Mountains Of Central Argentina Research Articles

Fire effects on the reproductive potential of two dominant woody species along an elevation gradient in central Argentina

Fire and elevation affect reproduction of woody species and, therefore, their distribution in the landscape; however, the effect of both factors are often confounded. In addition, plant size may also influence reproduction. Our objective was to investigate the combined effects of fire, elevation and pre-fire size on woody species reproductive potential in a seasonally dry mountain ecosystem. We tested the predictions that fire and elevation impair reproductive potential and that the negative effects of fire are enhanced at high elevation. Our study was carried out in the mountains of central Argentina, from 800 to 1700 m a.s.l. We selected individuals of two dominant resprouting woody species (Vachellia caven and Lithraea molleoides) in burned and comparable unburned areas. We estimated pre-fire size and fire damage level in each tree. We monitored parameters related to reproductive potential during four post-fire fruiting seasons in 185 V. caven and 78 L. molleoides trees. Our main results for V. caven show negative fire effects on most reproductive parameters, and on the expected number of germinable seeds per tree, which was estimated as an integrated parameter. The negative fire effects decreased over time until the fourth post-fire fruiting season, when we detected almost no fire effects. Moreover, the negative fire effects were greatly enhanced with elevation, while pre-fire size showed consistently positive effects on most reproductive parameters. For large trees located at low elevation, fire reduced the number of germinable seeds per tree by a factor of nearly six in the third post-fire fruiting season (from 2020 to 358 seeds), while at high elevation fire reduced germinable seeds by a factor of 15 (from 106 to 7 seeds) for similarly large trees. Small trees had a lower reproductive potential than large trees and the negative effects of fire were smaller but noticeable, and were enhanced by elevation, as in the case of large trees. For L. molleoides we found similar patterns to those of V. caven; however, since few trees produced seeds during the study, we did not compute formal statistics. We conclude that fire reduction should gradually increase reproductive potential, tree density and forest cover at high elevation, even when, according to previous studies, survival is not affected by fire or elevation in the study species.

Classification of rocky outcrops plant communities in the mountains of Central Argentina

AbstractAimsClassification of plant communities and identification of their diagnostic species in different types of rocky outcrops in mountains from Central Argentina. We also explored how these plant communities differ in their endemisms, chorotypes and non‐natives species composition, as well as in rock chemistry, elevation and climatic variables.LocationCórdoba Province, Central Argentina.MethodsThe study was based on 505 phytosociological relevés collected from 2009 to 2019 using the Braun‐Blanquet cover‐abundance scale. The hierarchical ISOmetric feature mapping and Partition Around Medoids (ISOPAM) analysis was applied. The vegetation matrix was ordinated through isometric feature mapping (ISOMAP), and the geochemical and bioclimatic variables were related to the ISOMAP ordination.ResultsWe identified 14 plant communities distributed in three main clusters. We recorded 59 endemic species at the national level and 28 narrow endemics, restricted to the study area and nearby mountains. The number of non‐native plants was relatively low (26 species). Perennial herbs (221 species), grasses (97 species) and shrubs (68 species) were the most prominent life forms. Plant communities were associated with rock chemistry (carbonate and acidic rocks), and also with elevation and climatic variables.ConclusionThis study highlights the remarkable heterogeneity of outcrop vegetation in Central Argentina. It reveals that elevation and rock type (geochemical composition) were relevant factors associated with the floristic composition of plant communities and also, that outcrop habitats comprise a high level of endemisms, as well as a low number of non‐native species, suggesting a high value for the conservation of local and regional biodiversity.

Fleshy‐fruited invasive shrubs indirectly increase native tree seed dispersal

Biological invasions are one of the main threats to biodiversity and ecosystem functioning in the Anthropocene. Fleshy‐fruited invasive plants establish mutualistic interactions with native seed dispersers and may affect the mutualisms between native partners, negatively by disrupting plant dispersal through competition for seed dispersers or positively by facilitating seed dispersal via the attraction of fruit‐eating animals. Moreover, the invaders' density in the neighborhood of native plants may modulate the direction and/or magnitude of such effects on natives. In mountains of central Argentina, the cessation of fruiting of the dominant native tree Lithraea molleoides overlaps with the beginning of the fruiting of invasive shrubs (Pyracantha spp.). This partial overlap allows for testing opposite predictions regarding the effect of invasive fruits on native seed dispersal. We compared frugivory by seed disperser birds on L. molleoides during non‐overlapping and overlapping periods, at six sites that differed in Pyracantha shrub density (high, low and no‐invasion). We counted frugivory during 2 h on 15 individuals of L. molleoides at each site and period, totaling 360 h of observation. Frugivory on the native tree was similar among sites during the non‐overlapping period and remained constant in both periods at non‐invaded sites. At invaded sites, frugivory increased from non‐overlapping to overlapping period and was greater at highly invaded sites. The resource provided by Pyracantha did not disrupt seed dispersal of the dominant native tree. Rather, it facilitated frugivory by seed dispersers and this effect may be exacerbated with higher fruit availability of invasives. Our results provide a counterview to the prevailingly negative impacts of invasive species on the seed dispersal of native species since the fruiting of invasive plants facilitated the seed dispersal of native species in a continental region contrasts with the mutualism disruption commonly observed in insular environments.

Are populations of Polylepis australis locally adapted along their elevation gradient?

ABSTRACT Mountain ecosystems are characterized by steep environmental gradients. Species with broad elevation distribution are exposed to contrasting climatic conditions along their gradients. In response to those changes, species might develop ecotypes adapted to the local climate. Early regeneration is the most critical stage for plant populations and, therefore, withstands strong selection pressures. Previous studies showed a unimodal pattern of intraspecific variability in fitness components among Polylepis australis populations along their elevation gradient in the mountains of central Argentina. Whether this variability is the result of local populations’ adjustments to their respective site remains unknown. We tested the hypothesis that P. australis populations from different elevations would be locally adapted to their local environments, where they would perform better than populations from other elevations (origins). We applied an experimental approach by establishing common gardens at three contrasting elevations. Seeds and saplings of P. australis populations from the low, mid- and high elevation belts of the species distribution gradient (i.e. three origins) were reciprocally sown and transplanted in three elevation sites (low, mid- and high). Seed germination success, sapling growth and mortality were monitored for three years. Our main results show that the origin of populations influenced germination success and sapling growth, whereas sapling mortality was marginally affected. Populations of both elevation extremes seem to be more adjusted to local conditions than the population from the intermediate elevation, probably due to the harsher environmental conditions for plant regeneration typical of the lower and upper elevation belts of semiarid mountains. Finally, our results strongly suggest that temperature rise due to climate change in this mountain area might have negative effects on the regeneration of P. australis populations.

Vegetation and flora of marble outcrops and their nearby matrices in mountains of central Argentina. Rock chemistry also matters

We present a comparative study of the flora and vegetation of marble outcrops and their nearby migmatite matrix from mountains in central Argentina. In all, we sampled 50 sites and recorded the cover-abundance of all vascular plants present according to the Braun-Blanquet cover-abundance scale. In addition, rock fragments were collected for chemical analysis (Ca2+, Mg2+, K and Na). Three plant communities were classified using ISOPAM, one occurring in the migmatite matrix and two others associated with calcic (richer in Ca2+) and dolomitic (richer in Mg2+) marble, respectively. The marble outcrops and nearby matrix vegetation differed in plant species and life form composition, as well as in diagnostic species. Rocky outcrops also exhibited differences in floristic composition between dolomitic and calcic marble. The overall number of species in the matrix vegetation was higher than in the outcrop communities, but dolomitic outcrops revealed a higher average species richness per relevé. We found a higher proportion of endemics in the marble vegetation with respect to the surrounding matrix communities, with herbs, grasses and subshrubs dominating in the marble outcrops, while trees and shrubs dominated the matrix vegetation. Taxa of the Southern-Brazilian and Chaquenian chorotypes were the most abundant in the three communities. Our results suggest that the marble outcrops harbor a flora including several highly restricted endemics, which is clearly distinct from that of the surrounding habitats, indicating that outcrop diversity should be taken into account in conservation policies.

Incidencia del fuego en un gradiente altitudinal de las sierras del centro de la Argentina

Fil: Arganaraz, Juan Pablo. Comision Nacional de Actividades Espaciales. Instituto de Altos Estudios Espaciales Mario Gulich; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba; Argentina

Can livestock coexist with Polylepis australis forests in mountains of central Argentina? Setting thresholds for a land sharing landscape

Developing a land sharing strategy requires a thorough understanding of what is the maximum productivity that can be achieved without altering key ecosystem processes. In the central Argentina highlands, Polylepis australis dominates the few remaining patches of forests and its evergreen trees are highly selected by domestic livestock. Grazing exclusion and low herbivory pressure allow P. australis forest expansion and soil conservation, while high herbivory pressure promotes forest retraction and environment degradation. However, the extent to which stocking densities should be reduced to allow forest expansion and stand maturation is still unknown. We aimed at answering this question by studying 15 stands located in paddocks with different management, from grazing enclosures to heavily stocked. In 2003 we selected 12 trees less than 2 m tall at each stand. Almost annually along 10 years, for each tree we registered survival, and if alive, we measured the height and two perpendicular diameters of the canopy. We built indicators of vertical and horizontal biomass accumulation rate along the study period and calculated an average effective stocking density (i.e., animal units per ha of non-rocky surface, AU ha−1) for each stand. We found a piece-wise relationship with two pieces between the accumulation rate of each biomass component and average stocking density. Biomass accumulation was maximum under grazing exclusion (i.e. zero stocking density). Between zero and 0.21 AU ha−1 we detected a strongly negative relationship among stocking density and biomass accumulation. Effective stocking densities lower than 0.12 and 0.06 AU ha−1 promoted a widespread vertical and horizontal biomass accumulation, respectively. Stands with stocking densities higher than 0.21 AU ha−1, had null horizontal and vertical biomass accumulation and higher tree mortality. We suggest that effective stocking densities lower than 0.12 AU ha−1 allow a land sharing strategy in central Argentina highlands, ensuring the conservation of a traditional economic activity and the restoration of Polylepis australis forests. Additionally, in areas where Polylepis australis is absent we suggest active restoration without herbivory pressure. Finally, we suggest that these management recommendations may be studied and promoted throughout the extension of Polylepis spp. forests in South America.

Regeneración de Sebastiania commersoniana (Euphorbiaceae) en relación al ganado y la distancia al bosque en las sierras del centro de Argentina

Entender los requerimientos de regeneración de especies leñosas es importante para guiar prácticas de conservación y restauración de los bosques. Evaluamos el nicho de regeneración de Sebastiania commersoniana en relación a la vegetación, suelo y luminosidad comparando micrositios con y sin renoval en dos potreros con densidad de ganado alta y baja y a tres distancias del borde de los parches de bosque dominados por la especie: -2 m (dentro del bosque), 1 m y 3 m (fuera del bosque). También evaluamos la densidad de renovales y la proporción de tallos ramoneados. Los renovales se encontraron en micrositios con abundante vegetación herbácea y suelo poco compactado. La densidad de renovales fue un 134 % mayor con baja densidad de ganado que con alta fuera del bosque, sin diferencias dentro, y disminuyó marcadamente al aumentar la distancia al borde. La proporción de tallos ramoneados fue 13 veces mayor ante alta densidad de ganado que ante baja. Concluimos que el establecimiento puede verse favorecido en micrositios con vegetación y suelo conservados; que el reclutamiento de renovales puede encontrarse limitado a las cercanías de los parches de bosque, y que la reducción en densidad de ganado puede favorecer la regeneración de la especie.

Effects of low‐density Pinus elliottii (Slash pine) afforestation on environmental conditions and native plant diversity, in the mountains of central Argentina

AbstractQuestionWhat effects do low‐density afforestation with Pinus elliottii have on the site conditions and plant diversity of the mountains of central Argentina?LocationSierra de Comechingones, central Argentina.MethodsWe studied the species richness and diversity and the physical and chemical properties of soils, in both the non‐afforested steppe (US) and the understorey of P. elliottii silvopastoral systems (SPS). Measurements were performed on three plots located in US and 18 experimental plots located in SPS, which differ in tree density (150, 250 and 450 trees/ha), pruning (with/without) and position (below – UC –, or outside – BC –, the vertical projection of the tree crown). In each plot, we measured soil variables organic matter (OM), pH, electrical conductivity (EC), moisture content (RH) and relative proportion of coarse fragments; as well as photosynthetically active radiation that reached the ground surface (PARi). At the same time, a floristic survey was performed, consisting of 117 sampling plots distributed equally between treatments. Richness, diversity and evenness indices were calculated for each treatment. Then, we carried out a PCA in order to identify the differences in life forms and environmental variables across the treatments.ResultsPARi ​​and pH were statistically significantly higher in US, while EC and RH were statistically significantly higher in SPS. Diversity indices did not differ significantly among the non‐afforested steppe (US) and the patches between crowns (BC), but were significantly higher in both these treatments than below the crown (UC). The higher richness in some of the life forms and light availability clearly separated US from UC in the PCA. All the species of interest (endemic, N‐fixing, medicinal, fodder) were found in the SPS.ConclusionsOur study indicates that the changes in site variables produced by low‐density afforestation generate niches for some species and, simultaneously, constitute a barrier to others. However, the fact that diversity indices and the presence of the species of interest showed no differences among the between‐crowns patches and the non‐afforested steppe, highlights the complex environment–vegetation relationships that take place in this kind of system.

Year-round presence of Slaty Thrush (Turdus nigriceps nigriceps) in mountains of central Argentina

The migration patterns of passerine species in the Neotropical region present several gaps of knowledge. The migratory behavior of the Slaty Thrush ( Turdus nigriceps nigriceps ) has been well characterized in their central and northern distribution along eastern slopes of the Andes from Argentina to Ecuador. The Slaty Thrush was historically considered a migrant breeder in the southern extreme of their distribution. In the present study, we show new evidence of the resident status of this species in its southernmost distribution on western slopes of Sierras Grandes and Sierras de Comechingones in Cordoba Province, Argentina. There, the Slaty Thrush has a year-round presence only at sites invaded by fleshy-fruited alien plants. The main invasive plants form dense patches of vegetation and offer an abundant fruit supply that is highly consumed by this bird species during autumn–winter, when there are no native fruits available. We suggest that the Slaty Thrush was a migrant species in past decades, but the recent invasion by fleshy-fruited species could explain its actual year-round presence by providing fruit in a period of the year of food shortage and new suitable habitats.

Reintroducing Guanaco in the Upper Belt of Central Argentina: Using Population Viability Analysis to Evaluate Extinction Risk and Management Priorities.

Wildlife reintroduction is an increasingly used strategy to reverse anthropocene defaunation. For the purpose of ecosystem restoration, in 2007 the guanaco (Lama guanicoe) was reintroduced to the Quebrada del Condorito National Park, situated in the mountains of central Argentina. With the aim of developing management recommendations, the project included permanently monitoring the population to evaluate its dynamics and the ecological response of the individuals released into the area. Nine years later and after two releases of guanacos (113 individuals in 2007 without and 25 in 2011 with a pre-adaptation period), only 24 individuals, which conform three reproductive groups, and one group of solitary males were settled in the Park. Here I modeled a population viability analysis to evaluate extinction risk, using VORTEX software. Initial population structure, specified age distribution, mortality and reproductive rates, and mate monopolization recorded during field work were used in the model, whereas the remaining used demographic parameters, such as age of first offspring, maximum number of broods per year, mean foaling rate, and length of fecundity period, were taken from the literature. Each of the three different scenarios (without supplementation of individuals, and with a realistic and optimistic supplementation) and two possible catastrophic events (fires and food shortage) covering 100 years was repeated 1000 times. Even though the guanaco reintroduction project can be considered to have been partially successful since its start, the model predicts that the current reintroduced population could be extinct in the next few decades if no reinforcements occur, and that only a continuous supplementation can reach the probability that the population survives over the next 100 years. I conclude that, so far, the current population is at a high risk of extinction if further supplementation of individuals is discontinued.

Water provisioning services in a seasonally dry subtropical mountain: Identifying priority landscapes for conservation

Summary The influence of landscape characteristics on dry season baseflow in mountain areas with a long dry season depends on a complex array of factors which need to be identified in order to prioritize landscapes for conservation of water provisioning services. Our objective was to detect which landscapes, as combinations of land cover types and topographical features are better suited to provide water during the dry season. We evaluated dry season water discharge (mm day−1) and rainfall during three years in 16 small headwater catchments (1.1–3.5 km2) in the mountains of central Argentina. For each catchment we estimated landscape variables as the proportion of five land-cover units and eight topographic properties. We analyzed water discharge as a function of landscape variables using regressions. Both rainfall and water discharge declined from years 1 to 3, but differences in water discharge among catchments were larger than differences among years, and consistent throughout time. Dry season water discharge was always higher in catchments located in rugged landscapes, with a high proportion of deep valleys and rock outcrops as compared to catchments in gentle landscapes with a high proportion of plains and covered with grasslands. We conclude that conservation priorities toward rugged landscapes would optimize water provisioning services. Reducing present rates of soil loss in deep valleys and controlling their incipient invasion by woody aliens is especially important. In coincidence, rugged landscapes host a higher diversity of various taxa.

Habitat selection by reintroduced guanacos (Lama guanicoe) in a heterogeneous mountain rangeland of central Argentina

Quebrada del Condorito National Park is located in the upper belt of the mountains of central Argentina and preserves a heterogeneous rangeland area. After the creation of the National Park, in 1996, domestic livestock were gradually removed to avoid soil loss and degradation due to overgrazing in this fragile ecosystem. Lack of large-scale herbivory allowed the expansion of tussock grasslands over grazing lawns. In 2007 a guanaco (Lama guanicoe) population was reintroduced; this large native herbivore, that had become extinct in the region was selected, because it is a low-impact grazer. Habitat selection by the guanaco population reintroduced to the National Park was studied. Seven habitat types previously defined for the region were considered, each one exhibiting a particular dominant plant growth form and different per cent cover of plant species. Guanacos made a positive selection of moist and dry grazing lawns, and avoided tussock grasslands and forests. The reintroduced guanacos selected landscapes with short plants and a high percentage of perennial graminoids and forbs, which are guanacos’ preferred food items. The results indicate that availability of forage of a nutritive value and dominant plant growth form largely explain habitat selection by guanaco in the National Park; this information can be useful for both the ongoing guanaco reintroduction project and the design of management strategies aimed at ecological restoration of this important rangeland region of central Argentina.

Wood-decaying polypores in the mountains of central Argentina in relation to Polylepis forest structure and altitude

Abstract To determine how altitude and forest successional stage are related to richness and composition of wood-decaying polypore fungi in Polylepis mountain forests of central Argentina we sampled 48 forest plots of 900 m 2 which included a range of successional stages and altitudes. We recorded a total of 19 species and our main results show that overall richness increased with forest successional stage and altitude, while endemic species richness was positively related only to altitude. Polypore community structure as exemplified by DCA Axes 1 and 2 was also related only to altitude with no pattern with forest successional stage, meaning polypore species are added during succession with no loss of early successional species. We conclude these forests must be managed to promote more mature forests and emphasis must be placed on a range of altitudes, especially highland areas where slow decomposition allows for a more diverse polypore community.

The Giant Hummingbird (Patagona gigas) in the Mountains of Central Argentina and a Climatic Envelope Model for its Distribution

I present the first published observations of the Giant Hummingbird (Patagona gigas) in the mountains of central Argentina. This species was recorded in early and late summer 2006 and 2007. This new range resembles other summer habitats of the species, which are in the Andes >500 km distant. A climatic envelope model configured with known locations obtained from the literature predicts a high probability of occurrence in its “new” range.

Avifaunal changes as a consequence of large‐scale livestock exclusion in the mountains of Central Argentina

Summary In the high Mountains of Córdoba (Central Argentina) large native herbivores were replaced completely by domestic livestock early in the 20th century. Recently, livestock were excluded in a large portion of the mountains to reduce alarming soil erosion rates, leading to an unnatural situation as the area has a long evolutionary history of large herbivore grazing. Many of the birds living in this area are endemic subspecies. Lack of large herbivore grazing can reduce plant diversity, but the response of birds is unknown. We surveyed birds in 46 1·8‐ha transects distributed across eight vegetation units under (a) traditional livestock rearing and (b) 4 years of livestock exclusion. We described bird communities per transect using density and richness. The effects of grazing situation and vegetation units on these parameters were analysed by two‐way analysis of variance (anova). Additionally, we analysed bird composition through detrended correspondence analysis (DCA). Livestock exclusion caused, in all vegetation units, significant reductions in observed bird density and richness when all species were included in the analysis, and when the 12 endemic subspecies were considered separately. An analysis for each guild showed a similar pattern but differences were significant only for richness of insectivorous and granivorous birds. Vegetation units always showed significant differences in bird density and richness, with no significant interactions between vegetation and grazing situations. Community composition described through DCA was different between vegetation units but not between grazing situations. Endemic birds were associated mainly with rocky areas. Synthesis and applications. In areas where large native herbivores are locally extinct, extensive exclusion of domestic livestock is not recommended where bird conservation is also a priority. Where possible, we suggest reintroducing native large herbivores. Where reintroductions are not feasible, livestock must be excluded only from those sites where it is most necessary, and maintained elsewhere at reduced stocking rates. To mimic past natural grazing regimes more effectively, livestock grazing regimes should incorporate temporal fluctuations at seasonal, yearly and decade scales.

Cover and growth habit of Polylepis woodlands and shrublands in the mountains of central Argentina: human or environmental influence?

AbstractAim To determine whether the cover and growth habit of the main forest forming species (Polylepis australis BITT.) in a mountain range with low human population density is mainly affected by anthropogenic activities or by environmental influences.Location Central Argentina.Methods Using GIS and field surveys we established 146 plots of 30 × 30 m located in five river basins differing in human impact. We measured P. australis cover, growth habit of each individual (number of basal ramifications), index of long term human impact (percentage of rock exposed by soil erosion due to livestock and fires), evidence of logging, fire scars, local relief, percentage of rock outcrops and altitude above sea level. We analysed the influence of independent variables on P. australis cover and growth habit (average number of basal ramifications per plot) using correlations and General Linear Models.Results Polylepis australis cover was greater at intermediate altitudes above sea level and in areas with reduced long term human impact. Contrastingly local relief, percentage of rock outcrops and logging in the recent past did not have a major influence on P. australis abundance. Growth habit varied in complex patterns. Individuals with fewer ramifications were found in valley bottoms and more disturbed basins, while more ramifications were found at mid‐ and upper slopes and well preserved basins. In valley bottoms, ramifications decreased with increasing altitude whereas the opposite trend was observed for mid‐slopes. Ramifications were positively related to fires in two river basins and in mid‐ and upper slopes but not in valley bottoms. Fire impact was always less in valley bottoms than at mid‐ and upper slopes.Main conclusions Human impact had a major role on P. australis cover, while growth habit was determined by complex combinations of potentially cumulative natural and anthropogenic factors. Even in sparsely populated mountains, both human impact and their interaction with natural environmental gradients influence plant communities and need to be understood for effective management.

Anthropogenic soil degradation affects seed viability in Polylepis australis mountain forests of central Argentina

South American Polylepis mountain forests belong to the most endangered forest ecosystem in the world. Reforestation measures have been strongly recommended but may be hampered due to the very low seed germination rates reported for several Polylepis species. In order to determine the causes behind reduced seed germination we analysed seed viability of Polylepis australis trees in the mountains of central Argentina. We picked seeds from seven heterogeneous areas (4–5 well-separated trees per area totaling 29 trees) with high within and between variation in degradation status. At the landscape scale we measured altitude above sea level and forest fragmentation in a radius of 1000 m around seven areas. At the mesohabitat scale we measured vegetation types and amount of soil erosion in a square of 90 m×90 m around each study tree. At the microhabitat scale we assessed site characteristics under the tree canopy. Additionally, we measured some individual characteristics of each tree. Average percentage of viable seeds was 23.0±15.7 S.D. and lack of an embryo was the main reason for seeds not being able to germinate. Landscape variables were not related to seed viability. At the mesohabitat scale, a multiple regression procedure showed that seed viability was positively associated with relatively undisturbed soils supporting tussock grasslands (38.7% of variance) and negatively associated with soil erosion (18.8% of the variance). Microhabitat variables and individual Polylepis characteristics were also related to seed viability, but explained less variability than mesohabitat characteristics. In order to improve seed viability, our data suggests that livestock pressure and burning practices should be reduced, as these are the main causes for erosion and other forms of soil destruction. For reforestation purposes, we recommend collecting seeds from undisturbed areas.

Anthropogenic soil degradation affects seed viability in Polylepis australis mountain forests of central Argentina

South American Polylepis mountain forests belong to the most endangered forest ecosystem in the world. Reforestation measures have been strongly recommended but may be hampered due to the very low seed germination rates reported for several Polylepis species. In order to determine the causes behind reduced seed germination we analysed seed viability of Polylepis australis trees in the mountains of central Argentina. We picked seeds from seven heterogeneous areas (4–5 well-separated trees per area totaling 29 trees) with high within and between variation in degradation status. At the landscape scale we measured altitude above sea level and forest fragmentation in a radius of 1000 m around seven areas. At the mesohabitat scale we measured vegetation types and amount of soil erosion in a square of 90m×90 m around each study tree. At the microhabitat scale we assessed site characteristics under the tree canopy. Additionally, we measured some individual characteristics of each tree. Average percentage of viable seeds was 23.0±15.7 S.D. and lack of an embryo was the main reason for seeds not being able to germinate. Landscape variables were not related to seed viability. At the mesohabitat scale, a multiple regression procedure showed that seed viability was positively associated with relatively undisturbed soils supporting tussock grasslands (38.7% of variance) and negatively associated with soil erosion (18.8% of the variance). Microhabitat variables and individual Polylepis characteristics were also related to seed viability, but explained less variability than mesohabitat characteristics. In order to improve seed viability, our data suggests that livestock pressure and burning practices should be reduced, as these are the main causes for erosion and other forms of soil destruction. For reforestation purposes, we recommend collecting seeds from undisturbed areas.

Seed bank dynamics in tall‐tussock grasslands along an altitudinal gradient

Abstract. We studied the germinable soil seed bank of tall‐tussock grasslands along an altitudinal gradient in the mountains of central Argentina. We selected 10 sampling plots at three altitudinal levels (1200 m, 1600 m and 2200 m). We assessed the composition of the established vegetation and took ten compound soil samples (0 ‐ 5 cm depth) at each plot in autumn and spring. The soil samples were sieved, chilled, and incubated in a glasshouse to assess the composition of the seed bank. The similarity between the composition of the seed bank flora and that of the established vegetation was low throughout the gradient. Most species did not change their seed bank strategy along the gradient. Seed bank richness and density increased with altitude. Most species had a persistent seed bank at all altitudinal levels, and the proportion of such species increased with altitude. These results suggest that a cold climate directly and/or indirectly favours the formation of seed banks and seed persistence in the soil.