1. Introduction
The Andes region in South America harbors one of the most biodiverse montane ecosystems globally [
1,
2]. The tropical Andean plant diversity is remarkably vast, and their habitat types are interconnected [
3,
4]. Grassland and shrubland communities at high elevations predominate in the Andean mountains [
5,
6]. The high Andean grasslands represent distinct ecosystems characterized by their high biodiversity and essential provision of ecosystem services [
7]. These ecosystems are fragile environments facing significant threats characterized by marked climatic conditions and variable food sources for grazing [
8]. Wildfires can also significantly impact the chemical, physical, and biological properties of soil due to their duration and intensity of burn [
9]. Indeed, soil plays a crucial role in supporting plant growth through nutrient cycling, mineral storage, and carbon sequestration [
10,
11]. Degradation of the biological, chemical, and physical properties of forest soils can temporarily or permanently limit the capacity for plant growth, suggesting that immediate fire impacts are concentrated on the surface soil horizon [
12]. The soils in these ecosystems sustain the grasslands, which serve as the primary food source for livestock. Andean grasslands are currently the ecosystems most affected (80%) by wildfires in the Peruvian Andes during the second half of the year [
13]. Where the role of the population in the Peruvian Andes is undeniable, as grassland fires are often attributed to human activity [
14,
15]. Grasslands play a vital role in livestock production as an economic activity in Peru, where there is the world's largest population of Alpacas, with around 4.5 million, comprising about 85% of the total population [
16]. However, fire activity in the context of climate change could limit vegetation succession by influencing the compositions of plant communities and soil properties [
6,
17].
A prescribed fire is the deliberate use of low-intensity fire in various countries to achieve diverse objectives, contingent upon factors such as climate conditions, forest fuel, and topography [
18,
19,
20,
21]. However, fire activity clearly alters the environment, including its effects on soil properties, which can be positive, neutral, or negative. Most studies suggest that soil tends to recover when soil heating is limited and fire intensity and severity are low [
22]. For instance, a study conducted in Spain documented negative impacts (50%) on the chemical and physical properties of forest soil up to nine years later, with some exceptions such as soil texture and invertebrate biomass [
11,
23]. In contrast, a study in Brazil conducted by [
24] reported that fire increased chemical properties while decreasing potential acidity and phosphorus content in the soil, with no observed alteration in soil physical properties due to the wildfire.
In this context, the impact of fire on soil properties can be relative, yielding significantly different outcomes based on biological, chemical, and physical factors. The extent of soil disturbance by wildfire depends on various factors including fire intensity, duration, recurrence, forest fuel load, and soil characteristics. This variability is evident in studies conducted across different regions such as the USA [
20,
25], Europe [
16,
19,
26,
27,
28,
29], and Asia [30,31 among others. The impact of burning and grazing on Paramo soils may primarily affect physical characteristics, and variations in chemical properties may not necessarily translate into differences in vegetation structure between grazed, burned, and undisturbed sites [
12]. Nevertheless, clear shifts in the relative abundance of plant growth forms have been documented [
32]. Additionally, while the recovery of certain soil properties and processes through reforestation may facilitate the restoration of native forests to conditions similar to those prior to wildfire occurrence, this process remains context-dependent [
33].
In general, high-, medium-, and low-severity fire activities can occur when vegetation is affected by a wildfire or controlled burning practice. In this paper, the term "wildfire" is used to describe any unplanned and uncontrolled fire that starts in grasslands due to burning practices. Low-severity fire activities, such as controlled burns, could have positive effects by accumulating organic matter in the soil due to the incomplete combustion of biomass [
34]. However, ashes produced during wildfires resulting from burns could also impact soil properties [
35,
36].
To predict fires and limit their impacts, new knowledge is needed about fire activity and the spatial and temporal distribution of factors affecting its occurrence. This is of utmost importance for agroforestry management and to reduce environmental degradation [
37]. Nevertheless, wildfire impacts resulting from burning practices have not been fully studied in Peruvian ecosystems. The objective of this study was to analyze the effect of fire activity on soil physicochemical properties and analyze its social context in Cusco, Peru, through two wildfire emergencies reported by the Government.
4. Discussion
Soil properties such as pH, electrical conductivity (EC), organic matter (OM), nitrogen (N), phosphorus (P), and potassium (K) in the Macay and Salloc communities (except for pH in Salloc) exhibit a predominant slight increase between the onset and culmination of the rainy season due to several factors. One contributing factor is the formation of ash and combustion residues, which may contain alkaline substances such as carbonates and oxides, thereby causing pH levels to rise [
59,
60]. Additionally, the authors note that another factor contributing to pH increases could be the high intensity of the wildfire. However, grasslands or shrublands typically exhibit low-to-moderate fuel loads, leading to wildfires of relatively moderate intensity and resulting in moderate burn severity compared to wildfires (Sanchez-Garcia et al., 2023). It is essential to recognize that this varies depending on the depth and intensity of the fire, as pH levels can experience a significant increase [
61]. Indeed, our results are more sensitive to changes at the surface level than at the subsurface level. Our pH values are consistent with studies conducted by [
62] and [
63] in central and northern Peru, respectively.
EC levels are higher in burned areas compared to unburned areas following a fire, attributed to the release of soluble inorganic ions from burned soil organic matter and the incorporation of ash into the soil [
11,
64,
65,
66]. Consequently, the presence of base cations in the ash, such as calcium, magnesium, and potassium, could also contribute to an elevation in EC [
67]. Our findings suggest that the increase in EC is a result of the incorporation of ash between the onset and culmination of the rainy season, yet EC subsequently returns to values more similar to those observed in unburned areas. These alterations are temporary, as the salts incorporated into the soil quickly diminish due to rainfall and runoff during the rainy period [
68]. Soil EC levels that are excessively high or low can limit crop growth [
69], however, the EC values estimated in the soil after the wildfire suggest low salt conditions, consistent with studies conducted by [
62] and [
70] in central and southern Peru, respectively.
The impact of fire on soil properties is typically contingent upon factors such as intensity, duration, and frequency, collectively constituting wildfire severity [
23,
28]
. The effects of very intense wildfires can lead to a decrease in organic matter compared to initial values, resulting in soil degradation [
71]
. However, a notable increase in organic matter can also be observed in the surface levels of the soil after a fire. This increase can enhance grassland production in terms of both quantity and quality throughout the year, while also allowing for the estimation of reserves of nitrogen, phosphorus, and potassium [
72]
. In contrast, organic matter levels in this study were found to be higher in burned areas compared to unburned areas. Our findings align with results obtained by [
63] in northern Peru.
In some cases, the availability of N, P, and K has been observed to decrease in the medium term (0–5 years) in Andean regions [
73]
. Despite the common occurrence of wildfires in these areas, relatively little is known about the short-term impact of wildfires on grasslands. The results for N, P, and K in this study indicate that wildfires did not have a negative effect on the physicochemical properties of the soils, thus maintaining the unaltered soil quality. This could be attributed to the potentially low severity of the wildfires resulting from minimal fuel loading from the grasslands. For instance, nitrogen levels increase after wildfires when temperatures do not exceed 400°C [
74]
. This notable increase in nitrogen can mitigate the impact of leaching and subsequent drainage by rainfall, which may otherwise result in a nitrogen deficit in the soil. An increase in phosphorus in burned areas compared to unburned areas was identified after the wildfire, possibly due to fire intensity, as elevated temperatures can trigger the mineralization of organic phosphorus, and the presence of ash derived from vegetation combustion can also influence this process [
9,
59]
. These elements have a beneficial impact on the soil, improving its fertility through the properties of ash [
75]
.
The increase in potassium (K) is typically attributed to burning or fires due to the accumulation of ash produced during the combustion of vegetation. Conversely, [
70] suggests a potential decrease in potassium, around 25%; however, its classification level remains unchanged as it remains above the optimal level. An increase in potassium was observed in both communities in the burned areas in this study, consistent with studies conducted in Peru by [
62,
63] and [
76]
.
Land use change and human-induced fires have transformed landscapes [
22]
, however, the most traditional and modern human uses of fire typically do not have significant direct impacts on soils in areas with low fuel loads. Fire can induce substantial soil alteration through indirect effects, including changes in vegetation restoration [
73]
. For instance, at the end of the dry period in 2022, both communities in Cusco exhibited adequate levels of nutrients for plant development. The delay in the start of the rainy season does not suggest significant soil leaching processes between September and November.
Despite some temporal variations in soil properties at the most superficial level (0-3 cm) and the documented objective of burning by farmer communities to improve soil fertility through interviews, seasonal changes in the physical and chemical properties of soils do not suggest a substantial contribution from grassland burning to soil fertility in our study area. Optimal soil fertility conditions typically support healthy plant growth and development, leading to greater productivity [
77]
. On the other hand, wildfires in grassland ecosystems can serve other purposes, such as stimulating the regeneration of specific plant species, maintaining diversity, or acting as a tool for reclaiming encroached grasslands [
23,
78]
. Indeed, our findings one-year post-fire suggest that wildfires stimulated the growth of other herbaceous species in Cusco. This is consistent with the perspectives of individuals interviewed across the study areas, who anticipate varying responses from the grasslands, both in terms of quantity and quality, in the coming months due to burning practices [
14,
15]
. Our findings also indicate vegetation recovery of up to 78% (or less), approximately three years after the wildfire. This aligns closely with the grassland recovery timeframe (1-4 years) reported by the population during the interviews.
The multifaceted nature of wildfires, which encompasses social, economic, and political factors, often complicates stakeholder efforts to reach a common understanding on how to address the problem and propose adequate solutions [
79]
. Current international governmental strategies are oriented towards adopting prevention measures and establishing control plans that include initiatives for impact mitigation training, prescribed burns, alternative methods for the disposal of agricultural waste, and imposing penalties for unauthorized burning [
80]
. However, in Peru, existing measures are predominantly punitive, encompassing both imprisonment and significant monetary fines [
81,
82], with a focus on short-term reactive management once a fire occurs. This reactive approach involves actions such as hiring personnel, procuring equipment to respond to wildfire emergencies, and providing firefighting training. Implementing policies in Peru that incorporate the use of fire by farming communities presents a significant challenge for decision-makers [
42,
83]
. Furthermore, there exists a wide range of sectoral, disciplinary, and personal perspectives among those involved in the different stages of wildfire management, which have yet to find a coordinated space for joint action. Therefore, research is needed in Peru to understand how people use fire (controlled burns or prescribed fire) and what role the involved institutions should play [
79]
.
On the other hand, the increasing frequencies of dry days or hot days in Peru are linked to the escalating impacts of wildfires on grassland ecosystems [
13,
41]
, creating conditions that have led to a rise in the frequency of wildfire emergencies and loss of human life. Indeed, extreme events such as droughts are associated with an approximate increase of up to 400% in wildfire frequency over the last two decades [
42]
. By the end of this century, the Intergovernmental Panel on Climate Change (IPCC) has projected that temperatures in tropical regions could potentially increase by up to 4.8 °C [
84]
. This underscores the importance of implementing appropriate measures and strategies in the management of fire use, known as corrective management, instead of solely prioritizing the management of wildfires, which involves both prospective and reactive approaches, by the government authorities of Peru. The concepts of corrective, prospective, and reactive management of disaster risk are documented in Peruvian law under SINAGERD [
82]
.
5. Conclusions
This study analyzed the effects of fire on soil properties in herbaceous grasslands and its social context in Cusco, southern Peru. Two wildfires that occurred in grasslands during 2022 in two farmer communities of Cusco-Peru were studied. Andean grassland ecosystems are fragile environments facing significant threats, necessitating better management strategies. The results indicate that soil property values initially increased after the fire, between the second and third seasons of analysis (the beginning of the rainy season and the rainy season), and showed a gradual reduction, mainly due to associated factors such as rainfall and runoff contributing to the leaching process. The values of electrical conductivity, organic matter, and NPK continued to increase in the four seasons due to the incorporation of ash into the soil resulting from the wildfires. Moreover, our findings suggest that modifications in soil properties are driven by the soil temperature during burning because the fuel load from grass is very low, contributing to the stimulation of regeneration of other herbaceous species after the rainy season. It is estimated that the load of vegetative fuel from the Andean grasslands after burning will be fully recovered between 4 and 6 years, a timeframe also described by the local population.
Given the burning practices carried out by the population and their interests, research on the comparison of burn severities by controlled burns on grasslands needs to be conducted. This should be approached cautiously, as fire behavior and combustion dynamics may modulate burn severity differently (whether it involves grassland fuels or other fuels). Our results can assist decision-makers in formulating policies, regulations, and proposals for reducing wildfire impacts, as well as restoring vegetation in the Andean region of Cusco.