Paper2 - v ol. 163, no. 5 the american naturalist may 2004...

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vol. 163, no. 5 the american naturalist may 2004 A Putative Mechanism for Bog Patterning M. Rietkerk, 1, * S. C. Dekker, 1, M. J. Wassen, 1, A. W. M. Verkroost, 1, § and M. F. P. Bierkens 2, k 1. Department of Environmental Sciences, Utrecht University, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands; 2. Department of Physical Geography, Utrecht University, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands Submitted August 7, 2003; Accepted December 3, 2003; Electronically published May 4, 2004 abstract: The surface of bogs commonly shows various spatial vegetation patterning. Typical are “string patterns” consisting of reg- ular densely vegetated bands oriented perpendicular to the slope. Here, we report on regular “maze patterns” on Fat ground, consisting of bands densely vegetated by vascular plants in a more sparsely vegetated matrix of nonvascular plant communities. We present a model reproducing these maze and string patterns, describing how nutrient-limited vascular plants are controlled by, and in turn control, both hydrology and solute transport. We propose that the patterns are self-organized and originate from a nutrient accumulation mech- anism. In the model, this is caused by the convective transport of nutrients in the groundwater toward areas with higher vascular plant biomass, driven by differences in transpiration rate. In a numerical bifurcation analysis we show how the maze patterns originate from the spatially homogeneous equilibrium and how this is affected by changes in rainfall, nutrient input, and plant properties. Our results con±rm earlier model results, showing that redistribution of a lim- iting resource may lead to ±ne-scale facilitative and coarse-scale com- petitive plant interactions in different ecosystems. Self-organization in ecosystems may be a more general phenomenon than previously thought, which can be mechanistically linked to scale-dependent fa- cilitation and competition. Keywords: hydrology, nutrient limitation, ombrotrophic, self- organization, solute transport, spatial patterns, vegetation patterns. The surface of bogs in North America and Eurasia com- monly shows various spatial patterning of hummocks and * E-mail: m.rietkerk@geog.uu.nl. E-mail: s.dekker@geog.uu.nl. E-mail: m.wassen@geog.uu.nl. § E-mail: a.verkroost@geog.uu.nl. k E-mail: m.bierkens@geog.uu.nl. Am. Nat. 2004. Vol. 163, pp. 699–708. q 2004 by The University of Chicago. 0003-0147/2004/16305-40052$15.00. All rights reserved. hollows (Sakaguchi 1980; Lindsay et al. 1985; Belyea and Lancaster 2002). Characteristic are the “string patterns” (Sakaguchi 1980; ²oster et al. 1983) consisting of regular densely vegetated bands (hummocks forming ridges) ori- ented perpendicular to the slope, alternating with wetter zones that are more sparsely vegetated (hollows forming pools). Current theoretical and empirical investigations show that spatial patterning in itself could be explained by a positive feedback between total plant productivity and thickness of the acrotelm (upper layer of peat) on slightly elevated, dryer sites, mainly because of increased produc-
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Paper2 - v ol. 163, no. 5 the american naturalist may 2004...

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