4.6 Article

Determinants and dynamics of banded vegetation pattern migration in arid climates

期刊

ECOLOGICAL MONOGRAPHS
卷 82, 期 1, 页码 3-21

出版社

WILEY
DOI: 10.1890/11-0362.1

关键词

aridity; Australia; banded patterns; Chihuahuan Desert; cross-spectral analysis; drought; patch dynamics; plant demography; remote sensing; self-organization; Somalia; tiger bush

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资金

  1. Fonds pour la formation a la Recherche clans l'Industrie et dans l'Agriculture (FRIA)
  2. Fonds David et Alice Van Buuren
  3. Agropolis Fundation
  4. Marie Curie (IEF FP7) grant

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Dense vegetation bands aligned 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 supposed 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 decimeters per year) is provided here for three independent dryland areas exhibiting periodic banded pattern: (1) the U.S. northeastern Chihuahuan Desert, (2) the Somalian Haud, and (3) the Mediterranean steppes of eastern Morocco. Migration speeds, averaged through time and space using Fourier cross-spectral analysis, are shown to be directly proportional to pattern scale (wavelength). A sequence of aerial photographs of the Chihuahuan Desert 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, the migration of banded patterns cannot be considered as systematic because in our observations of three other banded systems located in the Somalian Haud, central Australia, and western New South Wales, 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 semiarid 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.

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