Effect of fire on recruitment of two dominant perennial grasses with different palatability from semi-arid grasslands of NW Patagonia (Argentina)

Fire is a non-selective disturbance that impacts equally plant species that could be selected differentially by livestock. Post-fire recruitment dynamics is an important ecological process that has been barely studied in Patagonian grass species. This work analyzes the effect of fire on seed germination, seedling growth, and survival of Pappostipa speciosa (ex Stipa speciosa) and Festuca pallescens, two dominant perennial grasses from NW Patagonia that differ in palatability. We hypothesized that physical and chemical factors derived from fire differentially affect recruitment of these species. We performed experiments in the field and under laboratory and greenhouse conditions to study the integral effect of fire and of related abiotic factors (i.e., smoke, heat, charcoal, and ash) on different phases of recruitment of both species. Experimental burning promoted P. speciosa emergence over time, but they did not affect F. pallescens total emergence. Experimental burning decreased P. speciosa seedling growth (i.e., few leaves and small size), but they did not affect seedling survival. Smoke from laboratory experiments stimulated P. speciosa germination. Exposing F. pallescens seeds to 120°C decreased germination and seedling growth. Fire might act as a selective force on recruitment of both species, as well as changing competitive interactions during postfire regeneration. The effect of fire on the recruitment dynamics of the studied species depended strongly on both intrinsic species characteristics and meteorological conditions.     

Negative and positive interactions among plants: effects of competitors and litter on seedling emergence and growth of forest and grassland species

Living plant neighbours, but also their dead aboveground remains (i.e. litter), may individually exert negative or positive effects on plant recruitment. Although living plants and litter co‐occur in most ecosystems, few studies have addressed their combined effects, and conclusions are ambivalent. Therefore, we examined the response in terms of seedling emergence and growth of herbaceous grassland and forest species to different litter types and amounts and the presence of competitors. We conducted a pot experiment testing the effects of litter type (grass, oak), litter amount (low, medium, high) and interspecific competition (presence or absence of four Festuca arundinacea individuals) on seedling emergence and biomass of four congeneric pairs of hemicryptophytes from two habitat types (woodland, grassland). Interactions between litter and competition were weak. Litter presence increased competitor biomass. It also had positive effects on seedling emergence at low litter amounts and negative effects at high litter amounts, while competition had no effect on seedling emergence. Seedling biomass was negatively affected by the presence of competitors, and this effect was stronger in combination with high amounts of litter. Litter affected seedling emergence while competition determined the biomass of the emerged individuals, both affecting early stages of seedling recruitment. High litter accumulation also reduced seedling biomass, but this effect seemed to be additive to competitor effects. This suggests that live and dead plant mass can affect species recruitment in natural systems, but the mechanisms by which they operate and their timing differ.     

中亚热带4种森林凋落物量、组成、动态及其周转期

为研究亚热带次生林保护对森林生态系统养分循环等功能过程的影响。采用凋落物直接收集法,比较湘中丘陵区3种次生林(马尾松+石栎针阔混交林、南酸枣落叶阔叶林、石栎+青冈常绿阔叶林)和杉木人工林的凋落物量、组成特征及其周转期。结果表明:4种林分年凋落物量在414.4—818.2 g m-2a-1之间,3种次生林显著高于杉木人工林,3种次生林两两之间差异不显著,落叶对林分凋落物量的贡献最大,占林分凋落物量的59.9%—66.6%。杉木人工林和南酸枣落叶阔叶林的凋落物量月动态变化呈"双峰型",马尾松+石栎针阔混交林、石栎+青冈常绿阔叶林呈"不规则型"。优势树种的凋落物量对其林分凋落物量的贡献随林分树种多样性的增加而下降,杉木、马尾松凋落物量的月动态与其林分凋落物量的月动态基本呈一致变化趋势,但南酸枣、青冈、石栎没有一致的变化趋势。杉木人工林凋落物分解率最低(0.31),周转期最长(3.2 a),南酸枣落叶阔叶林分解率最高(0.45),周转期最低(2.2 a),凋落物的分解速率和周转随林分树种多样性增加而加快。可见,次生林凋落物量大,且分解快,周转期短,有利于养分归还和具有良好地力维持的能力。     

Effect of grass litter on seedling recruitment of the critically endangered Cistus heterophyllus in Spain

Cistus heterophyllus Desf. is an Iberian-north African endemic plant species with only one wild population left in Spain. A sowing experiment under controlled conditions was designed to assess both the seedling emergence rate and the growth fitness of C. heterophyllus on a litter layer of Brachypodium retusum (Pers.) Beau., which forms dense carpets around the remnant population of C. heterophyllus. In order to test the physical effects of B. retusum litter on Cistus seedling recruitment, six sowing treatments in pots were compared that combined three doses of litter (0, 0.6 and 1.1 kg m⁻²) and different physical locations of the seeds (above, below the litter layer or within a litter–peat mixture). B. retusum litter interfered with the seedling recruitment of C. heterophyllus, negatively affecting both seedling emergence and their early growth. Such an effect was more severe when the seeds were located above a 0.6 kg m⁻² litter layer, although seedlings from seeds sown under the litter showed a growth reduction ranging from 58% to 100% compared to the no-litter treatment. A significant negative effect of the litter–peat mixture on the number of leaves, leaf size and number of branches of seedlings was also inferred. These data provide experimental evidence on the serious threat that B. retusum litter represents for the conservation and regeneration of the last population of C. heterophyllus in Spain.     

Effects of leaf litter on woody seedlings in xeric successional communities

We investigated the effect of leaf litter on the establishment of Eucalyptus incrassata, a mallee eucalypt. It has been suggested that litter accumulation may hinder seedling establishment, and that the removal of litter may be one of the mechanisms through which fire enhances recruitment. We conducted factorial experiments testing the effects of three kinds of leaf litter on E. incrassata seeds and seedlings at three contiguous sites with different land use histories. One site was an uncleared E. incrassata open mallee woodland (Mallee site), one a cleared area that had been ungrazed for about five years (Pasture site) and the third an area of mallee rolled some 40 years ago and permitted to regenerate (Regrowth site). Litter had no effect on emergence of planted E. incrassata seeds, but emergence differed between sites. Overall, the percentage of seeds that germinated and emerged was substantial (mean 35.2% ± 25.9%). Seedling shoot biomass did not differ between sites or litter treatments. Although seedlings grown in Pasture litter suffered higher mortality rates, overall mortality rates were low (mean 13.2% ± 15.5%), suggesting that leaf litter has little effect on recruitment rates during winter and spring. We conclude that leaf litter does not affect emergence or growth in young E. incrassata seedlings during winter and spring, when most establishment occurs. Our results emphasize the difficulty in predicting litter effects on recruitment.     

Seed–litter–position drives seedling establishment in grassland species under recurrent drought

Changes in land use and climate interfere with grassland ecosystem processes. Here I experimentally investigated the combined effects of land‐use change related litter cover and contrasting water supply on seedling emergence. In this context, the role of the initial relative position of seeds, i.e. seeds on top of the litter versus seeds beneath the litter in interaction with water supply has not been investigated so far. I hypothesised that facilitative effects of litter on seedling emergence occur when seeds are covered by litter and deteriorate when litter covers the ground and seeds fall on it (seeds on top of the litter). Further, I hypothesised that the importance of seed position for seedling emergence will increase under conditions of recurrent drought. I performed a controlled pot experiment on seedling emergence of three common European grassland species (Pimpinella saxifraga, Leontodon autumnalis, Sanguisorba officinalis) by experimental manipulations of litter and water availability. Seedling emergence under moist conditions showed no significant differences between each litter position compared to the control across species. In contrast, under recurrent drought, seedling emergence was significantly higher below the litter compared to seeds on top of the litter and the control (i.e. no litter). In abandoned land, seedling emergence may be limited when seeds fall on ground‐covering litter. In contrast, in grasslands with regular low‐intensity land use, seedling emergence may be enhanced when a moderate level of litter covers seeds at the end of the growing season. Protective mechanisms that occur with seeds positioned beneath litter are particularly important under recurrent drought.     

Long‐term forest structure and regeneration after wildfire in Russian Karelia

We examined forest structure and regeneration in a 350‐ha forest dominated by Pinus sylvestris 31 yr after a wildfire in the Vienansalo wilderness, Russian Karelia. In most parts of the area, the 1969 fire was not stand replacing but had left larger trees alive so that the area generally remained forest covered. In some localities, however, all trees apparently died and distinct gaps were formed, suggesting that the fire severity varied considerably, contributing to increased variation in stand structure. Living and dead wood volumes were similar, 112 and 96 m³.ha^‐1, respectively. The tree species proportions of dead vs living wood indicated that prior to fire disturbance Picea was more common in the area. Regeneration was abundant (saplings, ca. 14 000 ind.ha^‐1, height 20 ‐200 cm) and tree seedling recruitment had occurred over a long period of time. Regeneration density was highest on the mesic Vaccinium‐Myrtillus forest site type, decreasing towards nutrient‐poor site types. The most common regeneration microsites were level ground (56% of saplings), immediate surroundings of decayed wood (23%) and depressions (11%). The high proportion of saplings on level ground suggests that after the fire regeneration conditions have been favourable across the whole forest floor. Nevertheless, the areas in the vicinity of decayed wood have been particularly important microsites for seedling establishment. The results provide an example of the effects of wildfire on forest structure in a natural Pinus sylvestris dominated forest, demonstrating the non stand replacing character of fire, high variability in stand structure and the abundance of post‐fire regeneration.     

Interactive influences of fire intensity and vertical distribution of seed banks on post‐fire recolonization of a tall‐tussock grassland in Argentina

Abstract Recolonization patterns of a tall‐tussock grassland differ between low‐frequency and high‐intensity fires. A series of laboratory and field experiments were performed on the seed bank and on seeds of the main colonizing species (Carduus acanthoides, Cirsium vulgare, Lotus glaber) to determine and compare the effects of fire frequency and fire intensity on their recolonization potential. Seed‐bank size of colonizing species did not show a significant variation with contrasting fire frequencies, so overall interval‐dependent effects do not seem to affect their propagule pool at the time of fire. However, frequency of fire modified the proportion of viable seeds and their dormancy state according to species. Accumulated emergence from experimentally buried soft‐seeds of Lotus was lower after high‐intensity fires (following wind direction) than after back‐fires (against wind direction), but no significant effects of fire‐front direction on seedling emergence were observed for hard‐seeds of Lotus nor Carduus and Cirsium. Seedling emergence from buried seeds of Cirsium was increased with doubling fuel loads, particularly from deepen soil layers, where Cirsium had most of their viable seeds after a low frequency of fire. Emergence from hard‐seeds of Lotus was less promoted than Cirsium by doubling fuel loads, and according to analysis of excavated seedlings, it was completely inhibited from upper soil layers of the seed bank. Integration of species‐specific and burial depth‐specific responses of Cirsium and Lotus seeds according to fuel load, vertical distribution of the seed banks, seed dormant states and mean emergence depths, resulted in expected emergence values which agree with their previously observed patterns of recolonization. Thus, event‐dependent mechanisms had a better predictive value on recolonization success of the studied species than the observed cumulative effects of fire history on their seed‐bank size.     

Contrasting demographics of tropical savanna and temperate forest eucalypts provide insight into how savannas and forests function. A case study using Corymbia clarksoniana from north‐eastern Australia

Eucalypts (Eucalyptus spp. and Corymbia spp.) dominate many communities across Australia, including frequently burnt tropical savannas and temperate forests, which receive less frequent but more intense fires. Understanding the demographic characteristics that allow related trees to persist in tropical savannas and temperate forest ecosystems can provide insight into how savannas and forests function, including grass–tree coexistence. This study reviews differences in critical stages in the life cycle of savanna and temperate forest eucalypts, especially in relation to fire. It adds to the limited data on tropical eucalypts, by evaluating the effect of fire regimes on the population biology of Corymbia clarksoniana, a tree that dominates some tropical savannas of north‐eastern Australia. Corymbia clarksoniana displays similar demographic characteristics to other tropical savanna species, except that seedling emergence is enhanced when seed falls onto recently burnt ground during a high rainfall period. In contrast to many temperate forest eucalypts, tropical savanna eucalypts lack canopy‐stored seed banks; time annual seed fall to coincide with the onset of predictable wet season rain; have very rare seedling emergence events, including a lack of mass germination after each fire; possess an abundant sapling bank; and every tropical eucalypt species has the ability to maintain canopy structure by epicormically resprouting after all but the most intense fires. The combination of poor seedling recruitment strategies, coupled with characteristics allowing long‐term persistence of established plants, indicate tropical savanna eucalypts function through the persistence niche rather than the regeneration niche. The high rainfall‐promoted seedling emergence of C. clarksoniana and the reduction of seedling survival and sapling growth by fire, support the predictions that grass–tree coexistence in savannas is governed by rainfall limiting tree seedling recruitment and regular fires limiting the growth of juvenile trees to the canopy.     

Dispersal and recruitment dynamics in the fleshy‐fruited Persoonia lanceolata (Proteaceae)

Question: What is the role of dispersal, persistent soil seed banks and seedling recruitment in population persistence of fleshy‐fruited obligate seeding plant species in fire‐prone habitats? Location: Southeastern Australia. Methods: We used a long‐term study of a shrubby, fleshy‐fruited Persoonia species (Proteaceae) to examine (1) seed removal from beneath the canopy of adult plants; (2) seedling recruitment after fire; (3) the magnitude and location of the residual soil seed bank; and (4) the implications for fire management of obligate seeding species. We used demographic sampling techniques combined with Generalised Linear Modelling and regression to quantify population changes over time. Results: Most of the mature fruits (90%) on the ground below the canopy of plants were removed by Wallabia bicolor (Swamp wallaby) with 88% of seeds extracted from W. bicolor scats viable and dormant. Wallabies play an important role in moving seeds away from parent plants. Their role in occasional long distance dispersal events remains unknown. We detected almost no seed predation in situ under canopies (< 1%). Seedling recruitment was cued to fire, with post‐fire seedling densities 6‐7 times pre‐fire adult densities. After fire, a residual soil seed bank was present, as many seeds (77‐100%) remained dormant and viable at a soil depth where successful future seedling emergence is possible (0‐5 cm). Seedling survival was high (> 80%) with most mortality within 2 years of emergence. Plant growth averaged 17 cm per year. The primary juvenile period of plants was 7–8 years, within the period of likely return fire intervals in the study area. We predicted that the study population increased some five‐fold after the wildfire at the site. Conclusions: Residual soil seed banks are important, especially in species with long primary juvenile periods, to buffer the populations against the impact of a second fire occurring before the seed bank is replenished.     

Pine Litter from Afforestations Hinders the Establishment of Endemic Plants in Semiarid Scrubby Habitats of Natura 2000 Network

A sowing experiment was carried out using three endemic secondary successional species that commonly co‐occur with Pinus halepensis in afforestations in southeast Spain. The experiment simulated the natural arrangement of needle litter over soil to test the litter's effect on seedling emergence and early growth of dwarf‐shrubs and annual species, the main components of some European Habitats of Community Interest in Spain. Three sowing treatments were compared in a growth chamber: (1) soil without litter taken from clearings in a pine plantation (BARE); (2) intact soil and litter forming two distinct layers as in the field (PINE); and (3) soil and pine litter mixed in the laboratory (PINEMX). Seedling emergence of Diplotaxis harra and Thymus zygis were seven and two times higher, respectively, on BARE than on the pine litter treatments. Pine litter significantly decreased seedling biomass, length, and number of leaves of D. harra and T. zygis. Thymus capitatum was weakly affected by the presence of pine litter. We suggest that plant recruitment in the understory of P. halepensis is partially controlled by interference of pine litter, which might affect dynamics of the studied species. We propose that management practices counteract this negative effect by manipulating the pine litter layer to achieve successful ecological restoration and conservation of endemic‐rich secondary communities in Natura 2000 sites in semiarid western Mediterranean areas.     

Effects of re‐introducing fire to a central Florida sandhill community

Abstract. A southern ridge sandhill site in central Florida, USA, was burned in 1989, 1991, and 1995 after 63 years of fire‐suppression to simulate a pre‐settlement fire regime. Fire changed species abundance and vegetation structure but caused only minimal changes in species turnover and diversity. There was a general trend for an increase in the cover of herbs following fire but this was a statistically significant effect for only one species, Liatris tenuifolia var. tenuifolia. Aristida beyrichiana increased, litter cover and litter depth were significantly reduced, and ground lichens were eliminated in response to burning. Scrub oaks and palmettos in the ground cover and small shrub layers (height ≤ 1 m) either increased or did not respond to burning, reflecting strong post‐fire resprouting. Diversity in the ground cover and small shrub layers were not affected by fire. Scrub oaks and palmettos in the large shrub and overstorey layers (height > 1 m) were reduced in density, basal area, and longest canopy measurements in response to fire. Species diversity also decreased within these layers following fire. Some Pinus elliottii var. densa survived fire, but their density was reduced. All Pinus clausa were eliminated by fire. Periodic burning can suppress the dominance of shrubs (Quercus spp.) while increasing the cover of grasses and herbs in southern ridge sandhill vegetation.     

Burning Influences on Wiregrass (Aristida beyrichiana) Restoration Plantings: Natural Seedling Recruitment and Survival

Regeneration and expansion of Aristida beyrichiana and Aristida stricta (wiregrass) populations in remaining fire‐maintained Pinus palustris (longleaf pine) stands of the southeastern United States has become an objective of land managers. Although growing‐season fire is required for successful wiregrass seed production, studies examining naturally occurring wiregrass seedling dynamics are few. This study investigates how seedling survivorship is affected by season of burn, seedling size, time since germination, and proximity to adult plants. Restoration at this research site was begun in 1992 with the planting of containerized longleaf pine and wiregrass seedlings. Study plots were established in November 1997 after a growing‐season prescribed fire (June 1996) that resulted in successful seed production and seedling recruitment. Burn treatment plots included (1) no burn (control), (2) fire in the dormant season of the first year after germination (March 1998), (3) fire in the growing season of the first year after germination (August 1998), and (4) fire in the growing season of the second year after germination (July 1999). Seedling mortality increased with growing season burning and close proximity to planted adults. Natural seedling recruitment continued into the second year after initial seed‐drop in all plots, which verifies that wiregrass seed banking occurs for a minimum of 2 years after seed drop. Where wiregrass management objectives include population expansion, seedling recruits should be allowed 1 to 2 years post‐germination without growing season fire for successful establishment.     

Mid-Spring Burning Reduces Spotted Knapweed and Increases Native Grasses during a Michigan Experimental Grassland Establishment

Infestations of the exotic perennial Spotted knapweed (Centaurea maculosa Lam.) hinder the restoration and management of native ecosystems on droughty, infertile sites throughout the Midwestern United States. We studied the effects of annual burning on knapweed persistence on degraded, knapweed‐infested gravel mine spoils in western Michigan. Our experiment included 48, 4‐m² plots seeded to native warm‐season grasses in 1999 using a factorial arrangement of initial herbicide and fertility treatments. Beginning in 2003, we incorporated fire as an additional factor and burned half of the plots in late April or May for 3 years (2003–2005). Burning increased the dominance of warm‐season grasses and decreased both biomass and dominance of knapweed in most years. Burning reduced adult knapweed densities in all 3 years of the study, reduced seedling densities in the first 2 years, and reduced juvenile densities in the last 2 years. Knapweed density and biomass also declined on the unburned plots through time, suggesting that warm‐season grasses may effectively compete with knapweed even in the absence of fire. By the end of the study, mean adult knapweed densities on both burned (0.4‐m²) and unburned (1.3‐m²) plots were reduced to levels where the seeded grasses should persist with normal management, including the use of prescribed fire. These results support the use of carefully timed burning to help establish and maintain fire‐adapted native plant communities on knapweed‐infested sites in the Midwest by substantially reducing knapweed density, biomass, and seedling recruitment and by further shifting the competitive balance toward native warm‐season grasses.     

Influence of fire severity on the regeneration,recruitment and distribution of eucalypts in the Cotter River Catchment,Australian Capital Territory

Abstract Plant responses to fire are variable between and within species and are influenced by numerous factors including fire severity. This study investigated the effects of fire severity on the regeneration and recruitment of forest eucalypts in the Cotter River Catchment, Australian Capital Territory (ACT). This study also examined the potential for the obligate seeder Eucalyptus delegatensis R.T. Baker (Myrtaceae) to expand into adjacent stands dominated by the facultative resprouter Eucalyptus fastigata H. Deane & Maiden (Myrtaceae) by seed shed and seedling establishment beyond the pre‐fire boundary. Sites were located in areas of either higher or lower fire severity, and transects were placed across the boundary of stands of E. delegatensis and E. fastigata. Species distributions, tree survival and seedling densities and heights were recorded, and the location of each boundary was determined as the region of maximum change in species composition along the transects. Eucalyptus delegatensis was the only eucalypt killed by higher severity fire. However, E. delegatensis seedling density was greater at higher severity sites than lower severity sites. Eucalyptus fastigata seedling density was low across all sites, with other eucalypts producing few, if any, seedlings. There was no evidence that E. delegatensis had increased its range into downslope stands dominated by E. fastigata. Patterns of vegetative recovery and seedling recruitment may be related to a number of factors, including differences in allocation patterns between seeders and sprouters, and the effects of overstory and understory competition. It is unclear what processes impede E. delegatensis seedling establishment beyond the stand boundary, but may involve an inability of E. delegatensis to shed seed sufficiently far downslope; unsuitable conditions for germination beyond the boundary; or, competition from a retained or resprouting overstory, despite the potential for increased dispersal distance soon after fire.     

Does predation contribute to tree diversity?

Seed and seedling predation may differentially affect competitively superior tree species to increase the relative recruitment success of poor competitors and contribute to the coexistence of tree species. We examined the effect of seed and seedling predation on the seedling recruitment of three tree species, Acer rubrum (red maple), Liriodendron tulipifera (yellow poplar), and Quercus rubra (northern red oak), over three years by manipulating seed and seedling exposure to predators under contrasting microsite conditions of shrub cover, leaf litter, and overstory canopy. Species rankings of seedling emergence were constant across microsites, regardless of exposure to seed predators, but varied across years. A. rubrum had the highest emergence probabilities across microsites in 1997, but Q. rubra had the highest emergence probabilities in 1999. Predators decreased seedling survival uniformly across species, but did not affect relative growth rates (RGRs). Q. rubra had the highest seedling survivorship across microsites, while L. tulipifera had the highest RGRs. Our results suggest that annual variability in recruitment success contributes more to seedling diversity than differential predation across microsites. We synthesized our results from separate seedling emergence and survival experiments to project seedling bank composition. With equal fecundity assumed across species, Q. rubra dominated the seedling bank, capturing 90% of the regeneration sites on average, followed by A. rubrum (8% of sites) and L. tulipifera (2% of sites). When seed abundance was weighted by species-specific fecundity, seedling bank composition was more diverse; L. tulipifera captured 62% of the regeneration sites, followed by A. rubrum (21% of sites) and Q. rubra (17% of sites). Tradeoffs between seedling performance and fecundity may promote the diversity of seedling regeneration by increasing the probability of inferior competitors capturing regeneration sites.     

Antagonistic effects of large- and small-scale disturbances on exotic tree invasion in a native tussock grassland relict

It is generally accepted that disturbances increase community invasibility. Yet the role of disturbance in plant invasions may be less predictable than often assumed, due to the influence of environmental stochasticity and interactions between disturbance regimes. We evaluated the single and interactive effects of prescribed burning (large-scale, infrequent event) and animal diggings (small-scale, frequent events) on the invasion success of Gleditsia triacanthos L. in a tussock grassland relict of the Inland Pampa, Argentina. Tree seedling emergence and survival were monitored over 4 years, after adjusting for propagule pressure through copious seed addition to all disturbance treatments. Burning altered community structure by suppressing tussock grasses and promoting exotic forbs, whereas simulated, armadillo-like diggings had little impact on herbaceous composition. Overall, seedling emergence rather than survival represented the main demographic bottleneck for tree invasion. Tree establishment success varied among seedling cohorts emerged in different climatic years. In a dry year, emergence was only slightly affected by disturbances. In contrast, for two consecutive wet years, initial burning and armadillo-like diggings exerted strong, antagonistic effects on tree recruitment. Whereas fire alone increased recruitment, the simulated burrowing regime prevented seedling emergence in both burned and unburned plots. The latter effect might be explained by reduced soil moisture, and increased seed burial and predation in excavated patches. Thus, the impact of a single, large-scale perturbation promoting woody plant invasion was overridden by a regime of small-scale, frequent disturbances. Our results show that grassland invasibility was contingent on inter-annual climatic variation as well as unexpected interactions between natural and anthropogenic disturbance agents.     

The effects of a high intensity fire on nutrient cycling in jarrah forest

The effects of high intensity fire on the cycling of nutrients in litter and canopy through fall were studied in pole stand jarrah (E. marginata Bonn ex Sm.) forest near Dwellingup, south-western Australia. In the first year following burning, twice as much litter fell on the burnt site as on an unburnt control site. Concentrations of phosphorus and nitrogen were higher in post-fire litter probably because crown scorch during burning prevented withdrawal of phosphorus and nitrogen into the tree before leaf fall. This, together with the increased weight of litter, resulted in a four-fold increase in the accession of phosphorus and nitrogen to the forest floor in litter one year after the fire on the burnt site. The concentrations of potassium, magnesium, sodium and chlorine in the litter were all significantly lower on the burnt site than on the unburnt site in the first year following burning. During the second year after the fire, significantly less litter fell on the burnt area than on the unburnt control site. Phosphorus concentrations in the litter from the burnt site remained 50% higher than in litter from the control but the other nutrient elements returned to their pre-fire levels. There are indications that more phosphorus and potassium are cycled via canopy leaching immediately after burning. In the second winter following the fire there were no significant differences in the amounts of nutrients in canopy leachate on the burnt and unburnt areas.     

Mechanisms controlling establishment of the non‐bradysporous Banksia integrifolia (Coast Banksia) in an unburnt coastal woodland

Abstract Remnant stands of the non‐bradysporous Banksia integrifolia on the Mornington Peninsula, Victoria appear to be in decline due to old age and other unknown factors. Many stands have been unburnt for >55‐100 years and there is little evidence of successful regeneration by seed. The cause(s) for this lack of recruitment are unclear. In the present study we quantified (i) seed production and germinability in four remnant forests in the region; (ii) the microsite conditions necessary for seedling emergence; and (iii) the effect of herbivore browsing on early seedling survival in order to understand this apparent recruitment failure. Despite large intra‐annual variation, no evidence was found that old forest trees do not produce viable seed. Emergence and survival of seedlings were not inhibited by the presence of groundlayer vegetation. Rather, vegetation facilitated early seedling survival by providing protection from browsing. Seedling transplants exhibited extremely high mortality (≥75%) due to browsing and summer soil desiccation and these factors appear to be major contributors to the lack of recruitment at the study site. Stand‐replacing recruitment is therefore considered to remain unlikely under the present conditions. Developing fire and/or grazing management regimes will be necessary to conserve the structural integrity of these coastal ecosystems.     

Abiotic barriers limit tree invasion but do not hamper native shrub recruitment in invaded stands

The interplay between the invasion of alien plant species and re-colonization of native plant species is important for conservation. Sandy coastal plains (called restinga in Brazil) were used as a model system to explore the abiotic barriers that potentially limit the initial establishment of alien and native woody plants in invaded and non-invaded areas. The study tested the influence of light availability, soil type and litter layer on recruitment of a wind-dispersed alien tree (Casuarina equisetifolia) and two bird-dispersed native shrubs under a Casuarina stand and in the preserved restinga. The effect of soil type and the physical and allelopathic effects of Casuarina litter on seedling emergence of the three species were also evaluated under greenhouse conditions. Low dispersal associated with low seedling emergence and zero survival of young plants (mainly due to microhabitat conditions) apparently prevents the spread of Casuarina in the preserved restinga. The main cause of low recruitment of native species in the Casuarina stand was the physical barrier of the litter. However, if seeds overcome this physical barrier, the presence of litter improves seedling emergence and survival of young plants, mainly because the litter increases soil moisture. Sowing seeds below litter and planting young plants of native shrubs on litter can improve the re-colonization of native plants in invaded areas. In conclusion, Casuarina invasion on sandy coastal plains is strongly limited by abiotic barriers, but anthropogenic disturbances are altering the key processes that naturally make the restinga resistant to invasion.