Predictions of plant migration under climate warming come mostly from models including only climate variables, neglecting the influence of non-climatic factors, such as soil properties and dispersal limitation. Soil properties might have a stronger effect on plant distributions in colder environments, where plant nutrient absorption capacity is inhibited, but this has rarely been tested. Macroecological studies of range dynamics rely on soil data at much coarser spatial resolution than that experienced by plants. In contrast, field studies along elevational gradients permit detailed soil data, while still covering a wide climatic gradient. Here, we first report an intensive field survey of four spring forest herbs and soil properties along an elevational gradient in southern Québec, Canada, testing the hypothesis that soil properties contribute to defining upper elevational range limits. We then report a seven-year transplant experiment with one species, Trillium erectum, testing the hypothesis that climate warming has already created suitable sites at high elevation, with its near-absence explained by dispersal limitation. In our field survey, soil properties had substantial impacts on the occurrence or abundance of all four species, and soil effects were more pronounced at higher elevations. For two species, T. erectum and Claytonia caroliniana, very infrequent occurrences at high elevation (>950m) were strongly associated with rare microsites with high pH or nutrients. After transplantation to high-elevation sites, T. erectum individuals grew to much smaller size and with very low probability of flowering (<10%) compared to individuals at low or mid-elevations (>60% flowering), suggesting that environmental factors rather than dispersal limitation constrain the species’ upper elevational range limit. Our study highlights that soil factors interact strongly with climate to determine plant range limits along climatic gradients. Unsuitable soils for plants at high elevations or latitudes may represent an important constraint on future plant migration.

Despite many studies showing biodiversity responses to warming, the generality of such responses across taxonomic groups remains unclear. Very few studies have tested for evidence of bryophyte community responses to warming, even though bryophytes are major contributors to diversity and functioning in many ecosystems. Here we report an empirical study comparing long-term change of bryophyte and vascular plant communities in two sites with contrasting long-term warming trends, using “legacy” botanical records as a baseline for comparison with contemporary resurveys. We hypothesized that ecological changes would be greater in sites with a stronger warming trend, and that vascular plant communities, with narrower climatic niches, would be more sensitive than bryophyte communities to climate warming. For each taxonomic group in each site, we quantified the magnitude of changes in species’ distributions along the elevation gradient, species richness, and community composition. We found contrasted temporal changes in bryophyte vs. vascular plant communities, which only partially supported the warming hypothesis. In the area with a stronger warming trend, we found a significant increase of local diversity and beta-diversity for vascular plants, but not for bryophytes. Presence absence data did not provide sufficient power to detect elevational shifts in species distributions. The patterns observed for bryophytes are in accordance with recent literature showing that local diversity can remain unchanged despite strong changes in composition. Regardless of whether one taxon is systematically more or less sensitive to environmental change than another, our results suggest that vascular plants cannot be used as a surrogate for bryophytes in terms of predicting the nature and magnitude of responses to warming. Thus, to assess overall biodiversity responses to global change, abundance data from different taxonomic groups and different community properties need to be synthesized.