Facilitation of Quercus ilex in Mediterranean shrubland is explained by both direct and indirect interactions mediated by herbs

Abstract

Summary 1.Competitive and facilitative interactions shape plant communities. Whereas a number of studies have addressed competition and direct facilitation among plants in dry ecosystems, indirect facilitation has received little attention. 2. We investigated the relative importance of direct and indirect facilitation by the nurse plant Retama sphaerocarpa on late-successional Quercus ilex seedlings mediated by herb suppression in a Mediterranean shrubland in 2006 and 2007. We also studied whether facilitation outcome depended on the size of the facilitated seedlings. 3. A field experiment was carried out to test the effect of (i) position of Q. ilex seedling with respect to shrub canopy (under shrubs or in gaps), (ii) herb competition (presence or absence), and (iii) seedling size. 2006 was an average rainfall year while 2007 had a much more humid spring and a dryer summer than 2006. 4. In both years, nurse shrubs reduced seedling mortality whereas herbs increased it. In the average rainfall year, seedling mortality under shrubs was unaffected by herbs whereas in gaps it was significantly higher in presence of herbs. This showed that the nurse shrub indirectly facilitated the seedlings by reducing the competitive capacity of herbs. Conversely, facilitation was predominately direct during the humid spring and dry summer year since herbs hindered seedling survival similarly under the nurse shrub and in gaps. The nurse shrub directly facilitated the seedlings by reducing seedling photoinhibition and water stress. 5. Improvement of environmental conditions by Retama benefited smaller seedlings but not larger seedlings since the nurse shrub reduced mortality of smaller seedlings relative to that in gaps, but this effect was not observed for larger seedlings. This indicates that individuals within a seedling population may not have the same response to facilitation. 6. Synthesis. Both indirect and direct facilitation are important mechanisms for Q. ilex regeneration in Retama shrubland and their importance seems to vary with climatic conditions. Indirect facilitation by release of herb competition under nurse shrubs is important in years of dry springs when competition between nurse shrubs and herbs is high, whereas direct facilitation mediated by microclimate amelioration increases with summer aridity.

Predation and aridity slow down the spread of 21-year-old planted woodland islets in restored Mediterranean farmland

“…We found low rates of seedling survival, consistent with previous studies on Quercus establishment in Mediterranean environments (Rey Benayas et al 2005;Castro et al 2006;Valdecantos et al 2006;Del Campo et al 2010, Cuesta et al 2010a. As we anticipated (H3), most of this mortality was a consequence of seedling predation; all of unprotected seedlings in the seeding experiment and at least 50 % of the naturally established seedlings (which were not protected) were predated by the end of the first growing season.…”

“…Key constraints on the speed of regeneration include (1) dispersal limitation because seed sources are remote and dispersal vectors may be rare (Rey Benayas et al 2008a;Pons and Pausas 2007a;Zamora et al 2010;Ramos-Palacios et al 2014); (2) seed predation Pérez-Ramos and Marañón 2008;Gómez and Hódar 2008;Leiva and Fernández 2003); (3) biotic limitation such as competition from established woody vegetation and herbaceous vegetation (Rey Benayas et al 2005;Cuesta et al 2010a), and herbivory Puerta et al 2012); and (4) abiotic limitation such as low water availability, extreme temperatures, poor soil structure and low nutrient availability (Rey Benayas 1998;Cuesta et al 2010b). Intensification of land use has brought remnant areas of natural or semi-natural vegetation into mainstream agriculture and as a result many of such areas have been lost or severely degraded.…”

Complex facilitation and competition in a temperate grassland: loss of plant diversity and elevated CO2 have divergent and opposite effects on oak establishment

“…Further work should be conducted in this area to show a direct causal relationship between micro-climate variables and plant facilitation at this site. Positive facilitative relationships between aboveground cover and seedling survival have been documented in grasslands (Dickie et al 2007), shrublands (Cuesta et al 2010), and temperate forest gaps (Montgomery et al 2010), although evidence for a relationship between herbaceous cover and shrub invasion in southwestern arid grasslands of the USA is varied (Van Auken and Bush 1997;Brown and Archer 1999;Van Auken 2000). In those examples where herbaceous biomass has been found to increase seedling survival, aboveground cover protects small seedlings from Survival (%) Fig.…”

“…Survival rates of young plants tend to increase with increasing canopy cover, particularly in ecosystems that experience extreme abiotic conditions (Bertness and Callaway 1994;Miriti 2006;Cuesta et al 2010;Bustamente-Sanchez et al 2011;Farrer and Goldberg 2011). This facilitation effect is due to amelioration of the microclimate under higher density canopies (Callaway 1995;Callaway and Walker 1997;Cuesta et al 2010;Bustamente-Sanchez et al 2011).…”

The ecological adaptability of four typical plants during the early successional stage of a tropical rainforest

“…Grasses can ameliorate the abiotic environment and facilitate the introduction of other species. However, shrubs show stronger effect on improving habitat conditions (Maestre et al 2009;Cuesta et al 2010) and attracting more seed dispersers (Hooper et al 2005) than grasses, which play a more significant function in facilitating forest regeneration (Cuesta et al 2010;Celis & Jose 2011;García-Orth & Martínz-Ramos 2011;Ortega-Pieck et al 2011).…”