Biophysical controls over fire regime properties in Central Portugal

Changes in bryophyte functional composition during post-fire succession

Climate and land-use changes are altering fire regimes in many regions around the world. To date, most studies have focused on the effects of altered fire regimes on woody and herbaceous communities, while the mechanisms driving post-fire bryophyte succession remain poorly understood, particularly in Mediterranean-type ecosystems. Here, we examined changes in bryophyte functional composition along a post-fire chronosequence (ranging from 1 to 20+ years) in Pyrenean oak woodlands (northeastern Portugal). To do so, we defined bryophyte functional groups based on seven morphological, reproductive, and life history traits. Then, we fitted linear and structural equation models to disentangle the direct and indirect effects of fire (time since fire and fire intensity), vegetation structure, climate, topography, and edaphic conditions on the abundance of each group. We identified two main functional groups: early colonizers (species with traits associated with strong colonization ability and desiccation tolerance) and perennial stayers (species with high competitive ability, i.e., large perennial mosses). Overall, the abundance of early colonizer species decreased with time since fire and increased with fire intensity, while the opposite was observed for perennial stayers. Thus, successional dynamics reflected a trade-off between species' competitive and colonization abilities, highlighting the role of biotic interactions later in succession. Patterns of functional composition were also consistent with changes in environmental conditions during succession, suggesting that species may experience stressful conditions (i.e., high radiation and low water availability) in early stages of post-fire succession. Our results also indicate that increased fire intensity may alter successional trajectories, leading to long-term changes in bryophyte communities. By understanding the response of bryophyte communities to fire, we were able to identify species with potential use as soil restoration materials.

Characterization of biophysical contexts leading to severe wildfires in Portugal and their environmental controls

Characterizing the fire regime in regions prone to extreme wildfire behavior is essential for providing comprehensive insights on potential ecosystem response to fire disturbance in the context of global change. We aimed to disentangle the linkage between contemporary damage-related attributes of wildfires as shaped by the environmental controls of fire behavior across mainland Portugal. We selected large wildfires (≥100 ha, n = 292) that occurred during the 2015-2018 period, covering the full spectrum of large fire-size variation. Ward's hierarchical clustering on principal components was used to identify homogeneous wildfire contexts at landscape scale on the basis of fire size, proportion of high fire severity, and fire severity variability, and their bottom-up (pre-fire fuel type fraction, topography) and top-down (fire weather) controls. Piecewise Structural Equation Modeling was used to disentangle the direct and indirect relationships between fire characteristics and fire behavior drivers. Cluster analysis evidenced severe and large wildfires in the central region of Portugal displaying consistent fire severity patterns. Thus, we found a positive relationship between fire size and proportion of high fire severity, which was mediated by distinct fire behavior drivers involving direct and indirect pathways. A high fraction of conifer forest within wildfire perimeters and extreme fire weather were primarily responsible for those interactions. In the context of global change, our results suggest that pre-fire fuel management should be targeted at expanding the fire weather settings in which fire control is feasible and promote less flammable and more resilient forest types.

Uncovering Vegetation Changes in the Urban–Rural Interface through Semi-Automatic Methods

Forest fires are considered by Portuguese civil protection as one of the most serious natural disasters due to their frequency and extent. To address the problem, the Fire Forest Defense System establishes the implementation of fuel management bands to aid firefighting. The aim of this study was to develop a model capable of identifying vegetation removal in the urban–rural interface defined by law for fuel management actions. The model uses normalised difference vegetation index (NDVI) of Sentinel-2 images time series and is based on the Welch t-test to find statistically significant differences between (i) the value of the NDVI in the pixel; (ii) the mean of the NDVI in the pixels of the same land cover type in a radius of 500 m; and (iii) their difference. The model identifies a change when the t-test points for a significant difference of the NDVI value in the ‘pixel’ as comparted to the ‘difference’ but not the ‘mean’. We use a moving window limited to 60 days before and after the analysed date to reduce the phenological variations of vegetation. The model was applied in five municipalities of Portugal and the results are promising to identify the places where the management of fuel bands was not carried out. This indicates which model could be used to assist in the verification of the annual management of the fuel bands defined in the law.