Research helps forests adapt to and mitigate a changing climate

"Resilient and diverse forests are critical to maintaining a livable planet." This simple statement encapsulates both a potential tragedy, if underestimated, and a critical imperative for humanity if fully accepted: which is to conserve and restore the planet's forests in the face of rapidly growing threats.

Forests perform a huge range of functions critical to a healthy biosphere. They stabilize soils, maintain moisture levels and fertility and are home to a vast diversity of plant, animal and microbial species, many of which sustain nearby human communities. Forests also sequester carbon and produce oxygen, and so are critical to a stable climate and a breathable atmosphere.

Maintaining and expanding natural forest cover is therefore an essential component of an intelligent response to the climate crisis. However, given the rapidity with which the climate is changing and the impacts of these changes on tree populations, it also presents a complexity of challenges.

Research spanning two decades and multiple continents, which has been reviewed in the recent article, The role of forest genetic resources in responding to biotic and abiotic factors in the context of anthropogenic climate change — part of the Forest Genetic Resources series in a special edition of the Forest Ecology & Management journal — sets out these challenges and points to strategies for addressing them when undertaking conservation and restoration projects.

Dr Judy Loo, Leader of Bioversity International's Forest Genetic Resources and Restoration Science Domain, who made the above statement, is one of the authors of the article. "Resilience," she explains, "comes from the ability to adapt to change; that ability comes largely from genetic diversity."

Species respond to a changing environment by means of one of three processes. The first is migration, in which a population moves over time to a more amenable environment.

Another, termed phenotypic plasticity, is when individuals change their physical characteristics (within limits that vary among species) to enable them to more easily survive the new conditions.

The third is adaptation via natural selection. For this, those with the traits that allow them to survive environmental stresses are the ones that live long enough to reproduce, passing those traits on to their offspring.

All of these processes require time to play out, migration and genetic adaptation especially. While some shifts brought by climate change will be gradual enough to allow tree species to respond by one of these means, others can be abrupt and destructive — such as flood, drought or fire — precluding most if not all options for survival of tree populations.

The upshot is while some species will adapt to the more gradual changes, and a few to the abrupt changes, for many species the rate of change of local conditions will outpace all available responses, resulting in species and populations becoming locally extinct.

If we are to take advantage of forests' potential for mitigating global carbon emissions, the risk of these extinction events must be minimized. This review of latest research offers critical insights into methods for selecting and breeding adapted and adaptable forest species to this end.

The main insight from the studies covered in the article affirms the importance of genetic diversity to the chances of adaptation. The authors explain that a high level of genetic diversity within a tree population confers evolutionary potential. And, since genetic diversity is maintained through gene flow -- the transfer and exchange (through pollination, for example) of genetic information between its members -- and since gene flow works better for larger and more connected tree populations, the more resilient forests are also those with good connectivity across landscapes.

This explains why the increasing fragmentation of forests has such an adverse effect on their resilience. It also points to opportunities for countering those trends, by intervening to reconnect forest fragments.

This is but one of a number of interventions that can help restore a landscape to a state of improved forest cover. The others entail boosting or mimicking the natural processes.

Assisted migration, for example, involves taking tree seedlings to an area where future environmental conditions are projected to be similar to their current environment. Selecting and breeding tree seedlings for traits to help cope with future stresses — pest or drought resistance, for example — is another.

The objective of these methods is to maximize the chances of maintaining forest genetic diversity through time and over landscapes. It is a complex and challenging mission, however, made all the more tricky by the unpredictability of future climate change impacts in a given locality. The research suggests that as a general rule, using a wide genetic mix of trees as part of the restoration or management strategy will improve the chances of success.

Given these challenges, and other risks, the paper recommends that projects follow the precautionary principle and incorporate a research component, allowing for ongoing adjustment of plans according to the new knowledge gleaned.

Discover the Forest Ecology & Management journal's special Forest Genetic Resources series

^{Photo: Butterfly in Owabi Forest Reserve, Ghana. Credit: Bioversity International/C. Zanzanaini}