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COORDINATION: Joaquim Sande Silva (CEABN InBIO).

CEABN TEAM: Ana Águas, Ernesto Deus, Filipe Xavier Catry, Francisco Moreira, Hugo Matias, Joaquim Sande Silva, Miguel Bugalho.

OTHER INSTITUTIONS: Altri Florestal SA, Centro de Ecologia Funcional (CFE/FCTUC).

Blue gum (Eucalyptus globulus Labill.) is a fast-growing tree species native to Australia, occupying around 23 % (740,000 ha) of Portuguese forested area. Planted trees are usually coppiced in rotations of 10-12 year, to supply the pulp industry, a strategic sector for the national economy.

The species is very well adapted to the ecological conditions in Portugal, often reaching yields above 20 m3/ha/year of wood in good sites. However this good adaptation is having other implications because the species is becoming naturalized. The establishment of wildlings i.e. naturally established plants, occurs in two main situations:

- Inside and in the close neighborhood of actively managed plantations;

- Within and around unmanaged, often abandoned, blue gum stands particularly after fire occurrence.

The first aspect has economic implications, due to the additional management costs needed to remove naturally established plants growing between plantation rows and close to edges. This problem brings consequences to individual forest owners and to the Portuguese pulp companies who are responsible for around 1/3 of all blue gum forested area. It also concerns the entities responsible for the management of roadsides and areas under power lines, where wildlings often establish.

The second aspect has strong ecological consequences, since the fast-growing blue gum plants may easily dominate the native plant communities at early successional stages resulting from abandoned land. Abandonment occurs mainly after the last harvest or after wildfires, revealing also a lack of awareness from land owners, who unconsciously contribute to an increased fire hazard resulting from these formations. One of the few published references on this topic mentions overall wildling densities of 0.88±0.98 wildlings/m2 in 72% of 39 systematically surveyed plots in Central Portugal.

Despite the importance of the species and the environmental problems it may cause if mismanaged, the literature dealing with the natural establishment of blue gum, is remarkably scarce. Thus, this research proposal was structured to tackle this knowledge gap using an integrated multi-scale approach, aimed at obtaining a comprehensive understanding of the naturalization process and respective mechanisms. All tasks were connected, each task using the results from the previous, for the selection of areas to be studied at a progressively finer scale.

Task 1 was a regional survey aimed at producing a map of regeneration potential for blue gum in Portugal, by adapting a modeling approach previously used by the ISA team. The model related recruitment probability with environmental coarse scale variables (topography, climate, soil). This map helped to the elaboration of environmental impact assessment reports, which are compulsory for large blue gum plantations in Portugal.

Task 2 was a stand scale survey aimed at relating stand characteristics like age, rotation and management practices, with wildling establishment. Results helped predicting and controlling wildling establishment, for example through the adoption of alternative harvesting programs. This task was replicated in Portugal a similar study performed in Australia, allowing to compare two geographically and ecologically distinct situations. The study was supervised by Professor Bradley Potts (Univ. of Tasmania), who integrated the project as a senior consultant.

At the site scale Task 3 assessed seed rain, seed bank and seedling characteristics along permanent transects installed perpendicularly to the stand edge in burned and unburned areas.

Task 4 assessed the soil properties and the soil cover characteristics at the microsite scale in burned and unburned areas, close to randomly chosen individual wildlings.

Results from Task 3 and 4 helped understanding the naturalization process and contribute to improve the fuel management practices for fire prevention, commonly used in plantations, in roadsides and under power lines. Data was analyzed in Task 5 and results were disseminated in Task 6 through a technical brochure and scientific publications.

The research work was essentially conducted by ISA and UC, comprising experts in fire ecology and seed ecology of exotic species. ISA integrated a PhD student who was almost fully dedicated to this project. Stakeholders were represent in this project by the Altri pulp company. Altri had a fundamental role in the project by providing an important part of the logistic needs, expertise in blue gum cultivation and access to the study sites and to a very comprehensive and detailed database with site and stand information for all blue gum plantations managed by Altri.

Documents available for download: