Bioversity International is coordinating a study on the use of native tree species to restore forests around the world, as a contribution to a review by the Food and Agriculture Organization of the UN (FAO) to be published in April 2013.
This blog post is from Bioversity researcher Riina Jalonen, based in Bioversity’s Regional office for Asia Pacific and Oceania in Malaysia. In a team of three foresters, and with a number of partners from the region, she studies genetic impacts of forest management and restoration to propose approaches for improving the sustainable use of and benefits from forest genetic resources.
Given the surge of interest in tree planting in recent years – FAO estimates that at least 5 million hectares of planted forests are established every year which is an area equivalent in size to Costa Rica – it could be easy to assume that all restoration efforts are successful in re-establishing forest ecosystems, as successes are promoted far more often than failures. Yet evaluating failures can be equally important when it comes to improving current techniques for recreating forests where they have been cut down.
FAO started to systematically collect information of tree planting activities only in its most recent Global Forest Resources Assessment 2010.pdf and data availability is still scant. Strikingly, however, the area of successfully established planted forests reported was less than half of the area where reforestation had been attempted. The difference probably reflects a low survival rate of seedlings which may result from a number of possible factors – perhaps the wrong species was planted for the site conditions (climate and soil) or perhaps planting or seedling care techniques were not appropriate or were poorly implemented.
Among the most notable and overlooked risk to the success of forest restoration is inadequate genetic diversity among the seeds of the species planted. Experts interviewed as part of Bioversity’s ongoing study have pointed out that to produce seedlings, people very commonly collect seed from only the one or two trees which are easiest to reach. Experts recommend that seed be obtained from no fewer than 30 widely spaced trees so that the planted forest incorporates enough genetic diversity to ensure the survival of seedlings and to avoid negative consequences of inbreeding in future generations.
If a new forest consists only of closely related trees, all of them with the same characteristics, there may not be enough genetic diversity among them to ensure that some proportion of the individuals, at least, are resistant to the various pests, diseases or adverse weather spells that may arise over the decades. Moreover, where all the trees in a forest are closely related, the next generation, arising from seeds resulting from crossings between them, is likely to be less vigorous.
The lack of genetic diversity among the founding tree population is not always immediately visible but generally becomes more evident as generations pass.
An additional challenge is that very little information is available about the genetic diversity of trees in the millions of hectares of planted and restored forests worldwide. This means that the current global scale of restoration efforts, positive as they are, may also have hidden vulnerabilities. And where planting efforts fail to establish vigorous forests that can survive and thrive over time, they represent a potentially enormous waste of resources.
The study which I am preparing together with Bioversity colleagues and other experts reviews the current knowledge and practices related to integrating genetic diversity into tree planting efforts to restore forests. We are focusing particularly on native tree species, the ones that occur naturally in the wild forests of any given region, because these species provide the habitat that local birds and animals need, as well as the forest products that local people use.
The study will include a set of recommendations for both restoration researchers and practitioners, including on the collection of propagation materials from fragmented forests and increasingly resiliency under environmental changes.
Better understanding of the importance of genetic considerations in forest restoration will go some way to improve the success of restoration efforts and ensure the provision of benefits from restored forests beyond the first generation of trees
Statistics in the text are from the FAO Global Forest Resource Assessment (2010) and concern forests established though tree planting and deliberate tree seeding, including both reforestation and afforestation.