Search

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. • We evaluated post-fire reproductive potential across elevation in resprouting species. • Reproductive potential decreased with elevation and was higher in larger trees. • Fire reduced reproductive potential up to the third post-fire fruiting season. • The fire effects on reproductive potential were worse at high than at low elevation. • A reduction in fire frequency could promote forest expansion at high elevation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enrichment planting with pines in A. araucana stands increase flammability by altering fuel structure. • Pines increase crown fire hazard by increasing the vertical continuity of fuels from the understory to the tree canopy. • Pines change litter attributes and increase fine fuel load on the ground surface. • Pine invasion into A. araucana open stands might also increase stand-level flammability. The introduction of non-native tree species for large-scale afforestation may alter the fire regime of native ecosystems by modifying fuel proprieties. We quantified changes in fuel abundance and structure resulting from the establishment of commercial Pinus spp. plantations in Araucaria araucana ecosystems in northwestern Patagonia, Argentina. Specifically, we assessed the amount, distribution, and condition (live/dead) of surface and standing fine fuel in A. araucana stands with mature pine plantations (i.e. > 20 cm dbh) and in stands dominated only by A. araucana (control). Our study shows that both types of stands are prone to wildfires, but pine plantations have fuel characteristics that imply greater flammability due to higher fuel load and vertical continuity in the understory and in the overstory canopy. In the absence of fuel mitigation practices, A. araucana stands with plantations exhibit greater flammability than the control A. araucana stands, potentially promoting the occurrence and spread of fires of greater severity. This study contributes to understanding the effects of enrichment planting of pines, and possibly pine invasions, on A. araucaria ecosystem flammability and their potential consequences on fire behavior. [ABSTRACT FROM AUTHOR]

Abstract: The Ordovician Ponón Trehué Formation is the only early Palaeozoic sedimentary sequence known to record a primary contact with the Grenvillian-age basement of the Argentinean Cuyania terrane, in its southwards extension named the San Rafael block. Petrographic and geochemical data indicate contributions from a dominantly upper continental crustal component and a subordinated depleted component. Nd isotopes indicate εNd of −4.6, ƒSm/Nd −0.36 and TDM 1.47Ga in average. Pb-isotope ratios display average values for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb of 19.15, 15.69 and 38.94 respectively. U–Pb detrital zircon ages from the Ponón Trehué Formation cluster around values of 1.2Ga, indicating a main derivation from a local basement source (Cerro La Ventana Formation). The Upper Ordovician Pavón Formation records a younger episode of clastic sedimentation within the San Rafael block, and it shows a more complex detrital zircon age population (peaks at 1.1 and 1.4Ga as well as Palaeoproterozoic and Neoproterozoic detrital grains). Detailed comparison between the two Ordovician clastic units indicates a shift with time in provenance from localized basement to more regional sources. Middle to early Upper Ordovician age is inferred for accretion of the Cuyania terrane to the proto-Andean margin of Gondwana. [ABSTRACT FROM AUTHOR]

Abstract: Herbivores are often an important factor hindering the recovery of woodlands. Browsing generally retards seedling and juvenile tree growth, but the exact impact of herbivores is still controversial. The high mountain areas of central Argentina consist of a mosaic of Polylepis australis Bitt. woodlands and different grassland types which are grazed by large domestic herbivores. To contribute to the management of these ecosystems, we performed an observational and an experimental study. In the first, we measured P. australis browsing intensity and size structure in areas with sparse woodland cover under two treatments. One treatment consisted of seven areas with high stocking rates, and the other consisted of five areas where livestock were reduced to low or moderate stocking rates 6–7 years prior to our measurements. In the experiment, we planted P. australis seedlings in a heavy grazed and an ungrazed area and measured growth and survival during 6 years. Our observational study showed that livestock browse heavily on P. australis, but a reduction of livestock densities reduced browsing rates and changed population size structure. The experimental results confirmed the high browsing rates, and showed that browsing negatively influences survival and height-growth. Our data suggests that heavy grazing by domestic herbivores retard P. australis woodland recovery, but a reduction in stocking rates promote changes that can lead to an increase in P. australis density. An adequate livestock management is therefore very important in the mountains of Córdoba. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

• Biomass accumulation of P. australis was measured for 10 years under livestock use. • Effective stocking densities lower than 0.12 AU ha−1 (animal units per ha) allows forest vertical biomass accumulation. • Effective stocking densities higher than 0.21 AU ha−1 are incompatible with forest conservation. • A land sharing strategy with low livestock production is possible. • Polylepis forests across the Andes could benefit from similar management strategies. 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. [ABSTRACT FROM AUTHOR]