Designing food and habitat trees for urban koalas: graft compatibility, survival and height of tall eucalypt species grafted onto shorter rootstocks

Abstract

The Corymbia and Eucalyptus species eaten by koalas are generally large trees, but these are often unpopular with urban landowners and councils because of the dangers of limbs falling from a great height. We aimed to develop shorter koala food and habitat trees for urban areas by heterografting tall eucalypt species onto rootstocks of shorter species and comparing their survival and growth with homografted trees and control ungrafted trees. In total, 12 of 14 interspecific scion/rootstock combinations were grafted successfully in the nursery but graft compatibility and field survival depended on taxonomic relatedness. The six interspecific combinations that had multiple surviving trees at 5 years after planting were all between species within the same taxonomic section or between a species and its own interspecific hybrid. Almost all trees died from grafts between species in different taxonomic sections. In most cases, the height of surviving interspecific grafted trees did not differ from control intraspecific grafted trees or from ungrafted trees of their scion species. Grafting elicited a ‘thrive or not survive’ response that diminished its usefulness for producing shorter trees. However, one combination, E. moluccana/E. behriana, had field survival of 40% and reduced height (4.0 m vs 9.9 m). These could be valuable habitat trees for koalas and other fauna in urban areas.

Designing food and habitat trees for urban koalas: identifying short ecotypes of Corymbia intermedia

“…The germination medium consisted of 100% shredded pine bark with 3 kg of 8-9 month slow release Osmocote TM fertiliser (Scotts International, Heerlen, The Netherlands), 3 kg lime (Unimin, Lilydale, VIC), 1 kg gypsum (Queensland Organics, Narangba, QLD), 1 kg Micromax R micronutrients (Scotts Australia, Baulkham Hills, NSW) and 1 kg Hydroflow TM wetting agent (Scotts Australia, Baulkham Hills, NSW) incorporated per m 3 (Trueman et al 2014). Seeds were covered with a thin layer of vermiculite and the 20 trays were placed in a random arrangement under mist irrigation in a translucent white polyethylene tunnelhouse in Gympie (26°09'S, 152°38'E).…”

“…One of our aims was to develop short trees by grafting scions from tall species that are eaten by koalas onto rootstocks from related short species. However, interspecific grafted trees either (a) survived well but grew tall or (b) were short but had high mortality (Trueman et al 2014).…”

Micropropagation of the therapeutic-honey plants

“…Plantlets were then transferred into 70-mL propagation tubes (Darby et al 2021) containing eucalypt seedling mix consisting of a 75/25 (v/v) mixture of shredded pine bark and perlite, with 3 kg of 8-9-month slow-release Osmocote fertiliser (Scotts International, Heerlen, Netherlands), 3 kg of lime (Unimin, Lilydale, Australia), 1 kg of gypsum (Queensland Organics, Narangba, Australia), 1 kg of Micromax micronutrients (Scotts Australia, Baulkham Hills, Australia) and 1 kg of Hydroflow wetting agent (Scotts Australia) incorporated per square metre (Trueman et al 2013a(Trueman et al , 2013b(Trueman et al , 2013c(Trueman et al , 2013d(Trueman et al , 2014. The plantlets were maintained at 28 C under a 16-h photoperiod (~50 mmol m -2 s -1 ) in a sealed 80-L plastic tub for a further 4 weeks.…”

Tissue Culture of Corymbia and Eucalyptus

“…Eucalypts are the world's most widely planted hardwood trees, with more than 20 million hectares established in plantations because of their wide diversity of species, suitability of individual species for different climates and soils, fast growth rates, and multiple products such as timber, pulp, fodder, biofuel, essential oil, and bioactive chemicals [1][2][3][4][5][6][7][8][9][10][11]. Eucalypt plantations are dominated by ten species, Corymbia citriodora (Hook.)…”