共查询到20条相似文献,搜索用时 364 毫秒
1.
Den Boychuk W. John Braun Reg J. Kulperger Zinovi L. Krougly David A. Stanford 《Environmental and Ecological Statistics》2009,16(2):133-151
We consider a stochastic fire growth model, with the aim of predicting the behaviour of large forest fires. Such a model can
describe not only average growth, but also the variability of the growth. Implementing such a model in a computing environment
allows one to obtain probability contour plots, burn size distributions, and distributions of time to specified events. Such
a model also allows the incorporation of a stochastic spotting mechanism.
相似文献
Reg J. KulpergerEmail: |
2.
Fiat boundaries: some implications for interpretation,decision-support,and multi-temporal analysis 总被引:1,自引:0,他引:1
Kim Lowell 《Environmental and Ecological Statistics》2008,15(4):369-383
Polygon-based thematic maps can be composed of boundaries that exist by definition—i.e., bona fide boundaries—or those that
exist relative to a specific interpretation of a spatial phenomenon—i.e., fiat boundaries. The construction of maps composed
of fiat boundaries is usually based on a subjective interpretive methodology that is affected by the data used to construct
the map and the minimum mapping unit employed. That fiat boundaries are not the same as bona fide boundaries affects their
use in computer-based spatial decision support tools. This is discussed both in terms of an analysis conducted at one specific
moment, and in respect to increasingly common multi-temporal analysis.
相似文献
Kim LowellEmail: |
3.
B. Gail Ivanoff 《Environmental and Ecological Statistics》2009,16(2):153-171
The concept of the renewal property is extended to processes indexed by a multidimensional time parameter. The definition
given includes not only partial sum processes, but also Poisson processes and many other point processes whose jump points
are not totally ordered. Various properties of renewal processes are discussed. Renewal processes are proposed as a basis
for modelling the spread of a forest fire under a prevailing wind.
相似文献
B. Gail IvanoffEmail: |
4.
B. Mike Wotton 《Environmental and Ecological Statistics》2009,16(2):107-131
Understanding and being able to predict forest fire occurrence, fire growth and fire intensity are important aspects of forest
fire management. In Canada fire management agencies use the Canadian Forest Fire Danger Rating System (CFFDRS) to help predict
these elements of forest fire activity. In this paper a review of the CFFDRS is presented with the main focus on understanding
and interpreting Canadian Fire Weather Index (FWI) System outputs. The need to interpret the outputs of the FWI System with
consideration to regional differences is emphasized and examples are shown of how the relationship between actual fuel moisture
and the FWI System’s moisture codes vary from region to region. Examples are then shown of the relationship between fuel moisture
and fire occurrence for both human- and lightning-caused fire for regions with different forest composition. The relationship
between rate of spread, fuel consumption and the relative fire behaviour indices of the FWI System for different forest types
is also discussed. The outputs of the CFFDRS are used every day across Canada by fire managers in every district, regional
and provincial fire management office. The purpose of this review is to provide modellers with an understanding of this system
and how its outputs can be interpreted. It is hoped that this review will expose statistical modellers and other researchers
to some of the models used currently in forest fire management and encourage further research and development of models useful
for understanding and managing forest fire activity.
相似文献
B. Mike WottonEmail: |
5.
David T. Butry 《Environmental and Ecological Statistics》2009,16(2):291-319
This paper examines the effect wildfire mitigation has on broad-scale wildfire behavior. Each year, hundreds of million of
dollars are spent on fire suppression and fuels management applications, yet little is known, quantitatively, of the returns
to these programs in terms of their impact on wildfire extent and intensity. This is especially true when considering that
wildfire management influences and reacts to several, often times confounding factors, including socioeconomic characteristics,
values at risk, heterogeneous landscapes, and climate. Due to the endogenous nature of suppression effort and fuels management
intensity and placement with wildfire behavior, traditional regression models may prove inadequate. Instead, I examine the
applicability of propensity score matching (PSM) techniques in modeling wildfire. This research makes several significant
contributions including: (1) applying techniques developed in labor economics and in epidemiology to evaluate the effects
of natural resource policies on landscapes, rather than on individuals; (2) providing a better understanding of the relationship
between wildfire mitigation strategies and their influence on broad-scale wildfire patterns; (3) quantifying the returns to
suppression and fuels management on wildfire behavior.
相似文献
David T. ButryEmail: |
6.
Léa Fortunato Chantal Guihenneuc-Jouyaux Margot Tirmarche Dominique Laurier Denis Hémon 《Environmental and Ecological Statistics》2009,16(3):341-353
Ecological studies enable investigation of geographic variations in exposure to environmental variables, across groups, in
relation to health outcomes measured on a geographic scale. Such studies are subject to ecological biases, including pure
specification bias which arises when a nonlinear individual exposure-risk model is assumed to apply at the area level. Introduction
of the within-area variance of exposure should induce a marked reduction in this source of ecological bias. Assuming several
measurements per area of exposure and no confounding risk factors, we study the model including the within-area exposure variability
when Gaussian within-area exposure distribution is assumed. The robustness is assessed when the within-area exposure distribution
is misspecified. Two underlying exposure distributions are studied: the Gamma distribution and an unimodal mixture of two
Gaussian distributions. In case of strong ecological association, this model can reduce the bias and improve the precision
of the individual parameter estimates when the within-area exposure means and variances are correlated. These different models
are applied to analyze the ecological association between radon concentration and childhood acute leukemia in France.
相似文献
Léa FortunatoEmail: |
7.
Roswitha Wiltschko Bettina Siegmund Katrin Stapput 《Behavioral ecology and sociobiology》2005,59(2):303-312
To analyze the navigational strategy of homing pigeons at familiar sites in view of a possible role of local landmarks, two groups of pigeons—one familiar to the release site, the other unfamiliar—were released with their internal clock shifted 6 h fast, with untreated birds of both groups serving as controls. The two groups showed median deflections of 67% and 57%, respectively, of the expected size, with no consistent difference in the size of the deflection between familiar and unfamiliar birds. This clearly shows that familiarity with the release site and with the local landscape features does not affect the size of the deflections induced by clock-shifting. Obviously, pigeons familiar with the release site do not change their navigational strategy, but still continue to determine their home course solely as a compass course. General problems with orientation by landmarks are discussed; however, landmarks may help birds to recognize a site and recall the respective course.
相似文献
Roswitha WiltschkoEmail: |
8.
Spatial pattern and persistence of historical fire boundaries in southern interior British Columbia 总被引:2,自引:0,他引:2
Geraldine J. Jordan Marie-Josée Fortin Kenneth P. Lertzman 《Environmental and Ecological Statistics》2008,15(4):523-535
Recent ecosystem and fire management research aims to quantify, model and understand historical fire disturbances focusing
on their frequency, size and distribution. Less attention, however, has been paid to fire boundaries and their location on
the landscape. Our study presents a spatial method to quantify the location, pattern and persistence of historical fire boundaries
using tree ring fire scar data in the lower Stein watershed (British Columbia). Data from Pinus ponderosa and Pseudotsuga menziesii collected in 35 one-hectare plots over a 412-hectare study area were analyzed for the period between 1879 and 1947 using
local spatial statistics and boundary detection techniques. Results of the analysis using local spatial statistic Moran’s
I showed significant clustering of boundaries near topographic breaks. To determine and test whether fire boundaries between
plots were persistent, we used boundary detection methods and developed a spatially restricted randomization test. The results
revealed that out of 86 possible boundary links, 8 were significantly persistent (P < 0.025) while another 8 were significantly rare (P < 0.025). These spatial methods can help determine the historical spatial configuration of persistent boundaries and can
be used to maintain natural forest dynamics.
相似文献
Geraldine J. JordanEmail: |
9.
Chang Xuan Mao 《Environmental and Ecological Statistics》2007,14(4):473-481
Consider the removal experiment used to estimate population sizes. Statistical methods towards testing the homogeneity of
capture probabilities of animals, including a graphical diagnostic and a formal test, are presented and illustrated by real
biological examples. Simulation is used to assess the test and compare it with the χ2 test.
相似文献
Chang Xuan MaoEmail: |
10.
11.
The influence of multiple anchored fish aggregating devices (FADs) on the spatial behavior of yellowfin (Thunnus albacares) and bigeye tuna (T. obesus) was investigated by equipping all thirteen FADs surrounding the island of Oahu (HI, USA) with automated sonic receivers
(“listening stations”) and intra-peritoneally implanting individually coded acoustic transmitters in 45 yellowfin and 12 bigeye
tuna. Thus, the FAD network became a multi-element passive observatory of the residence and movement characteristics of tuna
within the array. Yellowfin tuna were detected within the FAD array for up to 150 days, while bigeye tuna were only observed
up to a maximum of 10 days after tagging. Only eight yellowfin tuna (out of 45) and one bigeye tuna (out of 12) visited FADs
other than their FAD of release. Those nine fish tended to visit nearest neighboring FADs and, in general, spent more time
at their FAD of release than at the others. Fish visiting the same FAD several times or visiting other FADs tended to stay
longer in the FAD network. A majority of tagged fish exhibited some synchronicity when departing the FADs but not all tagged
fish departed a FAD at the same time: small groups of tagged fish left together while others remained. We hypothesize that
tuna (at an individual or collective level) consider local conditions around any given FAD to be representative of the environment
on a larger scale (e.g., the entire island) and when those conditions become unfavorable the tuna move to a completely different
area. Thus, while the anchored FADs surrounding the island of Oahu might concentrate fish and make them more vulnerable to
fishing, at a meso-scale they might not entrain fish longer than if there were no (or very few) FADs in the area. At the existing
FAD density, the ‘island effect’ is more likely to be responsible for the general presence of fish around the island than
the FADs. We recommend further investigation of this hypothesis.
相似文献
Laurent Dagorn (Corresponding author)Email: |
Kim N. HollandEmail: |
David G. ItanoEmail: |
12.
Bruce C. Glavovic 《Journal of Coastal Conservation》2008,12(3):125-134
Hurricanes devastated the Gulf coast of the USA in 2005. Hurricane Katrina, in particular, highlighted the compelling need
to build more sustainable and hazard-resilient communities. Much can be learned from recovery efforts to rebuild the Gulf
coast. Personal observations and interviews with planners, academics and others involved in recovery efforts inform this analysis,
which focuses on New Orleans. A conceptual framework is developed and principles and operational imperatives outlined to guide
action for building sustainable, hazard-resilient communities. Such communities will remain elusive unless ‘business as usual’
is confronted by a transformational process of developmental planning. Sustainable, hazard-resilient coastal communities are
founded upon robust ‘critical infrastructure’ that is secured by planning and decision-making processes that enable coastal
communities to build ‘layers of resilience’ to overcome ‘waves of adversity’. Planners need to take on a redefined role—as
‘new naval architects’—to design and build communities that are ‘sea-worthy’ in this age of coastal storms.
相似文献
Bruce C. GlavovicEmail: |
13.
Dimitris Karlis Vassilis G. S. Vasdekis Maria Banti 《Environmental and Ecological Statistics》2009,16(3):355-367
Heteroscedastic additive and multiplicative models are proposed to disaggregate household data on water consumption from Athens
and provide individual consumption estimates. The models adjust for heteroscedasticity assuming that variances relate to covariates.
Household characteristics that can influence consumption are also included into models in order to allow for a clearer measurement
of individual characteristics effects. Estimation is accomplished through a penalized least squares approach. The method is
applied to a sample of real data related to domestic water consumption in Athens. The results show a greater consumption of
water for males while the single-female households are these that use the lowest quantities of water. The consumption curves
by age and gender are constructed presenting differences between the two sexes.
相似文献
Vassilis G. S. VasdekisEmail: |
14.
Coverage, i.e., the area covered by the target attribute in the study region, is a key parameter in many surveys. Coverage
estimation is usually performed by adopting a replicated protocol based on line-intercept sampling coupled with a suitable
linear homogeneous estimator. Since coverage is a parameter which may be interestingly represented as the integral of a suitable
function, improved Monte Carlo strategies for implementing the replicated protocol are introduced in order to achieve estimators
with small variance rates. In addition, new specific theoretical results on Monte Carlo integration methods are given to deal
with the integrand functions arising in the special coverage estimation setting.
相似文献
Lucio BarabesiEmail: |
15.
Model averaging (MA) has been proposed as a method of accommodating model uncertainty when estimating risk. Although the use
of MA is inherently appealing, little is known about its performance using general modeling conditions. We investigate the
use of MA for estimating excess risk using a Monte Carlo simulation. Dichotomous response data are simulated under various
assumed underlying dose–response curves, and nine dose–response models (from the USEPA Benchmark dose model suite) are fit
to obtain both model specific and MA risk estimates. The benchmark dose estimates (BMDs) from the MA method, as well as estimates
from other commonly selected models, e.g., best fitting model or the model resulting in the smallest BMD, are compared to
the true benchmark dose value to better understand both bias and coverage behavior in the estimation procedure. The MA method
has a small bias when estimating the BMD that is similar to the bias of BMD estimates derived from the assumed model. Further,
when a broader range of models are included in the family of models considered in the MA process, the lower bound estimate
provided coverage close to the nominal level, which is superior to the other strategies considered. This approach provides
an alternative method for risk managers to estimate risk while incorporating model uncertainty.
相似文献
Matthew W. WheelerEmail: |
16.
R. Webster West Daniela K. Nitcheva Walter W. Piegorsch 《Environmental and Ecological Statistics》2009,16(1):63-73
A primary objective in quantitative risk assessment is the characterization of risk which is defined to be the likelihood
of an adverse effect caused by an environmental toxin or chemcial agent. In modern risk-benchmark analysis, attention centers
on the “benchmark dose” at which a fixed benchmark level of risk is achieved, with a lower confidence limits on this dose
being of primary interest. In practice, a range of benchmark risks may be under study, so that the individual lower confidence
limits on benchmark dose must be corrected for simultaneity in order to maintain a specified overall level of confidence.
For the case of quantal data, simultaneous methods have been constructed that appeal to the large sample normality of parameter
estimates. The suitability of these methods for use with small sample sizes will be considered. A new bootstrap technique
is proposed as an alternative to the large sample methodology. This technique is evaluated via a simulation study and examples
from environmental toxicology.
相似文献
R. Webster WestEmail: |
17.
In this paper we examine the use of data augmentation techniques for simplifying iterative simulation in the context of both
Bayesian and classical statistical inference for survival rate estimation. We examine two distinct model families common in
population ecology to illustrate our ideas, ring-recovery models and capture–recapture models, and we present the computational
advantage of this approach. We discuss also the fact that problems associated with identifiability in the classical framework
can be overcome using data augmentation, but highlight the dangers in doing so under both inferential paradigms.
相似文献
I. C. OlsenEmail: |
18.
When animals die in traps in a mark-recapture study, straightforward likelihood inferences are possible in a class of models.
The class includes M0, Mt, and Mb as reported by White et al. (Los Alamos National Laboratory, LA-8787-NERP, pp 235, 1982), those that do not involve heterogeneity.
We include three Markov chain “persistence” models and show that they provide good fits in a trapping study of deer mice in
the Cascade-Siskiyou National Monument of Southern Oregon where trapping mortality was high.
相似文献
Fred L. RamseyEmail: |
19.
Andrew O. Finley Sudipto Banerjee Ronald E. McRoberts 《Environmental and Ecological Statistics》2008,15(2):241-258
In efforts such as land use change monitoring, carbon budgeting, and forecasting ecological conditions and timber supply,
there is increasing demand for regional and national data layers depicting forest cover. These data layers must permit small
area estimates of forest area and, most importantly, provide associated error estimates. This paper presents a model-based
approach for coupling mid-resolution satellite imagery with plot-based forest inventory data to produce estimates of probability
of forest and associated error at the pixel-level. The proposed Bayesian hierarchical model provides access to each pixel’s
posterior predictive distribution allowing for a highly flexible analysis of pixel and multi-pixel areas of interest. The
paper presents a trial using multiple dates of Landsat imagery and USDA Forest Service Forest Inventory and Analysis plot
data. The results describe the spatial dependence structure within the trial site, provide pixel and multi-pixel summaries
of probability of forest land use, and explore discretization schemes of the posterior predictive distributions to forest
and non-forest classes. Model prediction results of a holdout set analysis suggest the proposed model provides high classification
accuracy, 88%, for the trial site.
相似文献
Ronald E. McRobertsEmail: |
20.
Hierarchical spatial point process analysis for a plant community with high biodiversity 总被引:1,自引:0,他引:1
Janine B. Illian Jesper Møller Rasmus P. Waagepetersen 《Environmental and Ecological Statistics》2009,16(3):389-405
A complex multivariate spatial point pattern of a plant community with high biodiversity is modelled using a hierarchical
multivariate point process model. In the model, interactions between plants with different post-fire regeneration strategies
are of key interest. We consider initially a maximum likelihood approach to inference where problems arise due to unknown
interaction radii for the plants. We next demonstrate that a Bayesian approach provides a flexible framework for incorporating
prior information concerning the interaction radii. From an ecological perspective, we are able both to confirm existing knowledge
on species’ interactions and to generate new biological questions and hypotheses on species’ interactions.
相似文献
Rasmus P. WaagepetersenEmail: |