Woody Invasive Research Digest, 3rd & 4th Quarters 2021

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 July 1 and December 31, 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!

Citation & Link: Ahmad, A., & Akbar, S. (2021). Molecular characterization of bacterial community composition in the rhizosphere of invasive plant species Amur honeysuckle (Lonicera maackii) in an urban wetland forest. Advances in Microbiology, 11(9), 469–487. https://doi.org/10.4236/aim.2021.119035

• Open Access: Yes
• Keywords: Amur honeysuckle, Lonicera maackii, impacts, soil interactions, mycorrhizal biacteria, wetlands, Midwest
• Full abstract:The goal of this research was to determine the effects of the growth of invasive plant Amur honeysuckle (Lonicera maackii) on the rhizosphere bacterial community composition, and diversity in an urban wetland forest ecosystem. Bacterial communities from the rhizosphere of 5 L. maackii plants and control bulk soils that did not have any L. maackii were investigated at Nina Mason Pulliam EcoLab (NMPE) using a culture-independent pipeline. Bacterial communities were characterized by PCR amplification and cloning 16S rRNA gene fragments following total DNA isolation from the soil samples. Microbial communities associated with both L. maackii rhizosphere and control sites showed high bacterial diversity within each site and taxa unique to individual sites were observed. Phylogenetic analyses revealed 80% of 400 16S rDNA clones were classified as α-, β- and γ-Proteobacteria, Acidobacteria, Actinobacteria, Cytophaga-Flexibacter-Bacteroides (CFB) group, and Verrucomicrobia. Members of the Proteobacteria and Acidobacterium represented 66.5% and 14.5% of the clone library, respectively, whereas the remaining bacterial divisions each comprised less than 7% of the clone library. Twenty-five 16S rDNA clones could not be classified into any known bacterial divisions. Statistical analyses showed significant differences in the presence of L. maackii on the proportions of 16S rDNA clones affiliated with Proteobacteria and Acidobacterium, suggesting bacterial community composition and structure does significantly change in the presence of L. maackii. However, sequence-based community analysis and the corresponding lack of intact microbial cultures limit understanding of the potential influences of enriched microbial taxa on plant hosts and their roles in ecosystem functioning.

Citation & Link: Boettcher, T. J., Gautam, S., & Cook, J. (2021). The impact of invasive buckthorn on ecosystem services and its potential for bioenergy production: a review. Journal of Sustainable Forestry, 1–23. https://doi.org/10.1080/10549811.2021.1992637

• Open Access: No
• Keywords: Common buckthorn, Rhamnus cathartica, glossy buckthorn, Frangula alnus, impacts, literature review, cost-benefit, disposal, bioenergy, Midwest
• Full abstract: Two species of invasive shrubs are causing extensive environmental harm across North America. Common buckthorn (Rhamnus cathartica L.) and glossy buckthorn (Frangula alnus P. Mill.), originally imported from Europe, have become naturalized in many different ecosystems and are causing negative effects on associated ecosystem services. These invasive plants often create dense, monotypic stands that out-compete native plant species for nutrients and light. Current control methods, including manual or mechanical removal, are expensive and are mainly limited to destroying the buckthorn on site. The high cost of removal may be a barrier for restoration. Economic valuation should be carried out in terms of ecosystems services to better understand the cost-benefit of removing buckthorn. A cost-effective solution for removing buckthorn should also be explored. In this review, the state of the knowledge on the effects of buckthorn and its cost associated with major ecosystem services were synthesized. Existing methods to harvest and transport buckthorn and potential new methods were compiled. Finally, a policy review of buckthorn was completed for states where buckthorn is most prevalent. Findings from this review will be important for applying an economic cost to buckthorn and revealing where more work can be done.

Citation & Link: Boettcher, T. J. (2021). Assessing buckthorn’s impact on ecosystem services and development of models to estimate its presence and abundance: steps towards eradicating invasive plant species in Wisconsin through bioenergy utilization. Master’s of Science Thesis, University of Wisconsin – Stevens Point. 114pp.

• Open Access: Yes
• Keywords: Common buckthorn, Rhamnus cathartica, glossy buckthorn, Frangula alnus, impacts, disribution modeling, disposal, bioenergy, Midwest, student research
• Full abstract: Two species of invasive shrubs are causing extensive environmental harm across North America. Common buckthorn (Rhamnus cathartica L.) and glossy buckthorn (Frangula alnus P. Mill.) have become naturalized in many different ecosystems. Management of these species can be expensive while leaving the populations intact can detract the value associated with affected ecosystem services, which are the direct or indirect benefits that society gains from ecosystem processes and functions. Therefore, it is in the best interest of landowners to remove buckthorn but also to find cost-effective methods for removal. The goal of this study was to better understand how buckthorn was affecting ecosystem services and to explore new methods for eradication. The 2nd chapter is a literature review covering the state of the knowledge on the effects of buckthorn with regards to major ecosystem services. It also reviews potential harvest systems for buckthorn biomass and policy surrounding buckthorn regulations. The 3rd chapter covers the modelling of buckthorn presence and abundance across Wisconsin using certain landscape-level and stand-level variables as predictors. We constructed a series of regression models including binomial regression for the probability of occurrence, and Poisson and negative binomial regression to model abundance using a two-phase, zero-inflated approach. The resulting zero-inflated model indicated that stem density, species diversity, and mean diameter at breast height of woody species (not including buckthorn) as well as distance to nearest house, housing density within 1 km, solar irradiation, percent silt, and latitude were important for estimating buckthorn presence and abundance. The models developed in this study can guide land managers who want to identify areas invaded by buckthorn for mitigation actions. Additionally, results from the review indicate that more work is needed for determining the cost of buckthorn on ecosystem services as well as determining a feasible harvest system.

Citation & Link: Chikowore, G., Steenhuisen, S.-L., Mutamiswa, R., Martin, G. D., & Chidawanyika, F. (2021). Integration of invasive tree, black locust, into agro-ecological flower visitor networks induces competition for pollination services. Arthropod-Plant Interactions, 15(5), 787–796. https://doi.org/10.1007/s11829-021-09851-3

• Open Access: No
• Keywords: Black locust, Robinia pseudoacacia, impacts, species interactions, pollinators, agriculture, international
• Full abstract: Invasion of ecosystems by alien species is a global concern. Robinia pseudoacacia L. (Fabaceae) is one such species which impacts on native diversity and ecosystem functioning. We assessed how R. pseudoacacia affects flower visitation by arthropods in commercial apple orchards in eastern Free State, South Africa. We used paired observations to compare the abundance and diversity of flower visitors and their interactions with the two plant species. Our results showed that R. pseudoacacia flowers attract African honey bees (Apis mellifera) more than apple flowers. However, flower visitation by Diptera, particularly March flies (Bibionidae) was higher in apple flowers. Arthropods of other orders appeared to be minor visitors for both plants as they were recorded in small numbers. Flower visitation rates by A. mellifera did not vary significantly between the two plant species, though it was marginally higher in R. pseudoacacia. The interaction network for the two plant species and their flower visitors showed high nestedness indicating that they are drawing from the same pool of pollinators. Therefore, there is competition for flower visitors between R. pseudoacacia and apples based on the number of shared partners, an interaction which may potentially affect apple pollination and ultimately compromise fruit quality and yields. These findings further support the need to sustainably manage R. pseudoacacia in all invaded habitats including agro-ecosystems.

Citation & Link: Coyle, D. R., Williams, B. M., & Hagan, D. L. (2021). Fire can reduce thorn damage by the invasive Callery pear tree. HortTechnology, 31(5), 625–629. https://doi.org/10.21273/HORTTECH04892-21

• Open Access: Yes
• Keywords: Callery pear, Pyrus calleryana, management, disposal, prescribed fire
• Full abstract:Callery pear (Pyrus calleryana) is an invasive tree across much of the eastern United States that can form dense thickets, and tree branches and stems are often covered in sharp thorns. Landowners and land managers attempting to manage callery pear infestations are faced with the challenge of killing and/or removing the trees while also avoiding thorn damage to equipment, which can lead to wasted time and increased costs. We evaluated fire as management tool to reduce the likelihood of equipment damage from callery pear thorns. Branches were collected in the field from callery pear trees that were killed by herbicide, and also from untreated trees, and half the branches from each group were then burned with a propane garden torch to simulate a low-intensity prescribed fire. After treatment, all branches were returned either to an old field or forest floor for 1 year, after which thorn puncture strength was evaluated and compared with freshly cut thorns. Herbicide treatment and location did not affect thorn strength, but burning reduced the likelihood that thorns would puncture a tire. Fire increased tip width, which reduced thorn sharpness. Burning also reduced wood strength, and fungi proliferated on burned thorns after 1 year in the field or forest. Both factors likely contributed to decreasing thorn strength and probability of puncture. Our results show that using prescribed fire as a management tool can weaken callery pear thorns and dull their tips, reducing the chance of equipment damage and costs associated with clearing land of this invasive species. Leaving cut callery pear trees on the ground for 1 year increased fungal colonization, which may also reduce thorn damage. Prescribed fire can be part of an effective integrated management plan for this, and possibly other, thorny invasive flora.

Citation & Link: Cruz, O., Riveiro, S. F., Arán, D., Bernal, J., Casal, M., & Reyes, O. (2021). Germinative behaviour of Acacia dealbata Link, Ailanthus altissima (Mill.) Swingle and Robinia pseudoacacia L. in relation to fire and exploration of the regenerative niche of native species for the control of invaders. Global Ecology and Conservation, 31, e01811. https://doi.org/10.1016/j.gecco.2021.e01811

• Open Access: Yes
• Keywords: Tree-of-heaven, Ailanthus altissima, black locust, Robinia pseudoacacia, germination, invasibility, climate change, prescribed fire, wildfire, international
• Full abstract:Invasion of forest ecosystems by invader plants and forest fires are two of the most serious environmental problems in the world. Climate change is believed to strongly influence these processes, and the invasibility of invasive alien plants (IAPs) is likely to enhance landscape degradation. Therefore, it is urgent to study the germinative behaviour of invasive alien plants in relation to fire and detect possible barrier species of IAPs among native species. Tree species are usually the most damaging group of invasive alien plants. Acacia dealbata Link, Ailanthus altissima (Mill.) Swingle and Robinia pseudoacacia L. are 3 very damaging exotic invader trees in Europe and many other parts of the world. Therefore, the germination behaviour (germination percentage, viability pregermination, viability postgermination and germination rate) of these three species was experimentally studied against different products associated with fire (heat, smoke, ash and charcoal). The germination of A. dealbata and R. pseudoacacia was strongly stimulated by heat, while smoke, ash and charcoal barely changed the control values. None of these factors stimulated germination in A. altissima. Very high temperatures inhibited seed germination of the three species. The germination of R. pseudoacacia seeds was faster than that of A. dealbata and A. altissima seeds. Of the three species studied, A. dealbata and R. pseudoacacia have greater invasibility than A. altissima. A key role in invasive plant control research is to provide information to guide the decisions of forest managers involved in restoration. A possible solution is to use the biotic resistance of native vegetation to control biological invasions. For this purpose and based on extensive bibliographic revision, the regenerative niches of the three invasive species (germination, seedling growth and adult height) were compared with those of native European species to identify candidates for barrier species of IAPs between native species. Among the native species of Europe with characteristics in their regenerative niche suitable to successfully compete against these IAPs are tall shrub species such as Adenocarpus lainzii (Castrov.) Castrov., Cytisus multiflorus (L’Her.) or Cytisus striatus (Hill) Rothm. and tree species such as Corylus colurna L., Pinus sylvestris L. and Quercus ilex L. Therefore, the sowing of a good combination of shrub and tree species, selected according to their geographical distribution, could be an effective ecological measure to control the invasion of IAPs in burned areas. This information can be very valuable for implementing restoration measures in burned areas and should be verified with field experiments.

Citation & Link: Cunningham, C. J. (2021). The effects of Amur honeysuckle (Lonicera maackii) and white-tailed dear (Odocoileus virginianus) on spider communities in a deciduous forest. Master’s of Science Thesis, Miami University, 53pp.

• Open Access: Yes
• Keywords: Amur honeysuckle, Lonicera maackii, species interactions, impacts, ecology, Midwest, student research
• Full abstract: Invasive Amur honeysuckle and overabundant white-tailed deer affect the vertical plant cover and standing litter biomass of southwestern Ohio forests, causing invertebrate habitat quality and quantity changes. Increasing plant structure caused by honeysuckle invasion were hypothesized to provide more habitat for above-ground invertebrates. White-tailed deer were hypothesized to negatively affect litter-dwelling invertebrates due to indirect effects on litter biomass, which reduces litter habitat for invertebrates. We analyzed the long-term responses of litter spiders to experimental exclusion of deer and the removal of honeysuckle over time, 2011-2019, and shrub layer spiders in 2019. Winkler extraction of litter samples was used to collect litter-dwelling spiders, and systematic visual searches were used to collect above-ground spiders. All spiders were identified to guild and the lowest possible taxonomic class. Deer exclosure treatments and greater litter biomass were associated with increased species richness and abundance of litter spiders over nine years. Shrub layer spiders had reduced abundance when honeysuckle was removed, and space and sheet weavers had greater abundance in plots with higher foliage height diversity. Litter spider communities diverged over time based on site and deer treatment, while differences in the 2019 above-ground spider community were caused by honeysuckle treatment and site differences.

Citation & Link: Demeter, A., Saláta, D., Kovács, E. T., Szirmai, O., Trenyik, P., Meinhardt, S., Rusvai, K., Neumann, K. V., Schermann, B., Szegleti, Z., & Czóbel, S. (2021). Effects of the invasive tree species Ailanthus altissima on the floral diversity and soil properties in the Pannonian Region. Land, 10(11), 1–10.

• Open Access: Yes
• Keywords: Tree-of-heaven, Ailanthus altissima, impacts, species interactions, soil interactions, international
• Full abstract: Tree-of-heaven (Ailanthus altissima) is one of the most dangerous and widespread invasive woody plant species in Europe. Despite the fact that A. altissima is in the focus of an increasing number of research projects, the impact of its mass spread on native vegetation, its diversity, and changes in soil quality are still incomplete. The current study addresses the effects of this invasive species on plant diversity and soil parameters simultaneously. The main objective of our research is to determine the impact of cover and mass of A. altissima on the diversity of each forest layer; the examined soil parameters and on other selected environmental variables. For botanical and pedological investigations we selected nine A. altissima-dominated sites in Central Europe, in the Pannonian Biogeographical Region. Based on our results, it can be stated that fully grown A. altissima-dominated stands can displace other taxa by their shading and allelopathy, thereby reducing canopy layer diversity. The increase in the species richness of the shrub layer had a positive correlation with the diversity of the floor layer and also with the humus and ammonia content of the soil. As the diversity of shrub layer and floor layer positively correlated with many soil parameters, the diverse vegetation of these layers can represent a potential opportunity for the regeneration of areas infected with A. altissima.

Citation & Link: Dubach, V., Schneider, S., Vögtli, I., Queloz, V., & Stroheker, S. (n.d.). Transmission of Verticillium nonalfalfae via root contact from inoculated Ailanthus altissima in close-to-nature conditions. Forest Pathology, e12720. https://doi.org/10.1111/efp.12720

• Open Access: Yes
• Keywords: Tree-of-heaven, Ailanthus altissima, soil interactions, biological control, international
• Full abstract:Ailanthus altissima is an invasive alien species in Europe. Biological control of this tree species by Verticillium nonalfalfae is a potential alternative control approach. This study investigates host specificity, pathogenicity and transmission of V. nonalfalfae to neighbouring plants with root contact in mini-ecosystems. V. nonalfalfae led to dieback of all inoculated Ailanthus trees. Furthermore, V. nonalfalfae was transmitted to neighbouring Ailanthus trees, causing wilt and dieback, and, in one case, to Quercus petraea, which did not display any disease symptoms. Lastly, V. nonalfalfae could not be detected in the soil, which suggests transmission via root contact.

Citation & Link: Hartshorn, J. A., Palmer, J. F., & Coyle, D. R. (2021). Into the wild: evidence for the enemy release hypothesis in the invasive Callery pear (Pyrus calleryana) (Rosales: Rosaceae). Environmental Entomology, nvab136. https://doi.org/10.1093/ee/nvab136

• Open Access: Yes
• Keywords: Callery pear, Pyrus calleryana, invasion ecology, species interactions
• Full abstract:Wild Callery pear (Pyrus calleryana Decne.) results from a cross between various cultivars of P. calleryana and any other Pyrus individual. While many cultivars of this species are still commercially produced and sold for horticultural purposes in the United States, Callery pear is a detrimental invasive species that encroaches on many managed and natural areas, damages equipment and injures people, pets, and livestock with its thorny branches, and likely causes detrimental ecological impacts. Despite its importance as an invasive species, the mechanisms behind Callery pear’s invasion and spread are unclear. To identify potential drivers of invasion, we quantified feeding of generalist and specialist herbivores on Callery pear and four native tree species, based on insect host ranges, with choice and no-choice experiments followed by field surveys of herbivory on these same tree species. Feeding by all herbivores was lower on Callery pear than on native tree species in no-choice assays. Specifically, feeding on Callery pear was moderate by generalists and very low by specialists. Specialist feeding on Callery pear was comparable to native species in choice assays but was significantly reduced in no-choice assays. Reduced specialist feeding along with moderate generalist feeding on Callery pear in the field provides evidence for the Enemy Release Hypothesis as a potential driving mechanism behind its invasion success.

Citation & Link: Jurkšiene, G., Tamošaitis, S., Kavaliauskas, D., Buchovska, J., Danusevicius, D., Baliuckas, V. (2021). Identification of Alnus glutinosa L. and A. incana (L.) Moench. hybrids in natural forests using nuclear DNA microsatellite and morphometricmarkers. Forests, 12, 1504, 1-18. https://doi.org/10.3390/f12111504

• Open Access: Yes
• Keywords: Black alder, Alnus glutinosa, genetics, native species, hybridization, international
• Full abstract: Two alder species (Alnus glutinosa and A. incana) have overlapping distribution, naturally occur in Lithuania, and are considered ecologically and economically important forest tree species. The objective of our study was to estimate the likelihood of spontaneous hybridizations between native alders in natural stands of Lithuania based on leaf morphology and nuclear microsatellite markers. The sampled trees were assigned to the three taxonomic groups of A. glutinosa, A. incana, and potential hybrids based on the leaf and bark morphological traits. The genetic differentiation and potential hybridization between these three groups was tested based on 15 nSSR markers. We identified studied Alnus spp. individuals as pure species and hybrids. Two microsatellite loci were reported as discriminating well between these species. We concluded that our results showed the highest likelihood of two genetic group structures, a clear genetic differentiation between the morphology-based groups of A. glutinosa and A. incana, and rather variable likelihood values in the putative hybrid group. The results provide important implications for genetic conservation and management of Alnus spp.

Citation & Link: Lamb, N., Havens, K., Holloway, J., Steffen, J. F., Zeldin, J., & Kramer, A. T. (n.d.). Low passive restoration potential following invasive woody species removal in oak woodlands. Restoration Ecology, e13568. https://doi.org/10.1111/rec.13568

• Open Access: Yes
• Keywords: Common buckthorn, Rhamnus cathartica, ecological restoration, Midwest
• Full abstract:The restoration of oak woodlands often requires removal and management of woody invasive plants. This can trigger germination of the soil seed bank, which can alter restoration trajectories. In degraded deciduous woodlands generally, it is unclear whether the soil seed bank will contribute native plant material in sufficient quantities to help achieve restoration goals and allow practitioners to rely on passive restoration without supplemental seeding. To support restoration decision-making around passive or active restoration in three Rhamnus cathartica-invaded forest preserves in the Chicago region, we asked: (1) Does the soil seed bank differ from standing aboveground vegetation at reference and unrestored sites? and (2) Can the species richness, Shannon diversity, floristic quality (measured by abundance-weighted mean coefficients of conservatism), or density of germinable seeds of native species in the soil seed bank be predicted by a site’s restoration status (reference or unrestored)? We found that species composition differed significantly between aboveground vegetation and the soil seed bank at reference and unrestored sites, with a significant interaction between restoration status and location. Despite high variation among the three forest preserves, restoration status also predicted native species richness, diversity, floristic quality, and seed density in the soil seed bank, with unrestored sites significantly lower than reference sites in all measures. Results suggest that reintroduction of native seeds will be necessary to fully restore desired native plant communities in oak woodlands following the removal of invasive woody plants.

Citation & Link: Li, G., Rogers, P. C., & Huang, J. (2021). Black locust (Robinia pseudoacacia L.) range shifts in China: Application of a global model in climate change futures. Climate Change Ecology, 2, 100036. https://doi.org/10.1016/j.ecochg.2021.100036

• Open Access: Yes
• Keywords: Black locust, Robinia pseudoacacia, climate change, distribution, international
• Full abstract:Black locust (Robinia pseudoacacia L.) has been widely used to restore degraded land in northern China for many decades, and the forest has become an important ecosystem in China. However, there is still knowledge gap about how the range shift of black locust in response to future climate change, which is the first step for adaptive management of black locust. Here, a global niche model of black locust was established by means of maximum entropy model (MaxEnt), 1174 global occurrences data, as well as 13 climatic variables. Then, the global niche model was projected to China under current climate (2000) and four future climate scenarios (2080). The results showed that the range of black locust is mainly controlled by temperature related variables rather than precipitation related variables. The latitude of potential range of black locust is mainly between 23° and 40° in China with the area of occupation being about 26.7% (25.7 × 105 km2) of China’s total land area. Future climate is conducive to the northward expansion of black locust in China with a speed of 21 km/decade, as well as an upward shift with a speed of 9.6 m/decade across climate scenarios. Relatively high stable ranges (87–94%) and quick range shift speed implies that little vulnerability of black locust in response to climate change, as well as little risk of extinction in China.

Citation & Link: Li, K., Ni, R., Lv, C., Xue, L., Zhang, C., Li, C., Shen, W., Guo, H., & Zhang, Y. (2022). The effect of Robinia pseudoacacia expansion on the soil particle size distribution on Mount Tai, China. CATENA, 208, 105774. https://doi.org/10.1016/j.catena.2021.105774

• Open Access: Yes
• Keywords: Black locust, Robinia pseudoacacia, soil interactions, impacts, international
• Full abstract:The soil particle size distribution (PSD) is a fundamental physical property that can affect soil nutrients, soil structure characterization and soil hydraulic properties. However, the effect of plant expansion on soil PSD is not clear. Therefore, in this study, fractal theory was applied to quantitatively describe the PSD. On Mount Tai, artificial afforestation with Robinia pseudoacacia is helpful in restoring ecosystems and improving soil quality. However, clonal spread allows R. pseudoacacia to easily escape cultivation, leading to the formation of mixed forests. Therefore, exploring the effect of R. pseudoacacia expansion on soil PSD is important. The results show that 1) R. pseudoacacia expansion increased the clay and silt contents and reduced the sand content; 2) R. pseudoacacia expansion significantly reduced the capacity dimension, entropy dimension, and correlation dimension and increased the width and asymmetry of the singularity spectra but was unrelated to the entropy dimension/capacity dimension; and 3) the capacity dimension was significantly positively correlated with the sand content and significantly negatively correlated with the silt and clay contents, but the asymmetry of the soil PSD was inconsistent with the capacity dimension. In summary, R. pseudoacacia can reduce the heterogeneity of the PSD by increasing the distribution range and density of the PSD. Our results provide important insight into the effect of plant expansion on soil PSD.

Citation & Link: Miścicki, S., & Wysocka-Fijorek, E. (2021). Elimination of black locust Robinia pseudoacacia L. as a non-native species in Bielański Forest (Las Bielański) in Warsaw, Poland – success or failure? Urban Forestry & Urban Greening, 64, 127274. https://doi.org/10.1016/j.ufug.2021.127274

• Open Access: No
• Keywords: Black locust, Robinia pseudoacacia, forestry, management, restoration, social sciences, evaluation, international
• Full abstract:We sought to determine the outcomes of 25 years of implementation of the plan for the elimination of the black locust from Warsaw’s Bielański Forest. Forty years was the planned duration of the work to eradicate the non-native species, through the removing of individual trees from stands, repeated every 8–10 years. We presumed that the effects of these silvicultural treatments were positive if during the 1992–2017 study period, it would be possible to note declines: in density (number of individuals per hectare) of black locust trees (even as density of maple trees increased); in the abundance of saplings of the species (as opposed to maple); and in the rate of advancement of the species from the low to the ‘high sapling’ layers (again as opposed to maple). Empirical data were collected from 29 permanent sampling plots every five years. However, just 7 years into the eradication effort, 1999 brought protests from people living close to the Forest, who were left uninformed about the intention to fell black locust trees. These protests proved so effective that they resulted in an almost-complete abandonment of the relevant silvicultural measures. Thus, 25 years on, the conservation goal set for the Forest had only been achieved in part, as the decrease in density of black locust trees in the forest observed for 1992–1997 was followed by a slower process of decline that by definition reflected natural processes, rather than the now-abandoned tree-felling measures. Furthermore, black locust trees were able to continue their advance up from the ‘low sapling’ to ‘high sapling’ layers. The 1999 event thus emphasised, not only the need to secure the participation and understanding of a local community in regard to forest management; but also the requirement that people be educated about their area’s valuable natural attributes, and about the need for nature conservation measures in general.

Citation & Link: Motti, R., Zotti, M., Bonanomi, G., Cozzolino, A., Stinca, A., & Migliozzi, A. (2021). Climatic and anthropogenic factors affect Ailanthus altissima invasion in a Mediterranean region. Plant Ecology, 222(12), 1347–1359. https://doi.org/10.1007/s11258-021-01183-9

• Open Access: Yes
• Keywords: Tree-of-heaven, Ailanthus altissima, invasibility, international
• Full abstract: Ailanthus altissima is an aggressive invasive tree worldwide, but the ecological factors that lead to the spread of this species in Mediterranean ecosystems are still unclear. Here we aim to identify such factors, focusing on the interaction of human activity with climatic conditions. We determined the occurrence and abundance of Ailanthus in 240 sites and studied their relationship with 20 variables representing climatic, geographic, and topographic factors, as well as land use, in the region of Campania (southern Italy). Overall, we found that temperature and rainfall in Campania are suitable for Ailanthus, with the only major constraint being the temperature at an altitude exceeding 900 m a.s.l.. We found that Ailanthus is unable to spread where the mean annual temperature is lower than 11.1 °C. By contrast, precipitation variables showed poor correlation with Ailanthus distribution, suggesting that rainfall in the selected study sites is suitable to sustain the growth of this tree. About land use variables, roads were the primary landscape feature along which this species spread and invaded new areas. Roads probably combine high propagule pressure and favorable growing conditions in terms of available resources i.e., light, water, and mineral nutrients, that allow Ailanthus to establish and spread along roadside edges in different ecosystems. In conclusion, we found that climate and human-associated variables are correlated with the current occurrence of Ailanthus, with the temperature being more influential at high elevation sites and road distance playing a prominent role in low elevation areas.

Citation & Link: Rivera, B.J. (2021). The establishment, control, and post-control response of Amur honeysuckle (Lonicera maackii). Master’s of Science Thesis, Purdue University, 91pp.

• Open Access: Yes
• Keywords: Amur honeysuckle, Lonicera maackii, species biology, reproduction, management, cut stump herbicide, physical control, student research, Midwest
• Full abstract:Amur honeysuckle (Lonicera maackii) is a shrub endemic to East Asia which has become invasive and nearly ubiquitous to the forest ecosystems of eastern North America. Through its extended growing season, competitive ability, and potential allelopathy, Amur honeysuckle alters native herbaceous-layer plant communities and inhibits the regeneration of native tree species. As such, it is representative of a range of invasive shrub species imported from East Asia. My thesis contributes to questions fundamental to the understanding this and other invasive shrubs: 1) How do species become invasive? 2) How can the invasions of the species be effectively controlled? 3) How does the ecosystem respond to treatment of the invasive species? First, I examined the role of self-compatibility within Amur honeysuckle. I compared the berry production, seed production, and germination rates between closed-pollinated and open-pollinated flowering branches of Amur honeysuckle individuals across multiple types of invasions (heavy, light, and sprouting). I found that Amur honeysuckle not only possesses the ability to self-pollinate, but that it can produce viable self-pollinated seed sets. This ability may help explain how Amur honeysuckle able to invade isolated forest patches far removed from the main invasion. Second, I evaluated the effectiveness of a novel herbicide adjuvant in reducing the amount of herbicide needed in the ‘cut-stump’ method of controlling Amur honeysuckle. Combining various concentrations of the most common herbicide in the world, glyphosate, with concentrations of cellulases derived from fungi, 2XL, I examined whether the cellulases improved the effectiveness of glyphosate, potentially by increasing glyphosate movement into the vascular tissue of Amur honeysuckle through the degradation of cell walls. While 2XL was not an effective adjuvant, glyphosate concentrations of less than half the recommended dosages were equally effective as higher concentrations in preventing sprouting of treated stumps. The ineffectiveness of 2XL may imply a need for protein-mitigated diffusion of glyphosate across cell walls and into the vascular tissue of the plant, which would be inhibited by the breakdown of cell walls. Finally, I tested how deeper intensities of mulching-head treatments affected the sprouting response of Amur honeysuckle and the response of the herbaceous-layer plant community after treatment. I found a negative relationship between the volume of sprouting Amur honeysuckle and increasing depth of mulching-head treatment. Additionally, increasing mulching-head intensities were correlated with increased herbaceous layer diversity and conservation value as represented by Floristic Quality Index. Mulching-head treatments are a promising tool in controlling heavy invasions of non-native shrubs.

Citation & Link: Schuster, M. J., Wragg, P. D., & Reich, P. B. (2021). Phenological niche overlap between invasive buckthorn (Rhamnus cathartica) and native woody species. Forest Ecology and Management, 498, 119568. https://doi.org/10.1016/j.foreco.2021.119568

• Open Access: No
• Keywords: Common buckthorn, Rhamnus cathartica, phenology, native plants, Midwest
• Full abstract:Common buckthorn (Rhamnus cathartica L.) is a prolific invader of forest understories throughout eastern North America. Its ability to invade is partially attributable to its relatively high shade tolerance and ability to capture light both early and late in the growing season because of its phenological differences from native species. Competitors that mitigate this phenological advantage by casting shade early and late in the growing season may therefore increase biotic resistance against invasion. However, controlled comparisons between buckthorn and other woody understory species are scarce and to what extent buckthorn’s phenology is truly exceptional is incompletely known. Here, we compare the spring and autumn phenologies of five shade tolerant, native woody species (Sambucus canadensis, Sambucus racemosa, Corylus americana, Cornus racemosa, and Acer saccharum) to those of buckthorn in two common garden experiments. Spring phenology of buckthorn was often comparable to the five native species considered. All native species broke bud no later than 7 days after buckthorn, with S. racemosa reaching spring phenophases consistently earlier than buckthorn. In contrast to spring, buckthorn fall phenology was distinct in comparison to some natives but not all. Native species started to senesce up to 20 days earlier than buckthorn, but both Sambucus species senesced slowly and held their leaves equally long as buckthorn. These findings illustrate that buckthorn does not possess unique phenology amongst understory species. Forest communities rich in deciduous shrubs or trees that are phenologically similar to buckthorn (particularly S. racemosa) likely limit buckthorn’s critical spring and fall carbon gains and exert greater biotic resistance to invasion by buckthorn.

Citation & Link: Sena, K., Gauger, L., Johnson, T., Shirkey, F., Caldbeck, W., Hammock, J., Kim, A., Mazza, B., Pethtel, I., & Leuenberger, W. (2021). Honeysuckle (Lonicera maackii) presence is associated with reduced diversity and richness of flowering spring flora in Central Kentucky. Natural Areas Journal, 41(4), 249–257. https://doi.org/10.3375/20-41

• Open Access: No
• Keywords: Amur honeysuckle, Lonicera maackii, impacts, species interactions, native plants
• Full abstract:Invasive plant species can have significant, adverse effects on forest ecosystems. By outcompeting native species for resources, invasive species suppress the richness and diversity of many forest communities. This study focuses on the associations of Amur honeysuckle (Lonicera maackii Rupr.) with spring flora in Raven Run Nature Sanctuary in Lexington, Kentucky, where abundant L. maackii threatens native biodiversity. Plots were surveyed for percent herbaceous groundcover and abundance of flowering spring flora at three levels of L. maackii density (high, low, and no L. maackii). Results indicate that L. maackii abundance is associated with lower species richness, abundance, and early-season diversity of flowering native spring flora. Importantly, this study extends the existing robust literature evaluating the widespread effects of L. maackii to the Kentucky River Palisades, a sensitive and botanically important corridor in central Kentucky.

Citation & Link: Terzi, M., Fontaneto, D., & Casella, F. (2021). Effects of Ailanthus altissima invasion and removal on high-biodiversity Mediterranean grasslands. Environmental Management, 68(6), 914–927. https://doi.org/10.1007/s00267-021-01522-6

• Open Access: No
• Keywords: Tree-of-heaven, Ailanthus altissima, impacts, restoration, grasslands, international
• Full abstract: Ailanthus altissima is one of the worst invasive plants in Europe in several habitat types, including high-biodiversity grasslands. The aim of this work was to evaluate the impact of the invasive A. altissima on high-biodiversity grassland vegetation and the effects of its removal on the recovery of native plant communities. The study area was within the Alta Murgia National Park (SE Italy). Seventeen vegetation quadrats were sampled in invaded grasslands and nine quadrats were sampled in nearby uninvaded areas. A. altissima was removed from six quadrats, which were sampled for two years after plant removal. Cluster analysis and non-metric multidimensional scaling ordination were used to identify and visualize the general vegetation pattern. Generalised Linear Models with different error structures were used to analyse the effects of A. altissima on native grasslands and vegetation recovery after removal. Results showed that the invasion of A. altissima changed drastically the community composition, reduced plant richness and diversity. Invaded stands had a greater presence of ruderal and widely distributed taxa, as opposed to a lesser presence of endemic and Mediterranean ones. The differences in the community composition between invaded and uninvaded quadrats became clearly detectable when A. altissima plants exceeded a threshold of 1 m of height and 50% of coverage. After A. altissima removal, the recovery of the grassland community was not completely achieved after two years.
  

  

Citation & Link: Uddin, Md. N., Asaeda, T., Sarkar, A., Ranawakage, V. P., & Robinson, R. W. (2021). Conspecific and heterospecific plant–soil biota interactions of Lonicera japonica in its native and introduced range: Implications for invasion success. Plant Ecology, 222(12), 1313–1324. https://doi.org/10.1007/s11258-021-01180-y

• Open Access: No
• Keywords: Japanese honeysuckle, Lonicera japonica, soil interactions, species interactions, invasibility, international
• Full abstract:We tested the ‘enemy release hypothesis’ in relation to Lonicera japonica to determine the effects of soil microbes on plant growth. It was hypothesized that plant performance in the introduced range in Australia would be increased by escaping natural enemies in soils in its native range of Japan, and thus there was increased likelihood of invasion success. Greenhouse experiments were carried out where plants (stem cuttings) of L. japonica were inoculated with soil microbiota (conspecifics vs. heterospecifics) from either the native range in Japan or the introduced range in Australia. Survival rates and plant growth characteristics were documented, and overall plant performance as feedbacks were calculated. The results showed that the growth of L. japonica was influenced by soil microbial communities. Plant growth performance indicated strong negative feedback when grown in its native-range soil and positive feedback when grown in its introduced range soil. Difference between ranges was noticed that includes more positive feedback when L. japonica was grown in conspecific soil compared to when it was grown in the conditioned by heterospecifics from the introduced range and more negative feedback in conspecific soils compared to heterospecific soil in the native range. The findings are consistent with the ‘enemy release hypothesis’ and clearly indicate that plant–soil microbes’ interactions of L. japonica can play an important role in facilitating the survival and growth of L. japonica in its introduced range.