Restoration ecology is a young academic field, but one with enough history to judge it against past and current expectations of the science's potential. The practice of ecological restoration has been identified as providing ideal experimental settings for tests of ecological theory; restoration was to be the Ôacid testÕ of our ecological understanding. Over the past decade, restoration science has gained a strong academic foothold, addressing problems faced by restoration practitioners, bringing new focus to existing ecological theory and fostering a handful of novel ecological ideas. In particular, recent advances in plant community ecology have been strongly linked with issues in ecological restoration. Evolving models of succession, assembly and state-transition are at the heart of both community ecology and ecological restoration. Recent research on seed and recruitment limitation, soil processes, and diversity-function relationships also share strong links to restoration. Further opportunities may lie ahead in the ecology of plant ontogeny, and on the effects of contingency, such as year effects and priority effects. Ecology may inform current restoration practice, but there is considerable room for greater integration between academic scientists and restoration practitioners. Ecological restoration is Ôintentional activity that initiates or accelerates the recovery of an ecosystem with respect to its health, integrity and sustainabilityÕ SER (2004). Restoration ecology is the field of science associated with ecological restoration. The practice of ecological restoration is many decades old, at least in its more applied forms, such as erosion control, reforestation, and habitat and range improvement. However, it has only been in the last 15 years that the science of restoration ecology has become a strong academic field attracting basic research and being published in indexed peer-reviewed journals (Fig. 1). Associated with this growth has been an increasing desire to define a scientific identity for restoration ecology and its relationship to ecological restoration.Early on, far-sighted ecologists recognized that the practice of ecological restoration could be an Ôacid testÕ of ecological theory (Bradshaw 1987), and conversely, recognized that the highly manipulative nature of ecological restoration provided an ideal setting for hypothesis generation and testing in ecology (Jordan et al. 1987b). One of the first attempts to delineate an ecological discipline centred on restoration was the seminal volume by Jordan et al. (1987a). In recent years, there has been considerable discussion of the conceptual bases of restoration ecology (Cairns & Heckman 1996;Hobbs & Norton 1996;Allen et al. 1997;Perrow & Davy 2002;Peterson & Lipcius 2003;Temperton et al. 2004; van Andel & Grootjans 2005;Aronson & van Andel 2005). There emerge two kinds of questions about the links between conceptual ecology and ecological restoration. First, what set of ecological principles and concepts serve as an essential basis for ...

SummaryIn Mediterranean ecosystems, competition between opportunistic grasses and slower‐growing woody species may affect the speed and path of ecosystem recovery and the success of restoration plantings after natural or human‐induced disturbance. In this experiment, competitive interactions between Mediterranean annual and perennial grass species (Avena fatua and Brachypodium retusum, respectively) and an important Mediterranean shrub (Rosmarinus offlcinalis) were examined under semi‐controlled conditions simulating wet and dry Mediterranean rainfall regimes. The identity of the grass competitor and the level of water availability in the plots interacted to produce differing rates of R. offlcinalis growth but similar levels of mortality. In particular, competition with the perennial grass resulted in very low rates of R. offlcinalis growth at both irrigation levels. Measurements of soil water content showed that both grasses reduced soil moisture to low levels, though this effect was temporary in the case of the winter annual grass. Resistance to hydraulic flow in roots was highest in the perennial grass, smaller but of similar magnitude in the shrub, and much lower in the annual grass. Transpirational response to decreasing leaf water potential was a quick, sharp drop in conductance in R. offlcinalis, in contrast to a moderated decline from much lower initial transpiration rates in B. retusum. The annual grass largely maintained both leaf water potential and transpiration through leaf‐tip senescence and death. Quantification of the rate of hydric recuperation of leaves after irrigation of drought‐stressed plants showed that the perennial grass recovered at a rate four times that of R. offlcinalis, suggesting a strategy for making quick use of rare summer rains that may contribute to its competitive success. The appropriateness of planting or suppressing grasses in restoration of disturbed sites in Mediterranean Spain is discussed.

Much recent attention has been focused on the invasion and dominance of annual grass species in areas thought to have been historically dominated by perennial life forms. Explanations of this phenomenon in the literature have focused on two mechanisms favoring annuals: ruderal strategy associated with disturbance, and stress escaping associated with dry sites or deserts. Here I present evidence from vegetation surveys at 50 sites across a 1,200 km band of the Iberian Peninsula-a source region for many invasive annuals-showing that relative annual versus perennial grass composition is not well correlated with degree of disturbance or average annual precipitation. However, annual dominance is strongly and significantly linked to the seasonality of precipitation, in particular the relative intensity of summer drought. Disturbance was significantly associated with annual grass dominance in Iberia, but with much less explanatory power than summer drought intensity. Slope, aspect, and soil parent material were not significantly correlated with annual versus perennial grass dominance. These results suggest that subtle differences in rainfall seasonality largely drive grass composition in herbaceous Mediterranean vegetation. Furthermore, the patterns of annual grass invasion observed in the world's other Mediterranean climate regions may be associated with similar climatic drivers.

In the Central Valley of California, native perennial grass species have been largely replaced by Eurasian annual species, while in many parts of the Mediterranean Basin native perennial grasses continue to dominate, even on disturbed or degraded sites. We assessed whether differences in summer rainfall patterns have lead to the development of different plant-water strategies between grasses from these two regions. We compared six measures of plant-water physiology for three guilds of grasses: California perennial grasses, Mediterranean perennial grasses, and Mediterranean annual grasses. Discriminant analysis distinguished between the three guilds; Mediterranean perennial grasses were characterized by a more conservative water-relations physiology than Mediterranean annual grasses, whereas California perennial grasses were in some ways intermediate between the two Mediterranean grass guilds. For individual traits, California perennial grasses were either intermediate or more like Mediterranean annuals than Mediterranean perennials. Our results suggest California perennials are more drought tolerant than Mediterranean annuals but less drought tolerant than Mediterranean perennials, despite the fact that California's Central Valley has a more intense summer drought than the Mediterranean Basin. These patterns may help explain why Mediterranean annuals, but not Mediterranean perennials, have been more successful invaders of interior California grasslands.