Spatial patterns in defoliation and the expression of clonal traits in grazed meadows Marie-Lise Benot, Anne Bonis, Nicolas Rossignol, and Cendrine Mony Abstract: Clonal plant species dominate meadow vegetation where grazing can generate spatial heterogeneity at different scales and can select for species that express particular sets of clonal traits. This in situ study aimed to characterize fine- grained spatial patterns of defoliation (<1 m) induced by contrasting cattle grazing intensities and to link these spatial pat- terns with the abundance of species-specific clonal traits. Using correlogams and synthetic spatio-temporal indices, the het- erogeneity of vegetation height and leaf damage was monitored along a cattle grazing gradient. Species were identified and their clonal traits retrieved from the database CLO-PLA3. Under moderate grazing, fine-grained spatial patterns of de- foliation were not stable over time. Defoliation was heterogeneous during the first months of the grazing season and then became homogeneous. Intensive grazing generated homogeneous defoliation, regardless of the date. In the study meadow, grazing gave rise to communities containing a greater abundance of annual species. However, clonal traits assumed to ena- ble clonal fragments to benefit from heterogeneity do not seem advantageous. Increasing grazing intensity promoted spe- cies with clonal traits expected to minimize costs associated with clonality (aboveground clonal growth forms, short- distance lateral spread, and (or) short-lived connections). Ungrazed conditions favoured species with clonal traits associ- ated with a high competitive ability. Key words: cattle grazing, correlogams, fine scale, spatial heterogeneity, vegetation height. Re ´sume ´: Les plantes clonales dominent la ve ´ge ´tation de prairies, ou ` le pa ˆturage peut ge ´ne ´rer une he ´te ´roge ´ne ´ite ´ spatiale a ` diffe ´rentes e ´chelles et se ´lectionner des espe `ces exprimant diffe ´rentes combinaisons de traits clonaux. Cette e ´tude a pour objectifs de caracte ´riser in situ les patrons spatiaux de la de ´foliation induite par diffe ´rentes intensite ´s de pa ˆturage bovin a ` e ´chelle fine (<1 m) et d’e ´tablir la relation entre ces patrons spatiaux et l’abondance des espe `ces et de leurs traits clonaux. Par l’utilisation de corre ´logrammes et d’indices spatio-temporels synthe ´tiques, les patrons spatiaux de la hauteur de la ve ´- ge ´tation et des traces de de ´foliation sur les plantes ont e ´te ´e ´value ´s le long d’un gradient d’intensite ´ de pa ˆturage bovin. Les espe `ces ont e ´te ´ identifie ´es et leurs traits clonaux renseigne ´s dans la base de donne ´es CLO-PLA3. Les patrons spatiaux de la de ´foliation ge ´ne ´re ´e par un pa ˆturage mode ´re ´ ne sont pas stables au cours du temps. La de ´foliation est he ´te ´roge `ne pendant les premiers mois de la saison de pa ˆturage puis s’homoge ´ne ´ise. Quelle que soit la date, le pa ˆturage intensif ge ´ne `re une de ´- foliation homoge `ne. Dans la prairie e ´tudie ´e, le pa ˆturage est a ` l’origine d’une plus grande abondance d’espe `ces annuelles dans les communaute ´s. Cependant, les traits clonaux cense ´s permettre aux plantes de be ´ne ´ficier de conditions environne- mentales he ´te ´roge `nes ne semblent pas avantageux dans la prairie e ´tudie ´e. Une intensite ´ de pa ˆturage croissante a favorise ´ les espe `ces avec des traits clonaux cense ´s minimiser les cou ˆts associe ´s a ` la clonalite ´ (forme de croissance clonale ae ´rienne, faible expansion late ´rale et (ou) connexions a ` courte dure ´e de vie). A ` l’inverse, les conditions non pa ˆture ´es ont favorise ´ les espe `ces pourvues de traits clonaux confe ´rant aux plantes une aptitude compe ´titive e ´leve ´e. Mots-cle ´s : pa ˆturage bovin, corre ´logrammes, e ´chelle fine, he ´te ´roge ´ne ´ite ´ spatiale, hauteur de la ve ´ge ´tation. [Traduit par la Re ´daction] Introduction Grazing is a complex biotic factorthat strongly influences the composition and structure of vegetation (Huntly 1991). In particular, grazing may affect vegetation by generating spatial heterogeneity within very local areas (<1 m) and across much larger regions (several hundred meters), (Riet- kerk et al. 2000; Adler et al. 2001; Augustine 2003; see also Olofsson et al. 2008 for the particular case of rabbit grazing). Grazing-induced heterogeneity is often considered in terms of species composition (Bakker et al. 1983; Posse et al. 2000; Augustine 2003; Loucougaray et al. 2004; Col- lins and Smith 2006; Oom et al. 2008), light availability (Bakker et al. 2003; Veen et al. 2008), or soil properties (Posse et al. 2000; Augustine and Frank 2001; Anderson et al. 2004; Zhou et al. 2008). By contrast, only a handful of studies have paid attention to the effect of spatial patterns of defoliation (i.e., the removal of aboveground tissues caused by grazing animals) on plant communities (Oom et al. 2008; Olofsson et al. 2008). Yet, grazing-induced defoli- ation primarily consists of discrete events of a single bite, and could thus be heterogeneous at fine scales (Schwinning and Parsons 1999; WallisDeVries et al. 1999; see also Weber et al. 1998). The spatial patterns of grazing-induced Received 27 June 2010. Accepted 17 November 2010. Published on the NRC Research Press Web site at botany.nrc.ca on 7 January 2011. M.-L. Benot, 1 A. Bonis, N. Rossignol, 2 and C. Mony. UMR CNRS 6553, ECOBIO, Universite ´ de Rennes 1, Campus de Beaulieu, 35042 Rennes CEDEX, France. 1 Corresponding author (e-mail: mlbenot@gmail.com). 2 Present address: INRA, UR1213 Herbivores, Theix, 63122 Saint-Gene `s-Champanelle, France. 43 Botany 89: 43–54 (2011) doi:10.1139/B10-082 Published by NRC Research Press