Theory 33/Grassland & Savanna/Tree cover
Tree Cover Is Rooting Depth
The claim
Savanna tree cover is set by the ratio of rooting depth to rainfall seasonality, so deep-rooted trees persist where rainfall is strongly seasonal.
01Mechanism
Deep roots access water through the dry season; the ratio determines whether trees can stay active while grasses senesce.
02Prediction
Cover should track the ratio.
03Refutation
Cover tracking rainfall would remove rooting depth.