How landscape modulators function: woody plant impact on seed dispersal and abiotic filtering O. Gabay • A. Perevolotsky • M. Shachak Received: 2 November 2011 / Accepted: 9 February 2012 / Published online: 21 February 2012 Ó Springer Science+Business Media B.V. 2012 Abstract The Mediterranean landscape is charac- terized by a heterogeneous structure: a mosaic of woody plants (trees or shrubs) with scattered patches of herbaceous vegetation. Although the herbaceous and woody patches are adjacent to each other, plant species composition in them is substantially different. This could be attributed to either differences in environmental conditions between patch types (i.e., abiotic filters), or to dispersal limitations caused by the woody plants acting as dispersal filters. In this article, we focus on the relative impact of woody plants, applying these two filter types, in determining plant species composition in Mediterranean woodland. We experimentally manipulated shade and litter cover and examined the effect of each of these factors on plant species composition. We used seed-traps to evaluate seed arrival in the patches, and experimentally removed the shrub canopy to study the effect of the shrub as a physical barrier to seed entry. Results showed that plant species number and composition were not significantly affected by shade and litter manipulation. The number of trapped seeds were significantly higher in the open patches than in the woody patches, and removal of woody plants increased the number of trapped seeds in both open and woody patches, as a result of eliminating the physical obstacle to free seed movement. Our findings show that woody plants affect the herbaceous plant community by influencing seed dispersal, and high- light that they affect other organisms not only by modifying resource availability but also through the creation of a new landscape structure. Keywords Ecological filtering Á Ecosystem engineers Á Mediterranean ecosystem Á Seed dispersal Á Woody plants Introduction Woody plants (trees or shrubs) can change biotic or abiotic conditions in their environment and thereby modify the availability of resources to other species (Callaway and Walker 1997). Therefore, woody plants form patches that differ from non-woody (herbaceous) patches in their microclimates, soil properties, and water availability. By causing state changes in biotic and abiotic conditions, woody plants act as ecosystem engineers (Jones et al. 1994). As their environmental impact involves patch creation rather than modifica- tion of ecosystem processes, they are considered also as landscape modulators (Shachak et al. 2008). O. Gabay (&) Á M. Shachak Blaustein Institutes for Desert Research, Ben-Gurion University, 84990 Midreshet Sede-Boqer, Israel e-mail: gabayofri@gmail.com A. Perevolotsky Department of Agronomy and Natural Resources, Agricultural Research Organization, 50250 Bet Dagan, Israel 123 Plant Ecol (2012) 213:685–693 DOI 10.1007/s11258-012-0033-5