Lauren D. Quinn

Invasiveness potential of Miscanthus sinensis: implications for bioenergy production in the United States

Miscanthus sinensis (Anderss.) is a perennial grass species that has been grown widely as an ornamental since the late 1800s and is now being considered for bioenergy production in the United States. With its ability to be grown from seed and tolerate cold climates, this species offers practical advantages over current cultivars of the higher‐yielding hybrid species, M.×giganteus. Yet a large‐scale release of M. sinensis for bioenergy production in colder northern regions could result in new invasions into natural areas. We show, with reference to historical records and data collected in six wild US populations of M. sinensis in 2009, that ornamental varieties of this species have a long history of localized escape in the Eastern United States, primarily within the Appalachian region. To prevent further escape and gene flow, we recommend the development of sterile or functionally sterile varieties of M. sinensis or the restriction of its usage as a donor of genetic material to new sterile cultivars of M. ×giganteus. Other appropriate precautions for new biomass varieties include experimental demonstration of low invasiveness in the target region ahead of commercial production, along with postintroduction stewardship programs.

Stress-Tolerant Feedstocks for Sustainable Bioenergy Production on Marginal Land

Given the mandated increases in fuel production from alternative sources, limited high-quality production land, and predicted climate changes, identification of stress-tolerant biomass crops will be increasingly important. However, existing literature largely focuses on the responses of a small number of crops to a single source of abiotic stress. Here, we provide a much-needed review of several types of stress likely to be encountered by biomass crops on marginal lands and under future climate scenarios: drought, flooding, salinity, cold, and heat. The stress responses of 17 leading biomass crops of all growth habits (e.g., perennial grasses, short-rotation woody crops, and large trees) are summarized, and we identify several that could be considered “all purpose” for multiple stress types. Importantly, we note that some of these crops are or could become invasive in some landscapes. Therefore, growers must take care to avoid dissemination of plants or propagules outside of cultivation.

Empirical evidence of long-distance dispersal in Miscanthus sinensis and Miscanthus × giganteus

Abstract Many perennial bioenergy grasses have the potential to escape cultivation and invade natural areas. We quantify dispersal, a key component in invasion, for two bioenergy candidates:Miscanthus sinensis and M. × giganteus. For each species, approximately 1 × 106 caryopses dispersed anemochorously from a point source into traps placed in annuli near the source (0.5 to 5 m; 1.6 to 16.4 ft) and in arcs (10 to 400 m) in the prevailing wind direction. For both species, most caryopses (95% for M. sinensis and 77% for M. × giganteus) were captured within 50 m of the source, but a small percentage (0.2 to 3%) were captured at 300 m and 400 m. Using a maximum-likelihood approach, we evaluated the degree of support in our empirical dispersal data for competing functions to describe seed-dispersal kernels. Fat-tailed functions (lognormal, Weibull, and gamma (Γ)) fit dispersal patterns best for both species overall, but because M. sinensis dispersal distances were significantly affected by wind speed, curves were also fit separately for dispersal distances in low, moderate, and high wind events. Wind speeds shifted the M. sinensis dispersal curve from a thin-tailed exponential function at low speeds to fat-tailed lognormal functions at moderate and high wind speeds. M. sinensis caryopses traveled farther in higher wind speeds (low, 30 m; moderate, 150 m; high, 400 m). Our results demonstrate the ability of Miscanthus caryopses to travel long distances and raise important implications for potential escape and invasion of fertile Miscanthus varieties from bioenergy cultivation. Nomenclature: Eulaliagrass, Miscanthus sinensis Anderss.; giant miscanthus, Miscanthus × giganteus Anderss Interpretive Summary: Eulaliagrass (Miscanthus sinensis) has already escaped from ornamental plantings to form large naturalized populations hundreds of meters from original planting locations (Quinn et al. 2010). Our results suggest that these new populations could have established following long-distance seed dispersal. Because the potential for long-distance dispersal and subsequent establishment has been demonstrated, it is important to take preventive measures to avoid further propagule pressure and gene flow into naturalized populations. As has been pointed out, breeders of bioenergy and ornamental varieties can take steps to minimize the potential for escape by selecting for nonshattering seedheads, engineering glabrous seeds, and inducing sterility (Quinn et al. 2010). Our results indicate a strong effect of wind speed on dispersal distance in M. sinensis. Growers should be aware of the need to monitor for escaped plants, particularly if producing fertile varieties. Because we show that most giant miscanthus (Miscanthus × giganteus) and M. sinensis seeds were trapped near the source, exhaustive monitoring efforts should be conducted on a regular basis within 50 m of production fields. In addition, because we know that a small proportion of seeds can disperse several hundred meters from a source, growers should also coordinate efforts with local land managers to ensure early detection and control of escaped plants in nearby natural areas.

Effects of Nitrogen Enrichment and Competition on Growth and Spread of Giant Reed (Arundo Donax)

Abstract Giant reed is an extremely aggressive riparian invader in California. Little is known about its response to nitrogen, which is often elevated in watersheds downstream from agricultural fields and wastewater treatment facilities. Two pot-experiments were conducted to quantify physiological responses of giant reed, and a co-occurring riparian species, common threesquare, to added nitrogen and to investigate a possible enhancement effect of nitrogen on the ability of giant reed to spread laterally belowground into a competitive environment. The first experiment measured shoot height, tissue biomass, and leaf area of giant reed and common threesquare, both herbaceous perennials, grown in pots with and without added nitrogen. The second experiment measured lateral rhizome growth, tissue biomass, and tiller production of giant reed in planters subjected to four possible treatments: with or without competition and with or without added nitrogen. Competition planters had previously been colonized by common threesquare and no-competition planters were unoccupied. Nitrogen-treated plants from the first experiment had greater overall shoot height. With added nitrogen, giant reed produced more root and shoot biomass, whereas common threesquare produced more rhizome and shoot biomass. In the second experiment, added nitrogen resulted in significantly greater rhizome length and greater production of tillers by giant reed regardless of competition. In competition plantings without added nitrogen, giant reed tiller production was reduced, whereas the addition of nitrogen nearly restored tiller production to levels attained without competition. Neither nitrogen nor competition significantly affected giant reed biomass production. Results of these experiments indicate the positive response of giant reed and a native riparian species to nitrogen enrichment and suggest that nitrogen can compensate for the effects of competition on giant reed in some cases. As a result, this species might be able to penetrate some environments without negative impacts from competing vegetation. Nomenclature: Common threesquare, Scirpus americanus Pers. SCPAM, giant reed, Arundo donax L. ABKDO

Navigating the “Noxious” and “Invasive” Regulatory Landscape: Suggestions for Improved Regulation

In the United States, only species listed on state or federal noxious weed lists are regulated. According to our analysis, these regulatory lists poorly represent invasive plants in unmanaged (i.e., nonagricultural) systems. To improve the representation of invasive plants on state regulatory lists, we recommend allocating listing authority to invasive species councils and provide guidance for the science-based reform of noxious weed lists. We also recommend commercial best practices to test for invasiveness prior to intentional introduction of new plant products. Finally, we introduce a negligence liability scheme to discourage the introduction of potential invaders. If adopted, our recommendations could benefit nonagricultural ecosystems and could have positive consequences for bioenergy producers and others in plant industry, who are under scrutiny for promoting potentially invasive species as energy crops. As the bioenergy industry gains momentum, a revised regulatory regime may alleviate the concerns regarding one potential negative consequence of novel plant introduction.

Environmental Tolerances of Miscanthus sinensis in Invasive and Native Populations

Miscanthus sinensis is a moderately invasive ornamental grass species being considered as a bioenergy species in the USA and elsewhere. In this study, we show the range of environmental conditions tolerated by this species in wild populations in the USA and in Japan. Six naturalized populations in the USA and five native populations in Japan were sampled in summer 2009. In each population, environmental factors (canopy cover and soil fertility) were measured, along with measurements of size and morphology for 30 plants. Relationships between M. sinensis size and environmental variables in the two countries were determined using linear mixed effects models. Results indicated that M. sinensis can tolerate extremely wide variation in soil and climate conditions in the populations we sampled across both ranges, suggesting that it could be successfully grown across a wide distribution in the USA, both intentionally as a bioenergy crop and unintentionally as an escaped invader. Plant size generally responded to different environmental conditions in both ranges, with USA plants being negatively influenced by canopy cover and Japanese plants being positively influenced by soil fertility measures. We recommend caution in growing M. sinensis for bioenergy or ornamental purposes to minimize escape outside of its native range.

Bioenergy Feedstocks at Low Risk for Invasion in the USA: a “White List” Approach

Proposed introductions of non-native bioenergy feedstocks have resulted in disagreements among industry, regulators, and environmental groups over unintended consequences, including invasion. Attempting to ban or “black list” known or high probability invasive species creates roadblocks without offering clear alternatives to industry representatives wishing to choose low invasion risk feedstocks. Therefore, a “white list” approach may offer a proactive policy solution for federal and state agencies seeking to incentivize the cultivation of promising new feedstocks without increasing the probability of non-native plant invasions in natural systems. We assessed 120 potential bioenergy feedstock taxa using weed risk assessment tools and generated a white list of 25 non-native taxa and 24 native taxa of low invasion risk in the continental USA. The list contains feedstocks that can be grown across various geographic regions in the USA and converted to a wide variety of fuel types. Although the white list is not exhaustive and will change over time as new plants are developed for bioenergy, the list and the methods used to create it should be immediately useful for breeders, regulators, and industry representatives as they seek to find common ground in selecting feedstocks.

Natural History Survey of the Ornamental Grass Miscanthus sinensis in the Introduced Range

Abstract Miscanthus sinensis is a perennial grass native to Asia, but since its introduction to the United States in the late 19th century, it has become both a major ornamental crop and invasive species. Previous studies of the ecology of M. sinensis in both its introduced and native ranges have suggested that it may be occupying a novel ecological niche in the introduced range. Miscanthus sinensis and its daughter species, Miscanthus × giganteus, are under evaluation as bioenergy crops; therefore, characterization of the ecology and environmental niche of M. sinensis is essential to mitigate the risk of fostering future invasion in the United States. In July 2011, we surveyed 18 naturalized M. sinensis populations spanning the U.S. distribution, covering a 6° latitudinal gradient from North Carolina to Massachusetts. Miscanthus sinensis populations ranged in size from 3 to 181,763 m2 with densities between 0.0012 and 2.2 individuals m−2, and strongly favored highly disturbed and unmanaged habitats such as roadsides and forest edges. Population size and individual plant morphology (i.e., tiller height, basal diameter, and tiller number) were not affected by soil characteristics and nutrient availability, though increased tree canopy cover was associated with reduced population size (P < 0.0001). Plant size and vigor were not significantly affected by low light availability, which supports previous suggestions of shade tolerance of M. sinensis. In summary, M. sinensis can tolerate a broad range of climatic conditions, light availability, and nutrient availability in the eastern United States, suggesting risk of further invasion beyond its current distribution in the United States. Nomenclature: Chinese silvergrass; Eulalia japonica Trin.; Miscanthus sinensis Andersson (Poaceae). Management Implications: Miscanthus sinensis is an extremely popular ornamental grass, and is currently naturalized across much of the eastern United States. There are > 100 named cultivars commercially available with tremendous phenotypic variation that may facilitate tolerance to a broad range of geographies in the introduced range. In this study, we surveyed 18 naturalized M. sinensis populations from North Carolina to Massachusetts to characterize the environmental, climate, and edaphic factors in invaded habitats, as well as describe individual and population-level phenotypic variation. The vast majority of M. sinensis populations are found in heavily disturbed habitats such as roadsides, utility rights-of-way, and managed forest edges. Populations ranged in size from 3 m2 to > 18 ha, and exhibited tolerance to edaphic conditions ranging in pH (4.2 to 7.3) and nutrient availability. The sampled latitudes represent a range of annual precipitation amounts and minimum temperatures—further support that M. sinensis has a broad environmental niche. Whether the populations originated from intentional plantings or from escaped ornamental plantings is equivocal. Thus, managers cultivating M. sinensis for commercial purposes (e.g., bioenergy, breeding, ornamental nursery stock) should employ best management practices to ensure that the wind-dispersed seeds do not enter sensitive habitat. It appears that M. sinensis is tolerant to disturbance common to rights-of-way (e.g., mowing), and prefers high light environments. Land managers should control M. sinensis prior to seed development to reduce propagule spread further, and integrate chemical and mechanical management to reduce population size. Because M. sinensis is such a popular ornamental grass it is unlikely that future introductions will be prevented; thus, future invasion mitigation would be facilitated by determining if specific cultivars are contributing to escape and prevent their sale.

Black Locust as a Bioenergy Feedstock: a Review

Short rotation woody bioenergy crops (SRWC) could contribute a substantial portion of the biomass required to meet federal mandates and offset carbon emissions. One SRWC with strong bioenergy potential is black locust (Robinia pseudoacacia L.), planted extensively for wood and energy applications globally, but under-studied in its native US. This member of the Fabaceae family can fix nitrogen, tolerate stress, and sequester carbon while generating biomass yields up to 14 Mg ha-1 yr-1. This article offers a comprehensive state-of-the-art review of production practices, biomass and energy yield estimates, environmental risks and benefits, and economic considerations for this promising feedstock.

Restoration for Resistance to Invasion by Giant Reed (Arundo donax)

Abstract The relationship between plant community composition and invasibility has been studied extensively but seldom in the context of ecosystem restoration. Experimental riparian restoration plots differing in species composition and density were established and evaluated for susceptibility to invasion by giant reed, a common riparian invader in California, and natural recruitment by riparian species over time. Plots were planted in 2002 with cuttings of common threesquare (a sedge), seepwillow (a shrub), and Gooddings willow (a tree) at two densities in monoculture and all possible mixture combinations. Giant reed rhizomes were introduced into half of the plots in the spring of 2003, while the remaining plots were allowed to undergo natural recruitment for an additional year. In late winter 2004, giant reed rhizomes were planted in the remaining plots. Both planting groups were followed for one growing season to evaluate giant reed establishment, survival, and growth. Community composition affected giant reed performance, particularly in 2003 before natural recruitment occurred. In that year, plots containing seepwillow + willow had the lowest giant reed shoot production, growth, and survival. All plots containing seepwillow were resistant to colonization by natural recruitment in 2004, but none of the planting treatments affected giant reed success in that year. Giant reed was more successful overall in 2004 despite deeper shade and drier soils. This pattern could be attributed to larger initial rhizome size in 2004, which allowed giant reed to overcome environmental stress during establishment. Planting density did not impact giant reed or natural recruitment independently, but may affect environmental parameters and warrants further study as a potential contributor to restoration success. Our results indicate that choice of species composition in restoration might impact giant reed invasion success initially, but community resistance might not be sustainable and maintenance-free over time. Nomenclature: Common threesquare, Schoenoplectus americanus (Pers) Volk. ex Schinz & R. Keller; giant reed, Arundo donax L. ABKDO; Gooddings black willow, Salix gooddingii C. Ball; seepwillow (mulefat), Baccharis salicifolia (Ruiz & Pavón) Pers.