Lessons learned from invasive plant control experiments: a systematic review and meta-analysis
TL;DR: It is suggested that information needed to inform invasive plant management can be better provided if researchers specifically address several limitations to successful invasive species control including: limited spatial and temporal scope of invasive plant control research, and incomplete evaluation of costs and benefits associated with invasive species management actions.
Abstract: Summary 1. Invasive plants can reduce biodiversity, alter ecosystem functions and have considerable economic impacts. Invasive plant control is therefore the focus of restoration research in invader-dominated ecosystems. Increasing the success of restoration practice requires analysis and synthesis of research findings and assessment of how experiments can be improved. 2. In a systematic review and meta-analysis of invasive plant control research papers, we asked: (i) what control efforts have been most successful; and (ii) what invasive plant control research best translates into successful restoration application? 3. The literature evaluated typically described experiments that were limited in scope. Most plot sizes were small (<1 m 2 ), time frames were brief (51% evaluated control for one growing season or less) and few species and ecosystems (predominantly grasslands) were studied throughout much of the literature. The scale at which most experiments were conducted potentially limits relevance to the large scales at which restorations typically occur. 4. Most studies focused on invasive species removal and lacked an evaluation of native revegetation following removal. Few studies (33%) included active revegetation even though native species propagule limitation was common. Restoration success was frequently complicated by re-invasion or establishment of a novel invader. 5. Few studies (29%) evaluated the costs of invasive species control. Additionally, control sometimes had undesirable effects, including negative impacts to native species. 6. Synthesis and applications. Despite a sizeable literature on invasive plant control experiments, many large-scale invasive plant management efforts have had only moderate restoration success. We identified several limitations to successful invasive species control including: minimal focus on revegetation with natives after invasive removal, limited spatial and temporal scope of invasive plant control research, and incomplete evaluation of costs and benefits associated with invasive species management actions. We suggest that information needed to inform invasive plant management can be better provided if researchers specifically address these limitations. Many limitations can be addressed by involving managers in research, particularly through adaptive management.
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TL;DR: 4 institutional frameworks that can facilitate science that will inform management, including boundary organizations, research scientists embedded in resource management agencies, formal links between decision makers and scientists at research-focused institutions, and training programs for conservation professionals are highlighted.
Abstract: There are many barriers to using science to inform conservation policy and practice. Conservation scientists wishing to produce management-relevant science must balance this goal with the imperative of demonstrating novelty and rigor in their science. Decision makers seeking to make evidence-based decisions must balance a desire for knowledge with the need to act despite uncertainty. Generating science that will effectively inform management decisions requires that the production of information (the components of knowledge) be salient (relevant and timely), credible (authoritative, believable, and trusted), and legitimate (developed via a process that considers the values and perspectives of all relevant actors) in the eyes of both researchers and decision makers. We perceive 3 key challenges for those hoping to generate conservation science that achieves all 3 of these information characteristics. First, scientific and management audiences can have contrasting perceptions about the salience of research. Second, the pursuit of scientific credibility can come at the cost of salience and legitimacy in the eyes of decision makers, and, third, different actors can have conflicting views about what constitutes legitimate information. We highlight 4 institutional frameworks that can facilitate science that will inform management: boundary organizations (environmental organizations that span the boundary between science and management), research scientists embedded in resource management agencies, formal links between decision makers and scientists at research-focused institutions, and training programs for conservation professionals. Although these are not the only approaches to generating boundary-spanning science, nor are they mutually exclusive, they provide mechanisms for promoting communication, translation, and mediation across the knowledge-action boundary. We believe that despite the challenges, conservation science should strive to be a boundary science, which both advances scientific understanding and contributes to decision making.
408 citations
Cites background from "Lessons learned from invasive plant..."
...This issue is exacerbated by the long time frames often required to publish research (Meffe 2001)....
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25 Feb 2013
TL;DR: Three basic questions arise: What kind of ecosystems are more (or less) likely to be invaded by alien plants, and what kind of plants are the most successful invaders and under what circumstances?
Abstract: Some 2500 yr ago, Heraclitus of Ephesus said that ‘All things change . . . and you cannot step twice into the same stream’. Today, ecologists would not only say the same about streams but also about vegetation. Plant communities change with time due to changes in the environment (Chapter 7), biotic interactions (Chapter 9) and invasions of alien species and genotypes, introduced intentionally or accidentally by humans. Invasions have received detailed attention only recently. There have always been migrating taxa, but now the rate of human-assisted introductions of new taxa is several orders of magnitude higher. In California, for example, more than 1000 alien plant species were intentionally or non-intentionally introduced and established viable populations over the last 250 yr. In the Galapagos Islands, over 3 million yr of their history, only one new plant species arrived with birds or sea currents every 10,000 yr. However, over the last 20 yr the introduction rate has been c. 10 species per yr, or some 100,000 times the natural arrival rate (Tye 2001). Three basic questions arise: 1 What kind of ecosystems are more (or less) likely to be invaded by alien plants? 2 What kind of plants are the most successful invaders and under what circumstances? 3 What is the impact of the plant invaders?
335 citations
TL;DR: The techniques of systematic reviewing widely adopted in other scientific disciplines are employed, to further the use of approaches in reviewing the literature that are as scientific, repeatable, and transparent as those employed in a primary study.
Abstract: Species introductions of anthropogenic origins are a major aspect of rapid ecological change globally. Research on biological invasions has generated a large literature on many different aspects of this phenomenon. Here, we describe and categorize some aspects of this literature, to better understand what has been studied and what we know, mapping well-studied areas and important gaps. To do so, we employ the techniques of systematic reviewing widely adopted in other scientific disciplines, to further the use of approaches in reviewing the literature that are as scientific, repeatable, and transparent as those employed in a primary study. We identified 2398 relevant studies in a field synopsis of the biological invasions literature. A majority of these studies (58%) were concerned with hypotheses for causes of biological invasions, while studies on impacts of invasions were the next most common (32% of the publications). We examined 1537 papers in greater detail in a systematic review. Superior competitive abilities of invaders, environmental disturbance, and invaded community species richness were the most common hypotheses examined. Most studies examined only a single hypothesis. Almost half of the papers were field observational studies. Studies of terrestrial invasions dominate the literature, with most of these concerning plant invasions. The focus of the literature overall is uneven, with important gaps in areas of theoretical and practical importance.
272 citations
Cites background from "Lessons learned from invasive plant..."
...Ideally, by using clearly defined protocols, the review process can be both repeated by others and more efficiently and accurately updated in the future (Littell et al. 2008)....
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TL;DR: This model of Phragmites establishment and reproduction describes the invasion as a symptom of watershed-scale land use and disturbance and advocates more holistic approaches to control and management that focus on improving water quality and minimizing human disturbance to deter future invasion and improve resilience of native plant communities.
Abstract: Studies on invasive plant management are often short in duration and limited in the methods tested, and lack an adequate description of plant communities that replace the invader following removal. Here we present a com- prehensive review of management studies on a single species, in an effort to elucidate future directions for research in invasive plant management. We reviewed the literature on Phragmites management in North America in an effort to synthesize our understanding of management efforts, identify gaps in knowledge and improve the efficacy of man- agement. Additionally, we assessed recent ecological findings concerning Phragmites mechanisms of invasion and integrated these findings into our recommendations for more effective management. Our overall goal is to examine whether or not current management approaches can be improved and whether they promote reestablishment of native plant communities. We found: (i) little information on community-level recovery of vegetation following removal of Phragmites; and (ii) most management approaches focus on the removal of Phragmites from individual stands or groups of stands over a relatively small area. With a few exceptions, recovery studies did not monitor vege- tation for substantial durations, thus limiting adequate evaluation of the recovery trajectory. We also found that none of the recovery studies were conducted in a landscape context, even though it is now well documented that land-use patterns on adjacent habitats influence the structure and function of wetlands, including the expansion of Phragmites. We suggest that Phragmites management needs to shift to watershed-scale efforts in coastal regions, or larger man- agement units inland. In addition, management efforts should focus on restoring native plant communities, rather than simply eradicating Phragmites stands. Wetlands and watersheds should be prioritized to identify ecosystems that would benefit most from Phragmites management and those where the negative impact of management would be minimal.
213 citations
TL;DR: How network-based principles might guide management policies to better live with invaders, rather than to undertake the daunting (and often illusory) task of eradicating them one by one is discussed.
Abstract: We review empirical studies on how bioinvasions alter food webs and how a food-web perspective may change their prediction and management. Predation is found to underlie the most spectacular damage in invaded systems, sometimes cascading down to primary producers. Indirect trophic effects (exploitative and apparent competition) also affect native species, but rarely provoke extinctions, while invaders often have positive bottom-up effects on higher trophic levels. As a result of these trophic interactions, and of nontrophic ones such as mutualisms or ecosystem engineering, invasions can profoundly modify the structure of the entire food web. While few studies have been undertaken at this scale, those that have highlight how network properties such as species richness, phenotypic diversity, and functional diversity, limit the likelihood and impacts of invasions by saturating niche space. Vulnerable communities have unsaturated niche space mainly because of evolutionary history in isolation (islands), dispersal limitation, or anthropogenic disturbance. Evolution also modulates the insertion of invaders into a food web. Exotics and natives are evolutionarily new to one another, and invasion tends to retain alien species that happen to have advantage over residents in trophic interactions. Resident species, therefore, often rapidly evolve traits to better tolerate or exploit invaders—a process that may eventually restore more balanced food webs and prevent extinctions. We discuss how network-based principles might guide management policies to better live with invaders, rather than to undertake the daunting (and often illusory) task of eradicating them one by one.
178 citations
Cites background from "Lessons learned from invasive plant..."
...Given that invasive species are notoriously difficult to remove (Gardener et al., 2010; Kettenring and Adams, 2011), it may be interesting to try to maintain ecological networks that...
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...Given that invasive species are notoriously difficult to remove (Gardener et al., 2010; Kettenring and Adams, 2011), it may be interesting to try to maintain ecological networks that are inherently difficult to invade....
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1,772 citations
TL;DR: For example, this paper found that areas of low plant spe- cies richness may be invaded more easily than areas of high plant species richness, and that this pattern may be more closely related to the degree resources are available in native plant communities, independent of species richness.
Abstract: Some theories and experimental studies suggest that areas of low plant spe- cies richness may be invaded more easily than areas of high plant species richness. We gathered nested-scale vegetation data on plant species richness, foliar cover, and frequency from 200 1-m 2 subplots (20 1000-m 2 modified-Whittaker plots) in the Colorado Rockies (USA), and 160 1-m 2 subplots (16 1000-m 2 plots) in the Central Grasslands in Colorado, Wyoming, South Dakota, and Minnesota (USA) to test the generality of this paradigm. At the 1-m 2 scale, the paradigm was supported in four prairie types in the Central Grasslands, where exotic species richness declined with increasing plant species richness and cover. At the 1-m 2 scale, five forest and meadow vegetation types in the Colorado Rockies contradicted the paradigm; exotic species richness increased with native-plant species richness and foliar cover. At the 1000-m 2 plot scale (among vegetation types), 83% of the variance in exotic species richness in the Central Grasslands was explained by the total percentage of nitrogen in the soil and the cover of native plant species. In the Colorado Rockies, 69% of the variance in exotic species richness in 1000-m 2 plots was explained by the number of native plant species and the total percentage of soil carbon. At landscape and biome scales, exotic species primarily invaded areas of high species richness in the four Central Grasslands sites and in the five Colorado Rockies vegetation types. For the nine vegetation types in both biomes, exotic species cover was positively correlated with mean foliar cover, mean soil percentage N, and the total number of exotic species. These patterns of invasibility depend on spatial scale, biome and vegetation type, spatial autocorrelation effects, availability of resources, and species-specific responses to grazing and other disturbances. We conclude that: (1) sites high in herbaceous foliar cover and soil fertility, and hot spots of plant diversity (and biodiversity), are invasible in many landscapes; and (2) this pattern may be more closely related to the degree resources are available in native plant communities, independent of species richness. Exotic plant in- vasions in rare habitats and distinctive plant communities pose a significant challenge to land managers and conservation biologists.
1,069 citations
TL;DR: This model does not represent the only evolutionary pathway to invasiveness, but is clearly an underappreciated mechanism worthy of more consideration in explaining the evolution ofinvasiveness in plants.
Abstract: Invasive species are of great interest to evolutionary biologists and ecologists because they represent historical examples of dramatic evolutionary and ecological change. Likewise, they are increasingly important economically and environmentally as pests. Obtaining generalizations about the tiny fraction of immigrant taxa that become successful invaders has been frustrated by two enigmatic phenomena. Many of those species that become successful only do so (i) after an unusually long lag time after initial arrival, and/or (ii) after multiple introductions. We propose an evolutionary mechanism that may account for these observations. Hybridization between species or between disparate source populations may serve as a stimulus for the evolution of invasiveness. We present and review a remarkable number of cases in which hybridization preceded the emergence of successful invasive populations. Progeny with a history of hybridization may enjoy one or more potential genetic benefits relative to their progenitors. The observed lag times and multiple introductions that seem a prerequisite for certain species to evolve invasiveness may be a correlate of the time necessary for previously isolated populations to come into contact and for hybridization to occur. Our examples demonstrate that invasiveness can evolve. Our model does not represent the only evolutionary pathway to invasiveness, but is clearly an underappreciated mechanism worthy of more consideration in explaining the evolution of invasiveness in plants.
1,012 citations
TL;DR: There is reasonable empirical evidence to suggest that genetic differentiation through rapid evolutionary change is important in plant invasions, and conceptual and methodological issues associated with cross-continental comparisons are discussed.
Abstract: Plant invasions often involve rapid evolutionary change. Founder effects, hybridization, and adaptation to novel environments cause genetic differentiation between native and introduced populations and may contribute to the success of invaders. An influential idea in this context has been the Evolution of Increased Competitive Ability (EICA) hypothesis. It proposes that after enemy release plants rapidly evolve to be less defended but more competitive, thereby increasing plant vigour in introduced populations. To detect evolutionary change in invaders, comparative studies of native versus introduced populations are needed. Here, we review the current empirical evidence from: (1) comparisons of phenotypic variation in natural populations; (2) comparisons of molecular variation with neutral genetic markers; (3) comparisons of quantitative genetic variation in a common environment; and (4) comparisons of phenotypic plasticity across different environments. Field data suggest that increased vigour and reduced herbivory are common in introduced plant populations. In molecular studies, the genetic diversity of introduced populations was not consistently different from that of native populations. Multiple introductions of invasive plants appear to be the rule rather than the exception. In tests of the EICA hypothesis in a common environment, several found increased growth or decreased resistance in introduced populations. However, few provided a full test of the EICA hypothesis by addressing growth and defence in the same species. Overall, there is reasonable empirical evidence to suggest that genetic differentiation through rapid evolutionary change is important in plant invasions. We discuss conceptual and methodological issues associated with cross-continental comparisons and make recommendations for future research. When testing for EICA, greater emphasis should be put on competitive ability and plant tolerance. Moreover, it is important to address evolutionary change in characteristics other than defence and growth that could play a role in plant invasions.
944 citations
TL;DR: This work devised a set of guidelines for undertaking formalized systematic review, based on a health services model, and highlights critical modifications to guidelines for protocol formulation, data‐quality assessment, data extraction, and data synthesis for conservation and environmental management.
Abstract: An increasing number of applied disciplines are utilizing evidence-based frameworks to review and disseminate the effectiveness of management and policy interventions. The rationale is that increased accessibility of the best available evidence will provide a more efficient and less biased platform for decision making. We argue that there are significant benefits for conservation in using such a framework, but the scientific community needs to undertake and disseminate more systematic reviews before the full benefit can be realized. We devised a set of guidelines for undertaking formalized systematic review, based on a health services model. The guideline stages include planning and conducting a review, including protocol formation, search strategy, data inclusion, data extraction, and analysis. Review dissemination is addressed in terms of current developments and future plans for a Web-based open-access library. By the use of case studies we highlight critical modifications to guidelines for protocol formulation, data-quality assessment, data extraction, and data synthesis for conservation and environmental management. Ecological data presented significant but soluble challenges for the systematic review process, particularly in terms of the quantity, accessibility, and diverse quality of available data. In the field of conservation and environmental management there needs to be further engagement of scientists and practitioners to develop and take ownership of an evidence-based framework.
848 citations