RECRUITMENT OF A MAST-FRUITING, BIRD-DISPERSED TREE - BRIDGING FRUGIVORE ACTIVITY AND SEEDLING ESTABLISHMENT

The recruitment of Phillyrea latifolia L. (Oleaceae), a bird-dispersed tree of Mediterranean forest, is described. Fruit removal by birds, s eed rain, post-dispersal seed predation, seed germination, and seedlin g emergence, survival, and establishment were studied. The main object ive was testing whether seed dispersal by birds produced a predictable seedling shadow as a result of coupled patterns of seed rain, seedlin g emergence, and seedling establishment. P. latifolia is a mast-fruiti ng species and large fruit crops were produced in only 2 (1981 and 198 9) out of 15 yr (1978-1992). We report here on the 1989 fruiting event at one scrubland and one forest site. Ripe fruits were available from mid-September to early June. Extensive removal by birds started after fruit crops of other species were depleted. Seed dispersers were more abundant, and fruit predators more scarce, in scrubland than in fores t. P. latifolia fruits were a major component in the diet of principal seed dispersers (Sylvia atricapilla and Erithacus rubecula) that depe nded almost exclusively on them for food late in the season. Fruit rem oval levels were higher, crops were depleted earlier, and individual p lants dispersed more seeds in scrubland than in forest. Crop size was the best predictor of number of seeds dispersed by individual plants i n scrubland, while fruit characteristics were more influential in fore st. Seed dispersal was largely a within-population phenomenon, as no s eed fall occurred in traps set beyond the distributional limits of P. latifolia in the study region. Frugivores produced a spatially predict able seed rain at the two sites. Seed rain was greatest beneath fleshy fruit-producing species (under female individuals in dioecious specie s) in scrubland and at forest-gap interfaces in forest. Post-dispersal seed predation was low at the two sites (39 and 54% after 1-yr exposu re). In forest, seed survival was lower in gaps than in forest interio r or forest edges. In scrubland, seed survival differed widely among m icrohabitats (defined by overlying plant species), ranging from 19% (o pen ground) to 61% (beneath Rosmarinus officinalis). In forest, densit y of emerging seedlings was unrelated to location in the habitat mosai c (gap, forest edge, interior). Seedling density did differ among micr ohabitats in scrubland, where emergence was greatest under fleshy frui t-producing species. Seedling survival was higher in forest than in sc rubland, where seedlings incurred greater mortality due to desiccation . In both sites, seedling survival depended significantly on microhabi tat and was depressed under adult conspecifics. The activity of frugiv ores directly impacted seedling distribution in scrubland, as spatial patterns of seed deposition were not overshadowed by later-acting fact ors, such as rodent seed predation or variation in germination. In for est, there was spatial discordance between seed rain and seedling dist ribution, as a consequence of uncoupled seed rain and seedling emergen ce. Spatial patterns of seed deposition by birds may thus have a lasti ng impact on the population dynamics of P. latifolia, but this will va ry among populations depending on the extent of coupling of the differ ent stages in the recruitment process (dispersal-seed rain-germination and seedling establishment).