Browsing by Autor "Silvia C. Gallegos"

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BIRD COMMUNITIES RESPOND TO THE SEASONAL FRUIT AND FLOWER AVAILABILITY IN A FRAGMENTED TROPICAL ANDEAN LANDSCAPE
(2024) Mariana Villegas; César Mayta; Cecilia L. López; Isabell Hansen; Silvia C. Gallegos
Fire is one of the main causes of fragmentation in tropical Andean forests. Fragmentation can influence plant reproductive phenology, which in turn affects bird communities. In the Bolivian Yungas, we investigated how the seasonal availability of fruits and flowers affects bird richness, abundance and bird community composition in forest edges and adjacent bracken (Pteridium ferns) dominated areas. We captured birds with mist nets at eight sites during the dry, transition and wet seasons, and recorded fruit and flower availability through phenological observations and plant collections. We examined variation in species richness and abundance using generalized linear mixed-effects models, and bird species composition in each season using multivariate analyses. Fruit availability was higher in the transition and wet seasons, and lowest in the dry season, while flower availability did not differ among seasons. Bird species richness and abundance were significantly higher in bracken areas, although there was significantly lower fruit availability than at the forest edge, and these were mainly generalist bird species that may be tolerant to disturbance. Total bird abundance increased with higher fruit availability in both habitats, and with flower availability at the forest edge. Bird species composition differed between forest edges and bracken areas in the transition and the wet seasons, being influenced by fruiting and flowering phenology in the dry and transition seasons, and elevation in all seasons. Our results show the varying seasonal influence of plant reproductive phenology on avian communities of disturbed habitats, although other large scale factors associated with fragmentation may also shape bird communities.
Bird perches and artificial bat roosts increase seed rain and seedling establishment in tropical bracken‐dominated deforested areas
(Wiley, 2024) César Mayta; Cecilia L. López; Mariana Villegas; Luís F. Aguirre; Isabell Hensen; Silvia C. Gallegos
Tropical forests are being reduced by human activities. The use of fire for agricultural expansion generates areas dominated by the bracken fern Pteridium , where forest regeneration is slow. This may be caused by seed limitation, especially of animal‐dispersed seeds, due to the absence of seed dispersers from the forest in deforested areas, calling for restoration strategies to assist forest regeneration. We installed bird perches and artificial bat roosts to evaluate their effect on the density, species richness, and composition of animal‐dispersed seeds and seedlings of tree and non‐tree species in bracken‐dominated areas in the tropical montane forest of Bolivia. We found that perches and bat roosts increased the density and species richness of animal‐dispersed seeds and established seedlings. The seeds and seedlings dispersed by birds were clumped under the perches, while the seeds and seedlings dispersed by bats were distributed around the roosts. Perches had a higher density and species richness of seeds and seedlings compared to bat roosts, suggesting that the use of perches could be a better option as a restoration tool in bracken‐dominated areas. The increase in seed rain and seedling establishment of animal‐dispersed species in perches and bat roosts supports seed limitation, hindering forest succession in bracken‐dominated areas. The use of bird perches accompanying other restoration techniques is a promising restoration strategy to accelerate forest regeneration in tropical areas dominated by Pteridium , which are widely distributed.
Bracken fern does not diminish arbuscular mycorrhizal fungus inoculum potential in tropical deforested areas
(Springer Science+Business Media, 2021) Cecilia L. López; César Mayta; Kazuya Naoki; Jorge A. N. Quezada; Isabell Hensen; Silvia C. Gallegos
Bracken fern facilitates tree seedling recruitment in tropical fire-degraded habitats
(Elsevier BV, 2014) Silvia C. Gallegos; Isabell Hensen; Francisco Saavedra; Matthias Schleuning
Challenges and opportunities for the Bolivian Biodiversity Observation Network
(Taylor & Francis, 2015) Miguel Fernández; Laetitia M. Navarro; Amira Apaza‐Quevedo; Silvia C. Gallegos; Alexandra Marques; Carlos Zambrana‐Torrelio; Florian Wolf; Healy Hamilton; Álvaro J. Aguilar-Kirigin; Luís F. Aguirre
Pragmatic methods to assess the status of biodiversity at multiple scales are required to support conservation decision-making. At the intersection of several major biogeographic zones, Bolivia has extraordinary potential to develop a monitoring strategy aligned with the objectives of the Group on Earth Observations Biodiversity Observation Network (GEO BON). Bolivia, a GEO Observer since 2005, is already working on the adequacy of national earth observations towards the objectives of the Global Earth Observation System of Systems (GEOSS). However, biodiversity is still an underrepresented component in this initiative. The integration of biodiversity into Bolivia’s GEO framework would confirm the need for a country level biodiversity monitoring strategy, fundamental to assess the progress towards the 2020 Aichi targets. Here we analyse and discuss two aspects of the process of developing such a strategy: (1) identification of taxonomic, temporal and spatial coverage of biodiversity data to detect both availability and gaps; and (2) evaluation of issues related to the acquisition, integration and analyses of multi-scale and multi-temporal biodiversity datasets. Our efforts resulted in the most comprehensive biodiversity database for the country of Bolivia, containing 648,534 records for 27,534 species referenced in time and space that account for 92.5% of the species previously reported for the country. We capitalise this information into recommendations for the implementation of the Bolivian Biodiversity Observation Network that will help ensure that biodiversity is sustained as the country continues on its path of development.
Differences in bird and bat traits, seed-dispersal interactions and functions between tropical montane forest and bracken-dominated areas
(Frontiers Media, 2025) César Mayta; Matthias Schleuning; Cecilia L. López; Mariana Villegas; Isabell Hensen; Silvia C. Gallegos
Most tropical plant species depend on animals to disperse their seeds. Seed dispersal by animals allows plants to colonize new sites in deforested habitats helping to accelerate forest recovery. However, deforestation can affect the interactions between animals and plants that are crucial for forest regeneration. In this study, we analyze the differences on the composition of functional traits and on seed-dispersal interactions and functions by birds and bats between forest and deforested areas dominated by bracken fern. At eight study sites, we captured birds and bats in bracken-dominated areas and at forest in the tropical montane forest of Bolivia and analyzed their droppings. We found a similar composition of functional traits related to animal size, gape width and degree of frugivory of bats in both habitat types. Hand-wing index of birds was significantly higher in bracken compared to forest. Birds had more interaction richness and abundance in bracken than in forest, and bats had more interaction abundance in forest than in bracken. The majority of seeds dispersed by birds and bats in bracken were from pioneer species. We conclude that, although seed dispersal by birds and bats is maintained in the bracken-dominated areas, most of the dispersed seeds belong to pioneer species. Pioneer species are unlikely to establish in bracken-dominated areas, making the natural regeneration process of these deforested areas very slow.
Disentangling the roles of bracken fronds and litter on natural seedling recruitment in fire-disturbed tropical montane habitats
(Elsevier BV, 2024) Cecilia L. López; César Mayta; A C.; Mariana Villegas; Emili Antonia Jiménez; Víctor Vásquez; Isabell Hensen; Silvia C. Gallegos
Tropical montane forests are diverse ecosystems often affected by uncontrolled human-induced fires causing tree mortality and creating large deforested areas. After fires, Pteridium spp. ferns (bracken) often dominate, and forest regeneration in these areas is slow. In this study, we evaluated the effects of bracken fronds and litter, as well as the micro-environmental conditions created by the fern, on the density and species diversity of naturally recruiting seedlings. At eight sites, 120 experimental plots were established among forest and bracken-dominated areas with the following treatments: (a) fronds and litter intact (F+L+); (b) fronds intact and litter removed (F+L-); (c) fronds removed and litter intact (F-L+); and (d) fronds and litter removed (F-L-). After one year, all seedlings were registered, identified and classified according to their life-form (tree, shrub, herb, vine), dispersal vector (wind- or animal-dispersed) and successional status (early-, mid-, and late-successional). For all treatments we assessed 12 micro-environmental variables. We identified 3649 naturally-recruiting seedlings corresponding to 278 species from 70 families. We found positive effects of bracken fronds particularly on tree seedling recruitment: treatments with fronds had greater densities of both animal- and wind-dispersed tree seedlings, 1.8 and 1.4 fold higher, respectively, compared to treatments without fronds. Similarly, the density of early-, mid- and late-successional tree species was 1.3, 1.7 and 1.9 times higher in treatments with than without fronds. Furthermore, species diversity of early-, mid- and late-successional tree species was higher in the treatments with fronds. The environmental conditions generated by bracken presence, such as photosynthetically active radiation, soil temperature, live bracken biomass and litter depth, had positive effects on seedling density of all, animal-dispersed and early-successional tree species, and negative effects on seedling recruitment of other life-forms, notably from early successional stages. To promote forest regeneration in bracken-dominated areas, active restoration measures such as direct seed addition and transplants of nursery-raised seedlings of mid- and late-successional species should be considered. Since bracken can hinder the establishment of some life forms and species but favor others, it is recommended to include a trait-based approach to understand species responses to environmental factors and select species that are optimally adapted to bracken-dominated habitat conditions to promote forest regeneration. • Bracken facilitates seedling recruitment of mid- and late-successional tree species. • Bracken fronds’ shade increases species diversity of tree seedlings. • Bracken litter decreases natural recruitment of herbs. • Animal-dispersed species have higher recruitment under bracken fronds and litter.
Diversidad arbórea del bosque tucumano-boliviano en la alta cuenca del río Bermejo (Tarija, Bolivia)
(2019) Silvia C. Gallegos; Freddy S. Zenteno-Ruíz; Stephan Beck; Ramiro Pablo López
Facilitative and competitive effects of bracken fronds and litter on tree seedling recruitment
(Frontiers Media, 2025) Cecilia L. López; César Mayta; Andrea Soliz; Isabell Hensen; Silvia C. Gallegos
Introduction Tropical montane forests are diverse ecosystems increasingly threatened by land-use change and frequent uncontrolled fires caused by humans. After these fires, affected areas are often dominated by ferns of the genus Pteridium (bracken), delaying the rate of forest regeneration. This study examined the facilitative and competitive roles of bracken fronds and litter on seedling establishment, recruitment success, and growth after 36 months, and the extent to which these effects depend on seed size in early plant development processes. Methods At eight sites, we conducted seed addition and seedling-transplant experiments in plots established in bracken-dominated areas, using the following treatments: (a) fronds and litter intact (F+L+); (b) fronds intact and litter removed (F+L−); (c) fronds removed and litter intact (F−L+); and (d) fronds and litter removed (F−L−). Results A total of 46,640 seeds from 24 tree species were sown and 1,070 nursery-raised seedlings transplanted. In treatments with fronds and litter, seedling establishment and recruitment success increased with seed size. In contrast, in the treatment without fronds and litter all the species had low performance. Fronds proved to be highly beneficial for all seed sizes and for all early development processes. Litter, on the other hand, had negative effects on small-seeded species during establishment, but had neutral to positive effects on the recruitment and growth of all species. Discussion The disadvantage of small seeds under bracken litter may be related to the high light requirements of seedlings, as litter accumulation reduces light transmission. Species with large seeds and shade tolerance benefit from bracken frond cover, suggesting that restoration strategies in bracken-dominated areas should prioritize these species. Moreover, planting seeds or seedlings shortly after fire, in the presence of bracken fronds and before litter accumulation would be most beneficial for tree species. Additionally, seed dispersers play a crucial role in transporting large seeds into bracken-dominated areas, emphasizing the need for an integrated approach that considers biotic and abiotic factors for effective forest recovery.
Factors limiting montane forest regeneration in bracken-dominated habitats in the tropics
(Elsevier BV, 2016) Silvia C. Gallegos; Stephan Beck; Isabell Hensen; Francisco Saavedra; Denis Lippok; Matthias Schleuning
Fenología reproductiva de la queñua (Polylepis incarum, Rosaceae) durante un ciclo anual en la puna mesofítica de La Paz, Bolivia
(2018) Cecilia L. López Alipaz; Alejandra I. Domic; César Mayta; Emilia García; Silvia C. Gallegos
In this study, the phenology of queñua (Polylepis incarum, Rosaceae) was evaluated during an annual cycle in the mesophytic puna of La Paz. The species is endemic to the Lake Titicaca basin. Like other species of the genus Polylepis, P. incarum is categorized as Endangered for Bolivia due to anthropic activities as firewood extraction and crop expansion. During one year (March 2015 - February 2016), we conducted monthly evaluations in a woodland located in the community of Kopacati, Copacabana department, La Paz, Bolivia. The objectives of the study were to identify flowering and fruiting times, and to assess the relationships between plant size, environmental factors and plant reproductive success. The species produces floral buds between July and August. The production of flowers in the female state occurs between July and November, and flowers in the male state, between July and October. The highest production of immature fruits took place in November, reaching maturity in December and January. Both precipitation and temperature showed a significant influence on flowers and fruits production. Diameter at breast height (DBH) was the only allometric character significantly associated to the production of flowers and fruits between trees and shrubs. There was no significant difference in the production of flowers and fruits between trees and shrubs. The phenological patterns informed for this species are similar those reported for P. tomentella and P. besseri. The results of the present study contribute to the knowledge about the reproductive biology of Polylepis incarum and to promote programs of conservation and reforestation of the species.https://doi.org/10.25260/EA.18.28.1.1.516
Forest recovery of areas deforested by fire increases with elevation in the tropical Andes
(Elsevier BV, 2013) Denis Lippok; Stephan Beck; Daniel Renison; Silvia C. Gallegos; Francisco Saavedra; Isabell Hensen; Matthias Schleuning
Habitat differences in seed‐dispersing vertebrates indicate dispersal limitation in tropical bracken‐dominated deforested areas
(Wiley, 2024) Silvia C. Gallegos; César Mayta; Mariana Villegas; Guido Ayala; Kazuya Naoki; Josef Rechberger; V. D. Zambrana Rojas; María Viscarra; Nuria Bernal‐Hoverud; Mauricio Espejo
Abstract Shifting agriculture and anthropogenic fires are among the main causes of deforestation in the tropics. After fire and land abandonment, vast deforested areas are commonly dominated by the bracken fern Pteridium for long periods. Although forest regeneration in bracken‐dominated areas is mainly hindered by dispersal limitation, little is known about the role of seed‐disperser communities in slow forest succession. Our objective was to unravel the differences in the properties of the seed‐disperser communities between forests and bracken‐dominated areas to assess their role in dispersal limitation to foster ecological restoration. We compared species richness, diversity, abundance, and composition of seed‐dispersing birds, bats, and medium and large terrestrial mammals between both habitats in a montane forest of Bolivia. The species richness and diversity were similar for bats and higher for birds in bracken‐dominated areas than in the forest, but species composition was different between both habitats and groups. Although species composition was similar between both habitats for terrestrial mammals, the abundance was higher in the forest than in bracken‐dominated areas. Differences in species composition of seed‐dispersing birds and bats could be one of the main causes of dispersal limitation in forest regeneration in tropical bracken‐dominated areas. The few shared species between both habitats could explain the low seed rain of animal‐dispersed forest tree species in bracken‐dominated areas and the consequent hindered forest regeneration. Future studies relevant to natural forest regeneration should focus on analyzing the effects of animal‐attractants such as perches, artificial bat‐roosts, and seedling transplants on disperser communities, seed dispersal effectiveness, and forest regeneration. Abstract in Spanish is available with online material.
Influence of Bracken Fronds and Leaf Litter Management on Soil Seed Bank Characteristics in a Fire‐Disturbed Tropical Montane Forest
(Wiley, 2025) Emili Antonia Jiménez; Cecilia L. López; Alfredo F. Fuentes; Isabell Hensen; Silvia C. Gallegos
ABSTRACT The bracken fern Pteridium spp. dominates postfire vegetation in tropical montane forests, where fronds, litter, allelopathy, and dispersal limitation hinder forest regeneration. However, this species' effect on soil seed bank remains poorly understood. We investigated the effects of bracken fronds and litter on the abundance, richness, and species diversity of the soil seed bank in a tropical montane fire‐deforested area in Bolivia. At eight study sites (1800–2350 a.s.l), soil samples were collected under five treatments: (a) fronds and litter intact (F + L+), (b) fronds intact and litter removed (F + L−), (c) fronds removed and litter intact (F−L+), (d) fronds and litter removed (F−L−), and (e) forest. Using the seedling emergence method, samples were assessed every 20 days over 8 months (September 2021–May 2022). Compared to intact bracken, forest areas showed 2.6, 1.7, and 1.5‐fold greater abundance, species richness, and diversity of zoochorous species, respectively. Among bracken treatments, abundance, richness, and diversity of zoochorous species decreased by 2.7, 2.6, and 2 times, respectively, when fronds and litter were removed, compared to the intact bracken treatment, but were not significantly different when only litter was removed. Our findings indicate that in bracken‐dominated environments, fronds and litter improve microclimatic conditions, maintaining the viability of zoochorous species in the soil seed bank. The removal of litter without cutting fronds reduces light interception and seed trapping while maintaining zoochorous seed germination capacity in the soil, and might be a better management strategy than removing fronds and litter to promote seedling recruitment from the soil seed bank.
Pleistocene climatic oscillations rather than recent human disturbance influence genetic diversity in one of the world's highest treeline species
(Wiley, 2015) Yanling Peng; Susanne Lachmuth; Silvia C. Gallegos; Michael Kessler; Paul M. Ramsay; Daniel Renison; Ricardo Suarez; Isabell Hensen
Our study shows that, unlike the case for other Andean treeline species, recent human activities have not affected the genetic structure of P. tarapacana, possibly because its inhospitable habitat is unsuitable for agriculture. The current genetic pattern of P. tarapacana points to a historically more widespread distribution at lower altitudes, which allowed considerable gene flow possibly during the glacial periods of the Pleistocene epoch, and also suggests that the northern Argentinean Andes may have served as a refugium for historical populations.
Pollen limitation and reproductive incompatibility system in a critically endangered tree, <i>Polylepis incarum</i> (Bitter) M. Kessler & Schmidt-Leb (Rosaceae)
(Taylor & Francis, 2021) Cecilia L. López; Alejandra I. Domic; César Mayta; Emilia García; Jorge A. N. Quezada; Silvia C. Gallegos
Anemophilous species depend on wind for sexual reproduction. When plants do not receive enough pollen and/or pollen has poor quality, they may experience pollen limitation. This can reduce the production of fruits and seeds with negative consequences on population dynamics. The self-compatibility system also plays an important role on the likelihood of a species suffering pollen limitation as it determines if plants can produce fruits and seeds in the absence of compatible mates. Here, we studied the breeding system of the Andean anemophilous tree Polylepis incarum, a critically endangered species endemic to Lake Titicaca. We conducted controlled experimental pollination experiments and florescence microscopy analysis to assess whether pollen limitation and the incompatibility system constrain fruit and seed production. Results showed that the seed set is limited by pollen availability, that P. incarum exhibits a pre-zygotic compatibility system and early inbreeding depression manifested during seed development. Therefore, self-pollination is a factor that could be partially associated with the production of non-viable seeds.
Secondary dispersal by ants promotes forest regeneration after deforestation
(Wiley, 2014) Silvia C. Gallegos; Isabell Hensen; Matthias Schleuning
Summary Many remnants of tropical forests are surrounded by deforested areas dominated by successional vegetation. Although secondary dispersal by scatter‐hoarding rodents and ants may influence seed predation and seedling recruitment, very little is known about its importance in degraded forest ecosystems. We studied the effects of secondary dispersal on seed predation, germination and seedling recruitment of the primarily bird‐dispersed tree C lusia trochiformis in a tropical montane forest in B olivia. We carried out exclosure experiments that allowed or excluded access to seeds by vertebrates in three habitat types (forest interior, degraded habitat close to and degraded habitat far from the forest margin) in a spatial block design at six sites. We offered a total of 1440 seeds (both with and without an aril) and marked half of them with a thread to follow their fate after 48 h and after 1 month. We found that secondary dispersal by ants was highest in the forest interior but was also frequent in degraded habitats close to and far from the forest edge. Secondary dispersal significantly increased seedling recruitment, particularly in the degraded habitats, probably because seeds were often dispersed to sites beneath the leaf litter. Recruitment success increased significantly with dispersal distance. High recruitment of secondarily dispersed seeds in the degraded habitat was due to the combined effect of reduced predation and increased germination of seeds that had been moved by ants. Synthesis . In the absence of secondary dispersal, seed germination and seedling recruitment were very low in degraded habitats. Seed dispersal by ants substantially increased natural regeneration in the deforested habitats. Our experiments thus demonstrate that the effects of biotic interactions on plant demography can vary across habitat boundaries at small spatial scales and that secondary dispersal is a crucial and overlooked process that can aid the regeneration of deforested habitats in the tropics.
The use of bird perches and artificial bat roosts to overcome dispersal and establishment limitation in bracken-dominated deforested areas
(Elsevier BV, 2026) César Mayta; Cecilia L. López; Mariana Villegas; Isabell Hensen; Silvia C. Gallegos
The failure of seeds to arrive at suitable sites (dispersal limitation) and/or unsuitable conditions for germination, seedling survival and growth (establishment limitation) can impede the regeneration of tropical forests. We installed bird perches and artificial bat roosts in deforested areas dominated by the bracken fern Pteridium in the tropical montane forest of Bolivia to evaluate their effect on dispersal and establishment limitations. We also analyzed the relationship between seed size and life-history strategies of plants subject to both limitations. We found that perches reduced dispersal and establishment limitation of all seed sizes (small and large) and life-history strategies (pioneer and non-pioneer). In contrast, bat roosts did not reduce dispersal and establishment limitation in any of the categories. Our results reinforce the observation that dispersal limitation is one of the main filters that plant species must overcome in bracken-dominated deforested areas. The installation of bird perches as well as direct sowing of animal-dispersed seeds and planting of seedlings are strategies that could effectively support the regeneration of these widely distributed deforested areas.
Trait‐based species selection for restoration: A case study from tropical landscapes dominated by bracken
(Wiley, 2025) Silvia C. Gallegos; Cecilia L. López; Kazuya Naoki; Andrea Soliz; A C.; César Mayta; Leslie Cayola; J. Sebastián Tello; Isabell Hensen
Abstract Deforestation leads to non‐forested areas that often need active ecological restoration to promote forest succession. Here, we developed a trait‐based approach to guide the design of restoration projects and tested our approach in tropical areas deforested by fires and dominated by bracken. Deforestation caused by human‐induced fires creates complex conservation problems in tropical areas. After fire, montane tropical deforested areas are often dominated by bracken fern ( Pteridium spp.), which prevents the establishment of many species of trees. This means that effective ecological restoration strategies are needed for forest recovery. We explored whether a trait‐based approach could be used to guide the selection of tree species in active restoration projects in deforested areas. We first tested whether traits could be used to predict which species can overcome bracken‐associated filters. We then tested the relationship between the trait‐based predictions for each species and their abundance in a reference old‐growth forest. To identify key traits, we conducted a seed addition experiment in bracken‐dominated areas that had developed 5–15 years after a fire, using 23 tree species common in the Bolivian montane forests, and monitored seedling establishment, survival and growth for 36 months. We then related seedling performance to the functional traits of adults and seedlings. We found that six functional traits improved tree seedling performance in bracken‐dominated areas, and that only one third of the species evaluated exceed a 25% probability of recruitment. Most of the favoured traits correspond to conservative strategies. The species dispersed by birds and with large seeds were the most likely to overcome the filters created by bracken. Based on the trait predictions, we found that the species predicted to overcome bracken are not common in old‐growth forests. Synthesis and applications . Our results can be used by stakeholders to select the species best suited for active restoration projects in bracken‐dominated areas throughout the tropical region. Furthermore, our trait‐based approach, which considers seedling performance in disturbed areas, can serve as a guide for species selection in restoration programmes in other disturbed systems.
Tree diversity of the Tucuman -Bolivian forest in the upper river basin of Bermejo (Tarija, Bolivia)
(2019) Silvia C. Gallegos; Freddy S. Zenteno-Ruíz; Stephan Beck; Ramiro Pablo López