Abstract
Vast dryland regions around the world are affected by the encroachment of woody vegetation, with important environmental and economical implications. Grassland-to-shrubland conversions are often triggered by disturbance of grassland vegetation, and the consequent formation of barren areas prone to erosion-induced nutrient losses. Inhibition of encroachment by erosion-induced depletion of soil nutrients contributes to the emergence of highly heterogeneous landscapes with shrub-dominated fertility islands surrounded by nutrient-poor bare soil. Here, we develop a process-based simplistic model thataccounts for the two competing processes of resource depletion and shrub encroachment by a non-linear diffusion mechanism. The proposed model is able to generate stable vegetation patterns with the same statistical properties as those observed in areas with well-developed fertility islands. We also show how a subsequent disturbance of shrubland vegetation can shift the dynamics toward states with smaller vegetation biomass. The process of land degradation may then occur through a number of irreversible intermediate transitions associated with losses in ecosystem function.
Highlights
The conversion of semiarid grasslands into shrublands (e.g., Scholes and Archer 1997) has been observed in many regions of the world, including North America (e.g., Archer 1989, van Auken 2000), South America (e.g., Adamoli et al 1990), Africa (e.g., Scott 1966, Hudak and Wessman 2001), and Australia (e.g., Sharp and Whittaker 2003)
The spatial and temporal dynamics of shrub vegetation and available resources expressed by Eqs. (5) and (6) generate vegetation patterns (Fig. 1) similar to those observed in regions where the existence of fertility islands has been welldocumented (e.g., Tiedermann and Klemmedson 1986)
In this model, vegetation patterns do not emerge as a result of prescribed spatially correlated heterogeneities associated with soils or micro-relief, but from the mutual inhibition between the two processes of resource depletion and shrub encroachment
Summary
The conversion of semiarid grasslands into shrublands (e.g., Scholes and Archer 1997) has been observed in many regions of the world, including North America (e.g., Archer 1989, van Auken 2000), South America (e.g., Adamoli et al 1990), Africa (e.g., Scott 1966, Hudak and Wessman 2001), and Australia (e.g., Sharp and Whittaker 2003) This process is often associated with the formation of heterogeneous landscapes with unfertile bare areas separated by nutrient-rich soil plots colonized by shrubs (Charley and West 1975, Schlesinger et al 1990). The erosion-driven degradation of intercanopy soils and the consequent emission and transport of nutrient-rich atmospheric dust are known to have important implications on regional and global climate (Ramanathan et al 2001, Rosenfeld et al 2001, Prospero and Lamb 2003), biogeochemical cycles (Duce and Tindale 1991, Swap et al 1992, Okin et al 2004), desertification (e.g., Schlesinger and Pilmanis 1998, Reynolds et al 1999, Maestre et al 2006), and human health (Dockery and Pope 1994)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
