Estela Raffaele

The historical range of variability of fires in the Andean–Patagonian Nothofagus forest region

The present synthesis addresses key questions about several extreme fire events that occurred in the Nothofagus forest region of southern Argentina and Chile in the late 1990s and early 2000s: (1) are there historical precedents for the extent and severity of these recent wildfires? (2) To what extent can large, severe fires be attributed to influences from modern humans, either indirectly through land-use practices or directly through ignition? (3) What are the relationships of these fire events to interannual climatic variability and trends? (4) What are the medium-term ecological consequences of these fire events, particularly in terms of the resiliency of the burned ecosystems? Historic fire regimes vary greatly across the different ecosystem types in the southern Andean region, and the tree-ring record shows that before the 20th century, large severe fires also played a significant ecological role in shaping even the wettest forests. Recent severe droughts at an annual time scale have been facilitated by a trend towards higher temperatures since the mid-1970s. In large parts of the region, the risk of wildfire ignition and spread has been exacerbated by increases in lightning associated with higher temperatures, increased ignitions associated with exurban development, and conversion of less flammable native vegetation to more flammable plantations of exotic conifers.

Effects of fire severity in a north Patagonian subalpine forest

Abstract Question: What is the relative importance of fire-induced canopy mortality, soil burning and post-fire herbivory on tree seedling performance? Location: Subalpine Nothofagus pumilio forests at Challhuaco valley (41°13′S, 71°19′W), Nahuel Huapi National Park, Argentina. Methods: We fenced and transplanted soils of three burning severities along a fire severity gradient produced by a fire in 1996. Over two growing seasons we monitored soil water, direct incoming solar radiation, seedling survival, final seedling total biomass and root/shoot ratio. Additionally, we assessed severity-related changes in soil properties. Results: Incoming radiation (an indicator of the amount of canopy cover left by the fire) was the primary factor influencing spring and summer top soil water availability, first and second-year seedling survival and seedling growth. While seedling survival and soil water content were negatively affected by increased radiation, seedling final biomass was highest in very open microsites. Burned soils showed lower water holding capacity and soil carbon; however these changes did not affect topsoil water, and, contrary to expectation, there was a slight tendency toward higher seedling survival on more heavily burned soils. Herbivory significantly reduced seedling survival, but only under high-radiation conditions. While the effect of radiation on final seedling biomass was not affected by herbivory, R/S ratios were significantly reduced by herbivory in high radiation microsites. Conclusions: Despite inducing faster aerial growth, increased radiation and herbivory in severely burned sites may effectively prevent post-fire regeneration in north Patagonian subalpine forest where seed sources are not limiting. Nomenclature: Correa (1969–1984). Abbreviations: HEF = herbivory effect; R/S = root:shoot final seedling biomass ratio; RAD = Direct incoming spring-summer integrated radiation; SBS = soil burning severity treatments; SWC = Gravimetric top soil water content.

Nectar production and pollination in Alstroemeria aurea : responses to level and pattern of flowering shoot defoliation

Alstroemeria aurea is a clonal perennial which occurs in the understory of the southern Andean forests. Plants consist of a series of 3-5 vegetative shoots and usually one flowering shoot sprouting each growing season from an underground rhizome. Inflorescences are terminal and synchronously protandrous. We compared the effects of defoliation of the flowering shoot on flower size, nectar production, pollen removal and deposition, and pollen grain size. Treatments were designed to test for the effects of level and position of leaf removal. They were: (1) 100 % defoliation; (2) all leaves from the upper half of the shoot removed ( = 50% UH); (3) all leaves from the lower half removed ( = 50% LH), and (4) control (i.e. no defoliation). Defoliation was performed in four flowering patches 4-7 d before anthesis. Flower size (estimated by inner tepal length) was slightly, but significantly reduced by the removal of the lower leaves (100% defoliation and 50% LH treatments). Sugar production/6 h tended to be higher in control shoots than in defoliated ones, but the response was heterogeneous among the four study flowering patches. Laboratory experiments suggest a great degree of autonomy of isolated flowers in terms of sugar nectar secretion, perhaps because of carbohydrates being stored in the nectaries prior to anthesis. No effect of defoliation was observed on the number of pollen grains removed from the anthers or deposited on the stigmas. Pollen grain size was significantly reduced by defoliation following the expected gradient Control > 50 % LH > 50 % UH > 100 % defoliation. To the extent that size reflects amount of reserves in pollen grains, defoliation might be affecting the post-pollination competitive ability of a donor plant.

Interactive effects of introduced herbivores and post‐flowering die‐off of bamboos in Patagonian Nothofagus forests

Abstract Question: In November 2000, Chusquea culeou, a bamboo species dominating Andean forest understories in southern Argentina and Chile, massively flowered and died over a north-south distance of ca. 120 km. Because bamboo is the major forage for large herbivores in these forests, we examined the interactive influences of the bamboo die-off and herbivory by introduced cattle on understory and tree regeneration. Location: Lanín National Park, Argentina. Methods: Permanent plots, in and outside livestock exclosures, were installed in a Nothofagus dombeyi forest in patches of flowered and non-flowered C. culeou. Plots were monitored over four years for changes in understory composition and tree seedling densities and heights. Results: After the C. culeou die-off, new establishment of N. dombeyi was low, both with and without herbivory. Livestock alone directly increased N. dombeyi seedling mortality through physical damage. However, tree seedling browse ratings and height growth were interactively affected by bamboo flowering and herbivory; unfenced plots in flowered bamboo patches had the shortest seedlings, highest browse ratings, and lowest tree seedling annual growth rates. Understory cover was higher where livestock were excluded, and this effect was intensified in the patches of flowered bamboo. Neither herbivory nor bamboo flowering resulted in major changes in species composition, with the exception of Alstroemeria aurea Conclusion: Effects of livestock on N. dombeyi regeneration were contingent on flowering of C. culeou Prior to introduction of livestock, N. dombeyi regeneration was probably successful beneath canopy gaps during windows of opportunity following bamboo die-off, but now livestock impede tree regeneration. Herbivory during bamboo withering periods also produces more open understories, particularly affecting palatable heliophyllous herb species such as Alstroemeria aurea The results underscore the importance of assessing herbivore impacts on tree regeneration during relatively short periods of potential tree regeneration immediately following rare bamboo flowering and die-off. Nomenclature: Correa (1969-1984).

Variable community responses to herbivory in fire-altered landscapes of northern Patagonia, Argentina

Landscapes in northern Patagonia have undergone dramatic changes in fire regimes over the last century. Superimposed on this changing vegetation mosaic are impacts from introduced herbivores. In this paper we identify synergistic interactions developing into positive fire-herbivory feedbacks that maximise vegetation change. Analyses of vegetation changes over 30 years at low altitude (c. 800m) montane forest indicates that fire-fragmented forest has coalesced despite relatively heavy grazing pressure. During recent fire suppression, vegetation shifted in dominance from short-lived resprouting species (mostly shrubs) to obligate seed-dispersed trees, some of them requiring initial facilitation by shrubs. Transitions from shrubland and grassland to forest were restricted to c. 20–30m from the nearest forested patches. Beyond this distance, shrublands and grassland are stable in time. In contrast, post-fire responses of high altitude (>1 000m) subalpine forests show a much higher sensitivity to herbivory. Experimental evidence suggests strong fire severity × herbivory interactions affect tree seedling mortality. Severe fires and/or repeated fire create conditions where trees are unable to establish due to unfavorable microenvironments and because fire-opened forests are more heavily used by herbivores. These patterns are consistent with century-long trends of increase in montane forest at the expense of shrublands and increase in shrublands over former subalpine forests.

Fire enhances the ‘competition-free’ space of an invader shrub: Rosa rubiginosa in northwestern Patagonia

Fire can influence reproductive phenology of plants, enhancing the reproductive rate of many species. Disturbances such as fire can promote the proliferation of exotic species in native plant communities. In this study we analyze the effect of fire on reproductive phenology in three native species (a shrub: Berberis buxifolia and two small trees: Maytenus boaria and Schinus patagonicus) and in an exotic shrub (Rosa rubiginosa). Flowering and fruiting phenology was monitored in neighbouring burned and unburned forests. The shrubs flowered and fruited in both sites, but the small trees did so only in the unburned site. There is no overlapping in the flowering and fruiting phenophases between the natives and the exotic species. Therefore, they do not compete in resource offering to pollinators and seed dispersers. Consequently, R. rubiginosa has a ‘competition-free’ space enhanced by fire, from the reproductive phenology perspective.

Fire as a driver of pine invasions in the Southern Hemisphere: a review

Contrasting evidence in the degree of post-fire conifer invasion reported for different regions of the Southern Hemisphere (SH) raises questions about the role of fire as a presumed driver of invasion. We studied the influence of fire on invasion responses (assessing ‘serotiny’ and ‘time’ as key factors to determine invasion) based on a review of case studies performed in natural habitats of the SH. Our work showed that burned environments have no lag time with respect to invasion and are more susceptible to serotinous pine invasion than are unburned environments. Also, serotinous pines reached extremely high densities in burned habitats, exceeding records for the same species in unburned habitats, as well as for non-serotinous pines in any habitat condition. Therefore, burned environments are impacted by conifer invasion earlier and more intensively than unburned ones. Overall, our work indicates that fire is a leading driver of invasion, but only for serotinous pines. This highlights the importance of considering life history traits of introduced species to determine the probability and extent of invasion in relation to disturbance. We discuss the implications of introducing serotinous species in regions of the SH where serotiny is absent from native flora. Lastly, we provide suggestions for prioritizing management and further study.

Succession of Ground-Dwelling Beetle Assemblages After Fire in Three Habitat Types in the Andean Forest of NW Patagonia, Argentina

Abstract Wildfires are one of the major disturbances in the dynamics of forests and shrublands. However, little is known about their effects on insect communities that contribute to faunal biodiversity and play key roles in the ecosystems dynamics. An intense and widespread fire occurred in 1999 in the Nahuel Huapi National Park in the Andean forest in northern Patagonia, Argentina. This fire affected adjacent, but different, habitat types. After the fire, beetle abundance, species richness and assemblage composition were compared among three habitats that were structurally different before the fire. These habitats were: 1) evergreen forest dominated by Nothofagus dombeyi (Mirb.) Oerst. (Fagales: Nothofagaceae), 2) a mixed forest of the evergreen conifer Austrocedrus chilensis (D. Don) Pic. Serm. and Bizzarri (Pinales: Cupressaceae) and N. dombeyi and 3) a shrubland with a diverse community of shrub species. The relationship between beetle diversity and vegetation structure was investigated over three consecutive years. Ground beetles were collected by pitfall traps, and plant species richness, vegetation cover, and height were measured. Beetle communities varied more over years between habitats during the early regeneration after fire. There was a shift in beetle assemblage composition with time after the fire in all habitat types, probably due to similar colonization rates and microclimatic conditions. Therefore, beetle succession was more influenced by recolonization and survivorship, accompanied by climatic conditions and recovery rate of plant communities over time, than it was influenced by pre-fire habitat conditions. These results suggest that in NW Patagonia, wildfire can have a substantial, short-term impact on beetle abundance and species composition. The pre-fire conditions of each habitat type determined the structure of post-fire communities of plants but not beetle assemblages. Wildfires produce simplification and homogenization of habitat types, and this was reflected by beetle diversity.

Are Northwestern Patagonian “mallín” wetland meadows reservoirs of Ochetophila trinervis infective Frankia?

Abstract“Mallín” (plural mallines) is a particular kind of wetland occurring in Patagonian steppe and forests. In Northwest Patagonia, mallines are humid meadows with high net primary production. It was previously found that a mallín soil in the steppe devoid of actinorhizal plants had a higher Frankia nodulation capacity in Ochetophila trinervis (sin. Discaria trinervis) than other soils in the region. Under the hypothesis that mallín wetland meadows are reservoir of infective Frankia, we studied the Frankia nodulation capacity in O. trinervis of 12 mallín and their neighbouring steppe soils, by using plant bioassays. A qualitative plant bioassay showed that infective Frankia was present in most soils. The number of nodules per plant in seedlings inoculated with mallín soils was negatively correlated with soil water content while the opposite was true for plants inoculated with soils from neighbouring steppe. A quantitative bioassay was performed with eight representative soils, selected according to the number of nodules per plant produced in the qualitative assay and to the presence or not of different actinorhizal plants at the sites. Frankia nodulation units per cm3 of soil (NU) in mallín soils were higher than those in steppe. Water and organic matter content of soils were correlated with the higher nodulation capacity of mallines, which may account for the saprotrophic growth of Frankia in soils. The symbiosis was effective in plants inoculated with all soil samples. These results suggest that Northwestern Patagonian mallín wetland meadows are reservoirs of infective and effective Frankia propagules in O. trinervis.

Consequences of fire and cattle browsing on ground beetles (Coleoptera) in NW Patagonia

Understanding the responses of natural communities to disturbances remains a challenging task in ecology. In northwestern Patagonia, the most important disturbances are fire and introduced ungulates. Although these disturbances have been present in this region since late eighteen century, their effects on arthropods diversity have been poorly studied. Here, we examined the short-term response of ground beetles (Coleoptera) to fire (burnt and unburnt) in browsed forests and to cattle browsing (cattle and no cattle) in post-fire forests. We collected ground beetles with pitfall traps and estimated beetle abundance, species richness, assemblage composition, abundance of trophic guilds and beetle characteristic species, and measured some habitat parameters. We found that burnt browsed forest had lower diversity and different assemblage composition than unburnt forest. Beetle abundance, assemblage composition and abundance of trophic guilds were similar in post-fire forests with and without cattle browsing. Conversely, beetle species richness was higher in cattle than in no cattle forests. Fire had a strong negative effect on beetle diversity probably by its effect changing habitat structure. Whereas fire had a homogenizing influence on beetle diversity with and without cattle, at small-spatial scales, browsing of cattle probably generate habitat heterogeneity enhancing beetle richness. The implementation of policies aimed to reduce the risk of fire and to maintain low-moderate cattle pressure appears to be vital to conserve the beetle assemblage in the Patagonian region.