Post-fire oak colonisation: Analysis of the concordance among factors of dispersal and establishment and economic valuation of ecosystem services

Abstract

Chapters 1 and 2 analyse the success of acorn sowing, with focus on acorn predation. Acorns were sown in two of the post-fire treatments, which differently affected foraging by wild boars and rodents. In Chapter 1, two different methods are tested to reduce acorn predation by rodents: deeper sowing and the application of a chemical repellent. As these methods were ineffective, in Chapter 2 a physical protecting device, named seed shelter, was tested. The seed shelter eliminated acorn predation by small rodents. Its use in a structurally more complex treatment, which reduced acorn predation by wild boars, minimised overall acorn predation. The document that describes the patent of the seed shelter is included as Appendix I. Chapters 3 and 4 analyse the success and implications of reforestation with nursery-grown seedlings. In Chapter 3, the survival of four species is tested in the three wood management treatments across two plots. The main objective of this chapter is to assess whether the cost of salvage logging may be compensated by the savings obtained by performing reforestation in a more accessible area devoid of dead boles and branches. The costs of all forestry activities were calculated and led to the conclusion that in burnt Mediterranean pine plantations salvage logging is not profitable. For Chapter 4, demographic and ecophysiological data are used to study the performance of two of the planted species (the evergreen Q. ilex and the deciduous Q. pyrenaica Willd.) at different elevation. While the lower plot was located within the known range of oak forests, the upper plot was above that range. Both species, particularly the deciduous oak, performed best at the upper plot, where survival still increased with elevation. The results are interpreted in the context of the implications of species range shifts for ecosystem restoration. Chapters 5 and 6 analyse the natural regeneration of the holm oak. Some large, mature holm oaks were unaffected by the fire next to one of the study plots, and they acted as seed sources. Chapter 5 investigates the preferences of European jays for the different post-fire treatments as habitat and as acorn caching locations. The burnt but standing pines still acted as habitat for jays, suggesting that leaving burnt trees standing may favour the natural colonisation by oaks of burnt pine forests if nearby seed sources exist. Chapter 6 studies the spatial and temporal patterns of recruitment of young holm oaks over seven years following the fire. The Non-Intervention areas favoured recruitment during the first years, but as the burnt pines collapsed, the main direction of seed dispersal changed towards patches of unburnt pines that remained within the plot. As these living pines reduced the growth of seedlings underneath them, there was a temporal shift in the demographic conflicts experienced by successive cohorts of oak recruitment. In the General Discussion, besides expanding on the implications of the individual studies, I provide an economic assessment of the different options for assisted regeneration under several scenarios. The specific costs are calculated in Appendix II. Planting seedlings was the most costly method for assisted oak regeneration, and sowing with the seed shelter was the least expensive regardless of the expected range of potential costs of the device. At the end of the Discussion I estimate the economic value of the ecosystem service of natural regeneration of oaks with the Replacement Cost method, considering the cost of reforestation on the one hand (Chapters 1 to 4) and the naturally regenerated seedling densities on the other hand (Chapters 5 and 6). Natural regeneration, including post-fire resprouting and seed dispersal, led to potential savings of hundreds of euros per hectare due to the reduced need for reforestation. The value of this service was particularly high near seed sources and in areas without post-fire human management, indicating that the common strategy of post-fire salvage logging may hamper the natural regeneration of oaks.