Post‐fire seed predation: Does distance to unburnt vegetation matter?

Human‐induced changes to fire regimes result in smaller, more patchy fires in many peri‐urban areas, with a concomitant increase in potential edge effects. In sclerophyll vegetation, many structurally dominant serotinous plants rely on the immediate post‐fire environment for recruitment. However, there is little information about how fire attributes affect seed predation or recruitment for these species. We examined the influence of distance to unburnt vegetation on post‐dispersal seed predation for five serotinous species from sclerophyll vegetation in the Sydney region, south‐eastern Australia; Banksia serrata L.f., Banksia spinulosa Sm. var. spinulosa, Hakea gibbosa (Sm.) Cav., Hakea teretifolia (Salisb.) Britten (all Proteaceae) and Allocasuarina distyla (Vent.) L. Johnson (Casuarinaceae). We used cafeteria trials and differential exclusion of vertebrates and invertebrates to test whether rates of seed removal for these five species differed among (i) unburnt, (ii) burnt‐edge (approx. 10 m from unburnt vegetation) and (iii) burnt‐interior (approx. 100 m from unburnt vegetation) locations. When all animals had access to seeds, seeds were removed at lower rates from burnt‐interior areas than from other locations. Vertebrates (small mammals) showed this pattern markedly the first time the experiment was run, but in a repeat trial this effect disappeared. Rate of seed removal by invertebrates differed among plant species but we did not detect any such differences for removal by vertebrates. Overall rates of seed removal also differed significantly between the two fires studied. Our results indicate that small mammal seed predation can be substantial for large‐seeded serotinous shrubs, and that differences in the perimeter: area ratio, severity or size of a fire are likely to affect seed predation.     

Is the reassembly of an arid spider assemblage following fire deterministic?

Fire is a common disturbance in many ecosystems, including arid Australia. Understanding whether fauna respond in a deterministic manner towards a single end‐point, or to multiple states, is of crucial importance for conservation management. Why different taxa or assemblages display single or multiple end‐points is also important to develop a synthetic theory of succession. To examine the post‐fire changes in assemblages of spiders, we established a chronosequence study in spinifex habitat of central Western Australia. Ground‐active spiders were pitfall‐trapped over nine months in sites representing experimental fires (0 and 0.5 years post‐fire) and wildfires (3, 5, 8 and 20 years post‐fire). There were significant non‐linear changes in species richness, evenness and composition of spiders with increasing post‐fire age. For all three measures, the assemblage appeared highly deterministic, converging towards the long unburnt state. Similarity in richness, evenness and species composition to the 20‐year‐old sites all increased with increasing time since fire (3–8 years). However, experimentally burnt sites did not neatly fit this sequence. We consider two alternative hypotheses to explain this second trajectory: inertia within the system or the rapid migration and recolonization from nearby surrounding unburnt areas. Analyses indicated that half of the 179 species had significant preferences for, or were restricted to, particular post‐fire ages. This suggests that adequate pyrodiversity, both in terms of post‐fire ages and/or scale and intensity of fires, may be important for the conservation of spiders in this habitat. However, owing to the high number of singletons and low indicator values, the significance of this result for conservation management remains equivocal. Despite this, the high degree of determinism provides hope that managers can develop a good predictive understanding of post‐fire successional changes in spider assemblages in arid Australia.     

Aerial dispersal ability does not drive spider success in a crop landscape

1. Although spiders can colonise ecosystems by air, dispersal capabilities differ among spider species. Web‐building spiders are thought to balloon at higher rates than hunting spiders. Spider success in agricultural systems may also depend on habitat preferences. Few studies have examined the success of aerially dispersing spiders in crop systems, and information about the dispersal capabilities of spiders in putative source habitats is limited. 2. Spiders were monitored in the air and on the foliage of vineyards and adjacent oak woodland in order to compare the aerial spider faunas between these disparate habitats and to determine whether highly dispersive species contributed disproportionately to the spider community in vineyards. 3. The results show that most aerially dispersing spiders in both habitats were web‐building dwarf spiders, Erigone spp. (Linyphiidae), although hunting spiders were also well represented in the air, especially in oak woodland. Most woodland spiders in the air appeared to be residents of oak woodland and probably dispersed only short distances. 4. Conversely, only a subset of the aerial spider fauna established in vineyards in high numbers. Spiders that dominated the aerial fauna were under‐represented on vineyard foliage, whereas several hunting spiders dispersed aerially at low rates but dominated vineyard spider composition. 5. These results suggest that aerial dispersal ability may allow spiders to reach crop systems, but that establishment depends on habitat preferences and/or competitive ability.     

Fire in the Suburbs: Ecological Impacts of Prescribed Fire in Small Remnants of Longleaf Pine (Pinus palustris) Sandhill

Abstract Logging, fire suppression, and urbanization have all contributed to the serious decline and fragmentation of Pinus palustris (longleaf pine) ecosystems in the southeastern United States. Effective management of the remaining patches of these pyrogenic communities must incorporate periodic low‐intensity fires, even where they are located on private lands in populated urban and suburban areas. To explore the effects of fire and its potential use for restoration and management of small fragments surrounded by suburban development, we conducted growing season prescribed fires in remnant longleaf pine sandhill patches in the suburbs of Gainesville, Florida. Density and composition of hardwoods were surveyed pre‐burn and 1 and 9 months post‐burn. Woody stem density decreased in the burn plots, predominantly in the smaller size classes. Flowering responses of forbs and small shrubs were surveyed six times post‐burn for 1 year. Overall, the burns did not yield greater densities of flowering stems, but burn patches had higher species richness and diversity than control patches. In addition, there were consistently greater numbers of “showy flowered” sandhill species in flower in burn patches relative to controls. The results of this research demonstrate that prescribed fire can be used for restoration and management of small remnants of longleaf pine sandhill in suburban neighborhoods. It is also clear that although a single prescribed burn can be effective, it will take more than one burn to attain desired restoration goals in degraded longleaf remnants.     

Evaluation of the effectiveness of an early peripheral burning strategy in controlling wild fires in north‐western Zimbabwe

A review of the occurrence of wild fires in Sengwa Wildlife Research Area (SWRA), Zimbabwe, is presented for the period 1965–1993. The effectiveness and desirability of early burning of peripheral areas introduced in 1979 are evaluated. More than 75% of wild fires occurred between July and October, 48.6% of which originated from communal lands. Early burning of peripheral areas led to significant reductions in extent of areas burnt, from annual mean areas of 115 km² (1965–1978) to 11 km² (1979–1993) because of effective control of fires, which originated from communal lands. Some areas did not burn at all after 1979, and the overall probability of burning dropped from 0.484 to 0.187. Whilst it may be desirable to keep fires out of SWRA in the short term, fuel build‐ups increase the fire hazard resulting in negative consequences on biodiversity in the long term. Consideration should be given to combine peripheral burning with low‐intensity prescribed burning of selected blocks to keep a semblance of natural fire regimes to ensure the maintenance of biodiversity while simultaneously reducing the fire‐hazard. An integrated fire management plan should be put in place for SWRA.     

Spiders provide important resources for an endangered lizard

Conservation management requires knowledge of how a target species interacts with other species. Some relatively common species can modify the environment to the advantage of rarer, endangered species. Thus, local enhancement of those common species can positively influence remaining populations of the rarer species. The endangered pygmy bluetongue lizard Tiliqua adelaidensis inhabits burrows that are constructed by lycosid and mygalomorph spiders. We recorded 490 burrows in a 1 ha plot at the end of one season, and then observed at regular intervals the formation and loss of burrows, and the changes in occupancy status of each burrow over the next season. We found spiders in 94% of all newly constructed burrows and deduced that they had built the burrows. We found no evidence that lizards dug new burrows or deepened existing burrows. The numbers of both lizards and spiders in the burrows declined over the spring and summer, with lizards moving from their burrows more often early in the season than later. However, there was no strong trend for lizards to replace spiders in burrows. In fact, lizards tended to occupy deeper burrows than spiders, suggesting little negative impact of lizards on spiders. However, spiders had a positive impact on lizards by providing the refuge burrows central for lizard survival. Although lizards readily accept artificial burrows, long-term conservation for the lizards must include viable spider populations to maintain a supply of suitable burrow refuges.     

Fire frequency and biodiversity conservation in Australian tropical savannas: implications from the Kapalga fire experiment

Abstract Every year large proportions of northern Australia's tropical savanna landscapes are burnt, resulting in high fire frequencies and short intervals between fires. The dominant fire management paradigm in these regions is the use of low‐intensity prescribed fire early in the dry season, to reduce the incidence of higher‐intensity, more extensive wildfire later in the year. This use of frequent prescribed fire to mitigate against high‐intensity wildfire has parallels with fire management in temperate forests of southern Australia. However, unlike in southern Australia, the ecological implications of high fire frequency have received little attention in the north. CSIRO and collaborators recently completed a landscape‐scale fire experiment at Kapalga in Kakadu National Park, Northern Territory, Australia, and here we provide a synthesis of the effects of experimental fire regimes on biodiversity, with particular consideration of fire frequency and, more specifically, time‐since‐fire. Two recurring themes emerged from Kapalga. First, much of the savanna biota is remarkably resilient to fire, even of high intensity. Over the 5‐year experimental period, the abundance of most invertebrate groups remained unaffected by fire treatment, as did the abundance of most vertebrate species, and we were unable to detect any effect of fire on floristic composition of the grass‐layer. Riparian vegetation and associated stream biota, as well as small mammals, were notable exceptions to this general resilience. Second, the occurrence of fire, independent of its intensity, was often the major factor influencing fire‐sensitive species. This was especially the case for extinction‐prone small mammals, which have suffered serious population declines across northern Australia in recent decades. Results from Kapalga indicate that key components of the savanna biota of northern Australia favour habitat that has remained unburnt for at least several years. This raises a serious conservation concern, given that very little relatively long unburnt habitat currently occurs in conservation reserves, with most sites being burnt at least once every 2 years. We propose a conservation objective of increasing the area that remains relatively long unburnt. This could be achieved either by reducing the proportion of the landscape burnt each year, or by setting prescribed fires more strategically. The provision of appropriately long unburnt habitat is a conservation challenge for Australia's tropical savanna landscapes, just as it is for its temperate forests.     

Rapid Recovery of an Urban Remnant Reptile Community following Summer Wildfire

Reptiles in urban remnants are threatened with extinction by increased fire frequency, habitat fragmentation caused by urban development, and competition and predation from exotic species. Understanding how urban reptiles respond to and recover from such disturbances is key to their conservation. We monitored the recovery of an urban reptile community for five years following a summer wildfire at Kings Park in Perth, Western Australia, using pitfall trapping at five burnt and five unburnt sites. The reptile community recovered rapidly following the fire. Unburnt sites initially had higher species richness and total abundance, but burnt sites rapidly converged, recording a similar total abundance to unburnt areas within two years, and a similar richness within three years. The leaf-litter inhabiting skink Hemiergis quadrilineata was strongly associated with longer unburnt sites and may be responding to the loss of leaf litter following the fire. Six rarely-captured species were also strongly associated with unburnt areas and were rarely or never recorded at burnt sites, whereas two other rarely-captured species were associated with burnt sites. We also found that one lizard species, Ctenotus fallens, had a smaller average body length in burnt sites compared to unburnt sites for four out of the five years of monitoring. Our study indicates that fire management that homogenises large areas of habitat through frequent burning may threaten some species due to their preference for longer unburnt habitat. Careful management of fire may be needed to maximise habitat suitability within the urban landscape.     

Spider assemblages in bird burrows

The arachnofauna of bird burrows, which are excavated in the soil, is incompletely understood. The bird burrows have a potential to serve as refugia for cavity-adopting spider species particularly in anthropogenic habitats formed by sand mining, which otherwise suffer from a limited availability of other types of cavities. We hypothesized that the presence of abundant food resources and safe shelter in bird burrows excavated in the soil allow the existence of specialized assemblage of spiders, similarly to those known from cavities and nests made by other birds and mammals. Here we examined 353 burrows that had been previously occupied by Riparia riparia, Merops apiaster or Passer montanus. The burrows were examined in early May and early September in 24 Czech sand pits and construction sites. The burrows hosted a species-rich assemblage of spiders that, however, occurred at low abundances. The spiders were represented prevalently by species known to have distributions centered in anthropogenic and urban habitats, including species that were never observed outside of heated buildings in the study area and species that only were previously known from mammalian burrows and loess and karstic soil crevices. Spider assemblages strongly differed between bird burrows and cavities and nests made by other birds and mammals. The species composition and overall low abundance of spiders in bird burrows was unexpected and was in strong contrast to previous observations of spider assemblages in cavities and nests made by other birds and mammals. Concluded, we rejected the initial hypothesis and, instead, we have shown that bird burrows are rarely occupied by spiders and if occupied, the spider species that adopt old bird burrows and the nests inside of them predominantly consist of species known to have their distribution centered to anthropogenic and urban habitats.     

Bromeliads provide shelter against fire to mutualistic spiders in a fire‐prone landscape

1. A key challenge in the study of mutualistic interactions is understanding sources of variation that strengthen or weaken these interactions. In spider–plant mutualisms, spiders benefit plants by improving plant nutrition and protecting plants from herbivory. Although the benefits of plants to spider growth and survival are often claimed, they are rarely demonstrated. 2. In this study, empirical evidence is provided that bromeliads (Bromelia balansae, Bromeliaceae) are essential for the resilience of the mutualistic bromeliad‐living jumping spider populations (Psecas chapoda, Salticidae) after a fire event, sheltering spiders from the heat of the flames. 3. Spider populations were compared before and after a natural fire event and it was shown that spiders of different ages survived the fire. The survival of such individuals allowed the population of P. chapoda spiders to recover rapidly, returning to pre‐fire levels in 5 months. 4. Bromeliads reduced the susceptibility of P. chapoda spiders to burning, and this mutualistic relationship contributed to the resilience of the spider population after a fire event. It is suggested that frequent fires in fire‐prone landscapes may have strengthened this spider–plant relationship, contributing to the maintenance and evolution of this association.     

Can burning restrict eucalypt invasion on grassy balds?

Abstract: Eucalyptus tereticornis seedlings occurring on the edges of grassy balds on the Bunya Mountains were burnt by four separate fires. From the results, a logistic model demonstrated that lignotuber size was positively related and fire temperature negatively related to survivorship. While mortality was high for young seedlings there was no mortality of 5‐year old survivors from these trials subject to repeat burning. The model predicted that burning every 2 years will not substantially limit seedling establishment. This prediction was strengthened by results verifying that management fires on the grassy balds are generally of low intensity. Fire intensity is weakly related to a Fire Danger Index, indicating that the timing of burning in relation to weather conditions will not substantially enhance opportunities for more intense fires. Thus, even with biennial burning under optimal conditions eucalypt forest will replace grassy balds where they adjoin. Regular burning by aborigines may have maintained grassy bald‐rainforest boundaries, but not boundaries with eucalypt forest. Seed dispersal and migration barriers may have limited the expansion of eucalypt forest. It is concluded that under current conditions the long‐term preservation of the grassy balds is only possible where they are entirely surrounded by rainforest and are regularly burnt.     

The effects of development,vegetation‐type conversion,and fire on low‐elevation Southern California spider assemblages

California sage scrub (CSS), a native ecosystem type of low‐elevation areas of Southern California, is increasingly threatened by urban development, altered fire regimes, and vegetation‐type conversion to non‐native grasslands. Using pitfall traps, we examined how suburbanization, type conversion, and fire influence ground‐dwelling spider assemblages in eastern Los Angeles County, CA, by surveying spiders in three habitats (CSS, non‐native grasslands, and suburban areas) before and after a fire that occurred in a small portion of our study site. Spider assemblages in the suburban habitat differed from those in CSS and non‐native grassland habitats, but CSS and grassland assemblages did not significantly differ. This suggests that the urban development, but not vegetation‐type conversion to non‐native grasslands, has significant effects on ground‐dwelling spider assemblages. Fire had no observable effect on assemblages. Because ground‐dwelling spiders were not impacted by fire and type conversion, increased fire frequencies, which often result in the establishment of non‐native grasses, may not deleteriously influence this animal group, a differing pattern from other taxonomic groups. However, the rapid urban development occurring in low‐elevation areas of Southern California means that species requiring non‐suburban sites for their survival (15 species, 24.1%) may be threatened and require conservation assessment.     

Simulating fire regimes in human-dominated ecosystems: Iberian Peninsula case study

A new fire model is proposed which estimates areas burnt on a macro‐scale (10–100 km). It consists of three parts: evaluation of fire danger due to climatic conditions, estimation of the number of fires and the extent of the area burnt. The model can operate on three time steps, daily, monthly and yearly, and interacts with a Dynamic Global Vegetation Model (DGVM), thereby providing an important forcing for natural competition. Fire danger is related to number of dry days and amplitude of daily temperature during these days. The number of fires during fire days varies with human population density. Areas burnt are calculated based on average wind speed, available fuel and fire duration. The model has been incorporated into the Lund‐Potsdam‐Jena Dynamic Global Vegetation Model (LPJ‐DGVM) and has been tested for peninsular Spain. LPJ‐DGVM was modified to allow bi‐directional feedback between fire disturbance and vegetation dynamics. The number of fires and areas burnt were simulated for the period 1974–94 and compared against observations. The model produced realistic results, which are well correlated, both spatially and temporally, with the fire statistics. Therefore, a relatively simple mechanistic fire model can be used to reproduce fire regime patterns in human‐ dominated ecosystems over a large region and a long time period.     

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.     

Crossing the uncrossable: novel trans‐valley biogeographic patterns revealed in the genetic history of low‐dispersal mygalomorph spiders (Antrodiaetidae,Antrodiaetus) from California

Antrodiaetus riversi is a dispersal‐limited, habitat‐specialized mygalomorph spider species endemic to mesic woodlands of northern and central California. Here, we build upon prior phylogeographic research using a much larger geographic sample and include additional nuclear genes, providing more detailed biogeographic insights throughout the range of this complex. Of particular interest is the uncovering of unexpected and replicated trans‐valley biogeographic patterns, where in two separate genetic clades western haplotypes in the California south Coast Ranges are phylogenetically closely related to eastern haplotypes from central and northern Sierran foothills. In both instances, these trans‐valley phylogenetic patterns are strongly supported by multiple genes. These western and eastern populations are currently separated by the Central Valley, a well‐recognized modern‐day and historical biogeographic barrier in California. For one clade, the directionality is clearly northeast to southwest, and all available evidence is consistent with a jump dispersal event estimated at 1.2–1.3 Ma. During this time period, paleogeographic data indicate that northern Sierran rivers emptied to the ocean in the south Coast Ranges, rather than at the San Francisco Bay. For the other trans‐valley clade genetic evidence is less conclusive regarding the mechanism and directionality of biogeographic exchange, although the estimated timeframe is similar (approximately 1.8 Ma). Despite the large number of biogeographic studies previously conducted in central California, to the best of our knowledge no prior studies have discussed or revealed a northern Sierran to south Coast Range biogeographic connection. This uniqueness may reflect the low‐dispersal biology of mygalomorph spiders, where ‘post‐event’ gene exchange rarely erases historical biogeographic signal.     

Potential role of ignition management in reducing unplanned burning in Arnhem Land,Australia

Fire management attempts to coerce fire into a desired regime using three primary strategies: prescribed burning, fire suppression and ignition management. The West Arnhem Land Fire Abatement project (WALFA), where prescribed Early Dry Season burning is used to reduce unplanned Late Dry Season burning, is heralded as model for prescribed burning. However, a previous analysis found that Late Dry Season area burnt in WALFA had been reduced further than would be expected based purely on the Early Dry Season treatment area. This study investigated whether treatment has reduced the number and size of unplanned fires. Daily burnt area mapping from MODIS satellite sensors was used to identify individual fires to compare fire activity before and after management was introduced in WALFA (2005) and in a control region in East Arnhem Land. Late Dry Season area burnt reduced after treatment in WALFA but also in the control region. The number of fires in August–October increased after treatment. There is a period from early August until late September when human ignitions can cause huge fires. Late Dry Season area burnt was strongly influenced by the size of the largest single fire and only weakly by the number of ignitions. Early Dry Season area burnt had modest effects on both the number and maximum size of Late Dry Season fires. Eliminating the largest fire in each 1600 km² sample block would have halved the total Late Dry Season area burnt. A similar reduction could be obtained from a 14% annual treatment with Early Dry Season fire, but this may not reduce the overall area burnt. If overall fire frequency is the main threat to biodiversity in the savannas, then the best solution will be to prevent the small subset of fires that have the potential to become very large.     

Effects of Differences in Prescribed Fire Regimes on Patchiness and Intensity of Fires in Subtropical Savannas of Everglades National Park, Florida

Abstract We investigated effects of fire frequency, seasonal timing, and plant community on patchiness and intensity of prescribed fires in subtropical savannas in the Long Pine Key region of Everglades National Park, Florida (U.S.A.). We measured patchiness and intensity in different plant communities along elevation gradients in “fire blocks.” These blocks were prescribed burned at varying times during the lightning season and at different frequencies between 1995 and 2000. Fire frequency, seasonal timing, and plant community all influenced the patchiness and intensity of prescribed fires. Fires were less patchy and more intense, probably because of drier conditions and pyrogenic fuels, in higher elevation plant communities (e.g., high pine savannas) than in lower elevation communities (e.g., long‐hydroperiod prairies). In all plant communities fires became increasingly patchy and less intense as the wet season progressed and moisture accumulated in fuels. Frequent prescribed fire resulted in increased patchiness but a wider range of intensities; higher intensities appeared to result from regrowth of more flammable vegetation. Our study suggests that frequent early lightning season prescribed fires produce a wider range of post‐fire conditions than less frequent late lightning season prescribed fires. Our study also suggests that natural early lightning season fires readily carried through pine savannas and short‐hydroperiod prairies, but lower elevation long‐hydroperiod prairies functioned as firebreaks. Natural fires probably crossed these firebreaks only during drier years, potentially producing large landscape‐level fires. Knowledge of how patchily and intensely fires burn across a savanna landscape should be useful for developing landscape‐level fire management.     

Co‐occupancy of spider‐engineered burrows within a grassland community changes temporally

Burrow‐digging organisms act as ecosystem engineers, providing potential habitat to other organisms. In the Mid North region of South Australia, wolf and trapdoor spiders in fragmented grassland communities provide this service. Pygmy bluetongue lizards are an endangered skink, endemic to these grasslands. The lizards obligatorily use burrows dug by these spider groups as refuges, basking sites and ambush points. We investigated the occupancy of these spider burrows by lizards and other organisms within the grassland community, identifying the occasions that burrows were shared by multiple taxa. We found that the lizards and trapdoor spiders are predominantly solitary, while wolf spiders co‐shared burrows more frequently with either weevils or snails. There were numerous taxa that were found to regularly co‐share with other taxa, particularly snails, centipedes and weevils. There was a strong temporal influence on burrow sharing, with most co‐sharing occurring late in summer. This study provides an insight into the use of burrows by the lizards and co‐existing taxa within these grassland communities. The dynamics of burrow‐use by other taxa have the potential to influence long‐term conservation of these lizards as burrow availability is crucial to their survival in these grasslands.