JR Arevalo A Naranjo L Agudo and M Salas

'Department of Ecology, Universidad de La Laguna, La Laguna 38206,

Islas Canarias, Spain 2Department of Geography, Universidad de Las Palmas de Gran Canaria, Las Palmas de Gran Canaria 35003, Islas Canarias, Spain 3Aula de la Naturaleza, Universidad de Las Palmas de Gran Canaria, Las Palmas de Gran Canaria 35003, Islas Canarias, Spain

Invasive alien species can have a detrimental economic impact on human enterprises such as agriculture, grazing, forestry and tourist activities. Invasive species have been identified as one the major threats to ecosystems and biodiversity, as well as human well-being. The main objective of our study is to determine whether regeneration of the exotic Pinus pinea is able to compete with the regeneration of the native P. canariensis. The study area is located in the Natural Park of Tamadaba, 1400 m asl., in the NW of Gran Canaria island (Canary Islands). Stems and regeneration of P. canariensis and P. pinea were mapped in five randomly selected plots where both species were planted together around 45 years ago. Densities and basal areas of both species were also recorded. A monitoring of the survivorship of seedlings of both species was carried out during two years. A group of individuals of P. canariensis were excluded from grazing to determine the effect of grazing in the survivorship of the species.

Although the dispersal ability of P. canariensis was more effective, once the individuals of P. canariensis and P. pinea had been established, there was not difference in survivorship. Also, we did not find differences in survivorship for individuals excluded vs. non-excluded from grazing.

Despite the stability of the exotic species, this can change with the introduction of a dispersal vector of the seeds, a squirrel, Atlantoxerus getulus, which was introduced in Fuerteventura (the closest island to Gran Canaria) with an estimated population of 1

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