Influence Of Vegetation Structure Research Articles

Influence of vegetation structure and climatic conditions on abundance of free-living Amblyomma ticks (Acari; Ixodidae) in a Costa Rican dry forest

Resumen. Diferencias entre hábitats y la variación en las condiciones ambientales son factores que frecuentemente afectan la abundancia en las poblaciones de muchos animales, y el efecto de esta variación puede afectar de manera diferente cada estadio del ciclo de vida de un animal. En este estudio se compara el efecto de diferentes hábitats y cambio en las condiciones ambientales (e.g., temperatura y precipitación) sobre la abundancia de larvas, ninfas y adultos de garrapatas duras (Amblyomma spp.) en un bosque seco tropical. La abundancia de larvas fue alta en todos los hábitats, pero las ninfas y adultas fueron más abundantes en aquellos sitios más boscosos (mayor cobertura forestal). Los sitios boscosos posiblemente proporcionan condiciones más adecuadas para la sobrevivencia de los tres estadios de las garrapatas (larvas, ninfas y adultas) durante los periodos de búsqueda de huéspedes. Se encontró también que el pico de abundancia de los tres estadios ocurrió durante o cerca de la estación seca. Esto sugiere que las garrapatas tienen un pico reproductivo asociado con la estación seca, pero solamente la abundancia de ninfas se correlacionó con la variación en las condiciones ambientales.

Vegetation diversity and structure influence small‐mammal communities in native and restored northern mixed grasslands

AbstractCurrent grassland restoration strategies aim to recreate grassland vegetation communities, and often rely on high‐diversity native seeding to promote vegetation diversity. Questions remain concerning the influence of vegetation richness and diversity on grassland fauna. Small‐mammal communities are integral parts of grassland ecosystems, but their responses to restoration are often mixed or overlooked. During July 2014 to 2016, we used Sherman live traps to survey grassland small‐mammal communities of 24 study sites in northeastern South Dakota and southeastern North Dakota, USA, to better understand their responses to vegetation cover type, diversity, richness, and site‐specific vegetation structure. Sites represented a vegetation species richness gradient and 3 vegetation cover types including low‐diversity restorations planted with dense nesting cover (DNC) seed mix, high‐diversity seeded restorations, and unseeded reference grasslands. Small‐mammal abundance was highest at low‐diversity DNC restoration sites and lowest in reference grassland. Small‐mammal diversity was highest at high‐diversity restoration sites and lowest at low‐diversity DNC restoration sites. Models assessing the influence of vegetation structure on the abundance of focal taxa differed. Deer mice (Peromyscus spp.) were negatively influenced by percent native vegetation cover, and voles (Microtus spp.) showed yearly variation and were influenced positively by litter depth and negatively by vegetation richness. Small‐mammal communities of low‐diversity DNC restorations differed from reference sites, but high‐diversity restorations were not different from reference or low‐diversity DNC sites. Thirteen‐lined ground squirrel (Ictidomys tridecemlineatus) abundance was higher at reference and high‐diversity restored sites, while low‐diversity DNC sites had higher deer mice abundance. Results indicate small mammals are unlikely to respond uniformly to vegetation characteristics, and diversity of seed mixes used in grassland restoration is likely to influence grassland small‐mammal communities.

Can urban forests provide acoustic refuges for birds? Investigating the influence of vegetation structure and anthropogenic noise on bird sound diversity

As a crucial component of terrestrial ecosystems, urban forests play a pivotal role in protecting urban biodiversity by providing suitable habitats for acoustic spaces. Previous studies note that vegetation structure is a key factor influencing bird sounds in urban forests; hence, adjusting the frequency composition may be a strategy for birds to avoid anthropogenic noise to mask their songs. However, it is unknown whether the response mechanisms of bird vocalizations to vegetation structure remain consistent despite being impacted by anthropogenic noise. It was hypothesized that anthropogenic noise in urban forests occupies the low-frequency space of bird songs, leading to a possible reshaping of the acoustic niches of forests, and the vegetation structure of urban forests is the critical factor that shapes the acoustic space for bird vocalization. Passive acoustic monitoring in various urban forests was used to monitor natural and anthropogenic noises, and sounds were classified into three acoustic scenes (bird sounds, human sounds, and bird-human sounds) to determine interconnections between bird sounds, anthropogenic noise, and vegetation structure. Anthropogenic noise altered the acoustic niche of urban forests by intruding into the low-frequency space used by birds, and vegetation structures related to volume (trunk volume and branch volume) and density (number of branches and leaf area index) significantly impact the diversity of bird sounds. Our findings indicate that the response to low and high frequency signals to vegetation structure is distinct. By clarifying this relationship, our results contribute to understanding of how vegetation structure influences bird sounds in urban forests impacted by anthropogenic noise.

Past and present biomass consumption by herbivores and fire across productivity gradients in North America

Herbivores and fire are important consumers of plant biomass that influence vegetation structure, nutrient cycling, and biodiversity globally. Departures from historic biomass consumption patterns due to wild herbivore losses, livestock proliferation, and altered fire regimes can have critical ecological consequences. We set out to (i) understand how consumer dominance and prevalence responded to spatial and temporal moisture gradients in Holocene North America and (ii) examine how past and present consumer dominance patterns in North America compare to less altered consumer regimes of modern Sub-Saharan Africa. We developed long-term records of bison abundance and biomass burning in Holocene midcontinent North America and compared these records to reconstructions of moisture availability and vegetation structure. We used these reconstructions to characterize bison and fire prevalence across associated moisture and vegetation gradients. We found that bison herbivory dominated biomass consumption in dry settings whereas fire dominated in wetter environments. Historical distributions of herbivory and burning in midcontinent North America resemble those of contemporary Sub-Saharan Africa, suggesting disturbance feedbacks and interactions regulate long-term consumer dynamics. Comparisons of consumer dynamics in contemporary North America with Holocene North America and Sub-Saharan Africa also reveal that fire is functionally absent from regions where it was once common, with profound ecological implications.

The influence of vegetation structure on lift-off velocity of diaspores during secondary wind dispersal

Lift-off velocity, the wind speed at which a diaspore starts moving during secondary wind dispersal, representing diaspore mobile capacity, may greatly depend on vegetation where dispersal takes place. However, how vegetation structure influences lift-off velocity and which is the most important vegetation attribute remain unknown. The vegetation with various attributes (four coverages-0, 10 %, 20 % and 30 %, three life-form compositions-herb, shrub and herb + shrub, two vertical patterns-one and two layers, and two horizontal patterns-uniform and aggregated) were set up for the wind tunnel experiment. Diaspores of 30 species varied in wing loading, terminal velocity, mass, projected area, length, width, height, and shape index were selected to measure their lift-off velocity within various vegetation structures. Lift-off velocity significantly increased with the increasing vegetation coverage, in the case of any life-form composition, vertical pattern and horizontal pattern of vegetation. For the vertical pattern of vegetation, the lift-off velocity in one-layer vegetation was significantly higher than that in two-layer vegetation, but only for 10 % vegetation coverage. Both the life-form composition and the horizontal pattern of vegetation had no influences on lift-off velocity. The correlation between lift-off velocity and diaspore attributes (length, width, height, projected area, mass and wing loading) increased with vegetation coverage and the correlation in two-layer vegetation was larger than that in one-layer vegetation. Our results indicate that vegetation coverage is the key vegetation attribute determining lift-off velocity during secondary wind dispersal. Lift-off velocity is also influenced by diaspore traits, but their relationships tend to be regulated by vegetation attributes, especially the coverage and vertical pattern of vegetation. Our study demonstrates the important role of vegetation coverage in determining the second dispersal capacity, which is helpful to understand the dispersal strategies of plants in response to vegetation structure and succession.

Using high-resolution LiDAR-derived canopy structure and topography to characterise hibernaculum locations of the hazel dormouse

The hazel dormouse is predominantly an arboreal species that moves down to the ground to hibernate in the autumn in temperate parts of its distributional ranges at locations not yet well understood. The main objective of this study is to test whether environmental characteristics surrounding hazel dormouse hibernacula can be identified using high-resolution remote sensing and data collected in situ. To achieve this, remotely sensed variables, including canopy height and cover, topographic slope, sky view, solar radiation and cold air drainage, were modelled around 83 dormouse hibernacula in England (n = 62) and the Netherlands (n = 21), and environmental characteristics that may be favoured by pre-hibernating dormice were identified. Data on leaf litter depth, temperature, canopy cover and distance to the nearest tree were collected in situ and analysed at hibernaculum locations in England. The findings indicated that remotely sensed data were effective in identifying attributes surrounding the locations of dormouse hibernacula and when compared to in situ information, provided more conclusive results. This study suggests that remotely sensed topographic slope, canopy height and sky view have an influence on hazel dormice choosing suitable locations to hibernate; whilst in situ data suggested that average daily mean temperature at the hibernaculum may also have an effect. Remote sensing proved capable of identifying localised environmental characteristics in the wider landscape that may be important for hibernating dormice. This study proposes that this method can provide a novel progression from habitat modelling to conservation management for the hazel dormouse, as well as other species using habitats where topography and vegetation structure influence fine-resolution favourability.

Mice population dynamics and structure over time and space after wildfires

AbstractRodents respond quickly to changes in habitat structure after wildfires. They constitute important prey items for vertebrate predators and influence vegetation structure and regeneration. Assessing the population dynamics of rodents in burnt areas, whether individuals originate from in situ survival or from ex situ immigration, is therefore a key question in understanding the recovery of trophic networks after disturbance. This study aimed to identify the recovery strategies of rodent populations in recently burnt forests in the Mediterranean basin using body condition, reproductive output, sex ratios, and distance covered by wood mice and Algerian mice. Sampling stations were set up at increasing distances from the perimeter of recently burnt areas. Rodents were captured using Sherman traps and measured. Wood mice and Algerian mice lived syntopically within the recently burnt areas studied, the former species being more abundant and the second one selecting drier areas. Results indicated that time since fire, shrub cover, and distance to the perimeter of the burnt area influenced wood mice and Algerian mice population structures. Adult female wood mice mainly remained close to the burnt area perimeter, due to this species' matriarchal structure, while juvenile males dispersed farther into the burnt area. Adult females were also recaptured more frequently than other age and sex categories over time, whereas males covered greater distances. These findings suggest that the recovery strategy of these widespread Mediterranean rodents is mainly driven by ex situ immigration from unburnt areas. These results will be useful for post‐fire management decisions such as non‐intervention, salvage logging or the conservation of open areas, given that mice are a fundamental component of the ecosystem. Results also suggest that management should focus on maintaining good connectivity between burnt and adjacent unburnt areas to support mice populations and facilitate other longer‐term conservation benefits.

The influence of vegetation structure on sleeping site selection by chimpanzees (Pan troglodytes troglodytes).

Sleep is an important aspect of great ape life; these animals build sleeping platforms every night. In a community of chimpanzees, each subgroup selects a sleeping site where each individual builds a sleeping platform, mostly on a tree. Previous studies have measured the heights of sleeping platforms and sleeping trees to test the predation avoidance and thermoregulation hypotheses of sleeping site selection. However, it remains unclear how components of vegetation structure (vertical and horizontal) together determine the selection of sleeping sites by chimpanzees. Using botanical inventories around sleeping sites in a tropical rainforest of Cameroon, we found that chimpanzees preferentially sleep in trees measuring 40-50 cm in diameter. Regarding height, on average, sleeping trees measured 26 m and sleeping platforms were built at 16 m. To build sleeping platforms, chimpanzees preferred four tree species, which represent less than 3% of tree species in the study area. We demonstrate that the variation in abundance of tree species and the vertical and horizontal structure of the vegetation drive chimpanzee sleeping site selection. It was previously thought that preference for vegetation types was the driver of sleeping site selection in chimpanzees. However, results from this study indicate that the importance of vegetation types in sleeping site selection depends on their botanical characteristics including the variation in tree size, the abundance of all trees, the abundance of sleeping trees, and the occurrence of preferred sleeping tree species, which predict sleeping site selection. The height and diameter of trees are considered by chimpanzees when selecting a particular tree for sleeping and when selecting a site with a specific vertical structure. In addition to tree height, the abundance of smaller neighboring trees may also play a role in the chimpanzee antipredation strategy. Our results demonstrate that chimpanzees consider several vegetation parameters to establish sleeping sites.

Grazing regime effects on bird biodiversity overwhelmed by an interference competitor

The majority of the world's mammal biomass is domestic livestock. Intensive livestock grazing can negatively impact some elements of biodiversity. We quantified the effects of grazing management on bird occupancy over a 10-year period in patches of Australian endangered temperate woodland within paddocks subjected to one of three grazing regimes: continuous set stocking, rotational, and total livestock exclusion. Grazing may affect birds through altering resource availability, influencing vegetation structure, or affecting the occurrence of noisy miners (Manorina melanocephala), a native honeyeater that engages in interference competition with other birds.Using Bayesian generalized linear mixed models and multispecies occupancy modelling, we quantified relative and interactive effects on bird biodiversity of grazing, vegetation structure, and noisy miner occupancy. We found only muted grazing regime effects on woodland birds. However, many species responded to vegetation structure. Small invertivorous woodland birds responded positively to sapling abundance, and some (larger) species responded positively to the abundance of trees >50 cm. Furthermore, species richness increased with increased sapling abundance and trees >50 cm. The largest effects were associated with noisy miner occurrence, which drove reductions in small-bodied, invertivorous birds, effectively “swamping” the positive effects of vegetation attributes on these species.The profound impacts of noisy miners present challenges for bird conservation in woodland ecosystems, especially those subject to grazing. Management to reduce grazing pressure by domestic livestock may eventually help limit the impacts of the noisy miner, in part by facilitating natural regeneration of temperate woodlands to which small-bodied woodland birds respond positively.

PERAN TAMAN HUTAN HUJAN TROPIS INDONESIA TERHADAP IKLIM MIKRO (Studi Kasus di Taman Hutan Hujan Tropis Indonesia Kawasan Kantor Gubernur di Kota Banjarbaru Provinsi Kalimantan Selatan)

In line with the increasing population and the community's need for city facilities and infrastructure, urban development continues to increase. The paradigm of urban development should have changed and needs to be designed early towards the city with a better, more balanced way of life and still paying attention to environmental quality. The level of environmental comfort decreases as a result of the imbalance between built-up space and green open space (RTH) with the three main functions of urban vegetation being structural function, environmental function and visual function. RTH has a role in shaping the comfort of the urban climate through ecological functions, namely as a regulator of air temperature and humidity, so that it can be used as input in improving the quality of the microclimate by improving the quality of urban RTH so as to minimize the decline in environmental quality. The purpose of the study was to analyze the influence of vegetation structure and the role in improving the microclimate at each Tropical Rainforest Miniature RTH location in the Governor's Office area in Banjarbaru City. Banua Botanical Garden as a research site located in the Banjarbaru City Area, South Kalimantan Provincial Government Office Complex. The influence of vegetation structure on Location I which is dominated by lawns/grasses and shrubs with horizontal and columnar header shapes with low header density. Meanwhile, in Location II, the shape of the canopy is columnar and horizontal with a medium canopy density and has a tree height of 3-4 meters, slightly reducing the air temperature around the RTH. For Locations III and IV, they have a pyramid-shaped and spherical header shape that acts as a counterweight to increasing air humidity and decreasing air temperature. The role of the Tropical Rainforest Miniature RTH in the Governor's Office area in Banjarbaru City in improving the microclimate based on air temperature at locations I, II, III and IV, namely 30.1°C, 29.2°C, 28.0°C and 27.3°C. It can be seen that location III and location IV have the lowest temperature because they have characteristics of vegetation structures that can lower air temperature. For humidity parameters, it will adjust to air temperature conditions as well as wind speed will adjust to the vegetation structure in the RTH.

Effects of precipitation variation and trampling disturbance on seedling emergence of annual plants in a semi-arid grassland

Precipitation change and grazing are the main factors influencing vegetation structure and dynamics in semi-arid grassland. However, the effects of precipitation variation and livestock trampling on the seedling emergence patterns of plants remain largely unknown. In this study, an experiment with four gradients of trampling (no-trampling, light, moderate, and heavy) and three precipitation treatments (ambient precipitation, +30% precipitation, and −30% precipitation) was conducted to assess the effects of trampling disturbance and precipitation variation on seedling emergence of annual plants. The results showed that an increase in precipitation significantly improved total seedling emergence by 3.5–3.6 times and seedling density of grasses by more than 4.1 times under trampling conditions, while significantly improving total seedling emergence and density of forbs under no-trampling conditions. Moreover, +30% precipitation significantly improved the seedling proportion of grasses under light, moderate, and heavy trampling, while decreasing the seedling proportion of forbs. Seedling emergence of forbs was more sensitive to trampling disturbance, and seedling emergence of grasses was more sensitive to precipitation changes, especially under trampling conditions. Light and moderate trampling with a +30% precipitation increase promoted seedling emergence of grasses, and no trampling with a +30% precipitation increase improved seedling emergence of forbs. Thus, targeted grazing management measures should be implemented for plant communities dominated by either grasses or forbs under changing precipitation conditions.

Application of active acoustic transducers in monitoring and assessment of terrestrial ecosystem health—A review

AbstractUrbanization, agricultural production, natural resource extractions and climate change are global drivers of terrestrial ecosystem degradation and decline in ecosystem health. Assessing vegetation structures provides valuable direct and indirect information on biodiversity and ecosystem health, since plant communities govern terrestrial ecosystem functions and overall biodiversity.A growing body of literature supports the hypothesis that acoustic profiling and characterization of soundscapes may reveal natural patterns and ecosystem responses to environmental disturbances. Although assessments of ecosystem soundscapes are a promising tool for ecological monitoring, the influence of vegetation structure on acoustic indices remains largely unaddressed. An effective non‐invasive approach to monitoring ecosystem health includes use of active acoustic transducers, which convert mechanical/acoustic energy into electrical energy and visa‐versa.This article reviews and discusses possible applications (and also constraints) of active acoustic transducers in monitoring and assessments of terrestrial ecosystem health. Specifically, this article includes a brief introduction to the basic principles of sound and types of active acoustic transducers. Moreover, we provide reviews of common uses of active acoustic transducers in assessing plant structures and plant functional traits.We emphasize that active acoustic transducers can be used to analyse plant characteristics in a remote, scalable, non‐invasive and cost‐effective manner to characterize overall terrestrial ecosystem health. Suggestions and recommendations for future research and management directions that may facilitate applications of acoustic transducers to natural terrestrial landscapes are provided.

Influence of vegetation structure, seasonality, and soil properties on rodent diversi community assemblages in west Mount Kilimanjaro, Tanzania.

Rodent diversity and community assemblages are affected by several biotic and abiotic factors such as vegetation structure and seasonality. Vegetation structure particularly ground cover influences rodent diversity and community assemblages through provision of food resources and protection from predators. Such information is important for understanding species–habitat relationships for management and conservation. This study was conducted to determine the influence of vegetation structure, seasonality, and soil properties on species richness, abundance, community assemblages, and habitat association of rodents in west Mt Kilimanjaro. Rodent trapping was conducted using removal and capture–mark–recapture (CMR) methods with medium‐sized Sherman's live traps, snap, and Havarhart traps. Rodents were trapped during wet and dry seasons for three consecutive nights at 4 weeks intervals from April 2020 to March 2021. Environmental variables including vegetation structure, soil physical properties, and disturbance levels were recorded for each habitat type. Fourteen species of rodents were trapped in 25,956 trap nights. Rhabdomys pumilio, Praomys delectorum, and Lophuromys verhageni were the most dominant species across all habitats and seasons. L.verhageni occurred in all habitats while R.pumilio was restricted from occurring in montane forests. Moreover, species richness and abundance were influenced by habitat types, seasonality, soil type, and ground cover. Generally, both species richness and abundance were higher in fallows and montane forests and significantly lower in plantation forest and agricultural fields. In addition, rodent diversity was highest in fallows, followed by montane forests, and lowest in agricultural fields. Furthermore, rodents were associated with habitat types and vegetation structure forming two major community assemblages that significantly differed between habitats. Our study conclude that, community assemblages of rodents on Mt. Kilimanjaro were affected by functional spatial heterogeneity of the habitats occupied. Therefore, use of different habitats by rodents may be indicative of the landscape integrity and ecosystem changes based on species assemblages.

Vegetation structure and livestock grazing intensity affect ground-foraging birds in xerophytic forests of Central-East Argentina

Ground birds are strongly associated with the vegetation structure in natural environments under livestock grazing. Birds that fed on the ground may be the most affected by overgrazing, while those that fed on the shrub layer may respond positively to shrub encroachment in open xerophytic forest. Therefore, evaluating changes in bird species associated with a particular stratum can provide valuable information on the health, productivity, and functionality of the ecosystem. Here, we explore the relationships between vegetation structure and grazing intensity with the individual responses of terrestrial bird species in forests of Central-East Argentina. We tested the hypothesis that vegetation structure and grazing intensity affect the occupancy of 12 ground-foraging bird species. We used hierarchical single-species occupancy models with a Bayesian approach, considering points nested within farms, to estimate the influence of vegetation structure and grazing intensity on the bird occupancy. Vegetation structure variables were related to the occupancy of 11 out of 12 species. Three of these species also responded to grazing intensity. Occupancy of most open country bird species was favored by increasing grass cover but disfavored by increasing shrubs and tree density. Therefore overgrazing, with its consequent low grass cover, negatively affected the presence of open country bird species. On the other hand, occupancy of forest species was favored by either shrub or tree density or by forest age (larger diameter of trees at breast height - dbh). Based on specific responses of bird species, we propose that species directly related to grass cover and grazing intensity, such as the Spotted Nothura (Nothura maculosa), are potential indicator of low grazing intensity in forests of central-east Argentina. In turn, the Ultramarine Grosbeak (Cyanoloxia brissonii), a forest species associated with dense woody sites with high grazing intensity and low grass cover, could be a good indicator of overgrazing in these forests. Livestock management in these forests should promote environmental heterogeneity inside farms. Maintaining minimal livestock grazing in semi-open areas with mature trees and conserving areas of dense forest will be fundamental for achieving satisfactory compromises between the conservation of ground-foraging birds and livestock farming.

Looking up to the sky: using high resolution remote sensing to characterise hibernaculum locations of the Hazel Dormouse

The Hazel Dormouse is predominantly an arboreal species that moves down to the ground to hibernate in the autumn in temperate parts of its distributional ranges at locations not yet well understood. In this study, we tested whether environmental characteristics surrounding Hazel Dormouse hibernacula can be identified using high-resolution remote sensing and data collected in situ. We modelled remotely sensed variables, including canopy height and cover, topographic slope, sky view, solar radiation and cold air drainage around 83 dormouse hibernacula in England (n=62) and the Netherlands (n=21), and identified environmental characteristics that may be favoured by pre-hibernating dormice. We also collected and analysed data on leaf litter depth, temperature, canopy cover and distance to the nearest tree collected in situ at hibernaculum locations in England. We found that remotely sensed data were effective in identifying attributes surrounding the locations of dormouse hibernacula and, when compared to in situ information, provided more conclusive results. Our study suggests that remotely sensed topographic slope, canopy height and sky view have an influence on animals choosing suitable locations to hibernate; whilst in situ data suggested that average daily mean temperature at the hibernaculum may also have an effect. Remote sensing proved capable of identifying localised environmental characteristics in the wider landscape that may be important for hibernating dormice. We also propose that this method can provide a novel progression from habitat modelling to conservation management for the Hazel Dormouse, as well as other species using habitats where topography and vegetation structure influence fine-resolution favourability.

The influence of forest characteristics on avian species richness and functional diversity in Southern Mistbelt Forests of South Africa

Changes to natural environments as a consequence of human population growth are a major threat to biodiversity. Natural habitat modifications, changes in vegetation structure and habitat characteristics have resulted in decreased species richness and functional diversity in wildlife populations. Species’ distributions, abundance and persistence are generally reliant on habitat suitability, landscape configuration and ability to disperse and colonise habitats. We aimed to determine the influence of vegetation structure, patch size and isolation distance on avian communities in Southern Mistbelt Forests in the provinces of KwaZulu-Natal and Eastern Cape, South Africa, across a variety of forest patches during the breeding and non-breeding seasons. We conducted fixed-radius point-count surveys to determine avian species richness and functional diversity, and quantified the vegetation foliage profile in 54 distinct forest patches across three study areas. Multivariate analyses showed significant differences in vegetation structure among forest patches and subsequent variation in avian species richness and functional diversity across the study areas during the non-breeding season. Avian beta diversity was significantly driven by the reduction in forest patch size and habitat structural complexity. Reduction in forest size and complexity reduced avian species richness and functional diversity. Increasing isolation distance negatively influenced avian diversity. We recommend further improving the regulatory standards concerning sustainable utilisation of forest resources that subsequently change forest characteristics to promote a healthy and diverse habitat structure and safeguard avian communities.

The formation of "mega-flocks" depends on vegetation structure in montane coniferous forests of Taiwan.

A mixed‐species bird flock is a social assemblage where two or more bird species are moving together while foraging and might benefit from increased foraging efficiency and antipredator vigilance. A “mega‐flock,” which includes flocking species from different vegetation strata, often exhibits high species diversity. Mechanisms for the formation of mega‐flocks have not yet been explored. In this study, we evaluated the influence of vegetation structure and bird species diversity in driving the occurrence of mega‐flocks. We investigated the composition of mixed‐species flocks, local bird communities, and vegetation structure in five vegetation types of two high‐elevation sites in central Taiwan. Mega‐flocks occurred more frequently in pine woodland than later successional stages of coniferous forests. However, species richness/diversity of local bird communities increased along successional stages. Therefore, vegetation variables exhibit more influence on the occurrence of mega‐flocks than local bird communities. Besides foliage height diversity, understory coverage also showed positive effects on flock size of mixed‐species flocks. Our results indicated that pine woodlands with more evenly distributed vegetation layers could facilitate the interactions of canopy and understory flocks and increase the formation of mega‐flocks and thus the complexity of mixed‐species flocks.

Late Pleistocene shrub expansion preceded megafauna turnover and extinctions in eastern Beringia

The collapse of the steppe-tundra biome (mammoth steppe) at the end of the Pleistocene is used as an important example of top-down ecosystem cascades, where human hunting of keystone species led to profound changes in vegetation across high latitudes in the Northern Hemisphere. Alternatively, it is argued that this biome transformation occurred through a bottom-up process, where climate-driven expansion of shrub tundra (Betula, Salix spp.) replaced the steppe-tundra vegetation that grazing megafauna taxa relied on. In eastern Beringia, these differing hypotheses remain largely untested, in part because the precise timing and spatial pattern of Late Pleistocene shrub expansion remains poorly resolved. This uncertainty is caused by chronological ambiguity in many lake sediment records, which typically rely on radiocarbon (14C) dates from bulk sediment or aquatic macrofossils-materials that are known to overestimate the age of sediment layers. Here, we reexamine Late Pleistocene pollen records for which 14C dating of terrestrial macrofossils is available and augment these data with 14C dates from arctic ground-squirrel middens and plant macrofossils. Comparing these paleovegetation data with a database of published 14C dates from megafauna remains, we find the postglacial expansion of shrub tundra preceded the regional extinctions of horse (Equus spp.) and mammoth (Mammuthus primigenius) and began during a period when the frequency of 14C dates indicates large grazers were abundant. These results are not consistent with a model of top-down ecosystem cascades and support the hypothesis that climate-driven habitat loss preceded and contributed to turnover in mammal communities.

Disentangling direct and indirect effects of local temperature on abundance of mountain birds and implications for understanding global change impacts.

Unravelling the environmental factors driving species distribution and abundance is crucial in ecology and conservation. Both climatic and land cover factors are often used to describe species distribution/abundance, but their interrelations have been scarcely investigated. Climatic factors may indeed affect species both directly and indirectly, e.g., by influencing vegetation structure and composition. We aimed to disentangle the direct and indirect effects (via vegetation) of local temperature on bird abundance across a wide elevational gradient in the European Alps, ranging from montane forests to high-elevation open areas. In 2018, we surveyed birds by using point counts and collected fine-scale land cover and temperature data from 109 sampling points. We used structural equation modelling to estimate direct and indirect effects of local climate on bird abundance. We obtained a sufficient sample for 15 species, characterized by a broad variety of ecological requirements. For all species we found a significant indirect effect of local temperatures via vegetation on bird abundance. Direct effects of temperature were less common and were observed in seven woodland/shrubland species, including only mountain generalists; in these cases, local temperatures showed a positive effect, suggesting that on average our study area is likely colder than the thermal optimum of those species. The generalized occurrence of indirect temperature effects within our species set demonstrates the importance of considering both climate and land cover changes to obtain more reliable predictions of future species distribution/abundance. In fact, many species may be largely tracking suitable habitat rather than thermal niches, especially among homeotherm organisms like birds.

Patterns and determinants of lichen abundance and diversity across a subarctic to arctic latitudinal gradient

AbstractAimLichens are a major component of Arctic biodiversity. However, they appear vulnerable to climate change, as they are exposed to warmer temperatures and increased competition with vascular plants. Our study aims to evaluate lichen cover, species richness, functional diversity and community composition among the dominant vegetation types along a 640‐km latitudinal gradient, and to identify environmental determinants related to patterns in lichen communities.LocationFrom subarctic (56°N) to arctic (62°N) Nunavik (Québec, Canada).TaxonLichens.MethodsWe characterized macrolichen communities at the species level in 42 sites across a latitudinal gradient, and identified latitudinal trends in lichen cover, species richness and functional diversity. Using linear models and distance‐based redundancy analysis, we investigated the effect of climate, vegetation, topography and soil characteristics on lichen communities.ResultsLichen cover and species richness were the lowest at high latitudes, while functional diversity increased with increasing latitude. Vegetation types and surficial deposits were strongly related to lichen cover and richness. However, these factors did not influence functional diversity, which was mainly driven by climatic conditions.Main conclusionOur results highlight the importance of vegetation structure in lichen communities and corroborate the negative relationship between vascular plant abundance and lichen abundance and species richness. While we found no influence of vegetation structure on lichen functional diversity, further studies using targeted functional traits are needed to accurately investigate the impact of ongoing changes in northern vegetation on ecosystem functioning.