Plants of B. serrata and I. Anemonifolius resprout after fire, although the species differ in morphology (single-stemmed small tree, multistemmed low shrub respectively). If fires occur before newly established plants are fire-tolerant, populations will decline. The age of first fire tolerance was found to be lower in B. serrata (6 years) than in I. Anemonifolius (about 13 years). Rates of survival between and during fires were measured in the field along with rates of stem regrowth in fire-tolerant B. serrata juveniles. These results were used to predict rates of population decline under repeated fires sufficiently closely spaced to prevent the survival of newly established genets. In both species, juveniles were more prone to death than adults in fires and high-intensity fires caused most deaths. In B. serrata, adult stems (>2.0 cm d.b.h.) are mostly fire-tolerant, but fires less than 10 years apart can prevent many juveniles which survive from reaching adulthood. This restriction is less likely in I. Anemonifolius. As a result stands of B. serrata may decline more rapidly than I. Anemonifolius under 5-year fire cycles. I. Anemonifolius populations, however, may be more prone to decline when the interval between fires is slightly longer (e.g. 10 years) because lignotubers in young juveniles develop at a slower rate than in B. serrata. Extinction or substantial depletions of adult numbers may be approached in stands of either species after 50 years under some repeated 5- or 10-year fire cycles. The rate of such declines will depend directly on the structure of populations (proportions of adults and juveniles). Declines in populations of these resprouters may be likely under current fire regimes within the Sydney region of New South Wales, although these species are more likely to persist through long runs of frequent fire (<lo year interval) than some cohabiting species of obligate seeders.
Fire intensity and seasonality affected the release of seed in Banksia ericifolia L.f, and the post-fire emergence of seedlings. Mean maximum temperatures recorded in a heathland burn in May 1977 at heights of 0.5, 2 and 3 m were about 400, 275 and 175°C respectively. Variability in maximum temperature was dependent on the age and position of B. ericifolia stands. Release of seed held on B. ericifolia bushes increased significantly after fire. The proportion of seed released on unburnt controls stayed constant. Seeds were released earlier and quicker from cones exposed to high fire temperature maxima than from those exposed to low fire temperature maxima. Up to 80% of the seed bank was released 95 days after the fire. A greater proportion of the seed bank emerged and established as seedlings 5 months after the fire in May than after a fire the previous February. Seedling emergence and mortality were broadly related to rainfall over this period. The relationship between various fire regimes and abundance in B. ericifolia populations is discussed.
Flowering, pollination and reproductive phenology of the tree, Avicennia marina (Grey mangrove), were examined on the south-east coast of Australia in New South Wales. Individual flowers are protandrous and open for 2-5 days, while a flower cluster has open flowers for 2-4 weeks. About 16000 pollen grains and four ovules are produced per flower. Self-pollination of an individual flower is unlikely because of protandry, but the sequence and synchrony of flowering, together with pollinator behaviour, favour geitonogamy. Some fruit is set when cross-pollination is restricted by bagging flowers, which indicates partial self-compatibility. Subsequently, fruit abortion is higher in the bagged treatment than in those open-pollinated; this may reflect some pre-dispersal inbreeding depression. Between 4 and 41% of open-pollinated flower buds set fruit, most of which had one or rarely two seeds. Phenologically, each reproductive stage is unimodal and the whole process from bud initiation to abscission of mature fruit is completed within a year. Initiation of floral buds, flowering, growth and abscission of fruits are almost synchronous among fecund trees at a particular latitude each year. Latitudinal differences occur consistently among populations that are separated by less than 2° of latitude; those at lower latitudes flower earlier. Flowering of individual trees varies greatly between years and many trees fail to reproduce each year, although the populations remain fecund from year to year. A flexible breeding system and regular population fecundity ensure annual propagule supply in the populations studied.
Buoyancy of propagules of Avicennia marina (Forsk.) Vierh. was observed in the laboratory and in the field. Under constant exposure to seawater in the laboratory, propagules that shed their pericarp sank while those that retained their pericarp floated. The time taken for propagules to shed their pericarps varied greatly between trees in a population and between populations. However, more propagules lost their pericarps and sank faster in 10% seawater than in full seawater. Propagules that had sunk in 10% seawater refloated after several days' immersion. In the field, propagules placed at three tidal levels and exposed to differing periods of tidal inundation all lost their pericarps and sank within 24 h with no differences detected between tidal levels. Field observations were also made where brackish and seawater sites could be compared. Propagules shed their pericarps faster and sank earlier at the brackish site, although after 24 h more than 80% of propagules had sunk at all sites. After 48 h propagules in the brackish site began to refloat. These observations suggest that most A. marina. propagules strand and establish near the parent tree populations and only a few are dispersed more widely.
Evidence is presented for the existence of two genecoiogically differentiated groups in Leptospermum flavescens in the Sydney region. A morphologicai study of 18 attributes of herbarium specimens indicates three groups of plants: one small-leaved, one large-leaved and one intermediate. Comparative cultivation under standard conditions and seed germination experiments indicate only two discrete groups, because the intermediate group behaves similarly to the large-leaved group. Correlation of population distribution with soil nutrient status suggests that organ size in the large-leaved group is phenotypically plastic in relation to low soil nutrients. This is confirmed by comparative cultivation under high and low nutrient regimes. Reciprocal transplanting of cuttings on a small scale suggests that the two groups are intolerant of each other's habitats.
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