Genetics

Global climate change has profound consequences for tropical forest ecosystems. The evolutionary adaptability of a species, its capacity to survive environmental change, depends on the genetic diversity present among the individuals of the species.

Increasing ecological adaptability

The keys to securing the adaptability of tropical forest ecosystems to a changing global climate are diversity (both species and genetic diversity) and mobility.

Diversity : Genetic diversity within tree species is also important. Responses to climate change among individual trees within a species can also vary. So maintaining high genetic diversity within species can increase the probability that at least some individuals will survive to represent the species in the future forest. These genetic variants will then be able to pass on the genes that enable survival in a warmer world to their offspring. Until recently, it has been recommended that seeds should be collected from trees growing as close as possible to the restoration site (because they are genetically adapted to local conditions and they maintain genetic integrity). Now, the idea of including at least some seeds from the warmer limits of a species’ distribution is being considered in order to broaden the genetic base from which genetic variants that are suited to a future unknown climate might emerge through natural selection. The warmer limits of a species distribution would typically include the southern-most populations of species in the northern hemisphere, the northern-most populations of species in the southern hemisphere and the lower elevation limit of montane species.

Mobility : Trees cannot ‘run away’ from climate change, but their seeds can. So, any actions that facilitate seed dispersal across landscapes will increase the probability that more tree species will survive. The mobility of seeds across landscapes can be maximised by planting framework tree species, as they are specially selected for their attractiveness to seed-dispersing wildlife. Tree species that have large seeds, particularly those that would have depended on extirpated large animals (e.g. elephants or rhinos) for their dispersal, should also be targeted for planting. Without their seed dispersers, human intervention to move their seeds (or seedlings) might be their only remaining chance of dispersal. Campaigns to prevent the hunting of seed-dispersing animals are obviously important in this regard. Increasing forest connectivity at the landscape level also facilitates seed dispersal because many seed-dispersing animal species are reluctant to cross over large open areas. This can be achieved by restoring forest in the form of corridors and ‘stepping stones’