Banksia Species Research Articles

Seed Bank Dynamics of Three Co-Occurring Banksias in South Coastal Western Australia: the Role of Plant Age, Cockatoos, Senescence and Interfire Establishment.

Seed bank dynamics of three co-occurring, non-sprouting Banksia species (B. baxteri, B. speciosa and B. coccinea) in patch-burnt scrub-heath (aged 10 and 21 years) were studied in the southern sandplains of Western Australia. In the younger plants, canopy seed storage was highest in B. coccinea. However, 21-year-old B. coccinea stored an order of magnitude fewer seeds than the other species and no more than young B. coccinea. Seed storage per year increased exponentially with plant age in B. speciosa and B. baxteri, whereas a quadratic function, peaking at 16 years, best described seed storage in B. Coccinea. Degree of serotiny was lowest in B. coccinea. Seed abortion did not vary between age cohorts but was highest in B. coccinea. Granivory ranged from 18 to 42% and was highest in the older plants and in B. baxteri. Cockatoos removed about 20% of cones in B. baxteri and B. coccinea and 10% in B. speciosa. Experimental cone removal accelerated follicle opening, especially in B. coccinea, irrespective of whether cones were placed on the ground (simulating cockatoo removal) or reattached to the plant (simulating plant death). Half the 21-year-old B. coccinea were dead and the remainder were considered senescent, as most branches showed dieback and cone fertility had fallen to 8%. Death of the other species was negligible, with cone fertility rising to a mean of 45% (B. speciosa) and 66% (B. baxteri). Interfire establishment was significant only in B. coccinea. The build-up of a viable seed bank with time occurred at a slower rate than for non-sprouting banksias in the northern sandplains.

Assessing the risk of invasive success in Pinus and Banksia in South African mountain fynbos

Abstract. South African mountain fynbos has been severely invaded by trees and shrubs introduced from other mediterranean‐climate regions. Management of these invasions should involve controlling current invaders and screening future introductions. Invasion windows are described and functional groups are defined for pines based on life history attributes important for invasion in the fire‐prone mountain fynbos. The most successful invasive pines here (Pinus halepensis, P. pinaster and P. radiata) are fire‐resilient and have small seeds, low seed‐wing loadings, short juvenile periods, moderate to high degrees of serotiny and relatively poor fire‐tolerance as adults. Other species with these attributes, especially from mediterranean‐climate regions, wouldbe high‐risk introductions. Taxa in other functional groups have not become major weeds even with widespread man‐aided dissemination.Experience with pine invaders was used to define functional groups in western Australian Banksia species (Proteaceae), shrubs and trees which include taxa with similar attributes to fynbos invaders (e.g. Hakea and Pinus spp.). Banksias have only recently been introduced to the Cape, and are likely to be increasingly cultivated for the cut flower market. Tall serotinous shrubs with many small seeds per plant, short juvenile periods and low fire tolerance were identified as high risk introductions. This group includes thicket‐forming species which maintain very large viable seed banks, e.g. Banksia burdettii, B. hookeriana and B. leptophylla. Low sprouting shrubs with few large seeds per plant and long juvenile periods are unlikely to become invasive in mountain fynbos.The approach of defining functional groups based on life history attributes and invasion windows is valuable for predicting the probability of invasive success. Chance interactions suchas an opportunistic dispersal mutualism between Pinus pinea and an introduced squirrel sometimes confound these predictions and underscore the idiosyncracies inherent in biological invasions.

Breeding System and Tests for Pollen-Limitation in Two Species of Banksia

Three factors that potentially influence fruit set (breeding system, inadequate cross-pollination and variable floral display) were examined for two species of Banksia. Firstly, self-pollination and autogamy treatments failed to produce any fruit in B. spinulosa and produced very few fruit in B. paludosa. This suggests that cross pollen is required to produce the level of fruit set observed in the field. Secondly, when plants were given abundant cross pollen, fruit set was not altered in B. spinulosa but was in B. paludosa. Although the number of follicles per inflorescence was was not different for open- pollinated (control) and manipulated B. paludosa inflorescences, the latter produced twice the proportion of inflorescences with follicles produced by control plants and twice the total number of follicles per plant. Thirdly, larger floral display in open-pollinated B. spinulosa plants was associated with a greater production of fruit. However, larger floral display was not associated with a greater reproductive output in B. paludosa, and we suggest that recurrent pollen-limitation in this species may be responsible for this result.

Fire-Related Dynamics of a Banksia Woodland in South-Western Western Australia

We studied the post-fire vegetation development of a low open woodland dominated by Banksia attenuata and B. menziesii near Perth, Western Australia. Two similar stands burned in autumn and spring displayed different regeneration patterns, with seedling regeneration occurring only in the autumn burn area. Vegetative regrowth was more rapid and post-fire species numbers were higher in the spring burn area. Introduced annuals increased significantly in the autumn fire area. Longer-term vegetation development was studied in a series of stands ranging in age since last fire from 1 to >44 years. Species richness was greatest in the 5-year-old stand, and many shrub species were most abundant 2-5 years after fire. Non-native annuals were found only in stands less than 5 years old since last fire. Dominance by the shrub Eremaea pauciflora increased with stand age, although shrub structure and total biomass did not vary greatly except in the oldest stand studied. The proportion of total shrub biomass accounted for by leaves declined with stand age. Both the two major Banksia species had mixed size structures with seedlings present in all stands, indicating that neither is dependent on fire for recruitment. The results indicate that while autumn burns promote seedling regeneration they may also increase invasion by non-natives, and spring burning may be preferable in these Banksia woodlands. Burning rotations longer than those required for fuel reduction purposes are necessary to maximise conservation values.

Seed Banks, Fire Season, Safe Sites and Seedling Recruitment in Five Co-Occurring Banksia Species

Quantity of seed stored in the canopy of 5 co-occurring Banksia species varied by nearly 2 orders of magnitude. The 3 species which resprout vegetatively after fire, produced less seeds and retained smaller seed banks than 2 non-sprouting species. Contiguous patches of scrub-heath were burned in spring and autumn. The spring fire was cooler, and both sets of seed released subsequently did not germinate until the following (common) winter. Rate of seed release was higher after the autumn fire. The non-sprouting species released more seeds after each fire and yielded more seedlings per parent than the resprouting species. Percentage (field) germination of the non-sprouters was not consistently different from that of the resprouters. Seeds exposed on the soil surface during summer soon lost viability compared with buried seeds. The large number of seedlings established up to 8 months after the spring fire resulted from many seeds escaping exposure by dispersal into litter-covered safe' sites. Although litter microsites covered only 30% of the ground surface after the spring burn, they accounted for 80% of seedlings both before and after the summer drought. Litter microsites covered only 14% of the autumn-burned site but accounted for 60% of seedlings before summer and 40% after summer, suggesting density-dependent thinning of seedlings. The autumn-burned site supported more than twice the density of seedlings than the spring-burned site by the end of the 1st winter. Summer mortality of seedlings was 32% in the spring-burned site and 65% in the autumn-burned site, equalizing the seedling:parent ratio at both sites. Net recruitment of 1-yr-old seedlings varied from 0 for 2 resprouters to >100 per parent for a non-sprouter.

Coexistence and Competitive Exclusion of Banksia hookeriana in the Presence of Congeneric Seedlings along a Topographic Gradient

Banksia hookeriana is restricted to the midrange of a gradient from a sand dune swale to a sand-over-limestone ridge in Western Australia. As a monoculture, B. hookeriana seedlings established equally at three sites along the gradient, but when mixed with seedlings of 4 other Banksia species abundant along the gradient, B. hookeriana was eliminated from all sites except where it occurs naturally. Drought stress, as measured by leaf xylem tension and stomatal conductance, increased with greater density of seedlings, with increase in elevation, and over summer. The negative interaction between certain habitats and interspecific competitive pressure in association with the 1st summer drought may account for the restricted distribution of this species.

Seasonal Variation in Flowering Intensity and Pollination Limitation of Fruit Set in Four Co-Occurring Banksia Species

Patterns of flowering, levels of fruit set and pollination limitation of fruit set were examined over four years in a group of four co-occurring Banksia species (Proteaceae) in south-eastern Australia

Fire temperatures and follicle‐opening requirements in 10 Banksia species

AbstractTemperature 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.

Seed Production and Mortality in a Rare Banksia Species

(1) Seed production and release by Banksia tricuspis, a small tree restricted to a 50 km2 area in south-western Australia, were assessed. Most plants in the study population flowered in the nineteenth year after fire and on average 16 500 ovules per adult were produced. (2) Most flower heads were destroyed by moth larvae and larval-seeking cockatoos. Of the 1 5 young seeds produced on average per adult, almost half aborted, apparently due to the constraints of the breeding system and limited supply of mineral nutrients. Beetle larvae destroyed a further 15% of mature seeds. (3) There was marked senescence and spontaneous release of seeds in the fourth and subsequent years. The mean value of eighty-four canopy-stored viable seeds per adult that remained were almost entirely accounted for by the size of the crops for the last 3 years. (4) All viable seeds were released in response to an autumn wildfire. Seedling establishment only occurred immediately after the fire. (5) Low seed production and rapid depletion of the canopy-stored seed bank are not sufficient in themselves to account for the rarity of B. tricuspis. Management in the wild should include conservation of cockatoos and other animals which consume the granivorous moth larvae and control of the fire regime.

Flower colour change in Banksia ilicifolia: A signal for pollinators

AbstractBoth birds and insects visit yellow flower heads of Banksia ilicifolia rather than those in the pink or red phases. Birds carry most pollen. Substantial nectar and pollen rewards are present only in the yellow phase. The timing of flower colour change also corresponds to a decline in viability of presented pollen and stigma receptivity. Colour change is age‐dependent rather than pollinator‐induced. Bird visits to yellow or red heads are essentially determined by the availability of nectar in each rather than differences in their visibility. Fruit set is negligible in the absence of pollinators but still < 1% in their presence. Banksia ilicifolia has the smallest heads and is the most localized of five co‐occurring and partly co‐flowering Banksia species. It is hypothesized that the restriction of flower colour change to B. ilicifolia increases the competitiveness of this species: bird visitors are directed to flower heads with abundant nectar, viable pollen and receptive stigmas, foraging and pollination efficiency thereby being enhanced without a marked reduction in long‐distance attractiveness of the tree to potential pollinators.

High-Levels of Outcrossing in Populations of Banksia spinulosa R.Br. and Banksia paludosa Smith

Rates of outcrossing were measured for two species of Banksia at Barren Grounds Nature Reserve, near Robertson, N.S.W. For B. spinulosa in a woodland area, both single-locus and multi-locus estimates of outcrossing approached the levels predicted for panmixia. A single-locus estimate for B. paludosa cohabiting the same site and a nearby heathland site gave similarly high estimates of outcrossing.

Seed bank dynamics of a serotinus, fire-sensitive Banksia species

Banksia burdettii is a locally abundant shrub restricted to a small area in south-western Australia. At the study site, the canopy-stored seed bank built up exponentially with plant age to yield a mean of 830 viable seeds per plant from about 212 000 ovules produced over 16 years. Seed availability was the net result per year of number of flower heads, extent of head removal by cockatoos, number of florets per head and number of fruits (follicles) per floret in the production phase and the extent of seed abortion, insect granivory, seed senescence and spontaneous seed release in the mortality phase. Plants are killed by fire and a substantial proportion of cones was consumed by a hot fire. Up to 87% of viable seed may survive and be released within 100 days of a fire, depending on intensity and season of burn. Plants which died in the absence of fire released little viable seed subsequently, while the remainder were consumed when fire occurred. Comparison of 25 reproductive attributes between B. burdettii and another two Banksia species occurring in the vicinity indicated that it has much in common with these serotinous, non-sprouters. Although viable canopy-stored seeds account for few of the original ovules, reproductive inefficiency, once a fire interval of 10 years is exceeded, cannot explain the restricted distribution of this species.

Effects of salinity and waterlogging on the vegetation of Lake Toolibin, Western Australia

AbstractIncreased rates of tree senescence and mortality in and adjacent to an ephemeral lake in the Western Australian wheatbelt have been attributed to increased levels of soil salinity and inundation following agricultural clearing. Winter lake salinities approximate freshwater lake values, but during periods when the lake is dry, capillary rise of groundwater is thought to increase surface soil salinity. An undescribed species of Melaleuca and Casuarina obesa dominated the seasonally inundated regions of the lake bed. Aeolian deposits of higher elevation were dominated by Eucalyptus loxophleba, Allocasuarina huegeliana or species of Banksia. Woodland of E. oleosa var. longicornis and E. salmonophloia occurred predominantly on upland fluviatile deposits of sand and sandy clays. Measurements of soil salinity and the calculation of percentage inundation from tree elevations and observations of tree vigour and xylem pressure potential response indicated that tree deaths in Melaleuca sp. and C. obesa were due to increased levels of salinity. Deaths and low vigours in E. rudis were attributed to both increasing salinities and prolonged inundation. We believe control of ground water levels should be a major consideration in the preservation of this ephemeral lake and the water fowl populations it supports.

Post-Fire Recruitment of Four Co-Occurring Banksia Species

(1) The factors responsible for genet mortality and survival after autumn and spring burns were studied for Banksia attenuate R. Br., B. leptophylla A.S. George, B. menziesii R. Br. and B. prionotes Lindley, in a 15-year-old stand of fire-prone scrub-heath in southwestern Australia. (2) Late summer to winter seed release from unburnt cones was recorded for B. menziesii (30%) and B. prionotes (3%0,) only. One hundred and forty days after both burns, more than 950%0 of seeds of all species were released, except for B. leptophylla which retained 17% of seeds in cones throughout the summer after the spring burn. The rate of seed release from burnt cones was significantly slower for all species after the spring than the autumn burn. (3) Post-dispersal seed predation after the autumn burn was negligible whereas it ranged from 90%/0 (B. prionotes) to 98%/0 (B. menziesii) after the spring burn. (4) Seed of all species germinated optimally at 15-20 'C. After the autumn burn, field germination inside enclosures ranged from 9% (B. menziesii) to 69% (B. leptophylla). More seeds of all species germinated in the unburnt than in the autumn burn site. No seed sown after the spring burn had germinated by the end of the following summer and their viability was severely reduced. (5) Most (54-97%/,) seedlings which established after the autumn burn had died, largely as a result of predation, by the end of the summer. Predation intensity was probably unnaturally high, due to the small size (c. 2 ha) of the resource-rich, autumn-burnt patch relative to the vast tracts of adjacent unburnt scrub-heath. Significantly fewer seedlings died inside enclosures after the autumn burn (32-520%0) than in the unburnt site (71-80%/,), indicating the importance of drought-induced mortality in maintaining even-aged populations in mature scrub-heath. (6) By the end of the first winter, the number of seedlings recruited per parent of all species was more than twice as high after the autumn than after the spring burn. More than 2 years after both burns, seedling replacement levels were higher than pre-burn adult densities for all species except B. menziesii. There was no recruitment in the unburnt area over the same period. (7) In order to maintain the populations of the Banksia species, extensive tracts of scrub-heath should be burnt in autumn, prior to the onset of winter rain. Conflicts between property protection and conservation cannot be resolved without information on the fireregime effects on scrub-heath populations.

Seed Bank Dynamics of Four Co-Occurring Banksia Species

(1) Age structure, phenology, infructescence (cone) and fruit (follicle) production, predispersal seed predation, and size and viability of the seed banks of four co-occurring Banksia species were studied in a fifteen-year-old stand of fire-prone scrub-heath in southwestern Australia. (2) Seeds released spontaneously during autumn germinated in the winter but nearly all seedlings died during the following summer. Recruitment is therefore largely confined to the immediate post-fire period. Seed-bank analysis indicated that, in order to maintain populations of the four Banksia species, the scrub-heath should be burnt at a frequency of no less than ten years. (3) Apart from the summer-flowering B. attenuata, the species flowered in winter. There were large variations in cone and follicle production between plants and between years within plants of all species. There was no support for the hypothesis that strongly serotinous species would show the highest variation in reproductive output. Follicle set was low for all species (01-4X7% of florets). (4) All species stored some seeds in the canopy for at least five years. There was no viable soil-stored seed bank. The mean number of canopy-stored viable seeds per plant ranged from 1344 (B. leptophylla) to 2 (B. menziesii). Extreme serotiny was recorded for B. leptophylla and B. attenuata in which seed older than the current year's crop comprised 92% and 80% respectively of the total viable seed bank. Corresponding values were 34% for B. prionotes and 25% for B. menziesii. The rate of decline in seed viability and pre-dispersal seed predation were lowest in the most serotinous species. (5) With the exception of lower follicle set in the two species which re-sprout after fires, there was no support for the hypothesis that such species would allocate less energy to sexual reproduction than the two non-sprouting species. Patterns of seed storage had a greater influence on reproductive allocation than mode of post-fire regeneration.

Resource Defense and Alternative Mating Tactics in the Banksia Bee, Hylaeus alcyoneus (Erichson)

AbstractSome males of the Australian colletid bee Hylaeus alcyoneus defend single flowering spikes of various species of Banksia, selecting spikes in the maturational state most attractive to foraging females. Other males do not engage in food resource defense but instead nonaggressively patrol a circuit that takes them to many spikes, some occupied, others not held by territorial males. When territory owners are experimentally removed, replacement males quickly claim the vacated spikes. Some of these males have been patrolling previously, showing that patrolling and territoriality are alternative tactics in a conditional strategy. Territorial males are larger on average than patrolling males, replacement territory holders, and females. Male territoriality at flowers appears in several other Hylaeus, and in these and other bees, resource defense tactics are often associated with specialized foraging requirements of females and a patchily distributed resource.

Impact of flower and seed predators on seed‐set in two Banksia shrubs

AbstractA non‐systemic Insecticide was used to exclude flower and seed predators from Banksia ericifolia and B. oblongifolia Inflorescenses. In B. ericifolia this treatment doubled the number of inflorescences that set seeds, and increased by 40% the number of seeds produced per Inflorescence. Insecticide treatment did not alter either of these components of seed‐set in B. oblongifolia partly because the experiment began too late to exclude flower predators In this species. The results obtained for B. ericifolia support the hypothesis that flower and seed predators explain, in part, the low incidence of seed‐bearing cones and the low seed:flower ratios reported for many Banksia species.Each Banksia species supports two guilds of Inflorescence predators. Two Lepidopteran species feed on young flowers; one of these causes tunnel damage to the rachis. Each Banksia species also supports five Lepidopteran and two Curcullonid seed‐predators. About 40% of these herbivorous Insects are common to both shrubs.

Honeyeaters and the Pollination Biology of Banksia prionotes (Proteaceae)

Honeyeaters such as Phylidonyris novaehotlandiae and Lichmera indistincta forage preferentially in regions of Banksia prionotes inflorescences where nectar and pollen are most abundant, removing pollen from freshly opened florets and transferring some of it to the stigmatic grooves of other florets on the same or different inflorescences. Each floret is protandrous, with pollen dispersal occurring during the first 4-8 h following initial presentation and significant esterase secretion by the stigma commencing after this phase has ended. Foraging by honeyeaters results in considerable pollen movement between florets on individual trees, although B. prionotes appears to be highly self-incompatible. Movement of honeyeaters and pollen between inflorescences on different trees occurs less frequently than between those on the same trees. Nevertheless, outcrossing leads to penetration of styles by tubes formed by pollen grains deposited in stigmatic grooves in some instances. Despite the small size and isolation of the population studied, the resultant level of follicle formation per infructescence, and percentage seed set, are greater than for most other Banksia species for which data are available.

Seed release in Banksia: the role of wet‐dry cycles

AbstractSeed release in two serotinous and two nonserotinous Banksia species from southwestern Australia increased many fold when burnt cones were subjected to wet‐dry cycles compared with those remaining air‐dry. The response was temperature‐dependent, increasing markedly in treated cones of B. leptophylla as temperature was lowered from 30 to 15°C. This episodic wetting requirement at cool temperatures for prolific seed release implies that, following summer fruit opening, dispersal is delayed until the onset of late autumn/early winter rains when conditions are suitable for germination (optimum at ∼15°C) and recruitment. Seed loss from post‐dispersal predation and exposure to high summer soil temperatures also would be minimized.

Flowering Biology and Phenology of Banksia integrifolia and B. spinulosa (Proteaceae) in New England National Park, N.S.W

The flowering biology and phenology of two species of Banksia, including anthesis rates, inflorescence survivorship and nectar production, were examined in the Northern Tablelands, N.S.W. Rainfall, temperature and wind are all important factors in determining nectar productivity and availability. The species investigated here are compared with other banksias studied elsewhere in Australia.