MAXIMUM ROOTING DEPTH OF VEGETATION TYPES AT THE GLOBAL-SCALE

The depth at which plants are able to grow roots has important implica tions for the whole ecosystem hydrological balance, as well as for car bon and nutrient cycling. Here we summarize what we know about the max imum rooting depth of species belonging to the major terrestrial biome s. We found 290 observations of maximum rooting depth in the Literatur e which covered 253 woody and herbaceous species. Maximum rooting dept h ranged from 0.3 m for some tundra species to 68 m for Boscia albitru nca in the central Kalahari; 194 species had roots at least 2 m deep, 50 species had roots at a depth of 5 m or more, and 22 species had roo ts as deep as 10 m or more. The average for the globe was 4.6+/-0.5 m. Maximum rooting depth by biome was 2.0+/-0.3 m for boreal forest, 2.1 +/-0.2 m for cropland, 9.5+/-2.4 m for desert, 5.2+/-0.8 m for sclerop hyllous shrubland and forest, 3.9+/-0.4 m for temperate coniferous for est, 2.9+/-0.2 m for temperate deciduous forest, 2.6+/-0.2 m for tempe rate grassland, 3.7+/-0.5 m for tropical deciduous forest, 7.3+/-2.8 m for tropical evergreen forest, 15.0+/-5.4 m for tropical grassland/sa vanna, and 0.5+/-0.1 m for tundra. Grouping all the species across bio mes (except croplands) by three basic functional groups: trees, shrubs , and herbaceous plants, the maximum rooting depth was 7.0+/-1.2 m for trees, 5.1+/-0.8 m for shrubs, and 2.6+/-0.1 m for herbaceous plants. These data show that deep root habits are quite common in woody and h erbaceous species across most of the terrestrial biomes, far deeper th an the traditional view has held up to now. This finding has important implications for a better understanding of ecosystem function and its application in developing ecosystem models.