- Plant characteristics are poor predictors of microsite colonization - 397 Journal of Vegetation Science 17: 397-406, 2006 © IAVS; Opulus Press Uppsala. Plant characteristics are poor predictors of microsite colonization during the first two years of primary succession Walker, Lawrence R. 1* ; Bellingham, Peter J. 2 & Peltzer, Duane A. 2 1 Department of Biological Sciences, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154- 4004, USA; 2 Landcare Research, PO Box 69, Lincoln 8152, New Zealand; E-mail bellinghamp@landcareresearch.co.nz; peltzerd@landcareresearch.co.nz: * Corresponding author; Fax +1 702 895 3956; E-mail walker@unlv.nevada.edu; Website http://biology.unlv.edu/NewPage/faculty/LR%20Walker.htm Abstract Questions: Do plant characteristics predict microsite coloni- zation in severe habitats dominated by abiotic factors? Spe- cifically, does colonization of microsites differ among shrubs, forbs and grasses or between wind- and water-dispersed plants, non-native and native plants, or N-fixing and non-N-fixing plants? Location: Kowhai River floodplain, Kaikoura, South Island, New Zealand. Methods: Five microsite characteristics were measured for > 1000 individuals representing 27 colonizing plant species on a two-year old surface of a primary succession on a New Zea- land floodplain. The microsite characteristics included surface contour (convex, concave, or flat), the position of the plant (e.g., upstream, downstream) relative to the closest rock with > 20 cm maximum dimension, the distance to that same rock, the depth of the base of the stem below the surface of a plane resting on the adjacent microrelief, and soil particle size (gravel, pebbles or sand). Results: All plants preferred concave microsites near large rocks relative to systematically placed null points. We found no clear preferences for microhabitats by dispersal mode, native vs. non-native status, or plants with or without nitrogen- fixing symbionts, but grasses preferentially colonized fine soil particles. Highly variable responses among species contrib- uted to these results. Better predictability of microsite prefer- ence was obtained for individual species than for plants grouped by characteristics. Conclusions: Our results suggest that in severe habitats with strong abiotic filters and low microsite availability, such as found in early primary succession, coarse categories of species characteristics are poor predictors of colonization success. Keywords: Dispersal mode; Filter; Floodplain; Functional group; Growth form; Native; New Zealand; Nitrogen fixation; Non-native; Surface contour. Nomenclature: Allan (1961) with amendments suggested by Connor & Edgar (1987); Webb et al. (1988); Edgar & Connor (2000). Introduction How plant species assemble and interact in succes- sion is a long-standing enigma with important implica- tions for ecological theory and restoration. One way to explore this issue is to examine plant characteristics (e.g., traits, attributes) thought to control colonization dynamics. Microsites that provide favourable condi- tions for seed germination and seedling establishment are often scarce on the infertile, unstable substrates that dominate primary succession. This scarcity of suitable sites, combined with a lack of significant biological legacies, makes primary seres excellent but often over- looked systems in which to examine colonization dy- namics and search for evidence of community assembly (Booth & Larson 1999; del Moral & Lacher 2005). Unpredictable disruptions of the abiotic environment are likely to predominate over biological determinism in severe environments (Walker & del Moral 2003). In contrast, most generalizations about plant assembly in- voke biotic filters (sensu Díaz et al. 1998) and derive from fertile, stable sites such as wetlands (Wilson & Whittaker 1995; Weiher et al. 1998), lawns (Wilson & Roxburgh 1994) and old fields (Fukami et al. 2005). Successful colonization of microsites can have long- lasting implications for ecosystem function (Díaz et al. 2004), species composition (van Andel et al. 1993), competitive success (Matthews 1992; S.D. Wilson 1999) and long-term successional trajectories (Walker & del Moral 2003). Initial partitioning of microsites among colonizing plant species in succession is thought to be controlled by dispersal dynamics (Wood & del Moral 1987; van der Valk 1992), order of arrival (Egler 1954), physiological tolerances of abiotic stresses (Chapin 1993) and relative success of certain plant characteristics (i.e. growth form and functional groups; Gitay & Noble 1997; Prach & Pyšek 1999) but it is still unresolved to what degree plant species that share similar characteris- tics tend to colonize similar microsites (Bell 2005).