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Ecological Genetics and the Restoration of Plant Communities

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Ecological Genetics and the Restoration of Plant Communities panies restore drill pads. Prairie restoration projects of Ecological Genetics and all sizes are becoming common (Kline & Howell 1987). Hard rock and strip mines often require intense recla- mation (Schaller & Sutton 1978). Logged forests, aban- the Restoration of doned agricultural lands, and overgrazed rangelands all require large scale restoration efforts (Millar & Libby 1989; Jackson 1992; Roundy et al. 1995). Plant Communities: In the past, reclamation of degraded land has usually been accomplished with a few species that were often Mix or Match? exotic to the disturbed area. But there is growing awareness that restoring ecosystem function and bio- logical diversity often requires the use of native species. 1 Peter Lesica Many animals, especially insects, require specific native Fred W. Allendorf1 plants for food (Futuyma 1983). In addition, native plants often provide the specific vegetation structure re- quired for nesting or feeding (Bock et al. 1986; McAdoo Abstract et al. 1986; Wilson & Belcher 1989). Furthermore, exotics may compete with native plants (Bock et al. 1986; Lesica We present a conceptual framework for choosing na- & DeLuca 1996) and alter the frequency or intensity of tive plant material to be used in restoration projects ecosystem processes such as fire (Cox et al. 1990). For on the basis of ecological genetics. We evaluate both these reasons the use of native plants in ecological res- the likelihood of rapid establishment of plants and toration is becoming increasingly important. the probability of long-term persistence of restored or Much of the literature on ecological restoration per- later successional communities. In addition, we con- tains to the choice of species to be used (Chambers et al. sider the possible harmful effects of restoration projects 1984). It is becoming increasingly apparent, however, on nearby ecosystems and their native resident popu- that intraspecific genetic differentiation in relation to lations. Two attributes of the site to be restored play site ecology is also important (Belnap 1995). Many res- an important role in determining which genetic source toration sites, such as mine spoils, pose novel and se- will be most appropriate: (1) degree of disturbance vere challenges to vegetation, and only specific ecotypes and (2) size of the disturbance. Local plants or plants may be able to survive (McNeilly & Bradshaw 1968). from environments that “match” the habitat to be re- On the other hand, plants introduced from distant source stored are best suited to restore sites where degree of populations may not be adapted to the local climatic, disturbance has been low. Hybrids or “mixtures” of edaphic, or biotic environment (Millar & Libby 1989; genotypes from different sources may provide the Knapp & Rice 1994; Linhart 1995). best strategy for restoring highly disturbed sites to One goal of restoration is creation of self-supporting which local plants are not adapted. Cultivars that have communities that will provide ecosystem functions and been modified by intentional or inadvertent selection processes, as well as prevent erosion and provide habi- have serious drawbacks. Nevertheless, cultivars may tat for diverse native species (Bradshaw 1987). Rapid be appropriate when the goal is rapid recovery of establishment of plants with a high survival rate is im- small sites that are highly disturbed. portant to prevent erosion and invasion by exotics. In addition, the long-term persistence of restored or later Introduction successional communities is also important. Restoration of endangered species populations has received a good here has been an increase in efforts to restore habi- deal of attention recently (Bowles & Whelan 1994; Falk Ttats degraded by human activities throughout the et al. 1996), but our concern is with restoration and rec- world (Berger 1990; Anderson 1995; Hobbs & Norton lamation of native vegetation rather than reintroduc- 1996). Restoration projects vary greatly in size and de- tion of rare species. gree of disturbance to be ameliorated. Managers of na- Relatively little attention has been given to the effects tional parks and forests attempt to restore vegetation of of restoration projects on nearby ecosystems and their trails, roads, and campgrounds (Majerus 1997). Oil com- native resident populations. Potential threats to local communities and populations from restoration efforts 1Division of Biological Sciences, University of Montana, Mis- result from the introduction of genes and the loss of lo- soula, MT 59812, U.S.A. cally adapted genotypes. Species are likely to require the genetic variation found throughout their range in © 1999 Society for Ecological Restoration order to adapt to future environmental changes. Over 42 Restoration Ecology Vol. 7 No. 1, pp. 42–50 MARCH 1999 Ecological Genetics of Restoration the long term, local genotypes may be crucial to the per- ronments in western North America, but there is little sistence of populations or the species as a whole evidence for genetic differentiation among populations (Frankel & Soulé 1981). from most of these habitats (Wu & Jain 1978; Rice & Opinions differ on the correct strategy for choosing Mack 1991). The African grass Pennisetum setaceum has plant materials for restoration (Belnap 1995). Many res- adapted to widely different habitats on the island of torationists use cultivars selected for high performance Hawaii without detectable genetic differentiation (Will- in restoration situations (Wright 1975; Pater 1995; Shaw iams et al. 1995). & Monsen 1995), while others champion the use of local sources (Knapp & Rice 1994; Linhart 1995). A third strategy uses mixtures of populations or hybrid geno- Artificial Propagation types (Millar & Libby 1989; Munda & Smith 1995). We Strong inadvertent directional selection may occur dur- cannot recommend a single correct strategy for any spe- ing cultivation (Knapp & Rice 1994). Production of na- cific situation. Rather, we present a conceptual frame- tive plants for restoration involves collection of wild work for assessing the value of different strategies seed, and genetic variation can be lost through inade- across a wide array of situations. We approach this quate sampling (Brown & Briggs 1991). Assuming that problem by first reviewing the underlying genetic prin- there is genetic variation within cultivated populations, ciples and then placing these principles in the context of some plants will be more vigorous under cultivation restoration ecology. Finally, we evaluate various strate- than others. These plants will produce more seed and gies for choosing restoration plant materials in light of be over-represented in standard nursery seed collec- ecological genetics theory. tions (Knapp & Rice 1994). It is impossible to predict what these inadvertent selection forces will be (Temple- Genetic Principles ton 1991). Intentional selection also often occurs during the Local Adaptation propagation of native plants for restoration (Voigt et al. 1987; Alderson & Sharp 1994). Several strategies are Numerous studies have demonstrated that plants evolve employed to select for desirable characters such as for- local ecotypes closely adapted to their immediate envi- age and seed production, seed germinability, and toler- ronment (Turesson 1922; Clausen & Hiesey 1958; Brad- ance of salt, heat, and drought. These strategies vary shaw 1972; Turkington & Harper 1979; Linhart & Grant from weak uniparental selection in a single generation 1996; but see Rapson & Wilson 1988). For example, Pen- to strong recurrent selection (Wright 1975; Vogel & Ped- stemon eatonii (firecracker penstemon) seed shows ap- ersen 1993). parently adaptive ecotypic differentiation for germination Selection will increase the frequency of alleles re- requirements. Seed from high-elevation populations re- sponsible for the desired trait but may also result in the quired long chilling periods, while those from low ele- deterioration of other aspects of performance (Hartl & vations needed only short chill times for germination Clark 1989). For example, selection for rapid growth of- (Meyer et al. 1995). High-elevation ecotypes may be able ten will also result in shorter life span. The two primary to establish an initial population in low-elevation sites, mechanisms of genetic correlation are pleiotropy (one but population growth could be curtailed by failure to gene having many phenotypic effects) and linkage dise- recruit a second generation due to inadequate chilling quilibrium (selection for one gene will also affect other periods. Atriplex canescens (fourwing saltbush) popula- closely linked genes on the same chromosome). Strong tions vary for cold hardiness. Warm desert populations directional selection will also reduce the genetically ef- may not survive in cold desert environments following fective population size and result in increased genetic a severe winter (Meyer & Monsen 1992). There is also a drift and more rapid loss of genetic variation. great deal of intraspecific variation for disease resis- tance in plants (Futuyma 1983; Burdon 1987; Aug- spurger 1988). Pacific slope plantings of interior strains Genetic Drift of Pseudotsuga menziesii (Douglas fir) have failed due to diseases of little consequence to resident populations Genetic drift refers to changes in allele frequency from (Silen 1978). generation to generation caused by sampling error. While many widespread species demonstrate adap- That is, the genes transmitted to progeny are an imper- tive genetic variation over their
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