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.

This publication provides qualitative and quantitative information on five distinct structures: living trees with decayed parts, trees with hollow chambers, trees with brooms, dead trees, and logs. Information is provided on the value of these structures to wildlife, the decay or infection processes involved in the formation of these structures, and the principles to consider for selecting the best structures to retain.

Aim To investigate how species richness and similarity of non-native plants varies along gradients of elevation and human disturbance.Location Eight mountain regions on four continents and two oceanic islands. MethodsWe compared the distribution of non-native plant species along roads in eight mountainous regions. Within each region, abundance of plant species was recorded at 41-84 sites along elevational gradients using 100-m 2 plots located 0, 25 and 75 m from roadsides. We used mixed-effects models to examine how local variation in species richness and similarity were affected by processes at three scales: among regions (global), along elevational gradients (regional) and with distance from the road (local). We used model selection and information criteria to choose best-fit models of species richness along elevational gradients. We performed a hierarchical clustering of similarity to investigate human-related factors and environmental filtering as potential drivers at the global scale. ResultsSpecies richness and similarity of non-native plant species along elevational gradients were strongly influenced by factors operating at scales ranging from 100 m to 1000s of km. Non-native species richness was highest in the New World regions, reflecting the effects of colonization from Europe. Similarity among regions was low and due mainly to certain Eurasian species, mostly native to temperate Europe, occurring in all New World regions. Elevation and distance from the road explained little of the variation in similarity. The elevational distribution of non-native species richness varied, but was always greatest in the lower third of the range. In all regions, non-native species richness declined away from roadsides. In three regions, this decline was steeper at higher elevations, and there was an interaction between distance and elevation. Main conclusionsBecause non-native plant species are affected by processes operating at global, regional and local scales, a multi-scale perspective is needed to understand their patterns of distribution. The processes involved include global dispersal, filtering along elevational gradients and differential establishment with distance from roadsides.

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The coarse-scale population structure of pathogenic Armillaria (Fr.) Staude species was determined on approximately 16 100 ha of relatively dry, mixed-conifer forest in the Blue Mountains of northeast Oregon. Sampling of recently dead or live, symptomatic conifers produced 112 isolates of Armillaria from six tree species. Armillaria species identifications done by using a polymerase chain reaction based diagnostic and diploid–diploid pairings produced identical results: 108 of the isolates were Armillaria ostoyae (Romagn.) Herink and four were North American Biological Species X (NABS X). Five genets of A. ostoyae and one of NABS X were identified through the use of somatic incompatibility pairings among the putatively diploid isolates. Armillaria ostoyae genet sizes were approximately 20, 95, 195, 260, and 965 ha; cumulative colonization of the study area was at least 9.5%. The maximum distance between isolates from the 965-ha A. ostoyae genet was approximately 3810 m, and use of three estimates of A. ostoyae spread rate in conifer forests resulted in age estimates for the genet ranging from 1900 to 8650 years. Results are discussed in relation to possible mechanisms that influenced the establishment, expansion, and expression of these genets; the genetic structure and stability of Armillaria; and the implications for disease management in this and similar forests.