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Termite mounds can increase the robustness of dryland ecosystems to climatic change

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Science  06 Feb 2015:
Vol. 347, Issue 6222, pp. 651-655
DOI: 10.1126/science.1261487
  • Fig. 1 Patterned termite mounds in real ecosystems.

    (A) False-color infrared Quickbird satellite image (2.4-m resolution) of termite mounds at MRC; mounds appear as small red spots, indicating high primary productivity (larger red patches are abandoned cattle corrals). (B) Presumed termite mounds in northwestern Tanzania (–1.29158 latitude, 34.37146 longitude) identified by using Google Earth (2006 image copyright DigitalGlobe). Barren halos are visible around many mounds, as predicted by our model. (C) Grass-dominated mounds in Kenya’s Masai Mara, taken from hot-air balloon; elephants in the photo provide scale. (D) Tree-dominated mounds in Sofala, Mozambique, taken from helicopter (image courtesy of Marc Stalmans). (E) Light detection and ranging (LIDAR) hillshade image of termite mounds in South Africa’s Kruger National Park, from (25). (F) Termite mounds on Bangweulu floodplain, Zambia (image courtesy of Frans Lanting).

  • Fig. 2 Vegetation patterns obtained with stochastic rainfall and termite-induced heterogeneity.

    (A) Stochastic rainfall (brown curve) based on observed mean-monthly rainfall (blue curve) at MRC, 1999–2013. (B) Transect of predicted vegetation biomass density through a mound (solid curve) and in the absence of mounds (dashed curve). (C to E) Model outputs showing (C) 123- by 123-m region encompassing seven hexagonally distributed mounds; (D) 20.5- by 20.5-m region with only one mound, showcasing halo effect (for comparison, Fig. 1, B and D); and (E) 2- by 2-m region showing patchy off-mound vegetation and homogeneous on-mound vegetation. Green represents vegetation; brown represents soil. Darker green regions have higher biomass. Parameterization is provided in table S1.

  • Fig. 3 Correspondence of predicted and observed vegetation patterns.

    (A) Photograph of 3.5- by 6-m region of matrix vegetation taken from 10 m height. (B) 1.5- by 1.5-m section used in the analysis, from white square in (A). (C) Binary transformation of (B) (white represents vegetation, black represents soil). (D) Model output used for comparison, with parameterization as in Fig. 2. (E) Normalized radial spectrum of real images (n = 14 samples) and model simulations (n = 192 samples), as a function of wave number.

  • Fig. 4 Termite mounds increase ecosystem robustness.

    (A and B) Semilogarithmic phase diagrams under increasing (blue) and decreasing (red) rainfall for (A) model with no termite mounds and (B) the modified model with 50% on- versus off-mound improvement in both growth rate and infiltration efficiency. (A) Without mounds, one hysteresis cycle occurs (i), corresponding to sudden transitions to and from desertification. (B) Adding mounds generates two hysteresis cycles, corresponding to loss/recovery of matrix vegetation (i) and desertification/revegetation (ii). For both (A) and (B), we used fixed rainfall rates and parameters as described in table S1 and fig. S5.

  • Termite mounds can increase the robustness of dryland ecosystems to climatic change

    Juan A. Bonachela, Robert M. Pringle, Efrat Sheffer, Tyler C. Coverdale, Jennifer A. Guyton, Kelly K. Caylor, Simon A. Levin, Corina E. Tarnita

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Supplementary text
    • Figs. S1 to S8
    • Table S1
    • Full Reference List

    Images, Video, and Other Other Media

    Movie S1
    Sequence of snapshots obtained with the modified model with one mound, stochastic rainfall rate, and parameterization as in Fig. 2. The red solid circle in the rainfall function panel represents the actual value of R(t), whereas the mean value is given by the brown curve. This movies shows the whole mound and surroundings (~20m lateral size). Note that, with this dynamic rainfall function, there is a realistic delay between the rainfall rate and the effects on the vegetation; thus, only well into the dry season the system loses most of its vegetation, which resists on the mound and as underground biomass. Once the rain season is well underway, vegetation is regenerated in the whole ecosystem, with patterns that change as water availability changes.
    Movie S2
    Sequence of snapshots obtained with the modified model with one mound, stochastic rainfall rate, and parameterization as in Fig. 2. The zoom is at 2m×2m, as in Fig. 2E. The red solid circle in the rainfall function panel represents the actual value of R(t), whereas the mean value is given by the brown curve. This movie shows a zoom of the area close to the mound boundaries.

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