to construct a multi-scaled history of vegetation pattern and change in the Fleurieu Peninsula, South Australia over the last c. 8000 years. Aims to better understand post-European landscape transformation and address the inherently historical components of the problems of regional biodiversity loss, land sustainability and the cumulative contribution to global climatic change. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geographical and Environmental Studies, 2001
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Photorealistic visualisation of urban greening in a low-cost high- density housing settlement.Donaldson-Selby, Gavin Hugh. January 2005 (has links)
Apartheid housing policies of the pre-1994 South African government, and the low-cost highdensity housing programmes of the post-1994 government, has given rise to numerous urban environmental problems, some of which could be addressed in a cost-effective and sustainable manner through urban greening, while simultaneously promoting biodiversity. Public participation in the planning of urban greening has been identified as being of vital importance, without which urban greening projects run a high, and expensive, risk of failure. Previous studies indicate that the greening priorities of residents in low-cost high-density housing settlements may differ considerably from those of managers and experts tasked with the protection and extension of the natural environment resource base. A system of participatory decision support is therefore required to reconcile the greening requirements of the community, and the ecological benefits of biodiversity. If language, literacy, map literacy and numeracy difficulties are to be avoided, and a sense of place or belonging is to be invoked, such a participatory decision support system should, ideally, be visually based, and capable of generating realistic eye-level depictions of the urban landscape. New computer-based landscape visualisation applications, which can directly utilise GIS, CAD and DEM data to produce detailed photo-realistic viewsheds, were deemed better suited to the task of visualising urban greening than existing GIS based mapping systems, CAD and traditional landscape visualisation methods. This dissertation examines the process of constructing a 3D computer model of the Mount Royal low-cost high-density housing settlement, situated in the eThekwini Municipality, KwaZulu-Natal, South Africa. Visualisations including terrain, natural features, indigenous vegetation, houses and roads were produced and submitted, with a questionnaire, to experts from different disciplines, Mount Royal residents and neighbors. Results from the expert survey indicate moderate support for visualisation in professional decision-making. However, both experts and residents expressed strong support for the accuracy and credibility ofthe visualisations, as well as for their potential in a participatory decision support system. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
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An assessment of the effect of season of grazing, stocking rate and rainfall on the dynamics of an arid rangeland on the west coast of South Africa.West, James Alexander. January 2005 (has links)
A grazing trial investigating the effect of season of grazing and stocking rate initiated
at the Nortier Experimental Farm in 1988 provided an opportunity to assess the
response of the veld to both grazing and environmental influences in an arid
environment. The trial allowed an assessment of the relative influence of internal
(equilibrium) and external (non-equilibrium) forces on the dynamics of an arid
rangeland. This study involved the analysis of a nine year data set stretching from
1988 to 1996 and served to provide evidence supporting the existence of an
equilibrium/non-equilibrium continuum in rangeland dynamics. The most significant
implication of this result is that rangeland systems should not be classified as either
equilibrial or non-equilibrial, but rather according to a continuum extending between
equilibrium and non-equilibrium poles. The exact position of any system on this
continuum is a function of the relative influence of internal and external forces on its
species dynamics.
The dynamics of the veld at the Nortier Experimental Farm showed significant
response to both grazing and environmental variables suggesting conformity to both
equilibrial and non-equilibrial paradigms. Both ordination and analysis of variance
highlighted the importance of rainfall particularly in the fluctuations of the
predominant grass species, Ehrharta calycina, which increased in abundance with
rainfall. Partial ordination enabled the assessment of species variation following the
removal of variation associated with rainfalL Partial ordinations revealed the gradual,
directional movement of samples through multivariate space in response to grazing
treatments. Individual plant species were also shown to be responding to grazing, the
extent of which was influenced by season of grazing and stocking rate.
Both the partial ordinations and the ANOVA showed Melothria sp., Tetragonia
fruiticosa and Hermannia scordifolia as increasing and Ruschia caroli as decreasing
in absolute abundance in response to grazing. Season of grazing was shown to
significantly influence the abundance of H. scordifolia over time.
The 'shrublherb complex', which constitutes the 'key resource' at the Nortier
Experimental Farm displayed an increase in absolute abundance over the duration of
the trial. This increase in absolute abundance was accompanied by an increase in the
relative abundance of the palatable component of this resource. The application of
medium to heavy stocking rates during spring, summer and autumn and low stocking
rates during winter resulted in elevated absolute abundances of palatable plants.
Furthermore, low stocking rates, when averaged across all season of grazing
treatments, resulted in a significantly higher absolute abundance of unpalatable plants.
These findings provide the basis for the development of management principles for
the Strandveld Vegetation Type.
The application of medium to heavy stocking rates within a rotational grazing system,
as recommended by the literature dealing with grazing systems in the Karoo, is
supported by the results of the Nortier grazing trial. Medium to heavy stocking rates
should be applied during spring, summer and autumn and low stocking rates during
the winter months. Furthermore, it is recommended that rests of between 12 and 14
months should be afforded to portions of the veld periodically due to the variability in
growth, flowering and fruiting times ofdifferent plants in the Karoo. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
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Quantifying thresholds for native vegetation to salinity and waterlogging for the design of direct conservation approachesHorsnell, Tara Kathleen January 2009 (has links)
A field-based project was undertaken to develop and test a mechanism which would allow for the correlation of the health of vegetation surrounding playa lakes in south-west Australia with the natural variation in salinity and waterlogging that occurs spatially and temporally in natural systems. The study was designed to determine threshold ranges of vegetation communities using moderately extensive data over short temporal periods which will guide the design of potential engineering solutions that manipulate hydrological regimes to ultimately conserve and protect native vegetation. A pair of playa lake ecosystems, surrounded by primary production land, was modelled with hydro-geological data collected from March 2006 to March 2007. The data was used to determine the hydroperiods of vegetation communities fringing playa lakes and provide insight into the areas and species that are most affected by extreme rainfall events which are hypothesised to have a significant, rapid deleterious effect on the ecosystems. The methodology was multi-faceted and included; a detailed topographical survey; vegetation surveys; hydrological and hydro-geological monitoring over a 12 month period. 4 The hydro-geological data and vegetation data was linked with the topographical survey at a high resolution for spatial analysis in a Geographic Information System (GIS) to determine the degree of waterlogging experienced by vegetation communities over the monitoring period. The study has found that the spatial and temporal variability of hydroperiods has been reduced by rising groundwater levels, a result of extensive clearing of native vegetation. Consequently populations are becoming extinct locally resulting in a shift in community composition. Extreme summer rainfall events also have a significant impact on the health of vegetation communities by increasing the duration of waterlogging over an annual cycle and in some areas expanding the littoral zone. Vegetation is most degraded at lower positions in the landscape where communities are becoming less diverse and dominated by salt tolerant halophytic species as a result of altered hydrological regimes. Some species appear to be able to tolerate groundwater depths of less than 2.0 m from the surface, however there are thresholds related to the duration at which groundwater is maintained at this depth. Potential engineering solutions include groundwater pumping and diverting water through drains to maintain sustainable hydroperiods for vegetation in areas with conservation value. The effectiveness and efficiency of the engineering solutions can be maximised by quantifying thresholds for vegetation that include sustainable durations of waterlogging. The study has quantified tolerance ranges to salinity and waterlogging with data collected over 12 months but species may be experiencing a transition period where they have 5 sustained irreversible damage that will result in their eventual mortality. With long-term monitoring, the methodology developed and tested in the study can be used to quantify the long-term tolerance ranges that are important for the application of conservation approaches that include engineering solutions.
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Response of aquatic macroinvertebrate and aerial odonate assemblages to the removal of invasive alien trees in the Western CapeSharratt, Norma 12 1900 (has links)
Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Invasive alien trees, especially Acacia species, are a great threat to biodiversity in South African
rivers. The national Working for Water Programme is addressing the alien problem by removing
alien trees from river margins. The concern is that this may be creating even further disturbance
by affecting water quality and habitats. In particular, how is this affecting rare and endemic
species? Benthic macro invertebrates and aerial odonates were assessed along five Western Cape
rivers in alien-invaded, cleared and natural sites between December and March. The aim was to
assess the effect of both alien invasion and alien clearing on aquatic invertebrates. Odonata, being
easily sampled, were also assessed as they are severely affected by the lack of understorey plants
in shaded, alien-invaded sites. Odonata and benthic macroinvertebrates were treated as two
separate studies and no attempt was made to correlate the results obtained from both studies.
SASS5, a qualitative, rapid bioassessment technique, based on the sensitivity of the families
present, was used as a measure of river health and, indirectly, of water quality. SASS indicated a
decline in water quality conditions after alien clearing, a likely response to the greater insolation
as well as erosion of cleared banks, resulting in elevated temperatures and suspended solids and
lowered oxygen levels. Community responses to alien disturbance and other environmental
factors were analysed using PRIMER and CANOCO software. Assemblages of Odonata were
found to provide a rapid, cost-effective means of assessment and monitoring. Potential indicator
and detector species were also identified using the lndicator Value method. Assemblage patterns
of aquatic invertebrates, however, were dominated by between-river and seasonal effects.
Therefore, while SASS detected overall changes in river health, without identifying the cause,
potential aquatic detector taxa were identified that may be useful for linking general disturbance
to alien invasion or clearing. All indicator and detector taxa identified in both studies can be used
for long-term monitoring and for identifying biodiverse areas for clearing or protection. In both
studies, sensitive, endemic taxa were lost after clearing, being replaced by more tolerant,
widespread taxa. Recovery of the biota appears to follow the recovery succession of the
vegetation, with most sensitive or endemic taxa only appearing after the recovery of indigenous
plants. A number of recommendations are made regarding the restoration of both water quality
(particularly with respect to shade and soil erosion) and biotope availability (particularly in terms
of the recultivation of indigenous plants) in order to achieve biodiversity objectives. The role of
catchment management, prioritisation procedures and long-term monitoring are also discussed. / AFRIKAANSE OPSOMMING: Uitheemse, indringerbome, veral Acacia spesies, is 'n groot bedreiging vir biodiversiteit in Suid-
Afrikaanse riviere. Die nasionale Werk vir Water-projek spreek hierdie probleem aan deur
uitheemse bome van rivieroewers te verwyder. Die kommer is dat water kwaliteit en habitatte
sodoende verder versteur kan word. Byvoorbeeld, hoe word endemiese en bedreigde spesies
geraak? Akwatiese makroinvertebrate en volwasse Odonata in vyf Wes-Kaapse riviere is tussen
Desember en Maart bestudeer en gemonster in natuurlike gebiede, in gebiede waar indringerbome
teenwoordig is, en in gebiede waar hulle verwyder is. Die doel was om die effek van indringerverwante
impakte op akwatiese invertebrate vas te stel. Odonata is ook bestudeer omdat hulle
maklik gemonster kan word en omdat hulle ernstig geraak word deur indringers. Die uitheemse
plantegroei oorskadu die oewers en verhoed die groei van inheemse oewerplante. Die bentiese
makro-invertebrate en Odonata is as twee aparte studies behandel en geen poging is gemaak om
die resultate van die twee te vergelyk nie. SASSS, 'n kwalitatiewe, bioasseseringsmetode wat op
die sensitiwiteit van die aanwesige families baseer word, is gebruik om waterkwaliteit op 'n
indirekte manier te bepaal. SASS het aangedui dat daar 'n afname in waterkwaliteit is nadat
indringerplante verwyder is. Dit is moontlik as 'n gevolg van groter blootstelling aan sonskyn en
erosie van rivieroewers wat veroorsaak dat temperature en die hoeveelheid gesuspendeerde
materiaal verhoog word, en dat suurstof konsentrasies verminder word. Die gevolge van
indringerplante en ander omgewingsfaktore op akwatiese gemeenskappe is met PRlMER en
CANOCO sagteware ontleed. Groepering van Odonata kan gebruik word om op 'n maklike en
koste-effektiewe manier om die impak van indringerplante en hul verwydering te bepaal en te
monitor. Aanwyserspesies is ook deur middel van die 'Indicator Value' metode geïdentifiseer.
Die verspreidingspatrone van invertebraatspesies word deur geografiese en seisoenale effekte
oorheers. Dus, terwyl SASS veranderinge in waterkwaliteit kan aantoon, sonder om die oorsaak
daarvan te identifiseer, kan aanwyserspesies gebruik word om meer spesifieke impakte deur
indringerplantegroei, of indringerverwydering, te bepaal en te monitor. Hulle kan ook gebruik
word om gebiede met hoë biodiversiteit vir bewaring of indringerverwydering te identifiseer.
Beide studies dui aan dat sensitiewe en endemiese taksa na indringerverwydering verlore gaan,
en vervang word met meer geharde, wydverspreide taksa. Herstel van die biota volg op die herstel
van die plant gemeenskappe, en die mees sensitiewe of endemiese taksa herstel eers nadat die
inheemse plantegroei herstel het. 'n Aantal aanbevelings in verband met die restorasie van
waterkwaliteit (veral in terme van die hoeveelheid skaduwee en erosie) en die beskikbaarheid van
biotope (veral in terme van inheemse plante) om biodiversiteitsdoelwitte te bereik word gemaak.
Die rol van opvanggebied bestuur, voorrang prosedures en lang termyn monitering word ook
bespreek.
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Characterizing early-seral competitive mechanisms influencing Douglas-fir seedling growth, vegetation community development, and physiology of selected weedy plant speciesDinger, Eric J. 17 May 2012 (has links)
Three studies were conducted to characterize and present early-seral
competition between Douglas-fir seedlings and the surrounding vegetation
communities during Pacific Northwest forest establishment. The first experiment
served as the foundation for this dissertation and was designed to quantify tradeoffs
associated with delaying forest establishment activities by introducing a fallow year
in order to provide longer-term management of competing vegetation. A range of six
operationally relevant treatments were applied over two growing seasons that
included in the first (1) a no-action control, (2) a spring release only, (3) a fall site
preparation without sulfometuron methyl followed by a spring release, as well as (4) a
fall site preparation with sulfometuron methyl and a spring release. In the second
year, there was (5) a fall site preparation without sulfometuron methyl followed by a
spring release and also in the second year (6) a fall site preparation with sulfometuron
methyl and a spring release. Treatments 5 and 6 were left fallow without planting
during the first year. These treatments were applied in two replicated experiments
within the Oregon Coast Range.
After adjusting for initial seedling size, year-3 results indicated that plantation
establishment and competition control immediately after harvest (i.e. no fallow
period) enabled seedlings to be physically larger than those planted after a one year
delay. At the Boot study site, limiting vegetation below 20% for the first growing
season improved year-3 Douglas-fir seedling stem volume over 273 cm³. Delaying
establishment activities one year and reducing competing vegetation below 11%
enabled seedling volume after two years to be statistically the same as three year old
seedlings in the no-action control, a volume range of between 148 to 166 cm³.
Delaying forest establishment at Jackson Mast improved seedling survivorship over
88% when a spring heat event reduced survivorship of trees planted a year earlier to
less than 69%. The combined effect of applying a fall site preparation and spring
release was necessary to reduce competitive cover below 10% in the year following
treatment and provided longer-lasting control of woody/semi-woody plants. Less
intense control measures (i.e. no-action control and treatment 2) were not able to
restrain woody/semi-woody plant cover which grew to nearly 40% at Boot and over
24% at Jackson Mast in three years. No treatment regime provided multi-year control
of herbaceous species. Including sulfometuron methyl in the fall site preparation
tank-mix did not have a negative effect on seedling growth or provide significant
reductions in plant community abundance in the year following application when
compared to similar regimes that did not include the chemical. Delaying
establishment lengthened the amount of time associated with forest regeneration
except on a site that accentuated a spring heat event.
In the second study, horizontal distance and azimuth readings provided by a
ground-based laser were used to stem map seedling locations and experimental unit
features at Boot. These data were used to create a relative Cartesian coordinate
system that defined spatially explicit polygons enabling, for the first time, the ability
to collect positional data on competing forest vegetation within an entire experimental
unit. Deemed "vixels" or vegetation pixels, these polygons were assessed for
measures of total cover and cover of the top three most abundance species during the
initial three years of establishment. An alternate validity check of research protocols
was provided when total cover resulting from this vixel technique was compared to a
more traditional survey of four randomly located subplots. The resulting linear
regression equation had an adjusted R² of 0.90 between these two techniques of
assessing total cover. When compared within a treatment and year, total cover
differed by less than 12 percentage points between the two techniques. Analysis of
year-3 woody/semi-woody plant cover produced by the techniques led to identical
treatment differences. Two treatments resulted in woody/semi-woody cover of
approximately 1500 ft² by the vixel method and nearly 40% cover by the subplot
method while the remaining four treatments were grouped below 600 ft² or 20%
cover, respectively. With continued refinement, these techniques could visually
present forest development through all phases and provide long-term information
used to bolster growth and yield models, measures of site productivity, as well as
community ecology research.
The third study evaluated the season-long gas exchange and biomass
partitioning of four weedy plant species capable of rapidly colonizing Pacific
Northwest regenerating forests. Cirsium arvense, Cirsium vulgare, Rubus ursinus
and Senecio sylvaticus were studied at two sites. A greenhouse was used to introduce
two levels of irrigation (well-watered and droughty). These species were also studied
while growing among a larger vegetation community at a field site. Irrigation
treatments had little impact on gas exchange rates. Species achieved maximum
photosynthetic rates of 30, 20, 15 and 25 μmol CO₂ m⁻² s⁻¹ (respectively) prior to
mid-July coinciding with an active phase of vegetative growth. As the season
progressed, photosynthetic rates declined in spite of well-watered conditions while
transpiration rates remained relatively consistent even when soil water decreased
below 0.25 m³ H₂O/m³ soil. Water use efficiency was high until late-July for all study
species, after which time it decreased below 5 μmol CO₂ · mmol H₂O⁻¹. Multi-leaf
gas exchange measurements as well as biomass data provided a holistic view of plantlevel
mechanisms used to shunt activity toward developing tissues. Herbaceous
species had assimilation rates that differed vertically (within each species) by as much
as 10 to 20 μmol CO₂ m⁻² s⁻¹ from July to September as lower leaves senesced in
favor of those higher on study plants. Specific leaf area was greatest in June for all
species then declined indicating species placed little effort into sacrificial early season
leaves when compared to those higher on the plant that could continue to support
flowering or vegetative growth. The study of seasonal gas exchange in the presence
of declining water availability has helped to describe competitive mechanisms at
work during forest regeneration as well as provide physiologic support for the
application of vegetation management regimes. / Graduation date: 2013
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Dry woodland and savanna vegetation dynamics in the Eastern Okavango Delta, Botswana.Tedder, Michelle Jennifer. 15 November 2013 (has links)
The Okavango Delta is an extremely dynamic system with variable vegetation comprised of permanent
swamps, seasonal swamps, dry islands, floodplains and dry grassland, savanna and woodland. The system
is largely driven by the interaction between fire and the annual flood, which filters down from the
Okavango River catchments in Angola. While extensive research has been conducted on the flood-driven
vegetation little is known about the dry woodland and savanna regions bordering these flood-driven
habitats. A taxonomic classification of woody species composition resulted in eleven vegetation types.
These data were then reanalyzed in terms of woody species morphology allowing these eleven vegetation
types to be grouped into four functional response groups in order to provide a platform for improving the
understanding of how dry woodland and savannas interact with the environment. These four groups were
the savanna group mixed thornveld and the three woodland groups; mixed broadleaf woodland, shrub
mopane woodland and tall mopane woodland. Burning in mixed thornveld and mixed broadleaf woodland
was found to decrease woody species density and grass fuel loads and could be used for grazing
management to remove unpalatable growth and improve grass species composition, while burning in
shrub mopane woodland and mixed mopane woodland merely decreased the woody understory and is not
recommended. Utilization dominated by grazing livestock resulted in overutilization of the grass sward
leading to bush encroachment in both mixed thornveld and shrub mopane woodland, while utilization by
goats alone resulted in underutilization of the grass sward and a dominance of herbaceous annuals.
Livestock utilization had no effect on the occurrence of Pecheul-loeschea leubnitziae, a shrubby pioneer
previously thought to be an indicator of overgrazing, however extensive P. leubnitziae cover was
associated with a sward dominated by shade-tolerant grasses with low forage quality. Shrub mopane
woodland and tall mopane woodland appear to be more stable vegetation states than mixed broadleaf
woodland and mixed thornveld being less vulnerable to colonization by pioneer species and alteration as a
result of utilization or environmental factors. For this reason management and monitoring of mixed
thornveld and mixed broadleaf woodland is essential to prevent vegetation degradation and to ensure
optimal forage availability for both livestock and wildlife. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
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