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Search Results: 1 - 10 of 326672 matches for " JUAN J. ARMESTO "
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Is natural history really dead?: Toward the rebirth of natural history
WILLSON,MARY F; ARMESTO,JUAN J;
Revista chilena de historia natural , 2006, DOI: 10.4067/S0716-078X2006000200013
Abstract: in recent years natural history has been derided by some scientists as an old-fashion endeavor that does not follow the model of "hard" science and therefore should be considered "dead" and replaced by modern ecology, evolutionary biology, and conservation biology. we contend that natural history has much to offer to contemporary scientists and that it has a primary role in the creative process of generating novel hypotheses and designing significant field experiments and observations
Is natural history really dead?: Toward the rebirth of natural history Está realmente muerta la historia natural?: Hacia el renacimiento de la Historia Natural
MARY F WILLSON,JUAN J ARMESTO
Revista chilena de historia natural , 2006,
Abstract: In recent years natural history has been derided by some scientists as an old-fashion endeavor that does not follow the model of "hard" science and therefore should be considered "dead" and replaced by modern ecology, evolutionary biology, and conservation biology. We contend that natural history has much to offer to contemporary scientists and that it has a primary role in the creative process of generating novel hypotheses and designing significant field experiments and observations En a os recientes, la historia natural ha sido desacreditada por científicos que la consideran un modelo obsoleto de ciencia y que, en consecuencia, se trataría de una disciplina "muerta" que ha sido reemplazada por la ecología moderna, la biología evolutiva y la biología de la conservación. Argumentamos aquí que la historia natural tiene mucho que ofrecer a los científicos contemporáneos y que juega un rol principal en el proceso de creación de hipótesis y en el dise o acertado de observaciones y experimentos de campo
Quantity component of the effectiveness of seed dispersal by birds in the temperate rainforest of Chiloé, Chile
Salvande,Miguel; Figueroa,Javier A; Armesto,Juan J;
Bosque (Valdivia) , 2011, DOI: 10.4067/S0717-92002011000100005
Abstract: the quantity component of the disperser effectiveness of resident birds during the autumn-winter period has not yet been detailed in temperate rainforests of south america. in this study, the potentially frugivorous bird species in the temperate rainforests of southern chile during the austral autumn-winter were identified, and the quantity component of the disperser effectiveness of the birds (number of visits and number of seeds dispersed per hour) were evaluated for the tree species luma apiculata and aextoxicon punctatum. during the peak fruiting period of the both l. apiculata and a. punctatum 10 and 14, respectively, individuals of each species were monitored for a total of 10 days. results show that four bird species consumed l. apiculata fruits. the birds turdus falcklandii were the main fruit consumers (72 % of the visits), with a mean rate of 2.2 visits per hour and 49.2 seeds dispersed per hour. the frugivorous species visiting a. punctatum were t. falcklandii (97 % of the visits) and columba araucana (3 %). in a. punctatum, t. falcklandii consumed 65 fruits in 35 visits, with a mean rate of 1.8 visits per hour and 3.4 seeds dispersed per hour. in conclusion, t. falcklandii would be the most effective seed disperser bird for autumn-winter fruiting trees in the chiloé rainforest of our study site, at least with regard to the quantitative component of disperser effectiveness.
Limitantes físicos y bióticos de la regeneración arbórea en matorrales sucesionales de la Isla Grande de Chiloé, Chile
DíAZ,MARíA F; ARMESTO,JUAN J;
Revista chilena de historia natural , 2007, DOI: 10.4067/S0716-078X2007000100002
Abstract: successional shrublands created by clearcutting and burning of forests are frequent in chiloé island and surrounding mainland in southern chile. these areas are characterized by seasonally waterlogged soils, and vegetation dominated by sedges, ferns and shrubs, such as baccharis patagonica, with thick carpets of sphagnum moss occupying the spaces between shrubs. tree regeneration in these sites was shown to be sparse or completely lacking (< 0.3 seedlings m-2) compared with 7.2 seedlings m-2 in adjacent forests. colonization of shade-intolerant, pioneer trees may be reduced underneath baccharis due to crown shading and on top of sphagnum cushions, because of unfavorable conditions for tree establishment, including low ph and soil water saturation. we evaluated differences in germination rates among pioneer tree species grown in an experimental soil moisture gradient. seed germination percentage was low for drimys winteri and nothofagus nitida unrelated to humidity conditions but differed between substrates (moss vs. soil). embothrium had higher germination and survivorship when growing on sphagnum cushions. we also monitored seedling survival of two pioneer tree species (embothrium coccineum and drimys winteri) transplanted directly under baccharis shrubs, in open areas, or on moss patches. even though survivorship of embothrium and drimys under baccharis was < 40 %, in one of the study sites, there were no differences between treatments. waterlogged soils would constraint tree regeneration on successional shrublands due to a lack of elevated substrates. however, the presence of sphagnum cushions favors embothrium establishment, and thus may facilitate restoration of these sites
Limitantes físicos y bióticos de la regeneración arbórea en matorrales sucesionales de la Isla Grande de Chiloé, Chile Physical and biotic constraints on tree regeneration in secondary shrublands of Chiloé Island, Chile
MARíA F DíAZ,JUAN J ARMESTO
Revista chilena de historia natural , 2007,
Abstract: Los matorrales sucesionales establecidos después de la corta y quema de bosques son frecuentes en Chiloé y territorios continentales vecinos. Estos sitios son dominados por arbustos de Baccharis patagonica, musgos en cojín del género Sphagnum, plantas palustres y helechos. En estos sitios hemos registrado escasa o nula colonización arbórea (< 0,3 plántulas m-2) comparado con 7,2 plántulas m-2 en bosques inmediatamente adyacentes. La colonización de árboles pioneros sombra-intolerantes podría estar limitada, entre otros factores, por acceso a luz de las plántulas bajo la densa cobertura de Baccharis, o por la presencia del musgo Sphagnum magellanicum, el cual genera sustratos orgánicos anegados, pobres en nutrientes, ácidos y aislantes del calor. Para evaluar estas hipótesis se realizaron ensayos de germinación de semillas de tres especies le osas pioneras en gradientes experimentales de humedad del suelo, que simulaban las variaciones de humedad postperturbación en sitios dominados por matorral. Aunque la germinación fue baja o nula para Nothofagus y Drimys, no hubo efectos de las diferencias en humedad del suelo sobre la germinación, pero sí del tipo de sustrato. Embothrium coccineum presentó mayor germinación y supervivencia sobre sustrato de Sphagnum magellanicum. Se evaluó mediante trasplantes, la supervivencia de plántulas de dos especies de árboles pioneros (Embothrium coccineum y Drimys winteri) bajo y fuera de la cobertura de Baccharis y sobre el sustrato orgánico de Sphagnum magellanicum. Aunque la supervivencia de Embothrium y Drimys bajo Baccharis fue < 40 %, en uno de los sitios, no se observó diferencias entre tratamientos de cobertura ni sustrato. Los suelos anegados de las zonas de matorral serían limitantes para la regeneración de especies arbóreas pioneras debido a la falta de sustratos elevados. Sin embargo, la presencia de cojines de Sphagnum favorecería el establecimiento de Embothrium, especie que podría facilitar la restauración de estos hábitat Successional shrublands created by clearcutting and burning of forests are frequent in Chiloé Island and surrounding mainland in southern Chile. These areas are characterized by seasonally waterlogged soils, and vegetation dominated by sedges, ferns and shrubs, such as Baccharis patagonica, with thick carpets of Sphagnum moss occupying the spaces between shrubs. Tree regeneration in these sites was shown to be sparse or completely lacking (< 0.3 seedlings m-2) compared with 7.2 seedlings m-2 in adjacent forests. Colonization of shade-intolerant, pioneer trees may be reduced underneath Baccha
Quantity component of the effectiveness of seed dispersal by birds in the temperate rainforest of Chiloé, Chile Componente cuantitativo de la efectividad de dispersión de semillas por aves en el bosque templado de Chiloé, Chile
Miguel Salvande,Javier A Figueroa,Juan J Armesto
Bosque (Valdivia) , 2011,
Abstract: The quantity component of the disperser effectiveness of resident birds during the autumn-winter period has not yet been detailed in temperate rainforests of South America. In this study, the potentially frugivorous bird species in the temperate rainforests of southern Chile during the Austral autumn-winter were identified, and the quantity component of the disperser effectiveness of the birds (number of visits and number of seeds dispersed per hour) were evaluated for the tree species Luma apiculata and Aextoxicon punctatum. During the peak fruiting period of the both L. apiculata and A. punctatum 10 and 14, respectively, individuals of each species were monitored for a total of 10 days. Results show that four bird species consumed L. apiculata fruits. The birds Turdus falcklandii were the main fruit consumers (72 % of the visits), with a mean rate of 2.2 visits per hour and 49.2 seeds dispersed per hour. The frugivorous species visiting A. punctatum were T. falcklandii (97 % of the visits) and Columba araucana (3 %). In A. punctatum, T. falcklandii consumed 65 fruits in 35 visits, with a mean rate of 1.8 visits per hour and 3.4 seeds dispersed per hour. In conclusion, T. falcklandii would be the most effective seed disperser bird for autumn-winter fruiting trees in the Chiloé rainforest of our study site, at least with regard to the quantitative component of disperser effectiveness. El componente cuantitativo de la efectividad de la dispersión de semillas en aves residentes en los bosques lluviosos de Sudamérica durante el período de oto o e invierno no ha sido descrito con detalle. En este estudio se identificaron las potenciales especies de aves frugívoras de los bosques templados del sur de Chile durante el oto o austral y se evaluó el componente cuantitativo de la efectividad de las aves como dispersantes de semillas (número de visitas y número de semillas dispersadas por hora) en las especies arbóreas Luma apiculata y Aextoxicon punctatum. Durante el periodo de máxima fructificación de los árboles L. apiculata y A. punctatum fueron monitoreados 10 y 14 individuos, respectivamente, por un período de 10 días. Los resultados mostraron que cuatro especies de aves consumieron los frutos de L. apiculata. El ave Turdus falcklandii fue el principal consumidor de frutos (72 % de las visitas), con una tasa de 2,2 visitas por hora y 49,2 semillas dispersadas por hora. Los frugívoros que visitaron A. punctatum fueron T. falcklandii (97 % de las visitas) y Columba araucana (3 %). Aquí, T. falcklandii consumió 65 frutos en 35 visitas, con una tasa de 1,8 visit
Changes in tree species richness, stand structure and soil properties in a successional chronosequence in northern Chiloé Island, Chile
ARAVENA,JUAN C.; CARMONA,MARTíN R.; PéREZ,CECILIA A.; ARMESTO,JUAN J.;
Revista chilena de historia natural , 2002, DOI: 10.4067/S0716-078X2002000200007
Abstract: we studied a chronosequence of forest fragments in northern chiloé island, southern chile, with the aim of assessing ecosystem recovery patterns following anthropogenic disturbance. hypotheses regarding successional trends in tree species richness, the replacement of shade-intolerant by shade-tolerant species, and the impact of disturbance on soil properties were evaluated in nine forest stands. the chronosequence encompassed two early (minimum stand age <15 years), three mid-successional (30-60 years), three late-successional (129-134 years), and one old-growth stand (ca. 200 years). stand ages were estimated by coring a minimum of 30 canopy trees in each stand. early and mid-successional stands showed evidence of human disturbance by fire of moderate intensity, with few scattered old trees surviving the fire. we determined densities and basal areas of all trees in a 50 x 20 m plot, and densities of saplings and seedlings in subsamples of each plot. soil ph, total carbon (c) and nitrogen (n) contents, available n, and bulk density were used to characterize soil processes across the chronosequence. in contrast to the hypothesis that predicts a decline in tree species richness during the course of succession due to competitive exclusion of pioneers, species richness of canopy trees increased from 3 to 13 through the chronosequence. this trend was accompanied by a more even distribution of species importance values in late succession. changes in richness were unrelated to stem densities, which were highest in mid-successional forests. the number of species of woody seedlings and saplings did not change with stand age. most tree species, both shade tolerant and intolerants, were present as seedlings in all the stands, but canopy dominance shifted from shade-intolerants in early and mid-successional forests to shade-tolerant species in late-successional and old-growth stands. we did not observe a complete replacement of these two groups of species, as shade-intolerant t
Changes in tree species richness, stand structure and soil properties in a successional chronosequence in northern Chiloé Island, Chile Cambios en la riqueza de especies arbóreas, estructura de rodales y propiedades del suelo en una cronosecuencia sucesional en el norte de la Isla de Chiloé, Chile
JUAN C. ARAVENA,MARTíN R. CARMONA,CECILIA A. PéREZ,JUAN J. ARMESTO
Revista chilena de historia natural , 2002,
Abstract: We studied a chronosequence of forest fragments in northern Chiloé Island, southern Chile, with the aim of assessing ecosystem recovery patterns following anthropogenic disturbance. Hypotheses regarding successional trends in tree species richness, the replacement of shade-intolerant by shade-tolerant species, and the impact of disturbance on soil properties were evaluated in nine forest stands. The chronosequence encompassed two early (minimum stand age <15 years), three mid-successional (30-60 years), three late-successional (129-134 years), and one old-growth stand (ca. 200 years). Stand ages were estimated by coring a minimum of 30 canopy trees in each stand. Early and mid-successional stands showed evidence of human disturbance by fire of moderate intensity, with few scattered old trees surviving the fire. We determined densities and basal areas of all trees in a 50 x 20 m plot, and densities of saplings and seedlings in subsamples of each plot. Soil pH, total carbon (C) and nitrogen (N) contents, available N, and bulk density were used to characterize soil processes across the chronosequence. In contrast to the hypothesis that predicts a decline in tree species richness during the course of succession due to competitive exclusion of pioneers, species richness of canopy trees increased from 3 to 13 through the chronosequence. This trend was accompanied by a more even distribution of species importance values in late succession. Changes in richness were unrelated to stem densities, which were highest in mid-successional forests. The number of species of woody seedlings and saplings did not change with stand age. Most tree species, both shade tolerant and intolerants, were present as seedlings in all the stands, but canopy dominance shifted from shade-intolerants in early and mid-successional forests to shade-tolerant species in late-successional and old-growth stands. We did not observe a complete replacement of these two groups of species, as shade-intolerant trees were still present in the canopy and/or understory of older stands. The successional trend fits Egler's Initial Floristic Composition Model, whereby differences in life history attributes among tree species account for major changes in dominance through succession. Soil properties were generally similar across the chronosequence of stands, suggesting that both ecosystem processes and tree regeneration were fairly resilient to moderate-intensity fire. We conclude that because of the relatively short history of human impact in the area, largely limited to the 20th century, and the carry ove
Effects of Nitrate and Labile Carbon on Denitrification of Southern Temperate Forest Soils
Pérez,Cecilia A; Carmona,Martín R.; Fari?a,José M.; Armesto,Juan J.;
Chilean journal of agricultural research , 2010,
Abstract: the pressure for anthropogenic land use changes and logging of temperate forests in southern chile is rapidly increasing, with its potentially high impacts on the capacity of soils to retain important limiting elements. we tested the hypotheses that logging increases the denitrification rates and nitrate and c limitation of denitrifiers activity would be higher in soils of unlogged, old-growth forests than in soils of logged forests. potential denitrification rates were estimated by the acetylene inhibition assay in intact soil cores in laboratory short-term aerobic incubations using the following treatments: 0.7 mmol no3-n addition, the same nitrate addition plus 23.3 mmol c-glucose, and controls (no additions) with and without 10% v/v acetylene. forest logging did not significantly change soil nitrate content and c lability (e.g. soil c/n ratio). a nested two-factor anova for repeated measures showed that denitrification was enhanced by nitrate plus labile c additions in both forests, suggesting that in both logged and unlogged forests labile c and nitrate limit denitrifiers activity. increases were up to one order of magnitude when glucose was added to nitrate treated soils; from 373 ± 113 to 3353 ± 451 μg n2o-n m-2 d-1 in the unlogged, old-growth forest and from 1 369 ± 941 to 12 192 ± 7 474 μg n2o-n m-2 d-1 in the logged forest. we conclude that, denitrification would be enhanced in logged forests in the longer term due to a greater nitrate and labile c availability of both in disturbed soils.
Breeding system of Embothrium coccineum (Proteaceae) in two populations on different slopes of the Andes
ROVERE,ADRIANA E; SMITH-RAMíREZ,CECILIA; ARMESTO,JUAN J; PREMOLI,ANDREA C;
Revista chilena de historia natural , 2006, DOI: 10.4067/S0716-078X2006000200008
Abstract: plant breeding systems are considered to reflect species' life history characteristics, selection due to biotic or abiotic factors, pollination conditions, or a combination of these. reproductive systems may vary over ecological gradients. the breeding system of the ornithophilous embothrium coccineum (proteaceae) from temperate south america was studied by pollination treatments: manual self-pollination, manual cross-pollination, automatic self-pollination, and natural pollination. these treatments were conducted in a coastal western and an andean eastern population. embothrium coccineum was found to be self-incompatible and highly dependent on the pollinating agent at both sites. however, pollen limitations were greater in the coastal population, as breeding efficiency was lower. populations have different floral visitors whose identity differentially affects reproductive efficiency and pollen flow in e. coccineum
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