Spatial Patterns Of Occurrence Research Articles

The Effects of Temperature and Recovery of Vector on the Spatial Distribution of Dengue Fever Occurrences in Taiwan

TM4-O-08 Climate change has influenced the occurrence and distribution of vector-borne diseases in the world. Identifying vulnerable population in response to future changes of climate is therefore important for public health adaptation decision. Our study therefore conducted spatial analysis to examine the linkage between temperature and other environmental factors on dengue fever distribution and predicting the area with potential risk of dengue fever endemics in future climatic change. We used Geographical Information System (ArcGIS 8.2) to demonstrate the spatial patterns of dengue fever occurrence, climatic and nonclimatic factors. The basic spatial unit used in this study is township, and 357 townships with complete case number of dengue fever, weather, population density, and vector surveillance data were included in the analysis. Computerized database containing daily registration of dengue fever cases in Taiwan for the period of 1998 to 2002 were obtained from Taiwan CDC. Logistic regressions were further adopted to evaluate the linkage between spatial characteristics of climatic and nonclimatic factors, and occurrence of dengue fever to further identify risk factors of dengue fever distribution. Incidence rates per square kilometer were used to map out the incidence rate from 1998 to 2002 in each township. Significantly higher monthly average temperature could be observed in those townships with occurrence of dengue fever (nonparametric Mann-Whitney test). Significantly elevated risk of dengue fever occurrence could be observed, with odds ratios between 1.65 and 19.18, when the average monthly temperature for the specific township exceeded certain levels. Warmer winter season seemed to impose relatively higher risk than the warmer summer season. The recovery rate of household vectors higher than 30% in the township was also found to be associated with dengue fever occurrence (OR = 1.80; 95% CI, 1.05–3.02). However, greater population density did not seem to be a critical factor for increasing vector population in Taiwan. The map of risk scores, based on temperature and recovery rate of vector density over 12 months, were plot to indicate the areas with potential risk for dengue fever occurrence. In our study, 39 townships with scores higher than 10, account for almost 11% of 357 townships in Taiwan, have contributed to nearly 95% indigenous cases between 1998 and 2002. The predicted risk scores using temperature and recovery rate of vector density could be considered a worth-taking approach for identifying vulnerable regions in Taiwan to highlight those areas with greater potential risk for dengue fever outbreak in the future.

Community complexity: Stratifying monitoring schemes within a desert sand dune landscape

Landscapes of desert sand dunes are sometimes viewed as biologically and ecologically homogeneous, yet they can be deceptively complex. We analysed temporal and spatial patterns of species occurrence across a desert dune landscape to clarify the utility of a priori community divisions and how those designations facilitate evaluations of whether conservation objectives are being met, and whether adaptive management approaches are necessary. There was a high degree of community concordance within each of the taxonomic groups considered here; where significant patterns in community structure for one taxonomic group occurred, they were paralleled by other taxa in the same areas. Community divisions were identified that provided population sources for species such as federally threatened Coachella Valley fringe-toed lizards, Uma inornata, and endangered Coachella Valley milkvetch, Astragalus lentiginosus var coachellae, while adjacent communities appeared to be population sinks. Despite similarities in appearance and species occurrences, the eolian sand community of the Coachella Valley is a complex matrix of subdivisions, each with different relative species abundances, and different local population responses to changing resources. This degree of demographic asynchrony may provide a level of protection from regional extinction events. Recognizing community subdivisions allows monitoring sampling frames to be stratified and analyses be focused on habitats with similar population drivers, responses and constraints, therefore reducing statistical variance and increasing the power to detect departures from predicted population trends.

Seismic hazard analysis: a comparative study

The quantitative seismic hazard maps for the 1970s National Building Code of Canada were evaluated using the Davenport–Milne method. The Cornell–McGuire method is employed to develop recent seismic hazard maps of Canada. These methods incorporate the information on seismicity, magnitude-recurrence relations, and ground motion (or response) attenuation relations. The former preserves and depends completely on details of the historical seismicity; the latter smoothes the irregular spatial occurrence pattern of the historical seismicity into seismic source zones. Further, the Epicentral Cell method, which attempts to incorporate the preserving and smoothing aspect of these methods, has been developed. However, the impact of the adopted assumptions on the estimated quantitative seismic hazard has not been investigated. This study provides a comparative seismic hazard assessment using the above-mentioned methods and simulation-based algorithms. The analysis results show that overall the Davenport–Milne method gives quasi-circular seismic hazard contours near significant historical events, and the Cornell–McGuire method smoothes the transition of contours. The Epicentral Cell method provides estimates approximately within the former and the latter. Key words: epicentral cell method, probability, seismic hazard, Thiessen polygon, Voronoi, uniform hazard spectra.

Using Neutral Models to Identify Constraints on Low-severity Fire Regimes

Climate, topography, fuel loadings, and human activities all affect spatial and temporal patterns of fire occurrence. Because fire is modeled as a stochastic process, for which each fire history is only one realization, a simulation approach is necessary to understand baseline variability, thereby identifying constraints, or forcing functions, that affect fire regimes. With a suitable neutral model, characteristics of natural fire regimes estimated from fire history data can be compared to a “null hypothesis”. We generated random landscapes of fire-scarred trees via a point process with sequential spatial inhibition. Random ignition points, fire sizes, and fire years were drawn from uniform and exponential family probability distributions. We compared two characteristics of neutral fire regimes to those from five watersheds in eastern Washington that have experienced low-severity fire. Composite fire intervals (CFIs) at multiple spatial scales displayed similar monotonic decreases with increasing sample area in neutral vs. real landscapes, although patterns of residuals from statistical models differed. In contrast, parameters of the Weibull distribution associated with temporal trends in fire hazard exhibited different forms of scale dependence in real vs. simulated data. Clear patterns in neutral landscapes suggest that deviations from them in empirical data represent real constraints on fire regimes (e.g., topography, fuels). As with any null model, however, neutral fire-regime models need to be carefully tuned to avoid confounding these constraints with artifacts of modeling. Neutral models show promise for investigating low-severity fire regimes to separate intrinsic properties of stochastic processes from the effects of climate, fuel loadings, topography, and management.

LANDSCAPE CHARACTERISTICS INFLUENCE POND OCCUPANCY BY FROGS AFTER ACCOUNTING FOR DETECTABILITY

Many investigators have hypothesized that landscape attributes such as the amount and proximity of habitat are important for amphibian spatial patterns. This has produced a number of studies focusing on the effects of landscape characteristics on amphibian patterns of occurrence in patches or ponds, most of which conclude that the landscape is important. We identified two concerns associated with these studies: one deals with their applicability to other landscape types, as most have been conducted in agricultural landscapes; the other highlights the need to account for the probability of detection. We tested the hypothesis that landscape characteristics influence spatial patterns of amphibian occurrence at ponds after accounting for the probability of detection in little‐studied peatland landscapes undergoing peat mining. We also illustrated the costs of not accounting for the probability of detection by comparing our results to conventional logistic regression analyses. Results indicate that frog occurrence increased with the percent cover of ponds within 100, 250, and 1000 m, as well as the amount of forest cover within 1000 m. However, forest cover at 250 m had a negative influence on frog presence at ponds. Not accounting for the probability of detection resulted in underestimating the influence of most variables on frog occurrence, whereas a few were overestimated. Regardless, we show that conventional logistic regression can lead to different conclusions than analyses accounting for detectability. Our study is consistent with the hypothesis that landscape characteristics are important in determining the spatial patterns of frog occurrence at ponds. We strongly recommend estimating the probability of detection in field surveys, as this will increase the quality and conservation potential of models derived from such data.

Larval fish assemblage in the Baía River (Mato Grosso do Sul State, Brazil): temporal and spatial patterns

We sampled the Baia River (Mato Grosso do Sul State, Brazil) monthly, to survey taxonomic composition and temporal and spatial distribution of fish larvae. The ichthyoplankton was mainly composed by larvae of small and medium sized sedentary species and it was numerically dominated by six taxa: Plagioscion squamosissimus, Hypophthalmus edentatus, Hoplias aff. malabaricus, Bryconamericus stramineus, Serrasalmus spp. and Catathyridium jenynsii. These taxa present distinct temporal and spatial occurrence patterns: H. edentatus, B. stramineus and C. jenynsii are abundant between September and March in lentic areas; H. aff. malabaricus and Serrasalmus spp. were caught between October and February in lotic areas; whereas P. squamosissimus occurs in all sampled areas, with peak of capture in January. Hypophthalmus edentatus, H. aff. malabaricus, Serrasalmus spp. and B. stramineus were the taxa that most contributed to structure the assemblages temporally and spatially, and their abundances were influenced by the interaction of several environmental variables.

Patterns of spread and persistence of foot-and-mouth disease types A, O and Asia-1 in Turkey: a meta-population approach

Despite significant control efforts, foot-and-mouth disease (FMD) persists in Turkey, and new strains of serotypes A, O and Asia-1 are periodically reported to enter the country from the east. The status of FMD in Turkey is important regionally because the country forms a natural bridge between Asia where the disease is endemic, and Europe which has disease-free status. This study analysed spatial and temporal patterns of FMD occurrence in Turkey to explore factors associated with the disease's persistence and spread. Annual records of FMD distribution in Turkish provinces throughout 1990-2002, grouped by serotype (O, A and Asia 1), were analysed using geostatistical techniques to explore their spatial and temporal patterns. A meta-population model was used to test how disease status, expressed in terms of presence/absence, extinction, and colonization, and measured at the province level throughout the periods 1990-1996 and 1997 2002, could be predicted using province-level data on: ruminant livestock numbers; meat production-demand discrepancy (as a surrogate measure of animal and animal products marketing, i.e. long-distance contagion through the traffic of mainly live animals to urban centres); and the disease prevalence distribution as recorded for the previous year. A drastic overall reduction in FMD occurrence was observed from the period 1990-1996 to 1997-2002 when the disease was shown to retract into persistence islands. FMD occurrence was associated with host abundance, short distance contagion from adjacent provinces, and meat production-demand discrepancies. With FMD retracting into identified provinces, a shift in predictors of FMD occurrence was observed with a lower contribution of short-distance contagion, and a relatively higher association with meat production-demand discrepancies leading to live animal transport over long distances, and hence presenting opportunities for identifying critical-control points. The pattern of persistence differed according to serotype groups and is discussed in relation to their differential affinity to cattle and small ruminant hosts.

MOVEMENT PATTERNS AND SPATIAL EPIDEMIOLOGY OF A PRION DISEASE IN MULE DEER POPULATION UNITS

Spatial patterns of disease occurrence across a landscape are likely products of both the ecological processes giving rise to underlying epidemics and the physical pathways of disease spread. Spatially explicit epidemic models often rely on assumptions about system boundaries and processes for spread that may not faithfully represent true patterns of host or vector distribution and movements. As a foundation for future modeling and parameter estimation, we evaluated potential influences of distribution and movements of mule deer (Odocoileus hemionus) on the spatial epidemiology of chronic wasting disease (CWD) in north-central Colorado. We used cluster techniques to define mule deer population units based on location data, and then used these as the sampling unit for subsequent analyses. We found marked differences in prevalence between population units that appeared at least partially related to deer movements. Migration (mean migration rate = 44%) rather than dispersal movements (≤2% dispersal rate) app...

Spatial patterns of fire occurrence in Catalonia, NE, Spain

In this paper, we analyse spatial patterns of fire occurrence in Catalonia (NE Spain) during 1975–98. Fire scar maps, discriminated by means of 30–60 m resolution remote sensing imagery, have been used as a source of fire occurrence. We employ several visual or analytical approaches to interpret fire occurrence in this region, such as those of Minnich and Chou (1997), Ricotta et al. (2001) or Krummel et al. (1987). Crucial spatial patterns such as fire size distribution, fire frequency distribution, spots and residual vegetation islands are documented. In addition, several geographical layers were overlaid with burned area maps in order to determine interactions between fire occurrence and environmental parameters such as altitude, slope, solar radiation, and burned land cover. Assuming that fire occurrence is well determined by such a posteriori empirical factors we detect areas most prone to fire in this region and aim to enhance the local forest management and conservation plans.

포아송과정을 이용한 가뭄의 공간분포 분석

본 연구에서는 경기도 지역을 중심으로 관측자료로 부터 아울러 포아송 과정을 적용하여 가뭄의 재현 및 지속특성을 정량화하고 그 공간분포를 비교 분석해 보았다. 본 연구에서는 관측된 월 강수량 자료를 가뭄지수인 SPI로 변환하여 분석에 이용하였다. 특히, 가뭄의 공간분포 특성 파악을 위해 관측길이가 서로 다른 자료에 포아송 과정을 적용하는 경우의 장ㆍ단점 등을 파악해 보고자 하였다. 본 연구의 결과를 요약하면 다음과 같다. (1) 포아송 과정을 이용한 가뭄의 정량화는 특히 관측기록이 짧은 경우에 유리한 것으로 나타났다. 공간적으로 가까운 위치에 있는 두 지점의 특성이 관측기록의 길이에 덜 민감해 짐에 따라 전체적으로 유사한 특성을 나타냄을 확인할 수 있었다. (2) 지점별 관측기록의 길이가 크게 다른 경우 모형에 의한 가뭄의 공간적 특성 파악이 단순히 관측자료를 이용한 경우에 비해 우월할 수 있다. 본 연구의 경우에 있어서도 모형을 이용한 경우 가뭄의 공간분포가 관측을 직접 분석하여 얻은 가뭄의 공간분포보다 뚜렷하게 나타남을 확인할 수 있었다. This study quantifies and compares the drought return and duration characteristics by applying the Poisson process as well as based on by analyzing the observed data directly. The drought spatial distributions derived for the Gyunggi province are also compared. The monthly rainfall data are used to construct the SPI as a drought index. Especially, this study focuses on the evaluation of the Poisson process model when applying it to various data lengths such as in the spatial analysis 'of drought. Summarizing the results are as follows. (1) The Poisson process is found to be effective for the quantification of drought, especially when the data length is short. When applying the Poisson process, two neighboring sites are found insensitive to the data length to show similar drought characteristics, so the overall drought pattern becomes smoother than that derived directly from the observed data. (2) When the data length is very different site by site, the spatial analysis of drought based on a model application seems better than that based on the direct data analysis. This study also found more obvious spatial pattern of drought occurrence and duration when applying the Poisson process.

Clustering of Parkinson disease: shared cause or coincidence?

The spatial and temporal pattern of excessive disease occurrence, termed clustering, may provide clues about the underlying etiology. To report the occurrence of 3 clusters of Parkinson disease (PD) in Canada. We determined the population groups containing the clusters, geographical limits, and duration of exposure to the specific environments. We tested whether there was an excessive presence of Parkinson disease by calculating the probability of the observed cases occurring under the null hypothesis that the disease developed independently and at random in cluster subjects. Results of genetic testing for mutations in the alpha-synuclein, parkin, tau genes, and spinocerebellar ataxia genes (SCA2 and SCA3) were negative. The probabilities of random occurrence (P values) in the 3 clusters were P = 7.9 x 10 (-7)for cluster 1, P = 2.6 x 10 (-7)for cluster 2, and P = 1.5 x 10 (-7)for cluster 3. Our findings indicate an important role for environmental causation in Parkinson disease. A possible role exists for environmental factors such as viral infection and toxins in the light of current evidence.

GIS-supported investigation of human EHEC and cattle VTEC O157 infections in Sweden: geographical distribution, spatial variation and possible risk factors.

This article describes the spatial and temporal distribution of verotoxin-producing Escherichia coli among humans (EHEC) and cattle (VTEC) in Sweden, in order to evaluate relationships between the incidence of EHEC in humans, prevalence of VTEC O157 in livestock and agricultural structure by an ecological study. The spatial patterns of the distribution of human infections were described and compared with spatial patterns of occurrence in cattle, using a Geographic Information System (GIS). The findings implicate a concentration of human infection and cattle prevalence in the southwest of Sweden. The use of probability mapping confirmed unusual patterns of infection rates. The comparison of human and cattle infection indicated a spatial and statistical association. The correlation between variables of the agricultural structure and human EHEC incidence was high, indicating a significant statistical association of cattle and farm density with human infection. The explained variation of a multiple linear regression model was 0.56.

Distribution patterns and conservation status of four bustard species (Family Otididae) in a montane grassland of South Africa

The abundance and distribution patterns of four threatened species of bustards ( Eupodotis caerulescens, E. barrowii, E. melanogaster and Neotis denhami) in 3200 km 2 of montane grasslands in the Wakkerstroom district, South Africa were characterised and related to altitude, topography and land use. During 2001 and 2002, 61 car-driven transects (544 km in total) were carried out to count bustards at the onset of the breeding season. The spatial patterns of land use and bustard occurrence along transects were characterised using geostatistics. The influence of explanatory variables on each species occurrence was assessed using logistic regression. There were inter-specific differences in distribution, with E. caerulescens occurring at higher altitudes than the other species. These differences were partly explained by different habitat preferences. Population estimates for the study area were ≈1400 E. caerulescens, 150 E. barrowii and 30 male E. melanogaster. The main threats for the bustard populations in the region are commercial afforestations (mainly for N. denhami) and agricultural intensification (mainly for E. barrowii and E. melanogaster). The results of this study can be used as a baseline situation against which future monitoring could be compared. The used method proved to be effective for characterising occurrence patterns and censusing bustard populations in relatively large areas, as well as describing large-scale habitat patterns.

SPATIAL PATTERNS AND CONTROLS ON HISTORICAL FIRE REGIMES AND FOREST STRUCTURE IN THE KLAMATH MOUNTAINS

Fire exclusion in mixed conifer forests has increased the risk of fire due to decades of fuel accumulation. Restoration of fire into altered forests is a challenge because of a poor understanding of the spatial and temporal dynamics of fire regimes. In this study the spatial and temporal characteristics of fire regimes and forest age structure are recon- structed in a 2325-ha mixed conifer forest in the Klamath Mountains. Forests were multiaged and burned frequently at low and moderate severity, but forest age structure did not vary with aspect, elevation, or topographic position. Recently there has been an increase in forest density and a forest compositional shift to shade-tolerant species. Median fire return in- tervals (FRI) ranged from 11.5 to 16.5 yr and varied with aspect but not with forest composition or elevation. The median area burned was 106 ha, and the pre-Euro-American fire rotation of 19 yr increased to 238 yr after 1905. Intra-annual position of fire scars in the tree rings indicates that 93% of fires occurred during the dry midsummer through fall period. Spatial patterns of sites with similar fire dates were spatially coherent and separated from others by topographic features that influence fire spread. Thus, patterns of fire oc- currence tended to be fixed in space with timing of fires varying among groups of sites. Spatial and temporal patterns of fire occurrence suggest that managers using physical fea- tures to contain prescribed fire will create burn patterns consistent with historical fires in the Klamath Mountains.

The re-emergence of Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula) after localised possum eradication

AIM: To examine the spatial and temporal pattern of Mycobacterium bovis (bovine tuberculosis) infection in a population of brushtail possums (Trichosurus vulpecula) after localised possum eradication. METHODS: Possums on a 36 ha site were eradicated and re-population from the surrounding area studied using population surveys conducted approximately every 2 months for 40 months from the cessation of eradication activity (month zero), using a capture-release programme. At each trapping session, all possums were examined for clinical signs of tuberculosis. The diagnosis of tuberculosis was confirmed by the isolation of Mycobacterium bovis, and restriction endonuclease analysis (REA) was used to type the isolates. Infected possums were categorised as residents (present on the site for at least 6 months before diagnosis), range expanders (adult possums which had extended their nearby home ranges to become trappable within the study site), or juvenile immigrants (sub-adult possums which had dispersed into the site from an unknown distance away). This classification was used to identify the location where possums became infected. Capture locations and denning site locations were used to examine the spatial pattern of disease occurrence. RESULTS: Thirty cases of tuberculosis were diagnosed among the 370 possums identified on the study site. Four different REA types (Types 2, 3, 8 and 10) were identified. The first two cases of tuberculosis were diagnosed in Month 4, in mature male possums categorised as range expanders, the third case was diagnosed in Month 6 and the fourth case at Month 9. Each of the first four cases was infected with a different REA type. The subsequent temporal pattern of infection was consistent with transmission from range expander cases and dispersing juvenile immigrants to resident possums. Clinical incidence remained low but persistent until the third year, when the incidence of Types 2, 8 and 10 escalated. Type 3 infections showed an earlier incidence peak, but disappeared from the site when the last known case died at Month 20. Of the dispersing juvenile possums entering the site, four became clinically tuberculous and represented a source of re-infection of other possums. CONCLUSIONS: Re-emergence of tuberculosis after localised possum eradication was due to the continuing reintroduction of infection in mature and immature diseased possums, and not the survival of M. bovis in the environment.

Modelling the impact of different forms of wildlife harassment, exemplified by a quantitative comparison of the effects of hikers and paragliders on feeding and space use of chamois Rupicapra rupicapra

We developed a mathematical model to quantify and compare the impact of different forms of wildlife harassment, and applied it to compare the effects of hikers and paragliders on the feeding time and area of chamois Rupicapra rupicapra, considering differences between hikers and paragliders in terms of their prevalence and behaviour. Although many more hikers than paragliders visited the study area, the impact of paragliders was much stronger. With increasing paraglider traffic, the effects would steeply increase, whereas the effects of hikers approached an asymptote. With modification of input values and/or parameters, the model can be applied to other species, to compare the effects of other forms of wildlife harassment, and to simulate effects of changing conditions such as habituation of the animals or changes in the daily or spatial pattern of occurrence of tourism.

Landscape Ecosystems of the Mack Lake Burn, Northern Lower Michigan, and the Occurrence of the Kirtland's Warbler

Abstract The Kirtland's warbler (Dendroica kirtlandii Baird) is a federally endangered songbird that nests only in ecosystems dominated by young jack pine (Pinus banksiana Lamb.) in northern Michigan. Although considerable research has focused on the bird, comparatively little information is available on the specific landscape ecosystems occupied by the warbler. The 9,700 ha Mack Lake burn provided an opportunity to track the pattern of Kirtland's warbler occurrence in relation to the ecosystems of a highly diverse and productive area of its breeding range. Using a multifactor landscape ecosystem approach, two high-elevation and four low-elevation landform-level ecosystems were identified, described, and mapped. The spatial pattern of warbler occurrence over time was strongly mediated by the physical and biotic components of the ecosystems. During the first 3 yr of warbler occupation (1986–1988), the high-elevation landforms, characterized by relatively warm temperatures, moister, more fertile soils, and faster growing jack pines, supported 62% of the population. Thereafter, a major shift occurred to the low-elevation landforms. During the last 3 yr of record (1995–1997), the low-elevation landforms, characterized by colder temperatures, drier, less fertile soils, and slow-growing jack pines, supported 86% of the population. The juxtaposition of high- and low-elevation landforms, and the fine-scale ecosystem diversity within them, prolonged the duration of warbler occupancy beyond what would be expected in less heterogeneous conditions. As demonstrated here, the landscape ecosystem approach provides a sound, ecological framework for understanding patterns of Kirtland's warbler occurrence and for assisting managers in identifying appropriate management areas for the continued recovery of the species. FOR. SCI. 49(1):119–139.

Expansion of Elaeagnus umbellata on a gravel bar in the Naka River, Shikoku, Japan

Abstract The present study seeks to identify the expansion process of the shrub Elaeagnus umbellata Thunb. (Elaeagnaceae) on a gravel bar in the Naka River, Shikoku, Japan, in relation to the hydrogeomorphologic regime of the habitat. The establishment pattern was determined by a series of aerial photographs, and the establishment years were confirmed by examining tree rings taken from five different areas within the population. The topographic change of the river cross‐section was analyzed and it was found that the establishment occurred exactly when and where the riverbed began to stabilize. The three cohorts of 15‐, 10‐ and 4‐year‐olds were recognized, the younger individuals being downstream. The episodic age pattern was significantly synchronized with large floods occurring during the autumn fruit‐ripening season. These spatial and temporal occurrence patterns indicated the probability of hydrochory, which ultimately enhanced the dissemination of endozoochorous E. umbellata seeds into the newly created habitat on the downstream part of the gravel bar. Another cause of quick dominance was its vigorous sprouting ability, which enabled the established E. umbellata to withstand damage and sediment burial by strong floods. The erosion of the deepest part of the riverbed increased the relative elevation of the vegetated stand, which ultimately decreased the frequency and magnitude of disturbance during flood inundation after the 1980s. Consequently the hydrogeomorphic regime of the floods played an important role in habitat creation, seed dispersal, and in the survival of the established individuals, and it determined the population formation and expansion of E. umbellata on the riparian gravel bar.

A 500 hPa synoptic wildland fire climatology for large Canadian forest fires, 1959-1996

In Canada, the average annual area of burned forest has increased from around 1 million ha in the 1970's to over 2.5 million ha in the 1990's. A previous study has identified the link between anomalous mid-tropospheric circulation at 500 hPa over northern North America and wildland fire severity activity in various large regions of Canada over the entire May to August fire season. In this study, a northern North American study region of the hemispheric gridded 5° latitude by 10° longitude 500 hPa dataset is identified and analysed from 1959 to 1996 for a sequence of six monthly periods through the fire season, beginning in April and ending in September. Synoptic types, or modes of upper air behavior, are determined objectively by the eigenvector method employing K-means cluster analysis. Monthly burned areas from the Canadian Large Fire Database (LFDB) for the same period, 1959 to 1996, are analysed in conjunction with the classified monthly 500hPa synoptic types. Relationships between common monthly patterns of anomalous upper flow and spatial patterns of large fire occurrence are examined at the ecozone level. Average occurrence of a monthly synoptic type associated with very large area burned is approximately 18% of the years from 1959 to 1996. The largest areas burned during the main fire (May to August) season occur in the western Boreal and Taiga ecozones - the Taiga Plains, Taiga Shield, Boreal West Shield and Boreal Plains. Monthly burned areas are also analysed temporally in conjunction with a calculated monthly zonal index (Zi m ) for two separate areas defined to cover western and eastern Canada. In both western and eastern Canada, high area burned is associated with synoptic types with mid-tropospheric ridging in the proximity of the affected region and low Zi m with weak westerlies and strong meridional flow over western Canada.

Systematics of cretaceous and tertiary Nothofagoxylon: implications for Southern Hemisphere biogeography and evolution of the Nothofagaceae

Fossil woods with greatest anatomical similarity to modern Nothofagaceae are traditionally assigned to the organ genus Nothofagoxylon Gothan. All fossil wood records of Nothofagoxylon were re-evaluated so that recently collected specimens from the Antarctica Peninsula region could be assigned to taxa within this organ genus. Widespread synonymy was found within the published records of Nothofagoxylon, so that of the 16 described species, only seven were retained. Six of these fossil species were found to be present in Antarctica. In undertaking this review, some lauraceous woods assigned to Laurinoxylon Schuster were found to be nothofagaceous. Temporal and spatial patterns of occurrence of the Nothofagoxylon wood type help support current views that the centre of origin of the Nothofagaceae was within the Antarctic Peninsula–South America region during the Campanian followed by radiation into the lower southern latitudes throughout the Tertiary.