Ecological response to surface fires: insights from four plant communities in the eastern foothills of the Little Ararat Mountains

The majority of fires in Iran's natural areas are anthropogenic, frequently initiated deliberately prior to the rainy season or during periods of peak heat to diminish above-ground biomass and alter land use. Different ecosystems exhibit varying responses to surface fires based on their plant structures. The present study investigates the ecological resistance and resilience behavior against surface fire in four plant communities of shrubland and forest, which are located along an elevational gradient. Furthermore, this research aims to elucidate how grazing, as a disturbance factor, impacts the response of these communities to surface fire.

Focusing on four plant communities with the type species of: Calligonum crinitum, Rhamnus pallasii, Prunus lycioides, and Juniperus excelsa, the study was conducted from 2009 to 2022 in the east of Little Ararat Mountains foothills. These communities were situated along an elevation gradient ranging from 800 to 1900 meters. Each community was divided into two zones, designated as grazed and grazing excluded. Two categories of surface fire occurrences were identified: sites experiencing a single fire event and those with at least two fire events during the study period. Ecological resistance was quantified by comparing vegetation cover before and after the fire, while ecological resilience was assessed by evaluating the rate of recovery towards pre-fire vegetation cover in subsequent years. A general linear model was used to assess the effects of community, disturbances (fire and grazing), and fire frequency. Principal component analysis (PCA) was employed to analyze the relationships among vegetation cover, resistance, resilience, and precipitation.

Calligonum stood out as the community with the lowest resistance but the highest resilience compared to the other study areas. The communities exhibited a distinct gradient in both resistance and resilience that closely aligned with their respective elevations, with the high-altitude Juniperus community at one end of the spectrum and the low-lying Calligonum at the other. The protection status of the lands did not emerge as a significant factor influencing the ecological resistance. However, it did play a key role in determining their resilience levels, with protected areas generally exhibiting greater resilience than their unprotected counterparts, except in the case of the Rhamnus community. The analysis further reveals subtle responses to the frequency of surface fire events: Ecological resistance did not differ significantly between communities that experienced a single fire versus those that were impacted twice, with the notable exceptions of Juniperus and Prunus, which displayed reduced resistance following the second fire. In terms of resilience, a significant decline was observed in the Rhamnus and Prunus communities after the second fire, while the other two communities were able to maintain their resilience levels. Spatial mapping of the fire-affected locations showed a concerning result, with the majority of sampled points situated far from the full recovery isoline, indicating a general lack of ecological sustainability across the study area. Some points within the Prunus and Juniperus communities were found to be closer to this benchmark, suggesting enhanced ecological stability within these communities. In PCA Calligonum emerged as closely associated with resilience, Juniperus with resistance, Rhamnus with vegetation cover, and Prunus with a combination of cover and resistance.

Resilience-enhancing practices like moderate grazing exclusion can improve stability in most communities, but a comprehensive fire management strategy is needed accounting for the distinct fire response patterns across this elevation/vegetation gradient. The Prunus community exhibited the highest overall sustainability, suggesting its suitability for fire-prone environments. Allowing repeated fires can seriously impair long-term resistance and resilience, emphasizing the need for carefully planned fire management.