Roseli Lika Miashike¹, Alessandra R. Kortz¹, Hilton Thadeu Zarate do Couto2 and Vânia Regina Pivello1
1LEPaC, Ecology Dept.-IB, Universidade de São Paulo, Rua do Matão, Travessa 14, São Paulo, SP, Brazil
2LEFS-ESALQ, Universidade de São Paulo, Piracicaba, SP, Brazil
Certain life-story traits of invasive plants as well a strong propagule pressure are related to their high invasion success. For pine trees, a high production of small- or large-winged seeds with low mass, and early age of reproduction, associated with a high reproductive success and dispersal effectiveness allow many species to be highly invasive worldwide. In the Brazilian cerrado – the richest savanna of the world – pine tree species are highly invasive in the southeastern part of this biome. A good example concerns São Paulo state, where silviculture is a key economic activity, mostly based on Eucalyptus and Pinus species. Three pine species have been most intensively planted in São Paulo, i.e. P. elliottii, P. oocarpa and P. caribaea var. hondurensis. While P. elliottii has become the most threatening invasive species in the southern cerrado, episodes of invasion by P. oocarpa and P. caribaea are still very few and have not been detected in São Paulo state, even though these three species are phylogenetically very close.
Here we focus on the three most planted pine tree species in Southern Brazil (P. elliottii, P. caribaea and P. oocarpa) to (i) test the hypothesis that some key attributes, such as seed viability, germinability, growth rate and propagule pressure drive the greater invasiveness of P. elliottii, and (ii) assess the possibility of the other two species becoming invasive. Our results show that seed viability, germinability and the initial development period (from germination until seedling still having cotyledons) of P. elliottii are not higher than those of the other two pine species. Still, compared to other pine species, P. elliottii showed the slowest stem growth, shortest stems and lowest dry biomass after 24 weeks since germination, as well as the highest seedling mortality rate. On the other hand, P. elliottii produced the highest amount of seed within the 14-month period, at least twice as high as the other two species. In addition, P. elliottii seeds were dispersed up to 150 m. There is a stronger propagule pressure observed for P. elliottii relative to the other two species, caused by several human mediated introductions. Pinus oocarpa and P. caribaea performed highly regarding the life-story characteristics evaluated in this study (viability, germinability, growth rate, biomass production). Therefore, it is possible that these two pine species might also become successful invaders in the cerrado. Our findings have important implications for managers to monitor the emerging of pine individuals in the native ecosystems, and for predicting potential invasions.