Increasing temperature seasonality may overwhelm shifts in soil moisture to favor shrub over grass dominance in Colorado Plateau drylands
Ecosystems in the southwestern U.S. are predicted to experience continued warming and drying trends of the early twenty-first century. Climate change can shift the balance between grass and woody plant abundance in these water-limited systems, which has large implications for biodiversity and ecosystem processes. However, variability in topo-edaphic conditions, notably soil texture and depth, confound efforts to quantify specific climatic controls over grass vs. shrub dominance. Here, we utilized weather records and a mechanistic soil water model to identify the timing and depth at which soil moisture related most strongly to the balance between grass and shrub dominance in the southern Colorado Plateau. Shrubs dominate where there is high soil moisture availability during winter, and where temperature is more seasonally variable, while grasses are favored where moisture is available during summer. Climate change projections indicate consistent increases in mean temperature and seasonal temperature variability for all sites, but predictions for summer and winter soil moisture vary across sites. Together, these changes in temperature and soil moisture are expected to shift the balance towards increasing shrub dominance across the region. These patterns are strongly driven by changes in temperature, which either enhance or overwhelm effects of changes in soil moisture across sites. This approach, which incorporates local, edaphic factors at sites protected from disturbance, improves understanding of climate change impacts on grass vs. shrub abundance and may be useful in other dryland regions with high edaphic and climatic heterogeneity.
KeywordsDrylands Soil water modeling Climate change Ecohydrology Water balance Woody plant encroachment
This research was funded by the USGS National Park Monitoring Program and made possible by the National Park Service Inventory and Monitoring Division and the Southern Colorado Plateau Network (SCPN). We would like to thank Megan Swan and Jim DeCoster who manage the upland vegetation monitoring project for SCPN, and data managers Lee McCoy and Cindy Parker for their assistance with compiling vegetation, climate, and soils data as well as providing general consultation about details of the ecosystems in the study. Thanks also to James Allen and the Northern Arizona University field crews who collaborated with NPS to collect field data. Finally, we would like to thank four anonymous reviewers for valuable comments. Any use of trade, product, or firm names in this paper is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Author contribution statement
JBB, JRG, LPT, JRN, SMM, and MCD developed research ideas and approach, JRG, JBB, and CA developed and conducted analyses. JRG wrote the manuscript with assistance and editing from all co-authors.
- Andrews C, Bradford J, Norris J, Gremer JR, Duniway M, Munson S, Thomas L, Swan M (2018) Describing past and future soil moisture in the loamy upland shrubland community in Wupatki National Monument. Project Brief. National Park Service. Fort Collins, Colorado. https://www.nps.gov/articles/modeling-past-and-future-soil-moisture-in-parks.htm
- Bernacchi CJ, Portis AR, Nakano H, von Caemmerer S, Long SP (2002) Temperature response of mesophyll conductance. Implications for the determination of rubisco enzyme kinetics and for limitations to photosynthesis in vivo. Plant Physiol 130:1992–1998. https://doi.org/10.1104/pp.008250 CrossRefPubMedPubMedCentralGoogle Scholar
- Breshears DD (2006) The grassland–forest continuum: trends in ecosystem properties for woody plant mosaics? Front Ecol Environ 4:96–104. https://doi.org/10.1890/1540-9295(2006)004%5b0096:TGCTIE%5d2.0.CO;2 CrossRefGoogle Scholar
- Caudle DH, Sanchez H, DiBenedetto J, Talbot CJ, Karl MS (2013) Interagency ecological site handbook for rangelands. U.S. Department of the Interior, Bureau of Land ManagementGoogle Scholar
- Comstock JP, Ehleringer JR (1992) Plant adaptation in the Great-Basin and Colorado Plateau. Gt Basin Nat 52:195–215Google Scholar
- DeCoster JK et al (2012) Integrated upland monitoring protocol for the Southern Colorado Plateau Network. Natural Resource Technical Report NPS/SCPN/NRR–2012/577. National Park Service, Fort CollinsGoogle Scholar
- Diffenbaugh NS, Giorgi F, Pal JS (2008) Climate change hotspots in the United States. Geophys Res, Lett, p 35Google Scholar
- Epstein HE, Gill RA, Paruelo JM, Lauenroth WK, Jia GJ, Burke IC (2002) The relative abundance of three plant functional types in temperate grasslands and shrublands of North and South America: effects of projected climate change. J Biogeogr 29:875–888. https://doi.org/10.1046/j.1365-2699.2002.00701.x CrossRefGoogle Scholar
- Fleischner TL (1994) Ecological costs of livestock grazing in Western North America. Conserv Biol 8:629–644. https://doi.org/10.1046/j.1523-1739.1994.08030629.x CrossRefGoogle Scholar
- Hamlet AF, Salathé EP, Carrasco P (2010) Statistical downscaling techniques for global climate model simulations of temperature and precipitation with application to water resources planning studies. In: Chapter 4. Final Report for the Columbia Basin Climate Change Scenarios Project. Climate Impacts Group, Center for Science in the Earth System, Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, SeattleGoogle Scholar
- IPCC (2014) Climate change 2014: impacts, adaptation, and vulnerability. Part B: regional aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. In: Barros VR, Field CB, Dokken DJ, Mastrandrea MD, Mach KJ, Bilir TE, Chatterjee M, Ebi KL, Estrada YO, Genova RC, Girma B, Kissel ES, Levy AN, MacCracken S, Mastrandrea PR, White LL (eds) Cambridge University Press, Cambridge, p 688Google Scholar
- Jackson RB, Banner JL, Jobbagy EG, Pockman WT, Wall DH (2002) Ecosystem carbon loss with woody plant invasion of grasslands. Nature 418:623–626. http://www.nature.com/nature/journal/v418/n6898/suppinfo/nature00910_S1.html CrossRefGoogle Scholar
- Moss RH et al (2010) The next generation of scenarios for climate change research and assessment. Nature 463:747–756. http://www.nature.com/nature/journal/v463/n7282/suppinfo/nature08823_S1.html CrossRefGoogle Scholar
- Pinheiro J, Bates D, DebRoy S, Sarkar D, Team RC (2017) nlme: linear and nonlinear mixed effects models. R package version 3.1-131. https://CRAN.R-project.org/package=nlme
- Sala OE, Lauenroth WK, Golluscio RA (1997) Plant functional types in temperate semi-arid regions. In: Smith TM, Shugart HH, Woodward FI (eds) Plant functional types. Cambridge University Press, Cambridge, pp 217–233Google Scholar
- Soil Survey Staff NRCS, United States Department of Agriculture (2016) Web Soil Survey. https://websoilsurvey.nrcs.usda.gov/
- Walter H (1971) Ecology of tropical and subtropical vegetation. Oliver and Boyd, EdinburghGoogle Scholar
- Walter H (1973) Vegetation of the earth in relation to climate and the eco-physiological conditions. Translated from the second German edition by J. Wieser. Springer, New YorkGoogle Scholar