Javier González-Romero

Post-fire straw mulching is widely used to reduce soil erosion and facilitate vegetation recovery in fire-affected ecosystems. However, straw mulch may introduce agricultural weedy species, raising concerns about their persistence and potential effects on post-fire plant community assembly. This study evaluated the medium-term ecological implications of straw mulch application using a post-fire chronosequence in semi-arid Mediterranean ecosystems of southeastern Spain. Vegetation was surveyed in 54 plots (27 mulched and 27 untreated) distributed across sites representing 1, 2 and 6 years after fire (YAF). Species richness, diversity, composition and the abundance of agricultural weedy species were analysed to assess treatment effects across the chronosequence. Straw mulching increased species richness and diversity during the early post-fire stages, through the introduction of agricultural weedy species. Community composition differed significantly among post-fire stages and between treatments, although post-fire stage explained a substantially larger proportion of the variation than mulching treatment. The abundance of agricultural weedy species declined markedly along the chronosequence, and these species showed very low abundance at the site representing 6 YAF. Plant communities in mulched and untreated plots became more similar at the latest stage represented in the chronosequence. Overall, the results suggest that straw mulching can temporarily enhance plant diversity during early post-fire recovery without evidence of negative medium-term effects on vegetation recovery under the environmental conditions evaluated in this study. These findings support the use of straw mulching as a post-fire restoration measure in semi-arid Mediterranean ecosystems while highlighting the importance of considering straw provenance when assessing early community responses.

The modification of fire regimes and their impact on vegetation recovery, soil properties, and fuel structure are current key research areas that attempt to identify the thresholds of vegetation’s susceptibility to wildfires. This study aimed to evaluate the vulnerability of Mediterranean pine forests (Pinus halepensis Mill. and Pinus pinaster Aiton) to wildfires, analyzing two major forest fires that occurred in Yeste (Spain) in 1994 and 2017, affecting over 14,000 and 3200 hectares, respectively. Four recovery regions were identified based on fire severity—calculated using the delta Normalized Burn Ratio (dNBR) index—and recurrence: areas with high severity in 2017 but not in 1994 (UB94-HS17), areas with high severity in 1994 but not in 2017 (HS94-UB17), areas with high severity in both fires (HS94-HS17), and areas unaffected by either fire (UB94-UB17). The analysis focused on examining the recovery patterns of three spectral indices—the Normalized Difference Vegetation Index (NDVI), Normalized Moisture Index (NDMI), and Normalized Burn Ratio (NBR)—using the Google Earth Engine platform from 1990 to 2023. Additionally, the Relative Recovery Indicator (RRI), the Ratio of Eighty Percent (R80P), and the Year-on-Year average (YrYr) metrics were computed to assess the spectral recovery rates by region. These three spectral indices showed similar dynamic responses to fire. However, the Mann–Kendall and unit root statistical tests revealed that the NDVI and NDMI exhibited distinct trends, particularly in areas with recurrence (HS94-HS17). The NDVI outperformed the NBR and NDMI in distinguishing variations among regions. These results suggest accelerated vegetation spectral regrowth in the short term. The Vegetation Recovery Capacity After Fire (VRAF) index showed values from low to moderate, while the Vulnerability to Fire (V2FIRE) index exhibited values from medium to high across all recovery regions. These findings enhance our understanding of how vegetation recovers from fire and how vulnerable it is to fire.

Worsening climate change and increasing temperatures generate more sever and extended wildfires, raising concerns about ecosystem services. Prescribed burns (PB) are used to reduce forest fuel loads. Improving knowledge regarding the vegetation response after PB is essential for generating common points for monitoring ecological burning effects and generating a protocol or practice guide. We compared the PB seasonality of low-intensity (spring, summer, and autumn) and unburned areas in a total of 12 plots in Pinus nigra Arnold ssp. salzmannii Mediterranean forest. Our vegetation analysis was short term (one year after each PB). We analyzed vegetation coverage, α-diversity (Pielou, Simpson, and Shannon’s index), life forms, and fire-adapted traits using the Canfield transect method, followed by statistical analyses such as non-metric multidimensional scaling (NMDS) and two-way ANOVA. α-diversity was significantly decreased (>55% of dissimilarity) in the burned plots during each season, with the lowest values after summer PB (69% of dissimilarity) when comparing the burned and unburned plots. There was a significant increase in hemicryptophytes (15−20%) and geophyte coverage (from 6% to 14%, or from 4% to 8% in certain cases) in the burned plots after PB seasonality; however, the phanerophytes were reduced (from 13% to 5%). Resprouters were more dominant after PB (an increase of 15–20%), which indicates that resprouters have a faster recovery and generate a fuel load quickly for highly flammable species such as Bromus after low-intensity burning. This suggests that low-intensity prescribed burning may not be the best methodology for these resprouting species. This study helps to understand how burning in the early season can affect inflammable vegetation and the change in fuel that is available in semi-arid landscapes. This is key to achieving the basis for the development of a standardized system that allows for the efficient management of forest services in order to reduce wildfire risks. One objective of this line of research is to observe the effects of recurrent burning in different seasons on vegetation, as well as plant−soil interaction using the microbial and enzyme soil activity.

The main objective of this project is to investigation and develop new tools aimed at adapting Iberian Aleppo pine forests to climate change, as well as their demonstrative application through forest management actions. will focus on the early detection of decay processes and on the improvement of the resilience of this ecosystem by increasing its vigour, its capacity to adapt to climatic aridification and the ability to recover its functions after natural disturbances. The geographical scope of the project will cover the potential area of distribution of the habitat subtype in the Iberian Peninsula, across sub-humid and semi-arid ecological gradient, including the Mediterranean slopes of the Catalan mountains and the Iberian System, the Ebro basin and the pre-Baetic mountain ranges. This will facilitate an integrated implementation of the methodology that involving the main stakeholders that are responsible for the regulation of forest management throughout the area:- To implement silvicultural treatments aimed at improving vitality and reducing the effects of reduced water availability in a scenario of recurrence of droughts and increased evapotranspiration.- To implement adaptive treatments to improve the resilience and adaptive capacity of Aleppo pine post-fire regeneration in a scenario of higher frequency and severe wildfires.After the implementation of ecohydrology and post-fire treatments, a monitoring program will be carried out in the forest stands where the treatments have been executed. We measure physicochemical and biologic parameters of soil and vegetation. Measurements will be realized after the execution and annually to study if the treatments have had the desired effects or not.

The current forest fire regimes are increasing due to high temperatures, global warming and frequency of wildfires in dry ecosystems like in the Mediterranean Basin. These issues are decreasing ecosystem’s resistance and resilience, worsening desertification, for this reason, it is of great importance to analyze the effects on the soil. However, it is now possible to apply some preventive tools to avoid wildfire effects or reduce their impacts on ecosystems. Fire is used as preventive tool, prescribed burning (PB) change both the fuel loads in forest ecosystems and vegetation strata. However, fire can produce changes in soil characteristics and physico-chemical parameters.The studied PB was carried out in spring 2021 (early burn) in SE Spain. The mainly vegetation is shrub (i.e., Macrochloa tenacissima (L.) Kunth, Cistus Clusii Dunal, Salvia rosmarinus (L.) Schleid) with poor dry soils formed mainly by cambisols. For improve the knowledge at short/medium-term PB effects on soil, this study attempted to analyze the ecological early PB effects on semi-arid land soils by CO2 flow soil respiration (SR) automatic chamber (CFLUX-1 Soil CO2 Flux System), minidisk infiltrometers for soil hydraulic conductivity (SHC) by infiltration rate and Water Drop Penetration Time (WDPT) methodology for measuring soil water repellency (SWR). It also analyzed soil physico-chemical properties. In addition, this study tries to generate a protocol or guide of good practices for PB. There were no significant differences in any studied variables after the 1-year period according to our formulated hypotheses. However, effects were observed on some parameters on the first days after the PB, such as SOM and nutrients.

The soil microbiota is vulnerable to burning; however, it shows some resilience. No indices have yet been developed to assess fire damage related to soil biota. We evaluated the biological soil indices recorded by a Biolog EcoPlate System in a Mediterranean ecosystem. The experiment was carried out in an outdoor forest lysimeter facility (MedForECOtron), where we simulated burns with different burn severities. Burning increased the metabolic diversity of bacteria and most C-substrate utilization groups. Soil organic matter, phosphorus, electric conductivity, and calcium increased with increasing burn severity. Microbial richness and activity, as well as the integrated capacity of soil microbes to use a C source, lowered by burning, but recovered 6 months later. The functional diversity and amount of the C source used by microbes immediately increased after fire, and values remained higher than for unburned soils. We evaluated the changes in the vulnerability and resilience of fire-adapted ecosystems to improve their adaptive forest management. We found that the high burn severity reduced microbial richness, functional diversity, and the C source utilization of soil microbes (marked vulnerability to high temperatures), which recovered in the short term (high resilience). These results help to understand the main mechanisms of the effects of wildfire on semi-arid Mediterranean ecosystems, whose field validation will be helpful for fire prevention planning and restoration of burned areas.

Wildfires have historically been a natural alteration in Mediterranean ecosystems. Despite these ecosystems' high resilience, the expected climate change scenarios may lead into more recurrent and severe wildfires, and erosion and degradation processes can be enhanced.Post-fire restoration measures, seek to minimize wildfire negative impacts on the burned area as well as its ecological rehabilitation. Among these measures, soil stabilization treatments like erosion barriers or mulching are key for erosion and flood control. Nevertheless, its economic viability can be limited, and therefore these treatments must be thoroughly evaluated considering their costs and their efficiency to achieve the objective. Additionally, there is a need to evaluate new techniques, which can be implemented in places where, due to the scarce vegetation, some traditional treatments as log barriers cannot be implemented.  This study seeks to evaluate the cost-efficiency of alternative post-fire emergency measures for erosion control in a semi-arid Mediterranean area.The study area is located in the SE of Spain, more specifically in Hellín (Albacete). Wildfire took place on July 27 of 2020, and severely affected 266 ha of Pinus halepensis forest. Soil erosion was measured in 9 different micro-catchments (≈0.5 ha) located in the burned area. Three groups of micro-catchments were created, and a different treatment was randomly applied to each group. The applied treatments were the combination of straw mulch (0.25 kg/m2) with contour-felled logs (ML), and prefabricated biodegradable barriers (350 m/ha), Easy-Barriers ® (EB). The last three micro-catchments were designated as control and no treatment was applied.  At the outlet of each micro-catchment, sediment traps were settled to measure sediment yield. Additionally, rainfall intensity and erodibility were measured with pluviometers installed on the field.The outcomes of the experiment, show that only the ML treatment resulted in a significant reduction (Kruskal-Wallis H test) of the eroded sediment for the first 15 months after fire. For the studied period, a total mean eroded sediment of 9.61 and 8.41 ton/ha was measured at the control and the EB traps respectively, while at the ML traps this amount was significantly lower (1.43 ton/ha).  The difference between the two applied treatments increased as the rainfall events occurred, due to the breaking of the EB and the transport downstream of the sediment they were retaining. Therefore, the measured sediment yield at the EB traps during the autumn of the second year was higher than in the control ones. According to these results, ML must be considered as an effective treatment to soil stabilization, whereas EB did not perform as expected. That underlines the need to improve the strength and durability of the EB, as their aim is to hold on until the vegetation recovery is sufficient to retain those sediments. As well, the efficiency of the combination of EB with mulch treatments should be studied as the use of EB considerably reduce costs and allows managers not to depend on the availability of material to place contour-felled logs throughout the burned area.

Forest fires and post‐fire practices influence sediment connectivity (SC). In this study, we use the ‘aggregated index of connectivity’ (AIC) to assess SC in five Mediterranean catchments (198–1090 ha) affected by a wildfire in 2012 in south‐eastern Spain. Two temporal scenarios were considered, immediately after the fire and before post‐fire management, and 2 years after the fire including all practices (hillslope barriers, check‐dams, afforestation, salvage logging and skid trails). One LiDAR (light detection and ranging)‐derived digital elevation model (DEM, 2 m × 2 m resolution) was generated, per scenario. The five catchment outlets were established as the computation target (AIC_OUT), and structural and functional SC were calculated. Index outputs were normalized to make the results of the non‐nested catchments comparable (AIC_N‐OUT). The output analysis includes the SC distribution along the catchments and at local scale (929 sub‐catchments, 677 in the burned area), the hillslope and channel measures' effect on SC, and a sedimentological analysis using observed area‐specific sediment yield (SSY) at 10 new (built after post‐fire practices) concrete check‐dams located in the catchments (SSY = 1.94 Mg ha⁻¹ yr⁻¹; σ = 1.22). The catchments with more circular shapes and steeper slopes were those with higher AIC_N‐OUT. The structural SC maps – removing the rainfall erosivity influence – allowed evaluating the actual role played by the post‐fire practices that reduced SC ( = − 1.19%; σ = 0.41); while functional SC was linked to the actual change of SC ( = + 5.32%; σ = 0.62). Hillslope treatments resulted in significant changes on AIC_N‐OUT at sub‐catchment scale with certain disconnectivity. A good and positive correlation was found between the SSY and the changes of AIC_N‐OUT. However, the coarse DEM resolution explained the lack of effect of the rock check‐dams – located on the secondary channels – on AIC_N‐OUT. AIC_N‐OUT proved to be a useful tool for decision making in post‐fire restoration, but an optimal input data is still necessary to refine calculations.