Teresa Fonturbel

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.

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.

Smouldering fire-induced changes in a Mediterranean soil (SE Spain): effects on germination, survival and morphological traits of 3-year-old Pinus pinaster Ait.

In the present study, a smouldering fire was reproduced in a substrate from a Pinus pinaster forest in the southeastern Iberian Peninsula. Experiments were carried out, in laboratory, using soil monoliths to assess the short-term fire-induced effects on germination, survival and morphological traits in young (3-year-old) specimens of Pinus pinaster Ait. The fire caused a severe reduction in the litter and humus layer relative to a control (unburnt) soil. A lower percentage of accumulated germination (29% in the burnt soil compared with 71% in the control soil) reduced final seedling density, and a lower seedling height was observed in burnt soil. Furthermore, the amount of biomass fixed per unit of leaf area and the concentration of foliar nutrients were lower in the seedlings grown in the burnt soil. However, the amount of biomass fixed per individual seedling was significantly higher in the burnt soil than in the control soil. The results confirm the observed lesser P. pinaster recruitment in burnt stands in southeastern Spain.

Shrub resprouting response after fuel reduction treatments: comparison of prescribed burning, clearing and mastication.

Fuel reduction treatments are commonly used to reduce the risk of severe wildfire. However, more information about the effects on plant resprouting is needed to help land managers select the most appropriate treatment. To address this question, we evaluated the resprouting ability of five shrub species after the application of different types of fuel reduction methods (prescribed burning, clearing and mastication) in two contrasting shrubland areas in northern Spain. The shrub species were Erica australis, Pterospartum tridentatum and Halimium lasianthum spp. alyssoides, Ulex gallii and Erica cinerea. For most of the species under study (E. australis, P. tridentatum, H. lasianthum spp. alyssoides and U. gallii), neither plant mortality nor the number nor length of sprouted shoots per plant differed between treatments, although in E. cinerea the number of shoots was more negatively affected by prescribed burning than by clearing or mastication. The pre-treatment plant size did not affect plant mortality or plant resprouting response, suggesting that this parameter alone is not a good indicator of plant resprouting after fuel reduction treatments. Stem minimum diameter after treatments, a proxy of treatment severity, was not related to plant mortality, number or length of resprouted shoots. The duration of temperatures higher than 300 °C during burning in plant crown had a negative effect on the length of resprouted shoots, only in E. cinerea. The results show that fuel reduction treatments did not prevent shrub response in any case. Some reflections on the applicability of treatments are discussed.

Nitrogen mineralization after clearcutting and residue management in a second rotation Eucalyptus globulus Labill. stand in Galicia (NW Spain)

Abstract• The effects of clearcutting and of different slash management procedures on N mineralization were assessed in a Eucalyptus globulus Labill. stand in Galicia (N W Spain). Treatments were no clearcutting (control), clearcutting combined with scattering, scattering + fertilization, windrowing, and two types of slash burning with two levels of severity: broadcast burning and windrow burning. Changes in mineral N were monitored in the soil during the 18 months following the treatments. Eleven years later, the treatment effects were again evaluated during a twelve month period to assess long-term effects.• During the first study period, slash burning led to a marked increase in the contents of N-NH4+, N-NO3− and N-mineralization in topsoil layers (0–10 cm). In contrast, clearcutting followed by either scattering or windrowing of residues had no effect on mineral N in the top soil or in situ mineralization, relative to the control. Ammonium was the predominant form of mineral N. No residual effects of the treatments were detected eleven years later.• Fire severity, in relation to slash burn type, had significant negative effects on post-burn N mineralization and nitrification in the first period studied, but no long-term residual effects were observed. Some practical consequences for sustainable management of such stands are suggested.Résumé• Les effets de la coupe à blanc et des différentes procédures de gestion des résidus d’exploitation sur la minéralisation de l’azote ont été évalués dans un peuplement d’Eucalyptus globulus Labill. en Galice (nord-ouest Espagne). Les traitements ont été : pas de coupe à blanc (témoin), coupe à blanc combinée avec dispersion, dispersion + fertilisation, andainage, et deux types d’écobuage à deux niveaux de gravité : incinération par surface et incinération des andains. Les changements en azote minéral ont été suivis dans le sol pendant les 18 mois suivant les traitements. Onze ans plus tard, les effets des traitements ont été de nouveau évalués au cours d’une période de douze mois pour déterminer les effets à long terme.• Au cours de la première période d’études, l’écobuage a conduit à une nette augmentation de la teneur de N-NH4+, N-NO3−, et à la minéralisation de l’azote dans la couche supérieure du sol (0–10 cm). En revanche, la coupe à blanc suivie d’une dispersion ou d’andainage de résidus n’a eu aucun effet sur l’azote minéral dans la partie supérieure du sol ou sur la minéralisation in situ, par rapport au témoin. L’ammonium a été la forme prédominante de l’azote minéral. Onze ans plus tard, il n’a pas été détecté d’effets résiduels des traitements.• La gravité des incendies, en relation avec le type d’écobuage, a eu des effets négatifs importants sur la minéralisation de l’azote et la nitrification après le feu dans la première période étudiée, mais des effets résiduels à long terme n’ont pas été observés. Certaines des conséquences pratiques pour la gestion durable de ces peuplements sont proposées.