The ecology of plant species at Sandford Rocks Nature Reserve (SRNR) was studied. The study site is an important nature reserve that contains relatively undisturbed natural vegetation. It has a mosaic of exposed granite rocks, scrublands and woodlands. The study involved: a description of the structure and composition of the vegetation; the population characteristics of selected Acacia species; aspects of reproduction in Acacia; germination and seedling characteristics of some Acacia and grass species that dominate the reserve; the effect of seed size on germination and seedling characteristics; and, the relationship of seed size to seed coat thickness in selected Acacia species. Five different areas were studied using the point centered quarter method to sample the woody perennial species. Thirteen Acacia species were examined for reproduction characteristics; and in 2 selected Acacia species, the effects of phyllode and/or inflorescence removal on reproduction was investigated. Germination tests were conducted to identify germination characteristics in 8 Acacia and 7 grass species dominant at SRNR. The possible effects of variation in seed size on germination; seedling characteristics; and, seed coat thickness were investigated in Acacia fauntleroyi and Acacia prainii. A total of 85 species from 20 families of woody perennials were collated. All areas were dominated by the Myrtaceae, Mimosaceae and Proteaceae families. There was considerable variability in the structure and composition of vegetation. Most species were present in particular sites and the composition of communities appears to be related to the heterogeneity of the habitat within the reserve. In areas of shallow or rocky soil, vegetation types present include Allocasuarina huegeliana woodland, Grevillea paradoxa low scrubland and Acacia neurophylla medium shrubland. / In a seasonally wet area, vegetation types present include low open grassland; Eucalyptus capillosa (wandoo) woodland; and, Acacia saligna thicket. In deep, dry sandy soil, vegetation types include Phebalium tuberculosum shrubland, Acacia acuminata and Acacia coolgardiensis thickets. On relatively flat areas that gain water from adjacent large granite hills, the vegetation consists mainly of tall, open woodlands of Eucalyptus species. Vegetation types include: medium tall Eucalyptus salmonophloia woodland with Kunzea pulchella shrubland at the periphery of the Eucalyptus woodland. At rock areas, vegetation types present include dense Leptospermum erubescens thicket, low open Acacia prainii and Dodonaea viscosa shrubland. Of the Acacia populations studied, in A. lasiocalyx no recent seedling establishment was observed. It is hypothesised that recruitment occurs in particular periods. As the plants are associated with rock and soils are generally shallow, it appears that recruitment depends on run-off water from the rocks in winter. Continuous recruitment seems to be the pattern in A. prainii with both seedlings and saplings represented. A. fauntleroyi forms relatively small populations; apparently long drought periods (>l00 d) result in mass death and limit its population size. In A. hemiteles, no seedling stage was found, root competition (for water) from associated Eucalyptus species presumably limits its recruitment. Reproductive success of Acacia is affected by rainfall. A wet winter is required to induce flowering and further rain is required after flowering to promote pod development and good seed set. / All Acacia species suffer from drought in the reproduction season, however they differ in their degree of susceptibility. Leaflessness and tree shape also affect Acacia fecundity. Plants bearing more phyllodes produce more flowers and pods, and branches in the upper part of the crown bear heavier inflorescences. In 1998, all Acacia species at SRNR produced mature seed of low weight, with many immature and diseased seed, which gave poor germination. A late spring frost in 1998 is believed to be responsible for limited seed development. In two selected Acacia species, removal of phyllodes reduced the number of pods produced. Presumably, phyllode removal reduces photosynthate produced, therefore the competition among inflorescences (or pods) for resources is more intense and subsequent abortions are likely to occur. All Acacia species studied showed best germination in the cool winter temperature range. Apparently, seeds are adapted to germinate in winter when seasonal moisture is more likely to be available. The best temperature however, varied slightly between species. The grass species dominant in the reserve, except for Aristida contorta, also had more germination in cooler rather than warmer temperatures. The flora of SRNR is similar to typical vegetation of the Southwest. Generally, Acacia species are present only in particular sites, presumably were habitat moisture allows. Seedlings of Acacia species growing in naturally dry areas have greater root: shoot masses than those growing in seasonally wet areas. Biomass partitioning is an apparent strategy to conserve water. Of the 7 grass species, Amphipogon strictus appears to have fastest growth. / Eriachne ovata has greater root than shoot mass, while in all other species, shoot mass is greater than root mass; a characteristic of species that grow well in moist habitats. The longest shoots and roots are in Austrostipa elegantissima, an understorey species of eucalypt woodland. In A. fauntleroyi, the degree of hard-seededness varies between seed sizes. There is a higher proportion of soft seed in smaller seed. Seed of different sizes show some responses to different pre-treatments and incubation temperatures for germination. Larger seeds generally germinate in greater numbers after higher treatment temperatures. The best treatment for small seeds is pre-treatment at 75°C and incubated at 15°C. For medium and large seed, best pre-treatment is at 75°C with incubation at 30°C or soaking in boiling water and incubation at either 15 or 3°C. In A. prainii, seed size; pre-treatment; incubation; and, their interaction all affected germination; larger seeds are more viable. The best treatment to promote germination of A. prainii is soaking in boiling water and incubation at 25°C. In both A. fauntleroyi and A. prainii, larger seeds produce larger seedlings. Seedlings from large seeds have the potential for more rapid pre-photosynthetic growth. Larger, heavier seed has a thicker seed coat. The seed coat of A. prainii is thicker than in A. fauntleroyi; the difference in seed coat thickness is reflected by more soft seed in A. fauntleroyi (35%) than in A. prainii (6%).

Previous research on coarse woody debris (CWD) indicated that moisture content and initial heterotrophic colonization of decaying wood can affect the decomposition process. Six heterotrophic treatments were created to simulate the effects of physical penetration of the bark and wood and the transmission of ascomycetes versus basidiomycetes into CWD. In 1995, 360 Douglas-fir (Pseudotsuga menziesii) were randomly placed at five replicate sites in old-growth stands. Each site had 6 heterotrophic (HET) x 2 moisture combinations (TENT). One set of logs representing the treatment combinations was used for sampling respiration and another set was used to measure volume affected by insect gallery excavations and fungal rot and to determine decay rates. Respiration was sampled three times during the summer of 2001. The results indicated that the HET treatments were no longer affecting respiration rates. Analysis of the average of the three sampling periods revealed no TENT effect but examinations of the individual sampling dates suggests that tented logs might have higher respiration rates than non-tented logs as summer progresses. In the aggregate, the TENT treatment reduced moisture content from 45% to 36%, a 20 percent reduction in moisture levels. The HET and the TENT treatments did not affect decay rates. The mean density change for the logs was -0.072 g/cm�� �� 0.03 and the mean decay constant was 0.026 �� 0.011. The TENT treatment did affect heterotrophic activity. The mean volume of wood borer excavation and extent of brown rot was higher in the tented logs (256 cm��) than in the non-tented logs (59.9 cm��). There was also a statistically significant interaction between the HET and TENT treatments. The largest differences in volume affected by wood borers and fungal rot were found in treatments that injected ascomycetes into the experimental logs. In sum, there was limited evidence that the differences in moisture content caused by the TENT treatment affected the decomposition process but the HET treatments appear to not be directly influencing decomposition after six years. The findings suggest differences in the initial community composition of heterotrophs have a decreasing impact on the decomposition process as it progresses. / Graduation date: 2004

Woody plant encroachment is a globally-prevalent vegetation change phenomenon that has shifted grass-dominated ecosystems to mixed grass and woody plant matrices over the last century. In the Rio Grande Plains of Texas, the introduction of N-fixing woody legumes has increased above- and belowground primary productivity and changed the litter chemistry of the system, accelerating rates of belowground biogeochemical processes. The purpose of this study was to assess the impact of grassland to woodland transition on i) P concentrations in soil physical fractions that differ in their organic matter turnover rates, ii) P availability within the soil over the course of woody encroachment and across the landscape, and iii) microbial community composition and diversity. Soil samples were collected in remnant grasslands and four woody landscape elements (clusters, groves, drainage woodlands, and playas) along a 135-yr chronosequence of woody plant encroachment. P was fractionated by the Hedley method and P concentrations were determined by alkaline oxidation and lithium fusion coupled with ascorbic acid colorimetry. Bacterial and fungal communities were characterized by molecular methods. Whole soil P concentrations were 2-5X greater in woody landscape elements than in grasslands, and nutrient concentrations increased linearly with time following woody plant invasion in all but the slowest-cycling physical fractions. Plant-available P and organic P increased dramatically with time following encroachment. Changes in P availability were more pronounced in drainages and playas than in upland clusters and groves. Analysis of the bacterial and fungal communities demonstrated that microbial communities in grasslands differ at both phylum and genus level from the flora of the wooded landscape elements. This study demonstrates that woody encroachment strongly influences the distribution and availability of soil P and indicates that nutrient cycles in the soil are closely linked and similarly affected by increased woody plant abundance. Microbial communities under woody species differ in composition from those of the grasslands, and are likely contributing to the observed changes in nutrient availability. Since N and P are generally the most limiting nutrients in terrestrial ecosystems, increased stores of P are likely to alter rates of microbial processes, plant-microbe and plant-plant interactions, and successional dynamics in this ecosystem and similar landscapes around the world.

Dissertation (M.S.)--The University of North Carolina at Greensboro, 2008. / Directed by Bruce Kirchoff; submitted to the Dept. of Biology. Title from PDF t.p. (viewed Feb. 2, 2010). Includes bibliographical references (p. 134-146).

Thesis (M.S.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. xv-130).

Evapotranspiration dominates the water budget in drylands, exerting important controls not only on the dynamics of water, but also on the amount and distribution of vegetation on a landscape. The spatial and temporal variability of vegetation cover imposes constraints on key ecohydrological processes that feedback to the dynamics of evapotranspiration and, most importantly, its partitioning between direct evaporation and transpiration from plants, one of the most significant ecohydrological challenges. Yet, lacking are systematic evaluations of how variations in woody plant cover--a fundamental vegetation attribute of landscapes that can vary spatially with amount of cover and temporally with leaf phenology-- influence the dynamics of soil microclimate and ultimately the partitioning of evapotranspiration into its components. This study presents the results of field experiments that systematically evaluated the effects of amount of canopy cover and its seasonality in both surface microclimate and soil evaporation. These field observations are complemented by controlled experiments that directly evaluate the relationship between amount of canopy cover and the partitioning of evapotranspiration, with an assessment of its larger-scale implications using a regional land surface-atmosphere model. Finally, this study presents a classroom-adaptation of the evapotranspiration partitioning experiment that was used to effectively translate new scientific concepts and information into k-12 classrooms. Overall, the results from this study provide a comprehensive understanding about the interactive ways in which canopy cover, canopy structure attributes and plant phenology influence soil surface microclimate--characterized by near-ground solar radiation and soil temperature--and soil evaporation. More specifically, the results illustrate how the main control of deciduous-woody vegetation on soil evaporation is the addition of litter to the surface. However, in absence of litter, attributes of woody cover influence soil evaporation variably with season and phenology. Further, The results from this study illustrate how the partitioning of evapotranspiration exhibits a non-linear response to amount of woody canopy cover. Notably, when incorporated into a regional surface-atmosphere model, this non-linearity strongly affects water fluxes, highlighting the potential implications for ecological, hydrological, and atmospheric processes associated with the partitioning of evapotranspiration, providing important insights for natural resource management.

Herbivores are important drivers and have a longstanding history in shaping our terrestrial environments. However, during the past decades, changes in woody vegetation in savanna and forest systems have been observed in southern Africa. Subsequently, concerns have been raised about the loss of (tall) trees in areas with elephant. The relative effects of browsing herbivores on vegetation and the potential browsing interaction with other herbivore species remain unclear and were examined using vegetation transects and exclosure experiments in savanna woodland and Sand Forest. Rainfall, fire and elephant were important savanna determinants. Especially rainfall positively affected woody densities, which were negatively affected by a longer exposure time to elephant, but not to elephant densities itself. In general, within South Africa’s savannas, tree height classes were absent from the population demography. Different height classes were likely to be impacted by different drivers. For example, seedling and sapling densities were greater with longer fire return periods and increased rainfall. The Sand Forest exclosure experiments showed that forest regeneration was impacted by nyala and both elephant and nyala, as the absence of both species increased tree densities. Both species combined, and individually, also affected tree species assemblages. In contrast, short term elephant access to a savanna area did not affect tree densities or species assemblages. In both savanna and Sand Forest elephant displaced mesoherbivores, and in Sand Forest both elephant and mesoherbivores displaced their smaller counterparts. The presence of competitive displacement also affected recruitment (i.e. seedlings and/or saplings) of woody vegetation both in Sand Forest and savanna. Thus, elephant and mesoherbivores exert direct and indirect (i.e. competitive displacement providing a window for recruitment) impact on vegetation. Active management of the herbivore species assemblage affects both vegetation and other herbivores, which effects potentially cascade into lower trophic levels, jeopardising biodiversity and ecosystem processes. Therefore, the full herbivore assemblage present and their combined and individual browsing effects need to be considered when setting management goals to conserve habitats and biodiversity across all trophic levels. In addition some contrasting results between Sand Forest and savanna emphasise the need for caution when extrapolating results from different areas and ecosystems. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.

No abstract available. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.

Forest floor calcium (Ca) declines in northern hardwood forests are of interest because Ca availability may limit future forest growth. In the 1990s investigations into Ca pools and fluxes across a northern hardwood forest chronosequence showed decreases across stand age in the mass of forest floor base cations and litterfall cation concentrations. I undertook a study of factors that influence litterfall chemistry to develop a better understanding of base cation biogeochemistry in developing northern hardwood forests. Although Ca, potassium (K), and magnesium (Mg) concentrations in litterfall significantly declined with stand age, species composition and soil nutrient availability also influenced litterfall chemistry. The interplay between these factors, such as the distribution of species with different nutrient demands in areas of base cation availability or limitation, influences forest floor chemistry and may impact the time in which soil Ca depletion occurs. Additionally, I examined the quantity and qualities (species composition, decay class, size, and nutrient concentrations and contents) of woody debris across the same northern hardwood forest chronosequence. The objectives of this study were to quantify cation pools in woody debris, describe how the qualities of these woody debris pools change with stand development, and establish a baseline for long-term measurements of woody debris accumulation and chemistry with stand age. Decomposition of woody debris transfers base cations to the forest floor, and may be partially responsible for forest floor Ca gains in young stands. Calcium and K pools in woody debris were most strongly influenced by woody debris biomass, whereas Mg content was influenced by both woody debris biomass and species composition. In young stands, woody debris pools were strongly influenced by management practices during harvest. By 20 years since harvest woody debris pools reflected processes of stand development. For example, from 20 to nearly 40 years since harvest woody debris biomass and species composition was dominated by mortality of early successional species. Woody debris in more mature stands reflected small-scale stochastic disturbances including disease and single-tree mortality. Litterfall and woody debris are each components of within-stand cation cycling that will be critical to future forest growth with limited Ca availability.

Densitometric, volumetric and paper-making traits of provenances of Pinus caribaea Morelet, P. oocarpa Schiede and P. patula SchiedeariclDeppe ssp. tecunumanii (Eguiluz and Perry) Styles were evaluated. Provenance mean values of densitometric density (DEN) and within tree density variation (VAR) were significantly different (p<0.05) at seven of the fourteen P.caribaea and at one of the seven of P. oocarpa and P. patula ssp. tecunumanii trials. Provenance mean valuesor volume under bark (VUB)and dry matter index (DMI) were significantly (p<0.05) different at all of the P. caribaea and at five of the P. oocarpa and P. patula ssp. tecunumanii trials. The inland provenances of P. caribaea were generally Higher for DEN and VAR than the coastal provenances, he Camelias, Mountain Pine Ridge, Rafael and Yucul provenances of P. patula ssp. tecunumanii were superior to P. oocarpa provenances for VUB and DMI in all of these trials and were superior to P. caribaea at two sites where the species were growing under similar conditions. Evaluation of densitometric races revealed large differences between species, provenances and sites for the width and density of latewood; this could explain much of the variation in VAR between these sources. The analysis of variance was used to assess genotype by environment interaction of DEN and VAR from eleven provenances of P. caribaea var. hondurensis Barrett and Golfari at eleven sites and from five provenances of P. oocarpa and four provenances of P. patula ssp. tecunumanii at sfx sites. Sites and provenances were significantly different for DEN and VAR in both series of trials out the site by provenance term was not statistically significant in either. Indications were that P. caribaea would be expected to have lower values of DEN and VAR at higher altitude. Provenances of P. oocarpa and P. patula ssp. tecunumanii were lower for VAR at sites of lower latitude but there were no individual site factors which could be correlated with DEN in these provenances. The comparison of full-scale pulping with micropulping of small wood samples from felled trees of six pine species in the Eastern Transvaal, South Africa, revealed positive and significant correlations for the pulp yield and paper strength traits. The correlation of tear index and VAR in these trees was positive and significant. Evaluation and analyses of a number of pine species and provenances by micropulping of cores from standing trees revealed significant differences for certain of the paper strength traits. The Caftas provenance of P. oocarpa was unusual in having high values for both tear index and burst index when grown in Zululand. Similar conclusions were reached for provenances of P. patula ssp. tecunumanii grown in the Eastern Transvaal. The conclusions of this thesis were: 1. Site climatic factors did not affect DEN and VAR of the different species and provenances in the same way; 2. The VAR term varied as a result of site, species and provenance; 3. There was no genotype by environment interaction for DEN«*rJ VAR; 4. The correlation of VAR with pulp and paper-making traits indicated that trees with high VAR were superior for tear index to trees with low VAR; 5. Micropulping of small wood samples could be used to assess the paper-making traits of individual trees.