María Florencia Urretavizcaya

Background: Wildfires represent a recurrent disturbance in the Patagonia Andean region, with increasing frequency in recent decades. Austrocedrus chilensis is an arbuscular mycorrhizal (AM) endemic conifer that is particularly vulnerable to fire, a situation that will worsen with climate change. In February 2015, a wildfire affected 5700 ha of Austrocedrus chilensis forests with varying severities (WFSs). The aim of this study was to determine and compare the density of AM spores (AMSs) in soil affected by different WFS and non-affected sites, considering site features. Methods: Ninety soil samples were collected from three sites 10 months and 5 years after the fire. The AMSs density was determined, a bioassay was set, and soil physicochemical features were evaluated. Results: After the wildfires, spores were significantly more abundant in sites affected by moderate severity fires. After 5 years, burned sites showed no differences between severities, but the driest sites showed no changes since the wildfires occurred. Seedlings from the bioassay showed less than 25% mycorrhizal colonization growing in soil from burned sites, regardless of fire severity, compared with unburned soils. Conclusions: For restoration strategies, it must be considered that wildfires reduce mycorrhizal spores and mycelium and alter soil properties, indicating that both WFSs require active restoration; under drier conditions, the spore banks do not change after a 5-year period.

Background: Wildfires represent a recurrent disturbance in the Patagonia Andean region with increasing frequency in recent decades. Austrocedrus chilensis is an arbuscular-mycorrhizal (AM) endemic conifer particularly vulnerable to fire, a situation that will worsen with climate change. In February 2015, a wildfire affected 5700ha of Austrocedrus chilensis forests with varying severities (WFS). The aim of this study was to determine and compare the density of AM spores (AMS) in soil affected by different WFS and non-affected sites, considering site features. Methods: Ninety soil samples were collected from three sites 10 months and 5 years after fire. AMS’ density was determined, a bioassay was set, and soil physicochemical features were evaluated. Results: after the wildfire, spores were significantly more abundant in sites affected by moderate severity fires. After 5 years, burned sites showed no differences between severities, but the driest sites showed no changes since fire occurred. Seedlings from the bioassay showed less than 25% mycorrhizal colonization growing in soil from burned sites, regardless fire severity compared with unburned soils. Conclusions: For restoration strategies, it must be considered that wildfires reduce mycorrhizal spores and mycelium, alter soil properties, and that drier conditions have less resilience, requiring active restoration.

Background: Severe wildfires in forest ecosystems promote soil erosion and the loss of fertile soil as a scarce natural resource. Our objective was to quantify post-fire ecosystem response in terms of soil accumulation and seed availability through redistribution. Within our study area in Northern Patagonia, Argentina, we chose three study sites at which forest fire events occurred in different years, namely 1 year post-fire (2022), 2 years post-fire (2021), and 8 years post-fire (2015). At each of the sites, we recorded both burned and control slope transects. Along these transects, three accumulation zones were differentiated, at each zone the amount of accumulated soil material as well as the number of seeds in it were determined. Results: We observed significant amounts of accumulated soil material along the slopes with the highest annual rates in the first year after the forest fire. The mean accumulated soil material (± standard deviation) over all slope accumulation zones increased from 9.5 ± 2.6, 15.9 ± 4.6 to 42.9 ± 14.0 kg*m⁻², at the 1 year-old, 2 years-old, and 8 years-old forest fires sites. Despite the generally high spatio-temporal variability of seed dispersal, the transects at the burned forest sites show significantly lower numbers of seeds than control transects. In the investigated burned forest sites, the total number of seeds of the four tree species found was 64, 250, and 252 seeds*m⁻² in the 1 year-old, 2 years-old, and 8 years-old site, respectively. In general, the more recent fire events had lower number of seeds, which increased with accumulated soil material and time. We also observed a greater number of shrub seeds in the burned sites, but these did not show a pattern with time since the wildfire events. Conclusion: Among the 14 species recorded, the tree Austrocedrus chilensis and the shrub Aristotelia chilensis emerge as key players in post-fire recovery, with the highest number of seeds at all study locations. Forest restoration after disturbance is a global challenge, especially in the context of large-scale forest fires. Understanding the risk of soil redistribution and seed availability will assist restoration efforts and ecosystem management.

Background: Fire is recurrent in Patagonian forests of Argentina, and is frequently associated with the die-off of bamboo (Chusquea culeou). Fire induces changes in soil properties, which may affect vegetation recovery. Aims: This study assesses how fire severity affects soil chemical properties in different Patagonian forests, in the absence and presence of C. culeou. Methods: We collected samples from the upper 5 cm of mineral soil from 44 plots distributed in five forest types affected by low-severity and high-severity fire, and unburned areas. Half of the plots also had C. culeou. Key results: Fire severity affected soil pH, organic matter, electrical conductivity, nitrogen, C:N ratio, and cation exchange capacity. Changes in organic matter and C:N ratio varied among forest type, and variations in pH and sodium were detected among forest types. The presence of C. culeou affected soil pH, C:N ratio, and calcium. Conclusions: The changes recorded were expected and could have a lasting effect on long-term productivity. Nothofagus pumilio and Nothofagus antarctica, and forests with C. culeou, varied in their soil chemical properties, sometimes regardless of fire. Implications: Considering the heterogeneity of vegetation and soil in postfire environments is vital for predicting possible successional trajectories and defining restoration objectives.

The availability of soil-stored seed determines initial plant functional types in post-fire landscapes. We evaluated the post-fire regeneration of Nothofagus pumilio forests, in Patagonia, Argentina, analyzing the soil seed bank (SSB) and the above-ground vegetation (AV). At three sites: La Colisión, Río Turbio and Monte Zeballos, burned in 2008, 1980 and 1941, respectively, we sampled the SSB and AV in two transects from the edge of the remaining forest, up to 90 m within the burned area, and recorded the emergence (198 soil samples) and presence of vascular species. To determine the effect of the distance to the remnant forest on the germinable seed bank, we performed simple linear regression analysis through the use of linear mixed-effect models, and we analyzed the similarity between the composition of SSB and AV with PERMANOVA. The emergence of plant growth forms had different patterns in relation to the distance from the forest in the three sites, which might be associated with the time of fire occurrence, and specific characteristics of each site. The emergence of N. pumilio was registered at more than one distance at the recent burning site. Herbs constituted the main source of cover with 69% of the composition, and native/endemic species represented 71%. This study contributes to the understanding of the relationship between the seed bank and standing vegetation and a better understanding of the resilience of post-fire N. pumilio forests. Our findings suggest that from 15–20 m from the edge, the SSB would be insufficient to ensure the spontaneous recovery of the forest, making active restoration necessary in order to tend to a recovery of the structure and functionality of the original community.

Questions: In terms of biodiversity conservation, forest plantations are often considered problematic because they usually have negative effects on natural ecosystems. Soil seed banks could play an important role in restoring vegetation that was originally present, by recruiting species that have disappeared above‐ground. We addressed this topic in plantations located in the Patagonian steppe by asking the following questions: Are richness, abundance and composition of steppe above‐ground vegetation and soil seed bank affected by plantations? Is species composition of the above‐ground vegetation and soil seed bank similar in plantations and in the steppe?Location: NW of Chubut Province, Patagonia, Argentina.Methods: We selected three plantations located in the steppe, and delimited three sectors: steppe, plantation edge and plantation interior. We compared richness and abundance by species origin and growth form among sectors for the above‐ground vegetation and soil seed bank compartments, using generalized linear mixed models. We compared species composition for each compartment and between them using permutational multivariate analysis of variance and non‐metric multidimensional scaling.Results: In above‐ground vegetation, we found a decrease in richness and abundance, and changes in composition from the steppe to the plantation interior. Richness and abundance of the soil seed bank did not show differences among steppe and the plantation sectors, although composition was different among them. Above‐ground vegetation and soil seed bank species composition were always different; native perennial herbs and shrubs were predominant in the above‐ground vegetation while exotic annual herbs dominated the soil seed bank.Conclusions: Our findings suggest that plant recruitment from the soil seed bank would not be sufficient for restoring depleted species pools in the above‐ground vegetation of plantations. Therefore, actions promoting native species reestablishment and control of exotics should be considered to reach the aim of restoring biodiversity in former plantations.

In Andean Patagonia, Argentina, severe wildfires produce high mortality in Austrocedrus chilensis forests. Owing to its high timber quality, A. chilensis trees are generally salvage logged right after wildfires. Post-logged areas result in open, denuded stands with low herbaceous or shrub cover, which precludes natural A. chilensis regeneration. In severely burned A. chilensis stands, we determined how different site conditions (salvage logging, SL, and without logging, WL), and the combination of different methods of control of above- and belowground competition and micro-environmental factors (incident radiation, soil temperature and soil moisture) affected survival, growth and hydric status of planted A seedlings. Two growing seasons after plantation, seedling survival was lower than 10% at SL sites, whereas it was near 90% at WL sites. Four seasons after establishment, and regardless of competition treatments, no seedlings survived at SL sites, whereas over 75% survived at WL sites. Radiation attenuation by canopy of WL sites benefitted A. chilensis seedling survival, and no additional control of early successional herbaceous species should be necessary to attain high seedling survival 4 years after restoration. Selective logging, by leaving ~50% of burned snags, and active restoration practices, may help reconcile economic needs of society and ecological requirements of A. chilensis for recovering former structure and functions.

Condiciones de suelo y vegetación en tres bosques quemados de Nothofagus pumilio en Argentina y experiencias para su restauración activa