Acacia s.l. communities comprise usually fire-prone ecological systems due to the tree architecture, canopy density, and connectivity. When dominant, acacias form open shrublands that enable light to reach underbrush, favoring the development of grasses. Depending on soil conditions (especially nitrogen content), rainfall and grazing intensity, grasses may produce critical loads of combustible biomass. (Fig. 4.) Understory shrubs (e.g. Aloysia gratissima in central Argentina) may also promote forest fires and may even increase fire intensity compared with grasses.

Fig. 4: Vachellia spp. scrub in central Argentina affected by the fire, on the left of the image. The accumulated grass biomass can be seen on the right of the image. © M. Karlin. …show more content…
(Butler & Fairfax, 2003.) Fires under such conditions alter both height and abundance of Acacia and other species modifying fire regimes, increasing intensity and frequency of new fire events. (Clarke et al., 2005.)
Rainy seasons alternated with dry seasons are usually the most favorable climatic conditions for the rise of fire risk. If such conditions are combined with high terrain slopes and windy conditions, fire expansion may become catastrophic and can affect importantly local vegetation survival and recovery.
Such conditions are typical in the central highlands of Argentina, where natural herbivores grow in low densities and the reduction of grass biomass depend almost exclusively on livestock. Fire is the main shaper of these environments; when fires are intense, they usually transform original woodlands of Lithraea molleoides and Schinopsis marginata into Acacia s.l. scrubs, where soil, vegetation, and fauna change their …show more content…
seed bank. In the Sydney region (Australia), Acacia species represent some of the earliest seedlings to emerge after the fire. Apparently, fire activates dormant seed bank and enhance the appearance of Acacia suaveolens seedlings in a high proportion during three months after fire. (Auld & Tozer, 1995.) Such Acacia pulses, if seedlings prosper, might foment the establishment of coetaneous populations. For plant species that are subject to significant levels of seed loss to predators, disease and/or decay, the timing of seeding events in relation to fire is likely to be an important determinant of post-fire recovery. (Wright et al.,