**Box ².**

*Fragmentation of Forest Habitat.*

#### **5.4 Conservation of the forest itself: prevention against rural fires**

The occurrence of mega-fires in recent decades, not only in Portugal (since the 1980s), but in other countries, introduces another problem to solve in landscape planning: rural fires. Admittedly, landscape management cannot solve all occurrences, especially when they are of criminal or negligent origin. Nevertheless, it can reduce the size of the fire, curb its progression and even promote its selfextinguishment.

### *Spatial and Temporal Variability Regarding Forest: From Tree to the Landscape DOI: http://dx.doi.org/10.5772/intechopen.91701*

One of the critical components of fire behavior is known to be basin morphology, including slope, aspect and altitude [59–61]. The slopes exposed to the north, with slopes >25%, are the least burning [62]. The speed of fire progression doubles for each 10° increase in slope [63] and is reduced when it reaches the top, due to the local wind from the opposite slope. When it reaches the ridge, if it does not progress in the opposite slope, the fire begins to plow toward the lower slope, more slowly than when the slope rises. Given this pattern of fire behavior, it is essential to create a landscape fire-prevention network directly related to the watershed morphology that contains or extinguishes the fire. Agee et al. [64] propose the installation of shaded fuel breaks as low-fuel vegetation strips or areas (note that they do not correspond to the fuel management strips provided for in Portuguese law, with no vegetation and bare soil). These authors propose that these shaded fuel breaks be networked, according to the site, and say they are more efficient if they are wide and have surface fuel control bands.

The key areas of the river basin in which to intervene for this purpose are the structuring lines of the landscape‑the streams and the ridges. According to Povak et al. [65], the waterlines and associated valley bottoms are more important for this purpose than the ridges. If the slope is too long, one or more fire retardant strips should be introduced downhill along the slope to avoid top-down and down-up fire [61]. To complete the structure, it is also necessary to create strips transverse to the slope. In the hillslope, the streams and the secondary ridges alternate, so it is in these secondary lines that these fire-retardant strips should be created [66].

Concerning the species to be used, there is a considerable debate about the higher or lower combustibility of species. In Portugal, *Eucalyptus globulus* Labill. and *Pinus pinaster* Aiton. have occupied the country and are currently the two species with the present main commercial value, since the industries related to the transformation of autochthonous species have practically disappeared, which discourages the owners for their use. The simple empirical observation of fires and their consequences, as well as the analyses carried out on the species that burned the most, allows to say that these two tree species are more combustible than the autochthonous tree species. From the available literature, Silva et al. [67] verified a tendency toward fire, in decreasing order of: pinewood, eucalyptus forests, broadleaf forests, unspecified coniferous forests, cork oak forests, chestnut orchards and holm oak. They also concluded that stand composition is the most important variable to explain the probability of fire. Calviño-Cancela et al. [68] also state that autochthonous species are more fire-resistant, as well as the studies concerning leaf litter combustibility [69]. In this context, it has to be admitted that species are not equally combustible and that, as might be expected, hardwoods other than eucalyptus are more fire-resistant and therefore can be regarded as fire-retardant. The landscape fire-prevention network should, therefore, be planned with different tree species, always avoiding monocultures. In this network, it is also possible to have the agricultural fields, pastures and, ultimately, voids (without shrub or tree vegetation) that, however, should be covered with herbaceous plants so as not to leave the soil uncovered and prevent its erosion.
