Does restoration help the conservation of the threatened forest of Robinson Crusoe Island? The impact of forest gap attributes on endemic plant species richness and exotic invasions

Invasive plant species are major drivers of biodiversity losses, especially on islands which are prone to invasions and extinctions. In the “endemic montane forest” of Robinson Crusoe Island (Pacific Ocean, Chile) invasive exotic plant species threaten conservation efforts by establishing in gaps and outcompeting native tree species regeneration. We compared gap attributes and ground vegetation cover in three gap types: those dominated by native species (<5 % cover of invasive species), invaded gaps (>30 % cover by invasive species), and treated gaps (invasive species removed). We examined (a) which gap attributes favored native and exotic species, (b) the relationship between gap size and species richness, and (c) species responses to invasion and treatment. Gaps ranged in size from 46 to 777 m² caused mainly by uprooted and snapped trees. Multi response permutation procedures showed a different floristic composition between natural, invaded and treated gaps. The presence of Myrceugenia fernandeziana (native species) and Aristotelia chilensis (invasive species) as gap border trees was positively and negatively correlated with native species richness, respectively. New gaps had more native species than old gaps, and smaller gaps contained relatively more native species than larger ones. An increase in invasive species cover was related to a decline in native species cover and richness. 1–6 years after treatment gaps tended to recover their native floristic composition. Highly effective conservation management programs will concentrate on monitoring gap creation, early control of invasive species, and by treating smaller gaps first.     

Invasive plant species thresholds in the forests of Robinson Crusoe Island,Chile

Background: Invasion by exotic plants worldwide can lead to the loss of native species, particularly on islands with a high proportion of endemic plants, such as Robinson Crusoe Island (RCI).

Aims: We studied the two most invasive exotic plant species occurring in the forest of RCI: Aristotelia chilensis and Rubus ulmifolius. We aimed at establishing thresholds for environmental and microsite variables related to invasion.

Methods: Environmental and forest understorey variables, including canopy gaps and invasive species cover were measured in non-invaded and invaded forest sites. We expected more invasion in plots located close to invasive shrublands, and in large gaps with high solar radiation.

Results: We found no relationship between the distance to invasive shrublands and invasion probability. Solar radiation tended to be slightly related with a higher cover of R. ulmifolius, the most abundant invasive exotic plant in RCI forests. Overall, the cover of native ferns appeared to inhibit invasion.

Conclusions: The identification of variable thresholds related to invasion can be useful for guiding management decisions. Our results suggest that management should consider monitoring forest canopy gap formation and promote the establishment of ferns to reduce the probability of invasive species establishing.     

Determinants of plant species invasions in an arid island: evidence from Socotra Island (Yemen)

Understanding the factors which affect the distribution of alien plants in arid islands is complicated by the complex and stochastic nature of the invasion process per se, the harsh environmental conditions, and the low number of researchers and sampling effort. We present the results of the most comprehensive inventory to date of alien vascular plant species occurring in Socotra Island, a global biodiversity hotspot just beginning to be developed. A floristic survey was conducted between 2006 and 2008 in 36 grid cells of 10?×?10?km. We integrated this data from this survey with those from scientific literature. We recorded 88 alien plant species. Tree and herbaceous species were the most common growth forms. Species from Asia and edible species were prevalent. We identified 80 species considered weeds worldwide with >50?% adapted to arid conditions. We used a two-part model to analyze the spatial distribution of naturalized and alien plant species in relation to environmental and anthropogenic factors. Altitude and human-related factors play a significant role in the distribution of both naturalized and invasive species. Notably, the latter can potentially spread mainly in the alluvial basal areas. This study underpins the knowledge about alien species and their spatial distribution in Socotra Island. It provides a baseline for plant invasion management and contributes data for the analyses of invasion processes on islands worldwide.     

Woody exotic plant invasions and fire: reciprocal impacts and consequences for native ecosystems

Fire regimes influence and are influenced by the structure and composition of plant communities. This complex reciprocal relationship has implications for the success of plant invasions and the subsequent impact of invasive species on native biota. Although much attention has been given to the role of invasive grasses in transforming fire regimes and native plant communities, little is known about the relationship between woody invasive species and fire regime. Despite this, prescribed burning is frequently used for managing invasive woody species. In this study we review relationships between woody exotic plant invasions and fire in invaded ecosystems worldwide. Woody invaders may increase or decrease aspects of the fire regime, including fire frequency, intensity and extent. This is in contrast to grass invaders which almost uniformly increase fire frequency. Woody plant invasion can lead to escape from a grass-fire cycle, but the resulting reduction in fire frequency can sometimes lead to a cycle of rare but more intense fires. Prescribed fires may be a useful management tool for controlling woody exotic invaders in some systems, but they are rarely sufficient to eliminate an invasive species, and a dearth of controlled experiments hampers evaluation of their benefits. Nevertheless, because some woody invaders have fuel properties that differ substantially from native species, understanding and managing the impacts of woody invaders on fire regimes and on prescribed burns should become an important component of resource and biodiversity management.     

Temporal changes in the island flora at different scales in the archipelago of SW Finland

Question: How have species richness and vegetation patterns changed in a group of islands in the northern Baltic Sea over a 58‐yr period of changing land use and increasing eutrophication? Location: A group of 116 islands, the Brunskär sub‐archipelago, in SW Finland. Methods: A complete survey of vascular plant species performed in 1947–1949 by Skult was repeated by our group using the same methodology in 2005–2007 (historical versus contemporary, respectively). DCAs were performed and total number of species, extinction–colonization rates, species frequency changes and mean Ellenberg indicator values for light, moisture and nitrogen and Eklund indicator values for dependence of human cultural influence were obtained for each island and relevé. Results: Species richness has declined on large islands and increased on small islands. The increase in number of species on small islands is driven by a strong increase in frequency of shore species, which in turn is induced by more productive shores. The decrease in species richness on large islands is related to overgrowth of open semi‐natural habitats after cessation of grazing and other agricultural practices. Conclusions: After the late 1940s, open habitats, which were created and maintained by cattle grazing and other traditional agricultural activities, have declined in favour of woody shrub and forest land. Shores have been stabilized and influenced by the eutrophication of the Baltic Sea, and the vegetation has become more homogeneous. This development, resulting in lower species diversity, poses a challenge for the preservation of biodiversity both on a local and on a landscape level.     

A taxonomic,biogeographical and ecological overview of invasive woody plants

Abstract. Invasive plants are considered to be a major threat to the earth's biodiversity, but have not been sufficiently investigated. To address this problem a relational database on invasive woody plants has been set up. It is based on 2045 bibliographical references and contains records on 653 species representing 110 families. The families with the largest number of invasive species are: Rosaceae, Mimosaceae, Papilionaceae and Pinaceae. Out of 1060 recorded invasive events an equal number are reported from continents and oceanic islands. The highest number of invasive woody species are recorded from Europe, followed by the Pacific islands, North America, New Zealand, Australia, Indian Ocean islands and southern Africa. Included in these regions are areas which have fewer highly invasive species, e.g. islands on continental shelves, such as the British Isles. Although most invasions occur in disturbed habitats, most natural communities are susceptible to woody plant invasions. Data on species attributes are only available for a minority of species but indicate that invasive woody plant species may be either insect or wind-pollinated, have a wide array of fruit types, fruit and seed sizes, number of seeds per fruit and dispersal agents. The relative frequency of several attributes varies with the degree of invasiveness. Thus it is not yet possible to determine which set of attributes favours invasiveness and therefore it is difficult to make predictions.     

Effects of experimental manipulation of light and nutrients on establishment of seedlings of native and invasive woody species in Long Island,NY forests

While earlier studies on the process of invasion often focused on single factors or on the general explanation of ‘disturbance,’ recent work has attempted to move towards a more mechanistic understanding of the factors that promote plant community invasion. Manipulative experiments provide a means for discerning causal relationships and interactive effects of environmental factors in promoting invasion; such experiments have been conducted in a number of grassland and shrub ecosystems. This study extends multifactor manipulative experiments into forest communities to compare factors influencing early seedling establishment for native and invasive woody plants. In Long Island, NY, invasion patterns are correlated with forest community type (pine barrens or hardwood), light availability, and soil N and Ca. We conducted manipulative field experiments in two different years to determine the relative importance and interaction of experimental gaps and N and Ca addition in pine barrens and hardwood forests in promoting invasion. We used seedlings of seven common native and invasive species in the first experiment, and 16 native and invasive species paired phylogenetically in the second experiment. Light had the strongest effect on plant growth; all plants grew more in gaps. We found no difference in the average growth rates of native and invasive species. Invasives responded more to high resources than did natives, with highest relative growth rates in gaps in the more fertile soils of the hardwood forests. Opportunities for invasion may differ from year to year, with differential success of invaders only in some years and under some environmental conditions. Clearly, to understand the complex interactions between resources and invasion in forests will require many manipulative experiments across a range of environments and using suites of invasive and native species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Invasion of alien woody plants on the islands of Mahé and Silhouette,Seychelles

Abstract. A method is presented for a quick and easily repeatable evaluation of the state of invasion of alien woody plants and the ecological status (prominence value, diversity, singularity and rejuvenation) of potentially important biodiversity sites in the Seychelles. The usefulness of this method has been tested in a survey on the islands of Mahé and Silhouette. The survey revealed 34 species as invasive alien species, the most prominent being Cinnamomum zeylanicum, Psidium littorale, Adenanthera pavonina and Tabebuia pallida. The greatest intensity of invasion was recorded in Intermediate Forests on moderate or gentle slopes and in stream ravines protected from desiccating winds and insolation. ‘Mountain Mist Forests’, ‘Palm Forests’ and ‘Glacis’ are the least invaded vegetation types. The difference in prominence values of alien and native plant species between leeward and windward sides is significant. Glacis habitats do not show a decline in protection values with decreasing altitude. Prominence values and percentage frequency of invaders are exceeded by the endemic palm Phoenicophorium borsigianum which is able to maintain itself in areas suffering from forest destruction and topsoil erosion.     

Plant invasions on small Mediterranean islands: An overview

Biological invasions have become one of the main drivers of habitat degradation and a leading cause of biodiversity loss in island ecosystems worldwide. The spread of invasive species poses a particular environmental threat on the islands of the Mediterranean Basin, which are hot spots of biodiversity and contain rare habitats and endemic species, especially on small islands, which are highly vulnerable to biodiversity loss. Following a recent survey, in this paper we aim to provide an overview of the present-day non-native vascular flora of small Mediterranean islands based on a sample of 37 islands located in the middle of the Mediterranean Sea, off the coast of Italy. By comparing the current data with those gathered during a previous survey conducted in the same study area, we also aim to highlight the main changes that have occurred in non-native plant species diversity, establishment and distribution in recent years and to present a first general overview of the most prominent plant taxa in the island’s introduced flora, focusing on those most responsible for these changes and those that pose the greatest environmental threats. We recorded 203 non-native plant species, 147 of which have established on at least one of the islands investigated. Overall, we detected a sharp increase in the number of species, in their levels of establishment and in the extent of their distribution within the study area in recent years. This may be explained by the intensification of research on plant invasions, as well as to new introduction, escape, establishment and invasion events on the islands in recent decades. The most remarkable plants detected include acacias and succulents, two groups that appear to be emerging very rapidly and to be posing new threats to the conservation of the islands’ natural environment, especially the genus Carpobrotus, whose spread into natural habitats containing rare and endemic taxa is seriously threatening biodiversity on both a local and global scale. On the whole, our results show that the plant invasion phenomenon in the study area has in recent years intensified considerably. As this process seems likely to continue, we should expect more establishment events in the future and the further spread of species that are already present. This is of particular conservation concern on the islands investigated in this survey, which are rich in endemisms, but have been facing deep socio-economic and environmental transformations in these last decades as a consequence of the abandonment of traditional management practices and the development of tourism. Our study thus confirms that plant invasions on Mediterranean islands are a serious environmental problem that threatens biodiversity conservation not only in the Mediterranean biogeographic region, but also on the global scale, and highlights the need to further increase efforts aimed at preventing, controlling or mitigating the effects of plant invasions in island ecosystems.     

Invasion of temperate deciduous broadleaf forests by N-fixing tree species – consequences for stream ecosystems

Biological invasions are a major threat to biodiversity and ecosystem functioning. Forest invasion by alien woody species can have cross-ecosystem effects. This is especially relevant in the case of stream–riparian forest meta-ecosystems as forest streams depend strongly on riparian vegetation for carbon, nutrients and energy. Forest invasion by woody species with dissimilar characteristics from native species may be particularly troublesome. The invasion of temperate deciduous broadleaf forests with low representation of nitrogen (N)-fixing species by N-fixers has the potential to induce ecosystem changes at the stream level. Although effects of tree invasion on stream ecosystems have been under assessed, knowledge of native and invasive tree characteristics allows prediction of invasion effects on streams. Here we present a conceptual model to predict the effects of forest invasion by alien N-fixing species on streams, using as a background the invasion of temperate deciduous broadleaf forests by leguminous Acacia species, which are among the most aggressive invaders worldwide. Effects are discussed using a trait-based approach to allow the model to be applied to other pairs of invaded ecosystem–invasive species, taking into account differences in species traits and environmental conditions. Anticipated effects of N-fixing species invasions include changes in water quality (increase in N concentration) and quantity (decrease in flow) and changes in litter input characteristics (altered diversity, seasonality, typology, quantity and quality). The magnitude of these changes will depend on the magnitude of differences in species traits, the extent and duration of the invasion and stream characteristics (e.g. basal nutrient concentration). The extensive literature on effects of nutrient enrichment of stream water, water scarcity and changes in litter input characteristics on aquatic communities and processes allows prediction of invasion effects on stream structure and function. The magnitude of invasion effects on aquatic communities and processes may, however, depend on interactions among different pathways (e.g. effects mediated by increases in stream nutrient concentration may contrast with those mediated by decreases in water availability or by decreases in litter nutritional quality). A review of the literature addressing effects of increasing cover of N-fixing species on streams suggests a wide application of the model, while it highlights the need to consider differences in the type of system and species when making generalizations. Changes induced by N-fixing species invasion on streams can jeopardize multiple ecosystem services (e.g. good quality water, hydroelectricity, leisure activities), with relevant social and economic consequences.     

Non-native species in urban environments: patterns,processes, impacts and challenges

Although urban ecosystems are hotspots for biological invasions, the field of invasion science has given scant attention to invasion dynamics and the challenges facing managers in towns and cities. This paper provides an introduction to the growing challenges of understanding and managing invasive species in urban systems, and the context for a special issue of Biological Invasions, comprising 17 papers, that arose from a workshop on “Non-native species in urban environments: patterns, processes, impacts and challenges” held in Stellenbosch, South Africa, in November 2016. Contributions explore the following key questions: Are patterns and processes of urban invasions different from invasions in other contexts? Why is it important to manage non-native species in urban ecosystems? What are the special management needs in an urban context? How can we bridge the gaps between science, management, and policy with regards to biological invasions in urban ecosystems? The papers in this special issue show that patterns and processes of urban invasions differ in many ways from invasions in other contexts, and that managing invasive species in cities poses unique and increasingly complex challenges. Progress in urban invasion science requires further work to: (1) address key limitations that hinder our understanding of invasion dynamics in cities; (2) clarify whether fundamental concepts in the field of invasion science are appropriate for urban ecosystems; (3) integrate insights from invasion science with those from the burgeoning literature on the “Anthropocene biosphere”, novel ecosystems, social–ecological systems, human–wildlife conflicts, urban green infrastructure, urban planning and design, and ecosystem services/disservices.     

Invasive aliens on tropical East Asian islands

Tropical East Asia (TEA) has numerous islands, both continental and oceanic. This study uses information on invasive aliens in terrestrial habitats on these islands to test the generality of the continental-oceanic contrast in invasibility, assess the conservation impacts of invasive species, and suggest ways to mitigate these. The continental islands of Hong Kong and Singapore are worst-case scenarios for continental invasibility and alien species often dominate in chronically disturbed sites, but very few have successfully invaded closed forests, with the exception of birds in Hong Kong. On other, less densely populated, continental islands, closed-canopy forests appear to resist invasions by all taxa, with few known exceptions. Forests on oceanic islands isolated by <100 km during the last glacial maximum appear no more susceptible to plant and invertebrate invasions than those on continental islands, but invasions by mammals are widespread. Snake invasions may be under-recognized. The remote oceanic Ogasawara (Bonin) Islands, >1000 km from the nearest continent, have a native biota of largely tropical East Asian origin and are suffering from alien forest invasions across the taxonomic spectrum. These patterns of invasibility are consistent with the idea that alien invasion is facilitated by the absence of native species in the same functional group. Alien invasives are not yet a major conservation problem in TEA, except on remote islands, but their dominance on disturbed sites may slow or prevent recovery of native biodiversity. Strict quarantine is impractical in TEA, although some major introduction routes could be blocked. Management efforts should focus on early recognition and immediate control of potential problem species.     

Habitat fragmentation,tree diversity,and plant invasion interact to structure forest caterpillar communities

Habitat fragmentation and invasive species are two of the most prominent threats to terrestrial ecosystems. Few studies have examined how these factors interact to influence the diversity of natural communities, particularly primary consumers. Here, we examined the effects of forest fragmentation and invasion of exotic honeysuckle (Lonicera maackii, Caprifoliaceae) on the abundance and diversity of the dominant forest herbivores: woody plant-feeding Lepidoptera. We systematically surveyed understory caterpillars along transects in 19 forest fragments over multiple years in southwestern Ohio and evaluated how fragment area, isolation, tree diversity, invasion by honeysuckle and interactions among these factors influence species richness, diversity and abundance. We found strong seasonal variation in caterpillar communities, which responded differently to fragmentation and invasion. Abundance and richness increased with fragment area, but these effects were mitigated by high levels of honeysuckle, tree diversity, landscape forest cover, and large recent changes in area. Honeysuckle infestation was generally associated with decreased caterpillar abundance and diversity, but these effects were strongly dependent on other fragment traits. Effects of honeysuckle on abundance were moderated when fragment area, landscape forest cover and tree diversity were high. In contrast, negative effects of honeysuckle invasion on caterpillar diversity were most pronounced in fragments with high tree diversity and large recent increases in area. Our results illustrate the complex interdependencies of habitat fragmentation, plant diversity and plant invasion in their effects on primary consumers and emphasize the need to consider these processes in concert to understand the consequences of anthropogenic habitat change for biodiversity.     

火与外来植物相互关系的研究进展

入侵种对本地的生态系统和生物多样性均有不良的影响,严重的会造成物种的灭绝和生态系统的崩溃,这已在全球范围引起广泛关注.在植物外来种与火生态因子的作用研究中发现,火与外来种的关系随物种生物学特性、火作用的时间、频度、强度不同而不同,火有时会有效地抑制外来种的生长和入侵,有时会促进一些外来种的生长和入侵.反之,一些外来种会对火的产生起到积极的作用,一些外来种又会抑制火的发生.火作为控制入侵种的一种方法,经科学地运用,可对某些入侵种起到有效的控制作用.     

The impacts of invasive ecosystem engineers in freshwaters: A review

1. Invasive species are a key stressor in freshwater ecosystems. When these species are also ecosystem engineers, their impacts are exacerbated because they modulate resource availability for a wide range of other species. The aim of this review is to synthesise existing knowledge of the impacts of invasive ecosystem engineers in freshwaters and identify knowledge gaps requiring further research.
2. The four questions explored in this review are: (1) What are the trends in research into invasive ecosystem engineers? (2) What are common negative effects of invasive ecosystem engineers in freshwater? (3) Do all impacts of invasive ecosystem engineers have negative consequences for biodiversity? (4) What happens when multiple ecosystem engineers interact? Four literature searches in Web of Science have been used to identify articles for the review and to estimate relative research effort between terrestrial, marine and freshwater ecosystems.
3. The number of research articles focusing on ecosystem engineers across all ecosystem types is increasing. Despite well-known examples of ecosystem engineer species in freshwaters (e.g. beaver), more research has focussed on terrestrial environments and invasive species.
4. The effects of invasive ecosystem engineers in freshwater systems are varied and often context dependent. Their effects on biodiversity or native ecosystem engineers are often shown to be negative; however, not all effects associated with these species are deleterious to native species. For instance, some invasive ecosystem engineers support native species through the provision of food or refuges.
5. Although freshwater ecosystems are often influenced by multiple species of ecosystem engineers (including native, invasive or both), little is known about interactions between these species or the combined effects of multiple ecosystem engineers. More research is also needed that relates the results of laboratory experiments to the field and develops methods for measuring factors that govern the impact of engineers on ecosystems. Understanding the spatial variability of the impacts of invasive ecosystem engineers as well as their interaction with anthropogenic stressors (e.g. hydrologic modification) is also necessary.
6. The lag in research surrounding invasive ecosystem engineers in freshwater compared to other biomes is concerning, as freshwater ecosystems support biodiversity disproportionate to the area they occupy. Creating predictive models of the impacts of freshwater ecosystem engineers would help anticipate the effects of invasive ecosystem engineers in freshwater and add to the broader understanding of their effects in other biomes.

     

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.     

Successful invasion of the neotropical species Piper aduncum in rain forests in Papua New Guinea

Abstract. Piper aduncum is a neotropical invasive species which has spread throughout Papua New Guinea over the past three decades. It has become a most successful alien woody plant in New Guinea, occurring from sea level up to 2000 m a.s.l. The species prefers initial stages of forest succession and is particularly common in recently abandoned gardens representative of a system of swidden agriculture. It often attains high cover, suppresses other pioneer species and becomes the absolute dominant species in these habitats. The species is now also spreading into naturally disturbed habitats far from direct human influence, such as natural tree‐fall gaps, landslides and frequently flooded stream banks. It has, however, never been found in a closed primary forest. The species germinates from faeces of mammal and bird species, and we conclude that dispersal through endozoochory contributes to this species’ extraordinary success in Papua New Guinea. A similar invasion behaviour has been documented over a large geographic area, from Malaysia to Fiji. Piper aduncum has attributes which are common amongst successful invasive species: (1) a large native geographic range; (2) aggressively colonizing disturbed habitats in its native area; (3) relatively small seeds; (4) a short juvenile period; (5) a large seed production every year.     

香港东北角吉澳群岛入侵植物调查

什么样的生态系统容易入侵是入侵生态学关心的核心问题之一。最近,我们对香港东北角吉澳群岛中的鸦洲湾、小鸦洲、鸦洲、拦船排、虎王洲、娥眉洲、往湾洲、吉澳等8个岛屿上的所有外来植物及本土植物的种类、数量和盖度进行了调查,结果表明:具有高钙低硅土壤基质的鸦洲、小鸦洲、鸦洲湾等三个小岛上分布有大量外来入侵植物的种类和数量,而具有高硅低钙土壤基质的拦船排、虎王洲、娥眉洲、往湾洲等岛屿上外来植物的种类和数量稀少,吉澳岛虽然外来植物的种类多,但外来植物的个体数量少。分析说明:钙离子可能是影响外来植物的入侵能力或生态系统的可入侵性的关键因子。此外,文章还讨论及介绍了外来植物在石灰岩生境、盐碱地、海岸沙滩、温带广布的各种钙土、地中海气候影响下形成的干旱土等钙离子丰富的生态系统中入侵情况。     

Invasive plant species in the West Indies: geographical,ecological, and floristic insights

The level of invasion (number or proportion of invasive species) in a given area depends on features of the invaded community, propagule pressure, and climate. In this study, we assess the invasive flora of nine islands in the West Indies to identify invasion patterns and evaluate whether invasive species diversity is related to geographical, ecological, and socioeconomic factors. We compiled a database of invasive plant species including information on their taxonomy, origin, pathways of introduction, habitats, and life history. This database was used to evaluate the similarity of invasive floras between islands and to identify invasion patterns at regional (West Indies) and local (island) scales. We found a total of 516 alien plant species that are invasive on at least one of the nine islands studied, with between 24 to 306 invasive species per island. The invasive flora on these islands includes a wide range of taxonomic groups, life forms, and habitats. We detected low similarity in invasive species diversity between islands, with most invasive species (>60%) occurring on a single island and 6% occurring on at least five islands. To assess the importance of different models in predicting patterns of invasive species diversity among islands, we used generalized linear models. Our analyses revealed that invasive species diversity was well predicted by a combination of island area and economic development (gross domestic product per capita and kilometers of paved roadways). Our results provide strong evidence for the roles of geographical, ecological, and socioeconomic factors in determining the distribution and spread of invasive species on these islands. Anthropogenic disturbance and economic development seem to be the major drivers facilitating the spread and predominance of invasive species over native species.     

Trade‐offs between savanna woody plant diversity and carbon storage in the Brazilian Cerrado

Incentivizing carbon storage can be a win‐win pathway to conserving biodiversity and mitigating climate change. In savannas, however, the situation is more complex. Promoting carbon storage through woody encroachment may reduce plant diversity of savanna endemics, even as the diversity of encroaching forest species increases. This trade‐off has important implications for the management of biodiversity and carbon in savanna habitats, but has rarely been evaluated empirically. We quantified the nature of carbon‐diversity relationships in the Brazilian Cerrado by analyzing how woody plant species richness changed with carbon storage in 206 sites across the 2.2 million km² region at two spatial scales. We show that total woody plant species diversity increases with carbon storage, as expected, but that the richness of endemic savanna woody plant species declines with carbon storage both at the local scale, as woody biomass accumulates within plots, and at the landscape scale, as forest replaces savanna. The sharpest trade‐offs between carbon storage and savanna diversity occurred at the early stages of carbon accumulation at the local scale but the final stages of forest encroachment at the landscape scale. Furthermore, the loss of savanna species quickens in the final stages of forest encroachment, and beyond a point, savanna species losses outpace forest species gains with increasing carbon accumulation. Our results suggest that although woody encroachment in savanna ecosystems may provide substantial carbon benefits, it comes at the rapidly accruing cost of woody plant species adapted to the open savanna environment. Moreover, the dependence of carbon‐diversity trade‐offs on the amount of savanna area remaining requires land managers to carefully consider local conditions. Widespread woody encroachment in both Australian and African savannas and grasslands may present similar threats to biodiversity.