SEED-GERMINATION AND SEEDLING PERFORMANCE OF 2 MEDITERRANEAN TREE SPECIES, HOLM OAK (QUERCUS-ILEX L.) AND ALEPPO PINE (PINUS-HALEPENSIS MILL.) - A MULTIFACTOR EXPERIMENTAL APPROACH

A two-level multifactor experimental approach was used to compare seed germination and seedling performance of two Mediterranean tree specie s: the early successional Aleppo pine (Pinus halepensis Mill.) and the late successional helm oak (Quercus ilex L.). In a first experiment g ermination rate was evaluated under the combined effects of shade, nit rogen availability, and pine or helm oak leaf litter. In a second expe riment we tested for the effects of shade, nutrient availability, and litter type on seedling survival, growth and biomass allocation. Helm oak showed higher germination rates under shaded than under unshaded c onditions, while Aleppo pine showed no differences between shaded and unshaded conditions. Nitrogen availability and litter type had no sign ificant effect on germination of either species. Both species showed i ncreased RGR, but also higher mortality rates, when grown in an enrich ed nutrient environment. While Aleppo pine showed no differences in RG R and mortality rate under different shading levels, RGR decreased and mortality increased for helm oak in full light. Increased radiation d ecreased LAR, SLA and height:diameter ratio, and increased RWR and R/S in both species, although Aleppo pine showed more pronounced changes. Unlike Aleppo pine, helm oak responded to increased nutrient availabi lity by decreasing R/S and increasing LAR. From these results, no seed -seedling conflicts were found in either species, but a trade-off does seem to exist for helm oak between biomass allocation traits deployed in response to increased nutrient availability and radiation. Aleppo pine outperformed helm oak under most environmental conditions tested and showed a wider regeneration niche.