Shrub expansion and alpine plant community change: 40-year record from Niwot Ridge, Colorado

ABSTRACT

Background: Alpine and arctic tundra are particularly sensitive ecosystems to the impacts of global climate change. Yet, warming studies versus observational studies in these ecosystems yield different and sometimes conflicting results. Many short-term changes may be phenotypic responses to warming rather than shifts at the community level.

Aims: We posit that long-term monitoring of permanently marked plots provides data for making predictions of the impact of climate change on alpine tundra communities.

Methods: We surveyed plant community composition and cover at four sampling time points over a forty-year span (1971–2011).

Results: We observed an expansion of shrub cover, both within the shrub tundra and encroaching into moist and dry meadow communities. This shrub cover expansion coincides with increased litter and decreased species richness at the plot level. Overall, despite some shifts in functional group cover and species richness, plant community composition remained mostly intact across forty years.

Conclusions: Our results corroborate with other published studies demonstrating the rapid expansion and impacts of woody shrubs in tundra ecosystems. This study demonstrates a surprising resistance of alpine tundra plant communities under current global climate change over a 40-year period. Additional studies are needed to disentangle the many potential drivers that explain plant community shifts and community stability.

KEYWORDS:

• Alpine
• plant community
• long-term monitoring
• shrub encroachment
• tundra

Acknowledgements

Hope Humphries and Paul Alaback provided valuable field assistance, as did Kelly Matheson at the Mountain Research Station, University of Colorado, Boulder. We thank the Weber-Wetzel lab group for their feedback on drafts of this manuscript, and C. Baskett and E. Kraichak for suggestions regarding analyses.

Data-availability

The data that support the findings of this study are openly available in the LTER Network Data Portal at http://doi.org/doi:10.6073/pasta/973821e62fd6d33481f31fc0201fbd5c, package number knb-lter-nwt.501.1.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Funding for this study was provided by NSF (ANS-0732885), the NSF-NIWOT LTER to the University of Colorado, Boulder [ANS-0732885] and Michigan State University (University Distinguished Professor fund) .

Notes on contributors

Klara Scharnagl

Klara Scharnagl is interested in fungal symbioses, and in using long-term monitoring to understand community dynamics of plants and fungi.

David Johnson

David Johnson is interested in urban ecology, herbivory and the effects of climate change on arctic and alpine plant communities

Diane Ebert-May

Diane Ebert-May is interested in the effect of climate change on alpine tundra plant communities and discipline-based biology education research.