Dissertations / Theses on the topic 'Exclosure'

A restored elk (Cervus elaphus) population in eastern Kentucky may be affecting ecosystem processes in a landscape composed of reclaimed grassland expanses and isolated forest remnants. Elk routinely select forested ridge-tops as resting and ruminating sites. These locations are characterized by sparse or absent leaf litter, trampled and diminished vegetation, large deposits of dung, and urine-saturated soils. In fall 2003, a series of fenced ungulate exclosures were constructed; 8 on highly disturbed forested ridge-tops and 8 on reclaimed grasslands. Soil analyses measured % moisture, pH, total nitrogen, total carbon, ammonium, nitrate, phosphorus, and major extractable cations in 0-10 cm and 10-20 cm cores. Litter depths and percentages of bare ground, vegetative cover, litter cover, and woody debris were measured. Sediment and water samples were collected monthly from sediment traps on reference and experimental ridge-tops. Studentfs t-tests were used to determine significance (p . 0.10) between treatments. Disturbed ridge-tops had higher soil ammonium (0.68 mg/kg, 10-20 cm) than reference sites (0.25 mg/kg) in spring 2004 and lower ammonium (0.72 mg/kg, 0-10 cm; 0.44 mg/kg, 10-20 cm) than reference sites (1.80 mg/kg, 0-10 cm; 0.94 mg/kg, 10-20 cm) in summer 2004. Total carbon was higher inside (67.57 g/kg, 0-10 cm) than outside (45.38 g/kg) of ridge-top exclosures in fall 2004. Soil moisture, litter depths, and vegetative cover were generally lower, while % bare ground was higher on disturbed ridge-tops. Sediment collected from traps averaged 2.21g/m2 inside exclosures, 2.86 g/m2 outside exclosures, and 0.39 g/m2 on reference ridge-tops. These data suggest that this reintroduced species is changing several attributes of the Cumberland Plateau landscape. The lack of a predator such as the gray wolf (Canis lupis) or cougar (Puma concolor) likely contributes to the development of habitual elk use of landscape features such as remnant ridge-top forests. Such concentrated use may create conditions for the colonization of certain plant species including rare natives and invasive exotics. Continued monitoring of high use areas is recommended so that managers can fully understand the long-term impact of the return of this large, gregarious herbivore, and that appropriate management actions can be developed to promote native biodiversity.

A vegetation assessment was conducted to understand the effect of feral goats (Capra hircus) on the vegetation of Isolated Hill Scenic Reserve located in Southern Marlborough. New Zealand forests evolved without the pressure of mammalian herbivores but following human settlement they became subject to intensive browsing following the introduction of exotic mammals. This study focuses on the presence of feral goats. Interest arises from the settlement of other countries and the subsequent liberations of feral goats which are now considered to be responsible for the significant removal of native vegetation as well as playing a dominant role in erosion. Changes in plant communities have occurred with the pressure of goat browsing as well as secondary effects such as habitat degradation The purpose of this research was to investigate the changes in plant species composition since the initial and subsequent research conducted in 1985 and 1994. An analysis of previous work on the diet of multiple introduced ungulate species was also conducted. Previous studies were not limited to only feral goat studies and included other introduced herbivores to provide a broad overview of diets. The New Zealand Forest Service implemented a programme for monitoring the seral forest in Isolated Hill Scenic Reserve using standard Forest Service vegetation quadrants. 32 quadrants were established, including three exclosures, in various locations around the Reserve to allow assessment of feral goat impacts on seral forests (forest whose constituents are of varied age classes). Nine forest service plots, including three exclosures were re-measured and an additional nine plots were measured. Given the progression of vegetation change that has been observed during the course of this study, both analytically and observationally, Isolated Hill Scenic Reserve in its current state, involving the notable presence of feral goats and the vegetation types will continue to diminish in diversity.

White-tailed deer (Odocoileus virginianus) have considerable impacts on woody and herbaceous vegetation. Many oak-hickory forests in the eastern U.S. are experiencing a lack of oak (Quercus) and hickory (Carya) regeneration, with deer being a likely culprit. Furthermore, few have studied deer use of different herbaceous food plot mixtures. I addressed these gaps in the literature by assessing deer impacts on forest and herbaceous vegetation in southern Illinois. I established 150 paired plots (enclosed and control) in June 2015 and measured 25 habitat variables to assess impacts of deer herbivory from August 2015 to August 2016. Oak seedlings were present more often and in higher numbers within enclosed plots (F1,299 = 6.25, P < 0.050 and F1,387 = 4.50, P < 0.050, respectively). There were no differences in the height of oak seedlings or the presence, number, or height of hickory seedlings in enclosed versus control plots (F1,53 = 0.010, P = 0.938; F1,299 = 0.850, P = 0.357; F1,267 = 1.16, P = 0.282; and F1,15 = 0.030, P = 0.855; respectively). During September-November 2015, I counted and marked fallen acorns within 50 random paired plots; the number of acorns discovered or lost did not differ between enclosed and control plots (F1,94 = 0.310, P = 0.578 and F1,8 = 0.120, P = 0.736, respectively). I suggest managers incorporate potential deer impacts when designing management plans to best encourage oak regeneration. During September-November 2015, I established 16 food plots (half tilled; each 0.05 ha in size), planted to 4 food plot types. I compared Big Tine Buck Brunch, Evolved Harvest Throw & Gro, Antler King No Sweat, and a food plot mixture that I created. I measured deer use via 2 methods: vegetation growth in exclosures versus control (i.e., unfenced) areas and camera traps. Deer used all 4 food plot mixtures (n = 292 – 2,522 pictures/plot over 9 weeks), having a negative impact on mean vegetation height outside of exclosures (F3,1148 = 6.71, P < 0.001). Analysis of camera data indicated that deer did not preferentially use any one food plot mixture over the others (F3,12 = 0.090, P > 0.050). There also was no difference in the proportion of deer pictured in the process of eating within each food plot mixture (F3,12 = 0.592, P > 0.050). I suggest any of these 4 food plot varieties could be planted by a hunter or wildlife manager in the Midwest and observe similar use by deer.

Kwongan, also known as sandplain heathland, occurs in remnant vegetation throughout the fragmented landscape of the Western Australian wheatbelt. This vegetation community has high levels of species richness and endemism, and is of high conservation value. In many vegetation remnants in the wheatbelt the native tree species Allocasuarina huegeliana (rock sheoak) is expanding out from its normal range and encroaching into kwongan. A. huegeliana may ultimately dominate the kwongan, causing a decline in floristic diversity. Altered disturbance regimes, particularly the absence of fire and reduced or absent browsing mammal herbivores, are likely to be responsible for causing A. huegeliana encroachment. This study used experimental and observational data from patches of kwongan in three Nature Reserves in the central and southern wheatbelt to investigate the role of fire, native mammal activities and interactions between these two factors in shaping A. huegeliana woodland–kwongan community boundaries. Investigations were carried out into the characteristics of encroaching A. huegeliana populations; the environmental factors affecting the extent of encroachment, naturally recruited juveniles, and seedling emergence and establishment; historical and current abundances of native mammals; and the effects of mammal herbivores on seedling establishment during inter-fire and post-fire periods. Results from this study confirm that A. huegeliana has encroached into kwongan throughout the wheatbelt region and recruitment appears likely to continue in most areas. Few of the environmental factors measured in this study affected the extent of encroachment, the locations of naturally recruited A. huegeliana juveniles, and seedling germination and establishment. Western grey kangaroos (Macropus fuliginosus) browsed extensively on seedlings, which largely prevented them from establishing in open areas of kwongan. However, numerous A. huegeliana seedlings escaped browsing herbivores by establishing in perennial shrubs, where they appeared to be tolerant of increased levels of inter-specific competition. There was no native mammal common to all three Reserves that declined around the time that A. huegeliana encroachment most likely began in the 1970s. In addition, tammar wallabies (Macropus eugenii) had little effect even where their densities were high. It is therefore unlikely that the decline of an individual mammal species initiated encroachment. A. huegeliana encroachment appears to be driven by increased propagule pressure, which is in turn caused by increased inter-fire intervals. Long periods of time without fire have enabled fire-sensitive A. huegeliana trees to produce increasing quantities of seed that are continuously released into kwongan. A range of other factors may interact synergistically with this process to affect encroachment and these are also discussed. This study considered the implications of these findings for management of remnant vegetation in fragmented landscapes, particularly kwongan in the Western Australian wheatbelt, and areas for further research are suggested.

A major challenge in agroecosystems is how to manage the systems so that it reduces crop pests and enhances natural pest control. This thesis investigates patterns of crop pests and top-down effects of birds and arthropod predators in relation to land-use composition across spatial scales. In paper (I) I examined the crop distribution and land-use types in relation to the crop raiding patterns in 15 transectsin sites close to and far from forests along with a questionnaire survey at household level. I found severe crop raiding close to forests, but it had no impact on crop composition growing between the two sites. In paper (II) I examined the effect of forest and tree cover, at local and landscape scales, on the abundance of arthropod predators by collecting specimens from 40 home gardens. My result showed higher abundance of arthropod predators when either the home garden or the surroundings had a high tree-cover, compared to when tree-cover at both scales was similarly either high or low. In paper (III) I investigated the effect of excluding birds and arthropod predators on leaf damage on rape seed in 26 home gardens. I found stronger top-down impacts from arthropod predators on crop pests in tree-poor gardens than in tree-rich gardens. There was no effect of birds. In paper (IV) I explored the effect of landscape complexity on bird and arthropod predation using plasticine caterpillars in 36 home gardens across landscapes. The rate of arthropod predation on caterpillars was higher in simple than in complex landscapes. The rate of bird predation did not vary between complex and simple landscapes. In simple landscapes, arthropod predation was higher than that of birds. The overall results suggest that simplified gardens/landscapes still have enough habitat heterogeneity to support arthropod predators for the significant top-down controlling effect on crop pests. However, I did not find clear effect of complexityon the top-down effect of birds.

At the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper 1: Manuscript; Paper 3: Manuscript; Paper 4: Manuscript

The loss of large-bodied herbivores and/or top predators has been associated with large-scale changes in terrestrial, freshwater, and marine ecosystems around the world. Understanding the consequences of these declines has been hampered by a lack of studies in relatively pristine systems. To fill this gap, I investigated the dynamics of the relatively pristine seagrass ecosystem of Shark Bay, Australia. I began by examining the seagrass species distributions, stoichiometry, and patterns of nutrient limitation across the whole of Shark Bay. Large areas were N-limited, P-limited, or limited by factors other than nutrients. Phosphorus-limitation was centered in areas of restricted water exchange with the ocean. Nutrient content of seagrasses varied seasonally, but the strength of seasonal responses were species-specific. Using a cafeteria-style experiment, I found that fast-growing seagrass species, which had higher nutrient content experienced higher rates of herbivory than slow-growing species that are dominant in the bay but have low nutrient content. Although removal rates correlated well with nutrient content at a broad scale, within fast-growing species removal rates were not closely tied to N or P content. Using a combination of stable isotope analysis and animal borne video, I found that green turtles (Chelonia mydas) – one of the most abundant large-bodied herbivores in Shark Bay – appear to assimilate little energy from seagrasses at the population level. There was, however, evidence of individual specialization in turtle diets with some individuals foraging largely on seagrasses and others feeding primarily on macroalgae and gelatinous macroplankton. Finally, I used exclusion cages, to examine whether predation-sensitive habitat shifts by megagrazers (green turtles, dugongs) transmitted a behavior-mediated trophic cascade (BMTC) between sharks and seagrasses. In general, data were consistent with predictions of a behavior-mediated trophic cascade. Megaherbivore impacts on seagrasses were large only in the microhabitat where megaherbivores congregate to reduce predation risk. My study highlights the importance of large herbivores in structuring seagrass communities and, more generally, suggests that roving top predators likely are important in structuring communities - and possibly ecosystems - through non-consumptive pathways.

In the western U.S., riparian ecosystems cover 1% of land area while supporting 70-80% of native species. 70% of this land area is available as range for livestock, who use riparian areas preferentially. Ecological concerns have led to numerous studies of the effects grazing has on these ecologically important, easily damaged ecosystems. Exclosure-based research has thoroughly examined the effects of livestock on riparian ecosystem health and function, but failed to investigate the potential for exclosures to intensify adverse effects of use at their boundaries, which could lead to overestimation of their benefits and impair their efficacy in management. This study attempts to supplement existing research by characterizing potential impacts, making exclosures a more informed and effective management strategy. Study exclosures were located on grazed public lands in southwest Montana. Riparian vegetative cover and channel morphology response variables were measured inside the exclosure and in two grazed reaches, one placed 0 to 20 m and one >50 m from the exclosure to capture differences in the spatial extent and severity of any impacts due to differences in livestock behavior caused by the exclosure's influence. Findings were that (1) results were consistent with previous exclosure studies using the same response variables to compare grazed and exclosed areas, (2) significant differences in herbaceous cover, bare ground cover, channel width, and bank angle between the two grazed subreaches were greater than corresponding grazed/exclosed comparisons, indicating that impacts to the subreach adjacent to the exclosure that are greater than corresponding improvements within, (3) spatially inconsistent impact zones within and among sites made it impossible to describe an overall impact zone adjacent to exclosures, but impacts to channel morphology, herbaceous cover, and bare ground occurred within 8 m of the exclosure, and within 2 m for bank angle, (4) data didn't support predicted relationships between impact severity and exclosure duration, size, or stocking rates, most likely due to the many other influencing factors that were not measured. Evidence supporting existence of exclosure-caused impacts should inform exclosure use and make it a more effective management tool, especially when considered in the context of how these impacts might encumber specific management goals.

Trophic downgrading of ecosystems necessitates a functional understanding of trophic cascades. Identifying the presence of cascades, and the mechanisms through which they occur, is particularly important for seagrass meadows, which are among the most threatened ecosystems on Earth. Shark Bay, Western Australia provides a model system to investigate the potential importance of top-down effects in a relatively pristine seagrass ecosystem. The role of megagrazers in the Shark Bay system has been previously investigated, but the role of macrograzers (i.e., teleosts), and their importance relative to megagrazers, remains unknown. The objective of my dissertation was to elucidate the importance of teleost macrograzers in transmitting top-down effects in seagrass ecosystems. Seagrasses and macroalgae were the main food of the abundant teleost Pelates octolineatus, but stable isotopic values suggested that algae may contribute a larger portion of assimilated food than suggested by gut contents. Pelates octolineatus is at risk from numerous predators, with pied cormorants (Phalacrocorax varius) taking the majority of tethered P. octolineatus. Using a combination of fish trapping and unbaited underwater video surveillance, I found that the relative abundance of P. octolineatus was greater in interior areas of seagrass banks during the cold season, and that the mean length of P. octolineatus was greater in these areas compared to along edges of banks. Finally, I used seagrass transplants and exclosure experiments to determine the relative effect of megagrazers and macrograzers on the establishment and persistence of three species of seagrasses in interior microhabitats. Teleost grazing had the largest impact on seagrass species with the highest nutrient content, and these impacts were primarily observed during the warm season. My findings are consistent with predictions of a behaviorally-mediated trophic cascade initiated by tiger sharks (Galeocerdo cuvier) and transmitted through herbivorous fishes and their predators.

Despite a long history, accurately quantifying biological diversity remains a priority for ecologists and the continuing development of novel tools and approaches has identified areas that require further investigation. Currently, the quantification of evolutionary diversity (phylogenetic diversity) is receiving intense and critical interest, but few have attempted to quantify among sample phylogenetic variation (beta diversity) and fewer still have measured the influence of grazing on the phylogenetic diversity of plant communities. Novel partitions of beta diversity, which quantify the independent influence of richness differences and species replacement, may better clarify how heterogeneity is structured within a system, but such metrics have not yet been developed for phylogenetic diversity or applied to grazing investigations. Furthermore, it has recently been re-emphasized that, when measuring within-community heterogeneity, the only appropriate approaches that facilitate the concurrent measurement of partitioned beta diversity are ‘multiple site beta diversity’ metrics. To date ‘multiple site’ heterogeneity metrics do not exist for phylogenetic diversity. Drawing on previously published derivations of pairwise beta diversity partitions and their phylogenetic analogs, I developed novel multiple site beta diversity tools for taxonomic and phylogenetic diversity that may better quantify community heterogeneity and suggest how these new tools may be useful for the practicing community ecologist. Using long term grazing exclosures, I combined novel beta diversity tools with paired plots across the exclosure fence and appropriate null models to test the influence of grazing on herbaceous alpine plant community heterogeneity. I show that (i) taxonomic and phylogenetic diversity provide differing results, (ii) that grazing influences within community heterogeneity of herbaceous plant communities, but that the response may be site dependent, and (iii) that richness and replacement metrics of beta diversity exhibit different responses to grazing. Novel metrics of partitioned taxonomic and phylogenetic beta diversity therefore provide useful insight into the structuring of herbaceous alpine plant communities. As such, within-community heterogeneity as measured by ‘multiple site beta diversity’ is an important attribute of any ecosystem and efforts aimed at quantifying and preserving biodiversity for ecosystem management or conservation should include it in their goals.

Nest predation is a major factor impacting duck production and recruitment on breeding areas in North America. I surveyed waterfowl managers employed by the U.S. Fish and Wildlife Service and U.S. state wildlife agencies to determine their beliefs about nest predation and its management. Over 64% of respondents believed that rates of nest success on their management units averaged <30% between 1996-2000. Managers believed habitat management and direct predator control were the most effective techniques to reduce nest predation. The construction of predator exclosures around nesting habitat also has been recommended to reduce nest predation. Between 1999-2001, I evaluated the effectiveness of 4 predator exclosures to enhance duck nest success at Bear River Migratory Bird Refuge, Utah. During this period, rates of nest success in the exclosures were slightly higher than that within control plots, but still <15%. Although published guidelines commonly recommended predator fences ≤ 117 cm in height, I observed red foxes jump the 114-cm-high fences. Additional research is needed to identify effective predator fence designs. Wildlife managers have argued that periodic disturbance of vegetation should be a component of management on waterfowl breeding areas. Although many techniques are available to manipulate vegetation, grazing by domestic livestock has been controversial. Some researchers have reported that livestock grazing is detrimental to nesting ducks whereas others have argued that it can be beneficial. I evaluated the impact of a short-duration, high-intensity winter livestock grazing program on duck nesting at Bear River Migratory Bird Refuge. Following a winter grazing treatment, I measured visual obstruction on both grazed and ungrazed plots during the spring nesting season. Although visual obstruction readings on grazed plots were lower than those on rested sites early in the nesting season, those differences diminished as the season progressed. Winter grazing may impact early-nesting ducks like mallards (Anas platyrhynchos), but not late-nesting species like cinnamon teal (Anas cyanoptera) and gadwall (Anas strepera). In designing grazing programs to manage nesting cover, managers should consider their waterfowl production goals, the composition of breeding duck populations, type of grazing system, and climatic conditions.

Benthic invertebrates play important roles as feeding resources for many organisms in different food webs. Shifts in predation of these organisms can generate cascading effects and potentially lead to the disappearance of one or more species from a site. Cascading effects can bring impacts to organisms who aren’t even directly involved, why studies in this field are important for understanding sudden changes in ecosystems. I examined the predation from fish and waterfowl on benthic invertebrates in the shallow and eutrophic Lake Tåkern in the plains of Östergötland County, southern Sweden. The study was experimental and used exclosures (three types, eight replicates) in the shape of 130-liter cages to examine the composition of invertebrates. It was conducted during early spring, a relatively unexamined period for this kind of study. I found no significant differences in the control treatment compared to any of the other treatments regarding biodiversity. The invertebrate fauna was dominated by a small number of species, with a relatively patchy spread throughout the sediment area. Furthermore, the results indicate that the fish hadn’t had the time to properly activate their predatory habits due to prolonged winter temperatures. The waterfowl were considered too absent during the test period to affect the invertebrate community. Future studies in this area are recommended to work with a greater sampling area, to reduce the influence of extreme values.

The deforestation of riparian areas is a major concern in southern Africa. These areas are characterized as fragile ecosystems which contribute largely to the regional and global biodiversity of the world. It is therefore important to restore these degraded areas along the natural rivers of South Africa to ensure the sustainability and biodiversity of riparian corridors. Riparian areas inside the National Parks of South Africa, and especially in Mapungubwe National Park, have a high esthetical value and should be preserved for future generations. The study was conducted in the Mapungubwe National Park, which is listed as a cultural world heritage site. Plans are in place to convert it into one of Africa's biggest Transfrontier Parks, called the Limpopo/Shashe Transfrontier Conservation Area (TFCA), which will be situated between neighbouring countries Zimbabwe, Botswana and South Africa. The main purpose of this project was to establish a demonstration site for the restoration of degraded, previously cultivated lands in the deforested riparian areas in the Mapungubwe National Park, Limpopo Province. Another aim of the project was to evaluate the theoretical assumption that the growth of trees on so called "activity lines" in the environment due to geological and soil characteristics is enhanced. "Activity lines" were identified by Mr. Lynn van Rooyen of South African National Parks (SANParks) and trees of which the growth was tested, were planted both on and off "activity lines". The selection of the right type of trees for the restoration of the deforested riparian areas during active restoration applications is very important and depends on a multitude of factors. These factors include aspects such as the location with its specific vegetation, soil type and climatic conditions, the historical background of the management practices such as previous land uses, as well as other environmental impacts that previously occurred in the area to be restored. The latter can be gained through interviews with previous and present managers of the area, as well as maps, reports and aerial photographs. Ten different indigenous tree species that previously occurred in the area were planted in an experimental demonstration site of approximately 70ha, which was enclosed by an electrical game fence. The ten tree species that were evaluated included: Faidherbia albida (Ana tree), Acacia nigrescens (Knob thorn), Acacia tortilis (Umbrella thorn), Schotia brachypetala (Weeping boer-bean), Acacia xanthophloea (Fever tree), Lonchocarpus capassa, recently renamed Philenoptera violacea (Apple-leaf), Salvadora australis (Narrow-leaved mustard tree), Adansonia digitata (Baobab), Combretum imberbe (Leadwood) and Xanthocercis zambesiaca (Nyala tree). With the aid of aerial photographs, phytosociological studies, interviews with previous and present land users and managers, as well as existing surrounding vegetation, four different zones within the enclosure were identified according to ecotones. The establishment, growth and survival rate of the different tree species were monitored using morphological and physiological vegetation sampling techniques, as well as leaf component analyses on individuals of selected species. Soil physical and chemical analyses were carried out in the four different blocks identified within the experimental site. Data analysis was carried out on both the soil and leaf component analyses using the CANOCO-package. The establishment of the experimental site was successful, and important information was collected on various aspects of restoration activities. Positive growth effects were also observed in certain indigenous tree species concerning the "activity line" effect, especially with regard to Acacia tortilis and Combretum imberbe. However, the preliminary results obtained through this pilot study showed no conclusive evidence to what exactly stimulated the enhanced growth phenomena observed in certain individual tree species planted on "activity lines". Additional watering was identified as the most important factor contributing to successful establishment and growth of indigenous tree species in this semi-arid area. Various results showed a multiplying effect when a combination of additional watering and "activity lines" was applied. It was concluded that, should any further restoration work be conducted in the degraded areas of the Mapungubwe National Park, the planting of trees should be done on "activity lines" and with the addition of water. This will result in higher establishment rates of transplanted trees and speed up the succession processes involved in the natural "healing process" of degraded areas. Parameters that should be used for monitoring tree growth include the trunk thickness at the base, trunk thickness at 30cm from the base, and the length of the tree in its natural growth form. Recommendations were also made as reference for future restoration practices to ensure better and more successful and sustainable outcomes in the planting of trees. These include the use of nurse plants such as Acacia tortilis and Salvadora australis to establish a more favourable microclimate for climax species, as well as the establishment of a preferred herbaceous layer. Care should be taken in the period required for the cultivation of indigenous trees before they are transplanted into the field, as a prolonged cultivation period could lead to a circular growth form of the root system, preventing sufficient penetration ability of the roots into deeper, more nutrient rich soils. Before trees can be planted into the field, a hardening period must be applied to all seedlings for at least a three week period. This entails the exposure to more direct sunlight for longer periods as well as a reduction in the water applied weekly. Special attention should be paid to the stresses caused by herbivory, especially that of termites and porcupines. The maintenance of the exclosure is a critical factor contributing to the successful outcomes of this particular restoration project. Problem animals, especially elephants, should be kept out of the exclosure at all costs. The results of this project can be used in this ongoing restoration program, as well as in other related projects in semi-arid, degraded savannah areas over the long-term.
Thesis (M.Sc. (Botany))--North-West University, Potchefstroom Campus, 2008.

The objective of this thesis was to investigate the effects of mammalian grazers, such as microtine rodents and reindeer, (top-down effects) and nutrient availability (bottom- up effects) on the plant community of a tundra heath. I conducted a large-scale fertilization experiment and studied the impact of grazers using exclosures. I measured the effects of fertilization and grazing on soil microbial activity and nutrient cycling. I investigated the responses to fertilization of the invertebrate community, I studied the effects on the quality of bilberry as food for mammalian herbivores, and I looked at how concentrations of nutrients and carbon-based secondary defences against herbivory fluctuated between seasons in unfertilized and fertilized treatments. The results of my thesis show that the plant community investigated is exposed to a strong top-down control by mammalian herbivores. On the fertilized and grazed areas the aboveground biomass of the vascular plant community did not increase compared to unfertilized areas. However, the productivity of the plant community was clearly nutrient- limited. During the eight years of the experiment, on the fertilized areas plant biomass was significantly increased inside the herbivore exclosures In my study mammalian herbivores at comparatively low densities and grazing outside the growing season were sufficient to control the biomass of a heterogeneous plant community. Microtine rodents (Norwegian lemmings and grey-sided voles) preferred the fertilized areas for overwintering. The food plant quality of bilberry for grey-sided voles was improved on the fertilized areas throughout the year. Grazing decreased the nitrogen storage in the aboveground plant biomass. Reindeer and rodents had also important indirect effects on the plant community by decelerating soil nutrient cycling and soil microbial activity. This effect may be accelerated by the impact of herbivore on plant species composition. Graminoids, which contained the highest nitrogen concentrations in their tissues, increased rapidly on the fertilized areas, but their abundance was significantly lower on grazed fertilized areas. The invertebrate community was detritus-based and received their energy indirectly from the litter via soil microbes and detritivores. Fertilization increased the biomass of invertebrate carnivores, but had no effect on the biomass of invertebrate herbivores. Apparent competition between detritivores and invertebrate herbivores, mediated by carnivorous invertebrates predating on both of them, is supposed to keep the densities and grazing pressure of invertebrate herbivores low. Grazing damage by invertebrates was very low and only 0.021 % of the total vascular plant biomass was removed.

Diss. (sammanfattning) Umeå : Umeå universitet, 2001, härtill 6 uppsstser.

digitalisering@umu

The object of this thesis was to study plant community structure, especially in relation to vertebrate herbivory, in an altitudinal gradient in the Fennoscandian mountain chain. A sowing experiment in a high alpine Ranunculus glacialis population showed that seeds germinated better in cleared microsites than under established individuals. This is contrasted with a hypothesis that predicts positive plant-plant interactions in high alpine environments. It was concluded that plant-plant interactions in die studied population varied from neutral to negative, whereas no indications for positive interactions were found. An exclosure experiment in a snow-bed showed that a lemming population consumed 33 % of the available graminoids and 66 % of the mosses from August to June during a population peak. The results shows that grazing needs to be considered as a structuring factor in snow-bed vegetation. The vegetation in exclosures in another snow-bed changed from a graminoid-dominated to a herb-dominated plant community during a long-term (six years) experiment No changes of the same magnitude were seen in a tall herb meadow on a lower altitude. Survival of transplanted adult shoots from the tall herb meadow was equally high in the snow-bed as on the meadow, and germination was also high on bare ground in the snow-bed. Grazing seemed to be a more important structuring factor in the snow-bed than in the more productive tall herb meadow. Raising the grazing pressure during one growing season by introducing microtine rodents into enclosures did not cause any large short-term effects on plant community structure in a tall hob meadow or in a snow-bed. Marked shoots showed that some preferred plant species had a high shoot mortality, but biomass for pooled categories of plants was not significantly affected. It was predicted that the tall herb meadow would be more grazing sensitive than die snow-bed, but productivity on the meadow seemed to be sufficiently high for the plants to compensate for the grazing during the growing season. A greenhouse experiment showed that voles, when grazing freely, have the potential to deplete productive field layer vegetation contrary to predictions from plant defence theories. A nitrogen-based defence did not prevent heavy shoot mortality for toxic tall herbs.

Diss. (sammanfattning) Umeå : Umeå universitet, 1993, härtill 5 uppsatser.

digitalisering@umu.se

L’inquiétude au sujet du devenir des forêts tempérées de moyenne montagne va croissant, du fait du changement climatique d’une part, et des difficultés de régénération liées à la pression exercée par les grands ongulés d’autre part. Les populations d’ongulés herbivores connaissent en effet une forte augmentation depuis le milieu du XXème siècle dans l’hémisphère Nord ; et leur abroutissement sélectif, dû à leurs préférences alimentaires, exerce une forte pression sur la régénération, dont l’intensité sur les essences varie selon leur appétence. La réponse de la régénération au changement climatique en termes de survie et de croissance demeure méconnue, mais de premiers résultats suggèrent qu’elle pourrait être encore plus affectée que les arbres adultes, et de manière différentielle également du fait des diverses autécologies des essences. Dans ce contexte de changements globaux, le recours aux forêts mélangées est envisagé comme une option valable de minimisation des risques. Comment caractériser la réponse de la régénération à ces deux pressions de sélection, et quel pourrait être l’avenir d’un peuplement mélangé dans ce contexte ? Notre étude se focalise sur les effets de l’abroutissement par les grands ongulés et du changement climatique sur la régénération du sapin, du hêtre et de l’épicéa en mélange. Nous utilisons pour cela diverses approches. Nous montrons que la germination et l’installation de semis de hêtres n’est pas affectée par l’éclairement au sol plus faible en situation de mélange. Nous mettons en évidence une quasi-inversion d’essences entre sapin et épicéa au niveau de la strate de régénération, bénéficiant à l’épicéa, lorsqu’ils sont soumis à une forte pression d’abroutissement. A l’échelle des traits foliaires, nous trouvons des réponses différentes entre les trois essences aux pressions du climat et de l’abroutissement, le sapin étant le seul à exprimer une réponse claire à l’abroutissement (tissus plus résistants, augmentation du rapport C/N foliaire). Nos résultats démontrent également une diminution de l’abroutissement avec l’augmentation de la température hivernale et un effet plus important de l’abroutissement que de la température printanière sur la croissance des semis de sapin, hêtre, érable. Enfin, via une approche de modélisation, nous avons simulé la dynamique d’un peuplement mélangé de sapin, hêtre et épicéa sur une durée de 100 ans, et montré une modification des seuils de tolérance à la sécheresse par l’abroutissement, et vaildé la possible disparition du sapin dans des scénarios comprenant abroutissement et changement climatique. Ces travaux soulignent l’influence des grands ongulés en interaction avec les conditions climatiques sur la dynamique de la régénération forestière, et l’importance de prendre cette pression en compte dans les protocoles de recherche destinés à étudier l’évolution de la régénération en contexte climatique changeant
There is growing concern about the future of temperate mountainous forests, because of climate change and of the difficulties in regenerating forests caused by large ungulates pressure. Herbivore ungulate populations have strongly increased since the middle of the XXth century in the northern hemisphere. By their selective browsing due to their dietary preferences, they exert a strong pressure on regeneration, which intensity on each tree species varies with their palatability. The response of regeneration to climate change in terms of growth and survival is still poorly known, but some results suggest it could be affected differentially given the different autecologies of the species. In such a global changes context, mixed forests are considered a valuable option of adaptation. How would the regeneration phase respond to those two pressures, and what could be the future of a mixed stand in such a context? This study focuses on the effects of browsing by large ungulates and climate change on mixed silver fir, Norway spruce and beech stand regeneration. We show that the lower amount of light reaching the ground in mixed stands does not affect beech regeneration germinating. We demonstrate a quasi-substitution of silver fir by Norway spruce saplings when submitted to high browsing pressure. At the finer scale of foliar traits, we find different responses among the three species to varying climate and browsing pressure, silver fir being the only species expressing an answer to browsing (increase in shoot mechanical resistance and in foliar C:N). Our results also demonstrate a decrease in browsing with increasing winter temperature, and a stronger effect of browsing than of spring temperature on saplings growth for silver fir, beech and sycamore maple. Finally, our simulations of the dynamics of a mixed silver fir-Norway spruce-beech stand suggest a shift in tolerance to drought thresholds due to browsing, and confirm the possible eradication of silver fir in scenarios combining browsing and climate change. This work highlights the influence of large ungulates interacting with climate conditions on forest regeneration dynamics, and the importance to consider this pressure in research protocols aiming at studying the behaviour of regeneration in changing climate contexts

Le brachypode rameux (Brachypodium retusum) est une espèce herbacée pérenne qui domine les pelouses sèches de Méditerranée occidentale. Dans notre zone d’étude du Sud de la France, la recolonisation spontanée est très faible après perturbation du sol. Cette observation ne correspond pas aux résultats d'études menées dans d'autres régions montrant une capacité de colonisation élevée. L'objectif principal de cette thèse était donc de tester les différentes hypothèses pouvant expliquer les différents patrons de colonisation.Dans un premier chapitre, nous avons testé si ces différents patrons de colonisation résultent d'une différenciation génétique entre les populations. Des marqueurs AFLP ont été utilisés pour analyser la structure génétique de 17 populations de Méditerranée occidentale dont la différenciation neutre entre populations. Dans un sous-échantillon de 13 populations françaises, la différenciation de traits phénotypiques sous sélection a été testée dans un jardin commun et comparée à la différenciation neutre. Dans le deuxième chapitre, nous présentons une étude sur la différenciation adaptative des traits phénotypiques et avons testé une potentielle réponse différentielle à la manipulation de facteurs environnementaux clés. Les deux derniers chapitres de la thèse ont analysé les facteurs environnementaux qui limitent la recolonisation in situ, indépendamment du génotype ou de la population. Dans le troisième chapitre, nous avons testé l’effet du pâturage et du feu sur le recouvrement végétatif ainsi que sur la reproduction sexuée de B. retusum installé. Enfin, dans le quatrième chapitre, nous avons mesuré l’effet de l’arrosage initial et du pâturage sur l’installation de plantules transplantées initialement germées en serre et de plantules issues de semis in situ. Nos résultats ont montré que les populations de B. retusum sont génétiquement différenciées pour les marqueurs neutres mais également pour les traits phénotypiques. Cette différenciation est supérieure à la dérive seule et suggère une adaptation aux conditions environnementales, en particulier aux températures estivales et à la fréquence du gel en hiver. Une réponse différentielle à la manipulation expérimentale de facteurs environnementaux (sol, pâturage, humidité du sol) a confirmé le caractère adaptatif de la différenciation génétique. Les expériences in situ ont montré que le feu a un effet positif sur la reproduction de B. retusum et sur la communauté végétale associée, alors que son recouvrement végétatif n’était pas supérieur à la moyenne de la communauté. L'exclusion du pâturage pendant deux saisons n'a eu d'incidence sur aucun des paramètres mesurés chez les populations adultes. L'arrosage initial a affecté l’installation des plantules au cours de la première saison. Au cours de la deuxième saison, l'effet seul de l’arrosage n'était pas significatif, cependant son effet est resté positif sur la survie uniquement dans les parcelles pâturées. Le pâturage, au début du cycle de vie de B. retusum, a eu un effet négatif sur le recrutement et la croissance des plantules. En conclusion, la différenciation adaptative entre les populations peut avoir contribué aux différences régionales en termes de capacité de colonisation et doit être prise en compte lors du ciblage des populations sources pour l'introduction de plantes en restauration écologique. La réponse positive de B. retusum a indiqué que le feu était une force sélective importante dans le passé qui pourrait être utilisée pour favoriser l'espèce et la communauté végétale associée dans des opérations de conservation et de restauration. L'exclusion du pâturage à court terme est tolérée par les populations adultes de B. retusum, mais l'abandon à long terme entraîne une diminution de son recouvrement par rapport aux graminées pérennes à croissance rapide
Ramose false brome (Brachypodium retusum) is a perennial herbaceous species that dominates dry grasslands of the Western Mediterranean. In our southern French study area, spontaneous re-colonisation is very low after soil disturbance. This observation does not correspond to the results of studies from other regions showing a high colonisation capacity. The major objective of this PhD thesis was to test different hypotheses potentially explaining the different colonisation patterns.In the first chapter, we tested whether these different colonisation patterns are the result of genetic differentiation among populations. AFLP markers were used to analyse genetic structure including neutral population differentiation in 17 Western Mediterranean populations. In a sub-sample of 13 French populations, differentiation in phenotypic traits under selection was tested in a common garden and compared to neutral differentiation. In the second chapter, we present a study on adaptive differentiation in phenotypic traits testing a potentially differential response to the manipulation of key environmental factors. The last two chapters of the PhD analysed environmental factors that limit re-colonisation in the field independent of genotype or population. In the third chapter, we tested the effect of grazing and fire on vegetative recovery as well as on sexual reproduction of established B. retusum and in the fourth chapter we measured the effect of initial watering and grazing on the establishment of transplanted seedlings pre-grown in a greenhouse and of field-sown seedlings.Our results showed that populations of B. retusum are genetically differentiated in neutral markers but also in phenotypic traits. This differentiation is superior to drift alone and suggests adaptation to environmental conditions, particularly to summer temperature and winter frost frequency. A differential response to experimental manipulation of environmental factors (soil, pasture, soil moisture) confirmed the adaptive character of genetic differentiation. The field experiments showed that fire has a positive effect on B. retusum reproduction and on the associated community whereas vegetative recovery was not higher than community average. Two seasons of grazing exclosure did not affect any of the measured parameters in adult populations. Initial watering affected seedling establishment in the first season. In the second season, the watering main effect was not significant but interestingly the effect remained positive on survival in grazed plots whereas no such effect was observed in exclosures. Grazing in early life cycle stages of B. retusum had a negative effect on seedling recruitment and growth.In conclusion, adaptive differentiation between populations may have contributed to regional differences in colonisation capacity and needs to be taken into account in targeting source populations for plant introduction in ecological restoration. The positive response of B. retusum indicated that fire was an important selective force in the past which may be used to favour the species and its associated plant community in current conservation and restoration management. Short-term grazing exclosure is tolerated by mature B. retusum populations but long-term abandonment results in a decrease of cover relative to high-growing perennial grasses. In early stages of seedling establishment grazing should be avoided to guarantee introduction success - or grazing stress needs to be compensated by watering

碩士
國立彰化師範大學
生物學系
90
The Su Tsao Wild Life Reserve is a very important perching habitat in southwest Taiwan for winter migrant birds. Feeding is the main activity to wintering shorebirds. Therefore, the exclosure experiment and the analysis of stomach content in shorebird were designed to assess the impact of feeding activities of winter shorebirds on the prey abundances in this Reserve Area. According to the experimental results and statistic analysis, I concluded that: (1) Except water depth, other environmental factors were no significance differences in every experimental day. (2) Feeding of shorebirds declined the numbers of the invertebrates, however, the numbers of birds were few, the numbers of the invertebrates no significant declined. (3) The reduced quantity of invertebrates was positively correlated with the numbers of shorebirds. (4) From the study of stomach contents, shorebirds consumed Thiara riqueti, Neanthes glandicincta, and Capitellidae sp.1. Exclosure experiment produced the same result. (5) At night, shorebirds still fed and reduced the numbers of invertebrates. The result also presented that the distribution of shorebirds was no concern with the invertebrate numbers. The possible reason for this would be the invertebrates were abundant to supply the consumptions of shorebirds. The feeding rate of shorebirds might be over estimated by mathematical magnification. In addition, more information about resident invertebrates, such as life cycle and activity times, will provide more thorough understanding in the feeding ecology of winter shorebirds.

Predators are a threat to many ground-nesting shorebirds, although it remains largely unknown how they interact with passive predator management techniques such as nest exclosures. I examined the effects of nest exclosures on incubating Piping Plovers (Charadrius melodus melodus) and their predators on nesting beaches in Kouchibouguac and PEI National Parks. A combination of behavioural observations, video monitoring of nests and an artificial nest experiment was used to examine the effects of nest exclosures in this study system. The behaviour of Piping Plovers did not differ between exclosed and unexclosed nests, although different types of predators seemed to have an effect on plover nest attentiveness. Predators visited exclosed nests more often than unexclosed nests and spent more time in the vicinity of exclosed nests than unexclosed nests. Since increased adult mortality and nest abandonment have been documented at exclosed Piping Plover nests, as well as nests of other shorebirds, the results of this study provide evidence of a link between predator harassment and these negative effects.

Woody vegetation patches play an important role in the savanna ecosystem. They provide habitat for animal species and are important for some ecological processes such as. However, the coexistence of trees and grass depend on several factors such as fire, elephant, rainfall and soil type. In Kruger National Park, factors that affect the survival of woody vegetation patches are elephants and fire. The loss of woody vegetation patches leads to fragmentation of the landscape. The main aim of this study was to determine the relative difference in the composition, complexity and configuration of woody vegetation patches in and out of the enclosures, and to evaluate the changes in number and size, shape and connectivity of woody vegetation patches between basalt and granite soils over a period of time. There was no linear relationship between composition and complexity and mean nearest neighbour with year, whilst edge density appeared to have a linear relationship with year. Based on edge density results, the results suggested that there was increase in landscape fragmentation in Kruger National Park. The increase in woody patch fragmentation can be attributed to the increase in elephant population, as well as fire frequency and intensity. There was no difference in the composition, complexity and configuration between the inside of the enclosure and the outside. The results show that there is difference between the basalt (Makhohlola) and granite (Nwashitshumbe) region. The results indicated that Makhohlola seems to be highly fragmented than the Nwashitshumbe. The basalt region is situated on rich soils and receives more rainfall than the granite region; hence thus plant growth is greater than that on granite region. High plant growth is associated with high fire frequency and intensity, which result high influence on woody vegetation. The basalt region is dominated with palatable vegetation, as result; the basalt region is associated with large number of herbivores. Due, to high number of herbivores, and high frequency and intensity, the basalt region may be highly fragmented. The change in woody vegetation patches over time, on both basalt and granite region was associated with the interaction between the increase in elephant density, and fire frequency and (or) intensity.

Internationally, the impacts of deer have been widely studied, but little work has been conducted in Australia. Sambar (Cervus unicolor Kerr) were introduced to Victoria in the 1860s from Sri Lanka, and have become established throughout eastern Victoria. This study is located in the Yarra Ranges National Park, 100 km north east of Melbourne. The park primarily consists of three protected water catchments that contribute approximately 50% to Melbourne’s water supply. This study was conducted from 2005 to 2008 in the Upper Yarra and O’Shannassy catchments. Large open areas covered by forbs and grasses periodically form adjacent to the water body of the Upper Yarra reservoir. Sambar are frequently observed at the largest of these areas known as The Flats. The impacts of sambar at this locality and in other areas of the catchments were investigated.
Faecal pellet transect surveys determined that sambar occupancy and density was greatest on open flats, lower on forest edges adjacent to open flats (< 250 m), and significantly less in other forested areas of the catchment. Observations of The Flats revealed that hinds were the main demographic class represented, with a mean group size of 39 individuals, and up to 70. This is the largest aggregation of sambar ever reported anywhere in the world, and equates to an approximate density of 200 km-2 at this site.
Selective exclosures effectively differentiated the offtake of forage by sambar from that of native herbivores. Sambar contributed to the majority of offtake at The Flats, and were able to obtain a substantial proportion of their daily food requirements from this source. A culling program began in the Yarra Ranges National Park in May 2008, to reduce the large numbers of deer in the park. The cull reduced the time spent by sambar on The Flats, as determined by faecal pellet accumulation plots, and significantly reduced faecal pellet load and forage offtake.
Sambar significantly decreased relative foliage cover of shiny nematolepis (Nematolepis wilsonii), a threatened understorey tree, through their antler rubbing activities. Thrashing of shiny nematolepis saplings also significantly decreased relative foliage cover, with sambar selecting saplings with a larger stem diameter from those available. Rubbed trees and thrashed saplings experienced damage to, on average, over half the stem circumference.
Selective exclosures allowed differentiation of sambar and native herbivore browsing on forest understoreys. Browsing by sambar in high densities prevented the vertical growth of plants in the understorey, with branches above 60 cm in height most commonly browsed. Plants in the understorey were more frequently and intensely browsed in areas of high sambar density. Three species were browsed to a significantly greater extent by sambar than native herbivores: hazel pomaderris (Pomaderris aspera), prickly tea-tree (Leptospermum continentale) and prickly bush-pea, (Pultenaea juniperina). Sambar significantly reduced plant biomass in forest understoreys where they occur in high densities.
The presence of large, open herb-rich areas drives the high local densities and associated impacts of sambar within the Yarra Ranges National Park. Future areas of research are identified and management recommendations are outlined. A sustained culling program appears to be the only practical option to reduce sambar density and impacts at this locality.

The Amazon rainforest harbors the planet's highest biodiversity among terrestrial ecosystems; however, the biology and ecology of most of its species are unknown. Niche partitioning is considered a key factor allowing species co-existence, especially for morphological similar species such as spiny rats of the genus Proechimys. I examined the extent to which habitat differentiation, species body mass, and diet could explain the community composition of small mammals at a site in the southeastern Amazon. Moreover, I radio-tagged sympatric species of Proechimys spp. and Mesomys stimulax (an arboreal spiny rat) to obtain detailed autoecology information, including habitat use and use of space. I found support for niche partitioning among species and associated small mammal species with distinct successional phases of gap dynamics. I also observed among Proechimys spp. a typical polygynous organization: females appeared to be territorial against females of any species of their genus; but male territories overlapped with those of several females. Mesomys stimulax showed evidence of monogamy and possible sociality, although sample sizes were small. To identify the importance of small mammals as seed disperser of Brazil nut seeds, I conduct experiments using a combination of fluorescent powder, seed exclosures, and track plates in forests with and without Brazil nut groves, and in forests with and without Brazil nut harvesting. Among small mammals, only Proechimys spp. removed, dispersed, and preyed upon Brazil nut seeds. Proechimys spp. sometimes scatterhoarded these seeds, and hence have the potential to play a significant role in recruiting new Brazil nut trees. I also trapped small mammals and measured forest structures on the same sites used for the seed dispersal experiment, to determine the ecological effects of Brazil nut harvest on small mammal communities; however, my results showed little evidence of changes associated with the seed exploitation. My results highlight the importance of habitat heterogeneity in structuring small mammal communities, and indicate that forest management practices that alter habitats, such as partial logging, also can be expected to alter small mammal composition and diversity. Proechimys spp. have the potential to play an important role in the ecological restoration of intensive exploited Brazil nut groves.