Experimental assessment of factors mediating the naturalization of aglobally invasive tree on sandy coastal plains: a case study fromBrazil

摘要

As all naturalized species are potential invaders, it is important to better understand the determinants of naturalization of alien plants. This study sought to identify traits that enable the alien tree Casuarina equisetifolia to overcome barriers to survival and reproductive and to become naturalized on sandy coastal plains. Restinga vegetation in Brazil was used as a model system to conceptualize and quantify key stressors (high temperature, solar radiation, drought and salinity) which can limit the initial establishment of the plants. Experiments were conducted to evaluate the effects of these environmental factors on seed persistence in the soil (field), germination (laboratory), survival, growth, phenotypic plasticity and phenotypic integration (greenhouse). Results show that the expected viability of the seeds in the soil was 50 months. Seeds germinated in a similar way in constant and alternating temperatures (20–40 °C), except at 40 °C. Low light, and water and salt stresses reduced germination, but seeds recovered germination when stress diminished. Young plants did not tolerate water stress (<2 % of soil moisture) or deep shade. Growth was greater in sunny than in shady conditions. Although a low degree of phenotypic plasticity is important in habitats with multiple stress factors, this speciesexhibited high germination plasticity, although young plants showed low plasticity.The positive effect of phenotypic integration on plastic expression in the shadeshows that in stressful environments traits that show greater phenotypic plasticityvalues may have significant phenotypic correlations with other characters, which isan important factor in the evolutionary ecology of this invasive species. Long-termseed persistence in the soil, broad germination requirements (temperature and lightconditions) and the capacity to survive in a wide range of light intensity favoursits naturalization. However, C. equisetifolia did not tolerate waterstress and deep shade, which limit its potential to become naturalized on sandycoastal plain.