The importance of forests to climatic stability and biodiversity is widely understood, and reflected in the surge of interest in recent decades in large-scale forest restoration projects. The latest such plans are extremely ambitious, requiring significant levels of investment: the Bonn Challenge, for example, brings together international commitments to restore 150 million hectares of lost forests and degraded lands worldwide by 2020; Initiative 20x20 aims to restore 20 million hectares by 2020 in Latin America and India’s Green Mission aims to restore 5 million hectares.
While the potential gains from reforesting landscapes are substantial, there is a need to confront the often disappointing reality: to date, many restoration projects have achieved only limited success, or have failed completely. The reasons for this are complex and not fully understood; there has been little by way of rigorous evaluation of the success factors for restoration projects. However a review of the studies that have been conducted has revealed important insights into the effect of tree genetics on the chances of success, and offers valuable pointers for future tree planting projects.
Projects designed to return degraded land to natural forest, with associated improvements in ecological function and biodiversity, rightly focus on native tree species. The review suggests that a deeper level of ecological awareness and a more nuanced approach to tree selection than have been previously deployed could help to attain the desired outcome of resilient, self-sustaining forest ecosystems.
Writing in a special edition of the Forest Ecology & Management journal, as part of the Forest Genetic Resources series, scientists report that inadequate attention to genetic considerations in choosing planting material can have an adverse impact on outcomes.
Even native tree species can be genetically ill-matched to the environmental conditions at the restoration site if the planting material is not well chosen. This can result in a deleterious effect on the trees' growth, potential for survival and reproductive success.
One solution is to optimize the genetic profile of the selected tree saplings by means of provenance trials, but this can take too long to be applicable to a pressing restoration schedule. It is also important that the planting material has an adequate genetic base: in other words, sufficient genetic diversity among the individual plants. However, evaluating the genetic diversity of planting material is also expensive and time consuming.
In their paper, Genetic considerations in ecosystem restoration using native tree species, the researchers point out that there are 'proxy' techniques for addressing both of these concerns, which can offer comparable benefits to the time-consuming genetic evaluations.
One example of such an approach entails taking a variety of seeds from a sufficient number (30 to 50) of well spaced trees that are thriving in an environment similar to the current (and, if possible, projected) future conditions at the restoration site. This then produces a tree population with a broad genetic base, allowing for natural selection and adaptation to the existing and future conditions at the site. The result is ultimately more likely to form a self-sustaining ecosystem than if such considerations are ignored.
One of the paper's authors and co-editor of the series, Dr Judy Loo — Leader of Bioversity International's Forest Genetic Resources and Restoration Science Domain — said:
"Paying attention to the genetic resources is key. It's commonly not done in restoration practice but is fairly straightforward, and draws on approaches already used in forest management. The aim is to make selections that give the best chance of restoring ecosystem values and functions, and also levels of biodiversity, as would be naturally supported by that landscape."
Planning for future environmental change, not least the expected impacts of climate change, complicates the process of choosing seed sources but considering source sites that are already experiencing some of the anticipated conditions, as well as maximizing genetic diversity, can mitigate against the risks, she explained.
Another recommendation emerging from the study is that practitioners move from short-term assessments of their restoration efforts (to date often measured in terms of the number of seedlings planted or their immediate survival rates) to long-term monitoring. This would effectively mean restoration research is conducted in situ, in parallel with practice, and would make observations from longer-term studies available to assist with planning and optimizing future restoration projects.
The authors conclude that researchers, policymakers and practitioners would benefit from the development and adoption of decision-support tools that take account of these recommendations, with the aim of maximizing the long-term viability of the restored forest landscapes.
- Download the paper: Genetic considerations in ecosystem restoration using native tree species
- Download the policy brief: Safeguarding investments in forest ecosystem restoration
This work contributes to Bioversity International's Initiatives on Productive and Resilient Farms, Forests and Landscapes, and Effective Genetic Resources Conservation and Use, and is part of the CGIAR Research Program on Forests, Trees and Agroforestry.
Photo: Forest scenery of Gede Pangrango in the morning. Credit: CIFOR/R. Martin