floristic composition of andean grassland in alto bío-bío national reserve (Lonquimay-Chile) and its relationship with the grazing regimen

Andean grasslands of the La Araucanía Region are used every year by Pehuenches communities as forage resources for their livestock. Grazing is one of the most important disturbances which affect natural meadows and can produce changes at community level in the species richness and plant composition. With the aim of determining the floristic composition of the Andean grasslands in the Alto Bío-Bío National Reserve (37o S y 70o W) and its relationship with the cattle load, we studied five sites within the reserve: Cuchares Grande, Cajón Chileno, Tralilhue, Cuchares Chico and Mancha de Pinos. In each site, we sampled 20 random plots recording all the species and their relative cover. We recorded a total of 89 species of vascular plants. Taxonomic richness is represented by two Pteridophyta and 87 Magnoliophyta species. In this last group, 25 species are Liliopsida and 62 are Magnoliopsida. All flora is distributed in 37 families and 72 genera. Greatest families, in species number, are Asteraceae (13), Poaceae (11), Cyperaceae (6) and Rosaceae (6). About the origin, 88 species are native and only 11 are introduced, representing 88% and 12%, respectively. Life forms are represented mostly by hemicryptophytes with 53%, then cryptophytes arround 17% and finally chamaephytes (15%). Grasslands wich have greater livestock density, have a higher proportion of introduced species and hemicryptophytes and a greater floristic similarity between them, while those with lower livestock densities have a higher native species proportion. These results suggest that cattle use could have a significant impact in the floristic composition of Andean grasslands. Even though, the low proportion of introduced species found, the high percentage of hemicryptophytes indicates an intermediate level of disturbance

Natives and non-natives plants show different responses to elevation and disturbance on the tropical high Andes of Ecuador

The aim was to assess patterns of plant diversity in response to elevation and disturbance in a tropical mountain. The study area was located in north-central portion of the Eastern Cordillera of the Ecuadorian Andes, on a road from 1,150 m a.s.l. (Osayacu) to 4,000 (Papallacta). Along a mountain road spanning a wide altitudinal gradient, at 20 elevations we sampled three plots: one at the roadside and two perpendicular to the roadside. The relationship between elevation and species richness was assessed using linear and quadratic regressions, the effect of disturbance on species richness was determined by ANCOVA and a t test with parameters obtained from quadratic equations. Similarity of species composition among the roadside and sites distant was evaluated with the Chao-Jaccard and classic Jaccard similarity indices, the distribution of non-native species according to their origin were analyzed with linear and quadratic regression. The native species showed a linearly monotonic decrease with elevation, whereas non-natives showed a quadratic distribution. Disturbed areas had the greatest number of non-native species and lower native species richness, showing also a high floristic similarity; less disturbed areas showed the opposite. The non-native species of temperate origin were more numerous and showed unimodal elevational distribution, while species of tropical origin were few and decreased linearly with elevation. We conclude that in a tropical highland mountain range, native and non-native plant species respond differently to elevation: native species exhibit a monotonically linear decrease, and non-native species show a unimodal trend. Disturbance positively affects non-native species showing higher richness and fewer species turnover. In addition, the non-native species are located along of the elevational gradient in relation to their biogeographic origin

Efecto de dos especies de plantas invasoras fijadoras de nitrógeno sobre las propiedades químicas del suelo en el centro-sur de Chile

Dos especies invasoras leñosas, Acacia dealbata y Teline monspessulana (Fabaceae), ampliamente distribuidas en el centrosurde Chile, poseen la capacidad de fijar biológicamente el nitrógeno atmosférico y contribuir a la fertilidad del suelo. Sepresentan evidencias de potenciales cambios ocasionados por estas especies en las propiedades químicas del suelo en áreasaltamente degradadas de la Región del Bío-Bío, Chile.Dos especies invasoras leñosas, Acacia dealbata y Teline monspessulana (Fabaceae), ampliamente distribuidas en el centrosurde Chile, poseen la capacidad de fijar biológicamente el nitrógeno atmosférico y contribuir a la fertilidad del suelo. Sepresentan evidencias de potenciales cambios ocasionados por estas especies en las propiedades químicas del suelo en áreasaltamente degradadas de la Región del Bío-Bío, Chile

What can possibly go wrong? The risks of introducing soil microorganisms from Antarctica into South America = ¿Qué puede salir mal? : Los riesgos de introducir microorganismos del suelo de la Antártida en América del Sur

Endophytic fungi form mutualistic associations with plant roots which can increase plant survival and resistance to stress. Recently, it has been proposed that endophytic fungi from Antarctica should be used to facilitate reintroduction and establishment of native plants in xeric environments of northern Chile. In this note, we suggest this is a risky proposition and may lead to biological invasions. It is difficult to predict which endophytic fungi will become invasive, where they will invade, or what their impacts will be. Organisms that move across continents may or may not become invasive depending on the interaction between the species and the invaded community; unexpected outcomes may occur due to adaptation and novel interactions of the introduced species in the new environment. The fact that these endophytes are mutualistic does not imply that they will not have negative effects on the recipient community, since they might promote invasion of other non-native species or may change the competitive relationships among native species. Further, taxonomically uncharacterized fungal isolates from plant roots are likely to contain non-beneficial species. The fact that these endophytic fungi species are from Antarctica does not ensure that they cannot invade elsewhere. It should be recognized that invasive microorganisms are extremely difficult to control. We strongly suggest that the further translocation, use and spread of endophytes from Antarctica should be halted until a risk assessment is undertaken. Biosecurity measures must be taken when considering transcontinental experiments. Based on previous experiences, it is likely that the risk and potential costs of introducing these new species significantly exceed any potential benefits of their introductionsLos hongos endófitos forman asociaciones mutualísticas con raíces de plantas y pueden mejorar la sobrevivencia y resistencia al estrés. Recientemente se ha propuesto usar hongos endófitos de la Antártida para facilitar la reintroducción y establecimiento de plantas nativas en formaciones xerofíticas del norte de Chile. En esta nota se sugiere que aquello es una propuesta riesgosa y puede conducir a invasiones biológicas. Es difícil predecir qué especies se convertirán en invasoras, dónde lo harán o cuáles serán sus efectos. Los organismos transportados entre continentes pueden o no convertirse en invasores, según las interacciones entre especies y con la comunidad invadida, y pueden ocurrir resultados inesperados debido a adaptaciones de especies invasoras al nuevo ambiente y a novedosas interacciones con especies introducidas en el nuevo ambiente. Estos endófitos mutualistas pueden tener efectos negativos en la comunidad receptora, como promover invasiones de otras especies exóticas o cambiar relaciones de competencia entre especies nativas. Los hongos endófitos de la Antártida no garantizan que no puedan invadir otros lugares. La falta de identificación taxonómica de tales hongos impide saber si estos inóculos contienen especies no beneficiosas, como patógenos del suelo. Los microorganismos invasores son extremadamente difíciles de controlar. Por ello, se recomienda que la translocación, uso y dispersión de hongos endófitos antárcicos debiera detenerse hasta tener una evaluación del riesgo de su introducción. Medidas de bioseguridad deben tomarse en experimentos transcontinentales. Según experiencias anteriores, el riesgo y costos potenciales de introducir estas especies pueden superar ampliamente cualquier beneficio potencial de su uso.Fil: Nuñez, Martin A. Consejo Nacional de Investigaciones Científicas y Técnicas-Universidad del Comahue. INIBIOMA. Grupo de Ecología de Invasiones; ArgentinaFil: Dimarco, Romina Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas-Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche. Grupo de Ecología de Poblaciones de Insectos; ArgentinaFil: Dickie, Ian A. Lincoln University. Bio-Protection Research Centre; Nueva ZelandaFil: Pauchard, Anibal. Universidad de Concepción. Facultad de Ciencias Forestales. Laboratorio de Invasiones Biolóogicas; Chile. Institute of Ecology and Biodiversity (IEB); Chil

The effect of disorder on the fracture nucleation process

The statistical properties of failure are studied in a fiber bundle model with thermal noise. We show that the macroscopic failure is produced by a thermal activation of microcracks. Most importantly the effective temperature of the system is amplified by the spatial disorder (heterogeneity) of the fiber bundle. The case of a time dependent force and the validity of the Kaiser effects are also discussed. These results can give more insight to the recent experimental observations on thermally activated crack and can be useful to study the failure of electrical networks.Comment: 22 pages, 11 fgure

Post-fire ecological restoration in Latin American forest ecosystems: insights and lessons from the last two decades

Wildfires are responsible for a substantial loss of forest ecosystem services globally and represent a major driving force of forest degradation across Latin American and the Caribbean (LAC). The detrimental effect of forest fires is particularly relevant in regions where fire has been historically absent or has rarely occurred. Nowadays, there is an increasing interest to promote and develop ecological restoration (ER) following fire. LAC constitutes a hotspot where work and interest in ER has been steadily increasing over the last decades, mainly due to the drive of a new generation of young and experienced ecologists and foresters. Despite the increasing attention in post-fire restoration in the region, there is a dearth of initiatives compiling and organizing all the available information on this topic. This work aims to address such constraint, providing current information on post-fire ER in LAC forests. After a brief contextualization of environmental and social consequences of wildfires, we collect and discuss recent advances on restoring degraded forests. From the conifer Mexican ecosystems to the Southern Patagonian evergreen forests, we look back over the last two decades (2000–2020) mainly discussing experiences of success and failure, as well as limitations of implementing approaches based on passive/natural restoration or active/assisted restoration. Furthermore, we also explore other aspects of the restoration process, including those related to social participation and community engagement (e.g. education in restored areas), the use of fire regulation and management to reduce fire risks and increase ecosystem resilience, educational aspects and intermediate approaches as agroforestry and silviculture practices. In the last sections, we identify three major categories of specific constraints that condition ER, including environmental limitations (biotic and abiotic factors), technical/management factors and the socio-economic challenge of restoration. Finally, we briefly discuss future perspectives for ER in LACPS was funded by the Regional Council of Education, University and Professional Training (Consellería de Educación, Universidade e Formación Profesional) from the Government of Galicia (Xunta de Galicia) through the Postdoctoral Plan “Axudas de apoio á etapa de formación posdoutoral nas universidades do Sistema universitario de Galicia”, (Ref - ED481B-2019-088). GS was funded by the Fondo Nacional de Desarrollo Científico y Tecnológico (Fondecyt Regular REF-1191905), and the “Fondo Interno para la Adquisición de Equipamiento Científico de la Universidad Católica de la Santísima Concepción (FIAEC 2019). RG was funded by Fondecyt (REF - 11170516). RG, AP were funded by Grant ANID PIA/BASAL FB210006. AF was funded by CERNAS, Centro de Estudos de Recursos Naturais, Ambiente e Sociedade (FCT-UID00681-2020-2023)S

Diferencias en la composición vegetal de un bosque de Araucaria araucana (Molina) K.Koch y Nothofagus antarctica (G. Forst.) Oerst. asociadas a un gradiente de invasión de Pinus contorta Douglas ex Loudon

Conifers are the most studied group of plants in invasion biology. Outside their natural range, they are capable of causing major community and ecosystem impacts. Pinus contorta, is currently considered one of the world’s most invasive tree species, especially in temperate ecosystems. This study aims to determine if the invaded vegetation differ along a P. contorta invasion gradient in the Malalcahuello National Reserve, located in the Andes of the Araucania Region, south-central Chile. 18 rectangular plots of 100 m2 were established in the invaded area in transects from the seed source to the native forest. Within each plot all pines were tallied when larger than 50 cm in height and their crown projection was recorded, as well as the presence and coverage of all plant species present and their life forms. The results indicate to the establishment of a gradient of invasion and increased richness, abundance and diversity of plant species from the areas closest to the source of seeds (higher invasion) to the native forest. In relation to life forms, only chamaephytes and hemicryptophytes show a significant association to the pine invasion, with lower richness and abundance in areas with higher pine cover. The establishment of pines seems to follow a dispersal Kernel, because the highest density occurred near the original stands and a steady decrease occurs with distance from the seed source. The invasion process in the area is still in development, so it is possible to infer that to progress this situation is expected to reduce species diversity even when the canopy of pines begins to close. This study indicates that P. contorta is capable of reducing plant diversity in mountain areas, especially when invades in high densities. These findings should be considered when controlling th is species. A restoration plan will be required in the areas of the gradient where P. contorta has displaced native species.Las coníferas son el grupo de plantas más estudiado en la biología de las invasiones, ya que fuera de su área de distribución natural son capaces de generar altos impactos comunitarios y ecosistémicos. Pinus contorta es en la actualidad una de las especies arbóreas más invasoras del mundo, especialmente en ecosistemas templados. Este trabajo tiene por objetivo determinar si la composición de la vegetación invadida difiere a lo largo del gradiente de invasión de P. contorta en la Reserva Nacional Malalcahuello, ubicada en el cordón montañoso andino de la Región de la Araucanía, centro-sur de Chile. Se levantaron 18 parcelas rectangulares de 100 m2 en el área invadida, en transectos ubicados desde la fuente de semillas hasta el bosque nativo. Al interior de cada parcela se contabilizaron todos los pinos mayores a 50 cm de altura y se les midió la proyección de copa, también se registró la presencia y la cobertura de todas las especies de plantas presente y se determinaron las formas de vida. Los resultados indican la presencia de un gradiente de invasión y un aumento de la riqueza, abundancia y diversidad de especies vegetales desde las áreas más cercanas a la fuente de semillas (zona de mayor invasión) hasta el bosque nativo. Respecto a las formas de vida, sólo caméfitos y hemicriptófitos muestran una asociación significativa a la invasión del pino, disminuyendo en riqueza y abundancia en áreas con mayor cobertura de pino. El establecimiento de los pinos sigue un Kernel de dispersión, ya que la mayor densidad ocurre cerca de los rodales originales y decrece continuamente con la distancia a la fuente de semillas. El proceso de invasión en el área aún se encuentra en desarrollo, por lo tanto es posible inferir que de progresar esta situación se espera que la diversidad de especies disminuya aún más cuando el dosel de los pinos comience a cerrarse. Este estudio permite concluir que P. contorta es capaz de reducir la diversidad vegetal en zonas de montaña cuando invade en alta densidad. Estos antecedentes debieran considerarse al momento de controlar la especie, generando un plan de restauración en aquellas zonas del gradiente donde P. contorta ha desplazado a las especies nativas

Failure time in the fiber-bundle model with thermal noise and disorder

The average time for the onset of macroscopic fractures is analytically and numerically investigated in the fiber-bundle model with quenched disorder and thermal noise under a constant load. We find an implicit exact expression for the failure time in the low-temperature limit that is accurately confirmed by direct simulations. The effect of the disorder is to lower the energy barrier.Comment: 11 pages, 6 figures; accepted for publication in Phys. Rev.

Iterative Reconstructions in Reduced-Dose CT: Which Type Ensures Diagnostic Image Quality in Young Oncology Patients?

To compare adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR) algorithms for reduced-dose computed tomography (CT). Forty-four young oncology patients (mean age 30 ± 9 years) were included. After routine thoraco-abdominal CT (dose 100%, average CTDI javax.xml.bind.JAXBElement@e7f585f 9.1 ± 2.4 mGy, range 4.4-16.9 mGy), follow-up CT was acquired at 50% (average CTDI javax.xml.bind.JAXBElement@2e35610f 4.5 ± 1.2 mGy, range 2.2-8.4 mGy) in 29 patients additionally at 20% dose (average CTDI javax.xml.bind.JAXBElement@37ad3473 1.9 ± 0.5 mGy, range 0.9-3.4 mGy). Each reduced-dose CT was reconstructed using both ASIR and MBIR. Four radiologists (two juniors and two seniors) blinded to dose and technique read each set of CT images regarding objective and subjective image qualities (high- or low-contrast structures), subjective noise or pixilated appearance, diagnostic confidence, and lesion detection. At all dose levels, objective image noise was significantly lower with MBIR than with ASIR (P < 0.001). The subjective image quality for low-contrast structures was significantly higher with MBIR than with ASIR (P < 0.001). Reduced-dose abdominal CT images of patients with higher body mass index (BMI) were read with significantly higher diagnostic confidence than images of slimmer patients (P < 0.001) and had higher subjective image quality, regardless of technique. Although MBIR images appeared significantly more pixilated than ASIR images, they were read with higher diagnostic confidence, especially by juniors (P < 0.001). Reduced-dose CT during the follow-up of young oncology patients should be reconstructed with MBIR to ensure diagnostic quality. Elevated body mass index does not hamper the quality of reduced-dose CT

Anisotropic colloids through non-trivial buckling

We present a study on buckling of colloidal particles, including experimental, theoretical and numerical developments. Oil-filled thin shells prepared by emulsion templating show buckling in mixtures of water and ethanol, due to dissolution of the core in the external medium. This leads to conformations with a single depression, either axisymmetric or polygonal depending on the geometrical features of the shells. These conformations could be theoretically and/or numerically reproduced in a model of homogeneous spherical thin shells with bending and stretching elasticity, submitted to an isotropic external pressure.Comment: submitted to EPJ