The coupling of recruitment and disturbance by fire in two resprouting Proteaceae species

Recruitment in plant populations is often tightly coupled to major disturbances such as fires. For species with persistent seed banks, fire-related cues may allow or enhance germination. The litter layer influences germination and may modify the impact of seed predators on seeds and seedlings. The litter layer is obviously affected by fire, providing one mechanism by which disturbance can determine recruitment. We tested the role of litter in the disturbance–recruitment coupling of two species with contrasting seed release timing after fire—Banksia serrata (canopy seed bank) and Telopea speciosissima (transient seed bank) by planting their seeds both early and late in the post-fire recruitment period (PRP) and manipulating litter density in orthogonal treatments. Vertebrate seed predators were excluded. Both species established more seedlings late in the PRP, although results were strongly influenced by very poor establishment at one site. Invertebrate seed predators consumed more T. speciosissima seeds in sites early (69.5%) than late in the PRP (51.2%), while consumption of B. serrata seeds was lower overall and comparable across sites (average 47.3%). Surprisingly, litter had very little effect on establishment and none on invertebrate seed predation, suggesting that other factors are more important. Recruitment was only loosely coupled to disturbance for the canopy seed bank species; for the transient seed bank species, the coupling was tighter but separated in time from the disturbance. Understanding both the strength and temporal aspects of the disturbance–recruitment coupling is necessary for appropriate management of plant functional diversity in fire-prone habitats.     

Effects of inter‐fire intervals on the reproductive output of resprouters and obligate seeders in the Proteaceae

Abstract Fire is often used as a management tool in fire‐prone communities to reduce fuel loads with the intention of reducing the severity and extent of unplanned fires, often resulting in the increased occurrence of fire in the dry sclerophyll vegetation of Australia. This study examined the effects of fire frequency (length of the inter‐fire interval) on the reproductive output of seven plant species in the Proteaceae, including obligate seeding shrubs (Hakea teretifolia, Petrophile pulchella), resprouting shrubs (Banksia spinulosa, Isopogon anemonifolius, Lambertia formosa) and resprouting trees (Banksia serrata, Xylomelum pyriforme). Reproductive output (measured as either number of confructescences or follicles) and relative size were estimated for 100 individuals at each of five sample sites, covering a range of past fire frequencies over 26 years including repeated short inter‐fire intervals. Patterns in reproductive output (after standardizing for size) were related to the life‐history attributes of the species. In areas that had experienced short inter‐fire intervals, obligate seeders had greater reproductive output compared with longer intervals, and the reproductive output of resprouting shrubs was less. Fire frequency did not affect reproductive output of the resprouting trees. The decreased reproductive output of the resprouting shrubs could be due to the allocation of resources to regrowth following fire rather than to reproduction. It is less clear what process resulted in the increased reproductive output of obligate seeders in high fire frequency areas, but it could be due to the most recent fires being more patchy in the areas experiencing shorter inter‐fire intervals, or it may have resulted from the selection for early reproduction in the high fire frequency areas. These results highlight the need to take into account past fire frequency at a site, in addition to time since the last fire, when planning prescribed fires.     

The absence of fire can cause a lag phase: The invasion dynamics of Banksia ericifolia (Proteaceae)

The transition from a species introduction to an invasion often spans many decades (a lag phase). However, few studies have determined the mechanisms underlying lag phases. Such a mechanistic understanding is vital if the potential ecosystem‐level impacts are to be predicted and the invasion risks to be managed proactively. Here we examine Banksia ericifolia, introduced for floriculture to South Africa, as a case study. We found 18 sites where the species has been planted, with self‐sustaining (naturalized) populations at four sites, and an invasive population at one site. The invasion originated from around 100 individuals planted 35 years ago; after several fires this population has grown to approximately 10 000 plants covering about 127 ha. The current invasion of B. ericifolia already has ecosystem‐level impacts, for example the nectar available to bird pollinators has more than doubled, potentially disrupting native pollination networks. If fires occurred at the other naturalized sites we anticipate populations would rapidly spread and densify with invaded areas ultimately become banksia‐dominated woodlands. Indeed the only site other than the invasive site where fire has occurred regularly is already showing signs of rapid population growth and spread. However, recruitment is mainly immediately post fire and no seed bank accumulates in the soil, mechanical control of adult plants is cheap and effective, and immature plants are easily detected. This study is a first in illustrating the importance of fire in driving lag phases and provides a valuable example for why it is essential to determine the mechanisms that mediate lag phases in introduced plant species. Serotinous species that have been introduced to areas where fire is suppressed could easily be misinterpreted as low risk species whilst they remain in a lag phase, but they can represent a major invasion risk.     

Variation in serotiny of three Banksia species along a climatic gradient

The degree of serotiny (i.e. the proportion of follicles remaining closed in each year's crop of cones since the last fire) was measured in Bank-sia attenuata, B. menziesii and B. prionotes at five sites along a climatic gradient extending 500 km north of Perth, Western Australia. The decrease in annual rainfall and increase in average temperature along the gradient paralleled a decrease in plant height and an increase in the degree of serotiny of all species. Extreme serotiny was recorded in the scrub-heath at the xeric end of the gradient whereas two species were essentially non-serotinous in the low woodland at the most mesic site. It is concluded that degree of serotiny is related to the fire characteristics of the site which depend on plant height. In xeric scrub-heath, the entire canopies of the Banksia spp. are consumed by fire which promotes massive release of seed. This facilitates recruitment in an otherwise unpredictable and unreliable seedbed. In mesic woodland, where cones rarely come into contact With flames, seeds are released spontaneously and site conditions are more conducive to recruitment in the inter-fire period.     

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

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

Changes in the stand structure (1975–2000) of coastal Banksia forest in the long absence of fire

Abstract Revisitation studies enable long‐term changes in vegetation to be deciphered and insights into plant community succession to be gained. This is particularly important when assessing the effects of fire exclusion in ecosystems where fire is thought to have once been common. Using two adjacent coastal Banksia integrifolia forest stands in southern Victoria, Australia initially surveyed in 1975 by Hazard and Parsons, we document the changes that occurred in the stand structure between 1975 and 2000. Western Park (WP) has now remained unburnt for over 100 years while Cerberus Naval Base (CNB) was most recently burnt in 1942. Banksia integrifolia densities have decreased at both sites over the 25‐years period by an average of 42–77%, as have other coastal native shrubs (e.g. Leptospermum laevigatum, Leucopogon parviflorus). Trees at WP appear to have died due to old age while mortality at CNB is presumed to be due to stand thinning in response to intense competition for light. Successful recruitment by Banksia has been minimal; trees less than 9 cm girth over bark at breast height (GBBH) were absent at CNB while no trees <19 cm GBBH were observed at WP. The long‐term absence of disturbance such as fire is suspected to be one of the causes of regeneration failure of the stand at WP. Gap phase regeneration is not apparent in B. integrifolia and hence, long‐term succession to a more grassy community is likely when fire is excluded for long periods.     

Inter- and intraspecific differences in the life history and growth of Caridina spp. (Decapoda: Atyidae) in Hong Kong streams

1. The life‐history pattern of three populations of Caridina cantonensis (Atyidae) and one population of Caridina serrata were studied in four Hong Kong streams: Pak Ngau Shek (PNS), Kap Man Hang (KMH), Pak Tam Chung (PTC), and Lung Fu Shan (LFS). Caridina cantonensis occurred at PNS, KMH and PTC while C. serrata was present at LFS only. Monthly quantitative sampling was carried out at each study site over 2 years to investigate life‐history patterns and cohort‐specific growth rates. 2. Breeding by both species was mainly restricted to the wet season, and there was an increase in the incidence of ovigerous females as water temperatures rose at the start of the summer monsoon. The number of cohorts and the frequency of recruitment of C. cantonensis (one to three times each year) were highly site‐specific, but consistent between years. 3. Shrimp growth was size‐dependent, and decreased with increasing body size. Caridina cantonensis at PTC had the highest cohort‐specific growth rates (0.05–0.14 mg ash‐free dry weight (AFDW) mg^?1 day^?1), followed by C. serrata at LFS (6% lower), and C. cantonensis at KMH and PNS (16–39% lower). Shrimp life spans exceeded 1 year (17–22 months), depending on site and species. 4. Sexual maturity occurred at an earlier age and at a smaller size in populations with higher growth rates. Shrimps at PTC and LFS matured at approximately 4 months old; this was 3 months earlier than at KMH and 5 months earlier than at PNS. Females of C. cantonensis at PTC and C. serrata at LFS may have bred twice during each breeding season, while females in the other two populations bred once only. The number of cohorts produced by each population in each year did not vary between the years of the study. Most sexually mature individuals only survived long enough (for 10–12 months after maturation) to breed during one season. 5. The mean brood size of C. cantonensis varied among streams and was 25–28% larger at PNS and KMH than at PTC. Egg size did not differ among populations. Larger brood sizes at PNS and KMH may have been a consequence of increased availability of algal food in these unshaded stream sites. Caridina serrata had similar egg and brood sizes to C. cantonensis, but females were smaller and reproductive investment was higher. Thus, the degree of intraspecific variation in atyid breeding in Hong Kong was at least equal to, if not greater than, the extent of interspecific variation. Interspecific differences in life history may reflect the frequency of droughts and spate intensity experienced by C. serrata at LFS.     

Population structure and spatial pattern in the dioecious shrub Ceratiola ericoides

Abstract. The dioecious shrub Ceratiola ericoides (Florida rosemary) dominates xeric, infrequently burned Florida scrub vegetation, often to the near-exclusion of other woody species. We studied the spatial pattern, age, sex and size structure of four populations in Florida, USA: two coastal scrub populations subject to recurrent local disturbances due to sand movement, and two inland scrub populations in sites periodically burned by stand-replacing fires. The age structure of individual genets was estimated from node counts and used to describe the age structure of the populations. The sex ratio of males to females was not significantly different from 1:1, except within a female-biased coastal population subject to frequent sand movement. Node counts indicated that the mean age for reproductive individuals was 15 - 16 yr for the inland populations and 13 - 16 yr for the coastal populations. In all sites, there was no difference in mean age between males and females. Vegetative reproduction was uncommon except for the least-disturbed coastal population where 72 % of the reproductive individuals originated through layering. Individuals were generally randomly dispersed at the coastal sites, whereas significant aggregation of males and females occurred in the inland sites where the populations were initiated following fire. Seedling recruitment was continuous in the disturbed coastal scrub site, where 35% of the individuals were juveniles. Most juveniles were dispersed from 0.5 to 0.75 m around females. At one of the inland sites, where juveniles comprised 11% of the population, juveniles were clustered at 0.25 to 5.75 m around females. Coastal populations were all-aged, while inland populations were uneven-aged. Recruitment appears to follow periods of disturbance; infrequent fire in the inland populations and continuous sand movement on the coast are factors initiating recruitment.     

The influence of fire frequency on arbuscular mycorrhizal colonization in the shrub Dillwynia retorta (Wendland) Druce (Fabaceae)

 Fire regimes have three inter-related components that can affect population dynamics: frequency, intensity and season. However, there has been little effort to study the effects of any of these components on arbuscular mycorrhizas (AM). In order to examine the long-term effects of fire frequency on AM colonization, the roots of Dillwynia retorta were examined at 32 sites supporting Hawkesbury Sandstone vegetation in the Sydney region of southeastern Australia. These sites were representative of the broad-scale variability in fire frequencies with respect to the length and timing of inter-fire intervals found in the Sydney region during the previous 30 years. The length of the shortest inter-fire interval was significantly correlated with total AM colonization, and the length of the longest inter-fire interval was related to the arbuscular colonization. The length of the most-recent inter-fire interval and the time since the shortest inter-fire interval were not related to AM colonization in D. retorta. Furthermore, AM colonization was directly related to the local abundance of the host plant, indicating that the effects of fire frequency on AM colonization are likely to occur indirectly via direct effects on the host plant. Canonical correspondence analysis demonstrated that the presence and abundance of alternate potential hosts had no influence on mycotrophy in D. retorta. Thus, the impact of fire on D. retorta was probably the main factor influencing its mycorrhizal status in relation to fire history. Accepted: 16 October 1998     

Population fluctuations and extinctions of small rodents in coastal southern California

Summary The population dynamics of three sympatric rodents, Microtus californicus, Mus musculus, and Reithrodontomys megatolis was studied at four sites in coastal southern California. The study was undertaken to determine the extent of local demographic diversity in rodent populations.The populations of all rodent species became extinct on one site, while on another site the populations fluctuated widely and on two other sites the populations remained relatively stable. The most common species, Reithrodontomys, exhibited differences in reproduction, age class structure, recruitment, and survivorship on the two sites which were monitored for relatively long terms. Immigration was the main source of new individuals entering the sites where the Reithrodontomys population was most persistent.On a local scale, some life history characteristics are affected in a density dependent fashion. When viewed on a global scale, the non-equilibrium nature of the rodent populations becomes clear.     

Predation of Northern Pike (Esox lucius L.) Eggs: A Possible Cause of Regionally Poor Recruitment in the Baltic Sea

Northern pike (Esox lucius) spawning habitat and egg mortality were studied in three spawning areas in 2001 along the Swedish coast of the Baltic proper: the Blekinge Archipelago, Kalmar Sound and coastal freshwater streams. Spawning peaked during the last week of April in streams, at temperatures ranging from 7.7 to 8.9 °C and during the first week of May in brackish waters, at temperatures ranging from 8.9 to 13.8 °C. Spawning occurred in shallow waters, at depths between 0.2–1.5 m, but generally most of the spawn was found in the shallowest areas. In streams, eggs were mainly attached to emersed vegetation, while in brackish sites pike eggs were well scattered among flooded emersed plants, submersed plants and filamentous algae. Mean egg density varied between 469–1829 m^–2 with the lowest density observed in Kalmar Sound. The calculated egg loss occurring from approximately one day after spawning to one day before hatching ranged from 41±7% in coastal streams to 67±6% in the Blekinge Archipelago and 100% in Kalmar Sound. The significant removal of eggs from spawning sites in Kalmar Sound and Blekinge was most likely due to predation from several fish species. In situ observations and stomach analyses suggested that many pike eggs in Kalmar Sound were lost to the three-spined stickleback (Gasterosteus aculeatus), a species that presently dominate the littoral small fish community. This study therefore suggests that egg predation by sticklebacks and other fishes may be a possible cause of the reported poor recruitment of coastal pike populations in the Kalmar Sound region.     

Demographic structure of California chaparral in the long-term absence of fire

Abstract. Demographic structure of 12 chaparral sites unburned for 56 to 120 years was investigated. All sites were dominated by vigorous shrub populations and, although there was colonization by seedlings of woodland tree species in several stands, successional replacement of chaparral was not imminent. Although successional changes in community composition were evident, there was no indication of a decline in species diversity. Non-sprouting species of Ceanothus suffered the greatest mortality at most, but not all, sites. Sprouting shrubs, such as Quercus and Heteromeles had very little mortality, even in stands more than a century old. All postfire resprouting species had multiple stems of different ages indicating these shrubs were capable of continuously regenerating their canopy from basal sprouts. Ceanothus populations were highly clumped and there was a significant correlation across all sites between variance/mean ratio and percentage mortality. As Ceanothus populations thinned, they became less clumped. In mixed chaparral stands, Quercus and Heteromeles were significantly taller than associated Ceanothus shrubs and overtopped the Ceanothus; at two sites, the density of live Quercus per plot was correlated with the density of dead Ceanothus. Thus, mortality of Ceanothus stems is likely related to both intra and interspecific interations. Seedling recruitment was observed for most shrub species that regenerate after fire by resprouting; seedling and sapling densities ranging from 1000–36 500 ha^-1 were recorded for Quercus dumosa, Rhamnus crocea, Prunus ilicifolia, Heteromeles arbutifolia and Cercocarpus betuloides. For all but the last species, seedlings and saplings were most abundant beneath the canopy cover and not in gaps. Across all sites, recruitment was significantly correlated with depth and bio-mass of the litter layer. Cercocarpus betuloides was present in several stands, but seedling establishment was found only in one very open, disturbed stand. Regardless of stand age, taxa such as Adenostoma, Arctostaphylos and Ceanothus, which recruit seedlings after fire, had no significant seedling production.     

Variation in the impact of exotic grasses on native plant composition in relation to fire across an elevation gradient in Hawaii

The impact that an exotic species can have on the composition of the community it enters is a function of its abundance, its particular species traits and characteristics of the recipient community. In this study we examined species composition in 14 sites burned in fires fuelled by non‐indigenous C4 grasses in Hawaii Volcanoes National Park, Hawaii. We considered fire intensity, time since fire, climatic zone of site, unburned grass cover, unburned native cover and identity of the most abundant exotic grass in the adjacent unburned site as potential predictor variables of the impact of fire upon native species. We found that climatic zone was the single best variable for explaining variation in native cover among burned sites and between burned and unburned pairs. Fire in the eastern coastal lowlands had a very small effect on native plant cover and often stimulated native species regeneration, whereas fire in the seasonal submontane zone consistently caused a decline in native species cover and almost no species were fire tolerant. The dominant shrub, Styphelia tameiameia, in particular was fire intolerant. The number of years since fire, fire intensity and native cover in reference sites were not significantly correlated with native species cover in burned sites. The particular species of grass that carried the fire did however, have a significant effect on native species recovery. Where the African grass Melinis minutiflora was a dominant or codominant species, fire impacts were more severe than where it was absent regardless of climate zone. Overall, the impacts of exotic grass‐fuelled fires on native species composition and cover in seasonally dry Hawaiian ecosystems was context specific. This specificity is best explained by differences between the climatic zones in which fire occurred. Elevation was the main physical variable that differed among the climatic zones and it alone could explain a large percentage of the variation in native cover among sites. Rainfall, by contrast, did not vary systematically with elevation. Elevation is associated with differences in composition of the native species assemblages. In the coastal lowlands, the native grass Heteropogon contortus, was largely responsible for positive changes in native cover after fire although other native species also increased. Like the exotic grasses, this species is a perennial C4 grass. It is lacking in the submontane zone and there are no comparable native species there and almost all native species in the submontane zone were reduced by fire. The lack of fire tolerant species in the submontane zone thus clearly contributes to the devastating impact of fire upon native cover there.     

Studies in the ecology of coastal heath in New South Wales

Effects of heating dry seed were investigated in Banksia serratifolia and B. ericifolia. Seeds were inviable after 7 min exposure at 150°C or higher temperatures but remained viable after exposure at 100°C and lower temperatures. Imbibed seeds show no dormancy, and seeds survive fire insulated from heat in the thick woody follicles which may persist unopened for several years on the parent plant but open following fire. Effects of nutritional supplements were observed in the seed germination and seedling survival and growth of Banksia serratifolia, B. aspleniifolia and B. ericifolia. Germination with radicle and hypocotyls extension was not significantly affected by a wide range of mineral nutrient regimes. In pot experiments using a heath soil seedling survival and growth were adversely affected by moderate additions of phosphate with surviving seedlings showing toxicity symptoms and poor development of proteoid roots. Moderate supplements of potassium had no adverse effect, and in B. serratifolia and B. ericifolia lessened the adverse effects of phosphate addition. The slow growth of the seedlings accords with the normal low nutrient availability in heath soils but seedlings show little capacity for rapid exploitation of any temporary increase of available nutrients after fire.     

Reproductive biology of the rare and endangered Banksia brownii Baxter ex R. Br. (Proteaceae)

Abstract Banksia brownii is an endangered species, now limited to ～ 15 disjunct populations in southwestern Western Australia. Data on flowering phenology, plant size, fruit set, pollination and the mating system were gathered for two of these populations between March and October 1993. Flowering for both populations followed a similar pattern, with open flowers first evident in April, and the number of inflorescences with open flowers peaking in June. At both locations, trees differed considerably with respect to their size, the total number of inflorescences produced and the length of their flowering season. Fruiting success was typically low, with approximately half of all inflorescences failing to develop into infructescences. Only 1. 8% of the flowers originally present on inflorescences developed into follicles. The distribution of follicles along each infructescence was non-random, with most forming in the middle third of the infructescence for reasons relating to nutrient supply and pollinator behaviour. More flowers opened during the day than at night, although pollen was lost from individual flowers during both periods. Honeyeaters such as Phylidonyris novaehollandiae were common at the two study sites, and often carried large loads of B. brownii pollen. Though less frequently caught, the nocturnal mammals Rattus fuscipes and Tarsipes rostratus also bore substantial amounts of pollen. Most inflorescences from which these mammals and birds were excluded remained barren. Fruiting success was further reduced when invertebrates such as Apis mellifera were also prevented from visiting inflorescences. The ability of B. brownii to set at least some fruit in the absence of biotic poli-nators indicates that the species is partially self-compatible. Honeyeaters foraged preferentially at inflorescences with one to two thirds of their flowers open, probing mainly along the ‘advancing front’ of open flowers. These animals moved more frequently between inflorescences on the same plant than between those on different plants, and were often recaptured in the same locations. Mammals also appeared to be sedentary. Both B. brownii populations had mixed mating systems, with genetically determined outcrossing rates of ～0.7. The unusually high level of selfing in each population is presumably a reflection of the species’ self-compatibility and the foraging behaviour of its pollinators.     

Fire temperatures and follicle-opening requirements in 10 Banksia species

Temperature requirements for follicle rupture were assessed in 10 Banksia species from south-western Australia. Species examined varied in degree of serotiny, persistence of dead florets, height, follicle size and number, and dependence on seed for regeneration. When treated for 2 min at temperatures over the range 100–500°C, follicles of some species ruptured at quite low temperatures (e.g. Banksia tricuspis with 50% opening at 145°C). Others required substantially higher temperatures (e.g. Banksia hookeriana with 50% opening at 390°C). There was a significant correlation between temperature requirements for follicle rupture and persistence of the highly combustible florets. However, there was no overall correlation between degree of serotiny and temperature requirements, nor with the other biological attributes assessed. Cone temperatures and follicle rupture in five co-occurring Banksia species were monitored for an experimental spring burn in Banksia- dominated shrubland. Temperatures recorded at follicle surfaces were higher than those needed for follicle rupture in the four species with persistent florets. Critical temperatures were rarely reached for the weakly serotinous Banksia menziesii which possesses bare cones and an open canopy.     

Demography of the long‐lived conifer Agathis ovata in maquis and rainforest,New Caledonia

Abstract. The endemic New Caledonian conifer Agathis ovata occurs as an emergent tree in fire‐prone shrublands (maquis), and fire‐sensitive rainforest. Growth, survivorship and recruitment over 5 yr were compared for populations from forest and maquis on ultramafic substrates in New Caledonia to investigate whether demographic behaviour varied in response to the strongly contrasting forest and shrubland environments. Growth of seedlings and of small (30–100 cm height) and large (100 cm height; 5 cm DBH) saplings was slow, but varied significantly among stages, site types and years. The greatest difference in growth rates was among stages, seedlings growing 0.34 cm.yr^?1, small saplings 1.06 cm.yr^?1 and large saplings 2.13 cm.yr^?1. Tree DBH increased by only 0.05 cm.yr^?1 and, based on these rates, individuals with DBH of 30 cm are estimated to be more than 700 yr old. Few trees (3.5%) produced cones in any year and seedling recruitment was low, but some recruitment was recorded each year in both maquis and forest. Rates of recruitment per parent were highest in forest (1.28.yr^?1, cf 0.78.yr^?1), but the higher density of trees in maquis meant that overall recruitment was greater there (92 ha^?1.yr^?1, cf 56 ha^?1.yr^?1). Seedling mortality ranged from 0.9 to 2.9% among years with no significant difference between maquis and forest. No sapling mortality was recorded, but annual tree mortality ranged from 0 to 1.4%. Evidence from a recently burned site indicated that while trees may survive fire, seedlings and saplings do not. Post‐fire seedling recruitment per ha from surviving trees was four times lower than in unburned sites, but growth rates were four times higher. Similar demographic attributes, including high survivorship, low growth rate and low rates of recruitment over a long reproductive life, characterize Agathis ovata populations in both maquis and rainforest in New Caledonia and are indicative of a broad tolerance of light environments that is unusual among tree species. These demographic attributes help to explain the long‐term persistence of the species in these strongly contrasting habitats.     

Invasion and persistence of bird-dispersed,subtropical thicket and forest species in fire-prone coastal fynbos

Abstract. Seedling abundance at four microsites (open fynbos, beneath emergent fynbos shrubs, beneath thicket, and beneath forest) was determined at three coastal dune landscapes, located along a gradient of increasing summer rainfall and where fire-dependent fynbos was the predominant vegetation. At all sites thicket seedlings were most common beneath emergent fynbos shrubs and under thicket clumps; seedlings of forest species were most abundant at forest microsites although some individuals were recorded beneath thicket. Very few thicket seedlings were observed in open fynbos. Birds play a keystone role in facilitating establishment of the fleshy fruit-bearing thicket flora. Seedling abundance at microsites of different thicket and forest species was generally unrelated to fruit abundance. Germination success of most species was highest under shaded conditions; soil organic content had no effect on germination. Removal of pulp and birdingestion enhanced the germination, relative to untreated controls, of two out of three species tested. A simple Markov model predicted a gradual increase in cover of the thicket and forest component and a gradual decline in fynbos under a ‘normal’ (20-yr interval) fire regime simulated over 10 cycles. Although inter-fire seedling establishment under emergent fynbos shrubs is important in the initial colonisation of fynbos by obligate resprouting thicket shrubs, these species persist and expand by vegetative recruitment after and between fires, respectively. In the prolonged absence of fire, the endemic-rich and fire-dependent fynbos flora would be replaced by species-poor forest and thicket.     

EFFECTS OF FIRE ON CLONAL GROWTH AND DYNAMICS OF PITYOPSIS GRAMINIFOLIA (ASTERACEAE)

The rhizomatous perennial Pityopsis graminifolia was studied in a Florida sandhill community in an annually burned site, a periodically burned site, and a site that has been protected from fire since 1965. These different fire regimes significantly affected the demography and life histories of both plants and plant parts in this clonal species. Fires resulted in reductions in ramet biomass and height, and an increase in the (root + rhizome)/shoot biomass ratio. Burning also decreased the total number of flower heads and new rhizomes produced per ramet. However, the survivorship of initiated rhizomes was greater in burned sites and resulted in a larger number of established daughter ramets per clone. As a result, in burned sites there was a shift in clone structure toward larger numbers of smaller ramets, but there were no significant reductions in seed or rhizome production on a per genet basis. The results showed that the responses to fire in P. graminifolia are different when measured at the genet vs. ramet level and that the effects of fire on clones can be explained by demographic responses of plant parts. Population regeneration in the study sites was dependent on successful clonal ramet production because no seedling recruitment was observed. This suggests that disturbances other than fire are important for new genet recruitment in these clonal populations.     

Population age structure of Pinus banksiana at the southern edge of the Canadian boreal forest

Abstract. To assess the effects of site type, forest initiation periods and fire regimes on the dynamics of Pinus banksiana (Jack pine), the age structure of 69 populations of the species was analyzed. Two landscapes with different fire regimes were selected in the southern part of the Canadian boreal forest in Québec: the ‘mainland landscape’ is characterized by a fire regime of large lethal fires, the ‘island landscape’ is affected by a complex fire regime including lethal and non-lethal fires. Age structure was compared between forest initiation periods and site types (mesic mainland, xeric mainland and xeric island) using the Shannon regularity index. An even-aged population structure was found within the first 100 yr following a lethal fire, while after that period the population structure becomes more uneven-aged. Under mesic conditions, populations tend to have an even-aged structure, under xeric conditions an uneven-aged structure. Natural openings present in xeric sites allow for recruitment in the absence of fire. This permits the self-maintenance of Pinus banksiana. Xeric island populations show more uneven-aged structures than xeric mainland populations. The occurrence of non-lethal fires on the islands creates uneven-aged structures. Further, the results suggest that the selection pressure of the island fire regime, favouring non-serotinous and mixed P. banksiana individuals, is one of the factors responsible for a higher recruitment in the absence of fire on islands than on the mainland.