Abstract
Forest fires can alter essential ecosystem processes, including soil nutrient cycling, potentially cascading into permanent vegetation changes. This is key to elucidate in ecosystems where fires are infrequent. We assessed the effects of fire severity on the spatio-temporal response of soil nutrients and plant diversity in old-growth forests of south-central Chile, 1, 2, and 3 years after a fire that occurred in 2015. Within ancient, old-growth Araucaria araucana (Mol.) K. Koch and Nothofagus pumilio (Poepp. and Endl.) Krasser forests, ranging from areas burned with fire of high severity to unburned forests, we evaluated nitrogen (N), phosphorus (P), potassium (K), and soil organic matter (SOM) content using spatial interpolation to predict their spatial distribution and assessed their availability over time. We also assessed plant species richness and abundance following the fire. The availability of N noticeably increased during the first year after fire but rapidly decreased in the following years, especially in areas of high fire severity. P, K, and SOM were less affected by the fire, remaining more constant over time. In the short term, plant species richness and diversity significantly decreased in severely burned areas, but over time, they became more similar to those of the unburned forests. The time since a fire and its severity determine a heterogeneous distribution of soil nutrients, with N shifting to a significantly lower availability after fire, which was more notable in areas of high fire severity. Here, vegetation exhibited a decrease in plant diversity and the establishment of exotic species, likely producing cascading effects at the community level.
Highlights
A forest fire is a wildfire that spreads uncontrolled through woody, shrubby, or herbaceous vegetation
There was a significant effect of fire severity, the time elapsed since the fire, and the interaction of both variables on the availability of N (Kruskal–Wallis; p-value < 0.05)
We found that the time elapsed since the fire and the interaction between fire severity and the time since the fire had significant effects on soil organic matter (SOM) content (Kruskal–Wallis; p-value < 0.05) and that fire severity by itself did not have a significant effect on the SOM content (Kruskal–Wallis; p-value > 0.05)
Summary
A forest fire is a wildfire that spreads uncontrolled through woody, shrubby, or herbaceous vegetation. Fires could be an essential and natural factor benefiting the functioning of numerous ecosystems worldwide (e.g., the savannas and the chaparral and boreal forests). In this context, they can be considered an important element that shapes the landscape, history, and evolution of vegetation [1], which helps to maintain the structure and function of fire-prone communities [2–4]. The overall effects of fires on forest ecosystems are complex, ranging from the removal of above-ground vegetation and litter to significant impacts on soil properties [11], and the magnitude of these impacts will depend on the severity, duration, and frequency of fire events [12]. Shifts in fire regimes can greatly affect important components of ecosystems, including soil structure, nutrition, and microbial diversity and functioning in forest soils
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