  Self-organized spatial patterns of vegetation are frequent in drylands and,
because pattern shape correlates with water availability, they have been
suggested as important indicators of ecosystem health. However, the mechanisms
underlying pattern emergence remain unclear. Some theories hypothesize that
patterns could result from a water-mediated scale-dependent feedback (SDF)
whereby interactions favoring plant growth dominate at short distances and
growth-inhibitory interactions dominate in the long range. However, we know
little about how the presence of a focal plant affects the fitness of its
neighbors as a function of the inter-individual distance, which is expected to
be highly ecosystem-dependent. This lack of empirical knowledge and system
dependency challenge the relevance of SDF as a unifying theory for vegetation
pattern formation. Assuming that plant interactions are always inhibitory and
only their intensity is scale-dependent, alternative theories also recover the
typical vegetation patterns observed in nature. Importantly, although these
alternative hypotheses lead to visually indistinguishable patterns, they
predict contrasting desertification dynamics, which questions the potential use
of vegetation patterns as ecosystem-state indicators. To help resolve this
issue, we first review existing theories for vegetation self-organization and
their conflicting predictions about desertification dynamics. Second, we
discuss potential empirical tests via manipulative experiments to identify
pattern-forming mechanisms and link them to specific desertification dynamics.
A comprehensive view of models, the mechanisms they intend to capture, and
experiments to test them in the field will help to better understand both how
patterns emerge and improve predictions on the fate of the ecosystems where
they form.
