Species may “select” microsites via germination cues that predict future habitat quality. We investigated germination responses to light and temperature as drivers of species' associations with tree and litter cover in a guild of winter annuals in Western Australia. Species responded differently to experimental light and temperature treatments, but these responses did not explain their microsite associations in the field.

Abstract

Questions

Annual species have evolved sets of germination cues that are thought to be predictive of the post-germination environment. In naturally patchy environments, germination microsites often vary considerably in the amount of light they receive and in the diurnal temperature fluctuations they experience. However, whether species' differential germination responses to light and temperature are associated with their spatial patterns of occurrence remains largely untested.

Location

Mediterranean-climate woodlands in Southwest Western Australia.

Methods

We surveyed species' occurrences in annual plant communities in 150 quadrats across gradients of canopy cover and litter cover. Nineteen species recorded in this survey were then included in a germination experiment that manipulated (1) Light vs Dark (12 h light or continuous dark) approximating seeds near the soil surface vs those covered by litter and (2) Cold vs Warm temperature regimes (7/18°C and 7/24°C) approximating diurnal fluctuations experienced in shaded vs sun-exposed microsites, respectively.

Results

In the germination experiment, six species had highest germination probabilities in the Light treatment (regardless of temperature), five in Cold + Light, one in Warm + Light, two were indifferent to the treatments, and four did not germinate at all. Binomial linear mixed-effects models showed that species' maximum responses to light and temperature did not explain their spatial distributions along canopy cover and litter cover gradients, contrary to theoretical expectations of germination being a strong driver of species' occurrences.

Conclusions

Despite variation in species' responses to experimental treatments, no association was found with their field microsite associations. Germination strategies in our system were wider than expected for Mediterranean systems. Our results support that germination cues are not strong drivers of microhabitat associations in this system.

With a field experiment, we studied nitrogen deposition and climate warming impacts on planted tree seedlings and associated understory plants in clear-cuts and forest edges. Microenvironments were assessed, including soil properties and edge effects. Microenvironmental effects on plants were habitat dependent. Moderate climate warming may enhance tree seedling performance and plant cover in a clear-cuts of Pacific Northwest coastal ecosystems.

Abstract

Questions

Do nitrogen deposition and climate warming affect tree seedlings and plant communities in different habitats? In these habitats, how do microenvironments, including soil properties and, when applicable, edge effects relate to plant performance?

Location

The University of British Columbia Malcolm Knapp Research Forest, Maple Ridge, British Columbia, Canada.

Methods

We assessed performance of Pseudotsuga menziesii (Mirb.) Franco, Thuja plicata Donn ex D. Don and Tsuga heterophylla (Raf.) Sarg. planted tree seedlings and associated vascular plant communities. Performance of tree seedlings (height) and under vascular plant communities (percent cover) were examined in an experiment with warming (open-top chambers) and nitrogen deposition (ammonium nitrate applied at 10 kg N ha⁻¹ year⁻¹) treatments applied to subplots in six forest edges and six clear-cuts (N = 298 total subplots).

Results

In clear-cuts, tree seedling height increased with experimental warming and differed among species, and vascular plant cover increased with warming. In clear-cuts, species identity, not soil variables, was a strong predictor of height, and plant cover was negatively related to pH. In forest edges, edge position and some soil variables were related to height, but not plant cover. There were no interaction effects found between experimental nitrogen deposition and warming.

Conclusions

Our results suggest that moderate warming can enhance tree seedling height and understorey vascular plant cover in clear-cuts in Pacific Northwest coastal ecosystems, but low nitrogen deposition may not have an effect alone or synergistically with warming.

The interactive effects of altered fire regimes and biological invasions on biodiversity are still poorly known. Using experimental data, we show that the identity of invasive species played a stronger role as a driver of change of savanna communities in Brazil. Communities invaded by Melinis minutiflora gained more species and were more temporally variable than those invaded by Urochloa brizantha.

Abstract

Aim

Changes in fire regimes and biological invasions are major threats to tropical savannas. Fire is a key driver of community composition in these ecosystems and can be used as a management tool to control some invasive alien species, while being advantageous to native ones. However, we still do not fully comprehend the interactive effects of these threats on native plant communities. Here, we conducted an experiment in southeastern Brazil to investigate how variation in the composition of native communities invaded either by Melinis minutiflora or Urochloa brizantha is affected by fire in different seasons: early-dry season, mid-dry season and late-dry season in comparison to fire suppression.

Location

Itirapina, state of São Paulo, southeastern Brazil (22°14′07″S 47°53′07″W).

Results

The effects of fire seasons and invasive species were independent for species richness but interactive for species gains and losses. In general, the identity of the invasive species was a key factor driving community dynamics, with fire seasons playing a weaker role. Invaded communities changed gradually over time and the major changes happened over longer time lags. Communities invaded by M. minutiflora gained more species than those invaded by U. brizantha. Thus, communities invaded by M. minutiflora also had more variation in their species richness through time than those invaded by U. brizantha.

Conclusions

Although biological invasions and fire seasons interacted as drivers of change in native savanna communities, the identity of the invasive species played a stronger role. Communities invaded by M. minutiflora gained more species and were more variable than those invaded by U. brizantha.

Latitudinal patterns of plant diversity were studied in boreal peatlands. Vascular plant diversity decreased with latitude in fens, whereas moss diversity increased in bogs and fens. Community uniqueness decreased with latitude in both habitats. Taxonomic and functional composition were primarily structured by contrasting local conditions in bogs and fens, whereas climatic variations along the latitudinal gradient played a secondary role.

Abstract

Questions

The latitudinal biodiversity gradient; i.e., the increase in biodiversity towards the equator, is one of the most prominent biodiversity patterns. Nevertheless, many questions remain to be answered about the influence of multiple environmental factors on the latitudinal biodiversity gradient, especially for mosses, and the functional diversity of mosses and vascular plants. This study aims at evaluating the influence of latitude, climate, environmental variables, and habitat types (bog vs fen) on taxonomic and functional diversity (α-diversity and β-diversity) and the composition of vascular plant and moss species.

Location

49° N to 55° N in Northwestern Quebec, Canada.

Taxon

Mosses, vascular plants.

Methods

We used a database containing 376 phytosociological plots (400 m²) sampled in boreal peatlands located along a 600-km latitudinal gradient. We evaluated changes in α-diversity and β-diversity in response to latitude, longitude, climate, and local abiotic variables for both taxonomic groups using linear mixed effect models. We evaluated the effects of these variables on taxonomic and functional composition using variance partitioning by redundancy analysis.

Results

Moss diversity increased with latitude, although the effects were masked by environmental variables, whereas vascular plant diversity decreased with latitude in fens and did not vary with latitude in bogs. We observed a decrease in taxonomic and functional uniqueness with latitude. Moss and vascular plant taxonomic and functional composition were primarily structured by contrasting local conditions in bogs and fens, whereas climatic variations along the latitudinal gradient played a secondary role.

Conclusions

Our results highlight the contrasting biodiversity patterns in both peatland types and the importance of local habitat conditions in structuring vascular plant and moss diversity. These patterns varied depending on the diversity indicator used, as α- and β-diversity and functional and taxonomic diversity were often decoupled. Future studies should therefore include more than one diversity indicator and consider the differences between ecosystems and taxon groups.

In this study, we estimated spectral and functional diversity in a common framework encompassing all their multivariate components. Our findings indicate that spectral diversity accurately captures the functional structure of plant communities and approximates species patterns in the functional space. Furthermore, we showed the efficient approximation of functional diversity patterns by spectral diversity across spatial scales and along ecological gradients.

Abstract

Question

Remote sensing is a fundamental tool to monitor biodiversity and spectral diversity may represent a proxy for different biodiversity facets such as taxonomic (TD) and functional diversity (FD). We used fine-resolution multispectral imagery to explore spectral diversity (SD) patterns across spatial scales (i.e., plot, transect, area), and assess SD relationships with TD and FD along an environmental gradient.

Location

Coastal sand dune, Viareggio, Italy (“Migliarino–San Rossore–Massaciuccoli” Regional Park, 43°83′ N, 10°25′ E).

Methods

We measured TD as species richness, while SD and FD were computed using probability density functions based on pixel and species position in multivariate spaces. We compared SD and FD patterns in space occupation, and we tested whether these patterns are coordinated along the sea–inland gradient. We also assessed univariate relationships between SD and biodiversity facets, and we tested how these facets were partitioned across scales.

Results

We found a strong correspondence between functional and spectral patterns in space occupation and along the environmental gradient, with a lack of significance when considering TD. However, TD and SD showed higher variation at broader scale while most FD variation occurred at plot level.

Conclusion

By measuring FD and SD with a common methodological framework, we demonstrate that SD approximates functional patterns in plant communities. Moreover, we show that SD retrieved using high-resolution images can capture different aspects of FD, and that the occupation of the spectral space is analogous to the occupation of the functional space.

We studied the effects of hydrology and geomorphology for seed dispersal and environmental filtering on riparian vegetation. Riparian seed bank and vegetation contained different species, but we found no clear effect of hydrochory. Geomorphologically different sections (lakes, slow-flowing and rapid sections) were more similar to each other than expected, and differences in trait composition of seed bank and vegetation were mostly based on seed longevity.

Abstract

Question

Riparian vegetation and seed banks are the foundation of functional riparian zones, yet insight in the processes that explain their composition is limited. We tested three theories fundamental to dispersal and environmental filtering of riparian seed banks and vegetation. Combining these theories, we expected hydrochory to lead to increased species richness downstream in both soil seed bank and vegetation with accumulation restarting after a lake section, and geomorphological filtering to lead to higher similarity of seed bank and vegetation composition locally and within lakes, slow-flowing sections and rapids, respectively, than between them.

Location

Svartån, a free-flowing river in central Sweden.

Methods

We surveyed riparian vegetation and conducted a germination experiment on riparian soil seed bank cores from lakes, slow-flowing sections and rapids. We combined these with trait data on seed dispersal syndromes, floating capacity of seeds and seed longevity. We analysed differences throughout the system with linear models and between process domains with Kruskal–Wallis tests and similarity in community composition with the Horn–Morisita similarity index.

Results

Our results indicated that species richness did not increase downstream and was relatively similar throughout lakes, slow-flowing sections and rapids for both riparian seed banks and vegetation. Seed floating capacity was similar throughout these river sections, too, and seed longevity was higher in seed banks than in vegetation.

Conclusions

Geomorphology and hydrochory were not as important drivers in this area for riparian seed bank and vegetation composition as expected. In the area and on the scale studied here, other local and regional environmental factors and dispersal syndromes are more likely to be determinants of riparian dynamics and composition. Continued studies of riparian seed banks can help improve our understanding of riparian composition and functioning in the future.

We identified three types of swamp forests across the flood-plains of the Caquetá River: permanent várzea, oxandrales and cananguchales. These forests showed successional patterns dissociated from their position relative to the main river channel. Still, they seemed more influenced by the interaction of floodings, sediment and nutrients input from white-water and/or black-water rivers, and peat accumulation.

Abstract

Questions

The fluvial dynamics of meandering white-water rivers of Amazonia drive vegetation primary succession. Directional successional processes have been recorded for the seasonal várzea forests that occupy well-drained soils on levees and point bars across the spatial gradient of the flood-plains. However, the types of forests occupying the swampy depressions interspersed between the point bars and their distribution along the flood-plain's spatial gradient are poorly understood. Here, we aimed to unravel the spatial patterns of swamp forests along the sequence defined by an axis perpendicular to the river and the relationship with edaphic and spatial factors.

Location

The flood-plains of the middle Caquetá River basin, Colombian Amazonia.

Methods

Forest types were identified by cluster analysis performed on 42 square plots (33 m × 33 m) set in poorly drained depressions of the flood-plain. Floristic composition and vegetation structure as response data, and edaphic and spatial variables as predictors, were analyzed through partial redundancy analysis (pRDA). The effect of geographic position was included by using the first two axes of a principal coordinates of neighbor matrix analysis as conditional factors in the pRDA.

Results

The three identified swamp forest types were not arranged along a directional spatial pattern. Permanent várzea forests, closest to the river, showed the greatest diversity and alluvial sediment input. Oxandrales, furthest from the river, dominated by Oxandra polyantha, showed the greatest tree density, basal area and soil sand content, and received additional flooding from black-water streams. Cananguchales, dominated by Mauritia flexuosa, exhibited the highest dominance and soil organic matter layer thickness. Distribution of the permanent várzea and oxandrales was relatively constrained by the distance to the river, whereas that of the cananguchales was not.

Conclusions

Flooding dynamics delay vegetation development of the swamp forests in permanent várzea and oxandrales. Cananguchales keep accumulating organic matter, becoming ombrotrophic peats after isolation from the river flooding influence. The swamp forests across these flood-plains are far from being arranged along a linear sequence.

This experimental study examines the changes in leaf functional traits in grassland species with different resource-use strategies along a soil phosphorus gradient. Findings indicate that within species there was a more acquisitive trait expression with increased phosphorus and more conservative with increased community biomass. Interestingly, the trait responses were generally consistent for species representing very different resource-use strategies and growth forms. The pictures show four species mixtures before trait measurements and harvest (May 2020).

Abstract

Questions

Increased soil phosphorus (P) availability in fertilized grasslands can drive both community degradation and delayed community recovery upon agricultural abandonment. Beyond describing grassland community patterns along gradients in P availability, it remains unclear how individual species with different strategies respond to increasing phosphorus. Here we studied intraspecific variability of leaf functional traits in response to soil phosphorus, for species with contrasting resource-use strategies.

Methods

We set up a pot experiment with communities containing four species, assembled from a pool of 20 mesotrophic grassland species growing along a soil P gradient. Species selection included various growth forms (grasses vs forbs) and resource-use strategies (acquisitive vs conservative resource use). We measured three variables characterizing the (a)biotic environmental context: bioavailable soil P concentration, total community biomass as a proxy for the intensity of competition, and the proportional biomass of a species in the community as a proxy for its competitive dominance. We investigated the effect of this environmental context on the expression of two leaf traits, specific leaf area (SLA) and leaf dry matter content (LDMC).

Results

We found an acquisitive trait expression within species (increase in SLA and decrease in LDMC) in response to increased soil P supply and a conservative trait expression (decrease in SLA and increase in LDMC) in response to an increase in total community biomass. Importantly, the trait responses to the environmental context were generally consistent for species representing very different resource-use strategies and growth forms.

Conclusions

Species responded with a shift from an acquisitive to a conservative trait expression in response to limited resources; i.e., driven by a decrease in soil phosphorus concentration or an increase in total community biomass. Unexpectedly, the intraspecific variability in response to the changing environmental conditions was not clearly mediated by the species’ strategy. These findings show that plant ecological strategies are probably not the main driver for intraspecific trait variability in an experimental grassland community.

Because of a lack of field data, ontogenetic patterns of herbaceous climbers like germination site and changes in root/shoot connection with the soil remain unclear. We provide rare quantitative data regarding this aspect and species richness and abundance in a tropical lowland forest. Few species fall neatly in the so far applied categories of vines, nomadic vines and hemiepiphytes.

Abstract

Background

In contrast to woody climbers, information on community composition or vertical extension within the forest is scarce for herbaceous climbers, even in well-studied field sites like Barro Colorado Island. Moreover, questions regarding ontogenetic patterns (site of germination, changes in root/shoot connection with the soil) are unresolved because of a lack of field data.

Location

Barro Colorado Island, Panama.

Methods

In 17 plots of 400 m² each, which were distributed all over the island, we recorded all potential hosts (trees, palms, lianas) with a diameter at breast height larger than 1 cm, and all climbing aroids attached to them. For aroids, we recorded species identity, number of shoots, root connections to the ground, and vertical shoot extension. By distinguishing three size classes for each species in our analyses we deduced the site of germination and ontogenetic changes in the root/shoot connection with the soil.

Results

Only 16% of all potential hosts were occupied by climbing aroids. We recorded 1196 individuals of 17 species. Aroids preferred larger trees and old-growth forest. Species differed strongly in vertical distribution. Hemiepiphytic species germinate epiphytically, often high up in tree crowns and later establish root contact with the soil, while the majority of species establish on or close to the ground and reach moderate heights of 5–15 m (forest height ca. 35 m). In all of these species, we observed dieback of the proximal portion of the shoot to a varying extent but contact with the soil was invariably retained via adventitious roots.

Conclusions

We provide rare quantitative data on species richness and abundance of herbaceous climbers in a tropical lowland forest. Few species fall neatly into the categories of vines, nomadic vines and hemiepiphytes. This highlights the need for longitudinal observational and experimental studies to resolve the current debate on the appropriate grouping of these climbers.

We investigated the variation of soil microclimate in time and space in a relict alpine system of northern Spain. Spatial microclimatic variation in one year was higher than in 10 years of microclimate monitoring in permanent plots, supporting the buffer effect of topography in alpine landscapes. Protected sites with relatively longer snow cover are key microclimatic refugia for preventing local extinctions.

Abstract

Questions

In alpine landscapes, topography creates a mosaic of microclimatic niches that might prevent local extinctions, but the influence of this spatial heterogeneity on plant communities is largely unknown. Here we ask (1) how soil microclimatic variation is comparable at temporal and spatial scales, and (2) how such variation influences species composition and local extinctions in relict alpine communities.

Location

Picos de Europa National Park, northern Spain.

Methods

We resurveyed permanent plots in four alpine sites following the recording of soil temperatures (temporal survey) for 10 years. We then sampled the spatial variation in species composition and microclimatic temperatures in 80 plots around the permanent plots (spatial survey). We evaluated the variation of six microclimatic indices between the temporal and the spatial surveys, and calculated the temporal trends observed in species cover. We finally predicted local extinction rates under microclimatic scenarios based on the observed microclimate–community relations.

Results

Despite high interannual variation, we found a 10-year trend of temperature warming on (microridge) fellfields and (microvalley) snowbeds. Microclimatic variation was larger in space than in time, with little temperature variation in snowbeds and extreme low temperatures recorded in fellfields. Species composition was mainly influenced by growing degree days (GDD) and freezing degree days (FDD), which were both related to snow cover duration. Plant cover of 16 species (out of 36 frequent species) showed significant responses to microclimatic variation. Local extinctions were mainly predicted under relatively hotter and more freezing conditions.

Conclusions

Our results support the idea that microclimatic spatial heterogeneity can reduce the negative influence of climate change on alpine plant communities. However, a continuous reduction of snow cover will result in a tipping point beyond which the buffer effect of this spatial heterogeneity will not be effective in protected microsites, leading to community homogenization. This process may have started in relict alpine communities where species from snowy microclimates are being outcompeted by species adapted to below-zero winter temperatures.