scholarly journals A System Dynamics Model Examining Alternative Wildfire Response Policies

Systems ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 49 ◽  
Author(s):  
Thompson ◽  
Wei ◽  
Dunn ◽  
O’Connor
Keyword(s):  
Forest Restoration ◽  
Transition Period ◽  
Structural Characteristics ◽  
Reference Conditions ◽  
Burn Severity ◽  
Dynamics Model ◽  
Successional Stage ◽  
Natural Fire ◽  
Return Interval ◽  
Burn Rate

In this paper, we develop a systems dynamics model of a coupled human and natural fire-prone system to evaluate changes in wildfire response policy. A primary motivation is exploring the implications of expanding the pace and scale of using wildfires as a forest restoration tool. We implement a model of a forested system composed of multiple successional classes, each with different structural characteristics and propensities for burning at high severity. We then simulate a range of alternative wildfire response policies, which are defined as the combination of a target burn rate (or inversely, the mean fire return interval) and a predefined transition period to reach the target return interval. We quantify time paths of forest successional stage distributions, burn severity, and ecological departure, and use departure thresholds to calculate how long it would take various policies to restore forest conditions. Furthermore, we explore policy resistance where excessive rates of high burn severity in the policy transition period lead to a reversion to fire exclusion policies. Establishing higher burn rate targets shifted vegetation structural and successional classes towards reference conditions and suggests that it may be possible to expand the application of wildfires as a restoration tool. The results also suggest that managers may be best served by adopting strategies that define aggressive burn rate targets but by implementing policy changes slowly over time.

Dynamic Analysis Helicopter Flight Simulator

2014 ◽  
Vol 543-547 ◽  
pp. 1305-1308
Author(s):  
Xiao Feng Liu ◽  
Jing Wei Yu ◽  
Hai Tao Wang ◽  
Zhao Wen Fang
Keyword(s):  
Kinetic Model ◽  
Dynamic Analysis ◽  
Simulation Analysis ◽  
Structural Characteristics ◽  
Reference Value ◽  
Simulation System ◽  
Flight Simulator ◽  
Dynamics Model ◽  
Helicopter Flight ◽  
Simulation Results

For helicopter structural characteristics, this article focuses on the helicopter to take off, hover and other state aerodynamic analysis, the establishment of the fuselage-landing gear dynamics model; while the helicopter simulator simulation system are described, and the kinetic model was built simulation analysis, simulation results and the actual flight conditions consistent, indicating that the model is correct, there is a certain reference value.

Simulation Analysis of Firing Dynamics on a New Heavy Machine Gun

2014 ◽  
Vol 574 ◽  
pp. 32-35 ◽  
Author(s):  
Zhi Teng Fan ◽  
Rui Lin Wang ◽  
Tao Li
Keyword(s):  
Boundary Conditions ◽  
Structural Optimization ◽  
Test Data ◽  
Simulation Analysis ◽  
Structural Characteristics ◽  
Prototype Model ◽  
Dynamics Model ◽  
Movement Characteristic ◽  
Parameter Matching ◽  
Heavy Machine

In order to study the automation dynamics of a certain type of Heavy Machine Gun, a virtual prototype model is established based on analysing the structural characteristics and movement principle. The dynamics model is created by ADAMS, including determining the boundary conditions of shooter and soil. The movement characteristic of bolt in rounds of continuous firing is analysed. Choosing the velocity of bolt as checkout targets, analysing the simulation result and test data comparatively, the feasibility of model is confirmation. So the foundation of further movement analysing, parameter matching and structural optimization about the rifle is laid.

scholarly journals Spatial Heterogeneity of Burn Severity and First-Year Vegetation Responses Following Fire on Subalpine Plateaus in Yellowstone National Park

1989 ◽  
Vol 13 ◽  
pp. 217-224
Author(s):  
Monica Turner ◽  
Robert Gardner ◽  
William Romme
Keyword(s):  
Yellowstone National Park ◽  
National Park ◽  
Large Scale ◽  
Tree Mortality ◽  
Vegetation Type ◽  
Fire Severity ◽  
Fire Effects ◽  
Time Of Day ◽  
Burn Severity ◽  
Natural Fire

The 1988 fires that burned in Yellowstone National Park presented ecologists with a unique opportunity to investigate ecological responses to large-scale fires (Christensen et al. 1989, Knight and Wallace 1989). The Yellowstone fires created an extremely heterogeneous landscape in terms of both the overall burning patterns and the variable fire severity within burned areas. Large fires rarely consume the entire forest because of the influence of wind variations, topography, vegetation type, natural fire breaks, and the time of day that the fire passed through (Rowe and Scotter 1973, Wright and Heinselman 1973, Van Wagner 1983). Direct fire effects such as tree mortality and organic matter consumption are related to locally variable parameters such as moisture content (Brown et al. 1985, Peterson and Ryan 1986, Ryan et al. 1988), and fire severity and return intervals are often strongly influenced by topographic and edaphic variability (Habeck and Mutch 1973, Romme and Knight 1981, Hemstrom and Franklin 1982, Whitney 1986). Therefore, burned landscapes generally contain areas of low as well as high intensity fire, usually in a complex mosaic (Van Wagner 1983). These variable fire intensities result in a heterogeneous pattern of burn severities (effects of fire on the ecosystem), as well as islands of unburned vegetation. The influence of burn severity on plant reestablishment following fire is well documented (e.g., Lyon and Stickney 1976, Rowe and Scotter 1973, Viereck 1983, Ryan and Noste 1985), and the importance of the effects of limited burns and low-intensity fires on the vegetation mosaic has been recognized (Habeck and Mutch 1973, Rowe 1983). However, few studies have dealt explicitly with the spatial variation of fire effects in a systematic and quantitative way.

Prefire heterogeneity, fire severity, and early postfire plant reestablishment in subalpine forests of Yellowstone National Park, Wyoming

1999 ◽  
Vol 9 (1) ◽  
pp. 21 ◽  
Author(s):  
Monica G. Turner ◽  
William H. Romme ◽  
Robert H. Gardner
Keyword(s):  
National Park ◽  
Lodgepole Pine ◽  
Fire Severity ◽  
Tree Density ◽  
Burn Severity ◽  
Percent Cover ◽  
Crown Fire ◽  
Successional Stage ◽  
Burned Areas ◽  
Pine Seedlings

The 1988 fires in Yellowstone National Park providedan opportunity to study effects of a large infrequent disturbance on a natural community. This study addressed two questions: (1) How does prefire heterogeneity of the landscape affect postfire patterns of fire severity? and (2) How do postfire patterns of burn severity influence plant reestablishment? At three sites, 100 sampling points were distributed regularly in a 1-km x 1-km grid and sampled annually from 1989 to 1992. Information was recorded on fire severity (damage to trees, depth of ash and soil charring, and percent mineral soil exposed); pre-fire forest structure (forest successional stage; tree density; tree species; tree size; and evidence of pre-fire disturbance by mountain pine beetle [Dendroctonus ponderosae Hopk.] or mistletoe [Arceuthobium americanum Nutt. ex Engelm.]); post-fire percent cover of graminoids, forbs, and low shrubs; number of lodgepole pine (Pinus contorta var. latifolia Engelm.) seedlings; and general topographic characteristics (slope and aspect). Fire severity was influenced by successional stage, with older stands more likely to be in the more severe burn class, and by tree diameter, with tree damage diminishing with tree size. Prefire bark beetle and mistletoe damage also influenced fire severity; severe prefire damage increased the likelihood of crown fire, but intermediate prefire damage reduced the likelihood of crown fire. Fire severity was not influenced by slope, aspect, or tree density. Postfire percent vegetative cover and density of lodgepole pine seedlings varied with burn severity. In lightly burned areas, percent cover returned to unburned levels by 1991. In severely burned areas, total percent cover was about half that of unburned areas by 1992, and shrub cover remained reduced. Recruitment of lodgepole pine seedlings was greatest during the second postfire year and in severe-surface burns rather than in crown fires. Continued monitoring of vegetation dynamics in Yellowstone’s burned forests will contribute to our understanding of successional processes following a disturbance that was exceptional in its size and severity.

scholarly journals ASPECTOS FLORÍSTICOS DE TRÊS ESTÁGIOS SUCESSIONAIS DE MATA CILIAR EM ARROIO DO PADRE, EXTREMO SUL DA MATA ATLÂNTICA

FLORESTA ◽  
2013 ◽  
Vol 43 (2) ◽  
pp. 191
Author(s):  
Tiago Schuch Venzke ◽  
Sebastião Venâncio Martins
Keyword(s):  
Forest Restoration ◽  
Secondary Forest ◽  
Riparian Forest ◽  
Floristic Composition ◽  
Primary Forest ◽  
Successional Stage ◽  
Regeneration Time ◽  
Mature Forest ◽  
Successional Stages ◽  
South Of Brazil

 O objetivo foi caracterizar a composição e as relações florísticas de estágios sucessionais de uma mata ciliar em um fragmento de Floresta Estacional Semidecidual no Município de Arroio do Padre, extremo sul do Brasil. A área amostral foi 1,2 ha, dividida em 0,2 ha para capoeira (5 anos de regeneração), 0,5 ha para floresta secundária (45 anos de regeneração) e 0,5 ha de floresta madura. Em parcelas de 10 x 10 m, foram amostrados todos os indivíduos arbustivo-arbóreos com DAP ≥5 cm. A riqueza nos três estágios sucessionais revelou 72 espécies, distribuídas em 52 gêneros e 33 famílias. A capoeira apresentou menor número de táxons, enquanto na fase madura ocorreram maior quantidade (49) e riqueza de espécies exclusivas (20). A composição florística foi influenciada pelo estágio sucessional, e a classificação das parcelas pela análise de similaridade formou agrupamentos conforme a idade da regeneração. Isso reflete a adaptação da comunidade às condições ambientais proporcionadas pelo avanço da sucessão ecológica. Assim, recomenda-se que as estratégias de restauração florestal considerem as espécies adaptadas ao estágio sucessional, a fim de maximizar os projetos de reflorestamento e restauração ecológica.Palavras-chave: Pelotas; Floresta Estacional Semidecidual; sucessão florestal; ecologia florestal. AbstractFloristic composition of three successional stages of a riparian forest in the municipality of Arroio do Padre, very south of Brazil. This research aims to characterize composition and floristic relations of three successional stages of a Riparian Semi-deciduous Seasonal Forest, in the municipality of Arroio do Padre, South of Brazil. The sample area was divided into 0.2 ha for ‘capoeira’ (five years of regeneration), 0.5 ha for secondary forest (45 years for regeneration), and 0.5 ha for mature forest (primary forest). Richness in the three succession stages included 72 species distributed into 52 genera and 33 families. ‘Capoeira’ presented lower quantity of taxa, whereas in the mature forest occurred greater number of species (49) and exclusive species (20). The floristic composition was influenced by successional stage and classification of plots by the similarity analysis clusters formed as the regeneration time. Differences in floristic composition reflect community adaptation to the conditions provided along succession. These variations reveal that the age of the succession reflects in forest floristic, and strategies for forest restoration should consider species adapted to successional stages in order to maximize native forests reforestation projects.Keywords: Municipality of Pelotas; Semi-deciduous Seasonal Forest; forest ecology.

scholarly journals Gas exchange, chemical composition and productive characteristics of tropical grasses deferred II: cultivars BRS Paiaguás and BRS Piatã

2021 ◽  
Vol 22 ◽  
Author(s):  
Francisca Gisele Rodrigues dos SANTOS ◽  
Ricardo Alves de ARAÚJO ◽  
Magno José Duarte CÂNDIDO ◽  
Marcos Cláudio Pinheiro ROGÉRIO ◽  
Clésio dos Santos COSTA ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Rainy Season ◽  
Transition Period ◽  
Structural Characteristics ◽  
Block Design ◽  
Critical Periods ◽  
Pasture Grass ◽  
Leaf Transpiration ◽  
Randomized Complete Block Design ◽  
Urochloa Brizantha

ABSTRACT This study aimed to evaluate the physiological parameters, the productive characteristics, structural and chemical composition of Urochloa Brizantha cultivars BRS and BRS Piatã submitted to two deferment periods and three using times. The experimental design was randomized complete block design in a factorial scheme 2 x 2 x 3, being two grass cultivars (Paiaguás grass and Piatã grass), two deferment periods (rainy season and dry-rainy transition) and three sealing times (40, 80 and 120 days). It was observed that, in the rainy season, the grasses had higher leaf transpiration rate when used for 40 days of deferment (1.66 µmol m2/s). During the rainy season, the Stomatal conductance was detected only in the grasses used with shorter seal, with an average of 0.07 µmol m2/s. In contrast, in the period of transition, the concentration decreased to 0.02 µmol m2/s. In a general way, the BRS Paiaguás presented lower content of NDF. The shorter cycle provided greater biomass production of total forage during the period of rain, approximately 2.78 times more than the same pasture grass deferred during the transition period. Generally, the periods of deferment and moments of use cause effects on structural characteristics of pasture, being that the period of deferment of the transition period and used for 40 and 80 days may be a strategy for keeping animals in critical periods.

scholarly journals Quantifying functional increases across a large-scale wetland restoration chronosequence

2021 ◽  
Author(s):  
Jacob Berkowitz
Keyword(s):  
Large Scale ◽  
Reference Conditions ◽  
Forested Wetlands ◽  
Additional Time ◽  
Successional Stage ◽  
Wetland Functions ◽  
Reference Wetland ◽  
Study Results ◽  
Restoration Chronosequence ◽  
Study Sites

Over 300,000 ha of forested wetlands have undergone restoration within the Mississippi Alluvial Valley region. Restored forest successional stage varies, providing opportunities to document wetland functional increases across a large-scale restoration chronosequence using the Hydrogeomorphic (HGM) approach. Results from >600 restored study sites spanning a 25-year chronosequence indicate that: 1) wetland functional assessment variables increased toward reference conditions; 2) restored wetlands generally follow expected recovery trajectories; and 3) wetland functions display significant improvements across the restoration chronosequence. A functional lag between restored areas and mature reference wetlands persists in most instances. However, a subset of restored sites have attained mature reference wetland conditions in areas approaching or exceeding tree diameter and canopy closure thresholds. Study results highlight the importance of site selection and the benefits of evaluating a suite of wetland functions in order to identify appropriate restoration success milestones and design monitoring programs. For example, wetland functions associated with detention of precipitation (a largely physical process) rapidly increased under post restoration conditions, while improvements in wetland habitat functions (associated with forest establishment and maturation) required additional time. As the wetland science community transitions towards larger scale restoration efforts, effectively quantifying restoration functional improvements will become increasingly important.

scholarly journals Sward structural characteristics and herbage accumulation of Panicum maximum cv. Mombaça subjected to rotational stocking managements

2009 ◽  
Vol 66 (1) ◽  
pp. 8-19 ◽  
Author(s):  
Sila Carneiro da Silva ◽  
Adriana Amaral de Oliveira Bueno ◽  
Roberta Aparecida Carnevalli ◽  
Marina Castro Uebele ◽  
Fernando Oliveira Bueno ◽  
...  
Keyword(s):  
Management Practices ◽  
Transition Period ◽  
Structural Characteristics ◽  
Block Design ◽  
Incident Light ◽  
Grazing Management ◽  
Panicum Maximum ◽  
Area Index ◽  
Horizontal Orientation ◽  
Guinea Grass

Grazing strategies promote changes in sward structure that can affect patterns of herbage accumulation and sward flexibility to management. This experiment evaluated sward structural characteristics and herbage accumulation of Mombaça guinea grass (Panicum maximum Jacq. cv. Mombaça) subjected to rotational stocking managements. Treatments involved grazing when swards reached either 95 or 100% interception of the incident light (LI), to post-grazing heights of 30 and 50 cm, and were allocated to 2,000 m² paddocks according to a randomised complete block design in a 2 × 2 factorial arrangement with four replications, from January 2001 to February 2002. Sward canopy changed from a vertical to a more horizontal orientation as the light interception area index and height increased from post to pre-grazing. Leaf canopy height pre-grazing was stable throughout the year and around 90 and 115 cm for the 95% and 100% LI treatments respectively, indicating a potential for development and use of target-based grazing management practices. Herbage mass pre and post-grazing was lower for the 95% than the 100% LI treatments, but with higher proportion of leaf and lower proportions of stem and dead material. Treatment effects on herbage accumulation were cumulative and became more evident as the experiment progressed, with up to 6 t ha-1 DM advantage to the 95/30 treatment. Although based on a single year experiment, grazing management should aim for low herbage mass during the transition period from winter to spring in order to allow fast recovery of swards and favour herbage accumulation during the following growing season.

scholarly journals Morphophysiology of tropical grasses under different water supply in two growing seasons: II. BRS Massai and BRS Tamani grasses

2021 ◽  
pp. 301-318
Author(s):  
Samuel Rocha Maranhão ◽  
◽  
Roberto Cláudio Fernandes Franco Pompeu ◽  
Ricardo Alves de Araújo ◽  
Marcos Neves Lopes ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Water Supply ◽  
Rainy Season ◽  
Transition Period ◽  
Structural Characteristics ◽  
Stem Elongation ◽  
Maximum Point ◽  
Dry Period ◽  
Growing Seasons ◽  
Daily Water

This study aimed to evaluate the physiological parameters and the biomass flow and structural characteristics of BRS Massai and BRS Tamani grasses under different irrigation conditions. The rating of gas exchange, biomass flow and structural characteristics were performed in dry periods and dry/rainy season, under the water supply of 30; 60; 90 and 120% of the reference evapotranspiration (ETo). The experimental design was completely randomized in a factorial arrangement 4x2 (water supply and grass). The experiment was conducted in pots with capacity for 7.5 dm³, using as substrate layer of 0-0.2 m soil. There was no effect (P < 0.05) between the gas exchange in the dry period, having the largest growing parameters of irrigation schemes. In the transition period of dry/rainy, we observed a reversal behavior in relation to the dry period, showing a rapid recovery of grasses under the minor water supply. It was observed quadratic behavior to concentrations of CO2 in the leaf mesophilic (Ci) with maximum point to the BRS Massai grass and minimum point to the BRS Tamani grass, where the major and minor Ci were 119 and 48 ppm in the water supply of 107 and 35% of ETo, respectively. In relation to the biomass flow, the BRS Tamani grass presented greater stem elongation rate and leaf senescence rate in relation to BRS Massai in both periods assessed. In the dry period, we observed a higher biomass production of green leaf blades in the BRS Tamani grass, while in the transition dry/rainy season, the results for this variable were similar, and at the same time that observed higher accumulation of green culm biomass to the BRS Tamani grass, which certainly affected its structure. It is concluded that the application of a minimum daily water supply of 30% of ETo allows the maintenance of BRS Massai and BRS Tamani grasses without incurring the death of tillers and reduction of regrowth vigor, whereas the water supply of 90% of ETo favors the morphophysiological characteristics, especially of BRS Tamani grass.

scholarly journals Effectiveness of Restoration Treatments for Reducing Fuels and Increasing Understory Diversity in Shrubby Mixed-Conifer Forests of the Southern Rocky Mountains, USA

Forests ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 508 ◽  
Author(s):  
Julie E. Korb ◽  
Michael T. Stoddard ◽  
David W. Huffman
Keyword(s):  
Prescribed Fire ◽  
Forest Restoration ◽  
Treatment Effectiveness ◽  
Conifer Forests ◽  
Mixed Conifer ◽  
Burn Treatment ◽  
Attack Tree ◽  
Natural Fire ◽  
Mixed Conifer Forests ◽  
And Control

Exclusion of natural surface fires in warm/dry mixed-conifer forests of the western U.S. has increased potential for stand-replacing crown fires and reduced resilience of these systems to other disturbances, such as drought and insect attack. Tree thinning and the application of prescribed fire are commonly used to restore more resilient ecological conditions, but currently, there is a lack of long-term data with which to evaluate restoration treatment effectiveness in forest types where resprouting shrubs dominate understory communities. At a mixed-conifer site in southwestern Colorado, we compared forest structure and understory vegetation responses to three restoration treatments (thin/burn, burn, and control) over 10 years in a completely randomized and replicated experiment. Forest density, canopy cover, and crown fuel loads were consistently lower, and crown base height was higher, in thin/burn than burn or controls, but the effects diminished over time. Ten years following treatment, >99% of all plant species within both treatments and the control were native in origin. There were no differences between treatments in understory richness, diversity, cover, or surface fuels, but graminoid cover more than doubled in all treatments over the 15-year monitoring period. Similarly, there was more than a 250% increase post-treatment in shrub density, with the greatest increases in the thin/burn treatment. In addition, we saw an increase in the average shrub height for both treatments and the control, with shrub stems >80 cm becoming the dominant size class in the thin/burn treatment. Conifer seedling density was significantly lower in thin/burn compared with burn and control treatments after 10 years. Taken together, these conditions create challenges for managers aiming to reestablish natural fire patterns and sustain mixed-conifer forests. To limit the dominance of resprouting shrubs and facilitate conifer regeneration after overstory thinning and prescribed fire, managers may need to consider new or more intensive approaches to forest restoration, particularly given current and projected climate change.

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