The following is a list of citations, links and abstracts of peer reviewed studies on woody invasive species of concern in the Great Lakes Region and their management, published between April 1 and June 30, 2021. You may be able to receive a personal-use copy of any copyrighted article by contacting the primary author. Subscribe to the Woody Invasive Research Digest to get an email when a new digest is posted!
- Open Access: No
- Keywords: Tree-of-heaven, Ailanthus altissima, allelopathy, species interactions, biopesticide, international
- Full abstract: The current study evaluated the allelopathic potential of the Persian silk tree (Albizia julibrissin) leaf residues on seed germination and biomass attributes of tree of heaven (Ailanthus altissima) seedlings. An experiment was conducted based on a completely randomized design by eight replications. Experimental treatments consisted of different levels of leaf residues at concentrations of 0%, 2.5%, 5%, and 7.5%. Germination index was used in order to investigate the effect of allelochemicals on seed germination. In addition, the effect of allelopathic materials on seedling biomass was measured by calculating the parameters of collar diameter, fresh and dry weight of seedlings, root dry weight, number of leaves, seedling weight vigor index and percentages of seedling water content index. The results revealed that seed germination index, seedling dry weight, seedling fresh and dry root weight and seedling weight vigor index significantly decreased at different concentrations of leaf residues compared to control, but the increase in concentration had no significant effect on these attributes. But higher concentrations of leaf residues had stronger inhibitory effects on seedling collar diameter, fresh seedling weight and the number of leaves per seedling. The present study clearly proved the allelopathic effects of the Persian silk tree (Albizia julibrissin) leaf residues on biomass attributes of the Tree of heaven (Ailanthus altissima) seedlings. In addition, the Persian silk tree (Albizia julibrissin) leaf residues can be used to control the irregular growth of Tree of heaven seed as an invasive species, as well as weed management in agroforestry systems which require further studies.
- Open Access: Yes
- Keywords: Amur honeysuckle, Lonicera maackii, impacts, ecology, species interactions, student research
- Full abstract: The purpose of this study was to determine what effect, if any, the removal of honeysuckle (Lonicera maacki) has on the diversity and abundance of terrestrial invertebrates in riparian areas. The study took place at 10 different sites along the Little Miami River in Greene County, Ohio. There were 4 sites where honeysuckle had been successfully removed, 3 where the site was fully invaded, and 3 that had had removal done, but had experienced some comeback. Leaf litter samples were collected at each site a total of 3 times. After collection, the leaf litter was placed in Berlese funnels to extract the terrestrial invertebrates. Once the invertebrates had been extracted, they were counted, identified to the taxonomic level of Order, and then dried to determine biomass. Data analysis showed that there was no significant difference between the abundance, diversity or biomass of the invertebrates found between the different types of sites. Future research may want to explore a similar question but identify the invertebrates to the species level.
- Open Access: Yes
- Keywords: Common buckthorn, Rhamnus cathartica, impacts, ecology, species interactions, student research, poster
- Full abstract: This study explores the relationship between the invasive shrub European buckthorn (Rhamnus cathartica) on invertebrate diversity in Northwestern College’s forest near Alton, IA. We performed pitfall sampling in June 2020 and found invertebrate richness and abundance to be nonsignificantly lower in high-density buckthorn plots than in treatment plots where buckthorn had been removed. We also found no relationship between buckthorn density and invertebrate diversity. Data from this study will supplement the data collected over the past 15 years to determine whether any seasonal or long-term trends in invertebrate diversity have been occurring since buckthorn were first removed from parts of the forest in 2005.
- Open Access: No
- Keywords: Black locust, Robinia pseudoacacia, impacts, species interactions, grasslands, ecology, international
- Full abstract: Invasive alien trees transform landscapes and subsequent ecosystem function. For grassland ecosystems, fragmentation following invasion by alien woody species is of concern. In this study, we examined how an invasive alien tree, Robinia pseudoacacia L. (Fabaceae) impacts grassland microclimates and the subsequent assemblages of endemic arthropods. The phenological trajectory of R. pseudoacacia, temperature and light intensity, as well as arthropod abundances in both invaded and uninvaded habitats, were monitored. Results showed that R. pseudoacacia significantly lowers average understory temperatures and light penetration in grassland ecosystems. Average temperatures were at least 2°C lower in understory habitats than open grasslands while light intensity was lower by more than 1200 lumens/ft^2. In addition, arthropod communities differed between invaded and uninvaded habitats. The most affected taxa were Acridids from the order Orthoptera as they were excluded from understory habitats while Coleopterans were more abundant under R. pseudoacacia. Apart from absence of main host plants, invasion mediated differences in microenvironments appeared to be the main driver of this shift in affected arthropod taxa.
Implications for insect conservation: These results highlight the need to sustainably manage R. pseudoacacia invasions especially in grassland ecosystems. In addition to their conservation value due to their role in nutrient cycling, grassland arthropods also serve as important indicators of ecosystem health. Hence, they can be used to monitor ecosystem recovery post invasive alien tree management.
- Open Access: No
- Keywords: Common buckthorn, Rhamnus chathartica, impacts, ecology, herbicide, off-target impacts
- Full abstract: Multiple factors including habitat loss, pollutants, invasive species, and disease have contributed to the global decline of amphibians, and further declines can be expected as a result of climate change. Warming temperatures may allow for range expansion of invasive plants, and because herbicides are the primary method to control invasive plants, chemical use may increase. A laboratory experiment was performed to examine the individual and combined effects of leachates from the invasive plant European buckthorn (Rhamnus cathartica, L.) and a triclopyr herbicide (Renovate® 3; 0.21 mg/L), which is commonly used to manage R. cathartica, on northern leopard frog (Lithobates pipiens, Schreber) tadpoles at 2 temperature regimes (20 and 25 °C). We measured tadpole growth weekly and body and intestine morphology at the conclusion of the experiment after 8 wk. In the presence of R. cathartica leachates, tadpole growth increased at 25 °C, but only during the first 3 to 4 wk of the experiment. From week 5 until the end of the experiment, tadpoles were significantly smaller at 25 °C compared with 20 °C, but had more developed limb buds at the end of the experiment (except in the triclopyr treatment). Triclopyr had minimal effects on tadpole growth at the low dose used in this study. These results encourage further examination of potential effects of global climate changes in combination with other environmental factors that may impact amphibian populations.
- Open Access: Yes
- Keywords: Amur honeysuckle, Lonicera maackii, invasion biology, spatial distribution, invasibility, student research
- Full abstract:The non-native invasive shrub Amur honeysuckle—Lonicera maackii—is one of the most prolific invasive plant species across Midwestern and Northeastern landscapes of the United States. The locations of 2,095 individual Amur honeysuckle stems were geolocated using handheld GPS units in the understory of mixed growth forests at two study sites located approximately 5 km apart in northwestern Greene County, OH. Each site has undergone different levels of anthropogenic disturbance through time. The stem position data was used to measure the spatial clumping distribution and the density of Amur honeysuckle. The spatial clumping of Amur honeysuckle stems was measured using the fractal box counting method at each study site without regard for streams, trails, or elevation. The density of Amur honeysuckle (number of stems per square meter) was measured in zones as a function of the horizontal distance perpendicular to the edge of streams, trails, and within elevation (area between contour lines). Amur honeysuckle density is found to be uncorrelated with its proximity to streams, trails, and elevation. The density of Amur honeysuckle as a function of distance from streams and trails does not reveal an edge effect. The fractal dimension (scaling exponent) was computed to be ~1.5 at each of the two sites which means that the spatial clustering is the same for actively managed (partial Amur honeysuckle removal) and unmanaged sites. These results suggest that the invasion potential of Amur honeysuckle is robust, and its distribution may not be constrained in riparian forests by the variables included in this study.
- Open Access: Yes
- Keywords: Management, grazing, agroforestry, international
- Full abstract: The high nature conservation value of floodplain ecosystems is severely threatened by invasive alien species. Besides adversely affecting native biodiversity, these species also pose a major threat from a wider socio-ecological perspective (e.g. ‘roughness’ increases flood risk). Finding options to control dense shrub layers consisting of invasive alien species is therefore of high priority for multipurpose management. We studied cattle grazing impacts on the cover, composition and diversity of the herb and shrub layers in floodplain poplar plantations along the Tamiš river, Serbia. Non-grazed, moderately grazed, intensively grazed and resting place stands were sampled in five locations in three sampling points. Non-grazed stands had substantially higher cover of invasive alien shrub species (on average 65%) than moderately and intensively grazed stands, and resting places (5.17, 0.02 and 0.00%, respectively), but without considerable differences between the grazing intensity categories. The number of invasive alien species in the shrub layer decreased considerably from non-grazed to intensively grazed stands. Species composition in the herb layer changed from non-grazed to intensively grazed stands, while resting places differed substantially from the other categories. Total species richness, richness of native generalist herbaceous grassland species, and the cover of palatable grasses were the highest in moderately and intensively grazed stands. Our results suggest that cattle grazing in floodplains is effective at controlling invasive alien shrub species. Furthermore, continuous moderate or intensive grazing would contribute to multifunctional management of invaded floodplains by enhancing local biodiversity, reducing flood risk, and providing additional grazing areas for the local community.
- Open Access: Yes
- Keywords: Callery pear, Pyrus calleryana, phenology, invasion biology, student research
- Full abstract: Pyrus calleryana is quickly becoming one of the most problematic invasive species in the Eastern and Central part of the United States. Pyrus calleryana is an early successional species that quickly proliferates in highly disturbed soils such as old fields and younger prairies. Currently, this species poses a large threat to land managers as it changes the successional trajectories of forest and prairie systems, creating new novel ecosystems. Pyrus calleryana outcompetes most native early successional species and is relatively understudied. The mechanisms Pyrus calleryana utilizes to dominate ecosystems are not fully understood, but one theory is that Pyrus calleryana has extended leaf phenology in comparison to other native woody successional species. We hypothesized that Pyrus calleryana has a longer leaf phenology than two native woody species, Populus deltoides and Plantanus occidentalis. We observed these three species at 3 sites in Dayton, OH from December 2019 to November of 2020. A frost event in May also gave us the opportunity to understand frost tolerance with these species. We found that Pyrus calleryana began leafing out almost a month before its native competitors in the spring and kept its leaves on significantly longer than both P. deltoides and P. occidentalis (p<0.001) throughout the fall. During the frost event, almost every single leaf on P. occidentalis died and almost 70% of the leaves on P. deltoides were damaged. However, Pyrus calleryana only had damage on 6% of its leaves. Our experiment suggests that Pyrus calleryana uses an extended leaf phenology as a mechanism to outcompete native successional species as it is able to photosynthesize longer, which builds up carbon and nutrient reserves, and is able to withstand frost events.
- Open Access: Yes
- Keywords: Amur honeysuckle, Lonicera maackii, genetics, Great Lakes Basin, student research
- Full abstract: Invasive species are a global problem that cause significant environmental and economic damage. It has been estimated that the cost of invasive species in the United States is at least 120 billion dollars annually. Lonicera maackii, commonly known as Amur honeysuckle, is an invasive shrub found in New York State. In invaded regions, L. maackii has caused decreased species richness of native plant and animal species. It has also negatively affected the native migratory bird populations that eat the plant’s berries. Currently, there is no available genomic sequence for any Lonicera species. With next generation sequencing, new information can be unveiled that can inform control strategies and provide a better understanding of L. maackii as an invasive species. In this study, a genome sequence was assembled for an individual of Lonicera maackii found in Western New York. The assembled genome was annotated using two different methods. Genes found through annotation provide direction for future work on optimum control strategies for the L. maackii invasion.
- Open Access: Yes
- Keywords: Tree-of-heaven, Ailanthus altissima, management, social science, international
- Full abstract: While cities are invasion hotspots, the view of urban residents on non-native species is critically understudied – an important knowledge gap since strategies on biological invasions could gain power by integrating human values, attitudes and perceptions. How citizens perceive the non-native tree Ailanthus altissima (tree of heaven) is unknown despite its abundance in many cities globally and its classification as invasive in many countries. In a quantitative survey with closed questions, we analysed (i) whether residents of Berlin, Germany knew the widespread species, (ii) how they perceived it in different urban situations, (iii) how they accepted different management strategies of it, and (iv) how the sociodemographic background of respondents predicted their preference and acceptability ratings. In total, we surveyed 196 respondents. Most respondents recognized the tree in a photograph, but few provided its correct name. Citizens’ preferences differed significantly among four urban contexts in which the species was shown, with prevailing approval for trees as a component of designed green spaces and less pronounced preferences for wild-grown trees in other urban spaces. When respondents were asked to indicate how the tree should be managed (three options), we found the most support for removal in problematic cases (‘adaptive on-site’ strategy); some support was found for the ‘leave alone’ strategy and least support for the ‘complete removal’ management strategy. Practitioners with expertise in urban landscaping were more critical of Ailanthus than laypeople. Ordinal logistic regression analyses showed that respondents with a ‘close to nature’ behaviour and attitude had a more positive view on Ailanthus and expressed more support for ‘leave alone’ management. Results demonstrate the importance of citizens’ context dependent views about a widespread invasive species, spanning from approval to disapproval in different situations. We conclude that urban management strategies concerning Ailanthus would gain support from citizens when combining multiple approaches: (i) to control the species in case of realized negative impacts; (ii) to prevent the invasion of the species in areas of conservation concern; and (iii) to develop novel approaches of integrating wild Ailanthus trees into urban green spaces. These insights could support management measures that need to be established due to the EU-Regulation on Invasive Alien Species.
- Open Access: Yes
- Keywords: Callery pear, Pyrus calleryana, grasslands, phenology, prescribed fire, physical control, invasion biology, student research
- Full abstract: Ecological invasion is one of the most important processes of global change influencing ecosystems in practically every biome on Earth. Invasive species shift ecosystem dynamics, community structures, nutrient cycling, and ecosystem function. Invasive species pose a significant challenge to land managers who are charged with maintaining biodiversity and managing long-term ecosystem structure. Pyrus calleryana is an ornamental tree species that escaped cultivation and grows rapidly in highly disturbed soils with high light intensities. Former agricultural fields are highly susceptible to invasion from Pyrus calleryana. Observational evidence suggests that two features of this species’ biology may be particularly important to invasion success: (a) an extended leaf phenology and (b) the ability to persist in grasslands following disturbance via epicormic sprouting. While this tree is one of the most problematic invasive species within the Eastern and Central parts of the United States, it is relatively understudied. This thesis is divided into two distinct studies that address the invasion biology of Pyrus calleryana. The first study, is an analysis of the timing of leaf development (phenology) in relationship to co-occurring native trees. In the second study, I conducted a replicated field experiment to assess P. calleryana sprouting as a mechanism of persistence in response to experimental disturbance treatments including prescribed fire and experimental freezing using a
treatment of liquid nitrogen. The experiments we conducted in this project are in cooperation with the conservation staff at the Five Rivers Metroparks and all activities took place on their properties. In the first study, I discovered that P. calleryana has a longer leaf duration than native trees through earlier leaf out, and delayed abscission. In addition, a late season frost event allowed for a serendipitous study that revealed much greater frost tolerance in P. calleryana than native trees. Extended phenology and frost tolerance indicate strong potential for growing season carbon acquisition for P. calleryana compared to native trees. In the field experiment, I discovered that common practices such as mowing and prescribed fire may be facilitating the invasion of Pyrus calleryana due to its aggressive sprout response. Data indicate that experimental freezing was marginally more useful than cutting or herbicide in sprout control; however, herbicide application was the only reliable method for preventing resprouting. The results of these studies illuminate the invasion biology and may help inform more effective management of this problematic invasive species across the region, leading to more sustainable management of biodiverse habitats.
- Open Access: Yes
- Keywords: Tree-of-heaven, Ailanthus altissima, biocontrol, species interactions, international
- Full abstract: Ailanthus altissima (Mill.) swingle is a highly invasive tree that has become established worldwide, especially in the Mediterranean Basin because of its good drought resistance. Ailanthus altissima is included in the list of Invasive Alien Species of the EU, so measures for eradication and management are required. Assessment for potential biological control agents is of great interest to manage this invasive tree in natural ecosystems. Verticillium dahliae Kleb. and Verticillium nonalfalfae Inderb. et al. (formerly V. albo-atrum Reinke & Berthold) have been reported as the causal agents of Verticillium wilt and mortality of ailanthus. Ailanthus trees with Verticillium wilt symptoms (wilt, premature defoliation, terminal dieback, yellow vascular discoloration, and mortality) were detected for the first time in 2007 in Celrà (42.040466N, 2.864436E) (Catalonia, Northeastern Spain), then spread to neighboring ailanthus populations. To our knowledge, this is the first report of V. dahliae and V. albo-atrum sensu lato causing Verticillium wilt on A. altissima in Spain. The study suggests the potential of native isolates of Verticillum spp. in the biological control of ailanthus in the Mediterranean Basin.
Citation & Link: Palmer, A. 2021. Examining the invasion of a bush honeysuckle using climate analysis. Honors Thesis in Biological Sciences, University of Arkansas.
- Open Access: No (embargoed until April 2022)
- Keywords: Amur honeysuckle, Lonicera maackii, invasion biology, ecological theories of invasion, student research
- Full abstract: Within the study of invasive plants, particular importance is placed on elucidating the mechanisms by which these plants proliferate and dominate within their introduced ranges. Several theories have been advanced to explain these invasions, each with different implications for the predicted range of invasive plants. Recent studies have provided support for the application of several invasion theories to Lonicera maackii, or what is more commonly referred to as bush honeysuckle. This species provides a unique opportunity to examine the efficacy of these theories in explaining the range expansion of invasive plants. L. maackii is endemic to eastern Asia, but it has invaded much of the eastern United States, posing a serious threat to the health of forests and other natural areas. To evaluate the application of biotic and abiotic theories of invasion for L. maackii, we modeled the climatic niche space of L. maackii in both its native and invasive ranges. We visually inspected and verified 1,046 L. maackii localities and 126 L. subsessilis localities, the sister taxon to L. maackii. After associating these localities with 19 climatic variables (BIOCLIM), we performed a principal component analysis (PCA) and observed a clear separation between the climatic conditions of the native East Asian L. maackii points and the invasive North American points. The climate niches of each population group (native L. maackii, invasive L. maackii, and L. subsessilis) were significantly different, suggesting that the North American population of L. maackii occupies a different climate niche than in its native East Asian range. This separation was consistent with the predicted verses observed probable occurrence maps of North America and East Asia which we built using Maxent. This change in L. maackii’s climatic niche lends support for ecological theories of invasion that feature biotic constraints on range expansion (like the Enemy Release and Novel Weapon Hypotheses) over theories relying on abiotic climatic constraints (like the Environmental Filtering Hypothesis).
- Open Access: Yes
- Keywords: Common buckthorn, glossy buckthorn, Rhamnus cathartica, Frangula alnus, Great Lakes Basin, invasibility, student research, poster
- Full abstract: Invasive species are of growing concern in the mid-west. Buckthorn is a woody perennial invasive species that outcompetes native understory plants for light and resources and greatly reduces regeneration of native tree species. Dense buckthorn patches reduce diversity of plants and insects. Previous studies have linked higher housing densities and landscape fragmentation to an increased chance of buckthorn being present in a forest. Our study looked at the presence of buckthorn in school forests and the relationship to five variables: housing density, road density, distance to nearest house, and distance to edge.
- Open Access: No
- Keywords: Amur honeysuckle, Lonicera maackii, impacts, species interaction, ecology, wetlands
- Full abstract: Wetlands are especially vulnerable to invasive plants because seasonal movements of sediments, water, nutrients, and debris from adjacent terrestrial habitats create ecological conditions suitable for invasion. Lonicera maackii is a relatively abundant and broadly distributed invasive shrub in the eastern U.S.A., yet few studies have simultaneously tested for effects of its leaf litter on multiple trophic levels within wetland food webs. Hatching success, hatchling survival, and hatchling size of tadpoles (Acris crepitans) were assessed using a laboratory mesocosm experiment with no-leaf, native-leaf, and L. maackii-leaf treatments. In the field, short-term (c. 3 week) and long-term (c. 2 years) mesocosm experiments assessed the initial and persistent impacts, respectively, of L. maackii on measures of primary productivity, invertebrate abundance and community structure, and oviposition preference and larval survival of Cope’s gray treefrog (Hyla chrysoscelis). Exposure of eggs to L. maackii leaves reduced body size at hatching and larval survival of newly hatched A. crepitans. In short-term experiments, L. maackii leaves reduced dissolved oxygen levels, filamentous algal biomass, and macroinvertebrate abundance, and altered macroinvertebrate community structure. In long-term experiments, duckweed cover was 15× times greater in mesocosms with L. maackii leaf additions. Oviposition by a local population of H. chrysoscelis was 10× lower in both short- and long-term mesocosms with L. maackii present. Although ecological impacts of L. maackii have been reported for terrestrial systems, our study is the first to demonstrate the simultaneous effects of its leaves on multiple trophic levels within replicated experimental wetlands. The relatively rapid decomposition of L. maackii leaves, and associated pulse of phenolic compounds, is the most likely proximate mechanism of the bottom-up effects we observed. The mechanisms, timing, and significance of effects is predicted to vary among natural wetlands.
Our study demonstrates multiple ecological impacts of a terrestrial invasive shrub within experimental wetlands. Detailed studies on the specific mechanisms, and their spatial and temporal variability in natural systems, will elucidate management strategies and improve the efficiency of wetland conservation efforts.
- Open Access: Yes
- Keywords: Tree-of-heaven, Ailanthus altissima, management, chemical control, herbicide, stem injection, international
- Full abstract: The present paper presents the results of the chemical control research of the species Ailanthus altissima, an invasive species that damages the lands on which it appears spontaneously, in the form of restricted areas. The total systemic herbicide Roundup, based on glyphosate, 360 g/l was used. Two methods of application were investigated, namely, by brushing on a 30 cm height of the tree trunk and by injection into holes made in the tree trunk. Undiluted herbicide was applied. The first method of application had almost no effect on Ailanthus altissima trees due to the fact that the herbicide cannot be absorbed through the mature bark of the trees. The second method of application gave very good results.
- Open Access: Yes
- Keywords: Callery pear, Pyrus calleryana, genetics
- Full abstract: Pyrus calleryana Decne. (Callery pear) includes cultivars that in the United States are popular ornamentals in commercial and residential landscapes. Last few decades, this species has increasingly naturalized across portions of the eastern and southern US. However, the mechanisms behind this plant’s spread are not well understood. The genetic relationship of present-day P. calleryana trees with their Asian P. calleryana forebears (native trees from China, Japan, and Korea) and the original specimens of US cultivars are unknown. We developed and used 18 microsatellite markers to analyze 147 Pyrus source samples and to articulate the status of genetic diversity within Asian P. calleryana and US cultivars. We hypothesized that Asian P. calleryana specimens and US cultivars would be genetically diverse and would show genetic relatedness. Our data revealed high genetic diversity, high gene flow, and presence of population structure in P. calleryana, potentially relating to the highly invasive capability of this species. Strong evidence for genetic relatedness between Asian P. calleryana specimens and US cultivars was also demonstrated. Our data suggest the source for P. calleryana that have become naturalized in US was China. These results will help understand the genetic complexity of invasive P. calleryana when developing management for escaped populations: In follow-up studies, we use the gSSRs developed here to analyze P. calleryana escape populations from across US.
Citation & Link: Xiao, Q., Li, Z., Qu, M., Xu, W., Su, Z., & Yang, J. 2021. LjaFGD: Lonicera japonica functional genomics database. Journal of Integrative Plant Biology.
- Open Access: No
- Keywords: Japanese honeysuckle, Lonicera japonica, genetics, international
- Full abstract: Lonicera japonica Thunb., a traditional Chinese herb, has been used for treating human diseases for thousands of years. Recently, the genome of L. japonica has been decoded, providing valuable information for research into gene function. However, no comprehensive database for gene functional analysis and mining is available for L. japonica. We therefore constructed LjaFGD (www.gzybioinformatics.cn/LjaFGD and bioinformatics.cau.edu.cn/LjaFGD), a database for analyzing and comparing gene function in L. japonica. We constructed a gene co-expression network based on 77 RNA-seq samples, and then annotated genes of L. japonica by alignment against protein sequences from public databases. We also introduced several tools for gene functional analysis, including Blast, motif analysis, gene set enrichment analysis, heatmap analysis, and JBrowse. Our co-expression network revealed that MYB and WRKY transcription factor family genes were co-expressed with genes encoding key enzymes in the biosynthesis of chlorogenic acid and luteolin in L. japonica. We used flavonol synthase 1 (LjFLS1) as an example to show the reliability and applicability of our database. LjaFGD and its various associated tools will provide researchers with an accessible platform for retrieving functional information on L. japonica genes to further biological discovery.
