The research team, led by M. M. Rago and M. F. Urretavizcaya of the Andean Patagonian Forest Research and Extension Center (CIEFAP) and Argentina’s National Scientific and Technical Research Council (CONICET), established 45 permanent plots spanning five forest types and three fire severity levels. The forests studied were dominated by Nothofagus pumilio, N. antarctica, N. dombeyi, Austrocedrus chilensis, and a mixed N. dombeyi–A. chilensis type — together accounting for 72 percent of the burned area. Plots were placed in unburned refugia, moderately burned sites, and severely burned ground, with three replicates for every combination of severity and forest type. When the team returned in January through March 2021, they sampled every vascular plant species, measured its aerial cover, and classified the community into three vertical strata below three meters in height.

The technical backbone of the study was a permutational multivariate analysis of variance, or PERMANOVA, built on Bray-Curtis distances calculated from species cover at each site. The analysis controlled for spatial autocorrelation using distance-based Moran’s eigenvector maps, ensuring that the patterns detected were not simply artifacts of plots lying close together in a mountainous valley. The results were unambiguous: both fire severity and forest type significantly shaped understory composition, with no interaction between the two. Fire severity explained 7 percent of the variation in plant assemblages, while forest type explained 14 percent — a larger share that reflects the strong environmental heterogeneity of the region, where precipitation drops from 2,400 millimeters in the west to 800 millimeters in the east across a single valley.

Indicator species analysis sharpened the picture considerably. In unburned sites, only native species served as indicators — among them the herb Osmorhiza berteroi and the fern Rumohra adiantiformis. In moderately burned sites, the native nitrogen-fixing herb Vicia nigricans and the violet Viola magellanica stood out with high fidelity. But in severely burned sites, the indicator list included exotic species: the annual herb Crepis capillaris and Epilobium brachycarpum, the latter a highly specific marker of recently disturbed ground. The team recorded 124 taxa across 48 families in total, the vast majority native and many endemic to South America, with native perennial herbs and shrubs dominating the growth forms throughout.

The trait-level comparisons revealed how fire severity acts as an ecological filter on community assembly. Total species richness peaked in moderate-severity sites at 23.6 species per 0.53 square meters, compared with 17.4 in unburned forests and 19.9 in high-severity sites — a pattern the authors attribute to the coexistence of fire-sensitive survivors and newly establishing colonizers. Native richness followed the same trajectory. Exotic cover, by contrast, was roughly five percentage points higher in both burned categories than in unburned sites, and the highest exotic richness appeared in burned N. dombeyi and mixed N. dombeyi–A. chilensis forests. Annual herbs, a hallmark of early disturbance, showed nearly four times the cover in high-severity sites compared with unburned ground. Nitrogen-fixing species and resprouting species both reached their greatest cover in moderate-severity sites, suggesting that moderately burned ground is actively rebuilding soil nutrient pools depleted by combustion.

Vertical structure told its own story. Overstory cover — the living canopy of foundational trees — was highest in unburned plots, as expected. But the upper understory stratum, between 1.5 and 3 meters, was most developed in high-severity sites, where shrubs such as Fabiana imbricata, Schinus patagonica, Aristotelia chilensis, and Ribes magellanicus had taken advantage of the sudden flood of light. The middle stratum, between 0.5 and 1.5 meters, was instead most developed in moderate-severity sites, dominated by perennial herbs and vines including Vicia nigricans, Mutisia decurrens, and the bamboo Chusquea culeou. The lower stratum, below half a meter, showed no significant differences across severity levels, indicating that ground-level cover had largely recovered within six years regardless of how hot the fire burned.

Regeneration data delivered the study’s most consequential finding. Among plots with pre-fire evidence of Chusquea culeou — the semelparous bamboo that flowers synchronously roughly every 60 years, then dies, producing masses of highly flammable dry biomass — regeneration occurred in 78 percent of moderate-severity plots but in only 20 percent of high-severity plots. In severely burned ground, the few cases of bamboo recovery were restricted to rhizome resprouting and appeared exclusively in N. pumilio forest. Seed regeneration of the foundational tree species, which depend entirely on seed dispersal from nearby unburned individuals because their wind-dispersed seeds travel only a few hundred meters and they lack persistent seed banks, was detected in 53 percent of unburned plots and 47 percent of moderate-severity plots — but in just 7 percent of high-severity plots, corresponding to a single N. dombeyi site.

The timing of the Las Horquetas fire added a rare ecological twist. It coincided with the post-flowering death of Chusquea culeou, which had flowered and seeded the year before — the same coincidence that accompanied historic fires in the region more than a century ago and in the widespread fire year of 1944. The bamboo’s post-flowering die-off created a pulse of flammable fuel that helped drive the blaze, yet its freshly produced seeds also offered a narrow window for post-fire recovery. The study’s results suggest that window closes quickly where severity is high: without surviving rhizomes or nearby seed sources, both the bamboo and the trees it once sheltered face strongly limited short-term re-establishment.

The broader implications reach beyond Patagonia. Fire regimes are intensifying worldwide, with more severe, frequent, and larger fires expanding the extent of early successional landscapes. In forests dominated by fire-sensitive species that cannot resprout and hold only transient seed banks, high-severity fires that burn large areas can push ecosystems past a threshold, shifting them toward flammable shrublands or grasslands — alternative stable states reinforced by positive fire-vegetation feedbacks. The Patagonian findings align with this framework: severely burned sites, with their shrub-dominated upper strata and depressed tree regeneration, are consistent with potentially divergent successional pathways that could lock in non-forest states, while moderately burned sites appear more likely to return to forest structure, particularly where tree seedlings were detected.

Land-use history compounds the challenge. The Cholila basin’s primary pre-fire land use was cattle grazing, and although the study did not quantify it, signs of livestock — dung and browsing — were recorded in several plots. Previous research in Andean-Patagonian forests has shown that introduced herbivores and fire act synergistically, altering plant reproductive phenology and facilitating the spread of exotic species. The elevated exotic cover in burned N. antarctica and N. dombeyi forests may therefore reflect not only fire-driven resource release and reduced competition, but also variation in grazing intensity and human activity across the landscape. For restoration practitioners, the message is clear: severity is the filter, forest type is the template, and grazing is the wildcard. Understanding the structure and dynamics of these early post-fire understory communities, the authors conclude, is essential for guiding burned ecosystems toward desirable states while sustaining the ecological processes — soil protection, nutrient cycling, and wildlife habitat — that early successional communities provide, and for maintaining the resilience of Patagonia’s temperate forests under fire regimes that show every sign of intensifying further.

Subject of Research: Understory vegetation development six years after a wildfire in the temperate forests of Patagonia, Argentina

Article Title: Understory vegetation development six years after a wildfire in the temperate forests of Patagonia, Argentina

Article References: Rago, M. M., & Urretavizcaya, M. F. (2026). Understory vegetation development six years after a wildfire in the temperate forests of Patagonia, Argentina. Frontiers in Forests and Global Change, 9, Article 1950264. https://doi.org/10.3389/ffgc.2026.1950264

Image Credits: AI Generated

DOI: 10.3389/ffgc.2026.1950264

Keywords: Understory, vegetation, development, years, wildfire, temperate, forests, Patagonia, Argentina, scientific research