Author
 |
Matlaga, David |
|
Davis, Adam |
|
Submitted to: Journal of Applied Ecology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/1/2012 Publication Date: 2/26/2013 Citation: Matlaga, D.P., Davis, A.S. 2013. Minimizing invasive potential of Miscanthus × giganteus grown for bioenergy: identifying demographic thresholds for population growth and spread. Journal of Applied Ecology. 50:479-487. Interpretive Summary: A fundamental challenge for bioenergy crop development is to evaluate and minimize the potential of such crops to escape cultivation and invade both arable lands and adjacent non-arable ecosystems. Crop sterility has been highlighted as a robust approach to minimize invasive potential. An example of one such crop is the C4 grass Miscanthus x giganteus (Mxg), a naturally forming sterile Asian hybrid, one of the top candidates for biomass production in the northern US corn belt. Efforts are underway to develop production systems for Mxg in its present sterile form and newly released transgenic cultivars with fertile seed. It remains unclear if sterile Mxg poses significant invasion risk through clonal recruitment and, for seeded varieties, to what extent fertile seed production must be suppressed among plants grown in biomass production fields to prevent spread. We constructed a model examining the growth of Mxg in time and space based on estimates of vital rates and dispersal dynamics obtained from field studies. Our model indicated that seed fertility is a critical parameter related to invasiveness of Mxg populations: if more than one out of 1 million seeds in a local population is able to germinate and survive to form a mature plant, the population will grow in numbers and spatial extent. Such models may be useful in identifying traits of non-invasive bioenergy crop cultivars to guide future breeding efforts. Technical Abstract: Production of herbaceous perennial bioenergy crops in the north central region of the USA is being targeted primarily at marginal lands to avoid conflicts between food and fuel. A fundamental challenge for biofeedstock development is to evaluate and minimize the potential of such crops to escape cultivation and invade both arable lands and adjacent non-arable ecosystems. Crop sterility has been highlighted as a robust approach to minimize invasive potential. An example of one such crop is the C4 grass Miscanthus x giganteus, a naturally forming sterile Asian hybrid, one of the top candidates for biomass production in the northern US corn belt. Efforts are underway to develop production systems for M. x giganteus in its present sterile form and newly released transgenic cultivars with fertile seed. It remains unclear if sterile M. x giganteus poses significant invasion risk through clonal recruitment and, for seeded varieties, to what extent fertile seed production must be suppressed among plants grown in biomass production fields to prevent spread. Using demographic and dispersal data for M. x giganteus we parameterized an age-structured spatial population model to evaluate the potential spatial population dynamics of sterile and fertile M. x giganteus. Our results indicate a growth rate for sterile M. x giganteus populations of slightly less than 1 (lambda = 0.929), indicating gradual population decline over the long-term. Production of one rhizome fragment per every two adult plants would allow for positive population growth (lambda > 1) among sterile populations. For fertile varieties, our model indicates that a very small proportion of seeds (0.000001) would need to germinate and establish to achieve a growing population (lambda > 1). Extreme caution should be taken in introducing fertile M. x giganteus considering that even under low seed-to-first year plant transitions (e.g., 0.000001 and 0.00001) relatively rapid spread rates are possible (4 and 40 m/yr, respectively). |
