Ecology, 94(9), 2013, pp. 2007–2018 Ó 2013 by the Ecological Society of America Climate interacts with soil to produce beta diversity in Californian plant communities B. M. FERNANDEZ-GOING, 1,5 S. P. HARRISON, 2 B. L. ANACKER, 3 AND H. D. SAFFORD 2,4 1 Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California 93106 USA 2 Department of Environmental Science and Policy, University of California, One Shields Avenue, Davis, California 95616 USA 3 Department of Evolution and Ecology, University of California, One Shields Avenue, Davis, California 95616 USA 4 USDA Forest Service, Pacific Southwest Region, 1323 Club Drive, Vallejo, California 94592 USA Abstract. Spatially distinct communities can arise through interactions and feedbacks between abiotic and biotic factors. We suggest that, for plants, patches of infertile soils such as serpentine may support more distinct communities from those in the surrounding non-serpentine matrix in regions where the climate is more productive (i.e., warmer and/or wetter). Where both soil fertility and climatic productivity are high, communities may be dominated by plants with fast-growing functional traits, whereas where either soils or climate impose low productivity, species with stress-tolerant functional traits may predominate. As a result, both species and functional composition may show higher dissimilarity between patch and matrix in productive climates. This pattern may be reinforced by positive feedbacks, in which higher plant growth under favorable climate and soil conditions leads to higher soil fertility, further enhancing plant growth. For 96 pairs of sites across a 200-km latitudinal gradient in California, we found that the species and functional dissimilarities between communities on infertile serpentine and fertile non-serpentine soils were higher in more productive (wetter) regions. Woody species had more stress-tolerant functional traits on serpentine than non-serpentine soil, and as rainfall increased, woody species functional composition changed toward fast-growing traits on non- serpentine, but not on serpentine soils. Soil organic matter increased with rainfall, but only on non-serpentine soils, and the difference in organic matter between soils was positively correlated with plant community dissimilarity. These results illustrate a novel mechanism wherein climatic productivity is associated with higher species, functional, and landscape-level dissimilarity (beta diversity). Key words: beta diversity; climate gradient; landscape diversity; precipitation; serpentine; soil fertility. INTRODUCTION Understanding the origins and consequences of spatial heterogeneity is a central goal of landscape and ecosystem ecology (Turner and Chapin 2005). Spatially distinct plant communities may arise not only as a direct consequence of heterogeneity in the physical environ- ment, but through interactions and feedbacks among biotic and abiotic factors (Meinders and van Breemen 2005). For example, in semiarid environments, moisture retention caused by small-scale topography gives rise to discrete patches of vegetation in which soil nutrients and water supply are enhanced, further accentuating the distinctness of patch and interpatch areas (Tongway and Ludwig 2005). In turn, landscapes containing higher diversities of community or habitat types support greater numbers of plant and animal species, underpin- ning the species–area relationship (Kallimanis et al. 2008, Hortal et al. 2009). In such mosaic environments, the sizes and spatial configurations of habitat patches exert strong influences on the movement of materials and organisms and hence on population viability (Fahrig and Nuttle 2005), ecosystem productivity (Loreau et al. 2003), and evolution (Hanski et al. 2011). Spatial habitat diversity may also be connected to large-scale patterns in species diversity, such as high species richness in productive climates (Francis and Currie 2003, Hawkins et al. 2003), although the relationship of habitat diversity to productivity remains largely unexplored. Recent evidence suggests that beta diversity, or spatial dissimilarity in species composition, increases with productivity (Chase and Leibold 2002, Chase 2010), including along climatically driven pro- ductivity gradients (Qian and Ricklefs 2007, Soininen et al. 2007, Field et al. 2009, Kraft et al. 2011). Higher productivity has been shown to correlate with both stochastic beta diversity, community dissimilarity aris- ing from ecological drift (Chase 2010), and ‘‘determin- istic’’ beta diversity, or community dissimilarity along biotic or abiotic gradients (Harrison et al. 2010). Manuscript received 15 November 2012; revised 7 March 2013; accepted 28 March 2013. Corresponding Editor: J. B. Yavitt. 5 E-mail: going@lifesci.ucsb.edu 2007