Mapping the global distribution of deep roots in relation to climate and soil characteristics

Global data sets of rooting depths, long-term means of monthly precipitation and potential evapotranspiration, and soil texture were used to predict the probability of deep rooting around the globe. Rooting depths were considered to be deep if 5% or more of all roots in a profile were located below 2 m depth. Spatially explicit global predictions were based on empirical models relating the probability of deep rooting with climate and soil texture. Based on these predictions, deep roots are most likely to occur in seasonally dry, semiarid to humid tropical regions under savanna or thorn-scrub vegetation or under seasonally dry semideciduous to evergreen forests. Deep roots are least likely to occur in arctic, boreal or cool-temperate regions and in per-humid climates such as equatorial rain forests. Under warm-temperate to tropical climates, rooting depths are more likely to be deep in coarse-textured and fine-textured soil than in soils of medium texture. These observations agree well with predictions based on a previously published conceptual model, according to which water infiltration depths and evaporative demand are the main climatic factors to determine vertical root distributions on a global scale.