Regular spatial patterns of vegetation are a common sight in drylands. Their formation
is a population-level response to water stress that increases water availability for the few
via partial plant mortality. At the individual level, plants can also adapt to water stress
by changing their phenotype. Phenotypic plasticity of individual plants and spatial
patterning of plant populations have extensively been studied independently, but the
likely interplay between the two robust mechanisms has remained unexplored. In this
paper, we incorporate phenotypic plasticity into a multi-level theory of vegetation
pattern formation and use a fascinating ecological phenomenon, the Namibian “fairy
circles,” to demonstrate the need for such a theory. We show that phenotypic changes
in the root structure of plants, coupled with pattern-forming feedback within soil
layers, can resolve two puzzles that the current theory fails to explain: observations of
multi-scale patterns and the absence of theoretically predicted large-scale stripe and
spot patterns along the rainfall gradient. Importantly, we find that multi-level responses
to stress unveil a wide variety of more effective stress-relaxation pathways, compared
to single-level responses, implying a previously underestimated resilience of dryland
ecosystems.
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