BIODIVERSITY RESEARCH: Turning up the heat: the impacts of Andropogon gayanus (gamba grass) invasion on fire behaviour in northern Australian savannas

Aim This study aimed to quantify changes in fire severity resulting from the invasion of Australia’s tropical savannas by the African grass Andropogon gayanus Kunth. (gamba grass). Location Mesic savannas of the Northern Territory, Australia. Method Byram’s fire‐line intensity (I_f), fuel load and architecture, and two post‐fire indicators of fire intensity – scorch height (SH) and char height (CH) of woody vegetation – were determined for fires in native grass savanna and A. gayanus invaded savanna. Leaf scorch is the height at which the fire’s radiant heat browns leaf tissue, and leaf char is the height that radiant heat blackens or consumes leaf tissue and provides an indirect measure of flame height. These data, and 5 years of similar data collected from the Kapalga Fire Project in Kakadu National Park, were used to develop empirical relationships between I_f and the post‐fire indices of fire intensity. Results A relationship between A. gayanus I_f and SH could not be developed because complete canopy scorch occurred in most A. gayanus fires, even at low I_f. In contrast, A. gayanus I_f was strongly correlated with CH. This empirical relationship was substantially different from that for native grass fires. For a given I_f, there was a significantly greater CH in invaded sites. This increase in radiant heat is attributable to the increased biomass (mean 3.6 t ha^?1 in native grasses compared to 11.6 t ha^?1 in A. gayanus) and height (approximately 0.5 m in native grasses compared to 4 m in A. gayanus) of the standing fine fuel. Main conclusion Andropogon gayanus invasion resulted in substantial changes in fire behaviour. This has important regional implications owing to the current (10,000–15,000 km²) and predicted (380,000 km²) area of invasion and the negative consequences for the native savanna biota that has evolved with frequent but relatively low‐intensity fire.     

Residual herbicide treatments reduce Andropogon gayanus (Gamba Grass) recruitment for mine site restoration in northern Australia

Weed invasion is a major threat to Australian tropical savannas, and controlling weeds is essential for successful re‐establishment of native species on disturbed sites. Gamba Grass (Andropogon gayanus) is an African grass which has invaded large areas of tropical savanna across northern Australia. Current management strategies in northern Australia focus on fire and glyphosate to effectively control mature plants; however, re‐establishment of infestations from the soil seed bank remains a major challenge to eradication efforts. This study focused on the effects of soil seed bank treatments on Gamba Grass recruitment on a mine site in northern Australia. Adult Gamba Grass plants within test plots were killed with glyphosate to exclude resource competition. Chemical, physical and biological treatments were then applied, and the treatment effects on subsequent Gamba Grass seedling emergence and survival quantified. Seedling emergence was significantly reduced by three of the four residual herbicide treatments tested. The most effective herbicide treatments, dalapon and sulfometuron, reduced emergence by 90% compared to the standard glyphosate treatment alone. This equated to a reduction in Gamba Grass seedling emergence from 1 seedling/m² to 1 seedling 10 m^?2, a major improvement for Gamba Grass management. These residual herbicide treatments significantly reduced the population density of Gamba Grass for at least 5 months after emergence. The physical and biological treatments did not have a significant effect on seedling emergence. This significant reduction in Gamba Grass seedling emergence and survival can substantially improve Gamba Grass management. Reducing re‐colonisation from the soil seed bank using residual herbicides provides a valuable management tool for land managers, integrating readily with established strategies for controlling the mature plants.     

Testing the grass-fire cycle: alien grass invasion in the tropical savannas of northern Australia

Abstract. Invasive alien grasses can increase fuel loads, leading to changes in fire regimes of invaded ecosystems by increasing the frequency, intensity and spatial extent of fires. Andropogon gayanus Kunth. (Gamba grass), a tall perennial grass from Africa, is invading ecosystems in the Top End of northern Australia. To determine whether A. gayanus alters savanna fire regimes, we compared fuel loads and fire intensities at invaded sites with those from native grass savannas. Savanna invaded by A. gayanus had fuel loads up to seven times higher than those dominated by native grasses. This higher fuel load supported a fire that was on average eight times more intense than those recorded in native grass savannas at the same time of year (means 15700 ± 6200 and 2100 ± 290 kW m⁻¹, respectively), and was the highest early dry season fire intensities ever recorded in the Northern Territory. These results suggest that A. gayanus is a serious threat to northern Australia's savannas, with the potential to alter vegetation structure and initiate a grass-fire cycle.     

Habitat Complexity and Invasive Species: The Impacts of Gamba Grass (Andropogon gayanus) on Invertebrates in an Australian Tropical Savanna

Habitat complexity is an important factor structuring local faunal assemblages. Many invasive plant species alter vegetation complexity because they are both functionally and structurally different from native flora. This study investigated the effects of an invasive grass (Andropogon gayanus Kunth.), which is invading undisturbed savannas in northern Australia. Although A. gayanus is a similar lifeform to that dominant in the native understory (i.e., a C4 grass), it is structurally different and significantly alters habitat complexity. We, therefore, hypothesized that there would be a substantial effect of the invasive grass on ant, spider, and other invertebrate assemblages. Contrary to our hypothesis, there was no effect of A. gayanus on ant species richness, abundance, or composition, nor were spiders or other invertebrates affected. Instead the change in weather conditions with season was more important in structuring the local invertebrate assemblages. Change in habitat complexity was most pronounced vertically, rather than horizontally at ground level, thus although there was a clear difference in the vertical structure between invaded and noninvaded habitats, the limited invertebrate response to different A. gayanus densities suggests some invertebrates are less sensitive to vertical changes in vegetation structure.     

Niche-based modelling as a tool for predicting the risk of alien plant invasions at a global scale

Predicting the probability of successful establishment of plant species by matching climatic variables has considerable potential for incorporation in early warning systems for the management of biological invasions. We select South Africa as a model source area of invasions worldwide because it is an important exporter of plant species to other parts of the world because of the huge international demand for indigenous flora from this biodiversity hotspot. We first mapped the five ecoregions that occur both in South Africa and other parts of the world, but the very coarse definition of the ecoregions led to unreliable results in terms of predicting invasible areas. We then determined the bioclimatic features of South Africa's major terrestrial biomes and projected the potential distribution of analogous areas throughout the world. This approach is much more powerful, but depends strongly on how particular biomes are defined in donor countries. Finally, we developed bioclimatic niche models for 96 plant taxa (species and subspecies) endemic to South Africa and invasive elsewhere, and projected these globally after successfully evaluating model projections specifically for three well‐known invasive species (Carpobrotus edulis, Senecio glastifolius, Vellereophyton dealbatum) in different target areas. Cumulative probabilities of climatic suitability show that high‐risk regions are spatially limited globally but that these closely match hotspots of plant biodiversity. These probabilities are significantly correlated with the number of recorded invasive species from South Africa in natural areas, emphasizing the pivotal role of climate in defining invasion potential. Accounting for potential transfer vectors (trade and tourism) significantly adds to the explanatory power of climate suitability as an index of invasibility. The close match that we found between the climatic component of the ecological habitat suitability and the current pattern of occurrence of South Africa alien species in other parts of the world is encouraging. If species' distribution data in the donor country are available, climatic niche modelling offers a powerful tool for efficient and unbiased first‐step screening. Given that eradication of an established invasive species is extremely difficult and expensive, areas identified as potential new sites should be monitored and quarantine measures should be adopted.     

Targeted control of widespread exotic species for biodiversity conservation: The Red Fox (Vulpes vulpes) in New South Wales, Australia

Summary   Widespread exotic species provide one of the greatest challenges to biodiversity conservation because they often have devastating impacts on native biota but are near impossible to eradicate. The Red Fox ( Vulpes vulpes ) is established across most of mainland Australia, where it has been linked to severe declines and extinctions of a broad suite of native fauna. A targeted approach to reducing the impacts of Foxes on biodiversity was instigated in New South Wales in 2001 under the New South Wales Fox Threat Abatement Plan. It is based on three simple steps. First, explicit priorities for Fox control are established by identifying which native species are at greatest risk from Fox predation and at which sites Fox control for these species is most critical. Second, high-frequency broad-area Fox-control programmes are established across all land tenures at these priority sites. Third, monitoring programmes are established to measure the response of targeted native fauna and Foxes to Fox control. Monitoring helps refine the priorities for control and the methods used over time. This approach provides a model for the strategic control of widespread exotic pests which threaten biodiversity.     

A model for range expansion of an introduced species: the common waxbill Estrilda astrild in Portugal

Abstract. The common waxbill Estrilda astrild was first introduced to Portugal from Africa in 1964, and has spread across much of the country and into Spain. We modelled the expansion of the common waxbill on a 20 × 20 km UTM grid in 4‐year periods from 1964 to 1999. The time variation of the square root of the occupied area shows that this expansion process is stabilizing in Portugal, and reasons for this are discussed. Several methods used to model biological expansions are not appropriate for the present case, because little quantitative data are available on the species ecology and because this expansion has been spatially heterogeneous. Instead, colonization on a grid was modelled as a function of several biophysical and spatio‐temporal variables through the fitting of a multivariate autologistic equation. This approach allows examination of the underlying factors affecting the colonization process. In the case of the common waxbill it was associated positively with its occurrence in adjacent cells, and affected negatively by altitude and higher levels of solar radiation.     

Invasion dynamics and potential spread of the invasive alien plant species Ageratina adenophora (Asteraceae) in China

Ageratina adenophora (Sprengel) R. King & H. Robinson (=Eupatorium adenophorum Sprengel) is one of the worst invasive alien species in China. Since A. adenophora was first noticed in Yunnan Province of China in the 1940s, its rapid spread has caused an ecological problem in south‐western China. Understanding its historical invasion pattern and its potential for further spread is needed to plan the management of the species. We reconstructed the historical process of its invasion and analysed its ecological preferences in the invaded region. After a lag phase of 20 years (1940–60), A. adenophora spread rapidly throughout the south and middle subtropical zones in Yunnan, Guizhou, Sichuan, and Guangxi, China, with an average expansion rate of 20 km per year. It spread relatively slowly in north subtropical areas, with an average expansion rate of 6.8 km per year. It has not established in warm temperate areas within the invaded regions. Although range expansion in Yunnan stopped after 1990, the expansion of its range into neighbouring provinces indicates that A. adenophora has not reached the full potential of its distribution and its range is still rapidly expanding within China. We applied ecological niche modelling (GARP — Genetic Algorithm for Rule‐set Prediction) to predict potential invasion areas in mainland China on the basis of occurrence points within colonized areas where A. adenophora has reached equilibrium. The predictions, confirmed by the range of values of four key environmental parameters, generally match the parameters of the geography and ecology in the invaded region. Southern and south‐central China have climatic conditions suggestive of a high potential for invasion by A. adenophora. Climatic conditions in northern and western China appear unsuitable for A. adenophora. Urgent measures should be taken to prevent this species from further spreading into the vast areas of potential habitat in southern and south‐central China.     

Nutrient Limitation in a Fire‐derived,Nitrogen‐rich Hawaiian Grassland1

Grasslands created by grass invasions into shrublands or woodlands followed by fire are now a dominant feature of many seasonally dry environments. In Hawaii Volcanoes National Park, introduced perennial grasses dominate grasslands created by fire in grass‐invaded woodlands. In a previous study, we found that net primary production in these grasslands is substantially lower than in unburned woodlands. Yet, our estimates of annual net nitrogen (N) mineralization showed higher rates in these savannas than in the unburned woodlands, rates that appear to greatly exceed annual N demand by the vegetation. We therefore hypothesized that N should not be limited to the plants growing in these sites. We tested this hypothesis with a 2‐yr fertilization experiment. At peak biomass, we found a 30 percent increase in live biomass in plots with N added and no increase in production with only phosphorus (P) added. N and P together were synergistic, suggesting that co‐limitation or P limitation becomes important when N is more available. Plants responded to added N by increasing individual leaf area and shoot length by over 50 percent. Tissue N was higher with added N; hence, biomass N was substantially higher. Tissue P concentrations declined with N addition but were elevated by P addition despite lack of a growth response to P alone. Overall, N limitation exists despite high annual rates of net N mineralization, and co‐limitation of production by P may occur when N is abundant. Here, asynchrony between plant nutrient demand and N availability may contribute to N limitation.     

Influence of Earthworm Invasion on Redistribution and Retention of Soil Carbon and Nitrogen in Northern Temperate Forests

We analyzed soil organic matter distribution and soil solution chemistry in plots with and without earthworms at two sugar maple (Acer saccharum)–dominated forests in New York State, USA, with differing land-use histories to assess the influence of earthworm invasion on the retention or loss of soil carbon (C) and nitrogen (N) in northern temperate forests. Our objectives were to assess the influence of exotic earthworm invasion on (a) the amount and depth distribution of soil C and N, (b) soil ¹³C and ¹⁵N, and (c) soil solution chemistry and leaching of C and N in forests with different land-use histories. At a relatively undisturbed forest site (Arnot Forest), earthworms eliminated the thick forest floor, decreased soil C storage in the upper 12 cm by 28%, and reduced soil C:N ratios from 19.2 to 15.3. At a previously cultivated forest site with little forest floor (Tompkins Farm), earthworms did not influence the storage of soil C or N or soil C:N ratios. Earthworms altered the stable isotopic signature of soil at Arnot Forest but not at Tompkins Farm; the alteration of stable isotopes indicated that earthworms significantly increased the loss of forest floor C but not N from the soil profile at Arnot Forest. Nitrate (NO₃^–) concentrations in tension and zero-tension lysimeters were much greater at Tompkins Farm than Arnot Forest, and earthworms increased NO₃^– leaching at Tompkins Farm. The results suggest that the effect of earthworm invasion on the distribution, retention, and solution chemistry of soil C and N in northern temperate forests may depend on the initial quantity and quality of soil organic matter at invaded sites.     

Impact of the invasive alien grass Melinis minutiflora at the savanna-forest ecotone in the Brazilian Cerrado

Exotic grasses are a serious threat to biodiversity in the cerrado savannas of central Brazil. Of particular concern is the possible role they may have in impeding tree regeneration at gallery (riverine) forest edges and increasing fire intensity, thereby driving gallery forest retreat. Here we quantify the effect of roads and distance from gallery forests on the abundance of the African grass Melinis minutiflora Beauv. and test for an effect of this species on woody plant regeneration and leaf area index. Melinis was present at approximately 70% of the sites near gallery forest edges, with its frequency declining sharply at greater distances from the edge. Melinis frequency was 2.8 times greater where roads were present nearby. Leaf area index (LAI) of the ground layer was 38% higher where Melinis was present than where it was absent. LAI was strongly correlated to fine fuel mass (r² = 0.80), indicating higher fuel loads where Melinis was present. The abundance of tree and shrub species in the ground layer was negatively related to LAI and to the presence of Melinis. The greater fuel accumulation and reduced tree regeneration caused by Melinis may cause a net reduction in forest area by increasing fire intensity at the gallery forest edge and slowing the rate of forest expansion.     

Introduction of the African Catfish Clarias gariepinus (BURCHELL, 1822) into Southern Brazil

We record here the introduction of the African catfish Clarias gariepinus into the Guaraguaçu River basin in Paraná State, Brazil, an area with an extremely rich endemic fish fauna, including many catfishes. C. gariepinus was introduced as escapees from ponds built for recreational angling. These catfishes are very large and hard predators, thus posing serious potential for impact on the native fish fauna. The impact of C. gariepinus needs study with emphasis on finding means for controlling its spread.     

Relative Roles of Disturbance and Propagule Pressure on the Invasion of Humid Tropical Forest by Cordia alliodora (Boraginaceae) in Tanzania

Current understanding of the vulnerability of tropical forests to plant invasion is limited but is widely believed to increase where forests: (1) suffer marked natural or man-made disturbance; and/or (2) are exposed to high propagule pressure of alien species. This study aimed, for the first time, to address the importance of propagule pressure and disturbance by examining the spread of an introduced tree, Cordia alliodora , from a single plantation into a surrounding mosaic of humid forest in the East Usambara Mountains, Tanzania. By assessing vulnerability to invasion along transects radiating from the plantation, the effects of distance (measure of propagule pressure), and disturbance could be discerned. For all life stages, distance from source population was the strongest correlate of density. A marked influence of disturbance was only evident for C. alliodora seedlings. Spatial variation in the densities of later life stages may be a function of past disturbances, less easy to assess from current surveys, especially following the marked self-thinning between seedling and adult densities. Nevertheless, the evidence suggests that propagule pressure is a more important determinant of Cordia density than disturbance. If this is true for other alien tree species in tropical forests, controlling for introduction effort is essential to assess the drivers of plant invasion. Given an annual population growth rate of ca 3.5 percent, equivalent to the population doubling every 20 yr, C. alliodora poses a significant threat to the East Usambaras as well as other humid forests where it is promoted for agroforestry.     

Variation in the impact of exotic grasses on native plant composition in relation to fire across an elevation gradient in Hawaii

The impact that an exotic species can have on the composition of the community it enters is a function of its abundance, its particular species traits and characteristics of the recipient community. In this study we examined species composition in 14 sites burned in fires fuelled by non‐indigenous C4 grasses in Hawaii Volcanoes National Park, Hawaii. We considered fire intensity, time since fire, climatic zone of site, unburned grass cover, unburned native cover and identity of the most abundant exotic grass in the adjacent unburned site as potential predictor variables of the impact of fire upon native species. We found that climatic zone was the single best variable for explaining variation in native cover among burned sites and between burned and unburned pairs. Fire in the eastern coastal lowlands had a very small effect on native plant cover and often stimulated native species regeneration, whereas fire in the seasonal submontane zone consistently caused a decline in native species cover and almost no species were fire tolerant. The dominant shrub, Styphelia tameiameia, in particular was fire intolerant. The number of years since fire, fire intensity and native cover in reference sites were not significantly correlated with native species cover in burned sites. The particular species of grass that carried the fire did however, have a significant effect on native species recovery. Where the African grass Melinis minutiflora was a dominant or codominant species, fire impacts were more severe than where it was absent regardless of climate zone. Overall, the impacts of exotic grass‐fuelled fires on native species composition and cover in seasonally dry Hawaiian ecosystems was context specific. This specificity is best explained by differences between the climatic zones in which fire occurred. Elevation was the main physical variable that differed among the climatic zones and it alone could explain a large percentage of the variation in native cover among sites. Rainfall, by contrast, did not vary systematically with elevation. Elevation is associated with differences in composition of the native species assemblages. In the coastal lowlands, the native grass Heteropogon contortus, was largely responsible for positive changes in native cover after fire although other native species also increased. Like the exotic grasses, this species is a perennial C4 grass. It is lacking in the submontane zone and there are no comparable native species there and almost all native species in the submontane zone were reduced by fire. The lack of fire tolerant species in the submontane zone thus clearly contributes to the devastating impact of fire upon native cover there.     

Risk Assessment and Invasion Characteristics of Alien Plants in and Around the Agro-Pastoral Ecotone of Northern China

Two risk assessment protocols were adopted to assess the risks posed by alien plants that naturalized or non-naturalized in the agro-pastoral ecotone of northern China (AGENC). In this study the Risk Assessment for Central Europe method revealed that more than two-thirds of the 19 naturalized and four-fifths of the 17 non-naturalized alien plants presented high or moderate risk, and all 36 alien plants were considered to be rejected for their potential agricultural and environmental risks under the Australian Weed Risk Assessment system. On the characteristics of plant invasions, more attention should be given to disturbed habitats rather than these relative natural or closed ecosystems, and also be prudent and careful of the alien plants that are introduced as useful plants from North or South America and unintentional introduction from Europe. Moreover, annuals needed special attention: three-quarters of the alien plants were annual species, only a few were biennial (8.3%), perennial (11.1%), liana and tree plants (2.8%). Plant invasions are not extremely serious in the AGENC, but there are several alien plants that have naturalized and spread themselves in the region. However, attention should be given in the future to predicting and preventing plant invasions in this fragile region.     

Assessing the vulnerability of riparian vegetation to invasion by Mimulus guttatus: relative importance of biotic and abiotic variables in determining species occurrence and abundance

Riparian habitats are particularly susceptible to invasion by non‐native plants. At present, attempts to build consensus as to what the primary drivers of plant invasion in riparian ecosystems might be is hindered by the absence of common standards for data collected on plant species (e.g. occurrence, or relative abundance). Mimulus guttatus L., a non‐native riparian plant species, was used as a model to determine how environmental drivers influence two aspects of invasibility: species occurrence and abundance (assessed in relation to three variables number of patches, patch area and number of stems per patch). Mimulus occurrence and abundance, together with 20 environmental variables, were surveyed in almost 700 contiguous 50‐m‐long riverbank segments within a catchment in north‐east Scotland. More than half of the segments had been colonized by Mimulus. Occurrence and number of patches responded to similar environmental gradients, particularly bare sediment, boulders, high soil moisture, short‐statured ruderal communities, and open canopies, and tended to be highest downstream where the river was widest. In contrast to occurrence and patch number, patch area and stem number per patch were higher in the upper reaches of the catchment and were positively associated with low tree canopy and vegetation dominated by light‐demanding species and smaller‐statured species. Patch area and stem number per patch were also positively related to grazing. This study has highlighted the importance of assessing more than one measure of invasion success (occurrence or patch number and either patch area or stem number per patch), as they are each determined by a different suite of environmental variables. Abiotic factors, such as sediment availability and presence of boulders, appeared to be the major determinants of occurrence and patch number, whereas biotic factors, such as interspecific competition and grazing, were more important ecological determinants underlying area and stem number per patch.     

Ecosystem Level Impacts of Invasive Acacia saligna in the South African Fynbos

Recent efforts to clear invasive plants from the fynbos of South Africa forces managers to think about how N₂‐fixing invasives have altered ecosystem processes and the implications of these changes for community development. This study investigated the changes in nitrogen (N) cycling regimes in fynbos with the invasion of Acacia saligna, the effects of clear‐cutting acacia stands on soil microclimate and N cycling, and how altered N resources affected the growth of a weedy grass species. Litterfall, litter quality, soil nutrient pools, and ion exchange resin (IER)‐available soil N were measured in uninvaded fynbos, intact acacia, and cleared acacia stands. In addition, a bioassay experiment was used to ascertain whether the changes in soil nutrient availability associated with acacia would enhance the success of a weedy grass species. Acacia plots had greater amounts of litterfall, which had higher concentrations of N. This led to larger quantities of organic matter, total N, and IER‐available N in the soil. Clearing acacia stands caused changes in soil moisture and temperature, but did not result in differences in IER‐available N. The alteration of N availability by acacias was shown to increase growth rates of the weedy grass Ehrharta calycina, suggesting that secondary invasions by nitrophilous weedy species may occur after clearing N₂‐fixing alien species in the fynbos. It is suggested that managers use controlled burns, the addition of mulch, and the addition of fynbos seed after clearing to lower the levels of available N in the soil and initiate the return of native vegetation.     

Genetic and behavioural evidence for a city-wide supercolony of the invasive Argentine ant Linepithema humile (Mayr) (Hymenoptera: Formicidae) in southeastern Australia

The success of invasive ants is frequently attributed to genetic and behavioural shifts in colony structure during or after introduction. The Argentine ant ( Linepithema humile ), a global invader, differs in colony genetic structure and behaviour between native populations in South America and introduced populations in Europe, Japan, New Zealand and North America. However, little is known about its colony structure in Australia. We investigated the genetic structure and behaviour of L. humile across Melbourne, Victoria by quantifying variation at four microsatellite loci and assaying intraspecific aggression at neighbourhood (30–200 m), fine (1–3.3 km) and regional (5–82 km) spatial scales. Hierarchical analyses across these scales revealed that most genetic variation occurred among workers within nests (∼98%). However, although low genetic differentiation occurred among workers between nests at the fine and regional scales (∼2%), negligible differentiation was detected among workers from neighbouring nests. Spatial genetic autocorrelation analysis confirmed that neighbouring nests were genetically more similar to each other. Lack of aggression within and across these scales supported the view that L. humile is unicolonial and forms a large supercolony across Melbourne. Comparisons of genetic structure of L. humile among single nests sampled from Adelaide, Brisbane, Hobart and Perth with Melbourne showed no greater levels of genetic differentiation or dissimilar spatial structure, suggesting an Australia-wide supercolony.     

A Landscape Perspective of the Stream Corridor Invasion and Habitat Characteristics of an Exotic (Dioscorea oppositifolia) in a Pristine Watershed in Illinois

The spatial distribution of exotics across riparian landscapes is not uniform, and research elaborating the environmental constraints and dispersal behavior that underlie these patterns of distribution is warranted. This study examined the spatial distribution, growth patterns, and habitat constraints of populations of the invasive Dioscorea oppositifolia in a forested stream corridor of a tributary of Drury Creek in Giant City State Park, IL. The distribution of D. oppositifolia was determined at the watershed scale mainly by floodplain structure and connectivity. Populations of D. oppositifolia were confined to the floodplain, with overbank flooding from the stream. Dioscorea oppositifolia probably originates in disturbed areas upstream of natural corridors, and subsequently, the species disperses downstream into pristine canyons or ravines via bulbils dispersing in the water. In Giant City State Park, populations of D. oppositifolia were distributed on the floodplain across broad gradients of soil texture, light, slope, and potential radiation. The study also examined the longevity of bulbils in various micro-environments to illuminate strategies for the management of the species in invaded watersheds. After 1 year, the highest percentages of bulbils were viable under leaves, and much lower percentages were viable over leaves, in soil, and in the creek (76.0±6.8, 21.2±9.6, 21.6±3.6, and 5.2±5.2%), respectively. This study suggests that management procedures that reduce leaf litter on the forest floor (e.g., prescribed burning) could reduce the number of bulbils of D. oppositifolia stored in the watershed.