Basal Resprouting Research Articles

Trees use more non-structural carbohydrate reserves during epicormic than basal resprouting.

Non-structural carbohydrates (NSCs) are crucial to support tree resprouting after disturbances that damage the crown or stem. Epicormic resprouting (from stem) could demand more from NSC reserves than basal resprouting (following top-kill), since epicormically resprouting trees need to maintain a greater living biomass. Yet, little is known about NSC use during epicormic resprouting, particularly the relative importance of stem and below-ground NSC reserves. We compared the distribution and magnitude of NSC decreases during epicormic and basal resprouting by experimentally removing crowns or stems of 14-year-old Eucalyptus obliqua L'Hér. trees in native forest, then harvesting these trees over a 10-month period (start, sprouts emerged, sprouts expanded) to measure changes in NSC concentration and mass by organ (stem, lignotuber, roots). We hypothesized that (i) NSC depletion during resprouting is primarily due to decreases in starch rather than soluble sugars concentrations; (ii) during epicormic resprouting, stem NSC concentrations are decreased irrespective of any decreases in roots; and (iii) absolute decreases in NSC mass are greater for epicormic than basal resprouting during the leafless period due to the carbon demands associated with maintaining greater living biomass. Results confirmed our hypotheses; starch was the primary storage carbohydrate, stems were an important source of starch during epicormic resprouting and carbon demands of maintenance functions were greater for epicormic resprouting, leading to greater decreases in NSC reserves. Roots were a more important starch storage organ than the lignotuber for both epicormic and basal resprouting. The proportional decrease in starch was severe for both modes of resprouting due to a long leafless period, after which trees resprouting epicormically relied on starch reserves for longer than those resprouting basally. It remains to be seen how the timing of disturbance affects the timing and vigour of resprouting, and how long-term NSC recovery differs for epicormic and basal resprouting.

Frequent wildfires erode tree persistence and alter stand structure and initial composition of a fire‐tolerant sub‐alpine forest

AbstractQuestionFrequent severe wildfires have the potential to alter the structure and composition of forests in temperate biomes. While temperate forests dominated by resprouting trees are thought to be largely invulnerable to more frequent wildfires, empirical data to support this assumption are lacking. Does frequent fire erode tree persistence by increasing mortality and reducing regeneration, and what are the broader impacts on forest structure and understorey composition?LocationSub‐alpine open Eucalyptus pauciflora forests, Australian Alps, Victoria, Australia.MethodsWe examined tree persistence and understorey composition of E. pauciflora open forests that were unburned, burned once, twice or three times by high‐severity wildfires between 2003 and 2013. At each of 20 sites (five per fire frequency class) we assessed extent of top‐kill and mortality of eucalypt clumps, spatial configuration of surviving and dead clumps, densities of new and lignotuberous eucalypt seedlings, and shrub and grass cover.ResultsAt least 2 yr after the last wildfire, proportions of top‐killed E. pauciflora stems were significantly higher, and densities of live basal resprouts significantly lower, at sites burned two or three times compared to once burned or unburned sites. Clump death increased to 50% of individuals at sites burned by three short‐interval wildfires, which led to changes in live tree patchiness, as indicated by nearest‐neighbour indices. Increased tree mortality was not offset by seedling recruitment, which was significantly lower at the twice‐ and thrice‐burned sites relative to single‐burn sites – although seedling recruitment was also influenced by topography and coarse woody debris. In addition to changes in the tree layer, the prominence of understorey shrubs was substantially reduced, and the frequency of grasses markedly increased, after two, and particularly three wildfires.ConclusionsOur study provides strong empirical evidence of ecologically significant change in E. pauciflora forests after short‐interval severe wildfires, namely, erosion of the persistence niche of resprouting trees, and a shift in understorey dominance from shrubs to grasses. Our findings highlight the need to consider the impacts of compounded perturbation on forests under changing climates, including testing assumptions of long‐term persistence of resprouter‐dominated communities.

Epicormic Resprouting in Fire-Prone Ecosystems.

Many plants resprout from basal buds after disturbance, and this is common in shrublands subjected to high-intensity fires. However, resprouting after fire from epicormic (stem) buds is globally far less common. Unlike basal resprouting, post-fire epicormic resprouting is a key plant adaptation for retention of the arborescent skeleton after fire, allowing rapid recovery of the forest or woodland and leading to greater ecosystem resilience under recurrent high-intensity fires. Here we review the biogeography of epicormic resprouting, the mechanisms of protection, the fire regimes where it occurs, and the evolutionary drivers that shaped this trait. We propose that epicormic resprouting is adaptive in ecosystems with high fire frequency and relatively high productivity, at moderate-high fire intensities.

Sprouting capacity of Persea borbonia and maritime forest community response to simulated laurel wilt disease

There are numerous examples of how exotic insect pests and pathogens have altered the dominance of native tree species. Changes to the structure of associated communities will depend on whether the affected species survives and if so, the degree to which it is diminished. In the southeastern USA, Persea borbonia, a common tree found in many coastal plain habitats, is the primary host of laurel wilt disease (LWD); infection rates and main-stem mortality are catastrophically high (>90%) in invaded populations. We simulated the effects of LWD prior to its arrival in coastal Mississippi by girdling and then removing the main stems of P. borbonia trees. Over a 2-year period, we monitored P. borbonia persistence via basal resprouts, understory light availability, and community structure. Removal of P. borbonia main stems resulted in a 50% increase in light transmission (measured at 1 m above ground level). All treated individuals produced basal resprouts, the size and number of which were positively related to initial tree girth. Post-treatment increases in basal area were greatest for the sub-canopy species, Ilex vomitoria, and were significantly higher in treatment versus control plots. Woody seedlings and herbaceous plants showed no significant trends in composition and abundance over time or between control and treatment plots. Our results suggest that removal of P. borbonia and subsequent resprouting causes shifts in P. borbonia size class frequencies and sub-canopy species dominance but has negligible impacts on understory plant community dynamics.

How does resprouting response differ among three species of savanna trees and in relation to plant size?

Cerrado tree species can survive fire by resprouting. Generally, large and less damaged plants produce new branches and leaves from stem buds (aerial), whereas small and highly injured individuals would resprout from the stem base or from underground organs (basal). We compared the three most common Cerrado woody plant species in a savanna area of the IBGE Ecological Reserve, Brasilia, Brazil, aiming to verify if the resprouting strategy (aerial or basal) differed between species and if that was related to plant size. Guapira noxia had small-sized plants, a higher percentage of trunk charred and more individuals with basal resprouting, while Eriotheca pubescens had large-sized plants with a greater intensity of aerial resprouting, Basal resprouting was associated with disturbance severity for Dalbergia miscolobium, while plant size was associated with aerial resprouting for E. pubescens. None of variables explained the variation in resprouting of G. noxia. The results showed that the post-fire regeneration strategy varied according to the species, confirming other studies of post-fire resprouting.

Mortality and recruitment of fire-tolerant eucalypts as influenced by wildfire severity and recent prescribed fire

Mixed-species eucalypt forests of temperate Australia are assumed tolerant of most fire regimes based on the impressive capacity of the dominant eucalypts to resprout. However, empirical data to test this assumption are rare, limiting capacity to predict forest tolerance to emerging fire regimes including more frequent severe wildfires and extensive use of prescribed fire. We quantified tree mortality and regeneration in mixed-species eucalypt forests five years after an extensive wildfire that burnt under extreme fire weather. To examine combined site-level effects of wildfire and prescribed fire, our study included factorial replications of three wildfire severities, assessed as crown scorch and understorey consumption shortly after the wildfire (Unburnt, Low, High), and two times since last preceding fire (<10years since prescribed fire, >30years since any fire). Our data indicate that while most trees survived low-severity wildfire through epicormic resprouting, this capacity was tested by high-severity wildfire. Five years after the wildfire, percentage mortalities of eucalypts in all size intervals from 10 to >70cm diameter were significantly greater at High severity than Unburnt or Low severity sites, and included the near loss of the 10–20cm cohort (93% mortality). Prolific seedling regeneration at High severity sites, and unreliable basal resprouting, indicated the importance of seedling recruitment to the resilience of these fire-tolerant forests. Recent prescribed fire had no clear effect on forest resistance (as tree survival) to wildfire, but decreased site-level resilience (as recruitment) by increasing mortalities of small stems. Our study indicates that high-severity wildfire has the potential to cause transitions to more open, simplified stand structures through increased tree mortality, including disproportionate losses in some size cohorts. Dependence on seedling recruitment could increase vulnerabilities to subsequent fires and future climates, potentially requiring direct management interventions to bolster forest resilience.

Post-fire resprouting strategies of rainforest and savanna saplings along the rainforest–savanna boundary in the Australian monsoon tropics

In tropical areas where climatic conditions support both rainforests and savannas, fire is considered one of the main factors determining their distribution, particularly in environments where growth rates are limited by water availability. The observed expansion of some rainforests into savannas suggests that rainforest saplings could have traits that enable them to survive in the savanna environment, including recovering from infrequent fires. We applied the Clarke (New Phytol 197:19–35, 2013) buds-protection-resources framework to the rainforest–savanna system of the North Kimberley (Western Australia), to compare the resprouting response of five savanna species saplings burnt by an ambient early dry season fire with seven rainforest species saplings burnt using an experimental treatment that mimicked a savanna fire. Most plants survived the fire, although plant mortality was higher for rainforest (19 %) than savanna (2 %) individuals, as was stem mortality (37 vs. 12 %). All rainforest and savanna species expressed aerial resprouting; two of the savanna species and two of the rainforest species did not express basal resprouting. After 1 year, most savanna individuals had more and longer shoots than the rainforest saplings and had regained their original height, while rainforest plants were on average 43 % shorter than their pre-fire height. These results suggest that, although rainforest species are less able to escape the ‘fire trap’ than savanna species, they are able to recover from a low-intensity fire.

Post-fire response of riparian vegetation in a heavily browsed environment

Severe wildfires infrequently occur in large heterogeneous riparian valleys. Riparian areas may affect fire behavior and the pattern of burning due to saturated soils and patchy fuels that may have high moisture content in live and dead stems. We examined the effects of a severe fire on the dominant riparian vegetation: thin-leaf alder, river birch and willow, in a broad riparian valley in Rocky Mountain National Park, CO, USA. We mapped the canopy stem mortality and basal resprouting of 4507 first year post fire and 643 second year post fire individuals that had been the dominant woody canopy. To examine the effect of herbivory on resprouting willow stems, we established a paired experiment with 22 willows exclosed in cages to prevent browsing and 22 uncaged control plants. Aerial seed rain sticky traps were established on transects throughout the study area and pre-fire seed rain density was compared with post-fire seed rain densities.Fire effects on willow were severe, with 91% of individuals having complete canopy loss. Fifty-one percent of thin-leaf alder individuals and 71% of river birch individuals also had complete canopy loss. Seventy-four percent of river birch, 45% of willow and 35% of thin-leaf alder resprouted from the base in the first summer post fire. In the second year post fire, 84% of river birch, 62% of thin-leaf alder and 55% of willow had resprouted. Willows inside exclosures had greater biomass at the end of the growing season compared with willows outside exclosures. Summer browsing resulted in significantly lower willow biomass compared with exclosed plants and the additive effect of summer and winter browsing resulted in control plants having 64% reduction in biomass. Post-fire aerial seed rain was 90% lower than pre-fire densities.Fire dramatically altered the riparian vegetation. Willow seed rain was nearly eliminated because most stems were killed by fire. Resprouting woody riparian vegetation was prevalent however, ungulate browsing of the resprouting willow stems could limit the regrowth of a tall willow riparian overstory.

Fire induced reproductive mechanisms of a Symphoricarpos (Caprifoliaceae) shrub after dormant season burning.

BackgroundSymphoricarpos, a genus of the Caprifoliaceae family, consists of about 15 species of clonal deciduous shrubs in North America and 1 species endemic to China. In North American tallgrass prairie, Symphoricarpos orbiculatus (buckbrush) is the dominant shrub often forming large colonies via sexual and asexual reproductive mechanisms. Symphoricarpos shrubs, in particular S. orbiculatus, use a unique sexual reproductive mechanism known as layering where vertical stems droop and the tips root upon contact with the soil. Because of conflicting societal values of S. orbiculatus for conservation and agriculture and the current attempt to restore historical fire regimes, there is a need for basic research on the biological response of S. orbiculatus to anthropogenic burning regimes.ResultsFrom 2007 through 2013 we applied prescribed fires in the late dormant season on grazed pastures in the Grand River Grasslands of Iowa. From 2011 to 2013, we measured how S. orbiculatus basal resprouting and layering stems were affected by patchy fires on grazed pastures, complete pasture fires on grazed pastures or fire exclusion without grazing for more than three years. We measured ramet height, ramet canopy diameter, stems per ramet, ramets per 100 m2, and probability of new layering stems 120 days after fire. Height in burned plots was lower than unburned plots but S. orbiculatus reached ~ 84% of pre-burn height 120 days after fire. Stems per ramet were 2x greater in the most recently burned plots due to basal re-sprouting. Canopy diameter and density of ramets was not affected by time since fire, but burned pastures had marginally lower densities than plots excluded from fire (P = 0.07). Fire triggered new layering stems and no new layering stems were found in plots excluded from fire.ConclusionsThe mechanisms of both basal sprouting and aerial layering after fire suggest S. orbiculatus is tolerant to dormant season fires. Furthermore, dormant season fires, regardless if they were patchy fires or complete pasture fires, did not result in mortality of S. orbiculatus. Dormant season fires can reduce S. orbiculatus structural dominance and maintain lower ramet densities but also trigger basal resprouting and layering.Electronic supplementary materialThe online version of this article (doi:10.1186/s40529-014-0080-4) contains supplementary material, which is available to authorized users.

Response of hardwood tree regeneration to surface fires, western Chaco region, Argentina

We assessed the response of seedlings and pole-sized individuals of Aspidosperma quebracho-blanco Schlecht., Schinopsis lorentzii (Griseb.) Engler and Ziziphus mistol Griseb. to surface fires. We assessed traits of fire resistance (bark thickness and bark density) and fire tolerance (mortality and sprouting type, basal or epicormic) in each species. Burns were carried out using two fine fuel loads (high, 8000kgha−1; and low 4000kgha−1, respectively) and two dates of fire application (early and late fire season). Field work was performed during 2008 and 2009. Using a randomized design, 120 2m×2m plots were burnt each year. Using ANOVA, we tested the effect of species, fuel load and date of fire on the bark char height of the bole. The resprouting pattern (basal or epicormic) and post-fire mortality (complete or top-kill) were analysed using a logistic regression approach. There were a significant effect of species (p<0.0001), fuel load (p<0.0001) and of the interaction year of burning *date of fire (p<0.0001) on the mean char height. A. quebracho-blanco had greater char height than S. lorentzii and Z. mistol (p<0.05), but differences between the latter two species were no significant. Diameter to breast height (DBH) was significant and positively correlated to char height for A. quebracho-blanco and Z. mistol. High fuel load produced higher char height than the low fuel load fires. A. quebracho-blanco had the greatest total, inner and outer bark thickness, and the lowest bark density among the studied species. It was followed by S. lorentzii, while Z. mistol had the lowest total bark thickness, the highest inner bark proportion and the highest bark density (p<0.05). The likelihood of complete mortality was significantly larger in Z. mistol than in A. quebracho-blanco and S. lorentzii. Mortality and top-kill were lower in the late season burns (p<0.05). Sprouting type was significantly affected by species (p<0.05), DBH, date of fire and by the interactions species×DBH and season of fire×DBH (p<0.0001). A. quebracho-blanco presented only basal resprouts, while the other two species showed both epicormic and basal resprouts. The two species with greater bark thickness had lower mortality than Z. mistol. Epicormic resprouts were not observed at the more severe late burns. The three species studied showed high resistance and tolerance to medium to high severity fires.

Driving factors of small-scale variability in a savanna plant population after a fire

The severity of fire impacts on fire-prone vegetation is often spatially heterogeneous, and may lead to small-scale patchiness in the structure of plant populations by affecting mortality, topkill, and reproduction. This patchiness, however, is not usually taken into account in fire ecology studies. We show that a dry-season fire may result in small-scale patchiness in the population structure of the common shrub Miconia albicans, mostly by differential topkill and resprouting. We related fire severity to population structure parameters of the study species and assessed the effects of fire on its soil seed bank. Basal area of non-woody live stems and of dead stems increased with fire severity, whereas that of woody live stems decreased, indicating topkill and resprouting. However, there was no relationship between fire severity and the total number of live or dead plants, showing that mortality in the fire was low. We found very few seedlings, indicating that resprouting, not germination from the soil seed bank, is the main recovery strategy of this species. The fire also affected the soil seed bank, as there were fewer seedlings emerging from soil collected in burned patches. Although this study was performed with a single species, it is likely that other species, especially those with basal resprouting, will show similar patterns of post-fire patchiness in population structure. This patchiness, in turn, may affect the spatial distribution of future fires, and should be taken into account in studies of fire ecology.

Bark thickness does not explain the different susceptibility of Australian and New Zealand temperate rain forests to anthropogenic fire

AbstractAimAnthropogenic fires caused New Zealand's temperate rain forests to decline rapidly from 80% to 50% cover after Polynesian arrival. In contrast, Australian temperate rain forests have remained stable in spite of a longer history of fire and human occupation. We evaluate whether New Zealand's conifer‐dominated forests declined because they lack fire resistance traits. We predicted that New Zealand species should have thinner bark than their Australian counterparts, and slower growing conifers should have relatively thicker bark than angiosperms.LocationTemperate rain forests of south‐eastern Australia, Tasmania and New Zealand.MethodsWe examined the ratio of bark thickness to stem diameter (relative bark thickness) as a standardized index (by tree size) of fire resistance. Nonlinear power models were fitted to examine trends in relative bark thickness between trees from New Zealand and Australia. Bark thickness was also compared between species pairs and congeners and by phylogenetically corrected ANOVA.ResultsAlthough angiosperms and gymnosperms in New Zealand had thin bark in a global context, they had significantly thicker bark than their Australian counterparts. Bark thickened more rapidly for small trees in New Zealand but declined with increasing stem diameter. Allocation to bark thickness was greater for larger stems in Australia. New Zealand gymnosperms had the thickest bark of all species examined.Main conclusionsFire resistance is a complex syndrome comprising functional traits that ensure protection (resistance – bark) from and recovery (resilience – resprouting) after fire. Thin bark in temperate rain forests suggests weak selection by fire on bark traits. However, the stability of Australian temperate forests in a flammable landscape emphasizes the importance of resprouting, especially basal resprouting, to forest persistence after fire. New Zealand forests do not resprout after fire and lack the fire resistance traits required for recovery from repeated anthropogenic fires.

Post-fire survival and regeneration of Eucalyptus globulus in forest plantations in Portugal

Eucalyptus globulus is one of the most important pulpwood plantation species in the world, and nowadays it is present in most continents. Some of the regions where E. globulus plantations have been expanding have a high incidence of wildfires; therefore, knowing the factors affecting the fire resistance and resilience of this species is particularly important for forest management. This is the case of Portugal, where nearly 1.4million ha of land burned in the last decade and where E. globulus has become the most widespread tree species. In this paper we assessed the short-term post-fire responses of E. globulus trees in four sites affected by wildfires, and investigated their potential relationships with fire severity descriptors and with tree and stand characteristics. One year after fire, individual tree mortality was low (3.9%) but most trees (79.2%) were top-killed (i.e. had stem mortality). Both post-fire tree mortality and top-kill increased with fire severity (expressed by maximum char height and/or char severity rating). Moreover, top-kill was positively related with vegetation cover and the proportion of pine trees in the stand, and was negatively related with tree diameter and the proportion of other broadleaved trees in the stand. The most common post-fire regeneration type among the sampled trees was basal resprouting (89.2%), though 20.9% had epicormic resprouting. The number of basal resprouts increased with char height, top-kill and diameter of the parent tree, and decreased with slope. In terms of post-fire growth, the height of the dominant resprout increased with the number of resprouts and with char severity, while it decreased in drier southern aspects. Results showed that E. globulus is a fire-resilient species with a very high probability of surviving fire; however, in forest plantations where trees are usually felled in short rotations (thus with limited size), individuals have a high probability of being top-killed. The presented models may be useful to help managers on the assessment of post-fire production losses and regeneration potential in E. globulus plantations.

Resprouting as a key functional trait: how buds, protection and resources drive persistence after fire

Resprouting as a response to disturbance is now widely recognized as a key functional trait among woody plants and as the basis for the persistence niche. However, the underlying mechanisms that define resprouting responses to disturbance are poorly conceptualized. Resprouting ability is constrained by the interaction of the disturbance regime that depletes the buds and resources needed to fund resprouting, and the environment that drives growth and resource allocation. We develop a buds-protection-resources (BPR) framework for understanding resprouting in fire-prone ecosystems, based on bud bank location, bud protection, and how buds are resourced. Using this framework we go beyond earlier emphases on basal resprouting and highlight the importance of apical, epicormic and below-ground resprouting to the persistence niche. The BPR framework provides insights into: resprouting typologies that include both fire resisters (i.e. survive fire but do not resprout) and fire resprouters; the methods by which buds escape fire effects, such as thick bark; and the predictability of community assembly of resprouting types in relation to site productivity, disturbance regime and competition. Furthermore, predicting the consequences of global change is enhanced by the BPR framework because it potentially forecasts the retention or loss of above-ground biomass.

Postfire Responses by Southern Arroyo Willow Forest and by Southern-Willow Scrub Dominated bySalix lasiolepisin San Diego County, California

Abstract We examined patterns of response of southern riparian forest and southern-willow scrub, both dominated by arroyo willows (Salix lasiolepis), sampled in 1999 prior to fire and in 2008 following an intense wildfire in San Diego County, California. Arroyo willows had vigorous basal and epicormic resprouting in the riparian forest and minimal mortality from fire. While no sapling of S. lasiolepis was noted in 1999, we observed four in 2008. The most striking change in understory of southern-willow scrub was the increase in nonnative plants, particularly graminoids. No willow-scrub plot experienced postburn mechanical disturbance. The herbaceous increase in southern-willow scrub was likely a result of timing of precipitation combined with fire and drought that opened the overstory of trees and shrubs. Interspecific competition for moisture between nonnative herbs and seedlings of S. lasiolepis might negatively impact recruitment of this species and impact its function in these ecosystems.

Costs of resprouting are traded off against reproduction in subtropical coastal dune forest trees

Resprouting can be an important means of regeneration for forest tree species resulting in multi-stemmed architecture, especially at less productive or frequently disturbed sites. However, the cost of resprouting may be traded off against growth or reproduction. In subtropical coastal forest in South Africa, trees grow on steep, sandy dunes with unstable soils and low to moderate nutrient availability. These coastal forests experience seasonally strong anticyclonic winds from August through October. We examined the hypothesis that basal resprouting resulting in multiple stems causes lower rates of sexual reproduction and recruitment by individuals. We examined whether trees traded off resprouting against seed output, seed size, seedling abundance and recruitment by seedlings. Species were designated as good and poor resprouters based on their frequency of multi-stemmed individuals at Cape Vidal. Good resprouters had more stems, produced less seed and had lower seed mass than poor resprouters, and had lower seedling abundance and fewer individuals in small diameter classes than large diameter classes. Seedling abundance in good resprouters was not influenced by the availability of understorey gaps. Good resprouters were most abundant on dune crests and seaward slopes that were exposed to sea winds. Persistence of established individuals by producing multiple stems from basal resprouts is important where a chronic disturbance regime potentially reduces the survivorship of single-stemmed individuals and thereby their opportunities for reproduction. Good resprouters appear to trade-off recruitment of new individuals for multiple stems that increase the persistence of established ones against disturbance. We conclude that multi-stemming arising from basal resprouts has evolved to promote individual persistence under low to moderate intensity but pervasive wind stress.

Post-fire tree mortality in mixed forests of central Portugal

Wildfires are a recurrent disturbance in the Mediterranean Basin. However, managers from this region are confronted with a lack of information on the effects of fire on most woody species, which is required for defining sustainable forest management strategies. Following a large wildfire in central Portugal (2003), we surveyed the area during the first year and assessed the vegetative condition of 1040 burned trees from 11 different species. Among those trees, 755 individuals were selected and monitored annually for 4 years. At the end of the study, almost all the broadleaved trees survived, while most coniferous died. In spite of the low mortality observed in broadleaves, most were top-killed and regenerated only from basal resprouts, which implies a slow recovering process. Quercus suber, however, showed vigorous post-fire crown resprouting and was the most resilient species. We fitted logistic regression models to predict the probability of individual tree mortality and top-kill from fire injury indicators and tree characteristics. Besides the differences between the two main functional groups (coniferous, broadleaved), bole char height and crown volume scorched or consumed were important predictors of tree responses. Additionally, the main factor determining crown mortality on broadleaved species was bark thickness. The selected models performed well when tested with independent data obtained on four other wildfires. These models have several potential applications and can be useful to managers making pre-fire or post-fire decisions in mixed forest stands in the western Mediterranean Basin.

Ecological impacts of buffel grass (Cenchrus ciliaris L.) invasion in central Australia - does field evidence support a fire-invasion feedback?

Buffel grass (Cenchrus ciliaris L.) has invaded extensive areas of arid and semi-arid Australia following its introduction as a pasture species and for erosion control. It has been suggested that buffel grass has initiated a positive fire-invasion feedback in central Australia, disrupting existing fire regimes, encouraging further buffel grass invasion, and disadvantaging the native woody flora in particular, but this hypothesis has not been tested quantitatively. This study investigated recently burnt woodland areas near Alice Springs for evidence of a fire-invasion feedback, including the impact of changing fire behaviour (intensity) on the native woodland overstorey flora. Despite the limitations inherent in a short study of ecological processes in a highly heterogeneous environment, substantial field evidence was found to support the existence of a buffel grass-initiated fire-invasion feedback. Buffel grass invasion was significantly correlated with increased fuel loads. Increased fuel loads were significantly correlated with increased burn severity, although the direct relationship between the proportion of buffel grass and increased burn severity was marginally non-significant. High field variance resulted in inadequate power to test whether or not the relative abundance of buffel grass had increased in the post-fire community. Burn severity was significantly correlated with the mortality of woodland overstorey species, and with the proportion of fire survivors that were reduced to basal resprouts. Seedling density of canopy species was low. It appears likely that future recruitment of canopy species will be hindered by the dense post-fire reestablishment of buffel grass cover at some sites. The overstorey flora is thus likely to be adversely affected by increased severity of fire associated with buffel grass invasion. As a result, there may be major change in the structure and composition of some woodlands.

Fire mediated edge effects in bayhead tree islands

Question: The role edges play in mediating the effects of disturbance is unclear. Bayhead tree islands, which experience above- and belowground fire, contain trees that recover from disturbance by seed (Pinus elliottii var. densa) and by sprouting (Gordonia lasianthus). How does distance-to-edge affect survival and post-fire response of trees with these contrasting life-history strategies? Location: Two bayhead tree islands at Archbold Biological Station, central Florida, North America. Methods: Stem diameter, depth of peat smoldering, char height, resprouting status, and location were recorded for all Pinus and Gordonia stems ≥8 cm. Distance to the edge of the tree island was quantified using GIS. Results: The focal species showed contrasting patterns of survival across the edge-to-interior gradient that reflected gradients of fire severity. Survival of Gordonia was lowest in the bayhead interior where peat smolder was deepest. Conversely, survival of Pinus was lowest near the edges where char heights were greatest. The distinct types of Gordonia resprouting (crown versus basal) also showed spatially contrasting patterns. Basal resprouting dominated near the edges and was positively influenced by char height, while crown resprouting was nearly constant across the edge-to-interior gradient and was negatively influenced by char height. Conclusions: The spatial patterns of tree survival and resprouting observed are likely due to gradients in intensity of peat smoldering and aboveground burning, coupled with differential susceptibility to these two types of fire. Despite the rarity of fire in wetland tree islands (compared to uplands) it may play an important role in structuring the spatial distribution of trees.

Comparing survival and size of resprouts and planted trees for post-fire forest restoration in central Portugal

The post-fire restoration of burned forests in the Mediterranean basin usually involves planting or direct seeding, often neglecting the use of natural regeneration through basal resprouting. This study compared the survival and size of planted and resprouted Fraxinus angustifolia (narrowleaf ash) and Quercus faginea (Portuguese oak) in a burned area in central Portugal, after a 20–22-month growing period. Adult ash and oak trees were burned in a wildfire in September 2003. The survival and height of resprouting suckers were assessed 21 months after fire. Seedlings coming from nurseries were planted in the same area during January to March, both in 2004 and 2005, and their survival and height were assessed 20–22 months after planting. Survival was higher in resprouts than in planted trees in the case of oak (98% against 77% and 67%, respectively, for trees planted in 2004 and 2005) but not for ash (100% against 87% and 97%). Plant height was much higher in resprouts than in planted trees (4–5 times higher in oak; 2–3.8 times higher in ash), and a similar pattern was found for basal diameter (3.5–4.5 times higher in oak; 3–5 times higher in ash). The results suggest that using natural regeneration through resprouting may be a cheaper and more effective technique than planting to restore burned forests with a large proportion of resprouter species, as is the case of many Mediterranean broadleaved forests.