Thiaki Creek: Cost-effective Rainforest Restoration for Carbon & Biodiversity

Key words: landscape resilience; rainforest fragments; connectivity; endangered species

Noel Preece

A large-scale reforestation experiment has begun in the Wet Tropics to examine the best and most cost-effective ways of reforesting a long-cleared grassed landscape to rainforest. The project is on Thiaki Creek, a highland tributary of the North Johnstone River which flows onto the Great Barrier Reef of Far North Queensland. The project is based on a fully replicated experimental design of 64 plots, covering over 20 hectares.

Part of the 20 ha experimental area in which the 64 plots are laid out. Rows were sprayed to suppress the exotic pasture grasses and the planters are planting the seedlings directly into the ground with planter spades.

The local ecosystem is moist complex notophyll vine rainforest (type 7.8.4) which can be seen in the background. This is State-listed (endangered) rainforest, home to endangered Cassowaries and six species of possum, and more than a hundred species of bird including the rare Grey Goshawk.

Aims: While forestry practices using monoculture tree species are well developed, reforestation practices using mixed native species for carbon sequestration and biodiversity are relatively poorly understood. Results of mixed plantings have been variable, regularly producing less than optimal outcomes and high establishment and maintenance costs have resulted in poor returns from investment. This is due to inadequate research on optimum site preparation, species mixes, spacings and propagation to achieve more cost effective outcomes.

Results and lessons: 27,000 trees were planted in January 2011, a few days before Cyclone Yasi. Early lessons learned are that spraying pasture grasses in strips, rather than blanket spraying the whole planting area, provides protection from erosion, wind and desiccation. Planting when the ground is saturated improves survival rates. An early experimental result demonstrates that forestry planting methods using planting spades take ¼ the time and 1/6 the expense of using augers, a common practice among landholders in the region, and the responses of mixed rainforest species is very good, with less than 6% loss.

Future directions: A range of studies has commenced on the site, including studies on soil carbon and nutrients; above ground carbon; plant diversity and plant functional traits; bee, fly, ant and dung beetle diversity and function; review of restoration practices; and economics. Future studies could include vertebrate roles and responses; competitive effects of tree mixtures; relationships of spacings and species to site capture rates and natural suppression of grasses; diversity versus productivity and resilience; mycorrhiza and other soil microbiota studies; soil hydrology and micro-climatology.
Stakeholders: The project is supported by a 5-year Australian Research Council Linkage grant, with the Universities of Queensland, Adelaide, Charles Darwin, Cambridge and Lancaster and Linkage partners Stanwell Corporation, Terrain NRM Ltd, Greening Australia and Biome5 Pty Ltd.

Contacts: Dr Margie Mayfield, University of Queensland, m.mayfield@uq.edu.au; Dr Noel Preece, Biome5 Pty Ltd, noel@biome5.com.au. Outlines of the Thiaki project are shown on: www.biome5.com.au/page/thiaki.html and www.mayfieldplantecologylab.org/site/Thiaki_Project.html