Forest tree genetic risk assessment systems: A tool for conservation decision-making in changing times

Changing climate conditions and increasing pest and pathogen infestations will increase the likelihood that forest trees could experience population-level extirpation or species-level extinction during the next century. Funds, however, will be limited for management and gene conservation efforts to preserve forest tree genetic diversity. The Forest Tree Genetic Risk Assessment System provides a framework for users to rank the relative risk of genetic degradation for multiple forest tree species. We have applied this framework for the species-rich forests of the Southern Appalachian Mountains of the southeastern United States. Species differ in their physiological tolerances, life history strategies, probabilities of population extinctions and colonizations, and dispersal abilities; these individualistic traits likely underlie the high variability in strength of climate response across wild species, even among those subjected to similar climatic trends (Parmesan 2006, Parmesan and Yohe 2003). In the face of these changes, an important goal will be to safeguard existing adaptedness and create conducive conditions for future evolution, with a focus on the conservation of variability in adaptive traits (Myking 2002). In the absence of good information about the genetic composition of species, or even an understanding of the relevant adaptive traits, several researchers have suggested using ecological and life-history traits to rank the predisposition of species to climate change and other threats, for conservation planning, for the evaluation of species’ genetic resources, and for the early detection of vulnerability (Aitken and others 2008, Bradshaw and others 2008, Myking 2002, Sjostrom and Gross 2006). The Forest Tree Genetic Risk Assessment System gives each species a rating for risk factors relating to (1) its intrinsic attributes, such as population structure, fecundity and seed dispersal mechanism, that may increase its vulnerability in the face of change, and (2) the external threats to its genetic integrity, including changing climate and insect and disease threats. Species may be additionally rated for a set of conservation modifiers, such as listed status and endemism. The factor index values are weighted and summed to give risk ratings for the species within a given region, which are ranked according to their overall susceptibility to genetic degradation. This system has the advantage of accounting for the interactions among threats that may result in the most severe impacts associated with climate change (Thomas and others 2004). Only by considering extinction as a synergistic process of external threats and intrinsic biological traits will it be possible to make predictions of risk that approximate reality for most species, and therefore to increase the likelihood that conservation efforts will be effective (Brook and others 2008). Additionally, the flexibility of the Forest Tree Genetic Risk Assessment System allows for its application at multiple scales and across any area for which the relevant data exist for the species of interest.