Rainfall intermittency and vegetation feedbacks in drylands

We discuss a simplifed, conceptual model for thedynamics of the soil-vegetation system in drylands. Themodel considers the different dynamical processes takingplace in vegetated and non-vegetated soil and it distinguishesbetween the upper soil layer, where rapid evaporation dominates,and the deeper root layer where only plant transpirationtakes place. We explore the role of rainfall intermittencyand of different plant colonization strategies, and discuss indetail the effect of two different vegetation feedbacks: reducedevaporation due to plant shading and increased infiltrationin vegetated areas. The results of the analysis indicatethat both temporal rainfall intermittency and the shading/infiltration feedbacks have a beneficial effect on vegetation.However, it turns out that in this model rainfall intermittencyand vegetation feedbacks have almost a mutuallyexclusive role: whenever one of these two components ispresent, the addition of the other does not further affect vegetationdynamics in a significant way.