Unburned Plants Research Articles

Functional mechanisms underlying the persistence of Opuntia ficus-indica in a Mediterranean-type ecosystem after fire

Changes in fire regime can favor invasive plants in Mediterranean-type ecosystems. The goal of this experiment was to understand the post-fire dynamics of the invasive cactus, Opuntia ficus-indica, by assessing the contribution and impact of clonal propagation and sexual reproduction on the recruitment of this species after fire. The number of O. ficus-indica new clones and seed-derived plants was estimated after a burn event in a natural area located in the western Mediterranean (Catalonia, NE Spain). Functional stress markers, relative growth rate, and contents of both growth- and stress-related phytohormones were measured. Furthermore, remaining plants damaged by fire were evaluated regarding fruit size, seed number, and viability, as well as other reproductive traits. Results showed that 95 % of the new recruits in the burned area were clones. Clones showed a higher water and chlorophyll content than seed-derived plants. The relative growth rate was consequently higher in clones than in seed-derived plants, which was also associated with higher contents of growth-related hormones (cytokinins and gibberellins) in the former. Furthermore, seeds produced by burned plants exhibited a thicker funicular envelope compared to seeds from unburned plants. It is concluded that, although clonal propagation was the main reproductive strategy observed after fire, its combination with sexual reproduction and efficient physiological strategies of survival guarantees persistence of this invasive plant species in burned areas due to an effective and fast recovery in cactus cover in the short term while contributing to the genetic variability in the population in the long term.

Beyond fire: Flower production naturally occurs and is also influenced by leaf removal in a Neotropical savanna herb.

Several herbaceous species exhibit mass flowering after fires in Neotropical savannas. However, unequivocal evidence of fire dependency and the consequences for plant reproduction are lacking. In nutrient-poor fire-prone savannas, the damage caused by fire and by other means (e.g., leaf removal, but not necessarily having a negative impact) constrains the maintenance and expansion of plant population by affecting the ability of individuals to recover. Therefore, the compensatory responses of plants to both damages should be convergent in such environments. Using Bulbostylis paradoxa-reported to be fire-dependent to flower-as a model, we investigated the role of fire and leaf removal in anticipating the flowering and reproduction periods, and its possible consequences on seedling establishment. We monitored 70 burned individuals, 70 damaged/clipped, and 35 without damage to estimate time for flowering, seed quality and germination parameters. To expand our sampling coverage, we examined high-resolution images from herbarium collections in the SpeciesLink database. For each herbarium image, we recorded the presence or absence of a fire scar, the month of flowering, and the number of flowering stalks. Bulbostylis paradoxa was fire-stimulated but not dependent on fire to flower, with 65.7% of the individuals flowering in the burned area, 48.6% in the clipped, and 11.4% in the control. This was consistent with the analysis of the herbarium images in which 85.7% of the specimens with flowers had fire scars and 14.3% did not. Burned individuals synchronized flowering and produced more viable seeds. However, the seeds might face a period of unsuitable ecological conditions after early to mid-dry season fires. Flowering of unburned plants was synchronized with the onset of the rainy season. Flexibility in flowering and vegetative reproduction by fragmentation confer to this species, and most likely other plants from the herbaceous layer, the capability of site occupation and population persistence in burned and unburned savanna sites.

Fire transforms effects of terrestrial subsidies on aquatic ecosystem structure and function.

Fire can lead to transitions between forest and grassland ecosystems and trigger positive feedbacks to climate warming by releasing CO2 into the atmosphere. Climate change is projected to increase the prevalence and severity of wildfires. However, fire effects on the fate and impact of terrestrial organic matter (i.e., terrestrial subsidies) in aquatic ecosystems are unclear. Here, we performed a gradient design experiment in freshwater pond mesocosms adding 15 different amounts of burned or unburned plant detritus and tracking the chronology of detritus effects at 10, 31, 59, and 89 days. We show terrestrial subsidies had time- and mass-dependent, non-linear impacts on ecosystem function that influenced dissolved organic carbon (DOC), ecosystem metabolism (net primary production and respiration), greenhouse gas concentrations (carbon dioxide [CO2 ], methane [CH4 ]), and trophic transfer. These impacts were shifted by fire treatment. Burning increased the elemental concentration of detritus (increasing %N, %P, %K), with cascading effects on ecosystem function. Mesocosms receiving burned detritus had lower [DOC] and [CO2 ] and higher dissolved oxygen (DO) through Day 59. Fire magnified the effects of plant detritus on aquatic ecosystem metabolism by stimulating photosynthesis and respiration at intermediate detritus-loading through Day 89. The effect of loading on DO was similar for burned and unburned treatments (Day 10); however, burned-detritus in the highest loading treatments led to sustained hypoxia (through Day 31), and long-term destabilization of ecosystem metabolism through Day 89. In addition, fire affected trophic transfer by increasing autochthonous nitrogen source utilization and reducing the incorporation of 15 N-labeled detritus into plankton biomass, thereby reducing the flux of terrestrial subsidies to higher trophic levels. Our results indicate fire chemically transforms plant detritus and alters the role of aquatic ecosystems in processing and storing carbon. Wildfire may therefore induce shifts in ecosystem functions that cross the boundary between aquatic and terrestrial habitats.

Life after a fiery death: Fire and plant biomass loading affect dissolved organic matter in experimental ponds.

Drier and hotter conditions linked with anthropogenic climate change can increase wildfire frequency and severity, influencing terrestrial and aquatic carbon cycles at broad spatial and temporal scales. The impacts of wildfire are complex and dependent on several factors that may increase terrestrial deposition and the influx of dissolved organic matter (DOM) from plants into nearby aquatic systems, resulting in the darkening of water color. We tested the effects of plant biomass quantity and its interaction with fire (burned vs. unburned plant biomass) on dissolved organic carbon (DOC) concentration and degradation (biological vs. photochemical) and DOM composition in 400 L freshwater ponds using a gradient experimental design. DOC concentration increased nonlinearly with plant biomass loading in both treatments, with overall higher concentrations (>56 mg/L) in the unburned treatment shortly after plant addition. We also observed nonlinear trends in fluorescence and UV-visibleabsorbance spectroscopic indices as a function of fire treatment and plant biomass, such as greater humification and specific UV absorbance at 254 nm (a proxy for aromatic DOM) over time. DOM humification occurred gradually over time with less humification in the burned treatment compared to the unburned treatment. Both burned and unburned biomass released noncolored, low molecular weight carbon compounds that were rapidly consumed by microbes. DOC decomposition exhibited a unimodal relationship with plant biomass, with microbes contributing more to DOC loss than photodegradation at intermediate biomass levels (100-300 g). Our findings demonstrate that the quantity of plant biomass leads to nonlinear responses in the dynamics and composition of DOM in experimental ponds that are altered by fire, indicating how disturbances interactively affect DOM processing and its role in aquatic environments.

Alteration of Organic Matter during Wildfires in the Forests of Southern Siberia

Large areas of forests burn annually in Siberia. Pyrogenic organic matter (PyOM) generated by wildfires acts as a stable carbon deposit and plays an important role in the global carbon cycle. Little is known about the properties of PyOM formed during fires in Siberian forests. In this work, we report the results of thermogravimetry (TG), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy applied to the study of the chemical composition, structure, and thermal stability of PyOM formed during surface and crown fires of moderate to high severity in southern Siberia. We studied the PyOM produced from the forest floor, down wood, cones, and outer bark of tree stems in Scots pine, larch, spruce, and birch forests. We calculated the thermal recalcitrance indexes (R50, Q3) based on TG/DSC data. We found that wildfires resulted in a strong decrease in thermolabile components in burned fuels, enrichment by aromatic structures, and a significant increase in thermal stability (T50) compared to unburned samples. In all the studied forests, bark PyOM revealed the highest value of T50 while forest floor PyOM had the lowest one. At the same time, our results indicated that the properties of PyOM were more strongly driven by wildfire severity than by fuel type. Overall, the thermal recalcitrance R50 index for PyOM samples increased by 9–29% compared to unburned plant residues, indicating a shift from low to intermediate carbon sequestration potential class in the majority of cases and hence less susceptibility of PyOM to biodegradation.

Characteristics of burned phytolith from representative plants in Northeast China and implications for paleo-fire reconstruction

Studies of the burned phytolith identification have provided a theoretical basis for paleo-fire reconstruction. However, as the most widely used method, the applicability of the visual identification method is still controversial due to its subjectivity. To gain a better identification of burned phytolith, this study used CIELAB color model to quantitatively analyze and distinguish the color characteristics of phytoliths from burned and unburned plant samples (n = 86) in northeast China. The results demonstrate that more than 60% of phytolith in burned plant samples appeared color changes. The burned phytolith percentages (BP/P) of different morphotypes were also with obvious differences, the phytoliths derived from hair cells and stomata have the highest BP/P values while those values of phytoliths from tracheary elements were relatively low, which may be due to the different anatomical origin of phytoliths, and the original cells closer to the outer epidermis were more prone to coloration. After measuring and comparing the chromatism values of phytoliths, it is concluded that the chromatism values of those phytoliths greater than 30 can be regarded as being exposed to fire. Moreover, the various hues from different species may be related to the flammability and combustion adequacy of plants. Finally, we proposed the phytolith morphotypes suitable for paleo-fire reconstruction in the study area according to the above results. Overall, our study provides a reliable basis for the identification of burned phytolith and a reference for reconstructing paleo-fires.

Post-fire peatland vegetation recovery: a case study in open rich fens of the Canadian boreal forest

Fire plays a major role in the structuring and functioning of boreal ecosystems. As peatlands are important components of boreal forests, the impact of fire upon these wetter ecosystems is increasingly studied, but with the focus on treed peatlands and Sphagnum-dominated bogs so far. Important fires occurring more frequently in the past decade in southern Northwest Territories (Canada) provide the opportunity to assess early post-fire vegetation regeneration in open rich fens (one, two, and five years post-fire) and to better understand early recovery succession. We aimed to (i) evaluate whether and how open rich fens are affected by fire, and (ii) describe short-term vegetation regeneration for both bryophytes and vascular species. A shift was observed between pioneer bryophytes and brown mosses between the second and fifth year post-fire. Vascular plants, especially slow-growing species and the ones reproducing mainly by seeds, recovered partially. The first bryophyte species recovering were pioneer species adapted to colonize burned environments such as Marchantia polymorpha L. or Ceratodon purpureus (Hedw.) Brid. For vascular plant species, the ones previously present and able to regrow rapidly from unburned plant structures (base of tussocks, rhizomes, roots) were represented by species like Betula glandulosa Michx. or Carex aquatilis Wahlenb. The wetter conditions and lower fuel availability of fen depressional biotopes were important factors controlling the resistance and regeneration of species associated with them.

Observations of supermicron-sized aerosols originating from biomass burning in southern Central Africa

During the 3 years of the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) campaign, the NASA Orion P-3 was equipped with a 2D stereo (2D-S) probe that imaged particles with maximum dimension (D) ranging from 10 < D < 1280 μm. The 2D-S recorded supermicron-sized aerosol particles (SAPs) outside of clouds within biomass burning plumes during flights over the southeastern Atlantic off Africa’s coast. Numerous SAPs with 10 < D < 1520 μm were observed in 2017 and 2018 at altitudes between 1230 and 4000 m, 1000 km from the coastline, mostly between 7–11° S. No SAPs were observed in 2016 as flights were conducted further south and further from the coastline. Number concentrations of refractory black carbon (rBC) measured by a single particle soot photometer ranged from 200 to 1200 cm−3 when SAPs were observed. Transmission electron microscopy images of submicron particulates, collected on Holey carbon grid filters, revealed particles with potassium salts, black carbon (BC), and organics. Energy-dispersive X-ray spectroscopy spectra also detected potassium, a tracer for biomass burning. These measurements provided evidence that the submicron particles originated from biomass burning. NOAA Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) 3 d back trajectories show a source in northern Angola for times when large SAPs were observed. Fire Information for Resource Management System (FIRMS) Moderate Resolution Imaging Spectroradiometer (MODIS) 6 active fire maps showed extensive biomass burning at these locations. Given the back trajectories, the high number concentrations of rBC, and the presence of elemental tracers indicative of biomass burning, it is hypothesized that the SAPs imaged by the 2D-S are examples of BC aerosol, ash, or unburned plant material.

Drought Increases Vulnerability of Pinus ponderosa Saplings to Fire-Induced Mortality

The combination of drought and fire can cause drastic changes in forest composition and structure. Given the predictions of more frequent and severe droughts and forecasted increases in fire size and intensity in the western United States, we assessed the impact of drought and different fire intensities on Pinus ponderosa saplings. In a controlled combustion laboratory, we exposed saplings to surface fires at two different fire intensity levels (quantified via fire radiative energy; units: MJ m−2). The recovery (photosynthesis and bud development) and mortality of saplings were monitored during the first month, and at 200- and 370-days post-fire. All the saplings subjected to high intensity surface fires (1.4 MJ m−2), regardless of the pre-fire water status, died. Seventy percent of pre-fire well-watered saplings recovered after exposure to low intensity surface fire (0.7 MJ m−2). All of the pre-fire drought-stressed saplings died, even at the lower fire intensity. Regardless of the fire intensity and water status, photosynthesis was significantly reduced in all saplings exposed to fire. At 370 days post-fire, burned well-watered saplings that recovered had similar photosynthesis rates as unburned plants. In addition, all plants that recovered or attempted to recover produced new foliage within 35 days following the fire treatments. Our results demonstrate that the pre-fire water status of saplings is an important driver of Pinus ponderosa sapling recovery and mortality after fire.

Fire as a novel technique to stimulate adventitious shoots in the laboratory

Fire-stimulated flowering and fire-stimulated resprouting are associated traits common in plants that evolved in fire-prone habitats, e.g., Vellozia pyrantha, an iconic plant that has economic potential and is endemic to a fully protected area. By combining a natural phenomenon that drives demography and in situ evolution, we tested if fire can be used as a novel technique for plant multiplication through vegetative bud activation in V. pyrantha. The basal parts of microplants cultivated for 60 days (5 to 6 cm tall) were exposed to a flame using a Bunsen burner for five periods controlled by a timer (2, 4, 6, 8, and 10 s) and compared to unburned plants (control). After 30 days, the number of new shoots was counted, and the length of the longest shoot produced per individual was measured. Adventitious shoot development started 7 days after the fire incidence. The number of shoots per individual and length of the longest shoot produced were significantly higher in the 6- to 10-s treatments. Fire was an efficient and cheap way to induce adventitious shoot formation. This new method could also be applied to other resprouter species from fire-prone environments in the world. By combining a natural phenomenon that drives evolution with the bud stimulus expected, we found fire as an efficient and cheap way to induce buds.

Effects of biological legacies and herbivory on fuels and flammability traits: A long‐term experimental study of alternative stable states

Summary Ecological memory, often determined by the extent and type of retained biological legacies present following disturbance, may produce persistent landscape patterns. However, after fire, the persistence or switch to an alternative state may depend on the complex interplay of ecological memory (biological legacies) and potential effects of new external factors influencing the post‐fire environment. The current study assesses both the strength of ecological memory resulting from biological legacies of pre‐burn vegetation types as well as post‐fire effects of livestock. Following a severe fire in 1999, we set up a network of long‐term exclosures to examine the effects of legacies and cumulative herbivory by cattle on fuel types, amounts, distribution, flammability and microenvironmental conditions in two post‐fire communities representing alternative fire‐driven states: pyrophobic Nothofagus pumilio subalpine forests and pyrophytic Nothofagus antarctica tall shrublands in northwestern Patagonia, Argentina. Our results show that the retained post‐disturbance legacies of tall shrublands and subalpine forests largely determine fuel and flammability traits of the post‐fire plant communities 16 years after fire. The importance of biological legacies retained from the unburned plant communities was reflected by the substantially higher amounts of total fine fuel, greater vertical and horizontal fuel continuity and the higher temperatures reached during experimental tissue combustion at post‐fire shrubland compared to post‐fire forest sites. We show that herbivores may produce antagonistic effects on flammability by decreasing tissue ignitability, total fine fuel and litter depth, and disrupting the vertical and horizontal fine fuel continuity, therefore reducing the probability of fire propagation. However, cattle can increase ratios of dead to live fine fuels, reduce soil moisture, and inhibit tree height growth to canopy size, consequently impeding the development of a closed pyrophobic forest canopy. Synthesis. Our results support the hypothesis that biological legacies, most importantly the dominance by pyrophytic woody plants that resprout vigorously vs. the dominance by pyrophobic obligate seeders, favour fuel and flammability characteristics at the community level which reinforce the mechanisms maintaining pyrophytic shrublands vs. pyrophobic forests. Herbivory by introduced cattle can partially blur sharp pyrophobic/pyrophytic state boundaries by promoting the development of novel post‐fire transitional states.

Post-fire resprout in an endangered and narrow endemic shrub from rupestrian grasslands, Serra do Cipó, southeastern Brazil

Although there is evidence that the vegetation from rupestrian grasslands is resilient to fire, investigations about the effects of increasing frequency of anthropogenic fires in the rare and endemic plants from this ecosystem are still incipient. In this study, we monitored the post-fire resprouting of the endemic and endangered shrub species Coccoloba cereifera Schwacke (Polygonaceae) from rupestrian grasslands, southeastern Brazil. Five months after the fire 100% of the monitored individuals resprouted. However, one year after the fire, the burned plants had the ramet length 24% lower and number of leaves 53.5% smaller in relation to unburned plants. Burned plants showed a much higher relative growth rate in number of leaves and much lower reproductive investment compared to unburned plants. Although the studied species showed a high ability to resprout after fire, the pattern of vegetative growth and reproductive investment showed by the burned plants suggested that the increasing frequency of anthropogenic fires represents a serious threat to C. cereifera.Keywords: Coccoloba cereifera, conservation, Espinhaco Range, plant growth, reproductive phenology.

Total soil available nitrogen under perennial grasses after burning and defoliation

Total soil available nitrogen concentrations (NO–3 + NH 4 + ) were determined underneath plants of the more-competitive Poa ligularis, mid-competitive Nassella tenuis and the less-competitive Amelichloa ambigua exposed to various combinations of controlled burning and defoliation treatments. Defoliations were at the vegetative (V), internode elongation (E) or both developmental morphology stages (V + E) during two years after burning in northeastern Patagonia, Argentina. Hypotheses were that (1) concentrations of total soil available nitrogen after burning are greater underneath burned than unburned plants. With time, these differences, however, will gradually disappear; (2) greater total soil available nitrogen concentrations are underneath plants of the more- than less-competitive perennial grasses; and (3) total soil available nitrogen is similar or lower underneath plants defoliated at the various developmental morphology stages in all three study species than on untreated controls at the end of the study. Concentration of total soil available nitrogen increased 35% (p 0.05) towards the end of the first study year. Total soil available nitrogen concentrations were at least 10% lower underneath the less competitive N. tenuis and A. ambigua than the more competitive P. ligularis on average for all treatments, although differences were not significant (p > 0.05) most of the times. Defoliation had practically no effect on the concentration of total soil available nitrogen. Rather than any treatment effect, total soil nitrogen concentrations were determined by their temporal dynamics in the control and after the experimental fire treatments.

Post-fire environments are favourable for plant functioning of seeder and resprouter Mediterranean shrubs, even under drought.

Understanding how drought affects seeder and resprouter plants during post-fire regeneration is important for the anticipation of Mediterranean vegetation vulnerability in a context of increasing drought and fire caused by climate change. A Mediterranean shrubland was subjected to various drought treatments (including 45% rainfall reduction, 7months droughtyr-1 ), before and after experimental burning, by means of a rainout-shelter system with an irrigation facility. Predawn shoot water potential (Ψpd ), relative growth rate (RGR), specific leaf area (SLA) and bulk leaf carbon isotopic composition (δ13 C) were monitored in the main woody species during the first 3yr after fire. Cistus ladanifer seedlings showed higher Ψpd , RGR and SLA, and lower δ13 C, than unburned plants during the first two post-fire years. Seedlings under drought maintained relatively high Ψpd , but suffered a decrease in Ψpd and RGR, and an increase in δ13 C, relative to control treatments. Erica arborea, E.scoparia and Phillyrea angustifolia resprouts had higher Ψpd and RGR than unburned plants during the first post-fire year. Resprouters were largely unaffected by drought. Overall, despite marked differences between the two functional groups, post-fire environments were favourable for plant functioning of both seeder and resprouter shrubs, even under the most severe drought conditions implemented.

Impacts of Land Management on the Resilience of Mediterranean Dry Forests to Fire

Wildfires have always been a part of the history of Mediterranean forests. However, forests are not always certain to regenerate after a wildfire. Whether they do depends on many factors, some of which may be influenced by land management activities. Failure to regenerate will cause a regime shift in the ecosystem, reducing the provision of ecosystem services and ultimately leading to desertification. How can we increase the resilience of Mediterranean forests to fire? Our approach to answering this question was twofold: first, we reviewed the literature to investigate chains of processes that allowed forests to regenerate (which we label Regeneration Mechanisms, or RMs); and second, we assessed the impact of selected management practices documented in the WOCAT database on these RMs. For the assessment, we evaluated the relation between the benefits and disadvantages of the land management practices on the one hand, and the hindering and supporting factors of the RMs on the other. We identified three distinct RMs that enable Mediterranean forests to recover, as well as the time frame before and after a fire in which they are at work, and factors that can hinder or support resilience. The three RMs enabling a forest to regenerate after a fire consist of regeneration (1) from a seed bank; (2) from resprouting individuals; and (3) from unburned plants that escaped the fire. Management practices were grouped into four categories: (1) fuel breaks; (2) fuel management; (3) afforestation; and (4) mulching. We assessed how and under what conditions land management modifies the ecosystem’s resilience. The results show that land management influences resilience by interacting with resilience mechanisms before and after the fire, and not just by modifying the fire regime. Our analysis demonstrates a need for adaptive—i.e., context- and time-specific—management strategies.

Structural determinants of increased susceptibility to dehydration-induced cavitation in post-fire resprouting chaparral shrubs.

It is well established that transpiration and photosynthetic rates generally increase in resprouting shoots after fire in chaparral shrublands. By contrast, little is known about how plant hydraulic function varies during this same recovery period. We hypothesized that vascular traits, both functional and structural, would also shift in order to support this heightened level of gas exchange and growth. We examined stem xylem-specific hydraulic conductivity (Ks ) and resistance to cavitation (P50 ) for eight chaparral shrub species as well as several potential xylem structural determinants of hydraulic function and compared established unburned plants and co-occurring post-fire resprouting plants. Unburned plants were generally more resistant to cavitation than resprouting plants, but the two groups did not differ in Ks . Resprouting plants had altered vessel structure compared with unburned plants, with resprouting plants having both wider diameter vessels and higher inter-vessel pit density. For biomechanics, unburned plants had both stronger and denser stem xylem tissue than resprouting plants. Shifts in hydraulic structure and function resulted in resprouting plants being more vulnerable to dehydration. The interaction between time since disturbance (i.e. resprouting versus established stands) and drought may complicate attempts to predict mortality risk of resprouting plants.

Beating the blaze: Fire survival in the fan aloe (Kumara plicatilis), a succulent monocotyledonous tree endemic to the Cape fynbos, South Africa

AbstractFire is central to the ecology of Mediterranean‐type climate ecosystems, but little is known about the fire ecology of succulent plants therein. This study investigated the fire ecology of an arborescent succulent monocot, Kumara plicatilis (L.) G. D. Rowley (Asphodelaceae), a Cape fynbos endemic. Habitat suitability was assessed to determine whether the species tolerates or ‘avoids’ fire, and fire survival traits (bark thickness and tissue water content) were measured. The population size structure and density of three K. plicatilis populations were assessed after natural fires, and resprouting potential was investigated. Kumara plicatilis adopts a dual fire survival strategy, occupying rocky sites to ‘avoid’ fire and possessing morphological features that afford fire tolerance, e.g. well‐protected apical meristems and thick corky bark. Bark thickness of burned individuals in situ was similar to unburned plants, suggesting that K. plicatilis bark provides effective insulation against fire. Mortality rates were 64%, 40% and 11%, and decreased as rock cover at the population level increased. All three populations showed reduced plant density post‐fire, with greater density reductions associated with lower rock cover. Small plants appear most vulnerable to fire damage due to lower absolute bark thickness and plant heights within the flame zone. Kumara plicatilis is an apical sprouter, recovering after fire or mechanical stem damage by onward growth from surviving stem apices, rather than resprouting. Post‐fire population recovery therefore likely depends on inter‐fire recruitment.

Growth and reproductive post-fire responses of two shrubs in semiarid Patagonian grasslands

Variation in fire intensity affects the post-fire survival and growth of shrubs. We examined effects of maximum fire temperature (a proxy for fire intensity) on the survival, growth and reproductive performance of the shrubs Mulinum spinosum and Senecio bracteolatus at 1 and 2 years post-fire in north-west Patagonian grasslands. We applied two fire temperature treatments to plants of each species. All M. spinosum plants survived fire treatments but high fire temperature notably decreased survival of S. bracteolatus. Bud position and plant architecture probably influenced shrub survival. During the first growing season, M. spinosum did not produce seeds whereas S. bracteolatus plants burned at low temperature produced three times more seeds and bigger seeds than unburned plants. Also, seeds from burned plants of S. bracteolatus had higher germinability than seed from unburned plants. High survival and resprouting capacity of M. spinosum even after high fire intensity indicate that this species might be less affected by changes in fire regime.

Size-dependent enhancement of water relations during post-fire resprouting

In resprouting species, fire-induced topkill causes a reduction in height and leaf area without a comparable reduction in the size of the root system, which should lead to an increase in the efficiency of water transport after fire. However, large plants undergo a greater relative reduction in size, compared with small plants, so we hypothesized that this enhancement in hydraulic efficiency would be greatest among large growth forms. In the ecotone between long-leaf pine (Pinus palustris Mill.) savannas and wetlands, we measured stomatal conductance (gs), mid-day leaf water potential (Ψleaf), leaf-specific whole-plant hydraulic conductance (KL.p), leaf area and height of 10 species covering a range of growth forms in burned and unburned sites. As predicted, KL.p was higher in post-fire resprouts than in unburned plants, and the post-fire increase in KL.p was positively related to plant size. Specifically, large-statured species tended to undergo the greatest relative reductions in leaf area and height, and correspondingly experienced the greatest increases in KL.p. The post-fire increase in KL.p was smaller than expected, however, due to a decrease in absolute root hydraulic conductance (i.e., not scaled to leaf area). The higher KL.p in burned sites was manifested as an increase in gs rather than an increase in Ψleaf. Post-fire increases in gs should promote high rates of photosynthesis for recovery of carbohydrate reserves and aboveground biomass, which is particularly important for large-statured species that require more time to recover their pre-fire size.

Fire refugia: The mechanism governing animal survivorship within a highly flammable plant

AbstractIdentifying factors that influence the survival of individuals during disturbance is critical to understanding patterns of species reassembly within ecological communities. Although most studies of recovery of populations post‐burning acknowledge the potentially important contribution of animals surviving in situ, few have measured the effectiveness of refugia. This paper tests the hypothesis that some plants with tightly packed leaf‐bases provide a refuge for invertebrates during fire (even when the plants themselves burn) by using the highly flammable grass tree (Xanthorrhoeaceae: Xanthorrhoea). Invertebrates were sampled from four unburnt and five experimentally burnt grass trees (Xanthorrhoea preissii Endl.). Also collected were invertebrates fleeing during burning. The dataset comprises 949 specimens, representing 81 species from 18 orders, of which 749 individuals were from unburned plants. Slaters (Isopoda), silverfish (Thysanura), spiders (Araneae) and bugs (Hemiptera) dominated assemblages of the unburnt grass trees. Despite grass trees burning at temperatures of up to 515°C, some invertebrates survived in situ. Species‐specific microhabitat preferences within the plant appeared to influence survivorship. Species collected in the crown of unburned plants were found more often alive on burnt plants than species typically inhabiting the dead skirt of decaying leaves (thatch). We contend that the mechanism causing differential mortality is fire temperature. In the dead skirt, temperatures reached 225.33 ± 66.57°C. In contrast, a region of mild temperature (25.00 ± 3.54°C) persisted throughout burning near the apical meristem (within the crown). We conclude that grass trees are a potential reservoir from which invertebrates might re‐colonize recently burnt areas. However, owing to species‐specific microhabitat preferences and differential mortality across microhabitats, the invertebrate assemblage remaining in situ will be restricted taxonomically compared with the original grass tree fauna. Moreover, different fire regimes might mediate the effectiveness of grass trees as refugia. Finally, we argue that in situ survival of invertebrates within plants with tightly packed leaf‐bases is an unrecognized global phenomenon applicable to a wide array of plant taxa.