Establishment and growth of seedlings of Eucalyptus obliqua: Interactive effects of litter, water, and pathogens

We studied how leaf litter, water and fungal pathogens affect the establish ment, survivorship, and growth of Eucalyptus obliqua using glasshouse and f ield experiments. In a glasshouse experiment, the presence of leaf litter o f E. obliqua increased the establishment of seedlings when the seeds were p laced beneath the litter, but dense litter layers reduced seedling emergenc e when seeds were placed on top. Results from a complementary experiment su ggest that the effect of litter may be mediated by the high humidity microe nvironment it creates, which may enhance imbibition of unburied seeds. In a nother glasshouse experiment, litter in combination with excessive water ap plications reduced seedling emergence and increased seedling mortality, but the addition of fungicide reverted these effects. Litter with lower water application or fungicide added increased seedling emergence. In all cases h igher biomass in seedlings growing in litter treatments was associated with earlier emergence. In two recently burnt sites, the density of seedlings o f E. obliqua was positively correlated to the presence of litter. Experimen tal addition of litter in the field reduced soil temperature during the sum mer, and together with watering, increased soil water content, and the wate r potential of established seedlings. However, neither treatment had any po sitive effect on their growth or survivorship. On the contrary, litter addi tion reduced the height and number of leaves, probably as a result of incre ased herbivory. We conclude that in Mediterranean-type systems litter may p roduce various effects on seedling establishment depending on their develop mental stage, and the season.