A computer model of succession and fire response of the high-altitude Eucalyptus forest of the Brindabella Range,Australian Capital Territory

The BRIND model, a computer model of the high altitude forests in the Brindabella Range near Canberra (Australian Capital Territory), is documented and the results of a series of tests on the model are provided. The BRIND model simulates a 1/12 ha forest stand by computing the growth of each individual tree in the stand. It considers establishment and death of trees on a tree-by-tree basis using stochastic functions. The model also simulates the effects of prescribed fire and wildfire on the forests. The model presently is restricted to southeasterly facing slopes (moist, sheltered situations) above 850 m in altitude. The BRIND model is tested in four ways: (1) A single example simulation (for 500years) is inspected for agreement with stand dynamics in wet sclerophyll forests. (2) By varying wildfire frequency, the model is used to develop a succession diagram for forests in the alpine ash (E. delegatensis) zone of the Brindabella Range. This diagram is considered in terms of the successional patterns described for this ecological zone. (3) By subjecting the model to different climatic conditions and wildfire frequencies, a simulated altitude zonation is developed. This simulated pattern of forest types is compared with the extant forest types in the Brindabella Range. (4) The model is tested on its ability to duplicate basal area, stocking density, and average diameters for different age stands found in an independent data set. The model was found to simulate patterns of vegetation that resemble those of the forests of the Brindabella Range in both space and time. The successional pattern was found to be complex and to differ from classic theories of succession originating with Clements. Potential model applications are discussed     

Mortality of lignotuberous seedlings of Eucalyptus species after an intense fire in montane forest

The survival of lignotuberous seedlings of Eucalyptus pauciflora, E. dalrympleana and E. dives following an intense experimental fire was monitored in montane forest in the Brindabella Ranges, Australian Capital Territory. Percentage survival was the same for each species (60%), but it was shown that an individual was more likely to survive if it was large and growing vigorously before the fire. Survival was also enhanced if the individual was growing in a patch of low litter load and if it experienced a locally low fire intensity. Lignotuberous seedlings of E. dalrympleana, a species of the subgenus Symphyomyrtus, recovered more quickly than the other two species which are of the subgenus Monocalyptus. This result parallels conclusions concerning different initial growth rates between seedlings of the subgenera.     

Fire disturbance and forest structure in an old‐growth Pinus ponderosa forest,southern Cascades,USA

Questions: Did fire regimes in old‐growth Pinus ponderosa forest change with Euro‐American settlement compared to the pre‐settlement period? Do tree age structures exhibit a pattern of continuous regeneration or is regeneration episodic and related to fire disturbance or fire‐free periods? Are the forests compositionally stable? Do trees have a clumped spatial pattern and are clumps even‐ or mixed‐age? How might information from this old‐growth forest inform current restoration and management practices? Location: A 235‐ha old‐growth forest in the Ishi Wilderness, southern Cascade Mountains, California. Methods: Age, size, and spatial pattern of trees were quantified in seven stands. Fire history was reconstructed using fire scar dendrochronology. The influence of fire on stand structure was assessed by comparing fire history with age, size, and spatial structure of trees and identifying and measuring trees killed by two recent fires. Results: Species composition in plots was similar but density and basal area of tree populations varied. Age structure for P. ponderosa and Quercus kelloggii showed periods of episodic recruitment that varied among plots. Fire disturbance was frequent before 1905, with a median period between fires of 12 years. Fire frequency declined after 1905 but two recent fires (1990, 1994) killed 36% and 41% of mostly smaller diameter P. ponderosa and Q. kelloggii. Clusters of similar age trees occurred at scales of 28‐1018 m² but patches were not even‐aged. Interactions between tree regeneration and fire promoted development of uneven age groups of trees. Conclusions: Fire disturbance strongly influenced density, basal area, and spatial structure of tree populations. Fire exclusion over the last 100 years has caused compositional and structural changes. Two recent fires, however, thinned stands and created gaps favorable for Q. kelloggii and P. ponderosa regeneration. The effects of infrequent 20th century fire indicate that a low fire frequency can restore and sustain structural characteristics resembling those of the pre‐fire suppression period forest.     

Vegetation responses to wildfire in native versus exotic Arizona grassland

Abstract. Grass and herb cover, and woody plant densities were measured on 25 native and 25 exotic grassland plots in southeastern Arizona between 1984 and 1990. At least 40 yr previously, the exotic plots had been seeded with two species of lovegrasses (Eragrostis spp.) native to southern Africa. A 1987 wildfire burned 11 native and 11 exotic plots. The fire reduced cover of both native and African grasses for two post-fire growing seasons. Herb cover as a whole increased after the fire for 2 yr, although there were important differences among species. One of two dominant shrubs (Haplopappus tenuisectus) was killed by the fire, while the other (Baccharis pteronioides) was little affected. Mesquite trees (Prosopis juliflora) were killed to the ground by the fire, but 62 of 66 trees had re-sprouted to an average 48% of pre-burn height by 1990. Native and exotic grasses appeared equally tolerant of fire, probably because both evolved in fire-type ecosystems. There was no evidence that fire can be used to permanently restore the diverse native flora to species-poor plantations of the South African exotics.     

The impact of <Emphasis Type="Italic">Solanum elaeagnifolium</Emphasis>, an invasive plant in the Mediterranean,on the flower visitation and seed set of the native co-flowering species <Emphasis Type="Italic">Glaucium flavum</Emphasis>

The sprouting response types of 1,151 cork oak (Quercus suber) trees one and half years after a wildfire in southern Portugal were characterised. It was hypothesised that different response types should occur according to the following conceptual model: an increased level of damage (fire severity) on a sprouting tree that suffered a crown fire was expected to be reflected in a sequence of four alternative events, namely (a) resprouting exclusively from crown, (b) simultaneous resprouting from crown and base, (c) resprouting exclusively from base and (d) plant death. To assess whether the level of expected damage was influenced by the level of protection from disturbance, we explored the relationships between response types and tree size, bark thickness and cork stripping, using an information-theoretic approach. The more common response type was crown resprouting (68.8% of the trees), followed by plant death (15.8%), simultaneous resprouting from crown and base (10.1%) and basal resprouting (5.3%). In agreement with the conceptual model, trees which probably suffered a higher level of damage by fire (larger trees with thinner bark; exploited for cork) died or resprouted exclusively from base. On the other hand, trees that were well protected (smaller trees with thicker bark not exploited for cork) were able to rebuild their canopy through crown resprouting. Simultaneous resprouting from the crown and base was determined mainly by tree size, and it was more common in smaller trees.     

Fire history of Araucaria–Nothofagus forests in Villarrica National Park, Chile

Aim In this study we examine fire history (i.e. c. 500 yr bp to present) of Araucaria–Nothofagus forests in the Andes cordillera of Chile. This is the first fire history developed from tree rings for an Araucaria–Nothofagus forest landscape. Location The fire history was determined for the Quillelhue watershed on the north side of Lanin volcano in Villarrica National Park, Chile. The long‐lived Araucaria araucana was commonly associated with Nothofagus pumilio and N. antarctica in more mesic and drier sites respectively. Methods Based on a combination of fire‐scar proxy records and forest stand ages, we reconstructed fire frequency, severity, and the spatial extent of burned areas for an c. 4000 ha study area. We used a composite fire chronology for the purpose of determining centennial‐scale changes in fire regimes and comparing the pre‐settlement (pre‐1883) and post‐settlement fire regimes. In addition, we contrasted Araucaria and Nothofagus species as fire‐scar recorders. Results In the study area, we dated a total of 144 fire‐scarred trees, representing 46 fire years from ad 1446 to the present. For the period from ad 1696 to 2000, using fire dates from Araucaria and Nothofagus species, the composite mean fire interval varied from 7 years for all fires to 62 years for widespread events (i.e. years in which ≥ 25% of recorder trees were scarred). Sensitivity to fire was different for Araucaria and Nothofagus species. More than 98% of the fires recorded by Nothofagus species occurred during the 1900s. The lack of evidence for older fire dates (pre‐1900) in Nothofagus species was due to their shorter longevity and greater susceptibility to being killed by more severe fires. Whereas the thin‐barked N. pumilio and N. antarctica are often destroyed in catastrophic fire events, large and thick‐barked Araucaria trees typically survive. The spatial extent of fires ranged from small patchy events to those that burned more than 40% of the entire landscape (c. > 1500 ha). Main conclusions Fire is the most important disturbance shaping the Araucaria–Nothofagus landscape in the Araucarian region. The forest landscape has been shaped by a mixed‐severity fire regime that includes surface and crown fires. High‐severity widespread events were relatively infrequent (e.g. 1827, 1909 and 1944) and primarily affected tall Araucaria–N. pumilio forests and woodlands dominated by Araucaria–N. antarctica. Although there is abundant evidence of the impact of Euro‐Chilean settlers on the area, the relative influence of this settlement on the temporal pattern of fire could only be tentatively established due to the relatively small number of pre‐1900 fire dates. An apparent increase in fire occurrence is evident in the fire record during Euro‐Chilean settlement (post‐1880s) compared with the Native American era, but it may also be the result of the destruction of evidence of older fires by more recent stand‐devastating fires (e.g. 1909 and 1944). Overall, the severe and widespread fires that burned in Araucaria–Nothofagus forests of this region in 2002, previously interpreted as an ecological novelty, are within the range of the historic fire regimes that have shaped this forested landscape.     

Decomposition of standing dead trees in the southern Appalachian Mountains

Summary Decomposition of standing dead trees that were killed by fire was examined for 10 species in the Great Smoky Mountains National Park. The decrease in wood density as fire age increased was used to estimate decomposition rates. Quercus prinus had the fastest decay rate (11% yr^-1) while Pinus virginiana had the slowest decay rate (3.6% yr^-1) for standing dead wood. Decay rates were intermediate between those reported in western USA and tropics for wood.     

The role of seedling age and size in the recovery of Allosyncarpia ternata following fire

Abstract This paper examines the effects of seedling size and age on fire tolerance of Allosyncarpia ternata (Myrtaceae), a dominant tree in patches of monsoon rainforest of the wet-dry tropics in the Northern Territory, Australia. We address the following questions: how large does a seedling have to be to tolerate fire; how old does it have to be to reach this fire-tolerant size; and how can land-management authorities best manage fire regimes to maintain Allosyncarpia forest? In a field experiment, shadehouse-grown seedlings aged from 8 months to 5 years were subjected to low- and high-intensity fires in September 1994. Among 5-year-old seedlings, mortality was independent of fire intensity. However, mortality of young (8-month-old) seedlings was significantly higher in the high-intensity fire. Three-year-old seedlings behaved in an intermediate manner; their survivorship and growth were marginally favoured by low-intensity fire, rather than high-intensity fire or no fire at all, and were dependent on pre-treatment seedling height. Thus, the critical age that distinguishes fire-tolerant from fire-sensitive seedlings is somewhat more than 3 years for relatively short seedlings and somewhat less than 3 years for taller seedlings. In August 1993, a wildfire penetrated several hundred metres into Allosyncarpia forest growing on a steep, rocky escarpment, where it caused severe damage to A. ternata seedlings. More than three-quarters of the ≥ 3.5-year-old seedlings (including some that had suffered the total loss of above-ground parts) recovered during the following wet season and showed higher growth rates than their unburned neighbours. New growth was also promoted in those tall seedlings and saplings that had sustained only partial leaf scorch. In contrast, all 18-month-old seedlings were killed by the fire. Measurements of leaf-scorch height in burned Allosyncarpia forest on the escarpment indicated a general uphill decrease in fire intensity, matching trends in increasing site rockiness and decreasing fuel density. An important implication for land management is that a fire-free interval of at least 3 years following a seed-fall event is required for a new generation of A. ternata germinants to progress into the cohort of established seedlings.     

Effects of Multiple Disturbances (Fire and Hurricane) on Epiphyte Community Dynamics in a Subtropical Forest,Florida, U.S.A.1

We addressed the interacting effects of a natural large–scale fire and a subsequent major hurricane on relative positions of epiphytes in a subtropical forest. In Everglades National Park, subtropical hammocks (hardwood tree “islands”; burned and unburned) during the Ingraham Fire (1989) were surveyed for trees and epiphytic bromeliads (Tillandsia spp.) one year before, as well as one and five years after, Hurricane Andrew (1992). We measured trees (species, diameter, and status [alive/dead]) and epiphytes (species, height, host tree characteristics, substrate life status, and density). The fire decreased the height of epiphytes during the hurricane because branches and bark of trees killed by the fire were unstable epiphyte substrates in the high winds. Proportions of epiphytes on Quercus virginiana were equally increased after the hurricane in both unburned and burned hammocks; the large size and bark characteristics resulted in greater proportional survival of epiphytes on this species. During the five years following the hurricane, changes in the distributions of epiphytes generally were toward pre–hurricane distributions, but recovery was faster in unburned than burned hammocks. We conclude that disturbances that kill trees are likely to amplify the vertical reduction of epiphytes during a subsequent hurricane and that effects of a single disturbance on plant populations can be influenced by the disturbance history of the system, including different types of disturbances.     

Growth responses of an African savanna tree, <Emphasis Type="Italic">Bauhinia thonningii</Emphasis> Schumacher,to defoliation,fire and climate

This study investigated the growth responses to defoliation, fire-exposure and climate factors of a widespread Africana savanna tree, Bauhinia thonningii Schumacher, at a site in central Zambia. Experimental trees (n = 47) were either exposed to fire (n = 12) in the first half of the dry season or protected from fire (n = 35). Some of the fire-protected trees (n = 12) were subjected to artificial defoliation in two consecutive years. Phenological responses (bud break, leaf flush and leaf production) to fire-exposure and defoliation were monitored on permanently marked sample shoots over a 2-year period. Radial tree growth (diameter at 1.3 m above ground) was measured annually over a 7-year period from 1998 to 2005. During the first two years, defoliation and fire-exposure advanced the onset of bud break and leaf flush but fire-exposed trees produced significantly less leaves than did trees protected from fire, probably because scorching caused more severe shoot die-back than is normal. Leaf production was also significantly affected by experimental treatments and their interaction with year. Although treatments had significant short-term effects on radial growth, previous-year growth significantly influenced current-year growth, thereby confirming the existence of autocorrelation in the time-series growth data of B. thonningii. The interaction between previous-year growth and climate factors explained a significant proportion (25–40%, P < 0.001) of the variance in annual tree growth. Variogram models predicted that a 2-year manual defoliation treatment would shorten the longer-term growth cycle while continuous fire-exposure extended the cycle by one year. The results are useful for the management of savanna trees.     

Effects of green tree retention and prescribed burning on the crown damage caused by the pine shoot beetles (Tomicus spp.) in pine-dominated timber harvest areas

Abstract: We explored how two recently introduced methods to promote biodiversity during the timber harvest in boreal forests – green tree retention and use of fire – may affect damages caused by pine shoot beetles (Tomicus piniperda and Tomicus minor; Col., Scolytinae) in the surrounding pine forests. The experimental design included 24 separate study sites, 3–5 ha each, which were assigned to different treatments according to factorial design. Retention levels included 0, 10, 50 m³/ha and uncut controls. Twelve of the sites were burned and thus there were three replicates of each treatment combination. Old and new fallen pine shoots were counted from transects in adjacent pine‐dominated forests 2 and 3 years after the treatments. Populations of Tomicus spp. in the sites were monitored using window traps before and after the treatments, and by examining felled sample trees. Numbers of fallen shoots returned to background levels around unburned and burned clearcuts with no retention trees in 3 years after the treatments, but remained still at increased level in burned harvested sites with 10 and 50 m³ of retained trees per hectare. Numbers of fallen shoots in burned uncut forests increased in one site only, where the fire was intense enough to kill large pine trees, but the damage did not extend outside the burned area. Shoot numbers remained at such low levels (<18 000 shoots/ha) in all treatment combinations that growth losses were not likely. Numbers of egg galleries of Tomicus spp. in trees killed by fire were low, indicating that burnings that take place after the swarming of Tomicus beetles create dead wood that is not optimal for the breeding of these pests. We conclude that green tree retention and prescribed use of fire do not automatically affect populations of Tomicus spp. more than traditional forestry operations (thinnings and clearcuttings) do.     

Effects of intense wildfires on the nesting ecology of oviparous montane lizards

In midsummer 2002–2003, intense wildfires raged through the Brindabella Range of south‐eastern Australia, including sites where we have studied the ecology of scincid lizards (especially Bassiana duperreyi) for decades. Data‐loggers measured the thermal regimes experienced by eggs during these fires (revealing lethally high temperatures in nests under logs in the forest but minimal effect in nests under rocks in clearings). Eggs from forest‐clearing nests hatched successfully. Reproductive output of lizards in one area was reduced in the years post‐fire (perhaps because of inadequate food [insect] abundance to fuel female reproduction) but soon recovered. The fires reduced vegetation density and thus increased the availability of sun‐exposed rocks that serve as potential nest sites. However, the magnitude and duration of these effects differed among sites. Five years after these intense fires, canopy openness (and thus, sunlight penetration to create thermally suitable nest sites) was indistinguishable from pre‐fire conditions. Our data reveal strong spatial heterogeneity both in the immediate effects of fire on lizard reproduction and in longer‐term post‐fire changes in habitat quality. Surprisingly, these intense wildfires had only transitory and local effects on nest‐site availability for the heliothermic lizards that we study, but impacts likely were more severe on sympatric taxa that depend upon moist cool microhabitats.     

Abrupt fire regime change may cause landscape‐wide loss of mature obligate seeder forests

Obligate seeder trees requiring high‐severity fires to regenerate may be vulnerable to population collapse if fire frequency increases abruptly. We tested this proposition using a long‐lived obligate seeding forest tree, alpine ash (Eucalyptus delegatensis), in the Australian Alps. Since 2002, 85% of the Alps bioregion has been burnt by several very large fires, tracking the regional trend of more frequent extreme fire weather. High‐severity fires removed 25% of aboveground tree biomass, and switched fuel arrays from low loads of herbaceous and litter fuels to high loads of flammable shrubs and juvenile trees, priming regenerating stands for subsequent fires. Single high‐severity fires caused adult mortality and triggered mass regeneration, but a second fire in quick succession killed 97% of the regenerating alpine ash. Our results indicate that without interventions to reduce fire severity, interactions between flammability of regenerating stands and increased extreme fire weather will eliminate much of the remaining mature alpine ash forest.     

Above-ground biomass and structure of pristine Siberian Scots pine forests as controlled by competition and fire

The study presents a data set of above-ground biomass (AGB), structure, spacing and fire regime, for 24 stands of pristine Siberian Scots pine (Pinus sylvestris) forests with lichens (n = 20) or Vaccinium/mosses (n = 4) as ground cover, along four chronosequences. The stands of the “lichen” site type (LT) were stratified into three chronosequences according to stand density and fire history. Allometric equations were established from 90 sample trees for stem, coarse branch, fine branch, twig and needle biomass. The LT stands exhibited a low but sustained biomass accumulation until a stand age of 383 years. AGB reached only 6–10 kg_dw m⁻² after 200 years depending on stand density and fire history compared to 20 kg_dw m⁻² in the “Vaccinium” type (VT) stands. Leaf area index (LAI) in the LT stands remained at 0.5–1.5 and crown cover was 30–60%, whereas LAI reached 2.5 and crown cover was >100% in the VT stands. Although nearest-neighbour analyses suggested the existence of density-dependent mortality, fire impact turned out to have a much stronger effect on density dynamics. Fire scar dating and calculation of mean and initial fire return intervals revealed that within the LT stands differences in structure and biomass were related to the severity of fire regimes, which in turn was related to the degree of landscape fragmentation by wetlands. Self-thinning analysis was used to define the local carrying capacity for biomass. A series of undisturbed LT stands was used to characterise the upper self-thinning boundary. Stands that had experienced a moderate fire regime were positioned well below the self-thinning boundary in a distinct fire-thinning band of reduced major axis regression slope −0.26. We discuss how this downward shift resulted from alternating phases of density reduction by fire and subsequent regrowth. We conclude that biomass in Siberian Scots pine forests is strongly influenced by fire and that climate change will affect ecosystem functions predominantly via changes in fire regimes. Received: 2 July 1998 / Accepted: 10 June 1999     

Prescribed Fire Effects on Wintering,Bark-Foraging Birds in Northern Arizona

ABSTRACT We examined effects of prescribed fire on 3 wintering, bark-foraging birds, hairy woodpeckers (Picoides villosus), pygmy nuthatches (Sitta pygmaea), and white-breasted nuthatches (S. carolinensis), in ponderosa pine (Pinus ponderosa) forests of northern Arizona, USA. During winters of 2004–2006, we compared bird density, foraging behavior, and bark beetle activity among burned treatment and unburned control units. Hairy woodpecker density was 5 times greater in burn units, whereas white-breasted nuthatches and pygmy nuthatches had similar densities between treatments. Compared to available trees, trees used by foraging hairy woodpeckers had 9 times greater odds of having bark beetles in control units and 12 times greater odds in burn units. Tree diameter appeared to be the main factor bark-foraging birds used in selecting winter foraging trees. Our results suggest that forest managers can use prescribed fire treatments without detrimental effects to wintering nuthatches, while providing additional food to hairy woodpeckers.     

Combining population genetics,species distribution modelling and field assessments to understand a species vulnerability to climate change

Climate change is recognized as a major threat to biodiversity. Multidisciplinary approaches that combine population genetics and species distribution modelling to assess these threats and recommend conservation actions are critical but rare. Combined, these methods provide independent verification and a more compelling case for developing conservation actions. This study integrates these data streams together with field assessments and spatial analyses to develop future genetic resource management recommendations. The study species was Callistemon teretifolius (Needle Bottlebrush), a shrub species endemic to the Mount Lofty and Flinders Ranges, South Australia, and potentially vulnerable to climate change. Chloroplast microsatellite and Amplified Fragment Length Polymorphism data were combined with species distribution modelling (MaxEnt), spatial analysis and field assessment to evaluate climate change vulnerability. Two major genetic groups were identified (Mount Lofty and Flinders Ranges). Populations in the Flinders Ranges, especially the Southern Flinders Ranges exhibited the highest genetic diversity, indicating a possible genetic refugium. Lower genetic diversity to the south in the Mount Lofty Ranges and north in the Gammon Ranges may be due to post‐glacial expansion into these areas from the Flinders Ranges or loss of alleles. Low levels of contemporary gene flow were identified, which suggests Callistemon teretifolius may have a limited capacity to respond to climate change through migration. Range restrictions were predicted for all future climates, especially in the north. It is likely that C. teretifolius will be adversely affected by climate change, due to limited gene flow, predicted range restriction and loss of suitable habitat. The Southern Flinders Ranges should be a priority for conservation because it contains the highest number of individuals and genetic diversity. We recommend monitoring and adaptive management involving restoration in the Southern Flinders Ranges, potentially incorporating genetic translocations from other areas to capture diversity, to assist C. teretifolius to adapt to climate change.     

Shoot regeneration after fire or freezing temperatures and its relation to plant life-form for some heathland species

Shoot regeneration after prescribed burning or following the freezing temperatures of winter was monitored for nineteen heathland species present in an Arctostaphyleto-Callunetum community in northeast Scotland. Species whose renewal buds were near the surface of the ground started to grow earlier in the spring than species with renewal buds above the surface, but grouping species according to the position of their renewal bud (i.e. their life-form) did not account for all of the interspecific variation apparent. In the case of shoot regeneration after fire, species whose renewal buds were destroyed by fire because they were above-ground started to regenerate about the same time as species with belowground buds, protected from fire, but reached their maximum frequency of occurrence later. Grouping species by life-form was of limited value as a means of interpreting this interspecific variation in the timing of shoot regeneration after fire. It would be unwise to use plant life-form as the sole basis for interpreting or predicting a species' response to temperature stress when extreme temperatures occur regularly, as they do in heathland. The possible use of other plant traits to interpret and predict interspecific variation in the regeneration rate of heathland plants is discussed.Nomenclature follows Tutin et al. (1964–1980) for vascular plants. Acknowledgements. The Nature Conservancy Council and Mr J. J. Humphries kindly allowed Dinnet Moor to be used for the work presented here. One of us (RJR) received financial support for field work from the Natural Sciences and Engineering Research Council of Canada.     

Regeneration of N.W. African Pinus halepensis forests following fire

Pinus halepensis forests of N.W. Algeria are subjected to frequent fires. During the fire the aboveground parts of plants are completely burned but only a few species are killed. Most perennial herb and shrub species survive owing to their underground organs and regenerate vegetatively in the next moist period. The semi-shrubs regenerate both vegetatively and from seeds. The most intensive growth of the shrub layer occurs during the first 2 years and in the 5th year, it reaches a height of 1–1.5 m. Pinus halepensis is completely killed by the fire and it regenerates from seeds only. The regeneration is retarded during the first 2–3 years, apparently by competition of the rapidly developing shrubs and semi-shrubs with P. halepensis. In the following years, there is a more rapid increase in both density and height, although by the 5th year after fire, the height does not exceed 0.5 m. The young trees overtop the shrub layer between 10 and 15 years after fire. The increase in density and cover supress the lower layers, in particular the herb layer. The reduction in density of trees in the following decades enables the herb layer to reconstitute its composition and cover.This process of regeneration resembles forest growth cycles rather than a secondary succession. The shrub and herb layers maintain their identity as they are mostly formed of the same individuals as before the fire; they merely regenerated their aboveground organs. Only the tree layer regenerates anew after the fire.     

How do slow‐growing,fire‐sensitive conifers survive in flammable eucalypt woodlands?

Question: To what extent do low flammability fuel traits enhance the survival and persistence of fire‐sensitive (slowing‐growing, non‐serotinous, non‐resprouting) dominant trees in highly flammable landscapes, under varying fire‐weather conditions? Location: Mixed forests co‐dominated by flammable Eucalyptus species and fire‐sensitive Callitris glaucophylla in Pilliga State Forest, southeast Australia. Methods: The influence of vegetation composition (relative abundance of Callitris and flammable Eucalyptus) on fire intensity and survival of fire‐sensitive Callitris was assessed across gradients of Callitris abundance in mixed Eucalyptus–Callitris forests that burned under low‐moderate and extreme fire‐weather conditions. Results: In areas that burned under low‐moderate fire‐weather conditions, as Callitris abundance increased, fire intensity declined and Callitris survival increased (46%). By comparison, in extreme fire‐weather conditions, lower fire intensity at higher levels of Callitris abundance, was not sufficient to increase Callitris survival (4%). Callitris survival was also positively related to trunk diameter. Ground fuel type, but not biomass, varied with vegetation composition. Conclusions: These results demonstrate that flammable feedbacks, mediated by low flammability fuel traits of dominant trees, can provide an important mechanism for enhancing the survival and persistence of slow‐growing, non‐serotinous, non‐resprouting, fire‐killed trees in highly flammable landscapes. By modifying vegetation and fuel structure, patches of fire‐sensitive Callitris reduce fire intensity, and thereby reduce Callitris mortality, enhancing population persistence. However, this feedback loop is insufficient to ensure Callitris survival under extreme fire‐weather conditions, when fire intensity is greater. After burning, stands remain vulnerable to future fires, until trees grow large enough to modify fuel levels and reduce stand flammability.     

Pyric tree spatial patterning interactions in historical and contemporary mixed conifer forests,California, USA

Tree spatial patterns in dry coniferous forests of the western United States, and analogous ecosystems globally, were historically aggregated, comprising a mixture of single trees and groups of trees. Modern forests, in contrast, are generally more homogeneous and overstocked than their historical counterparts. As these modern forests lack regular fire, pattern formation and maintenance is generally attributed to fire. Accordingly, fires in modern forests may not yield historically analogous patterns. However, direct observations on how selective tree mortality among pre‐existing forest structure shapes tree spatial patterns is limited. In this study, we (a) simulated fires in historical and contemporary counterpart plots in a Sierra Nevadan mixed‐conifer forest, (b) estimated tree mortality, and (c) examined tree spatial patterns of live trees before and after fire, and of fire‐killed trees. Tree mortality in the historical period was clustered and density‐dependent, because trees were aggregated and segregated by tree size before fire. Thus, fires maintained an aggregated distribution of tree groups. Tree mortality in the contemporary period was widespread, except for dispersed large trees, because most trees were a part of large, interconnected tree groups. Thus, postfire tree patterns were more uniform and devoid of moderately sized tree groups. Postfire tree patterns in the historical period, unlike the contemporary period, were within the historical range of variability identified for the western United States. This divergence suggests that decades of forest dynamics without significant disturbances have altered the historical means of pyric pattern formation. Our results suggest that ecological silvicultural treatments, such as forest restoration thinnings, which emulate qualities of historical forests may facilitate the reintroduction of fire as a means to reinforce forest structural heterogeneity.