Data from: Determinants and dynamics of banded vegetation pattern migration in arid climates

Dense vegetation bands aligned parallel to contour levels and alternating at regular intervals with relatively barren interbands have been reported at the margins of all tropical deserts. Since their discovery in the 1950s, it has been suspected that these vegetation bands migrate upslope, forming a space-time cyclic pattern. Evidence to date has been relatively sparse and indirect, and observations have remained conflicting. Unequivocal photographic evidence of upslope migration (a few dm yr-1) is provided here for three independent dryland areas exhibiting periodic banded pattern the U.S. northeastern Chihuahuan Desert (1), the Somalian Haud (2), and the Mediterranean steppes of eastern Morocco (3). Migration speeds, averaged through time and space using Fourier cross-spectral analysis, are shown to be directly proportional to pattern scale (wavelength). An aerial photography sequence of (1) showed that migration was not continuous but intermittent in response to fluctuating weather regimes. The rates at which bands expanded upslope and contracted downslope were better predicted by the change in annual rainfall than by its average level. However, migration of banded pattern cannot be considered as systematic because observations are reported from three other banded systems located in the Somalian Haud, central Australia, and western New South Wales in which migration was undetectable at the available image resolution. In each of the six sites under study, the modal value of band orientation axes was verified to be approximately orthogonal to the steepest slope. Our results underscore the importance of taking both the spatial structure and the past climate sequence into account for understanding vegetation dynamics in arid to semi-arid ecosystems. In addition, we show how Fourier spectral analysis applied to historical series of optical images can serve to quantify landscape dynamics at a decadal time scale.