DSpace Angular :: Browsing by Author "Armesto, JJ"

Browsing by Author "Armesto, JJ"

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Are Chilean coastal forests pre-Pleistocene relicts?: Evidence from foliar physiognomy, palaeoclimate, and phytogeography
(2006) Hinojosa, LF; Armesto, JJ; Villagrán, C
Aim We ask whether contemporary forests of the Chilean Coastal Range can be considered to be direct and conservative descendants of pre-Pleistocene palaeofloras that occurred in southern South America from the Palaeogene to early Neogene periods (65-10 Ma), maintaining foliar physiognomies that do not match their present-day climate. We also identify the most likely ancestors of present-day coastal forests.
Breeding biology of the Thorn-tailed Rayadito (Furnariidae) in south-temperate rainforests of Chile
(2005) Moreno, J; Merino, S; Vásquez, RA; Armesto, JJ
We conducted a study of the breeding biology of the Thorn-tailed Rayadito (Aphrastura spinicauda) in secondary forests on the continental island of Chiloe (42degreesS), southern Chile. Rayaditos are small insectivorous furnariids inhabiting the south-temperate forests of Chile and Argentina. We followed the reproduction of rayadito pairs breeding in nest-boxes. Rayaditos build their nests mainly of rhizomes and stems of epiphytic vines, grasses, and hairs during periods of at least a week, and show a marked population asynchrony in laying dates of more than two months (October-December). Rayaditos lay clutches of 3-6 eggs with a mode of 4 and laying occurs on alternate days. Eggs are 50% larger and hatchlings are 30% larger than expected from allometric equations. Most broods hatch synchronously. Nestling growth curves adjust well to logistic functions and at 2 weeks nestlings attain masses similar to asymptotic values. Nestling growth, which occurs over 3 weeks, is 27% slower than expected from allometry. Fledglings attain adult size with respect to tarsus length, but have less developed plumage and higher body mass than adults. Rayaditos exhibit clutch and brood reduction, suggesting possible food limitation. The protracted breeding periods may preclude second breeding attempts for most pairs in Chiloe. There is evidence for declines in parental quality with season. The low seasonal fecundity, large eggs, and prolonged dependence periods of a truly south-temperate species like the Thorn-tailed Rayadito reflect a 'slow' life history similar to that of tropical passerines.
Breeding system of Embothrium coccineum (Proteaceae) in two populations on different slopes of the Andes
(2006) Rovere, AE; Smith-Ramírez, C; Armesto, JJ; Premoli, AC
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 (Proteaccae) 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.
Community-wide germination strategies in a temperate rainforest of Southern Chile: ecological and evolutionary correlates
(2001) Figueroa, JA; Armesto, JJ
Delayed seed germination ('dispersal in time'), as a component of a plant's germination strategy, was studied in dicotyledoneous species of a temperate rainforest flora in Chiloe Island (42 degrees 30' S), southern Chile. The objective of this investigation was to assess, for this temperate rainforest flora, what proportion of interspecific variation in the time of seed germination-measured in days since the onset of seed dispersal in space-could be attributed to the plants' historical and phylogenetic background and what proportion was associated with life history and ecological attributes such as seed mass, life form, dispersal syndromes and dispersal periods. To characterise germination times for 44 species from Chiloe forests (n = 150 seeds sowed per species in laboratory assays), we computed the mean germination time (GT), in days since sowing, for all seeds germinated of each species. Seeds were taken from the plants at the onset of dispersal and germinated in Petri dishes at 10/20 degrees C. Considering all species, GTs varied between 3 and 385 days and presented an L-shaped frequency distribution. One-way ANOVAs measured the effects of each factor across all other variables. Two-way ANOVAs were used to assess significant interactions between factors. Multifactorial ANOVAs were used to evaluate the independent effects of each of six historical, phylogenetic and ecological factors on GT and to detect associations between factors. In one-way ANOVAs, phylogenetic grouping (at or above order) explained 12% of the variance in GT; dispersal period (summer v. mainly autumn dissemination of ripe seeds), biogeographic element (endemic, austral, neotropical or cosmopolitan) and dispersal syndrome (fleshy v. dry propagules) explained 7, 6 and 5% of the variance in GT, respectively. The factors life form (trees, shrub and woody vines combined, herbs and non-woody epiphytes) and seed mass (light v. heavy) explained the 4 and 2% of the variance in GT, respectively. Taxa related to Ranunculales presented the longest mean GT (148 days). Endozoochorous species had a more delayed germination than species with other dispersal syndromes. Herbs and non-woody epiphyte species showed mean GT (41 days) significantly shorter than trees and shrubs plus woody vines combined (86 and 85 days, respectively). All interactions in two-way ANOVAs were significant. Multifactorial ANOVAs revealed that the three major factors contributing to differences in GT in this temperate rainforest flora were phylogenetic relatedness, dispersal syndromes and life form (7, 6 and 6% of the interspecific variation, respectively). In this analysis, biogeographic element, dispersal period and seed mass were not significantly related to GT. For the factors examined, failure-time analysis, which takes into account all viable seeds not germinating in laboratory assays, confirmed results from multifactorial ANOVAs.
Disturbance and regeneration dynamics of an old-growth North Patagonian rain forest in Chiloe Island, Chile
(2004) Gutiérrez, AG; Armesto, JJ; Aravena, JC
1 Few studies have addressed the mechanisms of coexistence of shade-tolerant and intolerant tree species in the canopy of old-growth, lowland rain forests of southern South America. We explored the hypothesis that their forest dynamics result from frequent, single tree-fall gap episodes.
Diversity and host tree preferences of vascular epiphytes and vines in a temperate rainforest in southern Chile
(2003) Muñoz, AA; Chacón, P; Pérez, F; Barnert, ES; Armesto, JJ
Vines and epiphytes contribute importantly to the biodiversity of temperate rainforests of southern South America. However, compared with their tropical counterparts, these functional groups have received less attention. We evaluated diversity, floristic composition and relative abundance of vascular epiphytes and vines within a humid temperate forest in northern Chiloe Island, southern Chile. We assessed whether epiphyte and vine species exhibit preferences among host tree species and tested whether species richness on tree hosts differs from that expected by chance, by comparing observed frequencies of occurrence (FO) and species richness with randomly simulated frequency distributions generated under the assumption of no epiphyte preferences. Finally, we tested for associations of epiphyte and vine species with host tree size ( trunk diameter at breast height). Eleven species of ferns and nine angiosperms ( seven vines, one epiphytic angiosperm and one shrub) were recorded growing epiphytically in a sample of 499 trees. The most abundant species were three vines, Luzuriaga polyphylla (Hook.) Macbr., Griselinia racemosa (Phil.) Taub. and Mitraria coccinea Cav., and five species of filmy ferns (Hymenophyllaceae). Most epiphytes and vines (65%) showed preference for one or two tree species, with seven species being overrepresented on Podocarpus nubigena Lindl. hosts and 10 underrepresented on Drimys winteri J.R. et G. Forster. Epiphyte and vine species richness was significantly lower than expected by chance on D. winteri and higher than expected on Nothofagus nitida ( Phil.) Krasser. Three epiphytic ferns showed preferences for large-sized trees, while frequency of occurrence of three common vines was independent of host tree size.
Diversity, flower visitation frequency and generalism of pollinators in temperate rain forests of Chiloe Island, Chile
(2005) Smith-Ramírez, C; Martinez, P; Nuñez, M; González, C; Armesto, JJ
Species richness and taxonomic composition of pollinator assemblages are documented for 26 plant species from temperate rain forests of northern Chiloe Island, southern Chile (42 degrees 30'S). We investigated the patterns of generalism and specialization among plants and animal pollinators by comparing the flower visit frequency by different pollen vectors during the spring and summer months of three consecutive years (2000-2002). Species studied exhibited a range of floral morphologies (radial vs. zygomorphic, open vs. tubular) and rewards (nectar and/or pollen). Overall, we recorded 172 pollinator species, with an average of 6.6 species of pollen vectors/plant species. Pollinators visited an average of 15.2 plant species/pollen vector. Pollinator assemblages were dominated by Coleoptera (75 species), Diptera (56 species) and Hymenoptera (30 species), but passerine birds and hummingbirds were also important. The most specialized plants were vines, including the bee-pollinated genus Luzuriaga (Philesiaceae) and two endemic species of hummingbird-pollinated Gesneriaceae. Hymenoptera contributed 41.2% of all visits, with the bumblebee Bombus dalhbomi accounting for 22.5% of these. Plants with unspecialized flower morphology supported a higher species richness of pollinators, but visiting rates did not differ from specialized flowers. 2005 The Linnean Society of London, Botanical Journal of the Linnean Society.
Do carbon-based defences reduce foliar damage?: Habitat-related effects on tree seedling performance in a temperate rainforest of Chiloe Island, Chile
(2006) Chacón, P; Armesto, JJ
Carbon-based secondary compounds (CBSCs), such as phenols or tannins, have been considered as one of the most important and general chemical barriers of woody plants against a diverse array of herbivores. Herbivory has been described as a critical factor affecting the growth and survival of newly established tree seedlings or juveniles then, the presence of secondary metabolites as defences against herbivores should be a primary strategy to reduce foliar damage. We examined whether light-induced changes in leaf phenolic chemistry affected insect herbivory on seedlings of two rainforest tree species, Drimys winteri (Winteraceae) and Gevuina avellana (Proteaceae). Seedlings of both species were planted under closed canopy and in a canopy gap within a large remnant forest patch. Half of the seedlings in each habitat were disinfected with a wide-spectrum systemic insecticide and the other half were used as controls. Seedling growth, survival, and foliar damage (estimated by an herbivory index) due to insect herbivores were monitored over a period of 16 months (December 2001-April 2003). The total leaf content of phenols and condensed tannins were assessed in seedlings from both habitats. As expected, access to light induced a greater production of CBSCs in seedlings of both tree species, but these compounds did not seem to play a significant defensive role, as seedlings grown in gaps suffered greater leaf damage than those planted in forest interior. In addition, in both habitats, seedlings without insecticide treatment suffered a greater foliar damage than those with insecticide, especially 16 months after the beginning of the experiment. Canopy openness and herbivory had positive and negative effects, respectively, on seedling growth and survival in both tree species. In conclusion, despite the higher levels of defence in tree-fall gap, the higher densities of herbivore override this and lead to higher damage levels.
Foraging behaviour of bird pollinators on Embothrium coccineum (Proteaceae) trees in forest fragments and pastures in southern Chile
(2003) Smith-Ramirez, C; Armesto, JJ
We investigated the effects of forest patch size on the behaviour of birds feeding on the flower nectar of the proteaceous tree Embothrium coccineum J. R. et G. Forster, which is typically restricted to forest edges in agricultural landscapes in southern Chile. We quantified reproductive parameters of trees (no. inflorescences per branch, total and open flowers per inflorescence) in forest fragments varying from 1 ha (small), to 20 ha (medium) and to >150 ha (large), and in remnant trees in pastures. Visits to flowers by nectar-feeding birds were recorded during 30-min observation periods, spread throughout the day during two flowering seasons, November 1992 and 1993 (n = 242 periods overall). Aggressive encounters among flower visitors were recorded in 1992. We expected less visits to trees in pastures and small forest patches because abundances of Embothrium's main pollinators, the flycatcher Elaenia albiceps and the hummingbird Sephanoides sephaniodes, decreased in smaller patches. We found, however, that pollinator visiting rates were negatively correlated with forest patch area and were highest for pasture trees. This trend was largely due a decline in the number of visits by E. albiceps , the main flower visitor, in larger patches. Hummingbird visits did not change with forest patch size. Lower visitation rates to flowering trees in larger forest fragments seemed to be a consequence of territorial defence by E. albiceps and were unrelated to differences in floral display.
Importance of native bamboo for understory birds in Chilean temperate forests
(2004) Reid, S; Díaz, IA; Armesto, JJ; Willson, MF
In South American temperate rainforests, five endemic understory birds (four Rhinocryptidae and one Furnariidae) are often associated with the main understory plant, the native bamboo Chusquea valdiviensis (Poaceae: Bambusoideae). We studied the effects of bamboo cover on species abundance and richness of those understory birds and explored the functions of bamboo as food resource and escape cover. In Chiloe Island (42degreesS), southern Chile, we selected four old-growth forest patches >100 ha and in each patch conducted bird surveys in six plots with >70% understory cover. Three plots were dominated by native bamboo and three plots had a sparse bamboo cover. Bird abundance (point counts) was significantly correlated with both total understory cover and percentage of bamboo cover but was not correlated with other kinds of understory plant cover. Bird species richness was positively correlated with bamboo cover and negatively correlated with other kinds of understory cover but unrelated to total understory cover. Leaf-gleaners Magellanic Tapaculos (Scytalopus magellanicus), Ochre-flanked Tapaculos (Eugralla paradoxa), and Des Murs's Wiretails (Sylviorthorhynchus desmursii), and the ground-gleaner Chucao Tapaculos (Scelorchilus rubecula) were more abundant in high-bamboo plots; but the ground-gleaner Black-throated Huet-huet (Pteroptochos tarnii) was recorded more times in plots with low-bamboo cover.
Linking forest structure and composition
(2005) Díaz, IA; Armesto, JJ; Reid, S; Sieving, KE; Willson, MF
We show how Chilean forest bird species richness, abundance and guild structure changes as a function of structural properties of forest stands. We surveyed bird assemblages in two old-growth (>200 years), two mid-successional (30-60 years), and two early-successional forest stands (4-20 years), from November 1999 to September 2000, on Chiloe Island, southern Chile (42degreesS). Birds were grouped into four habitat-use guilds: large-tree users, vertical-profile generalists, understory species, and shrub-users that occasionally use forests. We recorded a total of 24 bird species: 21 in old-growth, 14 in mid-successional and 16 in early-successional stands. Large-tree users and understory birds were most abundant in old-growth stands, vertical-profile generalists were common in both old-growth and mid-successional stands, and shrub-users were only common in early-successional stands. For nine bird species we found significant relationships between their local abundance and forest structural elements. Higher bird densities in old-growth forests were associated with greater availability of canopy emergent trees, snags, logs and understory bamboo cover in this habitat. Accordingly, bird species diversity in forest stands can be predicted by the presence of these structural elements, and forests should be managed to conserve structural elements that create favorable habitat for bird species in order to prevent future species losses due to logging practices. (C) 2004 Elsevier Ltd. All rights reserved.
Litterfall dynamics and nitrogen use efficiency in two evergreen temperate rainforests of southern Chile
(2003) Pérez, CA; Armesto, JJ; Torrealba, C; Carmona, MR
In unpolluted regions, where inorganic nitrogen (N) inputs from the atmosphere are minimal, such as remote locations in southern South America, litterfall dynamics and N use efficiency of tree species should be coupled to the internal N cycle of forest ecosystems. This hypothesis was examined in two evergreen temperate forests in southern Chile (42degrees30'S), a mixed broad-leaved forest (MBF) and a conifer forest (CF). Although these forests grow under the same climate and on the same parental material, they differ greatly in floristic structure and canopy dynamics (slower in the CF). In both forests, biomass, N flux, and C/N ratios of fine litterfall were measured monthly from May 1995 to March 1999. There was a continuous litter flux over the annual cycle in both forests, with a peak during autumn in the CF. In the MBF, litterfall decreased during spring. In both forests, the C/N ratios of litterfall varied over the annual cycle with a maximum in autumn. Annual litterfall biomass flux (Mean +/- SD = 3.3 +/- 0.5 vs 2.0 +/- 0.5 Mg ha(-1)) and N return (34.8 +/- 16 vs 9.1 +/- 2.8 kg N ha(-1)) were higher in the MBF than in the CF. At the ecosystem level, litterfall C/N was lower in the MBF (mean C/N ratio = 60.1 +/- 15, n = 3 years) suggesting decreased N use efficiency compared with CF (mean C/N ratio = 103 +/- 19.6, n = 3 years). At the species level, subordinated (subcanopy) tree species in the MBF had significantly lower C/N ratios (<50) of litterfall than the dominant trees in the CF and MBF (>85). The litterfall C/N ratio and percentage N retranslocated were significantly correlated and were lower in the MBF. The higher net N mineralization in soils of the MBF is related to a lower N use efficiency at the ecosystem and species level.
Mating success of the endemic Des Murs' Wiretail (Sylviorthorhynchus desmursii, Furnariidae) in fragmented Chilean rainforests
(2006) Díaz, IA; Armesto, JJ; Willson, MF
We studied the effects of fragment size, vegetation structure and presence of habitat corridors on the reproductive success of the Des Murs' Wiretail (Sylviorthorhynchus desmursii Des Murs, Furnariidae), a small (10 g) understorey bird, endemic to South American forests. In a rural landscape of Chiloe Island, southern Chile (42 degrees S; 70 degrees W), we determined the mating and nesting success of wiretails in 28 territories distributed in seven small (1-20 ha) and two large (> 300 ha) forest fragments during the 1997-1998 breeding season. Wiretails inhabited dense bamboo thickets in the understorey of forest patches, dense shrublands covering old fields, and dense early successional forest vegetation. Wiretails avoided open pastures. Reproductive success depended solely on the probability of finding mates, and the main factor affecting mating success was the presence of corridors. Mated individuals occupied 72% of the territories in forest patches < 20 ha connected by corridors, 73% of the territories in large (> 300 ha) fragments, but only 20% of territories in isolated fragments surrounded by pastures. Because of the rapid expansion of pastures in southern Chile, the conservation of wiretails and other understorey birds will depend on the maintenance of travel corridors with dense understorey vegetation between forest fragments.
Nitrogen mineralization in epiphytic soils of an old-growth Fitzroya cupressoides forest, southern Chile
(2005) Pérez, CA; Guevara, R; Carmona, MR; Armesto, JJ
Epiphytic soils derive from organic matter accumulation on trunks and canopy branches of large trees. We compared chemical and physical properties, rates of net N mineralization, and bacterial biomass carbon associated with epiphytic soils and the forest floor of an old-growth, temperate forest dominated by the long-lived Fitzroya capressoides (Cupressaceae) in Chiloe Island, southern Chile. Epiphytic soils had lower density, higher moisture content, higher total carbon and nitrogen contents, and lower pH than forest floor; however, these differences were only slight. Microbial biomass and soil C/N ratios did not differ between soil types. We estimated similar N mineralization rates in epiphytic soil and in the forest floor, but there was a significant interaction between time of the year and soil type, resulting from higher N production in epiphytic soils in some months. Microbial net N mineralization in the epiphytic layer contributed ca 6% of the internal N circulation. Fitzroya trees may access these nutrients via adventitious root uptake and leaching to the forest floor, thus exploiting an alternative path of nutrient circulation in old-growth forests.
Regeneration microsites and tree species coexistence in temperate rain forests of Chiloe Island, Chile
(2003) Christie, DA; Armesto, JJ
1 We studied the importance of fallen logs as recruitment sites for tree species, their role in species coexistence, and also the influence of canopy openness and litter depth on tree species establishment in mid-successional and old-growth temperate rain forests of ChiloE Island, southern Chile.
Successional changes in soil nitrogen availability, non-symbiotic nitrogen fixation and carbon/nitrogen ratios in southern Chilean forest ecosystems
(2004) Pérez, CA; Carmona, MR; Aravena, JC; Armesto, JJ
Vast areas of southern Chile are now covered by second-growth forests because of fire and logging. To study successional patterns after moderate-intensity, anthropogenic fire disturbance, we assessed differences in soil properties and N fluxes across a chronosequence of seven successional stands (2-130 years old). We examined current predictions of successional theory concerning changes in the N cycle in forest ecosystems. Seasonal fluctuations of net N mineralization (N-min) in surface soil and N availability (N-a; N-a=NH4+-N+NO3--N) in upper and deep soil horizons were positively correlated with monthly precipitation. In accordance with theoretical predictions, stand age was positively, but weakly related to both N-a (r(2)=0.282, P<0.001) and total N (N-tot; r(2)=0.192, P<0.01), and negatively related to soil C/N ratios (r(2)=0.187, P<0.01) in surface soils. A weak linear increase in soil N-min (upper plus deep soil horizons) was found across the chronosequence (r(2)=0.124, P<0.022). N-min occurred at modest rates in early successional stands, suggesting that soil disturbance did not impair microbial processes. The relationship between N fixation (N-fix) in the litter layer and stand age best fitted a quadratic model (r(2)=0.228, P<0.01). In contrast to documented successional trends for most temperate, tropical and Mediterranean forests, non-symbiotic N-fix in the litter layer is a steady N input to unpolluted southern temperate forests during mid and late succession, which may compensate for hydrological losses of organic N from old-growth ecosystems.

Browsing by Author "Armesto, JJ"

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