High Fire Frequency Research Articles

Emergent gamma synchrony in all-to-all interneuronal networks.

We investigate the emergence of in-phase synchronization in a heterogeneous network of coupled inhibitory interneurons in the presence of spike timing dependent plasticity (STDP). Using a simple network of two mutually coupled interneurons (2-MCI), we first study the effects of STDP on in-phase synchronization. We demonstrate that, with STDP, the 2-MCI network can evolve to either a state of stable 1:1 in-phase synchronization or exhibit multiple regimes of higher order synchronization states. We show that the emergence of synchronization induces a structural asymmetry in the 2-MCI network such that the synapses onto the high frequency firing neurons are potentiated, while those onto the low frequency firing neurons are de-potentiated, resulting in the directed flow of information from low frequency firing neurons to high frequency firing neurons. Finally, we demonstrate that the principal findings from our analysis of the 2-MCI network contribute to the emergence of robust synchronization in the Wang-Buzsaki network (Wang and Buzsáki, 1996) of all-to-all coupled inhibitory interneurons (100-MCI) for a significantly larger range of heterogeneity in the intrinsic firing rate of the neurons in the network. We conclude that STDP of inhibitory synapses provide a viable mechanism for robust neural synchronization.

Transient BK outward current enhances motoneurone firing rates during Drosophila larval locomotion.

We combine in situ electrophysiology with genetic manipulation in Drosophila larvae aiming to investigate the role of fast calcium-activated potassium currents for motoneurone firing patterns during locomotion. We first demonstrate that slowpoke channels underlie fast calcium-activated potassium currents in these motoneurones. By conducting recordings in semi-intact animals that produce crawling-like movements, we show that slowpoke channels are required specifically in motoneurones for maximum firing rates during locomotion. Such enhancement of maximum firing rates occurs because slowpoke channels prevent depolarization block by limiting the amplitude of motoneurone depolarization in response to synaptic drive. In addition, slowpoke channels mediate a fast afterhyperpolarization that ensures the efficient recovery of sodium channels from inactivation during high frequency firing. The results of the present study provide new insights into the mechanisms by which outward conductances facilitate neuronal excitability and also provide direct confirmation of the functional relevance of precisely regulated slowpoke channel properties in motor control. A large number of voltage-gated ion channels, their interactions with accessory subunits, and their post-transcriptional modifications generate an immense functional diversity of neurones. Therefore, a key challenge is to understand the genetic basis and precise function of specific ionic conductances for neuronal firing properties in the context of behaviour. The present study identifies slowpoke (slo) as exclusively mediating fast activating, fast inactivating BK current (ICF ) in larval Drosophila crawling motoneurones. Combining in vivo patch clamp recordings during larval crawling with pharmacology and targeted genetic manipulations reveals that ICF acts specifically in motoneurones to sculpt their firing patterns in response to a given input from the central pattern generating (CPG) networks. First, ICF curtails motoneurone postsynaptic depolarizations during rhythmical CPG drive. Second, ICF is activated during the rising phase of the action potential and mediates a fast afterhyperpolarization. Consequently, ICF is required for maximal intraburst firing rates during locomotion, probably by allowing recovery from inactivation of fast sodium channels and decreased potassium channel activation. This contrasts the common view that outward conductances oppose excitability but is in accordance with reports on transient BK and Kv3 channel function in multiple types of vertebrate neurones. Therefore, our finding that ICF enhances firing rates specifically during bursting patterns relevant to behaviour is probably of relevance to all brains.

Geophysical features influence the climate change sensitivity of northern Wisconsin pine and oak forests.

Landscape-scale vulnerability assessment from multiple sources, including paleoecological site histories, can inform climate change adaptation. We used an array of lake sediment pollen and charcoal records to determine how soils and landscape factors influenced the variability of forest composition change over the past 2000 years. The forests in this study are located in northwestern Wisconsin on a sandy glacial outwash plain. Soils and local climate vary across the study area. We used the Natural Resource Conservation Service's Soil Survey Geographic soil database and published fire histories to characterize differences in soils and fire history around each lake site. Individual site histories differed in two metrics of past vegetation dynamics: the extent to which white pine (Pinus strobus) increased during the Little Ice Age (LIA) climate period and the volatility in the rate of change between samples at 50-120 yr intervals. Greater increases of white pine during the LIA occurred on sites with less sandy soils (R² = 0.45, P < 0.0163) and on sites with relatively warmer and drier local climate (R² = 0.55, P < 0.0056). Volatility in the rate of change between samples was positively associated with LIA fire frequency (R² = 0.41, P < 0.0256). Over multi-decadal to centennial timescales, forest compositional change and rate-of-change volatility were associated with higher fire frequency. Over longer (multi-centennial) time frames, forest composition change, especially increased white pine, shifted most in sites with more soil moisture. Our results show that responsiveness of forest composition to climate change was influenced by soils, local climate, and fire. The anticipated climatic changes in the next century will not produce the same community dynamics on the same soil types as in the past, but understanding past dynamics and relationships can help us assess how novel factors and combinations of factors in the future may influence various site types. Our results support climate change adaptation efforts to monitor and conserve the landscape's full range of geophysical features.

Recovery of Mediterranean Vegetation after Recurrent Forest Fires: Insight from the 2010 Forest Fire on Mount Carmel, Israel

AbstractThe December 2010 forest fire on Mount Carmel – the largest recorded in Israel – burned about 2500 ha of Mediterranean forest. We documented the immediate and short‐term changes of the vegetation following this fire. Relative vegetation cover and plant species richness were sampled in five sites in spring 2009 and 2010, prior to the fire, and were re‐sampled in 2011 and 2012. The number of recurrent fires (between 0 and 3) and time intervals between fires were documented for each site. We observed a strong decrease in total vegetation cover, associated with reduction of relative cover of woody vegetation. In the second year after the fire, shrubs and dwarf shrubs became dominant at all sites. Time intervals between fires played an important role in determining the extent of regeneration of the vegetation cover and plant species richness. Plant species richness immediately decreased after the fire in sites with a short fire interval, while in sites with a long fire interval, plant species richness increased. Relative plant cover was associated with the time from the last previous fire, and this association differed among different plant groups. These results suggest that vegetation and plant community regeneration after recurrent fires is accelerated when time intervals between fires are longer, whereas high fire frequency may suppress vegetation regeneration. Based on the results, we propose that forest regeneration after recurrent fires depends largely on time from the previous fire, rather than on the number of previous fires. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Navβ4 regulates fast resurgent sodium currents and excitability in sensory neurons.

BackgroundIncreased electrical activity in peripheral sensory neurons including dorsal root ganglia (DRG) and trigeminal ganglia neurons is an important mechanism underlying pain. Voltage gated sodium channels (VGSC) contribute to the excitability of sensory neurons and are essential for the upstroke of action potentials. A unique type of VGSC current, resurgent current (INaR), generates an inward current at repolarizing voltages through an alternate mechanism of inactivation referred to as open-channel block. INaRs are proposed to enable high frequency firing and increased INaRs in sensory neurons are associated with pain pathologies. While Nav1.6 has been identified as the main carrier of fast INaR, our understanding of the mechanisms that contribute to INaR generation is limited. Specifically, the open-channel blocker in sensory neurons has not been identified. Previous studies suggest Navβ4 subunit mediates INaR in central nervous system neurons. The goal of this study was to determine whether Navβ4 regulates INaR in DRG sensory neurons.ResultsOur immunocytochemistry studies show that Navβ4 expression is highly correlated with Nav1.6 expression predominantly in medium-large diameter rat DRG neurons. Navβ4 knockdown decreased endogenous fast INaR in medium-large diameter neurons as measured with whole-cell voltage clamp. Using a reduced expression system in DRG neurons, we isolated recombinant human Nav1.6 sodium currents in rat DRG neurons and found that overexpression of Navβ4 enhanced Nav1.6 INaR generation. By contrast neither overexpression of Navβ2 nor overexpression of a Navβ4-mutant, predicted to be an inactive form of Navβ4, enhanced Nav1.6 INaR generation. DRG neurons transfected with wild-type Navβ4 exhibited increased excitability with increases in both spontaneous activity and evoked activity. Thus, Navβ4 overexpression enhanced INaR and excitability, whereas knockdown or expression of mutant Navβ4 decreased INaR generation.ConclusionINaRs are associated with inherited and acquired pain disorders. However, our ability to selectively target and study this current has been hindered due to limited understanding of how it is generated in sensory neurons. This study identified Navβ4 as an important regulator of INaR and excitability in sensory neurons. As such, Navβ4 is a potential target for the manipulation of pain sensations.Electronic supplementary materialThe online version of this article (doi:10.1186/s12990-015-0063-9) contains supplementary material, which is available to authorized users.

Impacts of Wildfire Recency and Frequency on an Appalachian Oak Forest

Cabwaylingo State Forest in southern West Virginia has experienced numerous anthropogenic wildfires over the past 36 years. In this case study, we assessed the relationship between fire frequency and recency and stand composition and structure, with emphasis on oak and its competitors. Frequent and recent fire was significantly correlated with reduced red maple overstory stem density and basal area. Overstory oak density did not significantly vary with either fire frequency or recency. Total overstory basal area was greatest in areas of either no fire or nonrecent fire. Oak sapling density was significantly greater with high frequency and recent fire. Red maple sapling densities were greatest when fires were infrequent and recent, and red maple seedlings were greatest in no fire and low-frequency nonrecent fire areas. Our results suggest that recurring fire can enhance the development of large oak advanced reproduction. However, frequent fires without a sufficient fire-free interval could prevent the recruitment of oaks into the overstory.

Human Nav1.6 Channels Generate Larger Resurgent Currents than Human Nav1.1 Channels, but the Navβ4 Peptide Does Not Protect Either Isoform from Use-Dependent Reduction.

Voltage-gated sodium channels are responsible for the initiation and propagation of action potentials (APs). Two brain isoforms, Nav1.1 and Nav1.6, have very distinct cellular and subcellular expression. Specifically, Nav1.1 is predominantly expressed in the soma and proximal axon initial segment of fast-spiking GABAergic neurons, while Nav1.6 is found at the distal axon initial segment and nodes of Ranvier of both fast-spiking GABAergic and excitatory neurons. Interestingly, an auxiliary voltage-gated sodium channel subunit, Navβ4, is also enriched in the axon initial segment of fast-spiking GABAergic neurons. The C-terminal tail of Navβ4 is thought to mediate resurgent sodium current, an atypical current that occurs immediately following the action potential and is predicted to enhance excitability. To better understand the contribution of Nav1.1, Nav1.6 and Navβ4 to high frequency firing, we compared the properties of these two channel isoforms in the presence and absence of a peptide corresponding to part of the C-terminal tail of Navβ4. We used whole-cell patch clamp recordings to examine the biophysical properties of these two channel isoforms in HEK293T cells and found several differences between human Nav1.1 and Nav1.6 currents. Nav1.1 channels exhibited slower closed-state inactivation but faster open-state inactivation than Nav1.6 channels. We also observed a greater propensity of Nav1.6 to generate resurgent currents, most likely due to its slower kinetics of open-state inactivation, compared to Nav1.1. These two isoforms also showed differential responses to slow and fast AP waveforms, which were altered by the Navβ4 peptide. Although the Navβ4 peptide substantially increased the rate of recovery from apparent inactivation, Navβ4 peptide did not protect either channel isoform from undergoing use-dependent reduction with 10 Hz step-pulse stimulation or trains of slow or fast AP waveforms. Overall, these two channels have distinct biophysical properties that may differentially contribute to regulating neuronal excitability.

Influence of Fire Mosaics, Habitat Characteristics and Cattle Disturbance on Mammals in Fire-Prone Savanna Landscapes of the Northern Kimberley.

Patch mosaic burning, in which fire is used to produce a mosaic of habitat patches representative of a range of fire histories (‘pyrodiversity’), has been widely advocated to promote greater biodiversity. However, the details of desired fire mosaics for prescribed burning programs are often unspecified. Threatened small to medium-sized mammals (35 g to 5.5 kg) in the fire-prone tropical savannas of Australia appear to be particularly fire-sensitive. Consequently, a clear understanding of which properties of fire mosaics are most instrumental in influencing savanna mammal populations is critical. Here we use mammal capture data, remotely sensed fire information (i.e. time since last fire, fire frequency, frequency of late dry season fires, diversity of post-fire ages in 3 km radius, and spatial extent of recently burnt, intermediate and long unburnt habitat) and structural habitat attributes (including an index of cattle disturbance) to examine which characteristics of fire mosaics most influence mammals in the north-west Kimberley. We used general linear models to examine the relationship between fire mosaic and habitat attributes on total mammal abundance and richness, and the abundance of the most commonly detected species. Strong negative associations of mammal abundance and richness with frequency of late dry season fires, the spatial extent of recently burnt habitat (post-fire age <1 year within 3 km radius) and level of cattle disturbance were observed. Shrub cover was positively related to both mammal abundance and richness, and availability of rock crevices, ground vegetation cover and spatial extent of ≥4 years unburnt habitat were all positively associated with at least some of the mammal species modelled. We found little support for diversity of post-fire age classes in the models. Our results indicate that both a high frequency of intense late dry season fires and extensive, recently burnt vegetation are likely to be detrimental to mammals in the north Kimberley. A managed fire mosaic that reduces large scale and intense fires, including the retention of ≥4 years unburnt patches, will clearly benefit savanna mammals. We also highlighted the importance of fire mosaics that retain sufficient shelter for mammals. Along with fire, it is clear that grazing by introduced herbivores also needs to be reduced so that habitat quality is maintained.

Habitat differences do not explain population declines of sable antelope in an African savanna

AbstractSable antelope, Hippotragus niger, populations have declined substantially in Kruger National Park, South Africa despite large‐area protection from land use and poaching. Since Africa's large mammal populations are restricted to protected areas, understanding how to manage parks for biological diversity is critically important to the sustainability of faunal populations into the future. To better understand the drivers of sable decline, we analyzed landscapes where herds persist in the Pretoriuskop region of Kruger – identified by GPS collar telemetry data from eight individuals in five herds remaining in this area, and compared them to landscapes where sable herds have recently disappeared. We mapped these landscapes with satellite‐based spectral data on vegetation greenness and fire frequency and Carnegie Airborne Observatory LiDAR (Light Detection and Ranging) data on 3‐D vegetation structure. Within their home ranges, sable herds consistently selected areas with high fire frequency, high tree cover and low shrub cover. However, there were no consistent differences in habitat features between the home ranges of current sable herds and areas formerly supporting herds. Locally deteriorating habitat conditions were therefore not responsible for the decline in sables in this region of the park. Our study also illustrates how multi‐sensor, 3‐D mapping of ecosystems provides a means to assess causes and consequences of changing animal habitats over time.

Complex patterns in networks of hyperexcitable neurons

Complex patterns in neuronal networks emerge from the cooperative activity of the participating neurons, synaptic connectivity and network topology. Several neuron types exhibit complex intrinsic dynamics due to the presence of nonlinearities and multiple time scales. In this paper we extend previous work on hyperexcitability of neuronal networks, a hallmark of epileptic brain seizure generation, which results from the net imbalance between excitation and inhibition and the ability of certain neuron types to exhibit abrupt transitions between low and high firing frequency regimes as the levels of recurrent AMPA excitation change. We examine the effect of different topologies and connection delays on the hyperexcitability phenomenon in networks having recurrent synaptic AMPA (fast) excitation (in the absence of synaptic inhibition) and demonstrate the emergence of additional time scales.

Functional differentiation of biomes in an African savanna/forest mosaic

Tree densities in tropical and sub-tropical vegetation have, until recently, long been understood as increasing proportionally in response to precipitation. Current understanding is that trees are organised into alternative states with divergent properties that are linked, in the case of savannas, to frequent grass-fuelled fires or the absence of fire in non-savannas. In this paper we explored the hypothesis of functional divergence in three biomes, defined structurally by their dominant growth forms: savannas, ‘thicket’ and forest, within the vegetation of a South African park (Hluhluwe-iMfolozi). Thicket and forest both lack a continuous C4 grassy layer and are therefore non-savannas. ‘Thicket’, as defined here, has shorter trees than forests (4–6m vs. >10m) and, often a dense understorey of sub-shrubs. We analysed tree species composition in 253 sites across these three biomes. We then compared herbivore use and fire frequency among the three biomes. Finally we characterised functional traits for 58 tree species including several linked to fire and herbivore responses. In support of the emerging alternative states paradigm for both tree density and phylogenetic composition, we found that the three structurally defined biomes had separate tree species assemblages. Differences in growth form, especially the presence or absence of C4 grasses had key consequences for consumers with high fire frequency in savannas, low in thickets and none in forest and high grazing in savannas, high browsing in thickets and very low herbivory in forests. Trait analysis was consistent with these differences among biomes. Consumers appear to be important environmental filters by admitting some tree species to a biome and excluding others, depending on their functional traits. Positive feedbacks between vegetation and consumers may explain the coexistence of biomes in areas with similar climate and geology.

A new modeling approach estimates the relative importance of different community assembly processes

The relative importance of niche‐based (e.g., competitive or stress‐based) and stochastic (e.g., random dispersal) processes in structuring ecological communities is frequently analyzed by studying trait distributions of co‐occurring species. While filtering processes, such as the exclusion of stress‐intolerant species from particular habitats, increase the trait similarity between co‐occurring species, other processes, such as resource competition, can limit the similarity of co‐occurring species. Comparing the observed trait distribution patterns in communities to null expectations from randomized communities (e.g., a draw of the same observed richness from the regional pool) therefore gives a first indication of the dominant process driving community assembly.However, such comparisons do not inform us about the relative contribution of these different processes in shaping community compositions in case of their joint operation (a likely scenario). Using an Approximate Bayesian Computation approach, we develop a new method that allows inference of the relative importance of dispersal, filtering, and limiting similarity processes for the assembly of observed communities with known species and trait composition. We applied this approach to a tree community data set, collected across 20 plots along strong rainfall and fire gradients in a South African savanna.Based on comparisons with simulations, we find that our new approach is powerful in identifying which community assembly scenario has the highest probability to generate the observed trait distribution patterns, while traditional null model comparisons perform poorly in detecting signs of limiting similarity. For the studied savanna tree communities, our analysis yields that dispersal processes are most important in shaping the functional trait distribution patterns. Furthermore, our models indicate that filtering processes were relatively most important in areas with high fire frequencies, while limiting similarity processes were relatively most important in areas with low fire frequency and high rainfall. We conclude that our new method is a promising improvement on current approaches to estimate the relative importance of community assembly processes across different species groups, ecosystems, and biomes. Future model modifications (e.g., the inclusion of individual‐based processes) could provide further steps in uncovering the underlying assembly processes behind observed community patterns.

Historical agriculture and contemporary fire frequency alter soil properties in longleaf pine woodlands

Historical agriculture and contemporary disturbances such as fire can each affect soil properties, but the relative impact of their separate and combined effects is poorly understood. We investigated the effects of historical agriculture and contemporary fire frequency on soil properties of longleaf pine woodlands in the Southeastern United States. We sampled 24 pairs of sites from adjacent former agricultural and remnant longleaf pine woodlands based on high (⩾four since 1971) and low (<four since 1971) fire frequency. We found no evidence for interactive effects between agricultural history and fire frequency on measured mineral soil properties, yet each disturbance independently affected different aspects of the soil. Effects of past agricultural use were most apparent in the top 15cm of the mineral soil, with post-agricultural woodlands characterized by increased phosphorus and bulk density, as well as decreased organic matter and soil water holding capacity, compared to remnant woodlands. Some effects of past agricultural use, such as increased phosphorus, were also apparent as deep as 30cm into the soil profile. However, when expressed as stocks (to account for differences in bulk density) we found that organic matter content was similar among post-agricultural and remnant woodlands. With respect to contemporary fire frequency, less frequently burned sites had thicker O-horizons (litter and duff layers) and showed a trend of greater inorganic nitrogen in mineral soil, relative to frequently burned sites. Overall, our results indicate that agricultural legacies in soils persist 60years after agricultural abandonment and have impacts that may extend deep into the soil profile. Fire suppression additionally affects soils, resulting in additive effects of historical and contemporary disturbances. Additional research is needed to better determine if and how the combined effects of past and present disturbances will affect ecological systems. These combined and long-lasting impacts of historical and contemporary disturbances may help explain why restoration of native understory vegetation remains challenging.

Factors influencing the local scale colonisation and change in density of a widespread invasive plant species, Lantana camara, in South India

Identifying factors that underlie invasive species colonisation and change in density could provide valuable insights into the mechanisms of biological invasions and for invasive species management. We examined a suite of factors potentially influencing the landscape-level invasion of Lantana camara L., one of the most ubiquitous invasive species in South Asia. These factors included disturbance factors like forest fires, historical habitat modification, and edge effects, in addition to factors like propagule pressure and habitat suitability. We examined the relative importance of these factors on the colonisation and change in density of L. camara in the Biligiri Rangaswamy Temple Tiger Reserve, Western Ghats, India. We used extensive (1997–2008) datasets tracking the presence and abundance of L. camara and combined these with corresponding data on disturbances, propagule pressure, and habitat suitability. We used an information-theoretic model selection approach to determine the relative importance of each factor on the colonisation and change in density of L. camara. Colonisation was mainly a function of proximity to already established populations (i.e. propagule pressure), whereas increase in L. camara density appeared to be constrained by high fire frequency. Research and management efforts need to recognize the multidimensional nature of mechanisms underlying L. camara’s success during different invasion phases when strategizing interventions to mitigate its effects.

Dendrochronological reconstruction reveals a mixed‐intensity fire regime in Pinus sylvestris‐dominated stands of Białowieża Forest, Belarus and Poland

AbstractQuestionsWhat were the features of the historical forest fire regime, fire intensity in particular, in Pinus sylvestris‐dominated stands of Białowieża Forest? Did tree recruitment patterns relate to the fire history?LocationBiałowieża Forest, western Belarus and northeast Poland.MethodsWe used dendrochronological methods to reconstruct the fire regime in a 8.5‐ha mixed coniferous (Pinus sylvestris–Picea abies) forest stand located in the Belarusian part of Białowieża Forest. We analysed fire frequency at stand and point scale, seasonal distribution of fires and fire intensity. We compared the results to a previous study done in a 13.0‐ha site of similar habitat and stand structure, located in the Polish part of Białowieża Forest.ResultsWe reconstructed fires back to 1655, the most recent fire dating to 1918. Mean fire interval at stand scale during 1645–2010 was 9 ± 7.8 yrs (±SD). Fire frequency gradually declined after 1811, with mean fire interval at stand scale increasing from 5 ± 2.5 yrs prior to 1811 to 18 ± 9.3 yrs thereafter. Most fires were likely of low intensity, as suggested by (1) small average tree diameter (5.1 ± 2.9 cm) at the first scar, (2) absence of strong negative growth reactions after fire, and (3) high fire frequency likely limiting fuel build‐up. However, a fire in 1718 was intense and resulted in a wave of P. sylvestris regeneration. The reconstructed fire history in the Belarusian part of Białowieża Forest showed many similarities with that done in the Polish section of this forest. Similarities included dominance of low‐intensity dormant and early‐season fires, sporadic occurrence of high‐intensity fires, high fire frequencies between the 1650s and the early 1800s, and cessation of fires since the early 20th century. Six out of 50 fire dates reconstructed in both sites were common and represented a level of synchrony that was significantly higher than expected under a random pattern of fire occurrence.ConclusionsLow‐intensity surface fires dominated the historical fire regime of Białowieża Forest. However, occasional high‐intensity stand‐replacing fires led to successional changes at the stand scale.

Ecological Implications of Fine-Scale Fire Patchiness and Severity in Tropical Savannas of Northern Australia

AbstractUnderstanding fine-scale fire patchiness has significant implications for ecological processes and biodiversity conservation. It can affect local extinction of and recolonisation by relatively immobile fauna and poorly seed-dispersed flora in fire-affected areas. This study assesses fine-scale fire patchiness and severity, and associated implications for biodiversity, in north Australian tropical savanna systems. We used line transects to sample burning patterns of ground layer vegetation in different seasons and vegetation structure types, within the perimeter of 35 fires that occurred between 2009 and 2011. We evaluated two main fire characteristics: patchiness (patch density and mean patch length) and severity (inferred from char and scorch heights, and char and ash proportions). The mean burned area of ground vegetation was 83 % in the early dry season (EDS: May to July) and 93 % in the late dry season (LDS: August to November). LDS fires were less patchy (smaller and fewer unburned patches), and had higher fire severity (higher mean char and scorch heights, and twice the proportion of ash) than EDS fires. Fire patchiness varied among vegetation types, declining under more open canopy structure. The relationship between burned area and fire severity depended on season, being strongly correlated in the EDS and uncorrelated in the LDS. Simulations performed to understand the implications of patchiness on the population dynamics of fire-interval sensitive plant species showed that small amounts of patchiness substantially enhance survival. Our results indicate that the ecological impacts of high frequency fires on fire-sensitive regional biodiversity elements are likely to be lower than has been predicted from remotely sensed studies that are based on assumptions of homogeneous burning.

The relationship between past vegetation type and fire frequency in western Japan inferred from phytolith and charcoal records in cumulative soils

Phytolith and macrocharcoal records in cumulative soils were compared in five areas in western Japan, including two sites on the Tonomine Plateau where we examined those records. Past vegetation types, as represented by the compositions of phytolith assemblages, are closely related to macrocharcoal fluxes, regardless of age, suggesting that in Japan, fluxes in cumulative soils could be an indicator of fire frequency. On the Tonomine Plateau, phytolith and charcoal records indicate that, in the middle and late Holocene (at least 5000 to ∼1000 years ago), Sasa and Panicoideae species in a temperate climate. At least for approximately the last 600 years the Japanese pampas (Miscanthus sinensis) grassland has undergone annual burning. The results from the Tonomine Plateau site of this study and from four other sites suggest that macrocharcoal fluxes in cumulative soils of >10 particles·cm−2 y−1 indicate a high frequency of fires, resulting in the dominance of Andropogoneae species. Dominance of Pleioblastus species under the influence of fire was observed in soils with a charcoal flux of 2–10 particles·cm−2 y−1, suggesting that the species flourished under a moderate frequency of fire (possibly every several years or more). In soils with a charcoal flux of less than ∼1 particles·cm−2 y−1, there was no influence of fire on vegetation, and Sasa and Pleioblastus species flourished where the vegetation type was determined primarily by the climatic conditions. These findings indicate that macrocharcoal fluxes and phytolith assemblages exhibit a consistent relationship that is independent of age, and that macrocharcoal fluxes are linked to fire frequency, thus suggesting that the frequency of fire has determined the vegetation type in these areas. Therefore, phytolith and charcoal records in cumulative soils provide a context for quantitatively understanding the influence of fire on vegetation patterns in the past.

A computational model of pattern separation efficiency in the dentate gyrus with implications in schizophrenia.

Information processing in the hippocampus begins by transferring spiking activity of the entorhinal cortex (EC) into the dentate gyrus (DG). Activity pattern in the EC is separated by the DG such that it plays an important role in hippocampal functions including memory. The structural and physiological parameters of these neural networks enable the hippocampus to be efficient in encoding a large number of inputs that animals receive and process in their life time. The neural encoding capacity of the DG depends on its single neurons encoding and pattern separation efficiency. In this study, encoding by the DG is modeled such that single neurons and pattern separation efficiency are measured using simulations of different parameter values. For this purpose, a probabilistic model of single neurons efficiency is presented to study the role of structural and physiological parameters. Known neurons number of the EC and the DG is used to construct a neural network by electrophysiological features of granule cells of the DG. Separated inputs as activated neurons in the EC with different firing probabilities are presented into the DG. For different connectivity rates between the EC and DG, pattern separation efficiency of the DG is measured. The results show that in the absence of feedback inhibition on the DG neurons, the DG demonstrates low separation efficiency and high firing frequency. Feedback inhibition can increase separation efficiency while resulting in very low single neuron’s encoding efficiency in the DG and very low firing frequency of neurons in the DG (sparse spiking). This work presents a mechanistic explanation for experimental observations in the hippocampus, in combination with theoretical measures. Moreover, the model predicts a critical role for impaired inhibitory neurons in schizophrenia where deficiency in pattern separation of the DG has been observed.

Assessing the effects of multiple stressors on the recruitment of fruit harvested trees in a tropical dry forest, Western Ghats, India.

The harvest of non-timber forest products (NTFPs), together with other sources of anthropogenic disturbance, impact plant populations greatly. Despite this, conservation research on NTFPs typically focuses on harvest alone, ignoring possible confounding effects of other anthropogenic and ecological factors. Disentangling anthropogenic disturbances is critical in regions such as India’s Western Ghats, a biodiversity hotspot with high human density. Identifying strategies that permit both use and conservation of resources is essential to preserving biodiversity while meeting local needs. We assessed the effects of NTFP harvesting (fruit harvest from canopy and lopping of branches for fruit) in combination with other common anthropogenic disturbances (cattle grazing, fire frequency and distance from village), in order to identify which stressors have greater effects on recruitment of three tropical dry forest fruit tree species. Specifically, we assessed the structure of 54 populations of Phyllanthus emblica, P. indofischeri and Terminalia chebula spread across the Nilgiri Biosphere Reserve, Western Ghats to ask: (1) How are populations recruiting? and (2) What anthropogenic disturbance and environmental factors, specifically forest type and elevation, are the most important predictors of recruitment status? We combined participatory research with an information-theoretic model-averaging approach to determine which factors most affect population structure and recruitment status. Our models illustrate that for T. chebula, high fire frequency and high fruit harvest intensity decreased the proportion of saplings, while lopping branches or stems to obtain fruit increased it. For Phyllanthus spp, recruitment was significantly lower in plots with more frequent fire. Indices of recruitment of both species were significantly higher for plots in more open-canopy environments of savanna woodlands than in dry forests. Our research illustrates an approach for identifying which factors are most important in limiting recruitment of NTFP populations and other plant species that may be in decline, in order to design effective management strategies.

Fire, Drought, and Humans in a Heterogeneous Lake Superior Landscape

We used dendrochronology and historic data to examine spatial and temporal variation in the historic fire regime of a complex landscape adjacent to Lake Superior in the Huron Mountains, Michigan, USA. Across the study area, 330 dated fire scars were identified and cross-dated from 115 trees and seven sites, spanning the years 1439–2005. Most of the fires were small in spatial extent; larger fires were infrequent and occurred primarily in level landscape positions within 1.5 km of Lake Superior. Small, frequent fires also occurred at the higher elevations attributable to lightning ignitions. The mean fire interval (MFI) from 1439–1751 was 49 yr and then abruptly shortened to 18.5 yr until the 1900s, during which time the MFI across all sites was greater than 78 yr. From 1752–1900s, high fire frequency occurred even in relatively wet years, suggesting an increased human influence. We interpret these patterns in fire intervals in the context of topography and changes in human population, land use, and cultural perspectives on fire.