José A. Vega

Effectiveness of three post-fire treatments at reducing soil erosion in Galicia (NW Spain)

This study assessed the effectiveness of different methods of reducing soil erosion after a severe wildfire in Galicia (NW Spain). The treatments compared were: straw mulch (2.5 Mg ha–1), wood-chip mulch (4 Mg ha–1), cut-shrub barriers and control. Straw mulch provided an initial ground cover of 80% and the wood chips only 45%. Sediment yields were measured by means of sediment fences in 500-m2 bordered plots. During the first year after wildfire, mean precipitation was 1520 mm. The mean sediment yield in the control plots was 35 Mg ha–1. During this period, only straw mulch application significantly reduced soil erosion relative to controls (66%). The mean sediment yields in the wood-chip mulch and erosion barrier treatments, 33 and 30 Mg ha–1 respectively, were similar to rates in the untreated plots (35 Mg ha–1). Soil erosion decreased sharply during the second year after wildfire when mean precipitation was 1194 mm. Vegetation regrowth was very fast and treatments had no significant effect on the rate of recovery of vegetation cover, which was ~80% at the end of the study. The results obtained showed that ground cover was a key factor in determining post-fire soil loss. Stabilisation treatments such as wood-chip mulch and erosion barriers were not effective in reducing soil loss relative to the untreated control.

Spot fires: fuel bed flammability and capability of firebrands to ignite fuel beds.

A series of tests were conducted under laboratory conditions to assess, first, the capacity of several fuel beds to be ignited by firebrands and to sustain a fire and, second, the capability of different types of firebrands to ignite fuel beds. Fuel beds and firebrands were selected among the most common in southern Europe. Regarding fuel bed flammability, results show that grasses are more flammable than litter and, among litters, Pinus species are the most flammable. The increase in bulk density and fuel moisture content involves an increase in the time to ignition, and a decrease in the other flammability parameters. The capability of firebrands to ignite fuel beds is higher when the firebrands drop in the flaming phase and with no air flow than in glowing phase with air flow. Logistic regression models to predict fuel bed ignition probability were developed. As a whole, results show a relationship between ignition probability of fuel bed and type or weight of firebrands. Pinus pinaster cone scale, P. halepensis cone scale, and Eucalyptus globulus leaf and bark can have ignition probabilities at least twice higher than pine bark when falling while in flaming combustion.

A generic, empirical-based model for predicting rate of fire spread in shrublands

A shrubland fire behaviour dataset was assembled using data from experimental studies in Australia, New Zealand, Europe and South Africa. The dataset covers a wide range of heathlands and shrubland species associations and vegetation structures. Three models for rate of spread are developed using 2-m wind speed, a wind reduction factor, elevated dead fuel moisture content and either vegetation height (with or without live fuel moisture content) or bulk density. The models are tested against independent data from prescribed fires and wildfires and found to predict fire spread rate within acceptable limits (mean absolute errors varying between 3.5 and 9.1 m min–1). A simple model to predict dead fuel moisture content is evaluated, and an ignition line length correction is proposed. Although the model can be expected to provide robust predictions of rate of spread in a broad range of shrublands, the effects of slope steepness and variation in fuel quantity and composition are yet to be quantified. The model does not predict threshold conditions for continuous fire spread, and future work should focus on identifying fuel and weather factors that control transitions in fire behaviour.

Localisation of mineral uptake by roots using Sr isotopes

To assess the contribution of deep soil horizons to the mineral supply of trees, we investigated the natural variation in the87 Sr/86Sr isotopic ratio of plant-available strontium with soil depth. In three sites of North-western Spain, this ratio increased with soil depth. The comparison of isotopic ratios of tree leaves and roots at different depths showed that most of the Sr accumulation in Eucalyptus globulus and Pinus pinaster growing on shallow and poor soils in this rainy climate originated from the upper soil layers. As Ca and Sr behave similarly in the soil-plant system, this conclusion can be applied to Ca. This superficial uptake is attributed to the low availability of Sr and Ca in the soil as well as to the shortness of the drought period as compared to the length of the growth period. This technique appears to offer a promising way of studying relative root distributions in soils and plant competition for nutrients.

Biochemical Responses of Pinus pinaster Trees to Fire-Induced Trunk Girdling and Crown Scorch: Secondary Metabolites and Pigments as Needle Chemical Indicators

The biochemical responses to varying levels of localized heat damage to stems and crowns were studied in Pinus pinaster trees in Galicia, Spain. The objective was to ascertain the utility of secondary metabolites (total polyphenols, condensed tannins, astringency, free and esterified phenolic acids) and pigments (chlorophylls and carotenoids) as chemical indicators of localized fire damage. The study involved three levels of girdling by trunk heating (0%, 60%, and 75%), three levels of crown scorching (0%, 50%, and 75%), and all combinations of those trunk and crown treatment levels. Secondary metabolites and pigments were analyzed in needles before, during, and up to 8 months after fire treatments. High levels of polyphenols, condensed tannin, and pigments occurred in situations where the sole treatment was 75% crown scorching. Low levels of hydroxycinnamic acids were the result when the treatment was 75% trunk girdling. These responses occurred in the first two months after fire. Thereafter, normal values were observed. Low values of chlorophyll a/b ratio and high levels of free protocatechuic and esterified syringic acids were found to be long-term indicators of trunk girdling damage combined with crown scorching.

Post-Fire Management of Serotinous Pine Forests

The current chapter describes the ecological context and post-fire management practices for the most important and fire-prone coniferous tree species in the Mediterranean Basin, the serotinous pine trees. The state of art about evolution, habitat and adaptive strategies of Pinus halepensis Mill, Pinus brutia Ten. and Pinus pinaster Aiton are included. The management of burned areas, from emergency to long-term actions, are included but also the influence of climate change and the changing fire dynamics are discussed. To illustrate it, we included some case studies for the serotinous pine species in both Eastern and Western Mediterranean Basin.

Laboratory characterization of firebrands involved in spot fires

Abstract• IntroductionWildfires are considered the most important disturbance in the Mediterranean Basin, and some are propagated over long distances due to lift-off and ignition of firebrands.• ObjectivesTo improve our knowledge of firebrands involved in spotting fires, flammability characteristics of eight types of firebrands commonly generated by wildfires in Southern Europe were determined under laboratory conditions.• ResultsAll the firebrands tested showed 100% ignition frequency but with a wide range of time to ignition and flaming duration. Weight loss during combustion was exponentially related to time, and there was a decrease in the ratio of the weight at temperature T to the initial weight with increasing temperatures. In our experimental conditions, there was a significant effect of fuel moisture content on time to ignition, flaming duration, combustion and thermal decomposition. On the basis of the characteristics analysed, three firebrand groups have been identified in relation to spotting: heavy firebrands with ability to sustain flames, efficient for long-distance spotting (pine cones); light firebrands with high surface-to-volume ratio, efficient for short-distance spotting (leaves and thin barks); and light firebrands with low surface-to-volume ratio, efficient for short and, occasionally, long-distance spotting (all the other types of firebands).

Effects of soil burn severity on germination and initial establishment of maritime pine seedlings, under greenhouse conditions, in two contrasting experimentally burned soils

The effects of soil burn severity on initial establishment of maritime pine in burned areas are not well known. Many factors may interact in the field, thus making it difficult to determine the exact role played by soil burn severity in the post-fire regeneration process. Monoliths of two contrasting soils – an acid, coarse-textured soil, with high organic matter content, and a neutral heavy-textured soil with low organic matter content – were experimentally burned to provide two markedly different levels of soil burn severity. The burned monoliths were sown with Pinus pinaster seeds and then placed in a greenhouse under a preselected water regime to determine the effect of burn severity on emergence and initial establishment of pine seedlings. High soil burn severity in the coarse-textured soils delayed germination, increased mortality and temporarily decreased the height of pine seedlings in the first year after sowing. This response was affected by: soil heating level, soil C consumption, post-fire soil C, depth of burn and post-fire duff-depth. Ash had no influence on the above processes. These factors did not explain the variability in the response of regeneration variables in the heavy-textured soils. The applicability of the results to field conditions is discussed.

Response of maritime pine ( Pinus pinaster Ait.) recruitment to fire severity and post-fire management in a coastal burned area in Galicia (NW Spain)

The short-term effects of fire severity and post-fire management on maritime pine recruitment were evaluated in a mature serotinous pine stand in a coastal area of Galicia (NW Spain) burned by a wildfire occurred in the summer of 2001. Two levels of fire severity estimated by the levels of tree crown damage—scorched and unaffected crown—were compared. Seed dispersal and first cohort pine (November 2001) seedling density, before salvage logging, were significantly and positively affected by fire severity. Between November and January, a fungal attack caused a noticeable decrease in seedling density in both levels of fire severity. The first cohort survival was significantly reduced by harvesting and slash treatments carried out in February 2002. However, slash chopping favoured a new pine cohort, particularly in the unaffected crown plots, in which seedling density was significantly higher than in the scorched crown plots between July 2002 and February 2003. First cohort seedling survival and height were positively related. Fire severity levels, combined with post fire management, did not appear to determine final pine seedling density and height. Finally, reduction in seedling density caused by post-fire management did not threaten pine establishment and may reduce the need for subsequent thinning operations.

Reduction of nutrient losses with eroded sediments by post-fire soil stabilisation techniques

After an experimental fire in steep shrubland in a temperate–humid region (north-west Spain), the effects of two post-fire stabilisation treatments (grass seeding and straw mulching) on the chemical properties of eroded sediments, and the amount of nutrients lost with them, were evaluated relative to control burnt soil, over a period of 13 months. Total C and N concentrations, and δ13C, indicated that sediments were mainly contributed by charred plant and litter material. The highest concentrations of extractable base cations in the sediments occurred during the first 3 months following fire, especially for Na and K. As treatments had little or no effect on nutrient concentration in sediments, differences in nutrient losses were due to the 10-fold lower sediment production in mulching compared with other treatments. In control and seeding treatments, the accumulated amounts of nutrients lost with sediments were 989–1028 kg ha–1 (C), 77 kg ha–1 (N), 1.9–2.4 kg ha–1 (Ca), 0.9–1.1 kg ha–1 (Mg), 0.48–0.55 kg ha–1 (NH4+–N), 0.39–0.56 kg ha–1 (K), 0.19–0.34 kg ha–1 (Na) and <0.1 kg ha–1 (P and NO3––N). These values accounted for 22–25% (total C and N) and 5–12% (NH4+–N, Ca, P and Mg) of available nutrients in ash, and 1.0–2.4% of those in ash+topsoil. As nutrient and sediment losses were strongly correlated, the reduction of the latter by mulching application leads to an effective decrease of post-fire nutrient losses.