Strategies for Conserving Forest Genetic Resources in the Face of Climate Change

J. B. ST.CLAIR, G. T. HOWE Turk J Bot 35 (2011) 403-409 © TÜBİTAK Research Article doi:10.3906/bot-1012-98 Strategies for conserving forest genetic resources in the face of climate change John Bradley ST.CLAIR1,*, Glenn Th omas HOWE2 1USDA Forest Service, Pacifi c Northwest Research Station, 3200 SW Jeff erson Way, Corvallis, OR 97331 - USA 2Department of Forest Ecosystems and Society, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331 5752 - USA Received: 23.12.2010 Accepted: 29.01.2011 Abstract: Conservation of genetic diversity is important for continued evolution of populations to new environments, as well as continued availability of traits of interest in genetic improvement programs. Rapidly changing climates present new threats to the conservation of forest genetic resources. We can no longer assume that in situ reserves will continue to preserve existing genetic diversity. Management of reserves should become more active. In some reserves, existing genetic diversity should be preserved by creating stands that are more resistant to threats using silvicultural treatments such as thinning and prescribed burning. In other reserves, natural selection and adaptation to changed environments should be promoted by increasing within population genetic diversity and promoting gene fl ow. Th is may be done by locating reserves in areas of high environmental heterogeneity, minimizing fragmentation, and using assisted colonization to increase genetic diversity by establishing populations adapted to future climates within or adjacent to reserves. Th reats to native stands from climate change and other interacting threats should bring a renewed importance to ex situ collections, particularly for rare and disjunct populations and those at the warmer and drier edges of a species range. Assisted colonization to move threatened populations to new environments must be considered as an additional conservation measure. Key words: Climate change, genetic conservation, adaptation Introduction the future. Th e urgency for gene conservation has Conserving genetic diversity is an essential become greater with increasing evidence of global component of sustainable forest management. Th e climate change and associated risks of extirpation ability of trees and other forest plants to evolve to resist of species and populations. Th e Intergovernmental pests and adapt to changing climates depends upon Panel on Climate Change (IPCC) projects that global genetic diversity within species. Genetic diversity is average surface temperatures will rise about 1.8 to also critical for artifi cial selection and breeding for 4.0 °C during the 21st century, and up to 30% of the forest products and other environmental services. world’s species will be at increased risk of extinction We have an ethical obligation to protect genetic (Intergovernmental Panel on Climate Change, 2007). diversity for future generations, partly because we Although much of the focus of national programs cannot predict which traits will be important in of gene conservation has been on agricultural * E-mail: [email protected] 403 Strategies for conserving forest genetic resources in the face of climate change species, increased threats to native wild species from to losses from fi re, pathogens, insects, and invasive climate change bring increased attention to forest species. trees. Forest trees defi ne the essential characteristics Climate change alone represents a considerable of forests, and their long generation intervals put threat to genetic diversity (discussed below); but them at particular risk for maladaptation to climate climate change may also exacerbate threats from change (St.Clair & Howe, 2007). In this paper, we natural disturbances such as disease, insects, fi re, review threats to genetic diversity of forest plants, and extreme weather. Fires are expected to be more discuss factors that can be used to prioritize species frequent and increasingly severe with increasing and populations for conservation, and discuss temperatures and corresponding droughts strategies for gene conservation. Although other (Westerling et al., 2006). Native insects and diseases reviews of forest gene conservation exist, we focus may become epidemic as a result of climate change specifi cally on gene conservation threats, priorities, (Woods et al., 2005; Carroll et al., 2006). Climatic and strategies in relation to climate change. extremes may become more frequent in the future, Th reats to genetic diversity contributing to losses of forest genetic resources from drought, wind, and even, paradoxically, Th reats to forest genetic diversity include threats extremes in late spring and early fall frosts. Th reats to species, populations, and genetic variation within to genetic diversity from climate change and populations. Th ese threats are both natural and natural disturbances are further complicated by human-caused, although distinguishing which are interactions with habitat loss, deforestation, and poor which is increasingly diffi cult. Habitat loss and management. deforestation from urbanization, conversion to agriculture, overgrazing, overharvesting without Vulnerability and prioritization of species and regeneration, and replacement of native forests populations for gene conservation with non-native plantations are pervasive threats to Climate change will have widespread and long- forest genetic resources worldwide. Th e net decrease term consequences for many species. It has become in global forest area between 2000 and 2005 was increasingly clear that triage may be necessary to estimated to be 7.3 million hectares (FAO, 2006). prioritize species and populations for conservation. Th ese problems tend to be greatest in areas of high Th e simple answer for prioritization is to give greater population pressures and poverty. Low-elevation priority to those species and populations at greatest forests tend to be the most threatened, and this is risk. Determining those species and populations at signifi cant because adaptive genetic variation tends greatest risk, however, is not an easy task. Risk is to be geographically structured. Habitat loss and defi ned as the product of the impact of an occurrence deforestation can lead to fragmentation of remaining (i.e. the loss of genetic diversity) and the probability native stands, which can contribute to the decline of that occurrence. Some level of uncertainty will be of those stands by disrupting natural patterns associated with estimating impact and probability, of migration (gene fl ow) and reducing eff ective and so that must also be considered. population sizes. Impact depends on the value of the species, Even where forests are regenerated, management population, and genetic variants that are at risk practices can negatively impact genetic resources if of being lost, including value to society and to the straight, fast-growing, more pest-resistant trees are ecological integrity of ecosystems. Th us, we might selectively harvested, and poor trees are left as seed place greater priority on economically important trees (dysgenic selection). Replacement of native species. An example is Pseudotsuga menziesii stands with very diff erent species or genetically (Mirb.) Franco, a keystone species that defi nes distinct populations can lead to the loss of genetic the components and processes inherent in many diversity. For example, the wide use of grass and ecosystems in western North America. We might forb cultivars in restoration can lead to the loss of place greater priority on populations with unique signifi cant genetic variation in native populations and valuable genetic variants. Populations of Pinus of these species. Poor management can contribute radiata D.Don on Guadalupe Island, Mexico, or 404 J. B. ST.CLAIR, G. T. HOWE populations of Picea glauca (Moench) Voss in the Table 1. Species and populations most vulnerable to climate Ottawa Valley, Canada, are examples of populations change. that deserve a high priority because of their unique genetic characteristics that may be valuable to future ● Rare species generations (disease resistance in Guadalupe Island ● Species with long generation intervals (e.g., long-lived Pinus radiata and fast growth in Ottawa Valley Picea species) glauca; Ledig et al., 1998). Despite the intuitiveness ● Genetic specialists (species that are locally adapted) of placing a high priority on economically important species, these are also the species that may be well ● Species with limited phenotypic plasticity conserved in breeding programs (Lipow et al., 2002, ● Species or populations with low genetic variation Lipow et al., 2003). Society also values that which ❍ Small populations is rare, and so threatened species or populations, ❍ Species infl uenced by past genetic bottlenecks or species that are widespread but rare throughout ❍ much of their range, may be given higher priority. Inbreeding species Such is the case for Pinus torreyana Parry ex Carrière ● Species or populations with low dispersal and colonization in California, USA (Ledig et al., 1998) and Mexican potential spruces (Ledig et al., 2000). ❍ Fragmented, disjunct populations Th e probability that genetic diversity will be lost ● Populations at the trailing edge of climate change depends on human factors, natural processes, and ● Populations with “nowhere to go” their interactions. In evaluating human factors, we ● Populations threatened by habitat loss, fi re, disease, or insects must consider the probability of deforestation, land- use

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