Anomalies in grasstree fire history reconstructions for south‐western Australian vegetation

Abstract A new fire history for south‐western Australian sclerophyll forests was proposed recently based on grasstree (Xanthorrhoea preissii ) records that were interpreted to show a high frequency (3–5 years) ‘pre‐European burning regime’. Such a fire regime appears incompatible with the long‐term survival of many fire‐killed woody taxa. We investigated the local fire history in a small area of the northern sand‐plain shrub‐lands of south‐western Australia using 15 grasstrees, examining individual grasstree records in detail and comparing this with the decadal or averaged approach used in the original research, and with fire histories reconstructed from satellite images for the period since 1975. Results lead us to question the utility of the proposed grasstree fire history record as a tool for understanding past fire regimes for two reasons: First, inconsistencies in fire histories among individual grasstrees were considerable – some individuals were not burnt by known fires, while some apparently were burned many times during periods when others were not burned at all. Second, the grasstree record indicates a possible increase in patchiness of fires since 1930, while contemporary evidence and interpretations of the nature of Aboriginal (pre‐European) fire regimes would suggest the opposite. We believe that further research is needed to identify to what extent the grasstree method for reconstruction of fire histories can be used to re‐interpret how fire operated in many highly diverse ecosystems prior to European settlement of Australia.     

Grasstree (Xanthorrhoea preissii ) leaf growth in relation to season and water availability

Abstract Water stress usually arrests growth of even the most deep‐rooted species during summer drought in Mediterranean‐type climates. However, scant evidence suggests that grasstrees may represent an unusual exception. We used weather data and plant water potential to investigate the relationship between leaf growth and season in the grasstree, Xanthorrhoea preissii Endl. (Xanthorrhoeaceae). Leaf production in two contrasting habitats revealed continuous annual growth, oscillating between maximum rates (2.5–3.2 leaves/d) in late‐spring to autumn, to a minimum rate of 0.5 leaf/d during winter but never stopping. While the rate of leaf production during the fast‐growth season was positively correlated with temperature above 17–18°C, leaf elongation commenced substantially earlier in the year (from 12°C). Leaf water potentials cycled annually, with predawn readings commonly measured as zero during winter–spring and as low as ?1.26 MPa during summer, but never indicating stress by exceeding the turgor loss point. Leaf death was synchronized with summer drought. The fast (summer) growth period was characterized by rapidly fluctuating leaf production, particularly in banksia woodland, where plant growth reliably responded quickly to >18 mm of rainfall. Within 24 h of 59 mm of simulated rainfall, grasstrees in banksia woodland showed a marked increase in water potential, and leaf production reached 7.5 times the controls, confirming their capacity to respond to temporary spasmodic summer rains. Rainfall was the best climatic variable for predicting woodland grasstree leaf production during summer, whereas leaf production of forest grasstrees was most closely correlated with daylength. This plastic response of grasstrees between seasonal weather extremes is relatively rare among other mediterranean floras, and has implications for a recently proposed technique for ageing grasstrees.     

Plant size and season of burn affect flowering and fruiting of the grasstree Xanthorrhoea preissii

Flowering and fruiting were assessed on 14 populations of the grasstree, Xanthorrhoea preissii Endl., occurring in the Darling Range near Perth, Western Australia. Independent of site, season of burn or year of flowering, there was a strong relationship between plant height, which varied from 0.1 to over 2 m, and the incidence of postfire flowering, which varied from 1% (winter burn) to 75% (summer burn) of grasstrees present. There was no relationship between inflorescence dimensions, or flower or fruit production on a spike basis, and plant size/age (height). When standardized for height, spring‐burnt populations produced 40% as many inflorescences as autumn‐burnt populations and 20% as many as summer‐burnt populations. Inflorescences produced by spring‐burnt plants were moderately smaller than those by summer–autumn‐burnt plants. Fruit density per spike in autumn‐burnt plants was 80% of that in spring–summer‐burnt plants. The net effect was an average of 70 000 fruits produced per 100 summer‐burnt plants, 22 000 in autumn‐burnt plants, and 14 000 in spring‐burnt plants. Ecophysiological explanations of these results and their implications for population dynamics have yet to be explored.     

Continental‐scale syntheses of Australian pyromes – misclassification of south‐western eucalypt woodlands misinforms management

Global and continental‐scale analysis of ecological phenomena can offer important insights through the identification of patterns and associations not detectable at smaller scales. However, using proxies for ecological phenomena, such as vegetation mapping for spatially projecting fire regime niches and post‐fire plant responses, require critical examination of predictions to determine utility. Using local studies in south‐western Australia, we demonstrate that while this approach has been largely successful in mallee woodland and shrubland, it has failed in eucalypt woodland, with the consequence that values for a range of fire‐related parameters from the continent‐wide approaches, if adopted in informing management, would result in undesirable conservation outcomes for the world's largest extant temperate woodland.     

Vegetation and landscape connectivity control wildfire intervals in unmanaged semi‐arid shrublands and woodlands in Australia

Aim The aim of this study was to determine how spatial variation in vegetation type and landscape connectivity influence fire intervals in a semi‐arid landscape with low relief and complex mosaics of woodland and shrubland vegetation. Location Our study focused on a 15,500‐km² area of relatively undisturbed and unmanaged land in south‐western Australia, referred to as the Lake Johnston region. Methods We modelled fire‐interval data from a 67‐year (1940–2006) digital fire history database using a two‐parameter Weibull function, and tested for the effects of vegetation type and landscape connectivity on estimates of the length of fire intervals (Weibull parameter b) and the dependence of fire intervals on fuel age (Weibull parameter c). Results Vegetation type and landscape connectivity significantly influenced fire interval probability distributions. Fire intervals in shrublands (dense low shrub assemblage) were typically shorter (b = 46 years) and more dependent on fuel age (c = 2.33) than most other vegetation types, while fire intervals in open eucalypt woodlands were much longer (b = 405 years) and were less dependent on fuel age (c = 1.36) than in shrub‐dominated vegetation types. Areas adjacent to or surrounded by salt lakes burnt less frequently (b = 319 years) and fire intervals were less dependent on fuel age (c = 1.48) compared with more exposed areas (e.g. b < 101 years, c > 1.68). Fire intervals in thickets (dense tall shrub assemblage) were longer (b = 101 years) than would be expected from fuel loads, most likely because they were protected from fire by surrounding fuel‐limited woodlands. Main conclusions Fire intervals in south‐western Australia are strongly influenced by spatial variation in vegetation (fuel structure) and landscape connectivity. The importance of fuel structure as a control of fire intervals in south‐western Australia contrasts with other landscapes, where topographical gradients or climatic influences may override the effects of underlying vegetation. We found that, regardless of low relief, topographical features such as large salt lake systems limited the connectivity and spread of fire among landscape units in an analogous manner to lakes or mountainous features elsewhere.     

Two proxy records revealing the late Holocene fire history at a site on the central coast of New South Wales,Australia

Abstract: The local fire history of a coastal swamp catchment in New South Wales was reconstructed using two proxy records of fire: sedimentary macroscopic charcoal and fire‐scar analyses of Xanthorrhoea johnsonii. The charcoal analysis provided a record of fire activity spanning the last 2800 years, while the Xanthorrhoea record covered the last approx. 300 years. The ability of each method to accurately record fire events was verified by cross referencing against the recent (post 1968) historic fire record. Fire history was then extrapolated beyond the historic record, to reveal an unprecedented level of fire activity in the last 35 years, which coincides with increased human activity in the area. In the prehistoric period charcoal and fire scars are comparatively rare, which is most parsimoniously ascribed to little fire activity, but perhaps represents skilful fire manipulation, as is often attributed to Aboriginal people. The comparatively minor fluctuations in macroscopic charcoal during the prehistoric period were approximately coeval with previous evidence of late Holocene environmental change in south‐eastern Australia, suggesting that fire frequency at the site responded to climatic variability. The longer temporal perspective of this palaeoenvironmental approach provides information for the contemporary management of fire in this conservation reserve.     

Record error and range contraction, real and imagined, in the restricted shrub Banksia hookeriana in south-western Australia

Banksia hookeriana Meissn. (Proteaceae) is a fire‐killed shrub endemic to the northern sandplains of south‐western Australia that could be described as endangered based on its small geographical range (< 5000 km²) and area of occupancy (～500 km²). Impacts on the species’ geographical range by land clearance for farming and mining, and by altered fire regime, were investigated using three lines of evidence: records of herbarium collections, a comprehensive field survey of extant populations, and air photo and satellite images revealing the recent history of land clearance and fires. These show that the species’ range has contracted by up to 40% in area and 26% latitudinally through the loss of outlier and range limit populations since 1960. In addition, 22% of remaining native shrubland on the Eneabba sandplain has been lost over this period through clearing for farming and mining, representing further habitat loss for B. hookeriana. Detailed investigation of B. hookeriana herbarium collections (n = 46) revealed important errors that artificially affected the geographical range of the species and emphasized the importance of close examination of all data captured from collection records. Recorded locations occurred hundreds of kilometres outside the current geographical range of the species in areas with different climate and substrate. Incorrect species identification of herbarium specimens further extended the apparent geographical range of the species. On the other hand, credible records indicated the loss of the species from localities at the limits of its range. Overall, a disconcertingly high proportion of records contained errors that may be difficult to identify without close examination of the original collections and detailed ground‐truthing. Were these records to be used to model climate envelopes, identify potential habitat where the species might occur, or might migrate to either as pests or under climate change scenarios, or to analyse evolutionary or ecological theory (for example) — as is now becoming commonplace — large errors may ensue.     

Two fine‐resolution Pliocene charcoal records and their bearing on pre‐human fire frequency in south‐western Australia

Abstract Yallalie is a probable meteor impact crater and in the Upper Pliocene contained a substantial lake. Two Mid‐Pliocene finely laminated sediment records from Palaeolake Yallalie, from about 3 million years ago, provide evidence of fire and fire frequency in the sclerophyll woodland and heaths of south‐western Australia in the absence of humans. Fine charcoal was observed in all samples examined, and was deposited at a rate of about 0.3–0.8 cm² cm^?2 year^?1 in Palaeolake Yallalie. This evidence suggests the occurrence of annual fires occurring every year in the slightly warmer and wetter climate compared with today. The near coastal western location and the prevailing westerly winds probably carry charcoal from the near region or lake catchment scale. The data indicate that local fires occurred at a variety of time intervals between 3 and 13 years, with a typical average of 6–10 years. The results are comparable with those of Atahan et al. (2004) for the same site but from a period of about 200 000 years later in the Mid‐Pliocene. Thus, the records which differ in age by some hundreds of thousands of years have all recorded fire frequencies that are longer than for the historical period and this may have important implications for the long‐term survival of the integrity of the high biodiversity plant communities of the region.     

A fine-resolution Pliocene pollen and charcoal record from Yallalie, south-western Australia

Aim This paper aims to reconstruct a high‐resolution fire and vegetation history from a period when humans were absent in Australia. This is then used to comment on the frequency of natural fire in high biodiversity heathland, and to compare this with historical fire regime in the same region. Methods A section of varved sediment covering a period of c. 84 years was taken from Palaeolake Yallalie in south‐western Australia. The sediments were separated into approximately single to small multiples of years and then analysed for charcoal, pollen and sediment analysis to reconstruct the environmental conditions at the time. Results The charcoal record indicates fire recurrence to have been roughly between 5 and 13 years, a little longer than those of the historical period. The pollen record was dominated by Casuarinaceae, Myrtaceae and a large number of Proteaceae species; these are intermixed with Araucariaceae, Nothofagus and Podocarpus. This suggests there was a mix of sclerophyll woodland and a mosaic of rain forest elements, thus conditions must have been wetter, particularly in the summers, compared with today. Conclusions We assume that fire was most likely confined to the sclerophyll vegetation, and that fire has been a significant feature of the environment long before humans entered Australia. The slightly longer fire recurrence times compared with the present result from the intermittent nature of lightning and wetter summers at the time.     

Simplifying the savanna: the trajectory of fire‐sensitive vegetation mosaics in northern Australia

Aim Fire is a key agent in savanna systems, yet the capacity to predict fine‐grained population phenomena under variable fire regime conditions at landscape scales is a daunting challenge. Given mounting evidence for significant impacts of fire on vulnerable biodiversity elements in north Australian savannas over recent decades, we assess: (1) the trajectory of fire‐sensitive vegetation elements within a particularly biodiverse savanna mosaic based on long‐term monitoring and spatial modelling; (2) the broader implications for northern Australia; and (3) the applicability of the methodological approach to other fire‐prone settings. Location Arnhem Plateau, northern Australia. Methods We apply data from long‐term vegetation monitoring plots included within Kakadu National Park to derive statistical models describing the responses of structure and floristic attributes to 15 years of ambient (non‐experimental) fire regime treatments. For a broader 28,000 km² region, we apply significant models to spatial assessment of the effects of modern fire regimes (1995–2009) on diagnostic closed forest, savanna and shrubland heath attributes. Results Significant models included the effects of severe fires on large stems of the closed forest dominant Allosyncarpia ternata, stem densities of the widespread savanna coniferous obligate seeder Callitris intratropica, and fire frequency and related fire interval parameters on numbers of obligate seeder taxa characteristic of shrubland heaths. No significant relationships were observed between fire regime and eucalypt and non‐eucalypt adult tree components of savanna. Spatial application of significant models illustrates that more than half of the regional closed forest perimeters, savanna and shrubland habitats experienced deleterious fire regimes over the study period, except in very dissected terrain. Main conclusions While north Australia’s relatively unmodified mesic savannas may appear structurally intact and healthy, this study provides compelling evidence that fire‐sensitive vegetation elements embedded within the savanna mosaic are in decline under present‐day fire regimes. These observations have broader implications for analogous savanna mosaics across northern Australia, and support complementary findings of the contributory role of fire regimes in the demise of small mammal fauna. The methodological approach has application in other fire‐prone settings, but is reliant on significant long‐term infrastructure resourcing.     

Early Pleistocene vegetation change in upland south‐eastern Australia

Aim This study aims to improve our understanding of the late Cenozoic history of Australian rain forest and sclerophyll biomes by presenting a detailed pollen record demonstrating the floristic composition and orbital‐scale patterns of change in forest communities of upland south‐eastern Australia, during the Early Pleistocene. The record is examined in order to shed light on the nature of the transition from rain forest‐dominated ‘Tertiary’ Australian vegetation to open‐canopied ‘Quaternary’ vegetation. Location Stony Creek Basin (144.13° E, 37.35° S, 550 m a.s.l), a small, infilled palaeolake in the western uplands of Victoria, Australia. Methods A c. 40‐m‐long sediment core was recovered from the infilled palaeolake. Palynology was used to produce a record of changing vegetation through time. Multivariate analyses provided a basis for interpreting the composition of rain forest and sclerophyll forest communities and for identifying changes in these communities over successive insolation cycles. Results Early Pleistocene upland south‐eastern Australian vegetation was characterized by orbital‐scale, cyclic alternation between rain forest and sclerophyll forests. Individual intervals of forest development underwent patterns of sequential taxon expansion that recurred in successive vegetation cycles. Diverse rain forests included a number of angiosperm and gymnosperm taxa now extinct regionally to globally. Sclerophyll forests were also diverse, and occurred under warm and wet climate conditions. Main conclusions The Stony Creek Basin record demonstrates that as recently as c. 1.5 Ma diverse rain forests persisted in southern Australia beyond the modern continental range of rain forest. The importance of conifers in these rain forests emphasizes that they have no modern Australian analogue. Alternation in dominance between these forests and diverse, sclerophyllous open canopied forests was apparently driven by changes in seasonality, and may have been promoted by fire.     

Ngadju kala: Australian Aboriginal fire knowledge in the Great Western Woodlands

Indigenous fire knowledge offers significant benefits for ecosystem management and human livelihoods, but is threatened worldwide because of disruption of customary practices. In Australia, the historical prevalence and characteristics of Aboriginal burning are intensely debated, including arguments that Aboriginal burning was frequent across the continent. Frequent burning is supported by contemporary Aboriginal knowledge and practice in some regions, but in southern Australia evidence is typically limited to historical and ecological records. Towards characterizing Aboriginal fire regimes in southern Australia, we collaborated with Ngadju people from the globally significant Great Western Woodlands in south‐western Australia to document their fire knowledge. We used workshops, site visits, interviews and occupation mapping to aid knowledge sharing. Consistent with the established significance of Aboriginal fire in Australia, planned fires were important in Ngadju daily life and land management. However, Ngadju use of fire was characterized by its selectivity rather than its ubiquity. Specifically, Ngadju described only highly targeted planned burning across extensive eucalypt woodlands and sandplain shrublands. By contrast, frequent planned burning was described for resource‐rich landscape elements of more restricted extent (granite outcrop vegetation, grasslands and coastal scrub). Overall, Ngadju fires are likely to have resulted in subtle but purposeful direct effects on the vegetation and biota. However the extent to which they collectively constrained large, intense wildfires remains unclear. Ngadju demonstrated a predictive knowledge of the ecological consequences of burning, including attention to fine‐scale needs of target organisms, and application of diverse fire regimes. These are consistent with the recently proposed concept that Aboriginal burning was guided by ‘templates’ targeting different resources, although diverse regimes predominantly reflect edaphically driven vegetation patterns rather than template‐driven use of fire to create resource diversity. We conclude that Ngadju fire knowledge fills an important gap in understanding Aboriginal fire regimes in southern Australia, highlighting a novel balance between frequent and constrained use of fire.     

Implications of climate change for potamodromous fishes

There is little understanding of how climate change will impact potamodromous freshwater fishes. Since the mid 1970s, a decline in annual rainfall in south‐western Australia (a globally recognized biodiversity hotspot) has resulted in the rivers of the region undergoing severe reductions in surface flows (ca. 50%). There is universal agreement amongst Global Climate Models that rainfall will continue to decline in this region. Limited data are available on the movement patterns of the endemic freshwater fishes of south‐western Australia or on the relationship between their life histories and hydrology. We used this region as a model to determine how dramatic hydrological change may impact potamodromous freshwater fishes. Migration patterns of fishes in the largest river in south‐western Australia were quantified over a 4 year period and were related to a number of key environmental variables including discharge, temperature, pH, conductivity and dissolved oxygen. Most of the endemic freshwater fishes were potamodromous, displaying lateral seasonal spawning migrations from the main channel into tributaries, and there were significant temporal differences in movement patterns between species. Using a model averaging approach, amount of discharge was clearly the best predictor of upstream and downstream movement for most species. Given past and projected reductions in surface flow and groundwater, the findings have major implications for future recruitment rates and population viabilities of potamodromous fishes. Freshwater ecosystems in drying climatic regions can only be managed effectively if such hydro‐ecological relationships are considered. Proactive management and addressing existing anthropogenic stressors on aquatic ecosystems associated with the development of surface and groundwater resources and land use is required to increase the resistance and resilience of potamodromous fishes to ongoing flow reductions.     

Old‐growth forests,carbon and climate change: Functions and management for tall open‐forests in two hotspots of temperate Australia

Abstract

The prognosis and utility under climate change are presented for two old‐growth, temperate forests in Australia, from ecological and carbon accounting perspectives. The tall open‐forests (TOFs) of south‐western Australia (SWA) are within Australia’s global biodiversity hotspot. The forest management and timber usage from the carbon‐dense old‐growth TOFs of Tasmania (TAS) have a high carbon efflux, rendering it a carbon hotspot. Under climate change the warmer, dryer climate in both areas will decrease carbon stocks directly; and indirectly through changes towards dryer forest types and through positive feedback. Near 2100, climate change will decrease soil organic carbon (SOC) significantly, e.g. by ～30% for SWA and at least 2% for TAS. The emissions from the next 20 years of logging old‐growth TOF in TAS, and conversion to harvesting cycles, will conservatively reach 66(±33) Mt‐CO₂‐equivalents in the long‐term – bolstering greenhouse gas emissions. Similar emissions will arise from rainforest SOC in TAS due to climate change. Careful management of old‐growth TOFs in these two hotspots, to help reduce carbon emissions and change in biodiversity, entails adopting approaches to forest, wood product and fire management which conserve old‐growth characteristics in forest stands. Plantation forestry on long‐cleared land and well‐targeted prescribed burning supplement effective carbon management.

Abbreviations: C, carbon; CBS, clearfell, burn and sow; CO₂‐e, CO₂ equivalents; CWD, coarse woody debris; DOC, dissolved organic carbon; GHG, greenhouse gas; Mt, megatonnes; SOC, soil organic carbon; SWA, south‐western Australia; SWAFR, Southwest Australian Floristic Region; TAS, Tasmania; TOF, tall open‐forest; t‐C ha^?1 yr^?1, tonnes of carbon per hectare per year     

Response of plant species and life form diversity to variable fire histories and biomass in the jarrah forest of south‐west Australia

Frequent fires reduce the abundance of woody plant species and favour herbaceous species. Plant species richness also tends to increase with decreasing vegetation biomass and cover due to reduced competition for light. We assessed the influence of variable fire histories and site biomass on the following diversity measures: woody and herbaceous species richness, overall species richness and evenness, and life form evenness (i.e. the relative abundance or dominance among six herbaceous and six woody plant life forms), across 16 mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest stands in south‐west Australia. Fire frequency was defined as the total number of fires over a 30‐year period. Overall species richness and species evenness did not vary with fire frequency or biomass. However, there were more herbaceous species (particularly rushes, geophytes and herbs) where there were fewer shrubs and low biomass, suggesting that more herbaceous species coexist where dominance by shrubs is low. Frequently burnt plots also had lower number and abundance of shrub species. Life form evenness was also higher at both high fire frequency and low biomass sites. These results suggest that the impact of fire frequency and biomass on vegetation composition is mediated by local interactions among different life forms rather than among individual species. Our results demonstrate that measuring the variation in the relative diversity of different woody and herbaceous life forms is crucial to understanding the compositional response of forests and other structurally complex vegetation communities to changes in disturbance regime such as increased fire frequency.     

Relationships between expanding pinyon–juniper cover and topography in the central Great Basin, Nevada

Aim Increasing geographical range and density of conifers is a major form of land‐cover change in the western United States, affecting fire frequency, biogeochemistry and possibly biodiversity. However, the extent and magnitude of the change are uncertain. This study aimed to quantify the relationship between changing conifer cover and topography. Location The central Great Basin in the state of Nevada, USA. Methods We used a series of Landsat Thematic Mapper satellite images from 1986, 1995 and 2005 to map change in pinyon–juniper woodlands (Pinus monophylla, Juniperus spp.) in the montane central Great Basin of Nevada. We derived fractional greenness for each year using spectral mixture analysis and identified all areas with an above average increase in greenness from 1986 to 1995 and 1995 to 2005. Results Areas with high fractional greenness in 2005 were most likely to occur at elevations between 2200 and 2600 m a.s.l. Increases in fractional greenness between 1986 and 2005 were most likely to occur at elevations below 2000 m a.s.l. and on south‐facing slopes. However, relationships between elevation and increasing greenness for individual mountain ranges varied considerably from the average trend. Fractional greenness values measured by Landsat suggest that the majority of pinyon–juniper woodlands have not reached their maximum potential tree cover. Main conclusions Expansion of pinyon–juniper at low elevations and on south‐facing slopes probably reflects increasing precipitation in the 20th century, higher water use efficiency caused by increasing atmospheric CO₂ in the late 20th century and livestock grazing at the interface between shrubland and woodland. Identification of the spatial relationships between changing fractional greenness of pinyon–juniper woodland and topography can inform regional land management and improve projections of long‐term ecosystem change.     

Firescape ecology: how topography determines the contrasting distribution of fire and rain forest in the south‐west of the Tasmanian Wilderness World Heritage Area

Aim To test the hypothesis that ‘islands’ of fire‐sensitive rain forest are restricted to topographic fire refugia and investigate the role of topography–fire interactions in fire‐mediated alternative stable state models. Location A vegetation mosaic of moorland, sclerophyll scrub, wet sclerophyll eucalypt forest and rain forest in the rugged, fire‐prone landscapes of south‐west Tasmania, Australia. Methods We used geospatial statistics to: (1) identify the topographic determinants of rain forest distribution on nutrient‐poor substrates, and (2) identify the vegetation and topographic variables that are important in controlling the spatial pattern of a series of very large fires (> 40,000 ha) that were mapped using Landsat Thematic Mapper (TM) satellite imagery. Results Rain forest was more likely to be found in valleys and on steep south‐facing slopes. Fires typically burned within highly flammable treeless moorland and stopped on boundaries with less flammable surrounding vegetation types such as wet sclerophyll forest and rain forest. Controlling for the effect of vegetation, fires were most likely to burn on flats, ridges and steep north‐facing slopes and least likely to burn in valleys and on steep south‐facing slopes. These results suggest an antagonism between fire and rain forest, in which rain forest preferentially occupies parts of the landscape where fire is least likely to burn. Main conclusions The distribution of rain forest on nutrient‐poor substrates was clearly related to parts of the landscape that are protected from fire (i.e. topographic fire refugia). The relative flammability of vegetation types at the landscape scale offers support to the proposed hierarchy of fire frequencies (moorland > scrub > wet sclerophyll > rain forest) that underpins the ecological models proposed for the region. The interaction between fire occurrence and a range of topographic variables suggests that topography plays an important role in mediating the fire–vegetation feedbacks thought to maintain vegetation mosaics in south‐west Tasmania. We suggest that these fire–topography interactions should be included in models of fire‐mediated alternative stable vegetation states in other fire‐prone landscapes.     

Postfire response of North American boreal forest net primary productivity analyzed with satellite observations

Fire is a major disturbance in the boreal forest, and has been shown to release significant amounts of carbon (C) to the atmosphere through combustion. However, less is known about the effects on ecosystems following fire, which include reduced productivity and changes in decomposition in the decade immediately following the disturbance. In this study, we assessed the impact of fire on net primary productivity (NPP) in the North American boreal forest using a 17‐year record of satellite NDVI observations at 8‐ km spatial resolution together with a light‐use efficiency model. We identified 61 fire scars in the satellite observations using digitized fire burn perimeters from a database of large fires. We studied the postfire response of NPP by analyzing the most impacted pixel within each burned area. NPP decreased in the year following the fire by 60–260 g C m^?2 yr^?1 (30–80%). By comparing pre‐ and postfire observations, we estimated a mean NPP recovery period for boreal forests of about 9 years, with substantial variability among fires. We incorporated this behavior into a carbon cycle model simulation to demonstrate these effects on net ecosystem production. The disturbance resulted in a release of C to the atmosphere during the first 8 years, followed by a small, but long‐lived, sink lasting 150 years. Postfire net emissions were three times as large as from a model run without changing NPP. However, only small differences in the C cycle occurred between runs after 8 years due to the rapid recovery of NPP. We conclude by discussing the effects of fire on the long‐term continental trends in satellite NDVI observed across boreal North America during the 1980s and 1990s.     

某二级医院住院病历中不良事件风险评估的应用与研究

目的:通过病历中发生的不良事件及其风险度来评价病历质量,目的为加强病历环节和细节的质控,减少或杜绝病历中不良事件的发生,提高病历书写质量,保证医疗安全,减少医疗纠纷。方法:随机抽查2007-2010年某二级医院住院病历4837份,对其进行不良事件风险评估,对病历的终末质量和环节质量进行综合评价分析,找出影响医疗质量的相关联因素。结果:通过对某二级医院2007-2010年随机抽查的终末病历和病房中运行病历的不良事件风险评估,数据经过统计学处理后P值<0.01,说明总的病历中不良事件发生率年度间逐年减少,有极为显著的差别,证明此种病历评价方法切实可行。结论:病历中不良事件风险评估,是减少病历中不良事件发生的有效办法,可以消除病历书写中存在的医患矛盾和医疗纠纷隐患。     

Satellite microwave detection of boreal forest recovery from the extreme 2004 wildfires in Alaska and Canada

The rate of vegetation recovery from boreal wildfire influences terrestrial carbon cycle processes and climate feedbacks by affecting the surface energy budget and land‐atmosphere carbon exchange. Previous forest recovery assessments using satellite optical‐infrared normalized difference vegetation index (NDVI) and tower CO₂ eddy covariance techniques indicate rapid vegetation recovery within 5–10 years, but these techniques are not directly sensitive to changes in vegetation biomass. Alternatively, the vegetation optical depth (VOD) parameter from satellite passive microwave remote sensing can detect changes in canopy biomass structure and may provide a useful metric of post‐fire vegetation response to inform regional recovery assessments. We analyzed a multi‐year (2003–2010) satellite VOD record from the NASA AMSR‐E (Advanced Microwave Scanning Radiometer for EOS) sensor to estimate forest recovery trajectories for 14 large boreal fires from 2004 in Alaska and Canada. The VOD record indicated initial post‐fire canopy biomass recovery within 3–7 years, lagging NDVI recovery by 1–5 years. The VOD lag was attributed to slower non‐photosynthetic (woody) and photosynthetic (foliar) canopy biomass recovery, relative to the faster canopy greenness response indicated from the NDVI. The duration of VOD recovery to pre‐burn conditions was also directly proportional (P < 0.01) to satellite (moderate resolution imaging spectroradiometer) estimated tree cover loss used as a metric of fire severity. Our results indicate that vegetation biomass recovery from boreal fire disturbance is generally slower than reported from previous assessments based solely on satellite optical‐infrared remote sensing, while the VOD parameter enables more comprehensive assessments of boreal forest recovery.