Genetic Structure of Notholithocarpus densiflorus (Fagaceae) from the Species to the Local Scale: A Review of Our Knowledge for Conservation and Replanting Author(s): Richard S. Dodd Alejandro Nettel Jessica W. Wright Zara Afzal-Rafii Source: Madroño, 60(2):130-138. 2013. Published By: California Botanical Society DOI: http://dx.doi.org/10.3120/0024-9637-60.2.130 URL: http://www.bioone.org/doi/full/10.3120/0024-9637-60.2.130 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/ terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. MADRON˜ O, Vol. 60, No. 2, pp. 130–138, 2013 GENETIC STRUCTURE OF NOTHOLITHOCARPUS DENSIFLORUS (FAGACEAE) FROM THE SPECIES TO THE LOCAL SCALE: A REVIEW OF OUR KNOWLEDGE FOR CONSERVATION AND REPLANTING RICHARD S. DODD Department of Environmental Science Policy and Management, University of California, Berkeley, CA 94720 [email protected] ALEJANDRO NETTEL Campus del Mar, Universidad de Ciencias y Artes de Chiapas. Prolongacio´n Jua´n Jose´ Calzada s/n., Tonala´, Chiapas, Me´xico JESSICA W. WRIGHT USDA-Forest Service, Pacific Southwest Research Station, 1731 Research Park Drive, Davis, CA 95618 ZARA AFZAL-RAFII Department of Environmental Science Policy and Management, University of California, Berkeley, CA 94720 ABSTRACT Tanoak, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh (Fagaceae), is an important component of mixed-evergreen forests and woodlands in coastal California and Oregon, with incursions into the Sierra Nevada and the Klamath Ranges. Sudden Oak Death (SOD) is causing severe dieback and mortality in tanoak and could transform these ecosystems in areas where the pathogen Phytophthora ramorum S. Werres, A.W.A.M. de Cock can become established. Knowledge of genetic diversity within the species is important for both disease resistance screening, conservation and replanting in sites with high mortality. Here we review what has been learned about the genetic structure within tanoak since SOD has caused disease epidemics in the species. We review published work on genetic structure at the species level and provide some re-analyses of these data that show divergence across the geographic range. We also review recently published data on genetic structure at a fine spatial scale that provides some guidelines for the selection of trees as seed sources. Finally, we interpret a range of seed provenancing strategies in the light of our knowledge of tanoak genetic diversity. Key Words: Conservation, fine-scale genetic structure, genetic divergence, Notholithocarpus densiflorus, replanting, tanoak. Human-induced perturbations as a result of keystone species have been threatened or reduced resource use, habitat fragmentation and climate from overstory trees to understory shrubs. change are leading ecosystems to functional Chestnut blight is a notable example on the tipping points with potentially far-reaching con- American continent (Garnas et al. 2011) and sequences (Barnosky et al. 2012). In forested pandemics of Dutch elm disease have been ecosystems, the fine balance between a function- catastrophic across the northern hemisphere ing system in which hosts and pathogens co-exist (Brasier and Buck 2002). and the rapid decline that ensues when environ- The current epidemic of Sudden Oak Death mental conditions push the system out of (SOD) caused by the exotic pathogen Phy- equilibrium is an example of such a tipping tophthora ramorum S. Werres, A.W.A.M. de point. Recently, this has been exacerbated by the Cock has a very wide host range and is shaping movement of organisms globally, resulting in up to be a potentially devastating disease on exotic diseases with catastrophic consequences. tanoak, Notholithocarpus densiflorus (Hook. & Forest trees are particularly vulnerable because of Arn.) Manos, Cannon & S. H. Oh (Fagaceae), in long generation times and sedentary life histories, central and northern California (Rizzo et al. but they are also critically important as keystone 2005). Epidemiological risk analyses suggest that, species of the broader ecosystem. Over the last like other systems, tanoak forests are likely to be century, several forest tree diseases have caused transformed through the loss of overstory trees such severe host mortality that, what were once and may only avoid extinction through successful 2013] DODD ET AL.: GENETIC STRUCTURE OF NOTHOLITHOCARPUS DENSIFLORUS 131 resprouting (Cobb et al. 2012). If the disease organization of pedigrees and the effective limits takes the course predicted by Cobb et al. (2012), to recent seed and pollen dispersal. The latter can replanting will be necessary to augment genetic be important in resistance screening, where diversity that may be lost stochastically as stands sampling of relatives may be desirable and in regenerate vegetatively and to re-introduce diver- conservation and restoration where maximizing sity in stands that fail to resprout. Selection of for genetic diversity in seed selection is the goal. suitable seed sources will be critical to the We have been studying genetic diversity in conservation of genetic resources as well as for tanoak, with a view to understanding partitioning successful replanting. There is considerable de- of genetic diversity at the broad (Nettel et al. bate as to the optimum strategy for selecting seed 2009; Dodd et al. 2010) and fine-scale landscape sources that will maximize the likely success of levels (Dodd et al. 2013). Here, we review these local populations, while promoting a diverse gene earlier reports, re-analyze some of our earlier pool on which selection can act if environmental data with new tools and discuss the consequences conditions change (Breed et al. 2012). Seed for conservation and replanting strategies in the collection from local sources to maximize likely face of mortality from disease outbreaks. We locally-adapted genotypes may lead to inbreeding refer to replanting rather than restoration be- depression if population sizes have fallen below a cause we are not proposing strategies to restore threshold level (Eckert et al. 2010; Breed et al. the ecosystem to its former state, but we are 2012), whereas mixing seeds from different looking specifically at replanting of tanoak in geographic sources introduces the risk of out- areas where it has been lost through perturba- breeding depression if the source populations are tions such as SOD. from different locally adapted gene pools (Kra- mer and Havens 2009). Reciprocal transplant THE SPECIES studies are helpful to gain some insights among these competing scenarios. However, for many Tanoak (Notholithocarpus densiflorus)was tree species, such approaches are too time- recently attributed to its monospecific genus by consuming, so molecular marker data need to Manos et al. (2008) in recognition of its closer be used. Molecular methods allow the rapid affinities to Quercus, Castanea and Castanopsis documentation of genetic diversity, but in most than to the Asian stone oaks (Lithocarpus spp.). cases sequences of DNA, or analyses of DNA Tanoak is a restricted endemic to the California fragment sizes are confined to regions of the Floristic Province; the tree form, N. densiflorus genome that are not transcribed and are assumed var. densiflorus ranges from disjunct stands in to be selectively neutral. Although such DNA Ventura County, California to more continuous markers do not necessarily indicate genetic stands as far north as Coos County, Oregon adaptations, they do provide us with information (Tappeiner et al. 1990). Although it is best on evolutionary divergence that would indicate represented in the Coastal Ranges, it extends zones for conservation management (Moritz inland to the foothills of the Sierra Nevada. The 1999) and seed sources that should not be mixed dwarf form, N. densiflorus var. echinoides is more for planting if outbreeding depression is a common at higher elevations in the north-eastern concern. range of the species, particularly on serpentine. Spatial organization of genetic diversity is a Occurrence reports of the dwarf form should be property of species that derives from contempo- treated with caution as there is likely to be rary demographic processes and past environ- confusion over ecological dwarfism and geneti- mental events. At a broad spatial scale, encom- cally distinct forms (Dodd unpublished data). passing a range of environmental conditions, Tanoak is predominantly insect-pollinated (see evolutionary forces operate on the different gene Wright and Dodd this volume) and can produce pools and can lead to more or less divergent heavy crops of acorns that have a relatively high lineages (Hampe and Petit 2005). Detecting viability; in addition it is a prolific