High Fire Frequency Research Articles

Localization and function of the Kv3.1b subunit in the rat medulla oblongata: focus on the nucleus tractus solitarii.

The voltage-gated potassium channel subunit Kv3.1 confers fast firing characteristics to neurones. Kv3.1b subunit immunoreactivity (Kv3.1b-IR) was widespread throughout the medulla oblongata, with labelled neurones in the gracile, cuneate and spinal trigeminal nuclei. In the nucleus of the solitary tract (NTS), Kv3.1b-IR neurones were predominantly located close to the tractus solitarius (TS) and could be GABAergic or glutamatergic. Ultrastructurally, Kv3.1b-IR was detected in NTS terminals, some of which were vagal afferents. Whole-cell current-clamp recordings from neurones near the TS revealed electrophysiological characteristics consistent with the presence of Kv3.1b subunits: short duration action potentials (4.2 +/- 1.4 ms) and high firing frequencies (68.9 +/- 5.3 Hz), both sensitive to application of TEA (0.5 mm) and 4-aminopyridine (4-AP; 30 mum). Intracellular dialysis of an anti-Kv3.1b antibody mimicked and occluded the effects of TEA and 4-AP in NTS and dorsal column nuclei neurones, but not in dorsal vagal nucleus or cerebellar Purkinje cells (which express other Kv3 subunits, but not Kv3.1b). Voltage-clamp recordings from outside-out patches from NTS neurones revealed an outward K(+) current with the basic characteristics of that carried by Kv3 channels. In NTS neurones, electrical stimulation of the TS evoked EPSPs and IPSPs, and TEA and 4-AP increased the average amplitude and decreased the paired pulse ratio, consistent with a presynaptic site of action. Synaptic inputs evoked by stimulation of a region lacking Kv3.1b-IR neurones were not affected, correlating the presence of Kv3.1b in the TS with the pharmacological effects.

High-Threshold K+Current Increases Gain by Offsetting a Frequency-Dependent Increase in Low-Threshold K+Current

High-frequency firing neurons are found in numerous central systems, including the auditory brainstem, thalamus, hippocampus, and neocortex. The kinetics of high-threshold K+ currents (IK(HT)) from the Kv3 subfamily has led to the proposal that these channels offset cumulative Na+ current inactivation and stabilize tonic high-frequency firing. However, all high-frequency firing neurons, examined to date, also express low-threshold K+ currents (IK(LT)) that have slower kinetics and play an important role in setting the subthreshold and filtering properties of the neuron. IK(LT) has also been shown to dampen excitability and is therefore likely to oppose high-frequency firing. In this study, we examined the role of IK(HT) in pyramidal cells of the electrosensory lobe of weakly electric fish, which are characterized by high-frequency firing, a very wide frequency range, and high levels of IK(HT). In particular, we examined the mechanisms that allow IK(HT) to set the gain of the F-I relationship by interacting with another low-threshold K+ current. We found that IK(HT) increases the gain of the F-I relationship and influences spike waveform almost exclusively in the high-frequency firing range. The frequency dependence arises from IK(HT) influencing both the IK(LT) and Na+ currents. IK(HT) thus plays a significant role in stabilizing high-frequency firing by preventing a steady-state accumulation of IK(LT) that is as important as preventing Na+ current inactivation.

Late Quaternary grassland (Campos), gallery forest, fire and climate dynamics, studied by pollen, charcoal and multivariate analysis of the São Francisco de Assis core in western Rio Grande do Sul (southern Brazil)

We present a detailed pollen and charcoal record of a 368-cm-long sediment core from the lowland Campos (grassland) region near the city of São Francisco de Assis in the western Rio Grande do Sul State in southern Brazil. Based on four AMS radiocarbon dates, the record represents the last about 22,000 cal yr BP. The region was naturally covered by Campos throughout the recorded glacial and Holocene period under cold and relatively dry and warm and dry condition, respectively. Initial expansion of gallery forest after 5170 cal yr BP indicates a change to wetter climatic conditions. Maximum extent of gallery forest after 1550 cal yr BP reflects the wettest recorded period. There is some evidence of plant migration from the eastern Atlantic coastal lowland reaching the western lowland, first after mid Holocene times by Cecropia and, possibly, species of Myrsine and Moraceae and later, after about 1000 cal yr BP, by species of Alchornea and Acalypha. Multivariate analysis revealed that the long-term pollen composition dynamics is a two-phase process, with random, chaotic changes characterizing some periods when climate conditions were likely more stable, and directional compositional changes (phase transitions) in periods coincide with major climate and/or anthropogenic changes. Natural fires were rare during full- and lateglacial periods, but became frequent at the beginning of the Holocene, suggesting the beginning of human occupation of the western lowland at that time. Highest fire frequency is found during the wet late Holocene period, suggesting an increase of indigenous populations in the São Francisco de Assis region.

Distribution, habitat and conservation status of the eastern pygmy-possum Cercartetus nanus in Victoria.

We review the distribution, habitat and conservation status of the eastern pygmy-possum (Cercartetus nanus) in Victoria. Data on the habitat occurrences and rates of detection were gleaned from 133 published and unpublished fauna surveys conducted from 1968 to 2003 in Gippsland; northern Victoria; the Melbourne area and south-western region. C. nanus was reported from a broad range of vegetation communities, which predominantly included a dense mid-storey of shrubs rich in nectar-producing species such as those from the families Proteaceae and Myrtaceae. Survey effort using a range of methods was immense across surveys: 305,676 Elliott/cage trap-nights, 49,582 pitfall trap-nights, 18,331 predator remains analysed, 4424 spotlight hours, and 7346 hair-sampling devices deployed, 1005 trees stagwatched, and 5878 checks of installed nest-boxes. The surveys produced 434 records of C. nanus, with Elliott/cage trapping, pitfall trapping and analysis of predator remains responsible for the vast majority of records (93%). These data and those from the Atlas of Victorian Wildlife indicate that although C. nanus has a widespread distribution in Victoria, it is rarely observed or trapped in fauna surveys. Only 11 (8%) of the surveys we reviewed detected >10 individuals. C. nanus is likely to be sensitive to several recognised threatening processes in Victoria (e.g., feral predators, high frequency fire, feral honeybees). There is also evidence of range declines in several regions, which suggests that the species is vulnerable to extinction. Therefore, we recommend that it be nominated as a threatened species in Victoria.

New Developments in Epson's Inkjet Head Technology

Today, color inkjet printers are being used extensively in both offices and homes. Inkjet printers have many advantages including print quality, low cost, and a small footprint. Epson has continued to develop improved printheads. This paper describes new technology that doubles the nozzle count and firing frequency, while halving ink droplet size with respect to previously developed heads.In general, the types of piezo elements for printheads may be classified according to their oscillation mode: longitudinal or flexural. Heads of the latter type are used in low-cost printers. Although heads of the former type have been configured with multi-layer piezo elements, only heads of the latter type with a single layer have appeared in commercial products.Our new head incorporates a double layer of piezo elements that use the flexural oscillation mode. We reduced the size and optimized the geometry of the pressure chamber in order to obtain a high natural firing frequency. Furthermore, by completely covering the signal supplying electrodes with the piezo elements, the activating reliability and durability were enhanced.We have launched products such as the Stylus Photo RX500 and CX4600, Stylus C66, and PictureMate with this new improved head. Further development and optimization are ongoing.

GABA A receptor facilitation of neurokinin release from primary afferent terminals in the rat spinal cord

Our goal was to test the following hypotheses: 1) GABA A receptors facilitate neurokinin release from primary afferent terminals; 2) they do this by suppressing an inhibitory effect of GABA B receptors; 3) the activation of these two receptors is controlled by the firing frequency of primary afferents. We evoked neurokinin release by stimulating the dorsal root attached to spinal cord slices, and measured it using neurokinin 1 receptor (NK1R) internalization. Internalization evoked by root stimulation at 1 Hz (but not at 100 Hz) was increased by the GABA A receptor agonists muscimol (effective concentration of drug for 50% of the increase [EC 50] 3 μM) and isoguvacine (EC 50 4.5 μM). Internalization evoked by root stimulation at 100 Hz was inhibited by the GABA A receptor antagonists bicuculline (effective concentration of drug for 50% of the inhibition [IC 50] 2 μM) and picrotoxin (IC 50 243 nM). Internalization evoked by incubating the root with capsaicin (to selectively recruit nociceptive fibers) was increased by isoguvacine and abolished by picrotoxin. Therefore, GABA A receptors facilitate neurokinin release. Isoguvacine-facilitated neurokinin release was inhibited by picrotoxin, low Cl −, low Ca 2+, Ca 2+ channel blockers and N-methyl- d-aspartate receptor antagonists. Bumetanide, an inhibitor of the Na +-K +-2Cl − cotransporter, inhibited isoguvacine-facilitated neurokinin release, but this could be attributed to a direct inhibition of GABA A receptors. The GABA B agonist baclofen inhibited NK1R internalization evoked by 100 Hz root stimulation (IC 50 1.5 μM), whereas the GABA B receptor antagonist (2 S)-3-[[(1 S)-1-(3,4-dichlorophenyl)ethyl]amino-2-hydroxypropyl](phenylmethyl) phosphinic acid (CGP-55845) increased NK1R internalization evoked by 1 Hz root stimulation (EC 50 21 nM). Importantly, baclofen inhibited isoguvacine-facilitated neurokinin release, and CGP-55845 reversed the inhibition of neurokinin release by bicuculline. In conclusion, 1) GABA B receptors located presynaptically in primary afferent terminals inhibit neurokinin release; 2) GABA A receptors located in GABAergic interneurons facilitate neurokinin release by suppressing GABA release onto these GABA B receptors; 3) high frequency firing of C-fibers stimulates neurokinin release by activating GABA A receptors and inhibiting GABA B receptors, whereas low frequency firing inhibits neurokinin release by the converse mechanisms.

Fire and torrential rainfall: effects on the perennial grass Brachypodium retusum

Summer wildfires and autumn torrential rainfall are the background to the development of one of the most important environmental problems in the western Mediterranean area: erosion, degradation of soil structure and desertification. These processes especially affect plant communities located in old abandoned fields where woody sprouters are practically absent. Under these conditions, post-fire vegetation cover is dependent on obligate seeders and, in the short term, especially on resprouting perennial grasses. Brachypodium retusum is a rhizomatous perennial grass that plays a particularly important role in the resilience of these fire-prone Mediterranean ecosystems. In Mediterranean gorse shrublands, during the first few years after a fire, this species represents 90% of plant cover and biomass. The recurrence or severity of fire does not seem to affect the regeneration capacity of this species. After two years, even under high fire frequency (12 years) and high fire severity (> 400 °C), it recovers both cover and biomass. Nevertheless, this species, a key factor in the control of soil erosion, is extremely affected by erosion processes. A single extreme rainfall event reduces the rate of regeneration of B. retusum by about 50%. The reduction in the protective cover of this species may result in degradation and eventual self-induced degrading process in the ecosystem.

Pocono mesic till barrens in retreat: topography, fire and forest contagion effects

The Pocono mesic till barrens (PMTB) are a unique assemblage of fire-maintained shrub communities that support numerous rare species. Historically these barrens covered a large area in the vicinity of Long Pond, Pennsylvania, USA. However, due largely to regional fire suppression instituted in the early 1960s, over 70% of the area covered by barrens succeeded to fire-intolerant forest that does not support the rare species. We investigated the influence of forest proximity on barrens succession across three geomorphic types during periods of high fire frequency and fire suppression, testing the hypothesis that forest processes such as seed rain, shading, and detrital enrichment of soils enhances barrens succession through a contagion effect. Evidence of a forest contagion effect should be shown by increased rates of barrens succession with increasing proximity to the nearest forest edge. In order to detect a forest contagion effect, barrens persistence and barrens succession were modeled in proximity zones of 0-50 m, 50-100 m, 100-200 m, and greater than 200 m from the nearest forest edge. We used existing GIS data layers for fire, geomorphology, and vegetation distribution in 1938, 1963, and 1992. The layers were modified and overlain using ArcView software to determine persistence and succession rates for each unique combination of layers in each proximity zone from 1938 to 1963 (pre-fire suppression) and 1963 to 1992 (post-fire suppression). ANCOVA results indicate that proximity to the nearest forest edge significantly affected barrens persistence rates in both time periods, but succession rates were significantly affected in 1938 to 1963 only. Twenty-eight percent of the 1938 barrens succeeded to forest by 1963; 56% of the 1963 barrens became forest by 1992. Results support previous findings that barrens persistence is enhanced by increased fire frequency, and that barrens persist longer where they overlie flat glacial till than on other geomorphology types.

Firing patterns of low-threshold trapezius motor units in feedback-controlled contractions and vocational motor activities.

The study aimed to examine firing patterns of low-threshold trapezius motor units, with attention given to motor unit recruitment threshold. Different motor tasks were explored: shoulder elevation, arm movement in typing, and the motor response to mental stress. Contraction amplitudes in the range from 1 to 10% of the surface electromyographic (SEMG) signal at maximal voluntary contraction (1-10% EMGmax) were studied, representing the range of trapezius muscle activity commonly observed in daily living. Single motor unit activity was recorded by a quadrifilar fine-wire electrode. A surface electrode simultaneously recorded the SEMG signal. Low-threshold motor units showed a small increase in mean firing rate, from 10.5 to 12.5 pulses per second ( p<0.01), in constant-amplitude contractions when SEMG amplitude increased from <2% to >4% EMGmax. After the first few minutes, firing rates were similar for all motor units in a contraction, despite different recruitment thresholds. Firing rates of motor units with threshold <2% EMGmax were the same in constant-amplitude contractions, contractions with vocational arm movement, and contractions with imposed stress for SEMG amplitude at the same level. High-frequency firing patterns were observed in dynamic contractions, limited to bursts of up to a second duration. We conclude that low-threshold trapezius motor units have similar, stable firing rates in sustained contractions, independent of task and recruitment threshold, but with a small increase for increasing contraction amplitude.

Control of the temporal fidelity of synaptic transmission by a presynaptic high voltage-activated transient K current.

The type of K(+) channels controlling the waveform of the presynaptic spike and synaptic transmission were examined in the lamprey spinal cord. Reticulospinal neuron somata displayed a transient K(+) current with a high voltage-activation and inactivation. This current was selectively blocked by catechol at 100 microM. Reticulospinal axons also displayed a high voltage-activated fast K(+) current sensitive to catechol. The function of this presynaptic high voltage-activated fast K(+) current in controlling synaptic transmission was investigated by using paired intracellular recordings from reticulospinal axons and their targets. Blockade of this current by catechol (100 microM) prolonged the presynaptic spike elicited by a single stimulus leading to a potentiation of the postsynaptic EPSP. Calcium imaging of reticulospinal axons showed an increase in presynaptic calcium transients after blockade of the presynaptic K(+) current by catechol. During high frequency firing, catechol revealed an activity-dependent decrease in the spike duration, which resulted in a depression of synaptic transmission. These results suggest that the presynaptic high voltage-activated transient K(+) current acts to optimize the temporal fidelity of synaptic transmission by minimizing activity-dependent changes in the presynaptic spike waveform and calcium dynamics.

14C-AMS as a tool for the investigation of mercury deposition at a remote Amazon location

We present results of the atmospheric mercury deposition rate in the Amazon region during the last 43000 years. Lake sediment samples were collected from the Lagoa da Pata, a small and remote lake in northern Brazilian Amazon. The samples were divided in sub-samples, for C, Hg, N and 14C-AMS analyses. Three main paleoclimatic events could be identified. The mercury accumulation rates were found to be larger during the periods of the Holocene and Pleistocene associated with high temperatures and frequency of forest fires.

14C-AMS as a tool for the investigation of mercury deposition at a remote Amazon location

We present results of the atmospheric mercury deposition rate in the Amazon region during the last 43 000 years. Lake sediment samples were collected from the Lagoa da Pata, a small and remote lake in northern Brazilian Amazon. The samples were divided in sub-samples, for C, Hg, N and 14 C-AMS analyses. Three main paleoclimatic events could be identified. The mercury accumulation rates were found to be larger during the periods of the Holocene and Pleistocene associated with high temperatures and frequency of forest fires.

Regulation of orexin neurons by the monoaminergic and cholinergic systems

Orexins are a pair of neuropeptides implicated in energy homeostasis and arousal. Here we characterize the electrophysiological properties of orexin neurons using slice preparations from transgenic mice in which orexin neurons specifically express green fluorescent protein. Orexin neurons showed high frequency firing with little adaptation by injecting a positive current. The hyperpolarization-activated current was observed in orexin neurons by a negative current injection. The neurotransmitters, which were implicated in sleep/wake regulation, affected the activity of orexin neurons; noradrenaline and serotonin hyperpolarized, while carbachol depolarized orexin neurons in either the presence or absence of tetrodotoxin. It has been reported that orexins directly or indirectly activate the nuclei that are the origin of the neurons containing these neurotransmitters. Our data suggest that orexin neurons have reciprocal neural circuitries between these nuclei for either a positive or negative feedback loop and orchestrate the activity of these neurons to regulate the vigilance states.

Development of Brachystegia‐Julbernardia woodland after clear‐felling in central Zambia: Evidence for high resilience

AbstractQuestion: Does the development of Brachystegia‐Julbernardia (miombo) woodland after felling, and under a variable fire regime, occur via a serai stage of fire‐tolerant species?Location: Four sites in central Zambia, Africa.Methods: Trees in replicate plots were clear‐cut and stumps and resprouts enumerated. Species recruited into the tree layer (&gt; 2.0 m tall) were monitored for 11 years (1991–2001) and fire occurrence and herbaceous biomass assessed annually to determine fuel loads.Results: Fire frequency was variable at the study sites and fuel loads were generally too low to suppress woodland regeneration after felling. However, at one site a change from low to high fire frequency arrested woodland development and triggered a regression towards a ‘fire‐trap’ vegetation type in which a few fire‐tolerant species survived. There was no evidence to support the hypothesis that miombo woodland regeneration is facilitated by a sere of fire‐tolerant species. All regrowth after felling was from resprouting plants present before felling. Trees with a previous history of felling sprouted more vigorously than trees that had not been felled before. Species richness in the tree layer increased with time since felling because resprout species had different height growth rates.Conclusion: The resilience of miombo trees after clear‐felling is largely due to their capacity to regenerate vegetatively from resprouts and stumps after release from frequent fires. Coppicing is therefore recommended as a suitable management technique for miombo woodland in central southern Africa.

Chaotic firing in the sinusoidally forced leaky integrate-and-fire model with threshold fatigue

The leaky integrate-and-fire (LIF) model is one of the elementary neuronal models that has been widely used to gain understanding of the behavior of many excitable systems. The sinusoidally forced standard leaky integrate-and-fire model reproduces the quasiperiodic and phase locked discharge trains observed experimentally in neurons. However, this basic model fails to generate chaotic firing, whereas this form of behavior has been observed experimentally. We modify the standard LIF through the introduction of threshold fatigue responsible for progressive decrease of excitability during high frequency firing, as observed experimentally. We show that the dynamics of this neuron model under sinusoidal forcing are governed by the iterates of an annulus map and derive expressions for its two characteristic Lyapunov exponents. Using these exponents, it is shown that chaotic dynamics are possible for this model, unlike the standard leaky integrate-and-fire model. Chaotic dynamics occur when memory effects are strong and only under certain forms of threshold fatigue.

MinK, MiRP1, and MiRP2 Diversify Kv3.1 and Kv3.2 Potassium Channel Gating

High frequency firing in mammalian neurons requires ultra-rapid delayed rectifier potassium currents generated by homomeric or heteromeric assemblies of Kv3.1 and Kv3.2 potassium channel alpha subunits. Kv3.1 alpha subunits can also form slower activating channels by coassembling with MinK-related peptide 2 (MiRP2), a single transmembrane domain potassium channel ancillary subunit. Here, using channel subunits cloned from rat and expressed in Chinese hamster ovary cells, we show that modulation by MinK, MiRP1, and MiRP2 is a general mechanism for slowing of Kv3.1 and Kv3.2 channel activation and deactivation and acceleration of inactivation, creating a functionally diverse range of channel complexes. MiRP1 also negatively shifts the voltage dependence of Kv3.1 and Kv3.2 channel activation. Furthermore, MinK, MiRP1, and MiRP2 each form channels with Kv3.1-Kv3.2 heteromers that are kinetically distinct from one another and from MiRP/homomeric Kv3 channels. The findings illustrate a mechanism for dynamic expansion of the functional repertoire of Kv3.1 and Kv3.2 potassium currents and suggest roles for these alpha subunits outside the scope of sustained rapid neuronal firing.

Ionotropic NMDA receptor evokes an excitatory response in superior salivatory nucleus neurons in anaesthetized rats

Extracellular recordings were taken from preganglionic superior salivatory nucleus (SSN) neurons projecting to submandibular and intra-lingual ganglia, in order to study the action of SSN neurons resulting from ionophoretic application of ionotropic NMDA receptor agonist in urethane-chloralose anaesthetized rats. Single SSN neurons were identified by their antidromic spike responses following stimulation of the chorda–lingual nerve (CLN), chorda tympani branches (CTBs) and the lingual nerve (LN). About one-third (33%, 10/30) of the identified SSN neurons were induced to fire by ionophoretic application of the NMDA receptor agonists used, dl-homocysteic acid (DLH) and N-methyl- d-aspartic acid (NMDA). More than half exhibited firing at high frequencies, often exceeding 40 Hz. About one-fifth (20%; 6/30) of the identified SSN neurons exhibited orthodromic spike responses to the combination of NMDA receptor agonist application and sensory nerve (CLN or LN) stimulus. These excitatory responses evoked by application of NMDA receptor agonist were attenuated ( n=4) by ionophoretic application of dl-2-amino-5-phosphonovaleric acid (AP5; NMDA receptor antagonist). About half (47%) of the neurons did not respond to any combination of NMDA receptor agonist and sensory nerve stimuli. No differences were observed between SSN neurons with B fibre axons and those with C fibre axons in response to ionophoresis of the NMDA receptor agonists. The NMDA-sensitive neurons, which exhibited high frequency firing, were predominantly found in the rostral part of the SSN. In summary, activation of ionotropic NMDA receptors exerts an excitatory effect on about half of the SSN neurons. These data support the view that NMDA receptors are involved in information processing and transmission on SSN neurons.

Energy transfer from astrocytes to axons: the role of CNS glycogen

We tested the hypothesis that astrocytic glycogen supports axon function under both pathological and physiological conditions. Functional activity of the rat (RON) or mouse optic nerve (MON), representative central white matter tracts, was assessed electrophysiologically as the area under the supramaximal compound action potential (CAP). During aglycaemia the CAP area of rodent optic nerve persisted for up to 30 min, after which the CAP rapidly failed. Glycogen content measured biochemically during the aglycaemic insult fell with a time course compatible with its rapid degradation in the absence of glucose. Pharmacological up-regulation of glycogen content prior to the aglycaemic insult with incubation in hyperglycaemic ambient glucose delayed CAP failure, whereas down-regulation of glycogen content induced by nor-adrenaline accelerated CAP failure. Inhibiting lactate transfer between astrocytes and axons during aglycaemia, where glycogen is the only utilisable energy reserve, resulted in accelerated CAP failure, implying that glycogen-derived lactate supports function when exogenous energy metabolites are withdrawn. Under normoglycaemic conditions glycogen content decreased during high frequency axon discharge, although CAP function was fully maintained. Both prior depletion of glycogen content, or blocking axonal lactate uptake rendered nerves incapable of fully supporting CAP function during high frequency firing in the presence of normoglycaemic glucose. These results indicated that during aglycaemia and increased metabolic demand, astrocytic glycogen was degraded to form lactate, which was used as a supplemental energy source when ambient normoglycaemic glucose was incapable of meeting immediate tissue energy demands.

Towards an understanding of population change for the long-lived resprouting tree Angophora inopina (Myrtaceae)

In fire-prone habitats some long-lived tree species appear resilient to fire. However, fire frequency may affect recruitment patterns. This study investigates the reproductive features of the long-lived tree species Angophora inopina Hill in recognised priority conservation areas with a high fire frequency. Plants exhibit high survival rates when burnt and respond to fire events with high rates of growth, flowering and seed set. Aged capsules on plants contain few seeds but released seeds germinate readily, suggesting high viability, low dormancy and limited seed storage in aerial or soil seed banks. Population modelling indicates that the species will be resilient to low recruitment levels in the short term. However, over the long term, population structure is significant in determining the ability of the population to respond to recruitment cues. Thus, understanding and monitoring population structural change is a priority for this species.

Effects of fire history on the structure and floristic composition of woody vegetation around Kalumburu, North Kimberley, Australia: a landscape-scale natural experiment

Indigenous landscape burning is practiced around remote communities in the Kimberleys but has been replaced by wildfires across uninhabited areas. A landscape-scale natural experiment was established to investigate the effects of these different fire histories (derived from a 10-year Landsat remote-sensing sequence) on the floristic structure and composition of woody vegetation within and among three of the major vegetation types on three landscape types (sandplain, sandstone and volcanics) near Kalumburu in the North Kimberley bioregion.Substrate factors determine vegetation and associated fire patterns within the landscape such that each landscape type needs to be examined independently. Basalt soils are dominated by an open savanna and tend to have very high fire frequencies. Basalt vegetation showed few significant response variables to fire-history parameters. The total density of woody stems showed no significant relationship to fire-history variables, regardless of size class. The 0–2.0-m size class of Erythrophleum chlorostachys (F.Muell.) Baillon showed significant (P &lt; 0.005) responses to the various interactions involving all three fire-history variables, indicating that seedling density is sensitive to fire.Sandplain is dominated by open woodland, with relatively low fire frequency. Total stem density, shrub density and the densities of Grevillea agrifolia Cunn. Ex R.Br., Canthium sp. A and Stenocarpus cunninghamii R.Br. showed strong positive (P &lt; 0.005) relationships with the total number of fire-free months. In sandstone, the density of all woody stems, acacias and a range of mid-storey trees showed significant positive relationships with the total number of fire-free months. Other species showed strong relationships with the number of late dry season fires. Vegetation thickening was evident in sand environments through the accumulation of woody stems in fire-free years and in sandstone through the promotion of 'fireweeds' such as Acacia gonocarpa F.Muell. after fire events.Mid-storey tree species capable of resprouting after fire showed some evidence of structural suppression in response to frequent fire events, including Planchonia careya (F.Muell.) Knuth, Persoonia falcata R.Br. and Buchanania obovata Engl.Results are discussed in the context of indigenous landscape burning and biodiversity conservation.