Control Of Invasive Plants Research Articles

English

In this study, we investigated three different treatment options for controlling infestations of the aggressive Invasive Alien Plant Species (IAPS) Lantana camara at the Emantini Game Reserve in Swaziland. Treatment options included cut stump treatment, foliar spraying with herbicide and hand pulling using a manual plant puller. Results from this study indicated that foliar spraying significantly reduces new growth compared to other treatment options investigated. Associations between the various treatments and regrowth were not significant. Comparisons of the various treatments using a contribution index (CI) showed that foliar spraying is the most effective overall treatment for controlling L. camara at our study site. Foliar spraying worked best on plants less than 1.5 m high, but cut stump treatment was most effective for thickets where plants needed to be cut before being treated. To improve the effectiveness of foliar spraying, we suggest that this treatment option be used in combination with cut stump treatments. Findings from this study provide valuable information for the control of L. camara in different growth stages and levels of infestation. Recommendations for the control of this IAPS can be used in similar environments to effectively control infestations.   Key words: Invasive alien plant control, invasive alien plant species (IAPS), Lantana camara, Swaziland.

The Challenges of Alleviating Poverty through Ecological Restoration: Insights from South Africa's “Working for Water” Program

AbstractPublic works programs have been posited as win–win solutions for achieving societal goals for ecological restoration and poverty alleviation. However, little is documented regarding the challenges of implementing such projects. A commonly cited example is South Africa's invasive alien plant control program “Working for Water” (WfW), which aims to create employment via restoring landscapes invaded with alien plants. Recent studies have raised questions over the effectiveness of this program in achieving both its restoration and poverty alleviation goals. This is the first study that we are aware of that synthesizes the knowledge of managers on both the poverty alleviation and environmental outcomes of a public works project. Herein, we sought to understand the challenges and constraints faced by 23 WfW managers in fulfilling the program's environmental and poverty alleviation objectives. We found that the challenges most frequently cited by managers related to the capacity and competence of managers and teams, followed by challenges relating to planning and coordination, specifically the challenges of being flexible and adaptive when constrained by operating procedures. In addition, the current focus on maximizing short‐term employment was perceived by some as limiting the efficiency and long‐term effectiveness of the WfW program in achieving its environmental and social goals. We suggest that improving the conditions and duration of employment could improve the effectiveness of invasive alien plant control and ecological outcomes. We also suggest that WfW measure the impacts of their interventions through an adaptive management approach so that it can learn and adapt to the challenges it faces.

Toward Consensus-Based Actions that Balance Invasive Plant Management and Conservation of At-Risk Fauna

Limiting the spread of invasive plants has become a high priority among natural resource managers. Yet in some regions, invasive plants are providing important habitat components to native animals that are at risk of local or regional extirpation. In these situations, removing invasive plants may decrease short-term survival of the at-risk taxa. At the same time, there may be a reluctance to expand invaded habitats to benefit at-risk species because such actions may increase the distribution of invasive plants. Such a dilemma can result in "management paralysis," where no action is taken either to reduce invasive plants or to expand habitats for at-risk species. A pragmatic solution to this dilemma may be to develop an approach that considers site-specific circumstances. We constructed a "discussion tree" as a means of initiating conversations among various stakeholders involved with managing habitats in the northeastern USA to benefit several at-risk taxa, including New England cottontails (Sylvilagus transitionalis). Major components of this approach include recognition that expanding some invaded habitats may be essential to prevent extirpation of at-risk species, and the effective control of invasive plants is dependent on knowledge of the status of invasives on managed lands and within the surrounding landscape. By acknowledging that management of invasive plants is a complex issue without a single solution, we may be successful in limiting their spread while still addressing critical habitat needs.

Eradication and control of invasive alien plants in the Mediterranean Basin: towards better coordination to enhance existing initiatives

The European and Mediterranean Plant Protection Organization (EPPO), in the framework of its activities in the Mediterranean Basin, launched a questionnaire to gather information on eradication actions and control actions for invasive alien plants. Thirty‐four (34) eradication actions were reported, 16 occurring in Spain, 7 in Italy, 7 in France, 1 in Portugal, 1 in Malta, and 2 on the southern rim of the Mediterranean, with 1 in Israel and 1 in Tunisia. Twenty‐two (22) species were targeted, and the habitats where such actions were undertaken most frequently were coastal dunes, sandy shores and aquatic ecosystems. Most of the species that have been the object of an eradication action were known invasive species recorded in the EPPO lists, such as Ailanthus altissima, Buddleia davidii, Carpobrotus spp., Eichhornia crassipes, Ludwigia peploides, Pennisetum setaceum, Pistia stratiotes, Solanum elaeagnifolium and Sicyos angulatus. Other eradicated species have a limited distribution in the EPPO region and may represent emerging invasive plants, such as Ambrosia confertifolia, Cylindropuntia rosea, Leersia oryzoides, Leptochloa fusca subsp. uninervia and Marsilea drummondii. Control actions concerning 90 species were also reported. A large number of eradication actions, as well as management actions, are therefore happening in Mediterranean countries. At present countries appear to operate with complete autonomy, without consulting neighbouring countries or other stakeholders within the country. There is therefore a need for coordination of new eradication actions.

Vegetation response to removal of non-native feral pigs from Hawaiian tropical montane wet forest

Globally, non-native ungulates threaten native biodiversity, alter biotic and abiotic factors regulating ecological processes, and incur significant economic costs via herbivory, rooting, and trampling. Removal of non-native ungulates is an increasingly common and crucial first step in conserving and restoring native forests. However, removal is often controversial and there is currently little information on plant community responses to this management action. Here, we examine the response of native and non-native understory vegetation in paired sites inside and outside of exclosures across a 6.5–18.5 year chronosequence of feral pig (Sus scrofa) removal from canopy-intact Hawaiian tropical montane wet forest. Stem density and cover of native plants, species richness of ground-rooted native woody plants, and abundance of native plants of conservation interest were all significantly higher where feral pigs had been removed. Similarly, the area of exposed soil was substantially lower and cover of litter and bryophytes was greater with feral pig removal. Spatial patterns of recruitment were also strongly affected. Whereas epiphytic establishment was similar between treatments, the density of ground-rooted woody plants was four times higher with feral pig removal. Abundance of invasive non-native plants also increased at sites where they had established prior to feral pig removal. We found no patterns in any of the measured variables with time, suggesting that commonly occurring species recover within 6.5 years of feral pig removal. Recovery of species of conservation interest, however, was highly site specific and limited to areas that possessed remnant populations at the time of removal, indicating that some species take much longer (>18.5 years) to recover. Feral pig removal is the first and most crucial step for conservation of native forests in this area, but subsequent management should also include control of non-native invasive plants and outplanting native species of conservation interest that fail to recruit naturally.

Some Perspectives on the Risks and Benefits of Biological Control of Invasive Alien Plants in the Management of Natural Ecosystems

Globally, invasions by alien plants are rapidly increasing in extent and severity, leading to large-scale ecosystem degradation. Weed biological control offers opportunities to arrest or even reverse these trends and, although it is not always effective or appropriate as a management strategy, this practice has an excellent record of safety and many notable successes over two centuries. In recent years, growing concerns about the potential for unintended, non-target damage by biological control agents, and fears about other unpredictable effects on ecosystems, have created an increasingly demanding risk-averse regulatory environment. This development may be counter-productive because it tends to overemphasize potential problems and ignores or underestimates the benefits of weed biological control; it offers no viable alternatives; and it overlooks the inherent risks of a decision not to use biological control. The restoration of badly degraded ecosystems to a former pristine condition is not a realistic objective, but the protection of un-invaded or partial restoration of invaded ecosystems can be achieved safely, at low cost and sustainably through the informed and responsible application of biological control. This practice should therefore be given due consideration when management of invasive alien plants is being planned. This discussion paper provides a perspective on the risks and benefits of classical weed biological control, and it is aimed at assisting environmental managers in their deliberations on whether or not to use this strategy in preference, or as a supplement to other alien invasive plant control practices.

Specificity of extrafloral nectar induction by herbivores differs among native and invasive populations of tallow tree.

Invasive plants can be released from specialist herbivores and encounter novel generalists in their introduced ranges, leading to variation in defence among native and invasive populations. However, few studies have examined how constitutive and induced indirect defences change during plant invasion, especially during the juvenile stage. Constitutive extrafloral nectar (EFN) production of native and invasive populations of juvenile tallow tree (Triadica sebifera) were compared, and leaf clipping, and damage by a native specialist (Noctuid) and two native generalist caterpillars (Noctuid and Limacodid) were used to examine inducible EFN production. Plants from introduced populations had more leaves producing constitutive EFN than did native populations, but the content of soluble solids of EFN did not differ. Herbivores induced EFN production more than simulated herbivory. The specialist (Noctuid) induced more EFN than either generalist for native populations. The content of soluble solids in EFN was higher (2·1 times), with the specialist vs. the generalists causing the stronger response for native populations, but the specialist response was always comparable with the generalist responses for invasive populations. These results suggest that constitutive and induced indirect defences are retained in juvenile plants of invasive populations even during plant establishment, perhaps due to generalist herbivory in the introduced range. However, responses specific to a specialist herbivore may be reduced in the introduced range where specialists are absent. This decreased defence may benefit specialist insects that are introduced for classical biological control of invasive plants.

Effectiveness of Calluna-heathland restoration methods after invasive plant control

Restoring natural communities after invasive plant control is one of the fundamental challenges of ecological restoration. Despite advances in invasive control methods, restoration failures caused by a lack of native community re-establishment are common. This is especially frequent in the upland heathlands of Great Britain invaded by Pteridium aquilinum. As a consequence, active revegetation methods are needed to increase the performance of native plant species. Here, we assessed the effectiveness of Calluna-heathland vegetation restoration treatments on the developing plant community composition in combination with a set of recommended Pteridium-control methods applied at the local scale. Four stand-alone replicated experiments were set up in two regions of Great Britain. The experiments had a similar randomized block split- or split–split-plot design with six Pteridium-control treatments applied randomly to the main-plots (10m×40m); and Calluna-heathland vegetation site-specific restoration treatments applied to sub- and sub-sub-plots. The restoration treatments included stock-poof fencing, fertilizing, harrowing, seeding and prescribed litter-burning. The results showed that the effectiveness of site-specific Calluna-heathland restoration methods applied in conjunction with Pteridium-control methods was very low. Only sheep grazing and prescribed Pteridium-litter burning favoured the restoration of Calluna-heathland community composition. In contrast, fencing, fertilizing and harrowing were ineffective. Surprisingly, Calluna seeding only showed short-term positive effects when applied with asulam spray treatments. Considering the costs and benefits of the restoration measures studied as part of this integrated Pteridium-control/heathland restoration programme, the most successful methods were sheep grazing and prescribed Pteridium-litter burning; both are traditional methods of heathland management. It seems that effective restoration actions should initiate gradual change that aims to create a continuous transition to a more desirable conservation value state.

Invasive Alien Plants Elicit Reduced Production of Flowers and Fruits in Various Native Forest Species on the Tropical Island of Mauritius (Mascarenes, Indian Ocean)

Biological invasions constitute a major threat to biodiversity. However, while the impact of invasive alien animals on native biota is often unambiguous, the impacts of invasive alien plants (IAP) appear to be considerably less severe and, at times, more debatable. Invasion by alien plants co-occur with other drivers of habitat change such that assessing impacts of IAP independently of these other factors may be difficult. Generalisations can be misleading, because studies reveal different responses of native plants to the presence of IAP. Therefore, there is a need to understand general trends and exceptions within a particular habitat. In the island of Mauritius, mechanical control of invasive alien plants has been implemented for decades in lowland wet forests. Weeded and non-weeded areas are very similar in all aspects, except for the control of IAP, providing an opportunity to study how IAP are affecting native plants. We monitored the reproductive output of 20-40 individuals each, of nine selected native species from different forest strata, in both weeded and adjacent non-weeded areas in a lowlan d wet forest, through direct count/estimation of the number of flower buds, flowers and fruits. Flower bud, flower and fruit production were greater in the weeded area. These results are consistent with previous findings that noted greater regeneration of native trees in these areas. This study also provides clues to reported decline of shade tolerant understory vegetation in alien invaded forest and further stresses the importance of removing alien plants to restore biodiversity and function and achieve conservation success.

Evaluating Alternative Weed Management Strategies for Three Montana Landscapes

AbstractDetermining the best strategy for allocating weed management resources across and between landscapes is challenging because of the uncertainties and large temporal and spatial scales involved. Ecological models of invasive plant spread and control provide a practical tool with which to evaluate alternative management strategies at landscape scales. We developed a spatially explicit model for the spread and control of spotted knapweed and leafy spurge across three Montana landscapes. The objective of the model was to determine the ecological and economic costs and benefits of alternative strategies across landscapes of varying size and stages of infestation. Our results indicate that (1) in the absence of management the area infested will continue to increase exponentially leading to a substantial cost in foregone grazing revenues; (2) even though the costs of management actions are substantial, there is a net economic benefit associated with a broad range of management strategies; (3) strategies a that prioritize targeting small new infestations consistently outperform strategies that target large established patches; and (4) inconsistent treatment and short-term delays can greatly reduce the economic and ecological benefits of management.

Monitoring of the eggs of the Karkloof blue butterfly, <i>Orachrysops ariadne</i>, for its conservation management

The Endangered Orachrysops ariadne (Butler 1898) (Karkloof blue butterfly) is endemic to the Endangered Moist Midlands Grassland in KwaZulu-Natal, South Africa, and is extant at four sites. The results from the monitoring of the eggs laid by O. ariadne in a grassland area that is frequently burnt by poor rural people to ensure that palatable grass is available to their livestock, suggested the implementation of management interventions (fencing and firebreak burning) to prevent the local extinction of the butterfly. The number of eggs at the monitoring site declined dramatically between 2002 and 2003 and fluctuated after the management interventions were initiated properly in 2008, but had nearly reached the target number of 250 by 2013. An index count method for the monitoring of O. ariadne eggs at the other three known colonies, where plant invasion rather than uncontrolled burning is a major threat, was developed and shown to be efficient with regard to time relative to the number of eggs sampled. The host ant Camponotus natalensis (F. Smith 1858) (Natal sugar ant) was found to be present in all the host-plant patches at one colony site, indicating that all host-plant patches are likely to be breeding areas for the butterfly. Invasive plant control at and appropriate burning of the habitat of O. ariadne should assist in ensuring the survival of these colonies.Conservation implications: Adaptive monitoring and management of threatened endemic invertebrates and their habitats may be crucial for their continued survival. The development of efficient methods for the monitoring of such species is required where resources are limited, as threats to the species may cause sudden and irreversible declines in population size.

Control of Invasive Plants: Ecological and Socioeconomic Criteria for the Decision Making Process

Biological invasions have contributed to biodiversity loss, ecosystem degradation, and impairment of ecosystem services worldwide, requiring actions towards their prevention and control. Since human and monetary resources are both limited in most countries, priorities must be settled in the real world of biological invasion prevention and control. To support the decision making process regarding plant species already introduced, we propose a classification key, based upon biogeographical and ecological attributes of the target plant population. The key shall be applied to a particular biogeographical region, based on the premise that a species never invades two distinct ecosystems in the same way. The key categorizes the species according to the potential threats offered to the native biodiversity and ecosystem services in that region. Management strategies are recommended on the basis of both the species performance as invader and its economic importance in the region. We highlight the importance of ecological studies to categorize a species by the threats it offers to a specific ecological region, in order to avoid the waste of efforts and resources with non-risky species. Eradication experiments are equally important to find ecologically, technically and economically viable solutions for the problems derived from biological invasions.

Formas de preparo de solo e controle de plantas daninhas nos fatores agronômicos e de produção da mandioca

The study was conducted to evaluate ways of soil tillage and weed control on the production of cassava. Prior to planting the experiment, an area was left fallow, with a predominance of Brachiaria brizantha , and another area cultivated oat in the conventional tillage system. At the end of the cycle of oats the area was used for the experiment with cassava (cv IAC15). The experimental design was a randomized complete block with three treatments and six repetitions. The treatments corresponding to the types of tillage systems and crop driving were: T1-conventional tillage in the fallow and weed control (CT), T2 – No-till on the oat stubble without control of invasive plants (NTwwc) and T3 – No-till oat straw on the control of invasive plants (NTwc). For the treatment corresponding to conventional tillage (CT) of the experimental plots were prepared with a plow and a harrow leveling. The tillage was performed using mechanized planter. The harvest was performed 14 months after planting. The highest values for plant height and fresh weight of shoots were observed in treatments corresponding to the no-tillage system (NTwc and NTwwc). The greatest number of roots ha-1 was observed in NTwwc treatment differing only from the CT. No significant differences were observed for the fresh mass production of roots among the treatments. The highest value from starch content of roots obtained was in the NTwc treatment.

Linking Ecological Principles to Tools and Strategies in an EBIPM Program

I n ecosystems that are heavily invaded, it is common for the level of degradation to become so intense that the native plant seedbank is reduced. In these cases, active restoration that includes revegetation efforts and stress manipulations through herbicide use, tillage, periodic ooding, prescribed burning, or timely strategic grazing are often neces- sary to recover certain ecosystem functions. In wildlands and rangelands, herbicides and grazing are generally the most wide- ly used techniques for the control of invasive and weedy plants. Unlike cropland environments where all plants, except the crop, are considered to be weeds, in wildlands and rangelands there is often only one or a few invasive plants that are the target of control measures. These plants are generally grow- ing in association with several desirable species. Selectivity is then critical when developing an effective weed management program. Both strategic grazing and herbicides can be ap- plied selectively to alter the trajectory of a plant community to a more desired and functional state. DOI: 10.2458/azu_rangelands_v34i6_ditomaso

Complex interactions among biocontrol agents, pollinators, and an invasive weed: a structural equation modeling approach

Herbivores, seed predators, and pollinators can exert strong impacts on their host plants. They can also affect the strength of each other's impact by modifying traits in their shared host, producing super- or sub-additive outcomes. This phenomenon is especially relevant to biological control of invasive plants because most invaders are attacked by multiple agents. Unfortunately, complex interactions among agents are rarely studied. We used structural equation modeling (SEM) to quantify the effect of two biocontrol agents and generalist pollinators on the invasive weed Centaurea solstitialis, and to identify and quantify the direct and indirect interaction pathways among them. The weevil Eustenopus villosus is both a bud herbivore and a predispersal seed predator; the fly Chaetorellia succinea is also a predispersal seed predator; Apis mellifera is the primary pollinator. We conducted this work at three sites spanning the longitudinal range of C. solstitialis in California (USA) from the coast to the Sierra Nevada Mountains. SEM revealed that bud herbivory had the largest total effect on the weed's fecundity. The direct effect of bud herbivory on final seed set was 2-4 times larger in magnitude than the direct effect of seed predation by both agents combined. SEM also revealed important indirect interactions; by reducing the number of inflorescences plants produced, bud herbivory indirectly reduced the plant's attractiveness to ovipositing seed predators. This indirect, positive pathway reduced bud herbivory's direct negative effect by 11-25%. In the same way, bud herbivory also reduced pollinator visitation, although the magnitude of this pathway was relatively small. E. villosus oviposition deterred C. succinea oviposition, which is unfortunate because C. succinea is the more voracious of the seed predators. Finally, C. succinea oviposition indirectly deterred pollinator visitation, thereby enhancing its net effect on the plant. This study demonstrates the powerful insights that can be gained from the SEM approach in understanding the multiple direct and indirect interactions among agents and pollinators and their effects on an invasive weed. Such an approach may improve our ability to manage weeds with biocontrol agents by identifying pathways that could be exploited by future agents and minimizing the possibility of interference with established agents.

Challenges in invasive alien plant control in South Africa

CITATION: Van Wilgen, B. W. et al. 2012. Challenges in invasive alien plant control in South Africa. South African Journal of Science, 108(11/12), Art. #1445, doi:10.4102/sajs.v108i11/12.1445.

The effectiveness of classical biological control of invasive plants

Summary Invasive alien plants have serious economic and ecological impacts, for example, by displacing native plants and invertebrates, and their management is often costly and ineffective in the long term. Classical biological control using specialized, coevolved natural enemies from the native region of the invader is often advocated as a preferred alternative to chemical and mechanical control, but there is a lack of quantitative assessment of control of the target species and subsequent establishment of native vegetation and invertebrates. Meta‐analyses were carried out combining the results of 61 published studies (2000–2011) that quantified the impact of classical biocontrol at the level of individual target plants, target populations or non‐target vegetation. Factors associated with the control programmes (invasive region, native region, plant growth form, target longevity, control agent guild, taxonomy and study duration) were analysed to identify patterns in control success. On average, biocontrol agents significantly reduced plant size (28 ± 4%), plant mass (37 ± 4%), flower and seed production (35 ± 13% and 42 ± 9%, respectively) and target plant density (56 ± 7%). Beetles in the Chrysomelidae and Curculionidae families were more effective at reducing plant size than other groups. Non‐target plant diversity significantly increased by 88 ± 31% at sites where biocontrol agents were released, but it was largely unclear whether the replacement plant species were native or invasive. Synthesis and applications. The number of studies that provide quantitative indications of the effectiveness of biocontrol and the response of non‐target taxa has increased over the past decade, but remains small compared to the total number of publications on the classical biocontrol of invasive plants. Nonetheless, this study demonstrates the positive impacts of classical biocontrol and the re‐establishment of native plants in a broad range of systems and establishes the value of classical biocontrol for the control of invasive alien plants. The Chrysomelidae and Curculionidae families were the most effective agents and we recommend these be prioritized in cases where potential agents of different taxa have also been identified. In addition, data on the recovery of native plant species and the invertebrate community remain sparse and it is recommended that future studies report the identity of plant species that replace target species as well as invertebrate community responses.

Public Perception of Invasive Plant Species: Assessing the impact of workshop activities to promote young students' awareness

Invasive species are one of the main threats to biodiversity worldwide. Even though they are identified and recognized as such by the Portuguese law, the majority of the population is not yet aware of this problem. Aiming to increase awareness about biological invasions among young students, a workshop on Invasive Plant Species was organized at the Botanical Museum of the University of Coimbra. A total of 170 teenager students from five schools participated in the workshop. Three activities were prepared, focusing on: (1) identification of invasive plants, (2) competition between native and invasive plants and (3) control of invasive plants. One year later, questionnaires were sent to the participants, aiming to appraise workshop effectiveness, and this questionnaire revealed that these students know more about invasive plant species than a comparable group of students that did not participate in the workshop. The results clearly showed that practical informal education activities may be effective in raising public awareness. Questionnaires were essential to evaluate the knowledge acquired and retained by the students during the workshop.

The Art and Science of Restoration

The Art and Science of Restoration

Evaluating the cost-effectiveness of invasive alien plant clearing: A case study from South Africa

Conservation projects spend billions of dollars clearing invasive alien plants, yet few studies have measured the cost-effectiveness of doing this, especially over larger spatial and temporal scales, relevant to operational contexts. We evaluated the cost-effectiveness of South Africa’s national invasive alien plant control programme, Working for Water, in reducing invasive alien plant cover in the Krom and Kouga river catchments over 7years. We assessed change in invasive alien plant cover by comparing post-treatment cover with the first recorded pre-treatment cover across all 740 of the two project’s treatment sites (ranging from 0.03 to 227.6ha in size). We also used regression analysis to estimate the effect of predictor variables on the cost-effectiveness of invasive alien plant clearing. We found – by dividing the total costs by the change in invasive alien plant cover – that it cost 2.4 times more (1.5 times for the Krom, and 8.6 times for the Kouga project) to clear invaded land than the highest equivalent estimate made elsewhere. At current rates of clearing, it would take 54 and 695years to clear the catchments, in the Krom and Kouga, respectively, assuming no further spread. If spread is considered, current control efforts are inadequate, and invasions are likely to continue to spread in the catchments. Pre-treatment invasive alien plant cover and treatment costs per hectare had the greatest positive and negative influence, respectively on cost-effectiveness. Our assessment suggests that invasive alien plant control projects urgently need to monitor their cost-effectiveness so that management practices can be adapted to use scarce conservation funds more effectively.