In Pursuit of Cost-Effective Rainforest Habitat Restoration

Extensive land clearing is a major threat to biodiversity. Consequently, tree planting is a commonly used strategy to rapidly restore forest to degraded landscapes. However, its high cost prevents its use across the large areas needed to address the ongoing legacy of land clearing.

Tropical Ecosystems Hub researchers are responding to the need to find lower cost options to restore critical rainforest habitat without always undertaking a program of tree planting.

The team from Project 12.2: Harnessing Natural Regeneration for Cost-effective Rainforest Restoration are working to develop decision-support options to optimise regional investments using the most appropriate restoration method for any particular ecological and economic scenario.

This requires quantitative measurement of the pattern and speed at which rainforest regrowth occurs, so the project team has surveyed the vegetation structure and plant species diversity in a network of 29 sites that differ in their age of regrowth, across the Atherton Tablelands.

These field measurements are being combined with information about the age of regrowth and with similar data from a network of replanted sites, to compare the speed and success of unassisted regrowth with the outcomes of tree planting projects. The data will also enable the team to identify how much the outcomes vary among different sites, and will be combined with measurements of the sites’ other characteristics and surrounding vegetation to identify factors that may limit or accelerate regrowth.

In addition, the team has experimented with the use of woody debris in young restoration plantings to stimulate return of reptile diversity. They found that, after one year, the addition of woody debris increased the local abundance of reptiles and promoted colonization by at least one log specialist.

Another set of experimental trials has focused specifically on designing and testing management interventions which can overcome barriers to the regeneration of native rainforest trees within retired pasture. The early results have demonstrated that greater seedling recruitment can be promoted by grass suppression and provision of habitat structure to seed-dispersing birds. These results also show that some invasive non-native shrubs species (such as wild tobacco) can also facilitate the recruitment of rainforest seedlings. The team collated information from early intervention trials in tropical regions worldwide, which also show that management interventions to accelerate regrowth are most effective when a range of strategies are used in combination.

The knowledge gained from this work will help enable targeted restoration expenditure and the most effective allocation of investment. The project team will then apply this information at a landscape scale, to identify areas of highest potential for low-cost regrowth.