Plant architecture affects periodical cicada oviposition behavior on native and non-native hosts. Oikos

Variation in plant quality provides a basis for oviposition site selection for a variety of insects. Of the plant traits that infl uence plant-insect interactions, plant architecture has received little attention despite its putative role in modulating oviposition behavior. In a common garden comprised of native and non-native plant species, we assessed how host plant architecture and identity infl uenced the oviposition behavior of 17-year periodical cicadas (Homoptera: Cicadidae: Magicicada ). On each host, we quantifi ed the availability of branches suitable for oviposition and compared those measures with the branches used by ovipositing cicadas. Using this approach, we determined how the structural attributes of plants (i.e. branch diameter, length and incline) aff ected oviposition site selection. We then related cicada oviposition preferences to off spring performance by quantifying egg hatching success. On each host species, cicadas selectively used broader and longer branches for oviposition, suggesting that branch architecture provides a basis for oviposition behavior irrespective of plant identity. Broader and longer branches were more abundant on native than on non-native hosts in our study, contributing to greater oviposition loads among the native species. Egg hatching success was similar among native and nonnative hosts. However, it is possible that the use of native plants for oviposition could enhance off spring output because native hosts generally contained more viable eggs per egg nest and more egg nests per plant. While previous accounts of cicada oviposition preferences have focused on diff erences in oviposition loads among hosts, our evaluation of within-host branch selection by ovipositing cicadas helps to clarify oviposition preferences at a higher resolution and demonstrates that plant architecture provides an important basis for oviposition behavior. Furthermore, because branch structure can diff er substantially among host species, our results suggest that periodical cicadas may be sensitive to the changes in plant composition that often result from non-native plant invasions

Identifying invasive species threats, pathways, and impacts to improve biosecurity

Managing invasive species with prevention and early-detection strategies can avert severe ecological and economic impacts. Horizon scanning, an evidence-based process combining risk screening and consensus building to identify threats, has become a valuable tool for prioritizing invasive species management and prevention. We assembled a working group of experts from academic, government, and nonprofit agencies and organizations, and conducted a multi-taxa horizon scan for Florida, USA, the first of its kind in North America. Our primary objectives were to identify high-risk species and their introduction pathways, to detail the magnitude and mechanism of potential impacts, and, more broadly, to demonstrate the utility of horizon scanning. As a means to facilitate future horizon scans, we document the process used to generate the list of taxa for screening. We evaluated 460 taxa for their potential to arrive, establish, and cause negative ecological and socioeconomic impacts, and identified 40 potential invaders, including alewife, zebra mussel, crab-eating macaque, and red swamp crayfish. Vertebrates and aquatic invertebrates posed the greatest invasion threat, over half of the high-risk taxa were omnivores, and there was high confidence in the scoring of high-risk taxa. Common arrival pathways were ballast water, biofouling of vessels, and escape from the pet/aquarium/horticulture trade. Competition, predation, and damage to agriculture/forestry/aquaculture were common impact mechanisms. We recommend full risk analysis for the high-risk taxa; increased surveillance at Florida's ports, state borders, and high-risk pathways; and periodic review and revision of the list. Few horizon scans detail the comprehensive methodology (including list-building), certainty estimates for all scoring categories and the final score, detailed pathways, and the magnitude and mechanism of impact. Providing this information can further inform prevention efforts and can be efficiently replicated in other regions. Moreover, harmonizing methodology can facilitate data sharing and enhance interpretation of results for stakeholders and the general public.</p

Stakeholders' views on the global guidelines for the sustainable use of non‐native trees

A large number of non‐native trees (NNTs) have been introduced globally and widely planted, contributing significantly to the world's economy. Although some of these species present a limited risk of spreading beyond their planting sites, a growing number of NNTs are spreading and becoming invasive leading to diverse negative impacts on biodiversity, ecosystem functions and human well‐being. To help minimize the negative impacts and maximize the economic benefits of NNTs, Brundu et al. developed eight guidelines for the sustainable use of NNTs globally—the Global Guidelines for the Use of NNTs (GG‐NNTs). Here, we used an online survey to assess perceptions of key stakeholders towards NNTs, and explore their knowledge of and compliance with the GG‐NNTs. Our results show that stakeholders are generally aware that NNTs can provide benefits and cause negative impacts, often simultaneously and they consider that their organization complies with existing regulations and voluntary agreements concerning NNTs. However, they are not aware of or do not apply most of the eight recommendations included in the GG‐NNTs. We conclude that effectively managing invasions linked to NNTs requires both more communication efforts using an array of channels for improving stakeholder awareness and implementation of simple measures to reduce NNT impacts (e.g. via GG‐NNTs), and a deeper understanding of the barriers and reluctance of stakeholders to manage NNT invasions. Read the free Plain Language Summary for this article on the Journal blog

Fire and the invasive annual grass \u3ci\u3eMicrostegium vimineum\u3c/i\u3e in eastern deciduous forests

Non-native plant invasions have the potential to change natural and prescribed fire regimes by increasing fuel loads, continuity of fuels, and fuel composition, which may alter fire intensity, damage native species, and promote further invasions. In this project we sought to evaluate the interaction between fire and the invasive annual grass Microstegium vimineum in eastern deciduous forests. Our goal was to determine if invasions enhance fire intensity, including fire temperatures, flame heights, and fire duration, and negatively affect tree regeneration, and stimulate further invasions. We also sought to determine how prescribed fires and the timing of fires affect the density and demography of Microstegium and we tested the pre and post-fire management options for controlling the post-fire spread of Microstegium invasions. At Big Oaks National Wildlife Refuge in southeastern Indiana, we conducted large-scale prescribed fires to evaluate fire intensity in invaded and uninvaded areas and the response of experimental and naturally regenerating trees. In small-scale plots we manipulated the timing and frequency of fires and applied herbicide treatments to evaluate demographic responses of Microstegium. Our results show that maximum fire temperatures were on average 57% greater in Microstegium-invaded than uninvaded control areas. In addition, fires burned at temperatures over 300 °C for nearly twice as long and flame heights were 98% higher in invaded compared to uninvaded habitats. Microstegium invasion reduced survival of experimental trees by 37% in areas exposed to prescribed fire compared to uninvaded areas and tree survival in invaded, burned plots was 53% lower than invaded, unburned plots. Exposure to prescribed fire increased natural tree regeneration overall but there were 60% and 57% fewer tree seedlings in burned and unburned invaded plots, respectively, compared to control plots with the same treatments. Prescribed fire increased Microstegium biomass by five-fold the following growing season. Experimental spring fires significantly reduced Microstegium seedling numbers by ~75% immediately after the burn, but this did not result in reduced seed production at the end of season or seedling numbers the year following a burn. Burning for two springs in a row similarly reduced seedling numbers during each of the years when the burns were conducted, but this effect did not carry over to reduce Microstegium seedling numbers the following year. Similarly, fall fire reduced seedling numbers by ~50% the following spring, but this reduction also did not result in reduced seed production at the end of that season. The significant effects on seedling numbers but lack of effect on Microstegium seed production was likely due to growth compensation by the surviving plants. Grassspecific, post-emergent herbicide applied without fire was very effective at reducing population numbers, almost eradicating Microstegium populations, but fire reduced herbicide effectiveness. The results of this research demonstrate significant effects of a non-native grass invasion on fire intensity, tree regeneration, and subsequent invasions in eastern deciduous forests, an ecosystem where this phenomenon has not previously been observed. Fire was not useful as a management strategy for Microstegium invasions and interfered with an otherwise effective post-emergent herbicide. To avoid the damaging effects of intense fires in invaded areas, we recommend land managers use herbicides or other treatments to remove invasions prior to the application of prescribed fires

Invasive shrub distribution varies with distance to roads and stand age in eastern deciduous forests in Indiana, USA. Plant Ecology 184: 131–141. doi: 10.1007/ s11258-005-9057-4 Forman RTT

Abstract We documented the relationship between densities of invasive exotic shrubs, distance to road, and successional age of the forest in 14 forested sites throughout central and southern Indiana. Roadways are increasingly abundant, human-made features that can be conduits for the spread of invasive exotic plants in a number of ecosystems. Little is known, however, about the role of roads in eastern deciduous forest ecosystems where road density is high. Further, it is not known whether the distribution of exotic plants along roads depends on the successional age of the forest. In this study, densities of four of seven exotic shrub species declined with increasing distance to the nearest road across all successional ages. Greater densities of exotic shrubs were found in young and mid-successional forests than mature forests. However, there was no interaction between distance to road and forest age, suggesting that the role of roads in the invasion process does not change across forest successional ages. We outline several potential mechanisms that may drive patterns of shrub distribution along roadside edges as a guide for future research

Response of host plants to periodical cicada oviposition damage

Abstract Insect oviposition on plants is widespread across many systems, but studies on the response of host plants to oviposition damage are lacking. Although patterns of oviposition vary spatially and temporally, ovipositing insects that exhibit outbreak characteristics may have strong eVects on host plants during peak abundance. Periodical cicadas (Magicicada spp.), in particular, may reduce the performance of host plants when they synchronously emerge in massive numbers to mate and oviposit on host plants. Here we provide the Wrst experimental manipulation of host plant use by periodical cicadas to evaluate the impact of cicada oviposition on plant performance across a diversity of host species within an ecologically relevant setting. Using a randomized block design, we established a plantation of three native and three exotic host plant species common to the successional forests in which cicadas occur. During the emergence of Brood X in 2004, we employed a highly eVective cicada exclusion treatment by netting half of the host plants within each block. We assessed multiple measures of host plant performance, including overall plant growth and the growth and reproduction of individual branches, across three growing seasons. Despite our thorough assessment of potential host plant responses to oviposition damage, cicada oviposition did not generally inhibit host plant performance. Oviposition densities on unnetted host plants were comparable to levels documented in other studies, reinforcing the ecological relevance of our results, which indicate that cicada oviposition damage did not generally reduce the performance of native or exotic host plants

Cogongrass (Imperata cylindrica) invasions in the US: Mechanisms, impacts, and threats to biodiversity

Invasions of non-native species can suppress biodiversity and alter ecosystem functions, but for many of the most widespread invasive species the mechanisms underlying their invasive success and effects on native species are poorly understood. Here we evaluated the peer-reviewed literature on causes and impacts of invasion by cogongrass (Imperata cylindrica), one of the most problematic invasive plant species in the southeast US. We assess what is known about why cogongrass is particularly invasive and how it affects native communities and ecosystems, review patterns in research methods employed, and provide a roadmap for future research on cogongrass. Although many studies have focused on the basic biology and management of cogongrass, we found surprisingly few (30) studies that have directly tested mechanisms or impacts of cogongrass invasions. The most commonly tested mechanisms, disturbance and allelopathy, were evaluated 4 and 12 times, respectively, and studies on invasion impacts were limited to five studies total: native plant diversity (2 studies), nitrogen cycling (2), decomposition (1), and fine fuel loads (1). Excluding laboratory studies on allelopathy, 75% (6/8) of impact studies used observational methods, raising questions about cause and effect. Given the paucity of studies on the ecology of cogongrass invasions, and the need to protect conservation areas from invasions, we urge that research efforts focus on: (1) environmental correlates of distribution and performance, (2) the role of propagule pressure in invasion success, (3) enemy release and post-introduction evolution as mechanisms of invasion, and (4) experimental tests of community and ecosystem impacts of invasions

species.list

List of plant species identified in the experiment

percent.cover.summers

Percent cover of all plant species identified for summer dates in the experiment