Positive associations between the cushion plant Azorella monantha (Apiaceae) and alpine plant species in the Chilean Patagonian Andes

Low growing, compact cushion plants are a common and often dominant life form in temperate and subpolar alpine habitats. The cushion life-form can modify wind patterns, temperature and water availability and thus cushion species could be expected to act as nurse-plants facilitating the establishment of other alpine plant species on their surfaces. It has been suggested that the nurse effect should be most pronounced under more stressful environmental conditions, as found with increasing elevation in the alpine. One of the approaches used to detect the nurses has been the study of spatial associations among species, in which extreme clumping within or beneath one species has been interpreted as evidence of nursing. We characterized microclimatic conditions (soil and air temperature) within and outside cushions of Azorella monantha at two elevations (700 m a.s.l., corresponding to an elevation just above treeline, and 900 m a.s.l., corresponding to the upper limit of the cushion belt zone) on Cerro Diente in the Patagonian alpine of southern South America (50° S) and recorded all plant species growing upon cushions of various sizes and for paired sampling areas of equivalent sizes outside cushions. At 5 cm depth, soil temperature was slightly higher under cushions than under bare ground, but only significantly so at 900 m. Air temperature at ground level was significantly higher in the cushion microhabitat at both 700 m and 900 m, with the difference being more exaggerated at the highest elevation. At 700 m, a total of 27 species were recorded growing within cushions as compared to 29 outside cushions. At 900 m the corresponding numbers were 34 and 18. At the highest elevation, significantly more species grow within cushions than for equal areas outside cushions. Here moreover, 17 (48.6%) species grew preferentially within cushions, with eight of the latter being limited to the cushion microhabitat at this elevation. However, at 700 m there was no significant difference in species richness in the two microhabitats, and only one species (3.1%) grew preferentially on cushions. Considering individual species, nine occurring at both elevations showed non-preferential recruitment on cushions at 700 m, but significantly higher frequencies on cushions at 900 m. Results suggest striking altitudinal variation in the association with Azorella monantha on Cerro Diente, ranging from a very strong at 900 m to near absence at 700 m. Milder air and soil temperatures, shelter from wind, and greater water availability within cushions as opposed to outside cushions are discussed as possible factors favoring strong plant recruitment on cushions at higher elevations in the harsh Patagonian alpine environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Assessing the importance of disturbance, site conditions, and the biotic barrier for dandelion invasion in an Alpine habitat

Several factors have been identified as relevant in determining the abundance of non-native invasive species. Nevertheless, the relative importance of these factors will vary depending on the invaded habitat and the characteristics of the invasive species. Due to their harsh environmental conditions and remoteness, high-alpine habitats are often considered to be at low risk of plant invasion. However, an increasing number of reports have shown the presence and spread of non-native plant species in alpine habitats; thus, it is important to study which factors control the invasion process in these harsh habitats. In this study, we assessed the role of disturbance, soil characteristics, biotic resistance and seed rain in the establishment and abundance of the non-native invasive species Taraxacum officinale (dandelion) in the Andes of central Chile. By focusing on human-disturbed patches, naturally disturbed patches, and undisturbed patches, we did not find that disturbance per se, or its origin, affected the establishment and abundance of T. officinale. The abundance of this non-native invasive species was not negatively related to the diversity of native species at local scales, indicating no biotic resistance to invasion; instead, some positive relationships were found. Our results indicate that propagule pressure (assessed by the seed rain) and the abiotic soil characteristics are the main factors related to the abundance of this non-native invasive species. Hence, in contrast to what has been found for more benign habitats, disturbance and biotic resistance have little influence on the invasibility of T. officinale in this high-alpine habitat.     

Differential effect of inter- and intraspecific competition on the performance of invasive and native Taraxacum species

Inter- and intraspecific competitive abilities are significant determinants of invasive success and the ecological impact of non-native plants. We tested two major hypotheses on the competitive ability of invasive species using invasive (Taraxacum officinale) and native (T. platycarpum) dandelions: differential interspecific competitive ability between invasive and native species and the kin recognition of invasive species. We collected seeds from two field sites where the two dandelion species occurred nearby. Plants were grown alone, with kin (plants from the same maternal genotype) or strangers (plants from different populations) of the same species, or with different species in a growth chamber, and the performance at the early developmental stage between species and treatments was compared. The invasive dandelions outcompeted the native dandelions when competing against each other, although no difference between species was detected without competition or with intraspecific competition. Populations of native species responded to interspecific competition differently. The effect of kinship on plant performance differed between the tested populations in both species. A population produced more biomass than the other populations when grown with a stranger, and this trend was manifested more in native species. Our results support the hypothesis that invasive plants have better competitive ability than native plants, which potentially contributes to the establishment and the range expansion of T. officinale in the introduced range. Although kin recognition is expected to evolve in invasive species, the competitive ability of populations rather than kinship seems to affect plant growth of invasive T. officinale under intraspecific competition.     

The best for the guest: high Andean nurse cushions of Azorella madreporica enhance arbuscular mycorrhizal status in associated plant species

Positive interactions between cushion plant and associated plants species in the high Andes of central Chile should also include the effects of fungal root symbionts. We hypothesized that higher colonization by arbuscular mycorrhizal (AM) fungi exists in cushion-associated (nursling) plants compared with conspecific individuals growing on bare ground. We assessed the AM status of Andean plants at two sites at different altitudes (3,200 and 3,600 m a.s.l.) in 23 species, particularly in cushions of Azorella madreporica and five associated plants; additionally, AM fungal spores were retrieved from soil outside and beneath cushions. 18 of the 23 examined plant species presented diagnostic structures of arbuscular mycorrhiza; most of them were also colonized by dark-septate endophytes. Mycorrhization of A. madreporica cushions showed differences between both sites (68% and 32%, respectively). In the native species Hordeum comosum, Nastanthus agglomeratus, and Phacelia secunda associated to A. madreporica, mycorrhization was six times higher than in the same species growing dispersed on bare ground at 3,600 m a.s.l., but mycorrhiza development was less cushion dependent in the alien plants Cerastium arvense and Taraxacum officinale at both sites. The ratio of AM fungal spores beneath versus outside cushions was also 6:1. The common and abundant presence of AM in cushion communities at high altitudes emphasizes the importance of the fungal root symbionts in such situations where plant species benefit from the microclimatic conditions generated by the cushion and also from well-developed mycorrhizal networks.     

垫状植物囊种草对群落物种多样性的影响

在甘肃盐池湾国家级自然保护区内海拔4137 m处,选择典型的囊种草垫状植被设置研究样地,研究了垫状植物囊种草对群落物种组成和群落物种多样性的影响,并且定量的研究了囊种草对群落物种丰富度的影响能力和维持潜力。研究结果表明:囊种草为群落中增加了新的植物种类,并且提高了部分生境一般种的多度;囊种草的出现提高了群落物种密度和物种丰富度,进而提高了群落物种多样性;囊种草斑块的增加将会引起景观水平物种丰富度的增加,表明囊种草具有为群落中引入新的植物种类进而提高群落物种丰富度的能力;在景观水平,囊种草所创造的生境多样性则成为一种保障,可以维持景观中物种丰富度从而降低物种损失的风险,表明囊种草具有较高的群落物种丰富度维持潜力。     

An invasive dandelion unilaterally reduces the reproduction of a native congener through competition for pollination

The impact of invasive alien species on native species is of increasing global concern. Invasive plants have various negative effects on natives through competition; however, relatively little is known about competition for pollination. The relationship between Japanese native dandelions (Taraxacum spp.) and invasive congeners may be a typical case of such an interaction. For example, native dandelions are being replaced by invasive congeners, especially in urban and suburban areas of Japan. To explain this phenomenon, we hypothesized that when natives are mixed with attractive invasives, natives may suffer from reduced seed set because invasives deprive natives of pollinators or because pollinators frequently move between species, resulting in interspecific pollen transfer. To test this hypothesis, we studied the effect of the invasive dandelion T. officinale on the pollination and seed set of the native T. japonicum using artificial arrays of monospecific and mixed-species plots as well as natural populations. Taraxacum officinale attracted more pollinator visits, perhaps because it produced more nectar than T. japonicum. The number of pollinator visits to T. japonicum was reduced when the congeners were grown together, and pollinators moved frequently between the two species. The proportion of seed set for T. japonicum was reduced in the presence of T. officinale in both artificial arrays and natural populations. These results support our hypothesis that interspecific competition for pollination plays an important role in the recent replacement of native dandelions by invasive congeners in Japan. Because invasive dandelions are apomicts, negative effects are incurred only by sexual natives. Thus, this system can be recognized as a rare case of interspecific interaction through pollination.     

Alien dandelion reduces the seed-set of a native congener through frequency-dependent and one-sided effects

In conservation biology, increasing numbers of studies have focused on reproductive interference (RI) between a native species and related aliens. However, few studies have examined the frequency dependence of RI, despite of its key importance to invasiveness. Here, we report for the first time frequency-dependent RI in a pair of native and alien dandelions: Taraxacum japonicum and T. officinale, respectively. Taraxacum japonicum has been displaced rapidly by the alien congener T. officinale in Japan and its causal mechanism are still poorly understood. Field observations revealed that the seed-set of natives decreased substantially as the proportion of alien neighbors increased. Subsequently, in a field experiment, the removal of alien flowers only greatly increased the seed-set of natives. We synthesized these results with existing theoretical models of RI and concluded that RI, which is mediated by strong frequency dependence, is presumably responsible for the displacement of T. japonicum by T. officinale.     

Differential effects of reproductive interference by an alien congener on native Taraxacum species

Reproductive interference (RI) has been suggested to play a critical role in native plant displacement by alien congeners. However, although co-existence of native and alien congeners may provide an opportunity to refute the RI hypothesis, few studies have examined such a case. Using a native Japanese dandelion, Taraxacum longeappendiculatum, and a co-existing alien congener, Taraxacum officinale, we tested the hypothesis that differences in RI by the alien between native recipient congeners explain whether a native will co-exist with or be displaced by an alien. We conducted a field survey to investigate the effects of alien relative abundance on T. longeappendiculatum seed set, and a hand-pollination experiment to identify the extent of pollen interference by the alien on T. longeappendiculatum. We compared these results with those obtained previously for another Japanese native species, Taraxacum japonicum, which was displaced by the alien. In our field survey, alien relative abundance had little effect on seed set in nearby T. longeappendiculatum, and hand-pollination with mixed pollen grains produced no substantial decrease in seed set of the native species. Model selection supported these tendencies; the effect of RI by the alien differed between the two native species. Other potential factors, such as resource competition or habitat changes, could not explain the co-existence of T. longeappendiculatum with and exclusion of T. japonicum by the alien in the same explanatory framework. Considering the consistent explanatory power, the findings suggest that RI is a critical mechanism that can determine both co-existence with and displacement of native dandelions by an alien congener.     

Formation of a hybrid triploid agamosperm on a sexual diploid plant: evidence from progeny tests in Taraxacum platycarpum Dahlst.

Agamospermous dandelions of hybrid origin between a native sexual diploid species (Taraxacum platycarpum Dahlst. or T. japonicum Koidz.) and an alien agamospermous triploid [T. officinale Weber and T. laevigatum (Willd.) DC.] are now widely distributed throughout mainland Japan. These hybrid dandelions are known to be genetically variable. We hypothesized that this variability is maintained by repeated ongoing hybridization, based on the fact that triploid dandelions not only produce seeds agamospermously, but also produce some functional pollen grains that are able to sire seeds of sexual dandelions. To test this hypothesis, we examined whether heads of Japanese diploid dandelions produce new hybrid seeds after fertilization by pollen from triploid agamosperms under field conditions. One of the 430 tested plants grown from sexual dandelion seeds had morphological and molecular characteristics, which are consistent with a hybrid origin. The plant formed a hybrid surrounded by many individuals having recurved involucral bracts, in which frequency of T. officinale was very low (3.5 %). Cytological data and bagging experiments demonstrate triploidy and asexual seed production of the hybrid. Taken together, these results supported that the new hybrid is probably derived from a backcross of a hybrid to the native sexual species. Our findings provide evidence for the evolution of a new agamosperm through interspecific hybridization as a contemporary population process.     

Interspecific competition for seed production between two naturalized dandelions under different levels of fertilizer supply

Two naturalized dandelions,Taraxacum officinale andTaraxacum laevigatum, were grown in mixed stands at various plant densities and mixing ratios with various levels of fertilizer supply until seeds were produced. The effect of fertilizer supply on the competitive relationship for seed production between the species was analyzed. In pure stands, the simultaneous effects of plant density and fertilizer supply on mean plant weight were formulated for each species. By introducing the density conversion factor, the results of plant weight growth in mixed stands were formulated successfully.T. laevigatum produced more seeds thanT. officinale at the same plant weight. The relationship between mean plant weight and mean number of mature seeds produced per plant was also formulated for each species. Ratio diagrams were predicted with these formulas. The density conversion factors showed thatT. officinale was always dominant overT. laevigatum for plant weight growth within a generation. The ratio diagrams showed thatT. officinale became dominant overT. laevigatum for seed production with repeating generations at higher levels of fertilizer supply, but that the species with a larger ratio of plant density became dominant over the other species at lower levels of fertilizer supply.     

Alpine dandelions originated in the native and introduced range differ in their responses to environmental constraints

Few studies have compared the response of native and invasive populations under stressful conditions. Furthermore, there is little consensus as to whether a plastic response is related to invasiveness in stressful environments. Exotic species have recently been reported in the high Andes of central Chile, where individuals have to cope with drought and poor soils, in addition to extreme temperatures. We explored if the exotic species Taraxacum officinale (dandelion) has plastic responses to soil moisture and nutrient availability, and whether two sets of alpine populations derived from native and introduced populations can converge to similar plastic responses to environmental constraints. Using a common garden approach, we compared plants grown from seeds collected in alpine populations of its native range (Alps, France) and in alpine populations of its introduced range (Andes, Chile) under a drought experiment, a potassium gradient, and a nitrogen gradient. Plasticity was only found as a response to drought. Moreover, different responses were found between both origins. Andean individuals are drought-resistant, while individuals from the Alps were drought-sensitive. According to the nutrient experiments, Andean dandelions behave as a nitrogen demanding-potassium avoiding species, whereas individuals from the Alps did not show any particular dependency or repulsion tendency to either of these two nutrients. Results suggest that differences in life history traits of both derived sets of populations may have an important role in determining the response of dandelions under the evaluated conditions. However, the relative importance of genetic adaptation in these responses is still unclear. Although T. officinale is a cosmopolite weed, this is the first study that compares individuals coming from its native and invaded range under stressful conditions.     

Variation and response to experimental warming in a New Zealand cushion plant species

Cold adapted plants, such as cushion plants, may be particularly sensitive to climate warming because of their compact growth form and high branch density. In the oceanic southern hemisphere, cushion communities tend to have large range distributions at low latitudes (sea level to low alpine), thus providing an opportunity to test the effects of temperature on plant morphology and reproduction across gradients. Using Donatia novae‐zelandiae as a model species, we compared the leaf morphology, reproduction and responses to warming. Two low‐alpine sites (Maungatua (880 m a.s.l.), Blue Mountains (1000 m a.s.l.)) and two sea‐level sites (Waituna 1 (0 m a.s.l.), Waituna 2 (0 m a.s.l.)) in South Island, New Zealand were used. Donatia novae‐zelandiae cushions differed significantly between the high‐elevation and sea‐level sites both morphologically and in terms of reproduction. High‐elevation cushions produced more flowers (threefold more flowers per plant) and seeds (sevenfold more seeds per capsule) than at sea level, but leaves were larger at sea level (in length and specific leaf area). The cushions were also twice as compact at the high‐elevation sites. After two growing seasons of artificial warming, seed production (35%), leaf length (7%) and width (13%), and specific leaf area (63%) significantly decreased in D. novae‐zelandiae plants; flower production was not significantly affected. Cushion plant morphology and reproduction were significantly affected by environmental drivers at their establishment sites, but all populations responded negatively to artificial warming of 1–3°C. Many cushion plants are considered keystone species because of their propensity to facilitate the growth and establishment of other plant species, the inferred negative effects of global warming on cushion plant species may have a cascading effect on other alpine plant groups.     

Effective range of reproductive interference exerted by an alien dandelion, <Emphasis Type="Italic">Taraxacum officinale</Emphasis>, on a native congener

Reproductive interference (RI), defined as the fitness cost of interspecific sexual interactions, such as interspecific pollen transfer (IPT) in plants, is ecologically important. Theoretically, RI could result in competitive exclusion, as it operates in a frequency-dependent manner. Additionally, IPT may have a greater range than resource competition, although information about the range of IPT is lacking. In the present study, we measured the range of IPT exerted by Taraxacum officinale (an alien species) on a native dandelion, T. japonicum. We used two approaches. In one, we analyzed the RI effect on a native seed set at three spatial scales. In the second, we tracked IPT from alien to native flower heads using fluorescent pigments as markers. We estimated that pollination distances were in the order of several meters. These distances exceeded the mean distance from each native plant to the nearest alien. As hypothesized, the effect of RI reached farther than neighboring individuals. These data indicate the spatial range from which alien dandelions should be removed to allow the conservation of natives.     

Reduced soil compaction enhances establishment of non-native plant species

Many studies have shown that soil disturbance facilitates establishment of invasive, non-native plant species, and a number of mechanisms have been isolated that contribute to the process. To our knowledge no studies have isolated the role of altered soil compaction, a likely correlate of many types of soil disturbance, in facilitating invasion. To address this, we measured the response of seeded non-native and native plant species to four levels of soil compaction in mesocosms placed in an abandoned agricultural field in the Methow Valley, Washington, USA. Soil compaction levels reflected the range of resistance to penetration (0.1–3.0 kg cm⁻²) measured on disturbed soils throughout the study system prior to the experiment. Percent cover of non-native species, namely Bromus tectorum and Centaurea diffusa, decreased by 34% from the least to the most compacted treatments, whereas percent cover of native species, mostly Pseudoroegneria spicata and Lupinus spp., did not respond to compaction treatments. Experimental results were supported by a survey of soil penetration resistance and percent cover by species in 18 abandoned agricultural fields. Percent cover of B. tectorum was negatively related to soil compaction levels, whereas none of the native species showed any response to soil compaction. These results highlight a potentially important, though overlooked, aspect of soil disturbance that may contribute to subsequent non-native plant establishment.     

Nurse effect of Bolax gummifera cushion plants in the alpine vegetation of the Chilean Patagonian Andes

Abstract. It has been proposed that in the harsh arctic and alpine climate zones, small microtopographic variations that can generate more benign conditions than in the surrounding environment could be perceived as safe sites for seedling recruitment. Cushion plants can modify wind pattern, temperature and water availability. Such modifications imply that cushion plants could act as ‘nurse plants’ facilitating the recruitment of other species in the community. This effect should be more evident under stressful conditions. We tested these hypotheses comparing the number of species that grow inside and outside Bolax gummifera cushions at two elevations (700 and 900 m a.s.l.) in the Patagonian Andes of Chile (50°S). At both elevations, and in equivalent areas, the number of species was registered within and outside cushions. A total of 36 and 27 plant species were recorded either within or outside B. gummifera cushions at 700 and 900 m a.s.l., respectively. At 700 m a.s.l., 33 species were recorded growing within cushions and 29 outside them, while at 900 m a.s.l. these numbers were 24 and 13 respectively. At both elevations there were significantly more species growing within than outside cushions, and the proportion of species growing within cushions increased with elevation. Thus there is a nurse effect of cushion plants and it is more evident at higher elevations. Shelter from wind and increased soil water availability seem to be the factors that increase plant recruitment within cushions.     

Does global warming induce segregation among alien and native beetle species in a mountain-top?

The last few centuries have seen an increase in the mean air temperature of the planet, a phenomenon that is called “global warming”. One of the most sensitive habitats to the effects of global warming is the high-elevation mountain environments, because these habitats are characterized by low temperature. Cushion plants are one of the best-adapted growth forms in this habitat, generating more suitable sites for other plants and insects. In the present study, we experimentally evaluated the effects of global warming by open-top chambers on the abundance and interaction of two ladybirds at 3,600 m, growing over cushions of the Azorella monantha species in the Andes of central Chile. Additionally, we measured variation in temperature, water content, and food availability by the presence of open-top chambers as possible mechanisms of spatial segregation between ladybirds. Without open-top chambers, the abundance of native and alien beetles was similar; but with open-top chambers, the native beetle species is spatially segregated by alien species, decreasing in abundance. The open-top chambers increase temperature and food availability, but not water content. We suggest that under the global warming scenario, the native insects will decrease in abundance or become extinct by the presence of alien insects, at least in the high-elevation mountain environments.     

Higher plasticity in ecophysiological traits enhances the performance and invasion success of Taraxacum officinale (dandelion) in alpine environments

Phenotypic plasticity has long been suggested to facilitate biological invasions in changing environments, allowing a species to maintain a good ecophysiological performance. High-mountain habitats have been particularly useful for evaluation of the relative importance of environmental conditions in the colonization and invasion process, because they have heterogeneous and stressful climatic conditions, inducing photoinhibition. Light intensity is one of the most changing conditions along altitudinal gradients, showing more variability in higher altitudes. In this study, we analyzed the plasticity in photoprotective strategies and performance of the invasive Taraxacum officinale. Additionally, we tested whether higher plasticity enhances competitive ability in an alpine environment We conducted an experiment to evaluate plasticity with a second generation (F2) of T. officinale individuals from 1,600 to 3,600 m, in a greenhouse with variation in light intensity. Treatments consisted of transferring 120 individuals from each altitude to two conditions of light intensity. We then recorded concentrations of photoprotection pigment, de-epoxidation state of the xanthophyll cycle, foliar angles, photochemical efficiency by fluorescence of photosystem II, total dry biomass and flower production. Additionally, we compared plasticity in both photoprotective and performance traits between T. officinale and the co-occurring native species Hypochaeris thrincioides. Finally, we performed a manipulative experiment under two light regimes in order to assess the competitive outcome between the invasive T. officinale and the native H. thrincioides. Individuals from higher altitude showed significantly greater plasticity than individuals from lower altitude. Similarly, individuals under high light intensity showed higher levels of photoprotective pigments, biomass and flower production. On the other hand, the invasive plant species showed significantly greater plasticity than the co-occurring native species, and a strong negative impact on the biomass of the native plant. Phenotypic plasticity seems to be a successful strategy in T. officinale to compete with native species and may be positively associated with the success of invasions, being greater in individuals from more heterogeneous and stressful environments.     

Variation of biomass and morphology of the cushion plant Androsace tapete along an elevational gradient in the Tibetan Plateau

Alpine ecosystems are among those biomes that are most vulnerable to climate change. Cushion plants are an important life form of alpine ecosystems and will likely play a critical role for the resilience of these habitats to climate change. We studied cushion size distribution and different measures of the compactness of cushions (biomass and rosette density, leaf area index) of the cushion plant, Androsace tapete along an elevational gradient from 4500 to 5200 m a.s.l. in the Nyainqentanglha Mountains of the central Tibetan Plateau. Cushion size distribution, total cover, and compactness of cushions varied substantially along the elevational gradient. At the driest site at low elevation we found the lowest total cushion cover, a particularly high proportion of very small cushions, and the most compact cushions (highest rosette and biomass densities, and leaf area index (LAI) per cushion). Our results indicate that in the semi‐arid Tibetan Plateau water availability is the more important climate factor than temperature affecting cushion plant traits and morphology.     

Are boreal ecosystems susceptible to alien plant invasion? Evidence from protected areas

Although biological invasion by alien species is a major contributor to loss of indigenous biological diversity, few studies have examined the susceptibility of the boreal biome to invasion. Based on studies of other ecosystems, we hypothesized that alien plants will be restricted to disturbed areas near human activity and will not be found in natural areas of boreal ecosystems in Gros Morne National Park (Canada), a protected area experiencing a wide range of disturbance regimes. The distribution of alien plants in the region was evaluated using surveys, and study sites were established in naturally and anthropogenically disturbed habitats that had been invaded. Within study sites, randomization tests evaluated the importance of disturbance to alien plant invasion by examining changes in environmental conditions and species abundance within various disturbance regimes, while the importance of site characteristics limiting the distribution of alien plants were examined using Canonical Correspondence Analysis. Consistent with studies in a variety of biomes, areas of high disturbance and human activity had the greatest abundance of resources and the highest percentage of alien species. However, contrary to our hypothesis, natural areas of boreal ecosystems were found susceptible to alien plant invasion. Vegetation types vulnerable to invasion include forests, riparian areas, fens, and alpine meadows. Natural disturbance occurring in these vegetation types caused increases in bare ground and/or light availability facilitating alien plant invasion. Although high soil pH was associated with alien plants in these areas, disturbance was not found to cause changes in soil pH, suggesting susceptibility to invasion is pre-determined by bedrock geology or other factors influencing soil pH. Moose (Alces alces), a non-native herbivore, acts as the primary conduit for alien plant invasion in GMNP by dispersing propagules and creating or prolonging disturbance by trampling and browsing vegetation. The recurrent nature of disturbance within the boreal biome and its interaction with site conditions and herbivores enables alien plants to persist away from areas of high human activity. Managers of natural lands should monitor such interactions to decrease the invasion potential of alien plants.