The purpose of this research was to increase understanding of ecology and control of cogongrass (Imperata cylindrica (L.) Beauv.) to assist with management of this invasive grass. To address different aspects of cogongrass management, I examined factors that affect spread of cogongrass, effects of cogongrass on native plant communities, and use of three native species to suppress cogongrass. Relative susceptibility of pine-bluestem and pine-shrub vegetation associations to vegetative encroachment and seed dispersal of cogongrass were evaluated. Vegetative encroachment into burned and unburned areas of these two vegetation associations also was measured. Effects of infestation size on vegetative growth of cogongrass and relationships between military activity and establishment and growth of cogongrass on military firing points were investigated. I also compared frequency of cogongrass infestation and vegetative growth rates for unpaved roads with different levels of traffic and maintenance. Native plant richness, diversity, and abundance were compared between cogongrass infestations and in uninfested adjacent areas for longleaf pine-bluestem and ruderal, cleared areas. Morella cerifera (L.) Small, Chamaecrista fasciculata (Michx.) Greene, and Panicum virgatum L. were tested for their ability to suppress cogongrass re-growth after treatment with a herbicide. Mean vegetative encroachment of cogongrass was < 2 m/yr for both habitat types regardless of burning. Vegetative encroachment was more than double in burned plots compared to unburned plots. Spikelets of cogongrass consistently dispersed farther into pine-bluestem (x¯ =17.3 m) forests compared to pine-shrub forests (x¯ = 9.4 m). Vegetative encroachment was not affected by size of infestation for cogongrass patches on firing points (x¯ < 1 m/yr) (P > 0.643). In areas of soil disturbance from military equipment, vegetative expansion rates of 7-10 m/yr were recorded. There was a positive relationship between military troop use and cogongrass establishment for one of the 2 years of the study (P = 0.023). Growth and establishment of cogongrass did not vary for unpaved roads with differing levels of maintenance and traffic (P > 0.173). Species diversity and abundance of herbaceous vegetation was less in cogongrass infestations compared to uninfested adjacent areas. Complete suppression of cogongrass was not evident for any of three native species tested.

No description available.

No description available.

Grasslands provide fundamental ecosystem services in many arid and semi-arid regions of the world, but are experiencing rapid increases in fire activity making them highly susceptible to post-fire accelerated soil erosion by wind. A quantitative assessment that integrates fire-wind erosion feedbacks is therefore needed to account for vegetation change, soil biogeochemical cycling, air quality, and landscape evolution. We investigated the applicability of a novel tracer technique – the use of multiple rare earth elements (REE) - to quantify aeolian soil erosion and to identify sources and sinks of wind-blown sediments in a burned and unburned shrub-grass transition zone in the Chihuahuan desert, NM, USA. Results indicate that the horizontal mass flux of wind-borne sediment increased approximately three times following the fire. The REE-tracer analysis of aeolian sediments shows that an average 88% of the horizontal mass flux in the control area was derived from bare microsites, whereas at the burned site it was derived from shrub and bare microsites, 42% and 39% respectively. The vegetated microsites, which were predominantly sinks of aeolian sediments in the unburned areas, became sediment sources following the fire. The burned areas exhibited a spatial homogenization of sediment tracers, highlighting a potential negative feedback on landscape heterogeneity induced by shrub encroachment into grasslands. Though fires are known to increase aeolian sediment transport, accompanying changes in the sources and sinks of wind-borne sediments likely influence biogeochemical cycling and land degradation dynamics. Our experiment demonstrated that REEs can be used as reliable tracers for field-scale aeolian studies. / Geology / Accompanied by one compressed .zip file: MET_Tower_Data.zip

Many grasslands in arid and semi-arid regions are undergoing rapid changes in vegetation, including encroachment of woody plants and invasive grasses, which can alter the rates and patterns of fire and sediment transport in these landscapes. We investigated the spatial distribution of sediments at the scale of vegetated microsites for three years following a prescribed fire using a multiple rare earth element (REE) tracer-based approach in a shrub-grass transition zone in the northern Chihuahuan desert (New Mexico, USA). To this end, we applied REE tracers – holmium, europium, and ytterbium on shrub, grass, and bare microsites, respectively in March 2016. Soil samples were collected from both burned and control (not burned) sites before (March) and after (June) the annual windy season, from 2016 through 2018. Results indicate that although the horizontal mass flux (HMF) of wind-borne sediment increased approximately threefold in the first windy season following the fire, and the HMF of both plots were not significantly different after three windy seasons. Comparing REE concentrations in sediments from both plots over the three years and three annual windy seasons, we observed a post-fire shift in source and sink dynamics of sediments. The tracer analysis of wind-borne sediments indicated that the source of the HMF in the burned site was mostly derived from shrub microsites following the fire, whereas the bare microsites were the major contributors for aeolian sediment in control areas. The shift in sources and sinks, and the spatial homogenization of REEs indicate that the removal of shrub vegetation resulted in sediment redistribution to the bare microsites even three years after the prescribed fire. The findings of this study will improve our understanding of post-fire geomorphic processes at a microsite scale in a grassland ecosystem undergoing land degradation induced by shrub encroachment. / Geology

xviii, 105 p. : ill. (some col.) / Restoration of riparian ecosystems in semi-arid riparian ecosystems requires an understanding of geomorphic, hydrologic and biologic factors and how they relate to vegetation. Such an understanding allows prioritization of restoration projects and avoidance of activities that are either unnecessary or likely to fail. In this dissertation I examined a suite of factors controlling distribution of vegetation types in the Sprague Basin, OR, and used those factors to predict potential for natural recovery. Factors ranged from basin-wide (e.g. floodplain width and slope) to local (e.g. topography, hydrology and soil texture). Results of historical analysis and photographic mapping showed that basin-wide vegetation types have remained generally stable since the early 1940s and that wide floodplains have been without woody vegetation since the late 1800s. The most prevalent changes in floodplain vegetation due to land use included reduction of shrub cover in moderately wide floodplains and associated increases in herbaceous vegetation. Soil moisture conditions were studied using piezometers and nested clusters of soil moisture tension meters. The interrelations among soil texture, elevation and distance from the channel, and vegetation (herbaceous and woody) characteristics in the riparian zone were examined along 75 transects using a generalized additive model for non linear factors and Hurdle analysis for abundance data. On the Sprague mainstem, fine soils with high recession rates supported abundant shrubs, while on the Sycan (Sprague tributary) coarse soils with readily available moisture and greater subsurface water movements supported abundant shrubs. Habitats in the Sycan were well colonized with new shrub seedlings though long term persistence was unlikely. Results show that riparian shrubs are unlikely to influence stream shade or bank stability on the mainstem Sprague whether they germinate naturally or are planted through restoration efforts, as shrubs near the channel are unlikely to persist long term. In the Sycan, germination and persistence are more likely than on the Sprague, though risks of predation, trampling from grazers, and fluvial action will be constant threats to near-channel shrubs. Results emphasize the need to understand factors controlling vegetation prior to restoration in any basin or stream segment. / Committee in charge: Patricia F. McDowell， Chairperson； W. Andrew Marcus， Member； Patrick Bartlein， Member； Scott Bridgham， Outside Member

Radial growth characteristics of a high-elevation shrub species, sea buckthorn (Hippophae rhamnoides), were investigated at four sites in a river valley at altitudes ranging from 3,333 to 3,820 m a.s.l. close to the terminus of the July First Glacier in the western Qilian Mountains of northwestern China. Radial growth of the sea buckthorn was significantly and positively correlated with the mean monthly temperature in June of the current growing season. Based on the fact that fluctuations in the shrub’s radial growth and the glacier’s equilibrium-line altitude (ELA) are affected by climatic variables, a tree-ring width chronology of the four sites was used to reconstruct the ELA from 1950 to 2003. The resulting ELA model explained more than 55.3% of the variance in the ELA of the July First Glacier series. On a decadal time scale, the cumulative-departure curve of the reconstructed ELA series showed an increasing trend from the 1950s to the mid-1960s, followed by a descending trend from the mid-1960s to the mid-1970s. The ELA appears to have remained stable from the mid-1970s to the mid-1990s, but has displayed dramatic variations during the past decade.

I quantified seasonal variations in corticular photosynthesis in 1st through 5th order branches of Myrica cerifera L. (Myricaceae) in order to determine whether corticular photosynthesis contributes to whole plant carbon gain by reducing respirational CO2 loss. Maximum % refixation was 110 ± 39 % of CO2 efflux in the dark (Rd) in 1st order branches during winter, minimum was 18 ± 3 % in 5th order branches during summer. Variations in % refixation paralleled changes in photosynthetically active radiation (PAR). As light attenuated with increasing branch order % refixation decreased. Increased PAR in the winter due to a more sparse canopy lead to increases in % refixation. Total chlorophyll content and chlorophyll a:b ratios were consistent with shade acclimation as branch order increased. Corticular photosynthesis may be a mechanism to enhance shrub expansion due to increased whole plant carbon use efficiency (CUE) and water use efficiency (WUE) attributed to refixation.

Apesar de vários estudos já terem examinado os efeitos de queimadas naturais, respostas das aves, como variação do padrão da comunidade, guilda trófica e das espécies, ao manejo de fogo ainda não foram investigadas em reservas do Cerrado, Este trabalho teve como objetivo comparar a avifauna em trechos de campo sujo manejados (aceiros) e não manejados por fogo no Parque Nacional das Emas, Brasil Central. Este é o primeiro trabalho a avaliar os efeitos do manejo do fogo prescrito sobre comunidades de aves no Cerrado. Foram selecionados 12 locais de estudo. Em cada local, havia um transecto no aceiro e outro em campo sujo não manejado. Uma amostra consistiu em percorrer um transecto de 800m a pé, anotando as aves detectadas visual ou auditivamente a 15m do observador. Frequência de ocorrência e abundância das espécies e das guildas tróficas, riqueza total, abundância total da comunidade de aves e composição de espécies encontradas nos dois ambientes foram comparadas. No total, foram 881 registros e 41 espécies de aves. A riqueza e a abundância total de aves foram significativamente menores em aceiros. Houve diferença na composição de espécies de aves entre campos não manejados por fogo e aceiros. Dentre as guildas tróficas, os onívoros foram mais frequentes em campos não manejados. Granívoros, nectarívoros e onívoros foram mais abundantes em vegetação não manejada. Das 21 espécies analisadas separadamente, a coruja Athene cunicularia foi a única indicadora de aceiros e também mais frequente e abundante em aceiros. Por outro lado, foram identificadas quatro espécies indicadoras de campos sujos não manejados (Melanopareia torquata, Xolmis cinerea, Neothraupis fasciata e Coryphaspiza melanotis). Tais espécies podem ser usadas como indicadores ecológicos do regime e histórico do fogo e podem fornecer informações se os objetivos das ações de manejo do fogo estão sendo atingidos. Sete espécies foram mais frequentes e oito espécies foram mais abundantes em campos não manejados. Três dessas espécies são endêmicas do Cerrado (M. torquata, N. fasciata e Cypsnagra hirundinacea) e quatro estão sob algum grau de ameaça e são altamente sensíveis a distúrbios (Polystictus pectoralis, Alectrurus tricolor, C. melanotis e C. hirundinacea). Assim, cuidado e atenção devem ser redobrados para essas espécies, pois possuem alto valor para conservação e menor frequência ou abundância em aceiros. A menor riqueza e abundância de aves encontrada em aceiros devem estar relacionadas ao menor uso desse habitat, indicando menor disponibilidade de recursos como alimento, reprodução e abrigo, dado que o fogo altera a estrutura e composição da vegetação. Isso demonstra uma diminuição da qualidade do ambiental geral dos aceiros, provocada pela sua atual forma de manejo. Propomos que a queima dos aceiros seja feita em intervalos de 3 anos, em vez de 1 2 anos como tem sido realizada. Dessa forma, seria mantida a função dos aceiros como controle e barreira efetiva de incêndios e também para conservação da biodiversidade. / Several studies have investigated the effects of natural fires on Cerrado birds. However, avian responses to fire management have not been examined. We compared birds found in firebreaks (fire managed areas) and in fire unmanaged grasslands, in Parque Nacional das Emas, Central Brazil. This is the first study to evaluate the effects of prescribed fire on the Cerrado avifauna. We selected 12 study sites. We established one transect in the firebreak and another one in an unmanaged grassland area in each study site. Each bird count sample consisted of walking through an 800m transect recording birds seen or heard 15m from the observer. Species richness, total bird abundance, species composition, feeding guilds abundance and frequencies of occurrence and species abundance found in firebreaks and unmanaged grasslands were compared. In total, 881 individuals and 41 species were recorded. Species richness and total abundance were significantly lower in firebreaks. Species composition was different between firebreaks and unmanaged grasslands. Omnivores were more frequent and more abundant in unmanaged grasslands. Granivores and nectarivores were more abundant in unmanaged grasslands. Twenty-one bird species were analyzed separately, one of which (Athene cunicularia) was indicator of firebreaks and also more frequent and abundant in firebreaks. On the other hand, we identified four indicator species of unmanaged grasslands (Melanopareia torquata, Xolmis cinerea, Neothraupis fasciata and Coryphaspiza melanotis). These species might be used as ecological indicators of fire regime and history, and also give information if fire management goals are being achieved. Seven species were more frequent and eight species were more abundant in unmanaged grasslands. Three of them are endemic of Cerrado (M. torquata, N. fasciata and Cypsnagra hirundinacea) and four of them are highly sensitive to human disturbances and threatened with extinction in some degree (Polystictus pectoralis, Alectrurus tricolor, C. melanotis e C. hirundinacea). Caution must be redoubled to these species, as they are of high conservation priority and less frequent and abundant in firebreaks. The lesser avifauna complexity in firebreaks than in unmanaged areas might be connected to the low use of this habitat, thus indicating lower resource availability, such as food, sites for reproduction and refuge. This is because fire changes vegetation structure and composition. We propose that firebreaks should be burnt every 3 years, instead of 1-2 years. In this way, fire management would keep its function as effective fire barriers and would also keep biodiversity conservation.

Biodiversity rich regions worldwide face threats from various global change agents. This research quantifies environmental influences on vegetation, and the impacts of exotic woody plant invasion and anthropogenic nitrogen (N) deposition in a global biodiversity hotspot. The study was conducted in the montane grasslands of the Nilgiris, Western Ghats, and outlines potential management options for this region. Specifically, I examined (1) the role of environmental factors in influencing native plant distribution and ecosystem properties, (2) the status and impact of exotic shrub (Scotch broom, henceforth broom) invasion, (3) the role of disturbances in the success of broom, (4) the role of fire in restoring invaded grasslands, and (5) the impacts of terrestrial N loading on the grassland ecosystem. I used experiments and surveys to assess these. Distributions of several key species were explained by a few complex environmental gradients. In invaded-grasslands, broom populations consisted mainly of intermediate size and age classes, with no clear indication of population decline. Invasion negatively impacted plant community structure and drastically changed composition, favoring shade-tolerant and weedy species. However, invasion did not greatly alter ecosystem function. Fire successfully eliminated mature broom stands, but resulted in a short-term increase in broom seedling recruitment. At the end of 18 months, the fire effects on uninvaded-grasslands were not apparent, but there was no conclusive evidence of the formerly invaded patches attaining the composition of uninvaded-grasslands following burning. N fertilization strongly influenced soil N dynamics, and shoot N concentrations, but effects on aboveground production were weak. Surprisingly, N enrichment had positive effects on diversity in the short-term. It is clear that these grasslands need immediate management intervention to forestall degradation from invasion. Fire could be used to eliminate mature broom stands and deplete persistent seedbanks, which will facilitate colonization by shade-intolerant grassland plants. Active restoration should be mindful of environmental preferences of framework species. Long-term studies of the impacts of N deposition in the context of disturbances will help determine realistic critical thresholds and utilize disturbances to buffer the potential adverse effects of increasing N loading.