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Vol. 2 No. 3
2011

Fire resilience and forest restoration in mediterranean fire-prone areas

D. Moya 2*, J. De las Heras 2, P. Ferrandis 2, J. M. Herranz 2 and J. J. Martínez-Sánchez1
1Departamento de Producción Vegetal, Unidad Asociada al CSIC de “Horticultura Sostenible en Zonas Áridas” (UPCT-CEBAS), Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 48, 30203 Cartagena, Spain.
2Departamento de Producción Vegetal y Tecnología Agraria. Universidad de Castilla-La Mancha.
Campus Universitario, ETSI Agrónomos. 02071 Albacete, Spain
*Corresponding author to whom more information request should be addressed (e-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it ).
Additional keywords: wildfire, seed germination, soil seed bank; Pinus halepensis Mill., Pinus pinaster Aiton, Cistus, post-fire Management, fire ecology

INTRODUCTION
Mediterranean ecosystems are of importance worldwide because they are biodiversity hot spots. In these areas, forest fires have been modelling the landscape since the Pleistocene Era. Consequently, plant communities inhabiting this fire-prone area have developed adaptive traits (e.g. serotiny) or life-history strategies to persist, exhibiting a high degree of survival or recovering after frequent fires or other disturbances, such as severe drought. In general, this implies high resilience, but in recent years aridity and fire dynamics have been increasing due to global climate change, which has strongly affected the Mediterranean Basin. These changes are inducing higher risks of soil loss and lower plant productivity in the long term, which influences the resilience of the community present before the disturbance. Some species are pirophytes (fire adapted), such as Cistus sp. (Ferrandis et al., 1999a), or pirophyles (fire dependant). Pinus halepensis Mill. and some populations of Pinus pinaster Aiton have been catalogued as pirophylous species. They are not promoted by fire (Martínez-Sánchez et al., 1996) but show colonizer behavior in the absence of fire (Ayari et al., 2011).

The main four components of resilience are elasticity (recovery rate), amplitude (fire severity inducing no recovery), malleability (differences from the previous state) and damping (oscillation of ecosystem parameters). If the plant community does not recover after disturbance or natural characteristics do not achieve forest planning objectives, restoration and stand improvement through forest management are important choices for lowering the aridity risk (Figure 1).

FIGURA 1

EFFECT OF FIRE ON SEEDS
Soil is not a good heat conductor, so during a forest fire the heating rate decreases with increasing soil depth. In the Mediterranean Basin, the seed banks in the soil are usually accumulated in the upper layers, implying their transient nature and a strong influence of fire (Ferrandis et al., 2001a).

Regarding soil seed banks, the genus Cistus is an obligate seeder species with a broadly range in the Mediterranean area of central and eastern Spain. Usually, Cistus species are part of the community in the form of living plants, but they also have seed banks persistent over the long term. Some species, such as Cistus ladanifer and C. salvifolius, have shown dormancy in the absence of fire, although low and medium intensity fires do not influence germination values (Ferrandis et al., 1999c). In general, recurrent wildfires have a selective impact on the soil seed bank species; those with transient seed reserves are eliminated and those species with persistent, buried seed reserves tend to remain in the soil after the passage of fire (Ferrandis et al., 1999b).

Pinus halepensis and some populations of P. pinaster have shown adaptation to fire by storing seeds in closed, grey (serotinous) cones in the canopy. Seed germination is not improved by heating, although seeds from both species show fire resistance to severe fires (Martínez-Sánchez et al., 1995). Fire resistance is a result of anatomical characteristics of the seed coat with high insulation properties, such as wax and cutine cells covering the seed coat and high Si and Ca concentrations in the seed shell. Insulation properties were magnified in seeds in serotinous cones (Salvatore et al., 2010). Serotinous cones are efficient heat insulators according to anatomical and morphological characteristics, such as compressed, thicker scales with multiple layers (Moya et al., 2008c) (Figure 2).

FIGURA 2

POST-FIRE REGENERATION AND DYNAMICS
Several studies have examined floristic composition over the short term in post-fire Mediterranean ecosystems to describe community recovery (Figure 3). Results show the highest abundance and plant cover in the first 2 years after the fire, followed by a decrease in the long term until they reach characteristics similar to before the disturbance, according to the ‘‘initial floristic model’’ (Ferrandis et al., 1996; Herranz et al., 1996; Moya et al., 2009). In a very short time, the main contribution to the natural recovery of a Mediterranean plant community is from the resprouters (covering half of the area in the first weeks or months after the fire). In the middle-long term, seeders gain importance and dominate the surface the first or second year after the fire (Trabaud et al., 1997). However, natural recovery is influenced by many factors, such as stand structure, weather conditions or fire severity (Ferrandis et al., 2001b). In south-eastern Spain (semiarid ombroclimate), plant regeneration and recruitment after fire depends highly on the weather conditions of the first year (Martínez-Sánchez et al., 1998) but also greatly influences seedling mortality in the first two or three years, determining the density of sapling survival (Herranz et al., 1997). On the ground, bryophyte communities play a significant protective role in burned areas by preserving nutrient and soil losses, although the recovery model after fire differs from higher plants (Martínez-Sánchez et al., 2000).

Eventually, natural regeneration can be excessive, depending on site quality, leading to grossly overstocked areas covered by dense clumps of small trees and thickets which are competing for space and nutrients (dog-hair formation) and are delayed in reaching maturity (Moya et al., 2007; Moya et al., 2008a). In these cases, there is low light, water and nutrient availability due to inter- and intraspecific competition (Martínez-Sánchez et al., 2003).

FIGURA 3

EARLY POST-FIRE MANAGEMENT
Post-fire emergency actions are focused on protecting high risk areas by preventing erosion, flooding and soil losses. Salvage logging is one of the most common forest management emergency actions after fire in the short-term, but its ecological effects implications are not well known. Some studies found that salvage logging did not positively influence seedling survival, leading to a sapling deficit in natural recovery and forest development, especially when there is a low seedling density (Martínez-Sánchez et al., 1999). To reduce interspecific competition, early shrub clearing treatments (before the 2nd year after the fire) are recommended to increase sapling density of the main tree species. This silvicultural tool induces lower sapling mortality and improves the growth of the selected species when carried out early, especially in areas where the initial post-fire pine sapling density is not high enough to be successful in the early, critical, competitive period (De las Heras et al., 2001). Similarly, early silvicultural treatments are advised for improving the stand (Figure 4), although the optimum depends on the species and site quality (Moya et al., 2008b; Lopez-Serrano et al., 2010). The silvicultural treatments studied include thinning intensity, the age at which to carry out thinning and clearing, pruning (including height), shrub clearing and the effects of combined treatments, in the short and middle term (De las Heras et al., 2001; De las Heras et al., 2007; Moya et al., 2008b). The benefits related to early silvicultural treatments in Aleppo pine stands have been related to improved growth (in height and trunk diameter) in addition to an increase in canopy seed bank (De las Heras et al., 2007). Earlier arrival at the mature phase, measured by the reproduction stage, certain structural patterns and diversity parameters, has also been demonstrated (Moya et al., 2009).

FIGURA 4

LITERATURE CITED

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