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Woody plant encroachment facilitated by increased precipitation intensity

Nature Climate Change volume 3, pages 833–837 (2013)Cite this article

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Abstract

Global circulation models and empirical evidence suggest that precipitation events are likely to become more extreme across much of the globe1,2. As most plant roots are in shallow soils3,4,5, small but pervasive changes in precipitation intensity could be expected to cause large-scale shifts in plant growth, yet experimental tests of the effects of precipitation intensity are lacking6,7,8,9. Here we show that, without changing the total amount of precipitation, small experimental increases in precipitation intensity can push soil water deeper into the soil, increase aboveground woody plant growth and decrease aboveground grass growth in a savannah system. These responses seemed to reflect the ability of woody plants to increase their rooting depths and competitively suppress grass growth. In many parts of the world, woody plant abundance has multiplied in the past 50–100 years, causing changes in fire, forage value, biodiversity and carbon cycling10. Factors such as fire, grazing and atmospheric CO2 concentrations have become dominant explanations for this woody encroachment and semi-arid structure in general10,11,12. Our results suggest that niche partitioning is also an important factor in tree–grass coexistence and that the woody plant encroachment observed over the past century may continue in the future should precipitation intensity increase.

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Figure 1: Plant available water in control plots (blue symbols) and plots receiving fewer, larger precipitation events (treated; red symbols).
Figure 2: Woody plant growth in control plots (blue symbols) and plots receiving fewer, larger precipitation events (red symbols).
Figure 3: Grass height in control plots (blue symbols) and plots receiving fewer, larger precipitation events (red symbols).
Figure 4: The number of roots observed in control plots (blue symbols) and plots receiving fewer, larger precipitation events (red symbols).
Figure 5: Plant tracer uptake by depth in control plots (blue symbols) and plots receiving fewer, larger precipitation events (red symbols).

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Acknowledgements

We thank the Andrew Mellon Foundation, Alaska EPSCOR and the University of Alaska Anchorage’s Environment and Natural Resources Institute for financial support, South African National Parks for allowing us to do this research in Kruger, and E. February, W. Bond and the University of Cape Town for the shelters. Field managers: M. Cooper, M. Mazzacavallo, M. Keretetsi, S. Heath and L. Hierl. Field/laboratory assistants: W. Sibuye, R. Mashele, V. Sibuye and M. Rogers. Statistical advice: S. Durham. Experiments complied with the present laws of the Republic of South Africa. This research was supported by the Utah Agricultural Experiment Station, Utah State University, and approved as journal paper number 8538.

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Authors and Affiliations

  1. Department of Plants, Soils and Climate and the Ecology Center, Utah State University, Logan, Utah 84322-4820, USA

    Andrew Kulmatiski

  2. Department of Wildland Resources and the Ecology Center, Utah State University, Logan, Utah 84322-5230, USA

    Karen H. Beard

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A.K. and K.H.B conceived the research, oversaw measurements, analysed data and contributed to the preparation of the manuscript.

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Correspondence to Andrew Kulmatiski.

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The authors declare no competing financial interests.

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Kulmatiski, A., Beard, K. Woody plant encroachment facilitated by increased precipitation intensity. Nature Clim Change 3, 833–837 (2013). https://doi.org/10.1038/nclimate1904

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