Research Article |
Corresponding author: Chaeho Byun ( chaeho.byun@mail.mcgill.ca ) Academic editor: Graeme Bourdôt
© 2024 Chaeho Byun, Kripal Singh, Sun Hee Hong, Jangho Lee, Tae Kyung Yoon, Hojeong Kang.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Byun C, Singh K, Hong SH, Lee J, Yoon TK, Kang H (2024) Uprooting is a promising tool to control invasive giant ragweed and recover native diversity. NeoBiota 94: 311-331. https://doi.org/10.3897/neobiota.94.123363
|
Ambrosia trifida (giant ragweed) is an invasive species that causes habitat destruction and competitively excludes native plants in many parts of Europe and Asia. In this study, we evaluated the effects of selective cutting and uprooting on A. trifida and native plant diversity, as well as the effects of sowing the seeds of native annual, perennial and woody species after eradication. We hypothesised that: (i) selective uprooting will be more effective than cutting in controlling invasion by A. trifida because fewer propagules would be left behind, with no increase in the number of existing invasive propagules and (ii) sowing native seeds will increase invasion resistance and accelerate the recovery of native plant diversity. The eradication methods were applied in July 2022, seeds were sown in March 2023 and the response variables (i.e. importance values (%) of A. trifida and diversity index (H') of native species) were measured in September 2023. The importance values of A. trifida were lowest and diversity index of native species was highest in the uprooting treatment, supporting the first hypothesis. Sowing native seeds following invasion removal did not exert significant additional suppressive effects on invasion or increase native species diversity. These results reveal that selective uprooting is a promising tool to control A. trifida and to support the recovery of native diversity, while sowing native seeds does not improve the quality of restoration.
Ambrosia trifida, ecological restoration, eradication methods, diversity index, hand-pulling, native diversity, invasive plant management, selective cutting, selective uprooting
Biological invasion is a major factor contributing to global ecological and socioeconomic instability (
Ambrosia trifida L., or giant ragweed, is an annual herb native to North America (
A number of mechanical (physical), chemical and biological eradication methods for invasive plant species have been developed (
Extensive research suggests that sowing native seeds after the removal of invasive species can establish native vegetation cover and reduce the probability that invasive species regrow and establish as a result of niche pre-emption and resource utilisation (
Ambrosia trifida is a noxious weed and its control has been a challenging task at introduced sites and in its native range. The suppression of A. trifida in agricultural fields by the application of various herbicides, growing cover crops and diversifying cropping systems is rarely successful (
This study, therefore, aimed to investigate the effectiveness of mechanical control, including selective uprooting and selective cutting, on the dominance of A. trifida. Although the eradication of invasive species can suppress their dominance to some extent, the recovery of native diversity requires additional assistance (e.g. through sowing seeds following invasive plant removal) (
Experimental plots were installed in July 2022 at two sites in Busan, Republic of Korea separated by 18 km. Site #1 was located at 1200-5 Daejeo 2-dong, Gangseo-gu (35°11'46"N, 128°58'02"E) and site #2 was located at 1211 Hadan-dong (35°05'29"N, 128°56'40"E) (Fig.
We applied a split-plot design with main plots consisting of different eradication methods and subplots consisting of different seed mixtures for sowing. Based on the cover and distribution of A. trifida, two blocks at site 1 and four blocks at site 2 were established. Thus, a total of six blocks were prepared. Each block was 10 m × 10 m. Within each block at each site, three main plots measuring 2 m × 2 m were randomly developed and equidistant. All plots were placed 2 m inside the block and plots were situated with distance of 2 m from each other. Three plots represented three treatments (i.e. control (no action), selective cutting and selective uprooting). The layout of the main plots at the six blocks in two sites is shown in Suppl. material
Nine native species from three functional groups, annual (Lactuca indica, Elsholtzia splendens and Portulaca oleracea), non-woody perennials (Phragmites australis, Pennisetum alopecuroides and Plantago asiatica) and woody perennials (Lespedeza bicolor, Lespedeza juncea and Sorbaria sorbifolia) were identified for the current experiment. These native species were selected, based on their ability to suppress invasive plants in previous pot and field scale studies (
Seeds of native plants were purchased from authorised seed suppliers (in winter 2022). Seeds were obtained from multiple suppliers, because they could not be obtained from a single supplier. Seed suppliers included Aram Seeds (Seoul, Republic of Korea), Xplant (Seoul, Republic of Korea) and New Korea Farm (Seongnam, Republic of Korea) and others. Seed viability was standardised by applying the same number of viable seeds per species (600 seeds m-2) to experimental units. To determine the percentage of viable seeds, a germination test was conducted in the laboratory. All seeds were cold-stratified (6 months) at 3 °C before the germination test, following standard methods (
In August 2023, the number of shoots, plant height and plant cover of all species (including A. trifida) in each treatment and control plot were measured. For the number of shoots, we counted all shoots of each species in each plot manually. To determine plant cover, the percentage of each species was estimated using reference frames representing 50% and 25% of the total plot area. The main response variable was the importance value index, calculated based on the abundance of A. trifida. The importance value index (IVI) is a crucial metric in ecological studies, particularly when assessing the performance and impact of an invasive species (
ANOVA was used to evaluate the effects of various treatments on response variables. A generalised linear mixed model (REML; F-test) was used to account for the random block design (
Effects of various eradication methods on Ambrosia trifida performance (importance values (a) and seed yield (b)) and plant community diversity (c). Error bars indicate standard errors. Bars with the same letters were not significantly different at P < 0.05.
Effects of sub-treatments (sowing native seeds) within main treatments (eradication methods) on the importance values of Ambrosia trifida (a) and diversity of native plant communities (b). Error bars represent standard errors. Bars with the same letters were not significantly different. SM1 stands for seed mixture 1 (annuals), SM2 for non-woody perennials, SM3 for woody perennials.
The normality of residuals and homoscedasticity were evaluated, and the response variables were transformed when necessary. Amongst the main response variables, only invasive seed yield (g) was log-transformed during analysis. When significant (P < 0.05) treatment effects were detected, t-tests were used to compare means of treatments. ANOVA and correlation analyses were conducted using JMP (SAS Institute Inc., Cary, NC, USA). Pearson correlation coefficients were calculated for A. trifida importance values and the diversity index (H’) using data for 2023 in JMP.
The effects of different control measures on the performance of A. trifida (Fig.
Sowing native seeds did not have significant effects on the A. trifida importance value (F9,41 = 0.7458; P = 0.6653), while the main eradication treatments had significant effects (F2,41 = 9.2215; P = 0.0005) and the effect of the site factor was also significant (F1,3 = 21.5360; P = 0.0168) in a nested experimental design. The importance values of A. trifida were much lower in the subplots with uprooting than in the control (no seed added) (Fig.
Variations in plant cover of native species after eradication, but before sowing native species and after sowing seeds, were also observed (Table
Plant species and their cover before sowing native seeds (August 2022) and after sowing native seeds (September 2023). Species names in bold font were the sown species. PC, plant cover (%).
Species names | Growth habit | Native or not | Invasiveness | Sown species | PC 2022 (%) | PC 2023 (%) |
---|---|---|---|---|---|---|
Lespedeza bicolor Turcz.# | Perennial legume | Native | – | Sown | 23.00 | 37.25 |
Humulus japonicus Siebold & Zucc. | Perennial climber | Native | Invasive | – | 46.12 | 36.80 |
Pueraria lobata Maesen S. M. Almeida ex Sanjappa & Predeep | Perennial vines | Native | – | – | 28.37 | 34.00 |
Melothria japonica L. | Annual climber | Native | – | – | 10.67 | 33.22 |
Lactuca indica L. # | Annual herb | Native | – | Sown | 0 | 21.83 |
Rubus parvifolius L. | Perennial shrub | Native | – | – | 20.00 | 15.63 |
Acalypha australis L. | Annual herb | Native | – | – | 0 | 14.50 |
Achyranthes bidentata var. japonica (Miq.) Nakai | Annual herb | Native | – | – | 16.70 | 14.18 |
Pennisetum alopecuroides (L.) Spreng.# | Perennial grass | Native | – | Sown | 17.00 | 13.33 |
Commelina communis L. | Annual herb | Native | – | – | 0 | 11.49 |
Artemisia indica Willd. | Annual herb | Native | – | – | 2.50 | 10.75 |
Persicaria perfoliate (L.) H.Gross | Annual climbing | Native | – | – | 7.00 | 7.57 |
Paederia foetida L. | Perennial herb | Native | – | – | 18.5 | 7.20 |
Setaria viridis (L.) P. Beauv. | Perennial grass | Native | – | – | 7.00 | 6.04 |
Cocculus trilobus (Thunb.) DC. | Climbing shrub | Native | – | – | 8.25 | 5.50 |
Equisetum arvense L. | Perennial herb | Native | – | – | 3.00 | 5.50 |
Stachys japonica L. | Perennial herb | Native | – | – | 7.00 | 5.17 |
Phragmites australis (Cav.) Trin. ex Steud.# | Perennial grass | Native | – | Sown | 0 | 4.75 |
Glycine soja Siebold & Zucc. | Annual legume | Native | – | – | 0 | 4.14 |
Artemisia lancea Van. | Perennial | Native | – | – | 8.75 | 3.73 |
Digitaria ciliaris (Retz.) Koeler | Annual grass | Native | – | – | 0.67 | 3.65 |
Persicaria lapathifolia (L.) Delarbre | Annual herb | Native | – | – | 0 | 3 |
Stellaria aquatica (L.) Scop | Perennial herb | Native | – | – | 0 | 1.25 |
Lactuca scariola L. | Annual herb | Non-native | Invasive | – | 21.00 | 0 |
Fallopia dumetorum (L.) Holub | Annual climber | Native | – | – | 1.00 | 0 |
Amphicarpaea bracteata edgeworthii Benth. | Annual climber | Native | – | – | 6.67 | 0 |
Bidens pilosa L. | Annual herb | Non-native | – | – | 20.00 | 0 |
When invasive plants are partially removed, the effects on re-invasion can vary depending on the mode of reproduction of the invasive species, such as sexually (through seeds) and asexually (through rhizomes), as well as the persistence of the seed bank. For instance, re-sprouting from roots, rhizomes and plant stubs occurs in various invasive species (e.g. Cyperus rotundus, Lantana camara, Phragmites australis and Rosa rugosa), facilitating re-invasion after cutting or mowing aboveground plant parts. However, as observed in the current study on A. trifida (Fig.
The addition of native seeds following invasion control is an effective strategy for controlling re-invasion and increasing biodiversity (
The variations in plant cover of native vegetation between 2022 and 2023 can be attributed to the combined effects of invasive species removal, sowing of native species, differences in growth habits, improved environmental conditions and interspecific interactions. The eradication of A. trifida may have reduced competition for resources, such as light, water and nutrients and, thereby, allowed other species to flourish. The sowing mixtures of native species would be expected to directly increase the presence and cover of these species. This is evident from the appearance of species that were absent in 2022, such as L. indica and P. australis in 2023. Annual species such as L. indica and A. australis can quickly colonise and cover ground within a single growing season. Perennials, on the other hand, might show more substantial growth over several years. This explains why some annual species were completely absent in 2022 and appeared in 2023 after sowing, while some perennials maintained or slightly increased their cover. For example, M. japonica increased its cover from 10.67% to 33.22%, indicating a competitive advantage or favourable conditions for this species post-eradication. Likewise, the increase in cover of L. bicolor from 23.00% to 37.25%, might be due to reduced competition and to its being a sown species.
While native seed sowing suppressed A. trifida invasion to different extents in each treatment, it did not impact the recovery of native diversity significantly. Sowing native seeds following invasion removal has been reported not to be a promising strategy for increasing native plant biodiversity, as reported in recent studies of A. trifida (
A major limitation of this study was relatively short monitoring time (1 year or less) after restoration. We think that longer monitoring would have yielded better results. The short monitoring time may explain, at least partly, why sowing native seeds did not bring any additional benefit to the control of, or resistance to, A. trifida invasion. The seed mixtures of three functional groups of native plant species were employed: annuals, non-woody perennials and woody perennials, because we wanted to determine which functional group was most effective in providing biotic resistance to invasion in the year following eradication of A. trifida. Annuals were expected to perform better as they are usually fast-growing and become established in the first year after eradication. This is also expected, based on the limiting similarity hypothesis (A. trifida is also an annual plant species). However, we did not find any difference in biotic resistance to invasion between the functional groups of seeds; in fact, there was no difference between sowing and not sowing seeds. We only monitored plots soon after eradication because we considered one year as the critical window for invasive species re-invasion. If invasive species are not controlled within this short time frame, then it will be difficult to stop re-establishment of the invasive species afterwards. As we were acutely aware of the limited timeframe of this study, we ended up measuring the invasive seed yield as an indicator for potential future re-invasion after one year of monitoring.
One of the critical aspects of restoring native species using native seeds is the seed density. For instance, 600 pure live seeds (after considering germination rates per species) m-2 per subplot were sown. Originally, this density was considered sufficient in the initial experimental design, but under actual heterogeneous field conditions, many different factors can influence seeding efficiency. For example, the characteristics of experimental sites might not match the ecological niches of the restorative native species. In addition, it is also likely that seed density is reduced by their ingestion by some animals, such as birds, in the Spring. Considering these field limitations, we now consider that 10-fold higher seed density would have been required to obtain meaningful and significant results; in fact, this density was recommended by a seed-based restoration workshop at a conference of the Society of Ecological Restoration (SER).
The findings of this study have strong implications for the management of invasive plants and recovery of native plant diversity: (1) Cutting to eradicate plant invasion can result in wasted effort and resources, particularly if the targeted species can regrow or re-sprout from remaining plant parts. In the current study, cutting was selective and resulted in minimal disturbances of native vegetation. However, invasion was suppressed to only a small extent with insignificant differences between cutting plots and the control plot. Complete and destructive cutting of the entire vegetation may further increase invasion by reducing native plant diversity; (2) Selective uprooting is a promising tool for invasive plant management. Complete removal of invasive species from invaded communities and ecosystems will reduce competition pressure on native species for space, light and nutrients and form invasive propagules (roots, rhizomes, seeds etc.) and increase the performance (germination, establishment and diversity) of native communities; (3) Sowing seeds of diverse species following removal of the invasive species is critical for the rapid recovery of native diversity; (4) Compared with selective uprooting, mowing of all species is not an effective strategy for the management of invasive plants because it does not leave any native species to resist re-invasion; (5) Although this study was conducted solely at two field sites within the Republic of Korea, our findings can readily be extrapolated to other countries. This generalisability stems from the underlying ecological principles uncovered, namely, the importance of leaving no propagule behind for achieving effective eradication outcomes. This fundamental principle is relevant, irrespective of geographic context, making it applicable across diverse regions; (6) Lastly, it is important to consider the potential environmental or ecological side effects of selective uprooting. For instance, hand-pulling to uproot all invasive plants can slightly disturb soil composition, potentially impacting soil microorganism communities and the legacy effects of soil on biogeochemical processes. Therefore, selective uprooting must be executed with meticulous care to minimise disturbances to the soil surface and other native species.
This study concludes that selective uprooting is a more effective tool than cutting for suppressing A. trifida invasion and increasing the diversity of native plant communities. The findings of this study support the expectation that uprooting of invasive species before flowering with minimum habitat disturbances can immediately reduce competition for remaining native species and concurrently can increase native diversity in the next growing season due to decreases in the number of seeds of A. trifida, the invasive species. Suppression of plant invasion further increased after sowing native seeds; however, this was only valid if the invasive plant was eradicated by uprooting. Therefore, sowing seeds to restore native diversity at sites where A. trifida invasion has been eradicated by cutting may result in the waste of native seeds, time and other resources. Sowing native seeds after removal of A. trifida by cutting and uprooting facilitated recovery of native diversity; however, uprooting followed by sowing native plants was more effective.
We thank Dr. Ho Choi and Dr. Norul Sobuj for their assistance with the fieldwork. We also thank Dr. Minwoo Oh for drawing the study site map in QGIS. We thank Eulsukdo Ecological Park Nakdonggang Estuary Eco Center for field cooperation.
The authors have declared that no competing interests exist.
No ethical statement was reported.
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2022R1A2C1003504). This study was supported by a joint research project from the Ministry of Environment, Republic of Korea (Project number: 2021002270004).
CB conceptualised and designed the study; CB, KS and JL collected data, CB analysed and constructed graphs and tables; CB, KS and JL wrote the manuscript; SHH, TKY and HK reviewed and edited the manuscript; CB and SHH engaged in project collaboration.
Chaeho Byun https://orcid.org/0000-0003-3209-3275
Kripal Singh https://orcid.org/0000-0003-2845-7160
Sun Hee Hong https://orcid.org/0000-0001-7581-0604
Jangho Lee https://orcid.org/0009-0006-3274-6378
Tae Kyung Yoon https://orcid.org/0000-0003-0627-0135
Hojeong Kang https://orcid.org/0000-0002-2088-6406
Dataset was shared in the open access file directories of Figshare. https://doi.org/10.6084/m9.figshare.26425879.
Supplementary information
Data type: docx
Explanation note: fig. S1. Sown species: Photographs of native seeds used in this study. fig. S2. Experimental layout (blocks) in two sites.
Diversity index raw datasheets
Data type: xlsx