Most studies of invasive species have been in highly modified, lowland environments, with comparatively little attention directed to less disturbed, high‐elevation environments. However, increasing evidence indicates that plant invasions do occur in these environments, which often have high conservation value and provide important ecosystem services. Over a thousand non‐native species have become established in natural areas at high elevations worldwide, and although many of these are not invasive, some may pose a considerable threat to native mountain ecosystems. Here, we discuss four main drivers that shape plant invasions into high‐elevation habitats: (1) the (pre‐)adaptation of non‐native species to abiotic conditions, (2) natural and anthropogenic disturbances, (3) biotic resistance of the established communities, and (4) propagule pressure. We propose a comprehensive research agenda for tackling the problem of plant invasions into mountain ecosystems, including documentation of mountain invasion patterns at multiple scales, experimental studies, and an assessment of the impacts of non‐native species in these systems. The threat posed to high‐elevation biodiversity by invasive plant species is likely to increase because of globalization and climate change. However, the higher mountains harbor ecosystems where invasion by non‐native species has scarcely begun, and where science and management have the opportunity to respond in time.

Macaronesia is a biogeographical region comprising five Atlantic Oceanic archipelagos: the Azores, Madeira, Selvagen (Savage Islands), Canaries and Cape Verde. It has strong affinities with the Atlantic coast of the Iberian Peninsula and the north‐western fringes of Africa. This paper re‐evaluates the biogeographical history and relationships of Macaronesia in the light of geological evidence, which suggests that large and high islands may have been continuously available in the region for very much longer than is indicated by the maximum surface area of the oldest current island (27 Ma) – possibly for as long as 60 million years. We review this literature, attempting a sequential reconstruction of Palaeo‐Macaronesia from 60 Ma to the present. We consider the implications of these geological dynamics for our understanding of the history of colonization of the present islands of Macaronesia. We also evaluate the role of these archipelagos as stepping stones and as both repositories of palaeo‐endemic forms and crucibles of neo‐endemic radiations of plant and animal groups. Our principal focus is on the laurel forest communities, long considered impoverished relicts of the Palaeotropical Tethyan flora. This account is therefore contextualized by reference to the long‐term climatic and biogeographical history of Southern Europe and North Africa and by consideration of the implications of changes in land–sea configuration, climate and ocean circulation for Macaronesian biogeography. We go on to provide a synthesis of the more recent history of Macaronesian forests, which has involved a process of impoverishment of the native elements of the biota that has accelerated since human conquest of the islands. We comment briefly on these processes and on the contemporary status and varied conservation opportunities and threats facing these forests across the Macaronesian biogeographical region.

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Islands have long provided model systems in which ecologists and evolutionary biologists have developed, tested and refined models for species diversity (Whittaker and Fernández-Palacios 2007). In two recent papers, Emerson and Kolm (2005a, b) have presented and discussed multiple regression analyses from two oceanic archipelagos, the Canaries and Hawaii, demonstrating for plants and arthropods that islands of greater species richness also have higher proportions of single island endemics (SIEs). They claim this as evidence that higher species richness of a taxon drives higher rates of diversification in that taxon, i.e. that ''diversity begets diversity''. Their analysis is interesting, but given that it is an analysis of proportions of SIEs not rate of species production, it is ultimately inconclusive as to mechanisms leading to the relationship. It might tell us, as inferred by Emerson and Kolm (2005a, b), that high species richness creates the conditions for high rates of speciation through: 1) competitive interactions, 2) genetic drift due to small population sizes, and 3) greater community structural complexity. But it could also be that the relationship is a by-product of circumstances not adequately captured in their analyses.Herein, we develop an alternative model, positing that the opportunities for speciation have a broadly predictable relationship to the life cycle of oceanic islands. We term our model the island immaturity Á speciation pulse (IISP) model of island evolution. Intrinsic to this model is that opportunity drives speciation rate and that opportunity is greatest at a relatively early stage of an island's life cycle, when intrinsic carrying capacity exceeds species richness by the greatest margin, i.e. when there is greatest ''vacant niche space''. As islands mature, both richness and endemism increase in tandem, but as islands decline in their old age, opportunities for speciation diminish, in tandem with a reduced carrying capacity (and reduced numbers of SIEs). Our argument is that the mechanisms identified by Emerson and Kolm (2005a, b), whilst each having a role in island evolution, make for an incomplete set of key island mechanisms and that in particular they neglect the likely importance of competitive release early in the life cycle of an island, and of the subsequent decline in carrying capacity, for the proportions of single island endemics (see Peck et al. 1999).In setting out the IISP model, we describe the observations on which it is based, and then examine what we expect in terms of critical rates, and emergent patterns of SIEs, comparing our model with that put forward by Emerson and Kolm (2005a, b). We illustrate our model with reference to data for the arthropods and plants of the Canary Islands (cf. Emerson and Kolm 2005a). Prior observationsFirst, numerous analyses of species richness variation provide broad support for the idea of an environmentally-determined carrying capacity (K) for richness on

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Abstract. We studied the effects of windthrow on the understory plant species composition of a pine forest (dominated by Pinus strobus) and an oak forest (dominated by Quercus ellipsoidalis). We recorded the presence of vascular plant species in randomly located quadrats in the two forests, and in three microsite types associated with tipup mounds (pit, old soil and new soil) in the pine forest at irregular intervals over the course of 14 years. The understories of the two forests remained distinct throughout the study. The frequency of occurrence of a number of forest floor species considerably increased; few species decreased. The disturbance specialists Rubus idaeus and Polygonum cilinode increased in frequency throughout the study in the pine forest, but are beginning to decline in the less disturbed oak forest. Annuals and biennials preferentially colonized the disturbed soil of microsites on tipups, and declined in frequency after about 7 yr. Both forests have increased in understory species richness, but have not changed substantially in the distribution of growth forms. Despite early differences in species composition, microsite types associated with tipup mounds became more similar through time. Although small in magnitude, there was a directional change in understory composition at both forests, with no apparent sign of a return to pre‐disturbance conditions.

Islands are paradigms of the pervasive spread of alien plants, but little work has been done assessing pattern and cause of the distribution of such plants in relation to roads on oceanic islands. We studied richness, composition, and distribution of alien plants and compared them with native species along roads on Tenerife (Canary Islands). We studied a single road transect that sampled two contrasting wind-facing aspects (leeward versus windward) and ran from coastal Euphorbia scrubland through thermophilous scrubland to Makaronesian laurel forest at the top of a mountainous massif. We evaluated the effects of elevation, aspect, distance to urban nuclei, and several road-edge features (including road-edge width and management-implying disturbance intensity), using regression models, analysis of variance, and multivariate ordination methods. Richness of both endemics and native nonendemics was explained by elevation (related to well-defined vegetation belts), steepness of the edge slope, and cover of rocky ground. Despite a short elevational gradient (0-650 m), we found clear altitudinal zonation by biogeographic origin of both nonendemic natives and aliens, and altitudinal distribution of aliens followed the same zonation as that of natives. Alien species' richness was related to management intensity determining edge disturbance, roadedge width, and distance to the nearest urban nuclei (propagule sources). Different variables explained distribution patterns of natives, endemics, and aliens along roadsides on leeward and windward aspects. Altitude and aspect also had a strong influence on the frequency of life strategies (woody species, annuals and biennial/perennial herbs) of roadside plant communities. Due to harsher environmental filters operating on the leeward aspect, alien species were distributed along the altitudinal gradient in apparent consistency with general biogeographical affinities. Tropical/subtropical taxa showed exponential decrease with increasing elevation, Mediterranean taxa showed a unimodal response (i.e., maximum richness at mid elevation, minimum at the extremes of the gradient), and temperate taxa showed linear increase with elevation. Native but nonendemic species followed analogous trends to those of aliens. This suggests climatic matching as a prerequisite for successful invasion of this topographically complex island. Other road traits, such as edge width, slope steepness, soil cover, and road-edge disturbance intensity may play a complementary role, at a more local scale, to shape the distribution of alien plants on these island roads.