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Savanna Vegetation-Fire-Climate Relationships Differ Among Continents

Science  31 Jan 2014:
Vol. 343, Issue 6170, pp. 548-552
DOI: 10.1126/science.1247355

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  1. Fig. 1 Change in TBA of savannas relative to effective rainfall.

    The relationships between TBA and effective rainfall (in millimeters per year) across (A) Africa [coefficient of determination (r2) = 0.203, F(1, 363) = 92.4, P value = <0.001]; (B) Australia [r2 = 0.385, F(1, 1485) = 930.9, P value = < 0.001]; and (C) South America [r2 = 0.008, F(1, 300) = 2.6, P value = 0.111] are shown. Also depicted are the piecewise quantile fits of the 5th and 95th quantiles.

  2. Fig. 2 Climate domain of savannas in Africa, Australia, and South America.

    The savanna climate domain relative to (A) mean annual rainfall versus mean annual temperature and (B) effective rainfall versus annual temperature range. Black points represent all vegetated 0.5° grid cells within 30° of the equator across Africa, Australia, and South America. Gray points represent all 0.5° grid cells where savanna is present as in (14). Lines represent the 95th quantile of the density of these points for savanna on each continent.

  3. Fig. 3 Structural equation modeling of TBA for Africa, Australia, and South America.

    Structural equation modeling of TBA for Africa, Australia, and South America. (A) Conceptual model depicting theoretical relationships among moisture availability, soil fertility, plant growing conditions (temperature), and disturbance (fire frequency), and their effects on TBA either directly or indirectly as mediated by fire frequency. (B to D) The final model for each continent. Values associated with arrows are absolute path strengths, which combine positive and negative effects of indicators into a composite effect (17); the arrow thickness is proportional to the absolute path strength. The arrows from fire to TBA represent standardized path coefficients and are depicted in gray to express their negative impacts. Full models results are presented in (17).

  4. Fig. 4 Hypothetical shifts in aboveground woody biomass on three continents relative to a 4°C increase in mean annual temperature.

    Frequency distributions of the predicted anomalies in aboveground woody biomass (metric tons per hectare) with a 4°C increase in mean annual temperature, where a region-specific model and a global model are compared. Distributions are calculated at a 0.5° resolution. The global model shows the results of an analysis where “continent” is ignored (table S4).