Recruitment of Melaleuca quinquenervia (Myrtaceae) in the fringing forests of the Myall Lakes, NSW, Australia

Abstract

Context Melaleuca quinquenervia is a widespread, keystone species of eastern Australian coastal forested wetlands. Populations of M. quinquenervia in the fringes of Myall Lakes, New South Wales, Australia exhibit low numbers of juveniles, infrequent recruitment and a dominance of mature individuals, raising concerns about stand replacement from conservation managers. In contrast, M. quinquenervia often recruits in large numbers and is highly invasive in wetlands around the world. Aims To explore factors that limit recruitment of M. quinquenervia within its native range. Methods Field deployed seed traps; soil-core sampling; a burial longevity trial and depth of emergence experiment; laboratory temperature, salinity and light germination experiments; a transplantation experiment; monitoring of field germination; and a litter/leachate experiment. Key results Low seed viability (5–26%) is offset by high canopy seed loads (250 000 to 120 million seeds per tree) released continuously throughout the year with a peak fall in summer (2000 to 5000 viable seeds per m2 per month), coinciding with optimal germination temperatures. Seedling emergence is reduced below 5 mm soil depth, there is a very low soil seedbank reserve, and germination is light-dependant. M. quinquenervia exhibited reduced germination percentage and rate as well as reduced survival of seedlings at salinities higher than 15 dS m−1 EC (electrical conductivity). The most favourable sites for seedling establishment are permanently moist with low salinity, protected from wave action via sedge vegetation, and sheltered from prevailing winds. There is an inhibitory effect of Casuarina leachate on germination. Conclusions Germination in the field is episodic, and tied to specific environmental conditions. Highest losses occur at the seedling establishment phase. Implications Future research avenues and management recommendations are provided.