Editor's Choice: Sourcing propagules to achieve current and future restoration objectives

April 2014 (Issue 51:2)

Kettenring, K. M., Mercer, K. L., Reinhardt Adams, C., Hines, J. (2014), Application of genetic diversity–ecosystem function research to ecological restoration. Journal of Applied Ecology. doi: 10.1111/1365-2664.12202

Over the last few decades, numerous restoration projects have been initiated in a variety of ecosystem types. A common question for restorations is; where should we get the seed? Should we use seeds from a nearby location with similar environmental characteristics? Should we avoid cultivars, even ones that are known to establish quickly at our site? Or, perhaps we should use a variety of seed sources to maximize genetic diversity of seed mixes?

In this issue, Kettenring et al. (2014) review studies that have manipulated genetic diversity and discuss them in this restoration context. Genetic diversity–ecosystem functioning research (GDEF) has its roots in biodiversity–ecosystem functioning (BEF), which became very popular as a study topic in the early 1990s. Since around 2003, a new wave of studies has emerged on how genetic diversity is related to ecosystem functioning. This research is important because within-species diversity is probably declining more than species diversity. Although this field is not as old as BEF, researchers have found that higher genetic diversity can increase net primary productivity (Crutsinger et al. 2006), invasiveness (Vellend et al. 2010), persistence over time (Booth & Grime 2003), and insect abundances (Johnson et al. 2006). Many of the early studies were done on genetic diversity in Solidago altissima, which has multiple ploidy levels within this one species. Interestingly, the ploidy levels are associated with different levels of herbivory by gall-forming insects (Halverson et al. 2008).
The mechanisms behind GD–EF relationships are similar to those of BEF, that is, in genetically diverse mixes there may be: 1) genotypes with above average traits that are more likely to be included in genetically diverse mixes, 2) greater overyielding by genotypes with above average traits, or 3) genotypes that exhibit niche partitioning or facilitation, which can allow greater resource capture. It will be interesting to see if the same mechanisms are found behind BEF and GDEF relationships.

Traditionally, restorationists have emphasized locally adapted genotypes, assuming that these genotypes are better adapted to current conditions than seed from further away. However, in recent years, we have come to appreciate that our restorations are going to encounter changes in climate in the near future. Atmospheric temperatures and CO2 concentrations, and N deposition are all rising and will all be even higher in the future as restorations mature. Thus, the focus should be on how restorations will function under both current and future (and not past) conditions. Furthermore, the agents that caused the degradation of the site are often still present post-restoration, and some have argued that degraded sites are novel ecosystems that will be more difficult to restore than people realize. This might necessitate a shift in focus to trying to maximize genetic diversity in our mixes, possibly in combination with the local genotype approach (e.g. using many local sources for seeds instead of a single seed source). In contrast to plant restorations, animal conservationists have usually emphasized genetic diversity, and they have rescued small populations with input of genotypes from populations far removed from the small population. Furthermore, as Kettenring et al. (2014) point out, restoration objectives have progressed from emphasizing: 1) high initial plant establishment, to having that plus 2) long-term population persistence, to 3) having a fully functioning ecosystem at all trophic levels. Achieving the high levels of species and functional diversity of ‘remnant’ areas has proven to be challenging for restorations. It remains to be seen if the three goals outlined by Kettenring et al. (2014) are compatible or if trade-offs will occur among them. For example, having high initial plant establishment may lead to reduced population persistence of target species in the longer term (Martin and Wilsey 2012). Thus, the paper by Kettenring et al. (2014) is timely.

Kettenring et al. (2014) outline three approaches to propagule sourcing: 1) use of cultivars for high initial plant establishment, 2) use of local adaptation approaches for long-term population persistence, and 3) restoring genetic diversity for a fully functioning ecosystem. The real novelty here is the discussion of how these approaches may be mixed, that is the cultivar and genetic diversity approaches could be mixed to achieve high initial plant establishment and a restored functioning ecosystem, or the local adaptation and genetic diversity approaches could be mixed to achieve long-term persistence and restoring functioning ecosystems. Trade-offs may become apparent as these techniques are mixed, or they may provide a “win-win” approach in achieving objectives. In their review, they also call for future research on 1) selection, relatedness and spatial arrangements of genotypes, 2) relating traits that affect an ecosystem function to neutral and adaptive diversity, 3) conducting GDEF research over longer time frames and at larger geographic scales. On the whole, it is surprising how little empirical research has been done on these fundamental topics in restoration ecology. Kettenring et al. (2014) point out that most studies on GDEF have used plots < 1 m2 and monitored them for < 2 years. As the studies mature to become ‘long-term’, and as larger-scale studies are published, it will be interesting to see how processes like population persistence and resistance to environmental change are affected by GD. GD is expected to be especially important at larger spatial and temporal scales. The authors suggest that further study on these topics will help to advance theory on GDEF, but will also be highly relevant for improving restoration projects.
 

Brian Wilsey
Associate Editor

 

References

Booth, R.E. and J.P. Grime. 2003. Effects of genetic impoverishment on plant community diversity. Journal of Ecology 91:721-730
Crutsinger, G.M., Collins, M.D., Fordyce, J.A., Gompert, Z., Nice, C.C., and N.J. Sanders. 2006. Intraspecific diversity predicts community structure and governs an ecosystem process. Science 313:966-968
Johnson, M.T.J., Lajeunesse, M.J. and A.A. Agrawal. 2006. Additive and interactive effects of plant genotypic diversity on arthropod communities and plant fitness. Ecology Letters 9:24-34
Kettenring, K.M., Mercer, K.L., Reinhardt Adams, C. and J. Hines. 2014. Application of genetic diversity-ecosystem function research to ecological restoration. Journal of Applied Ecology 51:339-348 
Martin, L.M. and B.J. Wilsey. 2012. Assembly history alters alpha and beta diversity, exotic-native proportions, and ecosystem functioning of restored prairie plant communities. Journal of Applied Ecology 49:1436-1445
Vellend, M., Drummon, E. and H. Tomimatsu. 2010. Effects of genotype identity and diversity on the invasiveness and invasibility of plant populations. Oecologia 162:371-381.
Wilsey, B.J. 2010. Productivity and subordinate species response to dominant grass species and seed source during restoration. Restoration Ecology 18:628-637
 

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