David P. Matlaga

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.

Age-dependent demographic rates of the bioenergy crop Miscanthus × giganteus in Illinois.

Abstract Some plants being considered as bioenergy crops share traits with invasive species and have histories of spreading outside of their native ranges, highlighting the importance of evaluating the invasive potential before the establishment of large-scale plantings. The Asian grass Miscanthus × giganteus is currently being planted as a bioenergy crop in the north central region of the United States. Our goal was to understand the demographic rates and vegetative spread of this species in unmanaged arable lands in Illinois to compare with those of large-statured invasive grasses (LSIGs). We collected data from 13 M. × giganteus plantings in Illinois, ranging in age from 1 to 7 yr, recording tiller number, plant spatial extent, spikelet production, and plant survival over 4 yr. Additionally, to understand recruitment potential, we conducted a greenhouse germination experiment, and, to estimate establishment from rhizome fragments, field trials were performed. Miscanthus × giganteus demographic rates were age dependent. Spikelet production was high, with 1- and 4-yr plants producing an annual average of more than 10,000 and 180,000 spikelets plant−1, respectively; however, data from our germination trial suggested that none of these spikelets had the potential to yield seedlings. On average, plants expanded vegetatively 0.15 m yr−1. Tiller density within the center of a clone decreased with age, possibly leading to a “dead center” found among some LSIGs. Rhizome establishment increased with weight, ranging from 0 to 42%. Survival was low, 24%, for first-year plants but quickly climbed to an asymptote of 98% survival for 4-yr-old plants. Our results suggest that efforts should be made to eradicate plants that escape biomass production fields within a year of establishment, before the onset of high survival. Future work is needed to determine what types of natural and anthropogenic disturbances can fragment rhizomes, leading to regeneration. Nomenclature: Miscanthus × giganteus Greef et Deu ex Hodkinson et Renvoize, Giant miscanthus. Management Implications: As demand for alternative fuels continues to grow, biofuels from herbaceous perennial biomass crops will be an important component of the U.S. energy portfolio. Before growing such crops across wide areas, it is important to understand both the risks and benefits of such an action. Because of similarities between many bioenergy crops and plant invaders, and the onset of new projects to scale-up biomass production rapidly in the Midwest, it is important to understand the potential behavior of candidate species for bioenergy production outside of cultivation. We quantified the age-specific demographic rates of the Illinois clone variety of Miscanthus × giganteus, a leading bioenergy crop in the Midwest. All M. × giganteus demographic rates were strongly dependent on plant age. Spikelet production was low in first-year plants and rose to more than 180,000 spikelets per plant by the fourth year, but none yielded seedlings. Vegetative expansion of M. × giganteus was moderate compared with other large grasses; 4-yr-old plants were observed to have an average vegetative creep radius of 0.15 m yr−1. Survival of first-year plants was low, 24%, but quickly rose to 97% by the fourth year. The lack of viable seed production and slow vegetative expansion in M. × giganteus observed in this study suggest that the sterile clonal cultivar for this bioenergy crop has low invasive potential in Illinois, assuming that the tough rhizomes are not fragmented by disturbance. However, several similarities between M. × giganteus and other large-statured invasive grasses suggest that caution must be taken when introducing this species, and the potential for rhizome establishment and dispersal must be explored in greater detail.

Quantifying targets to manage invasion risk: light gradients dominate the early regeneration niche of naturalized and pre-commercial Miscanthus populations

Prospective bioenergy crops have caused concern about their invasive potential because they often share characteristics with known invasive species. Studies that examine the factors that limit regeneration of these crop species will be crucial for identifying vulnerable habitats and devising management strategies to reduce the likelihood of escape from cultivation. Using a response surface design, we investigated the influence of light availability, soil moisture, and litter cover on recruitment and establishment of a potential biofuel cultivar of Miscanthus as well as an invasive congener. Responses were similar for the two plant types. Light availability had a strong influence on seedling success at both stages, though light limitation prevented establishment only at the lowest light level. Although variation in recruitment rates was low within plant types, establishment varied extensively in response to different light conditions. Low variation in Miscanthus seedling recruitment that led to establishment of a seedling bank under a range of light intensities may facilitate a “sit and wait” situation that raises the likelihood of successful escapes. Therefore, management efforts that restrict seed movement and increase light competition for seedlings will be important for lowering invasion risk. As deliberate introductions of bioenergy crops increase, ecological studies that quantify conditions required for successful escapes will be key to helping agronomists and managers mitigate the risk of unintended invasions.

Managing spread from rhizome fragments is key to reducing invasiveness in Miscanthus × giganteus

Abstract Miscanthus × giganteus, a widely planted biofeedstock, is generally regarded as a relatively low invasion concern. As a seed-infertile species, it lacks a consistent mechanism of long-distance dispersal, a key contributor to invasion rate, and constitutes a low risk for cultivation escape. However, agricultural production shelters plants from stochasticity and increases propagule pressure, enhancing the potential for low-risk species to take advantage of rare dispersal opportunities. Weed risk assessments of M. × giganteus assume the rarity of events such as scouring and flooding that would facilitate secondary dispersal of vegetative rhizome fragments and the long-term sexual inviability of escapes. Combining data from small-scale rhizome fragmentation and movement experiments, and estimates from the literature, we parameterized an individual-based model to examine M. × giganteus spread given three dispersal scenarios. We further evaluated our estimates in response to different field edge buffer widths and monitoring intensities, two key strategies advised for containing biofuel crops. We found that clonal expansion from the field edge alone was sufficient to allow the crop to outgrow buffers of 3 m or less within 11 to 15 yr with low monitoring intensities. Further, models that included the possibility of rhizome dispersal from fields and scouring at field edges demonstrate the potential for long-distance dispersal and establishment with inadequate management. Our study highlights the importance of considering minimum enforced management guidelines for growers to maintain the ecological integrity of the agricultural landscape. Nomenclature: Giant Miscanthus, Miscanthus × giganteus J. M. Greef and Deuter ex Hodk. and Renvoize. Management Implications: Previous assessments of low invasion risk for sterile Miscanthus × giganteus are contingent on the rarity of events that would disperse plant rhizomes from the field edge. Our results demonstrate the importance of implementing monitoring strategies, augmented by field edge buffers that increase detection likelihood, to contain the invasion risk from large-scale cultivation of M. × giganteus. Early detection is key to increasing the success and decreasing the cost of invasive species control. Although opportunities for rhizomes to disperse should be rare, the accumulation of infrequent escapes from large-scale cultivation should be a matter of concern. The combination of field edge buffers and consistent monitoring should form a feasible strategy for containing cultivated plant escapes.

Bioenergy and biological invasions : ecological, agronomic, and policy perspectives on minimizing risk

Introduction 1) The Bioenergy Landscape Section 1: Biology, Ecology and Agronomy 2) Ecology of Candidate Crops outside of Cultivation & Naturalized Populations 3) Modeling a Potential Invasion 4) Potential Risks of Algae as Biofuel 5) Gene Flow and Invasiveness in Bioenergy Systems Section 2: Policy and Regulations 6) Risk Assessment: Parsing the Weeds from the Crops 7) Are Current Regulations and Policies Robust enough to Prevent Large-scale Invasion? Section 3: Mitigation 8) What Agronomic Methods would Increase or Reduce Invasive Potential? 9) How the Industry will Mitigate Invasion Risk 10) Eradication: Identifying the Last Resort as a First Step Summary

Lack of Impacts during Early Establishment Highlights a Short-Term Management Window for Minimizing Invasions from Perennial Biomass Crops

Managing intentional species introductions requires evaluating potential ecological risks. However, it is difficult to weigh costs and benefits when data about interactions between novel species and the communities they are introduced to are scarce. In anticipation of expanded cultivation of perennial biomass crops, we experimentally introduced Miscanthus sinensis and Miscanthus × giganteus (two non-native candidate biomass crops) into two different non-crop habitats (old field and flood-plain forest) to evaluate their establishment success and impact on ambient local communities. We followed these controlled introductions and the composition dynamics of the receiving communities over a 5-year period. Habitats differed widely in adult Miscanthus survival and reproduction potential between species, although seed persistence and seedling emergence were similar in the two biomass crops in both habitats. Few introductions survived in the floodplain forest habitat, and this mortality precluded analyses of their potential impacts there. In old field habitats, proportional survival ranged from 0.3 to 0.4, and plant survival and growth increased with age. However, there was no evidence of biomass crop species effects on community richness or evenness or strong impacts on the resident old field constituents across 5 years. These results suggest that Miscanthus species could establish outside of cultivated fields, but there will likely be a lag in any impacts on the receiving communities. Local North American invasions by M. sinensis and M. sacchariflorus display the potential for Miscanthus species to develop aggressively expanding populations. However, the weak short-term community-level impacts demonstrated in the current study indicate a clear management window in which eradicating species footholds is easily achieved, if they can be detected early enough. Diligent long-term monitoring, detection, and eradication plans are needed to successfully minimize harmful invasions from these biomass crops.

Decomposition and benthic macroinvertebrate communities of exotic Japanese knotweed (Fallopia japonica) and American sycamore (Platanus occidentalus) detritus within the Susquehanna River

ABSTRACT The invasive shrub Japanese knotweed (Fallopia japonica) is spreading through riparian forests in Central Pennsylvania. There is concern that detritus from this species may impact adjacent aquatic ecosystems, as allocthonous material forms the basis for aquatic food webs and may impact benthic community structure. This study compares key ecosystem processes within Japanese knotweed leaf litter to leaf litter of a native riparian species, American sycamore (Platanus occidentalis). We assess benthic macroinvertebrate communities and decomposition rates within experimental Japanese knotweed and American sycamore leaf packs at three sites within the Susquehanna River. Japanese knotweed detritus hosted a similar macroinvertebrate community to American sycamore and their assemblages had similar representation of functional feeding groups. The similarity between the invertebrate communities occupying American sycamore and Japanese knotweed detritus indicates that macroinvertebrates are able to utilize non-native litter for habitat and potentially as an energy source. American sycamore decomposed at a faster rate than Japanese knotweed, lending support to the Novel Weapons Hypothesis, which suggests that non-native species like Japanese knotweed may inhibit microbial colonization and subsequent litter breakdown. Our results suggest that invasion of Japanese knotweed along riparian corridors of large river systems may not have severe ecological consequences on local ecosystem processes.

Dispersal of Goeppertia marantifolia clonal offspring increases with greater canopy openness and larger plant size

Many plants within the neotropical understorey produce both seeds and clonal offspring. Plant attributes (i.e. size) and variability in light can influence seed dispersal but it is not known if these factors influence the dispersal of clonal offspring. Our goal was to determine if canopy openness and plant size influence clonal-offspring dispersal of the herb Goeppertia marantifolia, which produces clonal bulbils on above-ground shoots. We monitored plants in permanent plots with varying levels of canopy openness in Corcovado National Park, Costa Rica. We recorded canopy openness, leaf area and the distance clonal offspring travelled from their parent plant (N = 283). Our path analysis model demonstrated that canopy openness had a strong positive effect on dispersal distance, while the association between clonal-offspring dispersal distance and parent plant leaf area was only weakly positive. On average, plants experiencing high canopy openness dispersed their clonal offspring further than plants under low canopy openness (124 cm vs. 79 cm, respectively). Contrary to studies on species that utilize rhizomes and stolons for clonal reproduction, we found that in this bulbil-producing species light availability is positively associated with clonal dispersal distance. Therefore, the influence of resource availability on spatial population dynamics of clonal species may be influenced by the species’ growth-form.

Large size and high light do not lower the cost of reproduction for the Neotropical herb Goeppertia marantifolia

UNLABELLED • PREMISE OF THE STUDY Sexual reproduction is often associated with a cost in terms of reduced survival, growth, or future reproduction. It has been proposed that plant size and the environment (availability of key resources) can sometimes lower or even nullify the cost of reproduction.• METHODS We address this issue experimentally with the Neotropical herb Goeppertia marantifolia, by manipulating sexual reproductive effort and measuring the demographic performance of plants and of their clonal offspring, in the context of natural variation in light availability.• KEY RESULTS Plants in the high-reproductive-effort treatment grew less between seasons but did not differ in their probability of flowering the second season or in inflorescence size compared with plants in the low-effort treatment. Reproductive effort of parent plants influenced the leaf area of their clonal offspring. Plants that invested less in sexual reproduction produced clonal offspring that were initially larger than those produced by plants that invested more in reproduction. The magnitude of this effect was greater in parent plants that received two seasons of the manipulated reproductive effort than in those that received a single season. The trade-off between reproductive modes dampened with time, leading to smaller differences in clonal offspring leaf area between treatments over time.• CONCLUSIONS We found evidence of a cost of reproduction and trade-offs between reproductive modes, although the magnitude of these costs was small. However, we found no evidence of lower costs of reproduction for larger plants or for plants in higher-light environments over our 2-yr study period.