Germination and early survival of 'Eucalyptus blakelyi' in grasslands of the New England Tablelands, NSW, Australia

Abstract

Establishing native eucalypts in grasslands developed by the historical clearing of forests and woodlands has to overcome significant difficulties brought about by past land use activities and associated environmental changes. Options for establishment include natural regeneration from remnant trees, direct sowing or tree planting. 'Eucalyptus blakelyi' is a significant species on the New England Tablelands, being just north of the central part of its ecological range and is potentially useful for ecosystem rehabilitation, agroforestry and farm forestry. The aims of this series of studies are to determine the effects of cold temperatures resulting from microclimate changes on germination and early survival of 'E. blakelyi', the level of seed predation by ants, and the effectiveness of site preparation techniques on survival and growth of seedlings planted in grasslands. Germination of local seeds collected from the New England Tablelands was tested under constant and alternating temperatures, either in the dark or under 12 h light/dark cycle. 'E. blakelyi' exhibited optimal germination between 15 and 25°C with the maximum occurring at 15°C under constant temperatures, and at 15–25°C under alternating temperatures. Light had a significant and positive effect on germination under both constant and alternating temperature regimes, although this difference was not significant at temperatures around the optimum. Seedling survival decreased significantly as temperature decreased from −5 to −10°C, as exposure time to low temperature increased from 1 to 4 h, and as seedling age increased from 1 to 8 weeks. Ant predation was high with 73% of the seeds removed within 7 days. Four site preparation techniques (grazing exclusion, cultivation, burning and fertiliser) were used in a factorial arrangement to examine their interactions and influences on seedling survival and height growth 30 months after establishment. Grazing significantly reduced seedling survival and height, whereas soil cultivation and burning significantly increased them. Survival and height were consistently lower when fertiliser was added to grazed plots across all cultivation treatments including the control. When grazing was excluded, fertiliser significantly reduced survival with cultivated treatments, and increased height only with shallow cultivation (to a depth of 5 cm) while it significantly reduced height with deep cultivation (20 cm). The interactions amongst the various treatments identified that seedling survival and growth were best when grazing was excluded and the site was deep cultivated without the broadcast application of fertiliser. Fire has an additive effect on seedling survival and height growth. The main benefits of this combination of treatments lie in preventing browsing and trampling damage by livestock, reducing competition from the herbaceous layer, removing litter, and possibly alleviating potential allelopathic effects.