Hiking up to the next plot…
Examines how tundra plant communities — including Sphagnum mosses, dwarf shrubs, and other cold-adapted species — are shifting in composition, functional traits, and cover in response to warming temperatures, changing snowpack, and shrub encroachment across Arctic and alpine biomes.
Mountain and high-latitude ecosystems are warming faster than almost anywhere else on Earth, and the plants growing in these cold places are responding in ways that ripple through entire landscapes. Arctic and alpine tundra — the treeless zones found above timberline in places like the slopes around Gothic, Colorado, and across the circumpolar north — share many ecological traits: short growing seasons, plants kept small by cold and wind, and soils that are often cold, wet, or seasonally frozen. Understanding how these communities respond to climate warming is central to predicting the future of mountain meadows in the Gunnison Basin and similar high-elevation ecosystems worldwide.
A few key concepts help make sense of the findings that follow. Plant functional groups are a way ecologists simplify diverse communities by sorting species into categories that behave similarly — for example, deciduous shrubs (like willows), evergreen shrubs, graminoids (grasses and sedges), mosses, and lichens. Tracking how these groups change tells us whether a meadow is staying the same, gaining woody plants, or losing its moss carpet. Shrub encroachment refers to woody plants spreading into areas formerly dominated by herbaceous vegetation, a change that alters snow capture, soil temperature, wildlife habitat, and carbon storage. Permafrost — ground that stays frozen year-round — underlies much of the Arctic tundra and, in patches, some alpine areas; when it thaws, it releases stored carbon and reshapes hydrology. Litter quality (how easily dead plant material breaks down) and decomposition determine how fast nutrients cycle back into soils, and nitrogen retention describes the ecosystem's ability to hold onto this limiting nutrient rather than losing it to streams or the atmosphere.
Finally, researchers often summarize community change with measures like Simpson diversity, which captures both how many species are present and how evenly abundant they are. At the landscape scale, space use — how animals like reindeer or pikas distribute themselves and move across terrain — links vegetation change to wildlife. Together, these concepts let us connect what happens in a single one-meter plot to the broader fate of mountain ecosystems like those surrounding RMBL.
The modern study of tundra response to warming was built on coordinated, long-term plot networks distributed across the Arctic and alpine. A foundational synthesis demonstrated that experimental warming — typically using small open-top chambers that raise air temperature a few degrees — consistently increased deciduous and low shrubs and decreased mosses and lichens, while grasses and sedges showed more variable responses depending on local temperature and moisture . This established the now-classic expectation that warming favors woody plants at the expense of cryptogams.
Way in which individuals distribute themselves across landscape, including movement patterns and spatial organization like home range size and overlap
Shift toward woody plant encroachment into nonwoody meadows and grasslands
Classification of species with similar characteristics into plant functional groups or plant functional types to reduce complexity in ecological commu...
Long-term monitoring of tundra plant communities using standardized sampling within permanently marked study areas, employing various abundance quanti...
Measurement of leaf traits including nitrogen concentration, phosphorus concentration, specific leaf area, and tensile strength in African woody speci...
Processing of gridded climate data from the CRU TS3.1 dataset with lapse rate adjustment for elevation differences between grid cells and actual study...
1. Evaluating climate effects on plant-soil interactions in terrestrial ecosystems remains challenging due to the fact that floristic composition co-v...
Uplands are land areas lying above the elevation where flooding generally occurs—areas found beyond riparian zones. Uplands represent the vast majorit...
Parallel work using observational plots rather than experimental warming showed that these shifts were not just theoretical: tundra plots monitored over years to decades were already changing in ways tightly linked to recent summer warming, with shrub cover increasing and community composition shifting in the direction predicted by the experiments (Elmendorf et al., 2012). Together, these two lines of evidence — manipulation and monitoring — gave the field confidence that warming is a primary driver of contemporary tundra change.
A central narrative emerging from this body of work is that warming reshapes tundra communities through both compositional shifts and trait changes, but not always in lockstep. Across the tundra biome, plant community height has increased measurably with warming at essentially all sites studied, reflecting both the spread of taller species and growth of existing ones (Bjorkman et al., 2018). Other traits tied to leaf economics — such as leaf nitrogen content and specific leaf area — have lagged behind the rates of change predicted from temperature alone, suggesting that moisture availability and slow species turnover constrain how quickly communities can track climate (Bjorkman et al., 2018).
The rise of shrubs and decline of mosses and lichens documented in warming experiments (Elmendorf et al., 2012) matters because these groups differ dramatically in litter quality, decomposition rates, and how they interact with snow. Taller shrubs trap more snow, insulating winter soils, while loss of moss cover exposes soil and changes nitrogen retention. Importantly, traditional plant functional groups — the deciduous-shrub, graminoid, moss categories ecologists have long relied on — explain only about 19 percent of the variation in measured plant traits across the tundra, and they poorly capture differences in plant size (Bjorkman et al., 2018). In other words, lumping species into broad categories misses much of the ecologically meaningful variation, especially for the size-related traits that matter most for carbon storage and snow trapping.
Winter processes have emerged as equally important to summer warming. A large international review found that snow accumulation governs ground temperature, light, and moisture, sets the start and end of the growing season, and shapes everything from microbial activity to plant-animal interactions (Rixen et al., 2022). Critically, the timing of snowmelt achieved in experimental snow manipulations (advances of about 8 days, delays of about 5 days) is much smaller than the natural variation observed across landscapes within a single year (about 56 days) or between years (about 32 days), meaning experiments may underestimate the magnitude of change ecosystems already experience (Rixen et al., 2022).
Early work in the 1990s and 2000s established that tundra plots respond to warming and that snowpack and runoff in basins like the Gunnison are sensitive to climate. Syntheses in the 2010s pulled these site-level results into biome-wide pictures of vegetation change (Elmendorf et al., 2012) (Bjorkman et al., 2018). Research since 2020 has shifted toward integrating winter processes, trait-based ecology, and cross-site comparisons that span both Arctic and alpine systems. The Rixen et al. (Rixen et al., 2022) review exemplifies this trajectory, explicitly comparing experimental and natural-gradient approaches and calling attention to the mismatch between them.
Methodologically, the field is moving from counting species toward measuring traits — leaf nitrogen, specific leaf area, plant height — and from summer-focused plots toward year-round observation that includes snow dynamics, winter soil temperatures, and shoulder-season phenology. Gridded climate products processed with elevation corrections are increasingly paired with on-the-ground monitoring to link plot-scale change to regional climate. For mountain systems like those around RMBL, this integration is especially valuable because alpine sites sit at the intersection of strong elevational gradients in snow, temperature, and moisture.
Several questions stand out for the next decade. How quickly will tundra communities catch up to the trait changes already predicted by climate, and what role does moisture — not just temperature — play in setting the pace? Will continued shrub encroachment trigger feedbacks through snow trapping and decomposition that accelerate or buffer further warming, and how will these feedbacks differ between Arctic tundra underlain by permafrost and alpine meadows that lack it? Can functional classifications be redesigned to capture size-related traits that traditional groupings miss, improving predictions of carbon and nitrogen cycling? And finally, how should experiments be designed so their snowmelt manipulations better reflect the much larger natural variability that ecosystems actually experience? Answering these questions will require sustained long-term monitoring at sites like RMBL, paired with biome-wide synthesis.
Bjorkman, A. D., et al. (2018). Plant functional trait change across a warming tundra biome. Nature. →
Bjorkman, A. D., et al. (2018). Traditional plant functional groups explain variation in economic but not size related traits across the tundra biome. →
Elmendorf, S. C., et al. (2012). Global assessment of experimental climate warming on tundra vegetation: heterogeneity over space and time. →
Elmendorf, S. C., Henry, G. H. R., Hollister, R. D., et al. (2012). Plot-scale evidence of tundra vegetation change and links to recent summer warming. Nature Climate Change. →
Rixen, C., et al. (2022). Winters are changing: snow effects on Arctic and alpine tundra ecosystems. Arctic Science. →