Long-term impact of prescribed fire on soil chemical properties in a wildland-urban interface. Northeastern Iberian Peninsula

Wildfires are common in wildland-urban interfaces (WUIs), where they represent a severe threat to inhabited urban settlements endangering both infrastructure and human life. Given these hazards, it is critical that forest management tools be designed to reduce the risk of wildfire at the WUI. In this regard, a management tool that is increasingly being adopted is that of prescribed fires; however, a complete understanding of their impact has yet to be gained. The aim of this study, therefore, is to analyze long-term soil properties after a prescribed fire and observed if the prescribed fire avoids vegetal fuel continuity. Our study area occupies a Mediterranean forest in the urban settlement of Picarany in the municipality of Almoster (Tarragona, Spain). The vegetation is composed primarily of Pinus halepensis Miller. and Quercus ilex L. and the soil type is classified as Xerorthents. Soil sampling was carried out in four campaigns: just before the prescribed fire (BPF), just after (APF), one year after (1YAPF) and 13 years after the prescribed fire (13YAPF). In each sampling period, 30 samples were taken (0-2.5 cm) from a 72-m² experimental plot (4 × 18 m). The soil properties analyzed were total nitrogen (TN), soil organic matter (SOM), pH, electrical conductivity (EC) and extractable calcium (Ca), magnesium (Mg), potassium (K) and available phosphorus (P) concentrations. The carbon/nitrogen ratio was also calculated. A comparison of pre-fire values (2004) with long-term results (2017) shows increases of EC, Ca and Mg and decreases of TN and SOM. Despite these changes, the prescribed fire was found to be a good tool for managing forest areas. Indeed, the changes in soil properties did not represent a severely degradation of the soil and after 13 years there was no horizontal or vertical fuel continuity in the wildland-urban interface.

Mapping impact of intense rainfall on a high-severity burned area using principal component analysis

High-severity wildfires have a major impact on soil properties. Moreover, recently burned areas are highly sensitive to intense rainfall events. However, little is known about the impact of extreme rainfall on the relationship between soil properties and their spatial distribution. The objective of this study is to examine the effects of an intense rainfall event on soil properties and their spatial distribution in a small area using principal component analysis (PCA). The variables studied were aggregate stability (AS), total nitrogen (TN), soil organic matter (SOM), inorganic carbon (IC), C/N ratio, calcium carbonates (CaCO3), pH, electrical conductivity (EC), available phosphorus (P), extractable calcium (Ca), extractable magnesium (Mg), extractable sodium (Na) and extractable potassium (K). Each PCA (before and after intense rainfall event) allowed us to extract five factors. Factor 1 in the pre-intense rainfall event PCA explained the variance of EC, available P, extractable Mg and K; factor 2 accounted for TN, SOM (high loadings), IC and CaCO3 (low loadings); factor 3 explained AS, extractable Ca and Na; and, factors 4 and 5 accounted for C/N and pH, respectively. Factor 1 in the after intense rainfall event PCA explained the variance of TN, SOM, EC, available P, extractable Mg and K (high loadings) and pH (low loading); factor 2 accounted for IC and CaCO3; factor 3 explained extractable Ca and Na; factor 4 accounted for AS; and, factor 5 for C/N. The results showed that the intense rainfall event changed the relationship between the variables, strengthening the correlation between them, especially in the case of TN, SOM, EC, available P, extractable Mg and extractable Ca with AS. In the case of the pre-intense rainfall event PCA, the best- fit variogram models were: factors 1 and 2 – the linear model; factors 3 and 4 – the pure nugget effect; and, factor 5 – the spherical model. In the case of the factors after intense rainfall event PCA, with the exception of factor 5 (spherical model), the best fit model was the linear model. The PCA score maps illustrated a marked change in the spatial distribution of the variables before and after the intense rainfall event. Important differences were detected in AS, pH, C/N IC, CaCO3, extractable Ca and Na.

Effects of prescribed fires on soil properties: A review

Soils constitute one of the most valuable resources on earth, especially because soil is renewable on human time scales. During the 20th century, a period marked by a widespread rural exodus and land abandonment, fire suppression policies were adopted facilitating the accumulation of fuel in forested areas, exacerbating the effects of wildfires, leading to severe degradation of soils. Prescribed fires emerged as an option for protecting forests and their soils from wildfires through the reduction of fuels levels. However such fires can serve other objectives, including stimulating the regeneration of a particular plant species, maintaining biological diversity or as a tool for recovering grasslands in encroached lands. This paper reviews studies examining the short- and long- term impacts of prescribed fires on the physical, chemical and biological soil properties; in so doing, it provides a summary of the benefits and drawbacks of this technique, to help determine if prescribed fires can be useful for managing the landscape. From the study conducted, we can affirm that prescribed fires affects soil properties but differ greatly depending on soil initial characteristics, vegetation or type of fire. Also, it is possible to see that soil's physical and biological properties are more strongly affected by prescribed fires than are its chemical properties. Finally, we conclude that prescribed fires clearly constitute a disturbance on the environment (positive, neutral or negative depending on the soil property studied), but most of the studies reviewed report a good recovery and their effects could be less pronounced than those of wildfires because of the limited soil heating and lower fire intensity and severity.

Long-term dynamics of soil chemical properties after a prescribed fire in a Mediterranean forest (Montgrí Massif, Catalonia, Spain)

This study examines the effects of a prescribed fire on soil chemical properties in the Montgrí Massif (Girona, Spain). The prescribed forest fire was conducted in 2006 to reduce understory vegetation and so prevent potential severe wildfires. Soil was sampled at a depth of 0-5cm at 42 sampling points on four separate occasions: prior to the event, immediately after, one year after and nine years after. The parameters studied were pH, electrical conductivity (EC), total carbon (C), total nitrogen (N), available phosphorus (P), potassium (K⁺), calcium (Ca²⁺) and magnesium (Mg²⁺). All parameters (except pH) increased significantly immediately after the fire. One year after burning, some chemical parameters - namely, EC, available P and K⁺ - had returned to their initial, or even lower, values; while others - pH and total C - continued to rise. Total N, Ca²⁺ and Mg²⁺ levels had fallen one year after the fire, but levels were still higher than those prior to the event. Nine years after the fire, pH, total C, total N and available P are significantly lower than pre-fire values and nutrients concentrations are now higher than at the outset but without statistical significance. The soil system, therefore, is still far from being recovered nine years later.

Immunocytochemical evidence of hypothalamic regulation of adenohypophyseal VIP in the male rat

In order to check whether hypothalamic stimulatory or inhibitory factors exert any kind of modulation on the morphology of VIP-immunoreactive cells in the rat hypophysis, the transport of these towards the hypophyseal portal system was blocked by intraventricular administration of colchicine in adult male rats, thereafter performing a morphometric study after characterizing the VIP-immunoreactive adenohypophyseal cells by immunocytochemical techniques. Colchicine administration led to a significant increase (p < 0.01) in the number of reactive cells observed. These cells were characterized by a larger cellular area (p < 0.01), owing to increases in nuclear area (p < 0.05) and cytoplasmic area (p < 0.05). Their morphology became more regular, with a predominance of polygonal and oval cells. The results suggest that the VIP-reactive cells of the rat hypophysis are subject to a hypothalamic inhibitory influence and their activity increasing when the hypothalamic effect is interrupted by intraventricular administration of colchicine.