Population structure, seed loads and flowering phenology in three common (Melaleuca styphelioides, M. thymifolia, M. nodosa) and one rare (M. deanei) Melaleuca (Myrtaceae) species of the Sydney region

Abstract

Melaleuca deanei F.Muell. is listed under state and national protection legislation occurring as small, disjunct populations restricted to the Central Coast botanical district of New South Wales. This paper reports on the population structure, reproductive output and phenology of large and small field populations of M. deanei, compared with three common congeneric species in the area, namely, Melaleuca nodosa (Sol. ex Gaertn.) Sm., Melaleuca thymifolia Sm. and Melaleuca styphelioides Sm. Both M. deanei and M. styphelioides had few seedlings per population at the sites studied. Results indicated that seedling recruitment is rare and would appear to require specific conditions. In addition, M. deanei had a low incidence of flowering within the small populations, significantly fewer fruiting plants per population and significantly lower numbers of viable seeds per square metre, most likely compounding its limited recruitment. Flowering, when it occurred in M. deanei, was from mid to late October through to late November–early December with increased flowering in response to fire and along road edges. Further study is needed to determine reproductive success at the individual-plant level, the breeding system and recruitment requirements of these species.

Seed size and the regeneration niches of one rare (Melaleuca deanei) and three common (Melaleuca styphelioides,Melaleuca thymifoliaandMelaleuca nodosa)Melaleuca(Myrtaceae) species of theSydney region

“…Earlier work (Hewitt et al . ) found poor reproductive success within relatively smaller populations of M. deanei ; these populations had a lower incidence of flowering, lower proportions of fruiting plants and lower viable seed loads per unit area, compared with relatively larger populations or to populations of three common congeners ( M. styphelioides Sm., M. thymifolia Sm. and M. nodosa (Sol ex Gaertn.)…”

Genetic and environmental factors in the trade‐off between sexual and asexual reproduction of a rare clonal angiosperm

“…Fire also triggered seed release en masse in the field from a strongly serotinous canopy seed bank, with seed noted to then germinate readily within larger populations following rainfall. However, in all populations monitored, seedlings failed to survive longer than one year, with soil moisture adequate for germination and seedling survival apparently critical (Virtue ; Hewitt et al and and observations since).…”

“…In several populations of M. deanei , older plants were observed to senesce and die, some killed outright by intense fire, with younger plants resprouting or suckering, and no successful recruitment from seed (Hewitt et al and observations since). In the absence of sexual recruitment, population size in terms of genetic individuals is decreasing and many small populations (<50 stems) showed low genotypic diversity (Hewitt et al ) therefore few mates with which to outcross.…”

“…A demographic study confirmed no resource or pollen limitations on fruit set in populations of M. deanei when flowering occurred (Hewitt et al ). However, viable seed loads per unit area were significantly lower in small populations of less than 100 stems (Hewitt et al ), possibly explained by unsuccessful selfing. An outcrossing breeding system, combined with clonality in M. deanei, means that even when plants do flower, fertilisation may not occur.…”

“…A series of nested, replicated field studies in large and small populations of M. deanei over five years established on‐ground areas of occupancy, abundance, density, size‐class distributions, flowering phenology, floral types, fire responses, seed:ovule ratios, fruit set, seed loads and patterns of seed release and seedling recruitment (see Hewitt et al and for details of data collection and study sites).…”