Eucalyptus globulus Labill. regeneration from seeds in Portugal´s mainland

Abstract

Eucalyptus globulus Labill. is a plant species native to SE Australia, Tasmania and adjacent islands. It was introduced in Portugal in the mid-19th century. In 2005/06, it was the most abundant tree species in 23% of the afforested area in Portugal’s mainland. Forests dominated by this species are one of the most fire-prone forest types in Portugal. This thesis was aimed to contribute to a better understanding of the naturalization process in Portugal’s mainland, with a special focus on the role of fire in this process. A multiscale approach was used to address the problem. Natural regeneration of E. globulus from seeds occurs in every natural region of the territory and may reach high densities in some locations. Spatial distribution of both wildling occurrence and density is not uniform on national (mainland), regional, local, and stand scales. The existence of seed sources (reproductive trees) is of primary importance. Climatic and soil conditions affect the broad scale distribution of this regeneration and its performance. Site quality and forest management are fundamental on a local scale. Fire clearly plays a relevant role, inducing seed release from burnt trees, providing safe microsites for plant recruitment and development, and allowing for the establishment of plants in the mid-term. Moreover, litter charring enables the early development of E. globulus in otherwise toxic conditions. Maximum wildling densities observed were 0.3 plants m-2 and 9.9 plants m-2 inside unburnt and burnt plantations, respectively. Portuguese plantations, from a region with nationally moderate levels of seminal regeneration, had mean wildling densities 3.1 times higher than Australian plantations, from seven regions either inside or outside the native range. In summary, cultivated trees are able to produce offspring, which grows, establishes and may produce seeds next to parent trees, in many parts of Portugal’s mainland. Therefore, naturalization is in progress and widespread in this territory, and fire does facilitate it