Dissertations / Theses on the topic 'Cedar Mountain'

The Cedar Mountain Formation contains the most diverse record of Early Cretaceous dinosaurs in the western hemisphere. However, analyses of its faunas have been hindered because 1) most taxa are based on incomplete/fragmentary materials or incomplete descriptions, 2) most sites and some horizons preserve few taxa, and 3) the stratigraphy and geochronology are poorly understood. To help resolve these stratigraphic and correlation problems U-Pb LA-ICP-MS detrital zircon ages were obtained at significant sites and horizons. These dates indicate all sites at or near the base of the formation are no older than 122 to 124 Ma, thus all basal stratigraphic packages are time equivalent. Detrital zircons coarsely bracket the temporal span of the Ruby Ranch Member between about 115 Ma to 111 Ma while the base of the Mussentuchit Member is dated between 108 to 104 Ma and the top of the member is Cenomanian in age. Multivariate analyses utilizing Simpson and Raup-Crick similarity index and pair-group moving algorithms reveal that formationfs faunas fall into two groups. These groups are compared statistically with European, Asian, and Morrison faunas. Results indicate (1) that there is no close relationship between the Yellow Cat fauna and the Morrison Formation fauna and (2) corroborate long-standing hypotheses that the Yellow Cat fauna has European ties and the Mussentuchit fauna has Asian ties. Detrital zircon LA-ICP-MS U-Pb ages were used in this study to approximate the time of deposition of strata because volcanic ashes are rarely preserved in the formation. The ability to select the youngest crystals in a sample prior to applying analytical methods could substantially reduce the number of crystals and cost required to obtain these dates. To this end, the hypothesis that the most pristine, unabraded crystals should be younger than abraded crystals was tested by imaging detrital zircons via SEM, ranking the crystals by the degree of abrasion, and determining their ages. Results of this study partly corroborate the hypothesis in that there is a correlation between the degree of abrasion and ages – obviously abraded crystals are most likely the oldest while pristine to slightly abraded crystals are usually the youngest in a given sample.

The age of the Ruby Ranch Member (RRM) of the Cedar Mountain Formation in East-Central Utah was recently constrained using carbon isotope chemostratigraphy to span known excursions associated with the late Aptian. The RRM is characterized by calcrete horizons that are thought to occur across the C10 carbon isotope excursion. Along with carbonate stable isotope analyses and the region’s paleo-position in a depositional basin on the leeward rain shadow of the Sevier Orogenic belt, this interval is hypothesized to coincide with an aridification event. Our research objective is to quantify the extent of this aridity using clumped isotope paleothermometry (n = 7) and paleoprecipitation proxies (n = 51) for samples collected across the C10 chemostratigraphic interval. Two weathering indices, CIA-K and CALMAG, were applied to data obtained using X-ray fluorescence spectrometry. Using these proxies, we determined mean annual precipitation across the RRM at its type section. Precipitation values ( n = 27) obtained through CIA-K for identified paleosol horizons ranged between 795 and 1275 mm/year, and through CALMAG ranged between 735 and 1042 mm/year. Precipitation values decreased through the C10 interval which may indicate increased aridity. Clumped isotopes provided ?47 values ranging from 0.647 to 0.693‰. Paleotemperature measurements (n = 4) from accepted carbonate samples were between 27.9 and 46.3 °C. Isotopic compositions of water calculated from carbonates ranged between -4.4‰ and -1.9‰ VSMOW. Precipitation values and temperatures were not lowest during the C10 interval. Temperatures peaked at the end of the C10 interval and decreased afterward, indicating a potential for cooler, more arid conditions. These results suggest that carbon cycle changes during the mid-Cretaceous may have influenced paleoclimate conditions experienced in terrestrial settings.

Widespread mortality of quaking aspen (Populus tremuloides Michx.) has occurred over large expanses of the Western US during the 20th century. While much of this decline was due to conifer encroachment into seral aspen, significant aspen losses also occurred in areas of persistent aspen and may have been exasperated by drought conditions. Aspen decline has been especially notable at Cedar Mountain, Utah, an area of mostly private land and extensive persistent aspen coverage. The objectives of this study were to create a time series of live and dead aspen cover on the Cedar Mountain landscape, using remotely sensed imagery, and to test whether water stress correlated to the decline therein. To accomplish these objectives, a decision tree classifier was used to classify the Cedar Mountain area into live and dead aspen cover classes for the years 1985, 1990, 1995, 2001, 2005, and 2008. Thereafter, post-classification change analysis was performed to determine areas and time periods of elevated decline. Regression analyses were performed to ascertain correlations between climatic data and percent change in aspen cover. A topographic analysis using zonal statistics was also performed to determine landscape positions where aspen decline is more prevalent. The time series models indicated that aspen decline followed a step-wise pattern with an overall decrease of 23.57 % in aspen cover during a 23-year period. Considerable aspen decline occurred early in the study time frame, with decreases of 1.38 and 1.36 -1 in 1990 and 1995, respectively. The middle period between 1995 and 2001 had no net change in aspen cover. However, the end of the time series showed the greatest decline with decreases of 1.56 and 1.99 % yr-1 in 2005 and 2008, respectively. There was a correlation between percent change in aspen cover and precipitation, suggesting that drought weakens aspen, making it susceptible to future decline. The topographic zonal statistics revealed that drier landscape positions had greater frequencies of dead aspen. The most significant predictor of aspen decline was elevation, which was significantly greater in the live aspen for three of the five years.

The Mountain Hemlock (MH) zone includes all subalpine forests along British Columbia’s coast. It occurs at elevations where most precipitation falls as snow and the growing season is less than 4 months long. The zone includes the continuous forest of the forested subzones and the tree islands of the parkland subzones (Figure 1). Old-growth stands are populated by mountain hemlock, Pacific silver fir, and Alaska yellow-cedar, and are among the least-disturbed ecosystems in the world. Canopy trees grow slowly and are commonly older than 600 years, while some Alaska yellow-cedars may be up to 2000 years old. Understanding regeneration patterns in the MH zone has become increasingly important as logging continues towards higher elevations of the zone where snowpacks are deeper.

Quaking aspen (Populus tremuloides Michx.) is the most widespread deciduous tree species in North America and aspen ecosystems are highly valued for multiple use, being noted for forage production, understory diversity, wildlife habitat, timber, hydrological assets, and aesthetics. However, aspen communities in the Intermountain Region of the western United States are in evident decline, with certain areas experiencing rapid mortality over the past decade. One location of special interest is the quaking aspen on Cedar Mountain in Southern Utah, USA, an isolated population in the southwestern portion of aspen's geographic range. Lacking critical information on the location, extent, and magnitude of declining stands, land managers could utilize detailed spatial information to manage aspen on Cedar Mountain. To inform land managers of Cedar Mountain and develop methodologies applicable for aspen landscapes across the Intermountain West, a spatially explicit aspen stand type classification using multi-spectral imagery, digital elevation models, and ancillary data was produced for the 27,216-ha pilot study area. In addition, a statistical analysis was performed to assess the relationships between landscape parameters derived from the geospatial information (i.e. slope, aspect, elevation) and aspen on the Cedar Mountain landscape. A supervised classification composed of three aspen stand types (1-healthy, 2- damaged, 3-seral) was produced using Classification and Regression Tree (CART) analysis and validated using National Agriculture Imagery Program (NAIP) imagery. Within Cedar Mountain aspen cover, classification estimates were 49%, 35%, and 16% for healthy, damaged, and seral aspen stand types, respectively. Validation measures yielded an overall accuracy measure of 81.3%, (KHAT=.69, n = 446). Important landscape metrics for the three health classes were found to be significantly different. Damaged stands were found primarily at lower elevations on south-to-west (drier) aspects. Within the aspen elevation range, the mean elevation of damaged stands (2,708 m) was significantly lower than that of the mean elevation of healthy stands (2,754 m). Aspect (moisture index) was also significantly different, with damaged stands primarily on southerly (drier) aspects and healthy stands generally on northerly (wetter) aspects. Slope, however, was not found to be significantly different among aspen types.

The Cedar Mountain and Dakota Formations are significant gas producers in the southern Uinta Basin of Utah. To date, however, predicting the stratigraphic distribution and lateral extent of potential gas-bearing channel sandstone reservoirs in these fluvial units has proven difficult due to their complex architecture, and the limited spacing of wells in the region. A new strategy to correlate the Cedar Mountain and Dakota Formations has been developed using core, well-log, and 3D seismic data. The detailed stratigraphy and sedimentology of the interval were interpreted using descriptions of a near continuous core of the Dakota Formation from the study area. The gamma-ray and density-porosity log signatures of interpreted mud-dominated overbank, coal-bearing overbank, and channel sandstone intervals from the cored well were used to identify the same lithologies in nearby wells and correlate similar stratal packages across the study area. Data from three 3D seismic surveys covering approximately 140 mi2 (225 km2) of the study area were utilized to generate spectral decomposition, waveform classification, and percent less-than-threshold attributes of the Dakota-Cedar Mountain interval. These individual attributes were combined to create a composite attribute that was merged with interpreted lithological data from the well-log correlations. The overall process resulted in a high-resolution correlation of the Dakota-Cedar Mountain interval that permitted the identification and mapping of fluvial-channel reservoir fairways and channel belts throughout the study area. In the future, the strategy employed in this study may result in improved well-success rates in the southern Uinta Basin and assist in more detailed reconstructions of the Cedar Mountain and Dakota Formation depositional systems.

The Mountain Hemlock (MH) zone includes all subalpine forests along British Columbia’s coast. It occurs at elevations where most precipitation falls as snow and the growing season is less than 4 months long. The zone includes the continuous forest of the forested subzones and the tree islands of the parkland subzones (Figure 1). Old-growth stands are populated by mountain hemlock, Pacific silver fir, and Alaska yellow-cedar, and are among the least-disturbed ecosystems in the world. Canopy trees grow slowly and are commonly older than 600 years, while some Alaska yellow-cedars may be up to 2000 years old. Early regeneration failures followed slashburning and the planting of unsuitable species. Currently, the most successful and feasible option for reforesting cutovers is natural regeneration with a mix of the three main tree species, but uncertainties remain about the temporal and spatial pattern of regeneration, changes in species composition, and the time required for stand establishment after cutting. Our study addressed these concerns by examining regeneration patterns on 6 sites that were clearcut 11-12 years prior to sampling and left to regenerate naturally. The sites were located at the lower limits of the zone in the Tetrahedron Range, near Sechelt, at elevations from 1060-1100m.

Numerous well-preserved, exhumed paleochannels in the Morrison, Cedar Mountain and Dakota Sandstone formations are exposed east of Castle Dale, Utah. These channels consist primarily of point bar complexes and scattered, low sinuosity channels. To determine the vertical and lateral relationships of these channels within the Cedar Mountain and Dakota Sandstone formations, a 1:24,000 scale geologic map covering ~140 km2 was created showing the fluvial sandstones. In the study area the Cedar Mountain Formation consists, from bottom to top, of 2.5-10 m of Buckhorn Conglomerate Member equivalent units, ~80 m of the Ruby Ranch Member, and ~30 m of the Mussentuchit Member. The Dakota Sandstone consists of conglomeratic to sandy, meandering channel fills within the Mussentuchit Member. The Ruby Ranch-Mussentuchit member contact is diagnosed as the top of a laterally extensive, ~10 meter thick, maroon paleosol with calcrete horizons and root traces. When deeply weathered the contact is discernable as a shift from maroon mudstone to a pale green-white, silty mudstone. Like the balance of the Mussentuchit Member overbank deposits, the white-green mudstone is rich in smectitic clays. In the southern one-third of the mapped area, Ruby Ranch Member sandstones are thin, discontinuous channel segments surrounded by floodplain deposits. In the middle to northern area, point bar complexes dominate, some of which are laterally amalgamated. Flow direction data from four meander complexes and a low sinuosity channel indicate an average northeast flow. Dakota Sandstone channels all of which are within the Mussentuchit Member also flowed to the northeast but point bar complexes are both more numerous and more laterally continuous than in the Ruby Ranch Member, indicating deposition in an area with less accommodation space than during Ruby Ranch Member time. The data indicate the Dakota Sandstone consists exclusively of fluvial sandstones encased within the Mussentuchit Member of the Cedar Mountain Formation. Therefore, these units are coeval and simply different facies of the same depositional system. Consequently the Mussentuchit Member is considered a member facies of the Dakota Formation.

Thesis (MSc)--Stellenbosch University, 2008.
ENGLISH ABSTRACT: The Greater Cederberg Biodiversity Corridor (GCBC) is a large-scale conservation corridor situated in the south-western region of South Africa. Delineation of the GCBC was largely based on by vegetation data. The relevance of the GCBC for the conservation of the reptilian fauna in the area south of 31°S and west of 21°E is assessed in the present study. This entailed determining the GCBC’s coverage of regional reptile diversity patterns and assessing its potential conservation significance during possible climate induced changes in reptile distributions. Reptile species point distribution data from the preliminary (2007) SARCA (South African Reptile Conservation Assessment) database was used. Under-representation of the Tankwa Karoo in the dataset required a field survey of this region. Additionally, the biogeographical influence of the arid Tankwa Karoo Basin on the distribution of reptiles in the south-western districts of South Africa was investigated. Turnover across the Basin is high, species richness is lower than in surrounding mountainous areas and there are no species endemic to the area. The Tankwa Karoo Basin acts as a dispersal barrier for many reptile species occurring in the surrounding more mesic areas. At the same time, the ranges of a number of typical northern, arid adapted species extend southward along the Tankwa Plains. A number of species range extensions in the region are reported. Patterns of endemism, species richness and turnover were plotted from the point distribution data at quarter and eighth degree square resolution. Extensive sampling bias towards reserves and populated areas is apparent from the reptile species richness plots. This pattern is more pronounced for snakes than lizards. Reptile richness is particularly high along the north-south section of the Cape Fold Mountains and also relatively high along the south-western coast, peaking in the Lambert’s Bay area. The majority of the 20 reptile species endemic to the study area are associated with one of two identified centres of endemism: the Greater Cederberg area, or the narrow coastal zone stretching from the Lambert’s Bay area to the Cape Peninsula. An additional third set of endemics comprised of melanistic forms restricted to a number of different refugia, notably, Landroskop, the Cape Peninsula, Sladanha-Langebaan region, Piketberg Mountains and a confined area along the western section of the Cape Fold Mountains. Species richness and endemism patterns co-vary within the study area. Biotic regions were identified through hierarchical clustering of grid cells according to shared species occurrences. A Northern, Southern, Central and Western biotic region was identified. Classification tree methodology (CART) and Canonical Correspondence Analysis (CCA) were used to characterise defined biotic regions in terms of selected environmental variables. Four sets of species assemblages are described on the basis of these biotic regions – two major and two minor ones. Of the major assemblages the Northern assemblage can be described as an arid zone one and the Southern assemblage as a mesic zone one. The minor Central assemblage, comprising mainly rock-dwelling forms, represent evolutionary leftovers as a result of climate change induces cycles of contraction and expansion of arid and mesic faunas. The other minor one, the West Coast assemblage could be considered a sub-assemblage of the Northern one, with particular adaptation to the coastal climate. Environmental characterisation of the biotic regions reveals that these groupings are supported by an environmental signal. The contiguity of four distinct sets of reptiles, each with its own set of environmental requirements, in this relatively small geographic area clearly indicates that the southwestern region of South Africa is biogeographically complex. The GCBC incorporates the largely coinciding centres of endemism and richness along the West Coast and the greater Cederberg area. Although the centre of endemism for melanistic reptile forms, in the Saldanha-Langebaan area, falls just south of the GCBC boundary, the Corridor fulfils the requirements for effective conservation of reptiles in the area to a large degree. The north-south dispersal pathways provided by the Corridor along the Cape Fold Mountains is believed to be adequate to buffer climate change effects, however there is concern about its ability to contribute to the persistence of the assemblage associated with the narrow coastal zone in the west.
AFRIKAANSE OPSOMMING: Die Groter Cederberg Biodiversiteit Korridor (GCBK) is ‘n grootskaalse bewaringskorridor wat in die suid-westelike deel van Suid-Afrika geleë is. Die grense van GCBK is gebasseer op plantegroei data. In die huidige studie word die betekenis van die GCBK vir die bewaring van die reptiel fauna in die gebied suid van 31°S en wes van 21°O assesseer. Die mate waartoe die GCBK die patrone van reptieldiversiteit in die streek inkorporeer, asook die korridor se potensiaal om voorsiening te maak vir reptiel verspreidingsgebiede wat moontlik as gevolg van potensiële omgewingsverandering kan verskuif. Die beskikbare puntverspreidingsdata van die voorlopige (2007) SARCA (South African Reptile Conservation Assessment) databasis is gebruik. Swak verteenwoordiging van die Tankwa Karoo in die datastel het ‘n veldopname van die gebied genoodsaak. Verder is die biogeografiese invloed van die ariede Tankwa Karoo Kom op die verspreidingspatrone van reptiele in die suid-westelike deel van Suid-Afrika ook ondersoek. Die spesie omset van beide Noord na Suid en Wes na Oos oor die Tankwa is hoog, die spesierykheid is aansienlik laer as in die omringende bergagtige gebiede en daar is geen spesies wat endemies is tot die Tankwa Karoo nie. Die Tankwa Karoo Kom dien as ‘n barieêre teen spreiding vir sommige reptielspesies wat in die omringende gematigde gebiede voorkom. Terselfdertyd reik die verspreidings van ‘n aantal tipiese droogte aangepasde spesies vanuit die noorde suidwaarts langs die Tankwa Vlaktes. Nuwe verspredingsrekords wat ‘n paar spesies se gebiede uitbrei word ook raporteer. Die puntverspreidingsdata is geruik om die patrone van endemisme, spesierykheid en omset op kwart- en agtstegraad resolusie te plot. Spesierykheid kaarte toon ‘n duidelike neiging tot deegliker opnames in reservate en bewoonde gebiede. Hierdie patroon is meer opmerklik vir slange as akkedisse. Reptielrykheid is besonders hoog langs die noord-suid as van die Kaapse Plooiberge en ook relatief hoog langs die suid-wes kus met ‘n maksimum in die Lambertsbaai omgewing. Die meerderheid van die 20 reptielspesies wat endemies is aan die studie area is met een van twee geïdentifiseerde sentrums van endemisme geassosieer: die Groter Cederberg area óf die nou kussone wat vanaf Lambertsbaai tot Kaappunt strek. ‘n Derde stel endemiese spesies wat uit melanistiese vorme bestaan, is beperk tot ‘n aantal refugia, naamlik, Landroskop, Kaappunt, Saldanha- Langebaan omgewing, Piketberg berge en ‘n beperkte area langs die westelike dele van die Kaapse Plooiberge. Spesierykheid en endemisme patrone stem grootliks ooreen binne die studie area. Roosterselle is op grond van gedeelde spesiesamestellings met behulp van ‘n hieragiese groeperingsmetode (Incremental Sum of Squares) gegroepeer. Vier bio-areas, nl. ‘n Noordelike-, Suidelike-, Sentrale en Westelike bio-area is identifiseer. Klassifikasieboom metodologie (Classification and Regression Trees, CART) asook Kanoniese Annalises (Cannonical Correspondence Annalysis, CCA) is gebruik om hierdie geografiese areas in terme van ‘n aantal omgewingsveranderlikes te karakteriseer. Vier spesieversamelings, twee groter en twee kleiner versamelings, is in ooreenstemming met hierdie vier areas geïdentifiseer. Die Noordelike en Suidelike spesieversamelings is die groteres en kan beskryf word as die faunas van onderskeidelik ‘n ariede en gematigde sone. Die kleiner Sentrale versameling bestaan hoofsaaklik uit rots-lewende spesies en mag die evolusionêre oorblyfsels verteenwoordig van ariede en gematigde faunas waarvan die verspreidings herhaaldelik as gevolg van klimaatsveranderingsiklusse uitgebrei en gekrimp het. Die Weskus versameling is ook ‘n kleiner een en kan as ‘n sub-versameling van die Noordelike een beskou word, maar spesifiek tot die kus klimaat aangepas. Die klassifikasie van hierdie bio-areas word ondersteun deur die analiese van die omgewingsveranderlikes. Die feit dat vier kenmerkende versamelings reptiele, elk met sy besondere omgewingsvereistes, in hierdie relatief klein geografiese area ontmoet, dui daarop dat die suid-westelike deel van Suid-Afrika biogeografies kompleks is. Die GCBK inkorporeer die grootliks ooreenstemmende sentrums van endemisme en rykheid wat langs die Weskus en in die groter Cederberg area voorkom. Alhoewel die sentrum van melanistiese endemiese spesies, in die Saldanha-Langebaan omgewing, net buite die grense van die Korridor val, voldoen die GCBK grootliks aan die vereistes vir die effektiewe bewaring van reptiele in die gebied. Die voorsiening van noord-suid verspreidingsweë langs die Kaapse Plooiberge binne die Korridor word beskou as voldoende om die gevolge van klimaatsverandering te buffer. Daarinteen is daar kommer oor die vermoeë van die GCKB om ‘n doeltreffende bydrae te maak tot die voortbestaan van die spesieversameling wat met die nou kussone langs die Weskus geassosieer is.

Dissertation (PhD)--University of Stellenbosch, 2006.
ENGLISH ABSTRACT: The central goal in macroecology is to determine species diversity patterns across ecological gradients. Altitudinal and latitudinal patterns in species richness are often assumed to be analogous. Furthermore, the primary mechanisms underlying richness patterns along these two gradients might be similar. To date, few studies have tested whether the hypotheses proposed to explain latitudinal richness variation apply to patterns across altitude. This study therefore tests several hypotheses proposed to explain patterns in species diversity (i.e. ambient energy, productivity, area and geometric constraints) and their underlying mechanisms using altitudinal gradients in epigaeic ant and beetle species richness in the Greater Cederberg Biodiversity Corridor (GCBC) (Western Cape, South Africa). The study was conducted across an altitudinal gradient that was laid out from sea level to the top of a mountain (approximately 2000 m above sea level) and down the other side thereof. First, it was determined how the ant and beetle assemblages differ between the main vegetation types included in the transect and which environmental variables might underlie these differences. Thereafter, the variation in species richness and range size patterns of the two groups was investigated across the full altitudinal gradient. This is the first study that tests the applicability of two mid-domain models across such an altitudinal gradient using both complete and partial assessments. The models explained large proportions of the variance in range sizes across three domains but the ranges could have been constrained to show peaks in the middle of the domains due to the way in which the boundaries of the domains were selected. By contrast, the mid-domain models were not important in explaining species richness patterns, which suggests that they cannot explain diversity across the gradient. The species richness patterns of the two groups did not show the predicted mid-altitudinal peak. Moreover, it was demonstrated that different processes structure ant and tenebrionid assemblages across the same altitudinal transect. Ant species diversity was highly correlated to contemporary climatic variables, while historical factors appear to play a more important role in structuring tenebrionid beetle assemblages. Furthermore, support was found for the species energy theory in the ant assemblages, as well as for two of its underlying mechanisms, namely the more individuals hypothesis and the niche position mechanism. These results suggest that there are likely to be substantial and complex changes to ant assemblages under the predicted climate change scenarios for the region. Given the crucial role played by this group in ecosystem functioning (e.g. myrmecochory) it is suggested that these responses are not likely to be a response solely to vegetation changes, but might also precipitate vegetation changes. This study also forms the basis of a long-term monitoring programme to establish baseline data for the epigaeic ants and tenebrionids and to monitor changes in these communities due to climate change.
AFRIKAANSE OPSOMMING: Een van die sentrale idees in makro-ekologie is om die patrone in spesies diversiteit oor ekologiese gradiënte te ondersoek. Verder word daar aangeneem dat spesie rykheidspatrone oor hoogte- en breedtegradiënte analoog is aan mekaar en dat die primêre onderliggende meganismes van die patrone dieselfde kan wees oor hierdie twee gradiënte. Tot dusver het min studies getoets of die voorgestelde hipoteses wat breedtegradiënte in spesie rykheid verduidelik van toepassing is op hoogtegradiënte. Hierdie studie toets dus verskeie van hierdie hipoteses (aanvoelbare temperatuur, produktiwiteit, area en geometriese beperkinge) en hulle onderliggende meganismes in mier en kewer spesie rykheid in die Groter Cederberg Biodiversiteits Korridor (GCBK) (Wes Kaap, Suid Afrika). Die studie is uitgevoer oor ‘n hoogtegradiënt wat vanaf see vlak tot ongeveer 2000 meter bo seevlak en weer aan die ander kant van die berg af uitgelê is. Eerstens is daar bepaal hoe die mier en kewer diversiteit verskil tussen die hoof planttipes wat oor die hoogtegradiënt voorgekom het en watter omgewingsveranderlikes daarvoor verantwoordelik is. Daarna is die variasie in spesie rykheid en area van verspreiding van die twee groepe ondersoek oor die hele hoogtegradiënt. Hierdie is die eerste studie wat die toepaslikheid van twee mid-domein modelle oor so ‘n hoogtegradiënt toets met behulp van volledige en gedeeltelike ondersoeke. Die modelle het baie van die variasie in area van verspreiding verduidelik oor drie domeine maar die areas van verspreiding kon beperk gewees het om pieke in die middel van die domeine te vorm as gevolg van die manier waarop die grense van die domeine gekies is. In teenstelling, het die modelle nie spesie rykheid verduidelik nie en dus kan hulle nie spesie diversiteit oor hierdie gradiënt verduidelik nie. Die spesie rykheidspatrone van die twee groepe het nie die verwagte piek by midhoogte gewys nie. Verder het verskillende prosesse mier en kewer groeperings oor die hoogtegradiënt gestruktureer. Mier diversiteit was hoogs gekorroleer met kontemporêre klimaatsveranderlikes, terwyl historiese faktore belangriker was vir die kewers. Die spesie-energie teorie was ondersteun deur die data, asook die meer individue hipotese en die nis posisie meganisme. Hierdie resultaat dui daarop dat daar moontlik komplekse veranderinge in mier groeperings gaan plaasvind soos die klimaat verander. Miere vervul belangrike ekologiese prosesse in ekosisteme, wat beteken dat die laasgenoemde verandering nie bloot net gaan plaasvind as gevolg van veranderinge in die plantegroei nie, maar dat hulle self ook veranderinge kan veroorsaak. Hierdie studie vorm ook die basis van ‘n langtermyn moniteringsprogram om basislyn data vir hierdie twee ekologies belangrike groepe vas te stel en om veranderinge wat in hierdie gemeenskappe plaasvind, as gevolg van klimaatsverandering, te monitor.

Phytophthora lateralis is the causal agent of cedar root rot, a fatal forest pathogen whose principal host is Chamaecyparis lawsoniana (Port-Orford-cedar), a predominantly riparian-restricted endemic tree species of ecological, economical, and cultural importance to coastal Oregon and California. Local scale distribution of P. lateralis is thought to be associated with timber harvest and road-building disturbances. However, knowledge of the landscape-scale factors that contribute to successful invasions of P. lateralis is also important for effective land management of Port-Orford-cedar. P. lateralis is able to infest in wet conditions via stream networks (zoospore) and dry conditions via road networks (resting spore). This study tested the hypothesis that vehicles spread P. lateralis by relating its distribution to traffic intensive, anthropogenic disturbances (i.e. a road network, timber harvest) over a 31-yr period in a 3,910-km² portion of the Rogue River-Siskiyou National Forest in the Siskiyou Mountains of Oregon. Indices of road disturbance (presence/absence, configuration, length, density, road-stream network connectivity) and timber harvest (presence/absence, area, density, frequency) were related to locations of infested cedar populations from a USFS survey dataset using a geographic information system (GIS). About 40% of 934 7th-field catchments were infested with the pathogen. Total road length of the study site was 5,070 km; maximum road density was 8.2 km/km2 and averaged 1.6 km/km² in roaded catchments (n = 766). Timber activities extracted 17,370 ha (2,338 cutting units) of forest across 509 catchments; 345 catchments were cut ≥ twice. Maximum harvest density was 0.92 km²/km² ([mean] = 0.04). Both road networks and timber harvest patchworks were significantly related to cedar root rot heterogeneity. Chi-squared contingency tables showed that infestation rates were 2.2 times higher in catchments with roads compared to roadless catchments and 1.4 times higher in catchments with road-stream intersections compared to those that were unconnected. Infestation was twice as likely in catchments with both harvest and road presence than road presence alone. Single-variable logistic regression showed that a one percent increase in harvest density increased infestation odds 25% and a one-unit (km/km²) increase in road density increased infestation odds 80%. Road and stream network configuration was also important to pathogen distribution: 1) uninfested catchments are most likely to be spatially removed from infested, roaded catchments, 2) only 11% of 287 roaded catchments downstream of infested, roaded catchments were uninfested, and 3) only 12% of 319 catchments downstream of infested catchments were uninfested. Road networks and timber harvest patchworks appear to reduce landscape heterogeneity by providing up-catchment and down-catchment access to host populations by linking pathogenic materials to the stream network. Timber harvest data suggest that while infestation risk to Port-Orford-cedar populations remains high, management policies may have curbed infestation risk in timber-harvested catchments; if this is a result of specific P. lateralis mitigation policies adopted in the late 1980's or broader, region-wide conservation policies (i.e. the Northwest Forest Plan) is yet unclear.
Graduation date: 2012