Informing Seed Transfer Guidelines and Native Plant Materials Development: Research Supporting Restoration Across the Colorado Plateau and Beyond

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As restoration needs for natural landscapes grow due to higher frequency and/or intensity disturbances, pressure from invasive species, and impacts resulting from changing climates, considerable time and resources are being invested to guide the development and deployment of native plant materials (NPMs). Across lower elevations of the Colorado Plateau, a region composed primarily of public land where arid conditions make restoration especially challenging, NPM coordination has been spearheaded by the Bureau of Land Management’s Colorado Plateau Native Plant Program (CPNPP) since 2009. To help CPNPP achieve its vision of healthy and resilient native plant communities, the Southwest Biological Science Center (SBSC) has provided scientific support and leadership since 2010. SBSC’s research includes field, lab, and greenhouse activities, many of which currently culminate in the development of species-specific seed transfer zones. These zones are developed to protect species’ natural patterns of genetic variation and depict species’ adaptations to regional climatic gradients so that managers and practitioners can make informed seed transfer and plant material development decisions.

Background & Importance

Colorado Plateau native plant community

Colorado Plateau native plant community dominated by globemallow (Sphaeralcea parvifolia), Indian ricegrass (Achnatherum hymenoides), and sand dropseed (Sporobolus cryptandrus) west of Los Lunas, New Mexico. (Credit: Rob Massatti, USGS. Public domain.)

The majority of native plant materials (NPMs) utilized for restoration purposes are developed for widely distributed species that provide a variety of ecosystem services (Wood et al. 2015; Butterfield et al. 2017). Disturbed ecosystems benefit from the use of appropriate NPMs, which are those that display ecological fitness at the restoration site, are compatible with conspecifics and other members of the plant community, and that do not demonstrate invasive tendencies (Jones 2013). Furthermore, the use of appropriate NPMs can help address specific environmental challenges, rejuvenate ecosystem function, and improve the delivery of ecosystem services (Hughes 2008). While many NPMs have been developed (e.g., Aubry et al. 2005), there is interest in broadening the diversity of species available and the geographic representation of sources to provide appropriate choices in relation to the characteristics of any restoration site. In addition, researchers are providing guidance to managers and practitioners regarding how best to transfer NPMs across the landscape. For example, guidance on seed transfer has been derived from genecological studies, which utilize common gardens to correlate phenotypic variation to environmental gradients (summarized in Kilkenny 2015), molecular studies, which identify putative adaptive genetic loci and infer environmental drivers of variation (Shryock et al. 2017), and climate modeling studies, which can provide guidance when species-specific data are unavailable (e.g., Bower et al. 2014; Doherty et al. 2017). All of these approaches intend to improve the viability of NPMs at restoration sites, thereby improving outcomes and stretching limiting restoration resources (e.g., time and money).

Genetic data (which hereafter refers to molecular/sequencing data) have broad, often unrealized utility when considering the use of existing NPMs or development of new NPMs. A well-designed landscape genetic analysis can resolve patterns of neutral genetic diversity across a species’ distribution and delineate the geographic distribution of evolutionary lineages, which can impact restoration outcomes (Hufford and Mazer 2003; McKay et al. 2005; Frankham et al. 2011). For example, determining how long evolutionary lineages have been separated and their rate of gene flow can help practitioners identify regions of a species’ range where individuals should not be mixed, even if those individuals occupy similar environmental space (Massatti et al. 2018). In addition, neutral genetic diversity is well suited to determine taxonomic relationships in instances where morphology tends to be unreliable (Fujita et al. 2012). Landscape genetics can also identify adaptive genetic variation, or variation that may provide a benefit to the survival (and therefore reproductive capacity) of a species (Holderegger et al. 2006). Genetic variation that correlates with environmental gradients suggests adaptively significant environmental conditions that can aid in the development of seed transfer zones. Furthermore, the inclusion of existing NPMs in genetic analyses permits the assessment of how they represent the known neutral and adaptive genetic diversity of a species. As such, genetic analyses can guide the appropriate deployment of existing NPMs, as well as suggest what additional NPMs may be important to develop. For most of the important Colorado Plateau restoration species, knowledge on adaptive differentiation, genetic diversity, and spatial variation in standing genetic diversity is lacking.

Dryland, shrub-dominated plant community typical of sandy substrates

Dryland, shrub-dominated plant community typical of sandy substrates near Page, Arizona. (Credit: Rob Massatti, USGS. Public domain.)

General Methods

Leaf tissue samples for priority restoration species are field collected from sites located across the Colorado Plateau – sampling sites are stratified to represent the dominant, regional climatic gradients. Colorado Plateau collections are often supplemented with leaf tissues from herbarium vouchers or collected by collaborators so as to incorporate/identify genetic patterns across species’ western distributions. DNA is extracted and used to develop next-generation sequencing libraries at Northern Arizona University’s Environmental Genetics and Genomics Laboratory. Libraries are sequenced at the University of Oregon’s Genomics and Cell Characterization Core Facility on an Illumina HiSeq 4000. Data processing and analyses are completed at SBSC and take advantage of the USGS Yeti supercomputer.

Important Results

Genetically informed seed transfer zones for the Colorado Plateau and adjacent regions are available for James’ galleta grass (Pleuraphis jamesii; syn. Hilaria jamesii), small-leaf globemallow (Sphaeralcea parvifolia), and sand dropseed (Sporobolus cryptandrus). Pleuraphis jamesii and Sphaeralcea parvifolia showed distinct populations structure across their investigated distributions, and as a result, seed transfer zones reflect both genetic differentiation and putative adaptation. In contrast, Sporobolus cryptandrus did not display genetic structure indicative of evolutionary lineages, resulting in seed transfer zones that depict climatic adaptation only (Massatti 2019).

Future Directions

The development of genetically informed seed transfer zones for Indian ricegrass (Achnatherum hymenoides), hoary tansyaster (Machaeranthera canescens), and yellow beeplant (Cleome lutea) is in progress and should be available before September 2020. These seed transfer zones will be followed by similar results for priority restoration species in future years. The SBSC and CPNPP are undertaking other, field-based research efforts that will inform seed transfer guidelines and native plant materials development – these will be reported as they are completed.

References

Aubry, C. A., Shoal, R. Z., & Erickson, V. (2005). Grass Cultivars: Their Origins, Development, and Use on National Forests and Grasslands of the Pacific Northwest (p. 44). US Forest Service, Pacific Northwest Region.

Bower, A. D., Clair, J. B. S., & Erickson, V. (2014). Generalized provisional seed zones for native plants. Ecological Applications, 24(5), 913-919.

Butterfield, B. J., Copeland, S. M., Munson, S. M., Roybal, C. M., & Wood, T. E. (2017). Prestoration: using species in restoration that will persist now and into the future. Restoration Ecology 25, S155-S163.

Doherty, K. D., Butterfield, B. J., & Wood, T. E. (2017). Matching seed to site by climate similarity: Techniques to prioritize plant materials development and use in restoration. Ecological Applications, 27(3), 1010-1023.

Frankham, R., Ballou, J. D., Eldridge, M. D., Lacy, R. C., Ralls, K., Dudash, M. R., & Fenster, C. B. (2011). Predicting the probability of outbreeding depression. Conservation Biology, 25, 465–475.

Fujita, M. K., Leache, A. D., Burbrink, F. T., McGuire, J. A., & Moritz, C. (2012). Coalescent-based species delimitation in an integrative taxonomy. Trends in Ecology & Evolution, 27(9), 480-488.

Holderegger, R., Kamm, U., & Gugerli, F. (2006). Adaptive vs. neutral genetic diversity: implications for landscape genetics. Landscape Ecology, 21, 797–807.

Hufford, K. M., & Mazer, S. J. (2003). Plant ecotypes: genetic differentiation in the age of ecological restoration. Trends in Ecology & Evolution, 18(3), 147-155.

Hughes, A. R., Inouye, B. D., Johnson, M. T. J., Underwood, N. & Vellend, M. (2008). Ecological consequences of genetic diversity. Ecology Letters, 11, 609–623.

Jones, T. A. (2013). Ecologically Appropriate Plant Materials for Restoration Applications. BioScience, 63(3), 211-219.

Kilkenny, F. F. (2015). Genecological approaches to predicting the effects of climate change on plant populations. Natural Areas Journal, 35, 152–165.

Massatti, R., Prendeville, H. R., Larson, S., Richardson, B. A., Waldron, B., & Kilkenny, F. F. (2018). Population history provides foundational knowledge for utilizing and developing native plant restoration materials. Evolutionary Applications, 11, 2025–2039.

Massatti, R., 2019, Genetically informed seed transfer zones for Pleuraphis jamesiiSphaeralcea parvifolia, and Sporobolus cryptandrus across the Colorado Plateau and adjacent regions: U.S. Geological Survey data release, https://doi.org/10.5066/P9XLI7OD.

McKay, J. K., Christian, C. E., Harrison, S., & Rice, K. J. (2005). ‘How local is local?’ – A review of practical and conceptual issues in the genetics of restoration. Restoration Ecology, 13, 432–440.

Shryock, D. F., Havrilla, C. A., DeFalco, L. A., Esque, T. C., Custer, N. A., & Wood, T. E. (2017). Landscape genetic approaches to guide native plant restoration in the Mojave Desert. Ecological Applications, 27, 429–445.

Wood, T. E., Doherty, K., & Padgett, W. (2015). Development of native plant materials for restoration and rehabilitation of Colorado Plateau ecosystems. Natural Areas Journal, 35(1), 134-150.