2.1 Common Garden sites
This experiment, part of the ‘TropAdapt’ project (https://tropadapt.org/) was conducted across three common garden trials established within the Wet Tropics bioregion of far north Queensland, Australia: two in the coastal lowlands and one in the uplands. The first lowland site is located at the Daintree Rainforest Observatory (DRO) in Cape Tribulation (−16.10449 °S, 145.4511 °E) with an elevation of 52 m (a.s.l.), mean annual temperature (MAT) of 24.5 °C and a mean annual precipitation (MAP) of 3026 mm. The soil at the site is acidic, dystrophic, brown dermosol, formed in the colluvium from the metamorphic and granitic mountains to the west (Murtha 1989). The second lowland site was established on an old airstrip in Cow Bay (−16.22406 °S, 145.4220 °E) with a MAT of 24.4 °C and a MAP of 3439 mm. Although soils in the area were originally dominated by haplic, dystrophic, red ferrosols formed on an alluvial fan derived from basalt (Murtha 1989), an anthropogenic reworking of the site and augmentation with sand and gravels to form the airstrip have left the soils poorly structured. The upland study site is in the southern Atherton Tablelands (−17.43025 °S, 145.5153 °E) on Thiaki Creek Nature Reserve (https://www.biome5.com.au/thiaki) at an elevation of 980 m a.s.l. It has a MAT of 19 °C and receives a MAP of 2264 mm. The site is on a formed from Cainozoic Basalt (Malcolm et al. 1999). The property was previously managed as a cattle pasture for approximately 70 years, and subsequently used as a research site for several previous reforestation experiments (Charles et al. 2018) (Preece et al. 2015, Preece et al. 2017). The common garden plot used for this study is dominated by exotic grass species (e.g. Melinis minutiflora , Urochloa (Brachiaria ) decumbens andSetaria sphacelata ) and receives no shading from nearby trees.
The two lowland sites, DRO and Cow Bay are both located within the Daintree Rainforest and as such are similar both geographically and climatically. They differ primarily in soil nutrient status. The upland site Thiaki provides a climate contrast with MAT differing by ~ 5.5 °C and MAP differing by ~ 969 mm compared to the two lowland sites but does not suffer in terms of soil nutrient availability like the Cow Bay site. Comparison of tree performance across these three sites allows assessment of the effects of both climatic (upland vs lowland sites) and edaphic factors (low nutrient vs high nutrient sites).