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Fire management of California shrubland landscapes.

Fire management of California shrublands has been heavily influenced by policies designed for coniferous forests, however, fire suppression has not effectively excluded fire from chaparral and coastal sage scrub landscapes and catastrophic wildfires are not the result of unnatural fuel accumulation. There is no evidence that prescribed burning in these shrublands provides any resource benefit and in some areas may negatively impact shrublands by increasing fire frequency. Therefore, fire hazard reduction is the primary justification for prescription burning, but it is doubtful that rotational burning to create landscape age mosaics is a cost effective method of controlling catastrophic wildfires. There are problems with prescription burning in this crown-fire ecosystem that are not shared by forests with a natural surface-fire regime. Prescription weather conditions preclude burning at rotation intervals sufficient to effect the control of fires ignited under severe weather conditions. Fire management should focus on strategic placement of prescription burns to both insure the most efficient fire hazard reduction and to minimize the amount of landscape exposed to unnaturally high fire frequency. A major contributor to increased fire suppression costs and increased loss of property and lives is the continued urban sprawl into wildlands naturally subjected to high intensity crown fires. Differences in shrubland fire history suggest there may be a need for different fire management tactics between central coastal and southern California. Much less is known about shrubland fire history in the Sierra Nevada foothills and interior North Coast Ranges, and thus it would be prudent to not transfer these ideas too broadly across the range of chaparral until we have a clearer understanding of the extent of regional variation in shrubland fire regimes.

California↗

GABAB-receptor activation alters the firing pattern of dopamine neurons in the rat substantia nigra.

Previous electrophysiological experiments have emphasized the importance of the firing pattern for the functioning of midbrain dopamine (DA) neurons. In this regard, excitatory amino acid receptors appear to constitute an important modulatory control mechanism. In the present study, extracellular recording techniques were used to investigate the significance of GABAB-receptor activation for the firing properties of DA neurons in the substantia nigra (SN) in the rat. Intravenous administration of the GABAB-receptor agonist baclofen (1-16 mg/kg) was associated with a dose-dependent regularization of the firing pattern, concomitant with a reduction in burst firing. At higher doses (16-32 mg/kg), the firing rate of the DA neurons was dose-dependently decreased. Also, microiontophoretic application of baclofen regularized the firing pattern of nigral DA neurons, including a reduction of burst firing. Both the regularization of the firing pattern and inhibition of firing rate produced by systemic baclofen administration was antagonized by the GABAB-receptor antagonist CGP 35348 (200 mg/kg, i.v.). The GABAA-receptor agonist muscimol produced effects on the firing properties of DA neurons that were opposite to those observed following baclofen, i.e., an increase in firing rate accompanied by a decreased regularity. The NMDA receptor antagonist MK 801 (0.4-3.2 mg/kg, i.v.) produced a moderate, dose-dependent increase in the firing rate of the nigral DA neurons as well as a slightly regularized firing pattern. Pretreatment with MK 801 (3.2 mg/kg, i.v., 3-10 min) did neither promote nor prevent the regularization of the firing pattern or inhibition of firing rate on the nigral DA neurons produced by baclofen. The present results clearly show that GABAB-receptors can alter the firing pattern of nigral DA neurons, hereby counterbalancing the previously described ability of glutamate to induce burst firing activity on these neurons.

Animals↗

Fire warning and safety systems.

Fire Warning and Safety Systems was written to do more than just help hospitals prepare for surveys by the Joint Commission on Accreditation of Healthcare Organizations (JCAHO). Its primary purpose is to assist hospitals in developing a fire safety program that includes and incorporates the role and function of fire protection systems. The manual is also designed to enhance the reader's understanding of fire protection systems and to improve the reliability of such systems with a proper preventive maintenance program. Fire safety programs in hospitals are often developed on the basis of compliance with applicable code requirements and JCAHO standards. However, the codes contain what are generally considered to be minimum requirements. Often the requirements do not truly define performance objectives and, therefore, most hospitals do not truly know the level of fire protection or level of risk present in the facility. For this reason, one of the primary aspects of a hospital fire safety program should be the development of performance objectives that define the acceptable level of risk from fire. Once the level of risk has been identified, the role of building design and construction, fire protection systems, contents and furnishing, and facility staff can be evaluated and defined. This book primarily addresses the role of fire protection systems, although chapter 5 does contain a discussion of staff behavior, but primarily from the perspective of staff's role in fire extinguishment. Volume 2 of ASHE's Management and Compliance Series, Developing a Hospital Emergency Preparedness Program, further expands on staff's role and emergency preparedness. Various fire protection systems will be discussed throughout the manual. For each system, an overview of how the system functions is provided. The text also summarizes applicable code provisions that identify when such systems are required and how such systems are to be installed, inspected, tested, and maintained. After a brief description of the basic components of the systems, preventive maintenance guidelines are provided, including proper acceptance test procedures. Our experience indicates that many problems encountered by hospitals with fire protection systems have existed since the day the system was installed. Appendix A contains material that should assist facilities in developing a fire risk management program based on a fire risk assessment. Appendix B contains information about the suitability of various extinguishing agents to suppress a fire involving certain hazards.(ABSTRACT TRUNCATED AT 400 WORDS)

Building Codes↗

Restoring fire as an ecological process in shortgrass prairie ecosystems: initial effects of prescribed burning during the dormant and growing seasons.

Prior to Anglo-European settlement, fire was a major ecological process influencing the structure, composition and productivity of shortgrass prairie ecosystems on the Great Plains. However during the past 125 years, the frequency and extent of grassland fire has dramatically declined as a result of the systematic heavy grazing by large herds of domestic cattle and sheep which reduced the available levels of fine fuel and organized fire suppression efforts that succeeded in altering the natural fire regime. The greatly diminished role of recurrent fire in these ecosystems is thought to be responsible for ecologically adverse shifts in the composition, structure and diversity of these grasslands, leading specifically to the rise of ruderal species and invasion by less fire-tolerant species. The purpose of this study was to evaluate the ecological effects of fire season and frequency on the shortgrass prairie and to determine the means by which prescribed fire can best be restored in this ecosystem to provide the greatest benefit for numerous resource values. Plant cover, diversity, biomass and nutrient status, litter cover and soil chemistry were measured prior to and following fire treatments on a buffalograss-blue grama shortgrass prairie in northeastern New Mexico. Dormant-season fire was followed by increases in grass cover, forb cover, species richness and concentrations of foliar P, K, Ca, Mg and Mn. Growing-season fire produced declines in the cover of buffalograss, graminoids and forbs and increases in litter cover and levels of foliar P, K, Ca and Mn. Although no changes in soil chemistry were observed, both fire treatments caused decreases in herbaceous production, with standing biomass resulting from growing-season fire approximately 600 kg/ha and dormant-season fire approximately 1200 kg/ha, compared with controls approximately 1800 kg/ha. The initial findings of this long-term experiment suggest that dormant-season burning may be the preferable method for restoring fire in shortgrass prairie ecosystems where fire has been excluded for a prolonged time period.

Agriculture↗

Spatial distribution of forest fires and controlling factors in Andhra Pradesh, India using SPOT satellite datasets.

Fires are one of the major causes of forest disturbance and destruction in several dry deciduous forests of southern India. In this study, we use remote sensing data sets in conjunction with topographic, vegetation, climate and socioeconomic factors for determining the potential causes of forest fires in Andhra Pradesh, India. Spatial patterns in fire characteristics were analyzed using SPOT satellite remote sensing datasets. We then used nineteen different metrics in concurrence with fire count datasets in a robust statistical framework to arrive at a predictive model that best explained the variation in fire counts across diverse geographical and climatic gradients. Results suggested that, of all the states in India, fires in Andhra Pradesh constituted nearly 13.53% of total fires. District wise estimates of fire counts for Andhra Pradesh suggested that, Adilabad, Cuddapah, Kurnool, Prakasham and Mehbubnagar had relatively highest number of fires compared to others. Results from statistical analysis suggested that of the nineteen parameters, population density, demand of metabolic energy (DME), compound topographic index, slope, aspect, average temperature of the warmest quarter (ATWQ) along with literacy rate explained 61.1% of total variation in fire datasets. Among these, DME and literacy rate were found to be negative predictors of forest fires. In overall, this study represents the first statewide effort that evaluated the causative factors of fire at district level using biophysical and socioeconomic datasets. Results from this study identify important biophysical and socioeconomic factors for assessing 'forest fire danger' in the study area. Our results also identify potential 'hotspots' of fire risk, where fire protection measures can be taken in advance. Further this study also demonstrate the usefulness of best-subset regression approach integrated with GIS, as an effective method to assess 'where and when' forest fires will most likely occur.

Conservation of Natural Resources↗

Nutrient cycling responses to fire frequency in the Kruger National Park (South Africa) as indicated by stable isotope analysis.

Fires, which are an intrinsic feature of southern African ecosystems, produce biogenic and pyrogenic losses of nitrogen (N) from plants and soils. Because of the long history of fires in these savannas, it was hypothesized that N2 fixation by legumes balances the N losses caused by fires. In this study, the N2 fixation activity of woody legumes was estimated by analyzing foliar delta15N and proportional basal area of N2 fixing species along experimental fire gradients in the Kruger National Park (South Africa). In addition, soil carbon (C) and N pools, foliar phosphorus (P) and gross N mineralization and nitrification rates were measured, to indicate the effects of fires on nutrient stocks and the possible N cycling processes modified by fires. Although observations of increased soil C/N and mineralization rates in frequently burned plots support previous reports of N losses caused by fires, soil %N did not decrease with increasing fire frequency (except in 1 plot), suggesting that N losses are replenished in burned areas. However, relative abundance and N2 fixation of woody legumes decreased with fire frequency in two of the three fire gradients analyzed, suggesting that woody legume N2 fixation is not the mechanism that balances N losses. The relatively constant %N along fire gradients suggests that these ecosystems have other mechanisms to balance the N lost by fires, which could include inputs by atmospheric deposition and N2 fixation by forbs, grasses and soil cyanobacteria. Soil isotopic signatures have been previously used to infer patterns of fire history. However, the lack of a relationship between soil delta15N and fire frequency found in this study indicates that the effects of fires on ecosystem delta15N are unpredictable. Similar soil delta15N along fire gradients may reflect the contrasting effects of increased N gaseous emissions (which increases delta15N) and N2 fixation other than that associated with woody legumes (which lowers delta15N) on isotopic signatures.

Ecosystem↗

Role of persistent sodium and calcium currents in motoneuron firing and spasticity in chronic spinal rats.

After chronic spinal injury, motoneurons spontaneously develop two persistent inward currents (PICs): a TTX-sensitive persistent sodium current (sodium PIC) and a nimodipine-sensitive persistent calcium current (calcium PIC). In the present paper, we examined how these PICs contributed to motoneuron firing. Adult rats were spinalized at the S(2) sacral level, and after 2 months intracellular recordings were made from sacrocaudal motoneurons in vitro. The PICs and repetitive firing were measured with slow triangular voltage and current ramps, respectively. The sodium PIC was examined after blocking the calcium PIC with nimodipine (20 microM; n = 12). It was always activated subthreshold, and during current ramps in nimodipine, it produced a sodium plateau that assisted in initiating and maintaining firing (self-sustained firing). The sodium PIC oscillated off and on during firing and helped initiate each spike, and near threshold this caused abnormally slow firing (2.82 +/- 1.21 Hz). A low dose of TTX (0.5 microM) blocked the sodium PIC, sodium plateau, and very slow firing prior to affecting the spike itself. The calcium PIC was estimated as the current blocked by nimodipine or current remaining in TTX (2 microM; n = 13). In 59% of motoneurons, the calcium PIC was activated subthreshold to firing and produced a plateau that assisted in initiating and sustaining firing because nimodipine significantly increased the firing threshold current and decreased the self-sustained firing. In the remaining motoneurons (41%), the calcium PIC was activated suprathreshold to firing and during current ramps did not initially affect firing but eventually was activated and caused an acceleration in firing followed by self-sustained firing, which were blocked by nimodipine. The frequency-current (F-I) slope was 3.0 +/- 1.0 Hz/nA before the calcium PIC activation (primary range), 6.3 +/- 3.6 Hz/nA during the calcium PIC onset (secondary range; acceleration), and 2.1 +/- 1.3 Hz/nA with the calcium PIC steadily activated (tertiary range). Nimodipine eliminated the secondary and tertiary ranges, leaving a linear F-I slope of 3.7 +/- 1.0 Hz/nA. A single low-threshold shock to the dorsal root evoked a many-second-long discharge, the counterpart of a muscle spasm in the awake chronic spinal rat. This long-lasting reflex was caused by the motoneuron PICs because when the activation of the voltage-dependent PICs was prevented by hyperpolarization, the same dorsal root stimulation only produced a brief excitatory postsynaptic potential (<1 s). Both the calcium and sodium PIC were involved because nimodipine only partly reduced the reflex and there remained very slow firing mediated by the sodium PIC.

Action Potentials↗

Repetitive firing in layer V neurons from cat neocortex in vitro.

Input-output relations of large neurons from layer V of cat sensorimotor cortex were studied in an in vitro slice preparation using steps and ramps of intracellularly injected current. Depolarization attained during the interspike interval (ISI) was compared to the voltage levels required to activate a previously described (29) persistent sodium current (INaP). INaP was studied using a single-electrode voltage clamp in the same cells tested for firing behavior. Following an injected current step, firing rate declined smoothly to a steady level with a time course that was approximately exponential in most cells (tau, 9-43 ms). In most cells, the relation between firing rate and injected current (f-I relation) consisted of two linear segments, both for adapted, steady firing and for early intervals during adaptation. The slope of the steeper, initial (or sole) linear segment of the f-I curve averaged 26.2 Hz/nA during steady firing and was steeper when plotted for early interspike intervals. The variation of the depolarization at which spike initiation occurred (firing level) and the membrane potential between rhythmic spikes was examined during adaptation and steady firing. In most cells, firing level rose rapidly during a rhythmic train to a steady value. The steady firing level attained remained unchanged over a wide range of steady firing rates. Nevertheless, the mean depolarization during the interspike interval (V) increased approximately linearly with steady firing rate. Even at the slowest firing rates, V is sufficient to activate INaP. The use of injected current ramps demonstrated that neocortical cells were sensitive to rate of change of stimulus current (dI/dt) as well as its amplitude (I). The use of ramps followed by steady currents demonstrated that the repetitive response lagged behind changes in stimulus parameters and did not reach a steady state even during slow ramps; i.e., the response depended on time as well as on I and dI/dt. Instantaneous firing rate during the ramp increased linearly with time for a wide range of ramp slopes (dI/dt). The instantaneous firing rate of early interspike intervals was also linearly related to ramp slope for small ramp slopes. In spite of these linear relationships, quantitative analysis indicated that firing rate during ramp stimulation cannot, in general, be described by a simple linear combination of separate amplitude- and rate-dependent terms. The repetitive firing properties of the in vitro neurons are compared to those of in vivo neocortical neurons and other cell types.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

Population and clonal level responses of a perennial grass following fire in the northern Chihuahuan Desert.

Relationships involving fire and perennial grasses are controversial in Chihuahuan Desert grasslands of southern New Mexico, USA. Research suggests that fire delays the resprouting of perennial grasses well after two growing seasons. However, such results are confounded by livestock grazing, soil erosion, and drought. Additionally, post-fire grass responses may depend on initial clone size. We evaluated the effects of fire, grazing, and clone size on Bouteloua eriopoda (black grama) in southern New Mexico grasslands. Four 2-ha plots were established in each of four sites. Fire and grazing were applied or not applied in 1999 such that four treatment combinations were assigned randomly to plots within each site. Within each plot, small (0-10 cm(2) basal area), medium (10-30 cm(2)), and large ( > 30 cm(2)) clones were initially mapped in five 0.91-m(2) quadrats where grass attributes and litter cover were evaluated before and at the end of two growing seasons following fire. Maximum fire temperature was also measured. At a population level, canopy and litter cover were each approximately 50% less in burned than unburned areas. However, compared to initial levels, canopy height had increased by 10% at the end of the study, regardless of fire. At a clonal level, basal cover reductions were attributed mostly to large clones that survived fire. Smaller clone densities had decreased by as much as 19% in burned compared to unburned areas, and fire reduced the basal cover of medium clones. Basal and canopy cover, recruitment, and clone basal area decreased with increased fire temperatures. Almost all responses were independent of grazing, and interactive effects of grazing and fire were not detected. Fire did not kill all perennial grass clones, regardless of size. However, rapid responses were likely influenced by above-average precipitation after fire. Future studies in desert grasslands should examine how perennial grass dynamics are affected by fire, precipitation patterns, and interactions with grazing.

Analysis of Variance↗

Perceived risk of home fire and escape plans in rural households.

BACKGROUND: Homes in rural areas have a higher fire death rate. Although successful exit from a home fire could greatly reduce fire-related deaths and injuries, little is known about factors associated with behaviors of developing and practicing an escape plan. METHODS: Between July 2003 and June 2004, a baseline survey was administered, in person, to 691 rural households. Information collected included a history of previous home fire, perceived risk of home fire, existing smoke alarms and their working status, and home fire safety practices, as well as home and occupant characteristics. The association of residents' perceived risk of home fire and fire escape plans was assessed. RESULTS: Forty-two percent of rural households reported having a fire escape plan. Of the households with a plan, less than two thirds (56.9%) discussed or practiced the plan. Households with children were more likely to develop and practice a fire escape plan. Households with an elderly or disabled person were less likely to develop or practice the plan. Compared to respondents who perceived low or very low risk of home fire, those who perceived a high or very high risk had 3.5 times greater odds of having a fire escape plan and 5.5 times greater odds of discussion or practicing their plan. CONCLUSIONS: Increasing awareness of the potential risk of home fires may help occupants develop and practice home fire escape plans. In order to reduce fire deaths and injuries, different strategies need to be developed for those households in which the occupants lack the ability to escape.

Adolescent↗

Residential fire related deaths and injuries among children: fireplay, smoke alarms, and prevention.

BACKGROUND: The aim of the study was to describe the epidemiology of residential fire related deaths and injuries among children, and identify risk factors for these injuries through a linked dataset for the city of Dallas, Texas. METHODS: Data for all residential fires were linked with fire related injury data, using fire department records, ambulance transports, hospital admissions, and medical examiner records, for children 0-19 years of age. Causes of fires, including fireplay (children playing with fire or combustibles), arson and other causes, were determined by fire department investigation. RESULTS: From 1991-98, 76 children were injured in residential fires (39 deaths, 37 non-fatal). The highest rates occurred in the youngest children (<5 years) and in census tracts with lowest income. Fireplay accounted for 42% (32/76) of all injuries, 62% (15/24) of deaths in children 0-4 years, and 94% (13/14) of deaths from apartment and mobile home fires. Most of the fireplay related injuries (27/32, 84%) were from children playing with matches or lighters. Most started in a bedroom. Smoke alarms showed no protective efficacy in preventing deaths or injuries in fires started by fireplay or arson, but there was significant protective efficacy for a functional smoke alarm in fires started from all other causes (p<0.01). CONCLUSIONS: Residential fire related injuries among children in Dallas occurred predominantly in the youngest ages (<5 years) and in poor neighborhoods. Most of the deaths, especially those in apartments and mobile homes, resulted from fireplay. Smoke alarms appeared to offer no protection against death or injury in fireplay associated fires, possibly from the nature of the child's behavior in these fires, or from the placement of the smoke alarm. Prevention of childhood residential fire related deaths may require interventions to prevent fireplay in order to be successful.

Accident Prevention↗

Repetitive firing properties of developing rat brainstem motoneurones.

1. The repetitive firing properties of neonatal and adult rat hypoglossal motoneurones (HMs) were investigated in a brainstem slice preparation. Neonatal HMs could be classified into two main groups: (1) neurones with a decrementing or adapting firing pattern (type D); exhibiting an early and a late phase; and (2) neurones with an incrementing or accelerating firing pattern (type I). 2. The pattern of repetitive firing changed markedly during development. While most HMs recorded from young rats (< postnatal day (P) 4) were type D, the majority of HMs recorded during the second postnatal week were type I. In adults (> P21), nearly all HMs had a decrementing firing pattern, characterized by a brief period of adaptation and high steady-state firing rates. 3. The calcium-dependent after-hyperpolarization (AHP) was shortest in type I neonatal HMs, and decreased in amplitude during trains of action potentials (APs). In type D neurones, these same trains caused a slight enhancement of AHP amplitude. In adult HMs, with a decrementing firing pattern, trains of APs also caused summation of the AHP. 4. Type D neonatal HMs showed a progressive prolongation of the AP during repetitive firing. In contrast, type I neonatal HMs had almost no change in AP duration. In adult HMs the AP was short and experienced only a modest increase in duration during fast repetitive firing. 5. The function relating steady-state firing frequency to injected current (f-I curve) was linear. The mean steady-state f-I slope was significantly higher in neonates than in adults (approximately 30 vs. approximately 20 Hz nA-1), and was weakly correlated with input resistance. The f-I slope was negatively correlated with AHP duration in neonatal HMs only. In addition, for a given AHP duration the slope was higher in neonatal HMs. 6. Two threshold behaviours were observed among neonatal HMs: (a) a progressive rhythmic firing threshold, and (b) a sudden transition from subthreshold to regular repetitive firing. Current threshold for repetitive firing was strongly correlated with cell input conductance. Type I neonatal HMs had higher minimal steady firing rates (fmin) than type D HMs. In neonates, fmin was strongly correlated with AHP duration. Adult HMs showed a weaker correlation between these two parameters, and fmin was higher than predicted by AHP duration. 7. In summary, HMs responded to depolarizing current pulses with different firing patterns during postnatal development.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

Neuronal firing patterns from epileptogenic foci of monkey and human.

The chronic, recurrent seizures induced in the monkey by cortical scarring occur spontaneously for years and share much of the phenomenology of spontaneous seizures of focal cortical onset in the human. Chronic extracellular recording in the focus of the chronic epileptic monkey reveals: A spectrum of abnormalities of unit firing ranging from grossly abnormal firing patterns to normal activity. Group I (highly epileptic) neurons fire exclusively in bursts, which are invariant during different behavioral states and during operant conditioning. Although firing within the bursts is not easily modified, the interburst interval can be modified indicating that these apparently denervated cells still have some synaptic input. All group I cells are pyramidal neurons. Group II (weakly epileptic) neurons exhibit variable burst firing, which may be intermixed with normal unit firing. The firing patterns of these cells can be modified by synaptic inputs. During operant conditioning, burst firing can decrease; during drowsiness or when inattentive, burst firing can approach that characteristic of group I cells. There is a direct relationship between the number of group I epileptic (pacemaker) neurons in the focus and the epileptogenicity of that focus as measured by frequency of spontaneous seizures in that monkey. The distribution of neurons encountered in the focus varies. On average, approximately 10% are group I (pacemaker) neurons; group II constitute 40%; and 50% of cells encountered exhibit normal firing patterns. In addition to firing in unstructured bursts, an unusual burst structure termed the long-first-interval (LFI) burst has been described that appears to be unique to the chronic focus. It is so named because the first interspike interval is longer than the remaining interspike intervals in the burst. The long first interval is extraordinarily invariant. There is little relationship between unit firing in bursts and the interictal EEG. During early parts of a spontaneous seizure, the two events become time-locked. During seizures, unit firing is synchronous with surrounding neurons and the spike portion of the EEG (as in penicillin foci). Firing of group I neurons does not change significantly preceding a spontaneous seizure. Thus, group I neurons appear to act as pacemakers to the focus and group II cells provide the critical mass that, when synchronized to the burst firing of the pacemakers, is capable of initiating the ictal event.

Animals↗

Fire season and intensity affect shrub recruitment in temperate sclerophyllous woodlands.

The season in which a fire occurs may regulate plant seedling recruitment because of: (1) the interaction of season and intensity of fire and the temperature requirements for seed release, germination and growth; (2) post-fire rainfall and temperature patterns affecting germination; (3) the interaction of post-fire germination conditions and competition from surrounding vegetation; and (4) the interaction of post-fire germination conditions and seed predators and/or seedling herbivores. This study examined the effects of different fire intensities and fire seasons on the emergence and survival of shrubs representing a range of fire response syndromes from a summer rainfall cool climate region. Replicated experimental burns were conducted in two seasons (spring and autumn) in 2 consecutive years and fuel loads were increased to examine the effects of fire intensity (low intensity and moderate intensity). Post-fire watering treatments partitioned the effects of seasonal temperature from soil moisture. Higher intensity fires resulted in enhanced seedling emergence for hard-seeded species but rarely influenced survival. Spring fires enhanced seedling emergence across all functional groups. Reduced autumn recruitment was related to seasonal temperature inhibiting germination rather than a lack of soil moisture or competition. In Mediterranean-type climate regions, seedling emergence has been related to post-fire rainfall and exposure of seeds to seed predators. We think a similar model may operate in temperate summer rainfall regions where cold-induced dormancy over winter exposes seeds to predators for a longer time and subsequently results in recruitment failure. Our results support the theory that the effect of fire season is more predictable where there are strong seasonal patterns in climate. In this study seasonal temperature rather than rainfall appears to be more influential.

Climate↗

Dormancy and the fire-centric focus: germination of three Leucopogon species (Ericaceae) from South-eastern Australia.

BACKGROUND AND AIMS: Germination studies of species from fire-prone habitats are often focused on the role that fire plays in breaking dormancy. However, for some plant groups in these habitats, such as the genus Leucopogon (Ericaceae), dormancy of fresh seeds is not broken by fire cues. In the field, these same species display a flush of seedling emergence post-fire. Dormancy and germination mechanisms therefore appear complex and mostly unknown. This study aimed to identify these mechanisms by establishing dormancy class and testing the effects of a set of typical germination cues, including those directly related to fire and entirely independent of fire. METHODS: To classify dormancy, we assessed seed permeability and embryo morphology, and conducted germination experiments at seasonal temperatures in incubators. To test the effects of fire cues on germination, factorial combinations of smoke, heat and dark treatments were applied. Ageing treatments, using burial and seasonal incubation, were also tested. Germination phenology was established. KEY RESULTS: Seeds were dormant at release and had underdeveloped embryos. Primary dormancy of the study species was classified as morphophysiological. Seasonal temperature changes overcame primary dormancy and controlled timing of germination. Fire cues did not break primary dormancy, but there was a trend for smoke to enhance germination once this dormancy was overcome. CONCLUSIONS: Despite the fact that fire is a predominant disturbance and that many species display a flush of emergence post-fire, seasonal temperatures broke the primary physiological dormancy of the study species. It is important to distinguish between fire being responsible for breaking dormancy and solely having a role in enhancing levels of post-fire germination for seeds in which dormancy has been overcome by other factors. Biogeographical evidence suggests that morphological and physiological factors, and therefore seasonal temperatures, are likely to be important in controlling the dormancy and patterns of post-fire germination of many species in fire-prone regions.

Australia↗

Weak climatic control of stand-scale fire history during the late holocene.

Forest fire occurrence is affected by multiple controls that operate at local to regional scales. At the spatial scale of forest stands, regional climatic controls may be obscured by local controls (e.g., stochastic ignitions, topography, and fuel loads), but the long-term role of such local controls is poorly understood. We report here stand-scale (<100 ha) fire histories of the past 5000 years based on the analysis of sediment charcoal at two lakes 11 km apart in southeastern British Columbia. The two lakes are today located in similar subalpine forests, and they likely have experienced the same late-Holocene climatic changes because of their close proximity. We evaluated two independent properties of fire history: (1) fire-interval distribution, a measure of the overall incidence of fire, and (2) fire synchroneity, a measure of the co-occurrence of fire (here, assessed at centennial to millennial time scales due to the resolution of sediment records). Fire-interval distributions differed between the sites prior to, but not after, 2500 yr before present. When the entire 5000-yr period is considered, no statistical synchrony between fire-episode dates existed between the two sites at any temporal scale, but for the last 2500 yr marginal levels of synchrony occurred at centennial scales. Each individual fire record exhibited little coherency with regional climate changes. In contrast, variations in the composite record (average of both sites) matched variations in climate evidenced by late-Holocene glacial advances. This was probably due to the increased sample size and spatial extent represented by the composite record (up to 200 ha) plus increased regional climatic variability over the last several millennia, which may have partially overridden local, non-climatic controls. We conclude that (1) over past millennia, neighboring stands with similar modern conditions may have experienced different fire intervals and asynchronous patterns in fire episodes, likely because local controls outweighed the synchronizing effect of climate; (2) the influence of climate on fire occurrence is more strongly expressed when climatic variability is relatively great; and (3) multiple records from a region are essential if climate-fire relations are to be reliably described.

British Columbia↗

Correlated changes in the firing rate of human motor units during voluntary contraction.

Spike trains of long duration were recorded from concurrently active pairs of motor units in the human masseter and tibialis anterior muscles. An innovative analysis technique was used to investigate functional coupling between the motoneurons by plotting the discharge frequency of one motor unit with respect to the firing times of the other (peri-spike frequencygram). Conventional cross-correlograms of discharge times were also constructed for each pair to detect synchronous firing and to compare them with the peri-spike frequencygrams (PSFs). The PSFs were examined with the hypothesis that, if the net common input of the two motoneurons was excitatory, the firing frequency of both units should increase around the time of the synchronous discharge of both units (i.e., time zero in the cross-correlogram). Conversely, if the net common input was inhibitory, the firing frequency of both units should fall around time zero. In 24 out of 37 masseter pairs tested, either one (n = 20) or both (n = 4) units of the pair displayed a statistically significant increase (P < 0.001) in the firing frequency around time zero of the PSF. No significant decrease in the discharge frequency was ever detected in any of the units of the 37 pairs tested. The probability of occurrence of a significant increase in firing rate was found to be significantly higher X2 = 5, P < 0.05) in the pairs with significant synchronous firing (13 out of 15) than in the pairs without (11 out of 22). Moreover, the percentage increase in the discharge frequency was found to be significantly higher in the pairs with significant synchronous activity (1.4%) than in those without (0.74%). In 24 out of 56 tibialis anterior pairs tested, either one (n = 19) or both (n = 5) units of the pairs displayed significant changes (P < 0.001) in discharge frequency around time zero of the PSF. A reduction in the mean firing rate starting about 20 ms before time zero and ending around time zero was most commonly detected in the PSF, the probability of this occurrence being significantly higher (X2 = 6.7, P < 0.01) in the pairs with significant synchronous discharges (18 out of 41) than in the pairs without (1 out of 15). However, the mean percentage fall in the firing frequency during this "inhibitory" phase did not correlate in amplitude with the presence or the absence of significant synchronous activity (-1.4% and -1.1% respectively). In many of the cases, this "inhibitory" period was followed by an "excitatory" period where the firing frequency displayed a significant increase (from about 6 ms to 20 ms past time zero). Such dual changes in the firing rate were only found in the pairs with significant synchronous activity (13 of the 41 pairs). The mean percentage increase in the firing frequency during the "excitatory" phase was significantly higher in the pairs with synchronous firing than in the pair without (1.4% and 0.5% respectively). The specificity of the frequency changes was assessed by performing control analyses where the discharge from one unit was cross-correlated with the discharge from the other unit at a different time (time-shuffled pairs). Synchronisation peaks were never observed in the cross-correlograms of the time-shuffled pairs. Furthermore, none of the 18 time-shuffled pairs in the masseter showed significant frequency changes in the same time period as that seen with the non-shuffled pairs. In the tibialis, only 1 out of 31 time-shuffled pairs showed a significant frequency change in one motor unit, and that was in the opposite direction to the frequency changes found in the non-shuffled pairs. It is suggested that the PSF analysis is an important tool for investigating the functional relationship between individual motoneurons as they fire voluntarily.

Adult↗

Non-respiratory neurons in the Bötzinger complex exhibiting appropriate firing patterns to generate the emetic act in dogs.

This work was performed to prove the hypothesis that the pattern generator for the emetic act exists in the Bötzinger complex (BOT) and is driven by vagal afferents via the subpostrema portion of the nucleus of the solitary tract (mNST). Non-respiratory neurons (78) intermingling with BOT respiratory neurons in decerebrate dogs responded to pulse train stimulation of vagal afferents with a mean latency of 387 ms. During retching induced by vagal stimulation, one-half of the non-respiratory neurons exhibited high frequency burst firings synchronous with each retch (SH-firing, SH-neurons) and one-third of these neurons showed similar firings synchronous with the periods between retches (BH-firing, BH-neurons). Two-thirds of the SH-neurons and one-half of the BH-neurons fired with gradually augmenting frequencies (augmenting firing) during the period prior to retching, which may correspond to the period of prodromal signs of vomiting. Three SH-neurons were observed at fictive expulsion: all 3 exhibited burst firings concomitant with expulsion. During cooling block of transmission in the mNST, stimulation of the vagus nerve ipsilateral to the cooling failed to induce not only retching but also augmenting firing and SH-firing in all 11 BOT SH-neurons observed. In contrast, contralateral vagal stimulation induced retching and neuronal firings which had been observed before the cooling. These results support the hypothesis mentioned above. Respiratory firings were changed during retching in all BOT respiratory neurons observed. Respiratory firings were depressed during retching in the majority (15/25) of inspiratory (I) neurons and in a few expiratory (E) neurons (6/45). SH-firing was exhibited by 3 I- and 13 E-neurons. A few (2) I- and half (23) E-neurons showed BH-firing. These results indicate that all BOT respiratory neurons participate in central patterning of the emetic act.

Animals↗