The term erosion is evocative of gradual loss of not catastrophic, are often balanced by mutation and something important that will eventually undermine gene flow, and typically do not occur in concert across the health or stability of dependent individuals or the entire species. Generally, loss of genetic diversity is a communities. As applied to genetic diversity, erosion is more serious threat to species that were formerly more the loss of genetic diversity within a species. It can widespread and have lost habitat and diversity recently happen fairly quickly — as with a catastrophic event than to species that are naturally restricted in their or change in land use that removes large numbers of occurrence. individuals and their habitat. But it can also occur more Influences that could contribute to genetic erosion in gradually and go unnoticed for a long time. Genetic native plant species include: major losses of habitat erosion can represent the loss of entire populations and the resident plant populations; fragmentation of genetically differentiated from others, the loss or change habitat; management activities such as thinning, in frequency of specific alleles (i.e., different forms of a harvesting, or nursery selections that target certain gene) within populations or over the species as a whole, features of plants; and planting material from a narrow or the loss of allele combinations. genetic collection in revegetation efforts. For example, in [ genetic erosion can result a restoration effort in southern California for eelgrass from habitat loss and (Zostera marina), genetic analyses revealed that the transplanted eelbeds had significantly lower genetic fragmentation and seed diversity than natural, undisturbed beds. collections that are Genetic erosion can be addressed at several levels in the too restricted ] spectrum of management activities. Other than the obvious measures of avoiding major losses or fragmen- Genetic diversity is important to a species’ fitness, tation of habitat (to the extent it disrupts natural gene long-term viability, and ability to adapt to changing flow between populations), the risk of genetic erosion environmental conditions (as explained in Volume 1). in native plant species can be minimized in specific Also, plant populations that are less genetically diverse revegetation projects by following these four guidelines: may be more susceptible, in some cases, to pathogens or other environmental stresses. Genetically eroded Collect seeds or other propagation materials populations may be less competitive with introduced (cuttings, for example) in such a manner invasive species. Overall, genetic erosion can have that representative genetic diversity of the cascading effects throughout the ecosystem. geographic area is conserved. Guidance for genet- Some loss of genetic diversity is expected under natural ically appropriate collections can be obtained from the conditions as a result of natural selection and genetic references provided in this volume. Such collections con- drift (see Volume 3). However, these losses are usually sider the geographic source or provenance, the number

National Forest Genetics Laboratory (NFGEL) Genetic Resources Conservation Program Pacific Southwest Research Station University of California USDA Forest Service One Shields Avenue 2480 Carson Road Davis, CA USA 95616 Placerville, CA USA 95667 http://www.grcp.ucdavis.edu http://www.fs.fed.us/psw/programs/nfgel/ More Information Writing woody plant specifications for restoration and mitigation practices. (2000) S. Buis. Native Plants Journal 1:116-119. Genetic erosion, inbreeding, and reduced fitness in fragmented populations of the endangered tetraploid pea Swainsona recta. (2000) L. Buza, of parent plants, the number of seeds A. Young, and P. Thrall. Biological Conservation (or propagules) from each plant, and 93:177-186. their distance from one another. The Genetic sampling guidelines for conservation life-history features of a plant species collections of endangered plants. Center for will also help to guide appropriate Plant Conservation. (1991) In: D.A. Falk and K.E. genetic collections. For example, if the Holsinger (eds.). Genetics and conservation of rare plants. New York (NY): Oxford University species is dioecious, genetic collections Press. p 225-238. should reflect a balance of males and Genetic and demographic considerations in the females if collecting vegetative material sampling and reintroduction of rare plants. E.O. rather than seeds. If the plant species is Guerrant. (1992) In: P.L. Fiedler and S.K. Jain known to reproduce asexually, it is (eds.). Conservation biology: the theory and important to make collections from practice of nature conservation, preservation, various clones rather than within one and management. New York (NY): Routledge, or a few clones. Photo credits: (left two) Thomas D. “Tom” Landis, USDA Forest Service; (above) Chapman and Hall, Inc. p 321-344. James Denny Ward, USDA Forest Service. www.forestryimages.org. Loss of genetic diversity from managed popula- to release. The use of cultivars, per se, tions: interacting effects of drift, mutation, [ genetically eroded does not create genetic erosion. immigration, selection, and population subdivi- populations may be sion. (1987) R.C. Lacy. Conservation Biology However, if the cultivar is from a narrow 1:143-158. less competitive genetic base or has been genetically Population genetic analyses of transplanted eel- with introduced narrowed through nursery practices, grass (Zostera marina) beds reveal reduced and if it is used extensively to replace genetic diversity in southern California. (1996) invasive species ] original plant populations — or planted S.L. Williams and C.A. Davis. Restoration Ecology 4:163-180. in large numbers adjacent to plant Obtain geographic source infor- populations where interbreeding is likely Genetic erosion: No longer just an agricultural issue. (2004) D.L. Rogers. Native Plants Journal mation when purchasing plants to occur — this may contribute to 5:112-122. from a nursery. This information, as genetic erosion of the native plant Managing and monitoring genetic erosion. W.B. well as the collection methods and populations. Sherwin and C. Moritz. (2000) In: A.G. Young and conditions for growing out the plants, G.M. Clarke (eds.). Genetics, demography and will help you to determine whether Encourge and support nursery viability of fragmented populations. there is sufficient genetic diversity in management activities that aim Conservation Biology Series, Vol. 4 (Cambridge). the collection for your revegetation to maximize the proportion of p 9-34. project. By asking for this information, seeds that become healthy plantable seedlings. Good nursery The United States Department of Agriculture (USDA) it also helps to convey to the grower prohibits discrimination in all its programs and activities that this is an important part of the management — that is based on on the basis of race, color, national origin, gender, religion, awareness of possible genetic variation age, disability, political beliefs, sexual orientation and product’s value, and will provide marital or family status. (Not all prohibited bases apply to encouragement to collect and provide in seed characteristics, germination all programs.) Persons with disabilities who require alter- native means for communication of program informa- this information in the future. requirements, and growth patterns — tion (Braille, large print, audiotape, etc.) should contact includes measures to avoid inadvertent USDA’s TARGET Center at: (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write: USDA Use caution when planting culti- selection and minimize the impact on Director, Office of Civil Rights, Room 326-W, Whitten vars of native species. There is the genetic diversity of the original Building, 14th and Independent Avenue, SW, Washington, DC 20250-9410, or call: (202) 720-5964 (voice wide variation in genetic diversity in collection. (See Volume 10 for more or TDD). plants that are marketed as “cultivars” information.) USDA is an equal opportunity — depending on the original collection provider and employer. and the process it has experienced prior 2006