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A field experiment was designed to evaluate the importance offacilitative and competitive interactions in Picrishieracioides, a facultative biennial that colonises the early andthemid-stages of secondary succession in the Mediterranean region. Seedlings ofPicris hieracioides from populations of the early- (1year)and the mid-stages of field abandonment (15–40 years) were transplantedintwo adjacent old fields, abandoned for 4 (F4) and 20 years (F20) and thatdiffered markedly in floristic composition and vegetation structure. For twoyears, we experimentally manipulated competition (no-neighbours vs. naturalvegetation) and resource availability (addition of water and fertiliser vs.controls) in an attempt to evaluate their influence on survival, reproductivetiming, growth and reproductive output throughout the life cycle. Earlymortality was higher in non vegetated plots in both fields. Mortality ofseedlings was mainly due to herbivory by larvae of genusAgriotes. Flowering throughout the whole experiment wasalso facilitated by vegetation in the F4 field as a result of the positiveeffect of annual vegetation and remained unaffected in the F20 field because ofthe high competitive effect of established perennial vegetation. The additionofresources altered the effect of facilitation and competition on late seedlingsurvival. Survival was enhanced in the vegetated plots of the F4 field, becauseresource addition increased the shade provided by the canopy of vegetation,protected seedlings from temperature extremes and reduced water loss. Seedlingmortality also decreased in the F20 field but in a similar manner to vegetatedand non-vegetated subplots, and consequently the outcome of positive andnegative interactions remained neutral. The net effect of facilitation andcompetition resulted in interference later in the life cycle and appearedthrough final lower growth and reproduction in both fields. However, thegreatercompetition in 1994 than in 1995 in both fields, probably because the size ofthe rosettes, makes them less susceptible to competition, illustrates thedifficulty in predicting the outcome of competition solely of one season forfacultative biennial plants. The relative competition intensity calculatedusingonly survivors (RCI1) was unaffected by habitat fertility in bothfields. In striking contrast, the relative competition intensity calculatedusing seedling mortality (RCI2) was significantly higher in subplotswithout resource addition in both fields because of high seedling mortality invegetated subplots. Finally, there were no differences in the net effect offacilitation and interference processes among populations from early and midsuccessional stages showing that phenotypic plasticity buffers theenvironmentalselective pressures linked to successional processes.