Choosing the Right Seeds for a Changing World

One of the most exciting aspects of tropical rainforest restoration is the knowledge and data that comes with the resurgence of restored habitat. Rainforest Rescue is working in conjunction with James Cook University to better understand what rainforest plant species are capable of adapting to changing climatic conditions due to human-induced climate change. These insights will help with our tree planting decision-making and effective use of donor funding for essential restoration work. Here, Kali Middleby from JCU shares initial findings from their research, which is part of the TropAdapt project.

 

Researchers planting selected species at restoration sites to gauge adaptivity factors.  © Kali Middleby et al

 

In the face of climate change, restoring rainforests is about more than just planting trees; it’s about planting the right trees, in the right place, using the best-suited plant material. Our recent study, conducted with the support of Rainforest Rescue, has revealed valuable insights into how sourcing seeds from different geographic locations, or “provenances,” affect tropical tree growth and survival. This is a crucial consideration for ensuring both the success of rainforest tree plantings in the short term (fast canopy closure) and in building in the genetic diversity needed for forests to adapt over the long-term.

In rainforest restoration, selecting seeds from local sources has been the standard approach, based on the idea that local plants are best adapted to local conditions. However, with rapid climate change, local seeds may not always thrive as conditions shift. An alternative approach, called “climate-adjusted provenancing,” suggests sourcing ‘pre-adapted’ plant material – originating from areas with current climates similar to what’s expected in the future at the restoration site – could help build more resilient forests. But, identifying and implementing the appropriate strategy is context dependent and requires evidence on each species adaptive capacity, data that so far is lacking for tropical species.

 

What Are We Doing?

Our study, part of the TropAdapt project, examines the performance of native tree species from lowland and upland regions when planted at the same location. By establishing trials across three sites with contrasting climates and soil quality, we can explore how the climate of a tree’s origin and its planting site influence growth and survival, and thereby the success of tree planting efforts. In 2022, we set up experimental plantings at Rainforest Rescue’s Cow Bay nursery site, the Daintree Rainforest Observatory, and Thiaki Creek Nature Reserve. We’ve been closely monitoring the trees ever since.

 

Researchers at Rainforest Rescue’s Cow Bay Airstrip restoration site reviewing plant growth © Kali Middleby et al, James Cook University.

 

Species-specific variation highlights the complexity of local adaptation and choosing the right seed sources for restoration.

 

What Did We Find?

The most obvious effect we found was the clear impact of site on growth. Saplings planted at the Daintree Rainforest observatory, which were not limited by temperature, moisture, or nutrient availability thrived – with faster growing tree species reaching ~10m after 2 years of growth. Contrast this with the those at the Cow Bay site with its human-modified soils or Thiaki which is cooler and drier, where trees grew a lot slower. It really highlights how different potential growth rates can be across the environment.

Another notable observation is that for many species lowland origin trees grew faster and survived better than upland origin trees, even when planted in upland environments. This finding challenges the traditional view that local seeds are always the best choice for local plantings.

However, the strength of this provenance effect really varied by species (unsurprising as nature likes to be complicated). For example, fast-growing species like the Blue Quandong and Bleeding Heart showed marked differences between their lowland and upland provenances, with lowland provenances generally performing better at all sites. However, for Davidson Plum, the lowland and upland provenances performed similarly. This species-specific variation highlights the complexity of local adaptation and choosing the right seed sources for restoration.

 

Implications for Restoration Efforts

Our mixed evidence for local adaptation supports our suspicions that the “local is best” paradigm isn’t always true. For restoration practitioners, this offers some flexibility: if sufficient seed can’t be sourced close to the planting site, seeds from farther away may still thrive, helping to meet demand and scale up restoration efforts. This approach could boost early growth and survival rates, allowing forests to establish more quickly. However, it’s also important to balance this with a need to maintain genetic diversity to ensure forests remain resilient.

 

What’s Next?

We’re continuing to monitor these trees over time since local adaptation can become more apparent as trees reach maturity or encounter stressful conditions. We’ll also be exploring some of the reasons why some species and provenances perform better than others by measuring their physiological traits such as photosynthetic biochemistry, water use efficiency, and tolerance to drought and heat stress. Exploring the drivers and possible trade-offs between growth and tolerance is an important factor in selecting trees that can thrive long-term.

We look forward to continuing our work with Rainforest Rescue and other project partners. Science-informed restoration is key to creating adaptable and effective strategies for tropical rainforest conservation – helping protect these vital ecosystems for generations to come.

 

By Kali Middleby, PhD Candidate in Plant Ecophysiology at James Cook University. To find out more about the project data and insights relating to climate change and rainforest flora adaptations, read the preprint research paper. 

 

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