SEARCH · PubMed Health

Results for “Random forests”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources

PubMed2004

[Estimate of the validity of a new method for the isolation of rabies virus].

OBJECTIVES: No population-based studies have been conducted to show the potential for the use of virological diagnosis of the rabies virus. The objective of the present study was to estimate accuracy parameters for the isolation of the rabies virus in McCoy cells as an alternative method and to compare this with the use of murine neuroblastoma (N2A) cells, which is considered to be a reference method. METHODS: An evaluation was performed on 120 bats collected at random in the Atlantic Forest of the State of São Paulo. The immunofluorescence reaction was utilized for the detection of the rabies virus isolated from the brain of these bats and the presence of the virus was tested in the two cell culture systems. Two data sets were constructed with the results and the analysis was performed using the computer methods for diagnosis tests (CMDT) software by means of the two-graph receiver operating characteristic (TG-ROC) technique to determine sensitivity and specificity parameters, as well as other indicators such as efficacy, positive predictive value, negative predictive value and likelihood ratio. RESULTS: N2A cells presented 90% sensitivity and specificity, while McCoy cells presented 95% sensitivity and specificity. These values were based on cut-off points optimized for each cell type. CONCLUSION: The study showed that McCoy cells allowed the obtaining of accuracy estimates that were better than for N2A. The McCoy cell method is therefore an effective method for the isolation of the rabies virus.

Animals↗

PubMed2002

Distribution, density and migration dynamics of Ixodes ricinus in an area of the Jurassic mountains of Switzerland.

In an area of the Jurassic mountains of Switzerland ecological aspects of the tick species Ixodes ricinus were studied. In particular, the influence of temperature, humidity and vegetation parameters on tick density and distribution were investigated several times in six different habitat types. This was carried out on two scales; on a small scale, within a habitat type and on a larger scale, where all six habitat types were included. By a marking experiment, aspects of the migration dynamics of the ticks were studied. The densities of the six habitat types differed significantly in most of the cases. An analysis of the distribution pattern within a habitat type showed a contagious distribution mostly for the forests and the forest edge, whereas a random distribution was found as well, mainly for the meadows. But these distribution patterns tend towards randomness with time. On a small scale none of the factors showed an influence on tick distribution, therefore the most important factor on this scale might be the hosts of Ixodes ricinus. On a larger scale, temperature and humidity do in some cases influence tick densities. The marking experiment suggests an extremely high turnover of the ticks in an area with an average host density, probably due to passive transportation by hosts and to activation of resting individuals.

Altitude↗

PubMed2006

Do ectomycorrhizas alter leaf-litter decomposition in monodominant tropical forests of Guyana?

This work tested the hypothesis that ectomycorrhizas (EM) of Dicymbe corymbosa alter leaf-litter decomposition and residual litter quality in tropical forests of Guyana. Mass loss of leaf litter in litter bags was determined on three occasions, in two experiments, during a 12-month period. Paired root-exclusion plots were located randomly within a D. corymbosa forest. Both D. corymbosa and mixed-species leaf litters were reciprocally transplanted into their respective forest types. Elemental analysis was performed on the residual D. corymbosa leaf litter after 1 yr. Leaf litter mass loss in the D. corymbosa forest was not influenced by EM, despite high EM colonization. Elemental analysis of D. corymbosa leaf litter residues demonstrated reduced calcium levels in the presence of EM, which were negatively correlated with EM rootlet-colonizing mass. The lack of EM effect on the litter decomposition rate, coupled with high EM colonization, suggests an important but indirect role in mineral nutrient acquisition. Lowered Ca concentration in leaf litter exposed to EM may suggest a high Ca demand by the ectotroph system.

Calcium↗

PubMed2001

Leaf area distribution and radiative transfer in open-canopy forests: implications for mass and energy exchange.

Leaf area and its spatial distribution are key canopy parameters needed to model the radiation regime within a forest and to compute the mass and energy exchange between a forest and the atmosphere. A much larger proportion of available net radiation is received at the forest floor in open-canopy forests than in closed-canopy forests. The proportion of ecosystem water vapor exchange (lambda E) and sensible heat exchange from the forest floor is therefore expected to be larger in open-canopy forests than in closed-canopy forests. We used a combination of optical and canopy geometry measurements, and robust one- and three-dimensional models to evaluate the influence of canopy architecture and radiative transfer on estimates of carbon, water and energy exchange of a ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forest. Three-dimensional model simulations showed that the average probability of diffuse and direct radiation transmittance to the forest floor was greater than if a random distribution of foliage had been assumed. Direct and diffuse radiation transmittance to the forest floor was 28 and 39%, respectively, in the three-dimensional model simulations versus 23 and 31%, respectively, in the one-dimensional model simulations. The assumption of randomly distributed foliage versus inclusion of clumping factors in a one-dimensional, multi-layer biosphere-atmosphere gas exchange model (CANVEG) had the greatest effect on simulated annual net ecosystem exchange (NEE) and soil evaporation. Assuming random distribution, NEE was 41% lower, net photosynthesis 3% lower, total lambda E 10% lower, and soil evaporation 40% lower. The same comparisons at LAI 5 showed a similar effect on annual NEE estimates (37%) and lambda E (12%), but a much larger effect on net photosynthesis (20%), suggesting that, at low LAI, canopies are mostly sunlit, so that redistribution of light has little effect on net photosynthesis, whereas the effect on net photosynthesis is much greater at high LAIs.

Biomass↗

PubMed2001

Monitoring regional vegetation change using reflectance measurements from multiple solar zenith angles.

Many traditional models of vegetation canopy reflectance have commonly used one of two approaches. Either the canopy is assumed to consist of discrete objects of known reflectance and geometric-optics are then used to calculate shading effects, or, as in the turbid medium approach, the canopy is treated as a horizontally homogeneous layer of small elements of known optical properties and radiative transfer theory is used to calculate canopy reflectance. This paper examines the effect of solar zenith angle on the reflectance of red and near-infrared radiation from forests using a combination of these modelling approaches. Forests are first modelled as randomly spaced eucalypt crowns over a homogeneous understorey and the fractional coverage of four components: shaded and sunlit canopy and shaded and sunlit understorey are calculated. Reflectance from each fraction is then modelled for a range of solar zenith angles using the Verhoef SAIL model. The overall scene reflection as seen by a nadir viewing satellite sensor is compared for three forest types representing a gradient of crown density from open dry grassy woodlands to dense wetter closed forest with an understorey of mesophytic plants. Modelled trends in scene reflectance change are consistent with aircraft measurements carried out at three different solar zenith angles. Results indicate that an increase in both tree density and solar zenith angle leads to an increase in the dominance of shaded components. In the visible band, both the sparsely treed woodland and the medium density dry forest show similar trends to that predicted by a turbid medium model, however, the wet forest shows a less rapid decrease in reflectance with solar zenith angle. In the near-infrared band, as tree density increases from woodland to wet forest, overall scene reflectance shows increased departure from that modelled using the traditional assumption of smooth homogeneous canopies, changing from an increase with solar zenith angle for the woodland to a decrease with solar zenith angle for the forest types.

Ecosystem↗

PubMedDate not supplied

Effect of two natural light regimes and nutrient addition on the forest herb Begonia decandra (Begoniaceae).

The effect of two natural light-growing conditions (understory versus light gaps) and the interaction with nutrient availability (through fertilization) were studied in the understory herb Begonia decandra, in the Luquillo Experimental Forest in Puerto Rico. Sixteen potted plants obtained from cuttings were randomly chosen and distributed in each of eighth forest environments (four light gaps and four understories), for a total of 128 plants. Fertilizer was applied to half of the plants in each site. After seven months in the two given microenvironments, increased light and fertilization resulted in greater growth and some changes in the biomass allocation patterns. All measured variables responded similarly to reported changes for tree seedlings and saplings from other tropical and subtropical regions. Total growth parameters (height, biomass and leaf area) were very sensitive to increases in the main resource (light). The addition of nutrients was less important in producing changes in the allocation variables (root to shoot ratio, leaf area ratio, and specific leaf mass) under conditions of high light availability. Changes due to nutrient levels were relatively greater on plants grown under under-story conditions. Also, small light differences among sites can cause significant changes in the variables related to total growth. Lastly, plant mortality in the nutrient treatments was found to be independent of mortality in two forest light environments. Some hypotheses about resource acquisition and plant growth are not supported by this data.

Biomass↗

PubMed2003

An RAPD (random amplified polymorphic DNA) analysis of genetic population structure of Balea biplicata (Gastropoda: Clausiliidae) in fragmented floodplain forests of the Elster/Saale riparian system.

Eight German populations of the land snail Balea biplicata (Mollusca: Clausiliidae) were studied using the randomly amplified polymorphic DNA-polymerase chain reaction and morphometrics (principal component and discriminant analysis) to examine population structure and gene flow patterns in a fragmented landscape mosaic along the Elster/Saale riparian system, Germany. A variety of population genetic analyses targeting either more on the geographic scale of gene flow (genetic distances, F statistics, Mantel test) or on local genotypic structure (heterozygosity, linkage disequilibrium, bottleneck probability) showed that (1) the population system in total is governed by high gene flow independent of geographic distance, (2) genetic structure on the narrower sampling scale is mainly determined by stochastic processes due to genetic drift in small isolated and frequently recolonized populations, and (3) the morphometrical variation of the populations was related neither to habitat nor to genetic heterogeneity. The potentials for active and passive dispersal capacity of the snails and possible environmental impacts on their population structure are discussed.

Animals↗

PubMed1999

Characterization of radiation regimes in nonrandom forest canopies: theory, measurements, and a simplified modeling approach.

We used field measurements and Monte Carlo simulations of canopy gap-size distribution and gap fraction to examine how beam radiation interacts with clumped boreal forest canopies of aspen (Populus tremuloides Michx.), black spruce (Picea mariana (Mill.) B.S.P.) and jack pine (Pinus banksiana Lamb.). We demonstrate that the Beer-Lambert law can be modified to accommodate transmission of radiation through a clumped forest canopy as a function of path length or sun zenith angle. Multiband Vegetation Imager (MVI) measurements and Monte Carlo simulations showed that values of the zenith element clumping index (Omega(e)(0)) are typically between 0.4 and 0.5 in jack pine and black spruce and 0.65 in aspen. Estimates of LAI obtained from MVI measurements of the canopy gap fraction and adjusted for canopy clumping and branch architecture yielded LAI values of 3.0 in jack pine, 3.3 in aspen, and about 6.0 in black spruce. These LAI estimates were within 10-25% of direct measurements made at the same sites. Data obtained with the MVI, along with numerical simulations, demonstrated that assumptions of random foliage distributions in boreal forests are invalid and could yield erroneous values of LAI measured by indirect techniques and false characterizations of atmosphere-biosphere interactions. Monte Carlo simulations were used to develop a general equation for beam radiation penetration as a function of zenith angle in clumped canopies. The essential measurements included stem spacing, crown diameter, crown depth, and within-crown gap fraction.

Journal Article↗

PubMed2004

Particulate air pollution and panel studies in children: a systematic review.

BACKGROUND: Panel studies have been used to investigate the short term effects of outdoor particulate air pollution across a wide range of environmental settings. AIMS: To systematically review the results of such studies in children, estimate summary measures of effect, and investigate potential sources of heterogeneity. METHODS: Studies were identified by searching electronic databases to June 2002, including those where outcomes and particulate level measurements were made at least daily for > or =8 weeks, and analysed using an appropriate regression model. Study results were compared using forest plots, and fixed and random effects summary effect estimates obtained. Publication bias was considered using a funnel plot. RESULTS: Twenty two studies were identified, all except two reporting PM10 (24 hour mean) >50 microg x m(-3). Reported effects of PM10 on PEF were widely spread and smaller than those for PM2.5 (fixed effects summary: -0.012 v -0.063 l x min(-1) per microg x m(-3) rise). A similar pattern was evident for symptoms. Random effects models produced larger estimates. Overall, in between-study comparisons, panels of children with diagnosed asthma or pre-existing respiratory symptoms appeared less affected by PM10 levels than those without, and effect estimates were larger where studies were conducted in higher ozone conditions. Larger PM10 effect estimates were obtained from studies using generalised estimating equations to model autocorrelation and where results were derived by pooling subject specific regression coefficients. A funnel plot of PM10 results for PEF was markedly asymmetrical. CONCLUSIONS: The majority of identified studies indicate an adverse effect of particulate air pollution that is greater for PM2.5 than PM10. However, results show considerable heterogeneity and there is evidence consistent with publication bias, so limited confidence may be placed on summary estimates of effect. The possibility of interaction between particle and ozone effects merits further investigation, as does variability due to analytical differences that alter the interpretation of final estimates.

Air Pollutants↗

PubMed2000

Comparative phytosociology of tree sinusiae between contiguous forests in different stages of succession.

The Baturité Mountain Range, located in the State of Ceará (BRA), displays on its highest levels a vegetation viewed as a disjunction from the Atlantic Forest in the East of Brazil. Among the various attributes associated with this vegetation, the abundance of water resources and a high biodiversity have a more outstanding relevance. However, in view of the current accelerated deforestation process, those attributes may be threatened in a near future. Therefore, the present work is a comparative study with its focus on vegetal community organization (tree sinusiae) and the floristic similarity and the phytodiversity of two areas in different successive stages, preserved and deforested 24 years ago. The aim of that intent was to obtain information that could essentially shed light on the deforestation effects on tree vegetation and which could suggest scientific support regarding urgent projects of habitat reconstruction. The methodology used folowed the model utilized for rain forest, i.e. consisting of a random distribution of 10 x 20 m plots surveying the living woody species with DBH >/= 5 cm. The results obtained suggest that a possible new physiognomy type is emerging on the Baturite Mountain Range because of deforestation. The Myrtaceae and Mimosaceae families were the ones that contributed most significantly to species richness, being the most outstanding for Areas 1 and 2, respectively. The deforestation which occurred in Area 2 eliminated 28 species and gave birth to a current densely distinct floristic composition.

Brazil↗

PubMed2005

[Spatial and temporal pattern of Castanopsis fargesii seed rain in evergreen broad-leaved forest in Tiantong National Forest Park of Zhejiang, China].

Five mature plants of Castanopsis fargesii population were randomly chosen to study the spatial and temporal pattern of its seed rain in Tiantong National Forest Park, Zhejiang Province in 2003. The duration of seed rain observed from the five samples was about 45 days, from November 3rd to December 16th, with a distinguishable dropping peak between November 18th and 27th. The average seed rain density estimated from the traps deployed under the crown was 112.8 seeds.m(-2), ranging from 70 to 239.5 seeds.m(-2). Of the total acorns collected by seed traps, the viable accounted for 27.3%, the immature 25.7%, the eaten by rodents 5.0%, and the infected by larvae 42.0%. The acorns on the ground mainly distributed under the parent tree crown within 8 m from the trunk, and the spatial pattern of seed density on the ground fitted the quadratic distribution.

China↗

PubMed2004

Landscape character and fish assemblage structure and function in western Lake Superior streams: general relationships and identification of thresholds.

As part of a comparative watershed project investigating land-cover/land-use disturbance gradients for streams in the western Lake Superior Basin, we examined general relationships between landscape character and fish assemblage structure and function. We also examined the shape of those relationships to identify discontinuity thresholds where small changes in landscape character were associated with marked shifts in the fish assemblages. After completing a geographic analysis of second- and third-order watersheds in the western Lake Superior drainage, we randomly selected 48 streams along mature forest and watershed storage gradients in 2 hydrogeomorphic regions as our study sites. During the summers of 1997 and 1998, we used electrofishing to sample fish assemblages from each stream. Each of the landscape factors was significantly associated with fish assemblage structure and function based on analysis of covariance. Watershed storage was related to the greatest number of fish assemblage characteristics, but hydrogeopmorphic region and mature forest cover were strongly associated as well. The hydrogeomorphic region also mediated relationships between watershed character and fish assemblages. Discontinuity thresholds for our fish assemblages averaged 11% for watershed storage and 50% for watershed mature forest cover based on piecewise regression analysis. Although many of the landscape-fish relationships might have been manifest through effects on in-stream habitat, our results highlight the importance of management and land-use planning decisions at the watershed and landscape scales.

Animals↗

PubMed2003

Population substructures in the soil invertebrate Orchesella cincta, as revealed by microsatellite and TE-AFLP markers.

Microsatellite and three enzyme-amplified fragment length polymorphism (TE-AFLP) DNA markers were used to describe the population genetic structure in the soil dwelling collembolan Orchesella cincta (L.). Two forests were sampled according to a three-level nested hierarchical design, with fixed distances among samples within a parcel and among parcels within a forest. The largest component of variation was found at the smallest scale, within parcels (77-97%), while the smallest component of variation was found between forests. The two different methods to study population structure indicated a similar allocation of variance. Population genetic substructuring was revealed between samples on a scale of 50 m; the degree of substructuring however, varied between parcels and forests. One forest showed a high degree of structure as revealed by microsatellites, while another showed a low degree of structure. A significant deviation from random-mating (average FIS = 0.23) over the two forests was detected. Two of 18 samples showed a difference in population genetic structure between males and females. We discuss the fact that the population genetic structure of O. cincta is significantly affected by long-range dispersal, even though it is a small and wingless insect. This interpretation is supported by observations on tree-climbing behaviour in this species that may facilitate air dispersal. As a consequence, the assumption that migration a priori may be neglected in demographic analysis of O. cincta is incorrect.

Animal Migration↗

PubMed2006

Using forest inventory data to assess fisher resting habitat suitability in California.

The fisher (Martes pennanti) is a forest-dwelling carnivore whose current distribution and association with late-seral forest conditions make it vulnerable to stand-altering human activities or natural disturbances. Fishers select a variety of structures for daily resting bouts. These habitat elements, together with foraging and reproductive (denning) habitat, constitute the habitat requirements of fishers. We develop a model capable of predicting the suitability of fisher resting habitat using standard forest vegetation inventory data. The inventory data were derived from Forest Inventory and Analysis (FIA), a nationwide probability-based sample used to estimate forest characteristics. We developed the model by comparing vegetation and topographic data at 75 randomly selected fisher resting structures in the southern Sierra Nevada with 232 forest inventory plots. We collected vegetation data at fisher resting locations using the FIA vegetation sampling protocol and centering the 1-ha FIA plot on the resting structure. To distinguish used and available inventory plots, we used nonparametric logistic regression to evaluate a set of a priori biological models. The top model represented a dominant portion of the Akaike weights (0.87), explained 31.5% of the deviance, and included the following variables: average canopy closure, basal area of trees <51 cm diameter breast height (dbh), average hardwood dbh, maximum tree dbh, percentage slope, and the dbh of the largest conifer snag. Our use of routinely collected forest inventory data allows the assessment and monitoring of change in fisher resting habitat suitability over large regions with no additional sampling effort. Although models were constrained to include only variables available from the list of those measured using the FIA protocol, we did not find this to be a shortcoming. The model makes it possible to compare average resting habitat suitability values before and after forest management treatments, among administrative units, across regions and over time. Considering hundreds of plot estimates as a sample of habitat conditions over large spatial scales can bring a broad perspective, at high resolution, and efficiency to the assessment and monitoring of wildlife habitat.

Animals↗

PubMed1998

Primers of glycosaminoglycan biosynthesis from Peruvian rain forest plants.

We have developed a rapid, high throughput screening assay for compounds that alter the assembly of glycosaminoglycan chains in Chinese hamster ovary cells. The assay uses autoradiography to measure the binding of newly synthesized [35S]proteoglycans and [35S]glycosaminoglycans to a positively charged membrane. Screening over 1000 extracts from a random plant collection obtained from the Amazon rain forest yielded five plants that stimulated glycosaminoglycan assembly in both wild-type cells and a mutant cell line defective in xylosyltransferase (the first committed enzyme involved in glycosaminoglycan biosynthesis). Fractionation of an extract of Maieta guianensis by silica gel and reverse-phase chromatography yielded two pure compounds with stimulatory activity. Spectroscopic analysis by NMR and mass spectrometry revealed that the active principles were xylosides of dimethylated ellagic acid. One of the compounds also contained a galloyl group at C-3 of the xylose moiety. These findings suggest that plants and other natural products may be a source of agents that can potentially alter glycosaminoglycan and proteoglycan formation in animal cells.

Animals↗

PubMed1997

Use of olfactory cues in foraging by owl monkeys (Aotus nancymai) and capuchin monkeys (Cebus apella).

The authors tested free-ranging New World monkeys (nocturnal owl monkeys [Aotus nancymai] and diurnal capuchin monkeys [Cebus apella]) to determine the extent to which they use olfactory cues to locate food hidden in containers at 2 of 6 feeding sites within a 1 1/2-ha forested enclosure. These 2 sites were selected randomly for each trial and then were baited with banana and banana peel residue. The 4 other sites were unbaited and unscented. In trials in which the food was not visible to the monkeys, Aotus monkeys located the baited sites at a level greater than expected by chance, whereas Cebus monkeys did not. Use of olfactory information by Aotus monkeys in foraging may be an adaptation for nocturnal foraging because olfactory cues are more salient than visual cues at low light levels.

Animals↗

PubMed1988

Isolation of fecal coliforms from pristine sites in a tropical rain forest.

Samples collected from water accumulated in leaf axilae of bromeliads (epiphytic flora) in a tropical rain forest were found to harbor fecal coliforms. Random identification of fecal coliform-positive isolates demonstrated the presence of Escherichia coli. This bacterium was also isolated from bromeliad leaf surfaces. These data indicate that E. coli may be part of the phyllosphere microflora and not simply a transient bacterium of this habitat. The isolation of fecal coliforms from these sites was unexpected and raises questions as to the validity of using fecal coliforms as indicators of biological water quality in the tropics.

Anti-Bacterial Agents↗

PubMedDate not supplied

Diet survey of two cultural groups in a coastal British Columbia community.

OBJECTIVES: As part of a larger study of polychlorinated dibenzodioxin (PCDD) and dibenzofuran (PCDF) pollution, to describe and compare Aboriginal and non-Aboriginal residents' recalled diets. METHODS: We surveyed a stratified random sample aged 25 to 64 years: forest products mill employees (n = 84), Aboriginal reserve residents (n = 78), and other residents (n = 80). We administered a questionnaire on intake of fish/seafood, wild game and plants, domesticated animal meat and eggs, dairy products, vegetable oils and cereals; age, gender, childbearing, lactation, residence and smoking. We measured height and weight. RESULTS: Reserve residents ate less seafood, but more fish roe, eulachon grease, smoked salmon, clams and sea urchins, more deer organs, hamburger meat, pork, fried chicken, and hot-dogs, but less rabbit, beef steaks/roasts, high-fibre cereals, potato chips, bread, cheese and milk. CONCLUSIONS: We cannot yet quantify PCDD and PCDF intakes. The wild food consumption data are unique and may be useful for risk assessments in the target population and similar communities.

Adult↗