Factors explaining alien plant invasion success in a tropical ecosystem differ at each stage of invasion (original) (raw)
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Diversity and Distributions, 2011
Aim We used alien plant species introduced to a botanic garden to investigate the relative importance of species traits (leaf traits, dispersal syndrome) and introduction characteristics (propagule pressure, residence time and distance to forest) in explaining establishment success in surrounding tropical forest. We also used invasion scores from a weed risk assessment protocol as an independent measure of invasion risk and assessed differences in variables between high-and low-risk species.
Factors Associated with Alien Plants Transitioning from Casual, to Naturalized, to Invasive
Conservation Biology, 2008
To explain current plant invasions, or predict future ones, more knowledge on which factors increase the probability of alien species becoming naturalized and subsequently invasive is needed. We created a database of the alien plants in seminatural habitats in Ireland that included data on taxonomy, invasive status, invasion history, distribution, and biological and ecological plant characteristics. We used information from this database to determine the importance of these factors in increasing the ability of species to become naturalized and invasive. More specifically, we used two multiple logistic regressions to identify factors that distinguish naturalized from casual alien plant species and invasive from noninvasive, naturalized alien species. Clonal growth, moisture-indicator value, nitrogen-indicator value, native range, and date of first record affected (in order of decreasing importance) the probability of naturalization. Factors that distinguished invasive from noninvasive species were ornamental introduction, hermaphrodite flowers, pollination mode, being invasive elsewhere, onset of flowering season, moisture-indicator value, native range, and date of first record. Incorporation of phylogenetic information had little influence on the results, suggesting that the capacity of alien species to naturalize and become invasive evolved largely independently in several phylogenetic lineages. Whereas some of the variables were important for both transitions, others were only important for naturalization or for invasion. This emphasizes the importance of studying different stages of the invasion process when looking for mechanisms of becoming a successful invasive plant, instead of simply comparing invasive with noninvasive alien species. Our results also suggest that a combination of species traits and other variables is likely to produce the most accurate prediction of invasions.
Biotropica, 2014
Continental tropical forests are thought to be resistant to alien plant invasion due to a lack of disturbance, or low propagule pressure from introduced species. We assessed the importance of disturbance and edge effects by surveying areas of submontane and lowland forest of Amani Nature Reserve in the East Usambara mountains, Tanzania. These areas are in the vicinity of Amani Botanic Garden (ABG)-a propagule source for many alien plant species. We surveyed three edges in the vicinity of the ABG plantations, using plots interspersed along multiple 250 m transects. Survey plots were either in secondary or seminatural forest, representing a difference in past disturbance). Alien plant species richness and abundance declined with increasing distance from forest edges, indicating that edge effects were important. In addition, the effect of distance on richness and abundance of alien species as adults was much smaller in seminatural than secondary forest, emphasizing that invasion of seminatural forest is less likely to occur. Abundance and occurrence of individual species showed broadly similar declines with increasing distance from the forest edge, and lower abundance in seminatural compared to secondary forest. Alien species were dominant in 15 percent of plots surveyed. As 28 percent of the Amani nature reserve forest is within 250 m of an edge, the importance of disturbance and edges could make a potentially large proportion of the forest vulnerable to alien species invasion.
Influential factors and barriers change along the invasion continuum of an alien plant
Biological Invasions, 2023
Upon arrival to a new area, alien species have to overcome a series of biotic and abiotic barriers to survive, reproduce, and spread and thus, succeed along the invasion continuum. Failing to understand the role of the different sets of barriers and factors operating across the stages of the invasion continuum limit our ability to predict invasion dynamics, leading to misinformed management. Here, we explore how the European plant Cytisus scoparius overcomes the survival and reproductive barriers to establish along the roadsides of Nahuel Huapi National Park (Argentina). We evaluate the direct and indirect influence of climatic and landscape factors, species traits and their interaction with patch cover, plant height, and pollinator visitation rates as proxies of population persistence, plant growth, and reproduction, respectively. Cytisus scoparius cover was positively associated with the length of water shores and urban cover, factors that may relate to the arrival of propagules, new introduction events, and high levels of disturbance. Plant height was positively associated with annual precipitation and mean temperature. Visitation rates positively related to shrubland cover and to a lesser extent to slope, two factors that may influence pollinator availability and long-distance detectability, respectively. However, factors positively affecting survival had no effect (in the case of height) or negative effect (in the case of cover) on visitation rates, probably due to the saturation of the pollinator
Plants
To understand the factors that limit invasive expansion in alien species, it is critical to predict potential zones of colonization. Climatic niche can be an important way to predict the potential distribution of alien species. This correlation between niche and geographic distribution is called Hutchinson’s duality. A combination of global and regional niches allows four invasive stages to be identified: quasi-equilibrium, local adaptation, colonization and sink stage. We studied the invasive stages of six alien leguminous species either in the niche or the geographical space. In five of the six species, a higher proportion of populations were in the quasi-equilibrium stage. Notably, Acacia species had the highest proportion of populations in local adaptation. This picture changed dramatically when we projected the climatic niche in the geographic space: in all species the colonization stage had the highest proportional projected area, ranging from 50 to 90%. Our results are consis...
Journal of Asia-Pacific Biodiversity, 2018
Climate change, fire and habitat loss have been linked separately with selected aspect(s) of alien plant invasion. No attempt has also been made to simultaneously understand the linkages that exist among the three issues. There is a need of scientific literature that inter-links the three phenomena simultaneously with all the aspects of alien plant invasion. This would help to develop a comprehensive understanding about the role played by the issues directly and indirectly in magnifying habitat invasion. The present review is the first attempt to reveal in detail the complex environmental and ecological processes that synergistically link the issues with one-another and alien plant invasion. Scores were also assigned to secondary information and analyzed statistically. The three phenomena were precisely found to increase the problem through direct or indirect effects. While devising mitigation measures, such inter-linkages must be taken into account so that alien plant species could be managed efficiently.
Biological Conservation, 2004
Invasion of natural ecosystems by exotic species is a major threat to biodiversity globally. We assessed two alternative (but not exclusive) hypotheses to explain the success of exotic species in urban bushland on low fertility sandstone-derived soils in Sydney, Australia. These were that success of exotic species is promoted by: (1) plant attributes in particular disturbance types; and (2) freedom from herbivores. We tested these at sites subject to different types of disturbance: nutrient and water enrichment (below stormwater outlets), nutrient enrichment (riparian zones of creeks with an urban catchment) and physical disturbance (tracks), and control sites. At each site we estimated percentage cover of all species and surveyed leaves for damage by herbivores. Species were classified as native, non-invasive exotic or invasive exotic. We found that sites without any disturbance did not support exotic plants. Physically disturbed sites on low fertility soils supported only one exotic species, suggesting that nutrient enrichment is a critical prerequisite for exotic species invasion on low fertility soils. Exotic species cover was highest and native species richness most reduced in areas of highest nutrient enrichment. Both invasive exotic and non-invasive exotic species had significantly lower levels of leaf herbivory than native species, implying that release from pests alone cannot account for the success of invasive species. Specific leaf area of invasive exotic species was consistently higher than specific leaf area of non-invasive exotic and native species, regardless of disturbance type. In physically disturbed sites of higher soil fertility, exotic species were small herbs and grasses of long flowering duration and with small unassisted or wind-dispersed seeds. In sites subject to nutrient-enrichment, exotic species were more likely to be climbers, able to propagate vegetatively, and with seeds dispersed by vertebrates. Thus different plant attributes contribute to exotic species success under different disturbance types. The clearest consistent difference we found between invasive exotic and non-invasive exotic species was in specific leaf area, suggesting that large specific leaf area facilitates invasiveness.
Minimizing Risks of Invasive Alien Plant Species in Tropical Production Forest Management
Timber production is the most pervasive human impact on tropical forests, but studies of logging impacts have largely focused on timber species and vertebrates. This review focuses on the risk from invasive alien plant species, which has been frequently neglected in production forest management in the tropics. Our literature search resulted in 114 publications with relevant information, including books, book chapters, reports and papers. Examples of both invasions by aliens into tropical production forests and plantation forests as sources of invasions are presented. We discuss species traits and processes affecting spread and invasion, and silvicultural practices that favor invasions. We also highlight potential impacts of invasive plant species and discuss options for managing them in production forests. We suggest that future forestry practices need to reduce the risks of plant invasions by conducting surveillance for invasive species; minimizing canopy opening during harvesting; encouraging rapid canopy closure in plantations; minimizing the width of access roads; and ensuring that vehicles and other equipment are not transporting seeds of invasive species. Potential invasive species should not be planted within dispersal range of production forests. In invasive species management, forewarned is forearmed.
Forestry Studies
Morni Hills of Panchkula district, Haryana harbor floristically important tropical dry deciduous forests and are quite enriched with the phytodiversity of medicinally important plant species. But these forests are under huge pressure due to anthropogenic activities facilitating the establishment and spread of invasive plant species. So, the present study was conducted in the forests of Morni Hills to understand the ecology of invasive alien plant species growing there. During the study, the area was colonized by many invasive alien plant species, such as Ageratum conyzoides L., A. haustonianum Mill., Chromolaena odorata (L.) R.M. King & H. Rob., Lantana camara L., etc. In terms of longevity, the annual growth form dominated over the perennial. The family Asteraceae was dominant with 11 species, followed by Malvaceae and others. The biological spectrum showed that the dominant life form was therophytes followed by phanerophytes and others, indicating vegetation disturbance while duri...