Plant functional types (PFT) are increasingly used to outline biome-scale plant–environment relationship and predict global change effects on community structure. However, the potentials and ...limitations of the PFT approach have to be tested as they can be less sensitive than trait-based or species-level approaches. Here, we compare the responses of deciduous-evergreen shrub PFTs and species to gradual snow-related environmental conditions by also considering effects of aboveground architectural traits and neighboring shrubs. Five deciduous species and four evergreen dwarf shrub species were transplanted to be exposed to four levels of winter snow cover across mesotopographic gradients in northern Fennoscandian tundra. The survival and growth of individually tagged shoots were monitored over one year, and the change in cover of shrubs was monitored over four years. Evergreen species showed higher resistance to environmental severity and generally benefitted from higher abundance of neighboring shrubs. Deciduous species exhibited negligible to drastic responses to snow thickness and neighboring shrubs tended to have a negative effect on their performance and survival. Tall shoots of deciduous shrubs survived poorly under the thinnest snow cover. Overall, deciduous and evergreen PFTs showed modest differences in their performances along the gradient. Our results show that deciduous-evergreen leaf phenology categories predict shrub responses to changing environmental conditions only to a limited extent. Our findings highlight strong species-specific responses especially among deciduous shrubs, and a differential role of plant-plant interactions for shrubs. Our results emphasize that distribution patterns of arctic-alpine shrubs and shrub community responses to altered snow regimes depend on species-level plant functional attributes, species interactions and species-specific sensitivities to environmental severity.
For most experimental studies the short-term responses to manipulation often differ from the long-term changes in the community composition, dynamics or functioning. Such discrepancy limits the ...translation of experimental results into key ecological topics such as global environmental change.
Here we analyzed plant community dynamics from a 23-year transplant experiment in the Fennoscandian mountain tundra and explored how well the pattern of responses over the first 12 years of the experiment can predict longer-term changes. Sod-blocks of tundra heath vegetation were transplanted to a snowbed 150 m higher in elevation from their origin, where, with contrasting levels of soil wetness, half of the transplants were protected from mammalian herbivores. Throughout the experiment, community changes strongly depended on both plant functional types and experimental treatments. The first 12 years were characterized by a response to transplantation to the snowbed showing a strong increase of graminoid and a decrease of shrub abundances in the transplants. In the longer term, the community divergence increased in particular in response to grazing and soil wetness within the snowbed, while graminoid dominance disappeared. Markov chain models captured the main trends during the first 12 years but they failed to predict their relative abundance after 23 years. In particular, the late dominance of bryophytes in the wet snowbed, the recovery of shrubs in the dry exclosures, and the subordinate status of graminoids deviated from the extrapolation based on the medium-term trends.
Despite clear community dynamical trajectories detected in the first decade, the differences in the temporal scale of both treatment effects and plant functional type responses limited their ability to extrapolate longer-term trajectories. We find that increasing focus on long-term experiments is a crucial step to understanding the processes involved in the response of plant communities to global environmental change.
Experimental evidence shows that site fertility is a key modulator underlying plant community changes under climate change. Communities on fertile sites, with species having fast dynamics, have been ...found to react more strongly to climate change than communities on infertile sites with slow dynamics. However, it is still unclear whether this generally applies to high‐latitude plant communities in natural environments at broad spatial scales. We tested a hypothesis that vegetation of fertile sites experiences greater changes over several decades and thus would be more responsive under contemporary climate change compared to infertile sites that are expected to show more resistance. We resurveyed understorey communities (vascular plants, bryophytes, and lichens) of four infertile and four fertile forest sites along a latitudinal bioclimatic gradient. Sites had remained outside direct human disturbance. We analyzed the magnitude of temporal community turnover, changes in the abundances of plant morphological groups and strategy classes, and changes in species diversity. In agreement with our hypothesis, temporal turnover of communities was consistently greater on fertile sites compared to infertile sites. However, our results suggest that the larger turnover of fertile communities is not primarily related to the direct effects of climatic warming. Furthermore, community changes in both fertile and infertile sites showed remarkable variation in terms of shares of plant functional groups and strategy classes and measures of species diversity. This further emphasizes the essential role of baseline environmental conditions and nonclimatic drivers underlying vegetation changes. Our results show that site fertility is a key determinant of the overall rate of high‐latitude vegetation changes but the composition of plant communities in different ecological contexts is variously impacted by nonclimatic drivers over time.
Our results show that temporal vegetation turnover is larger on fertile than on infertile forest sites. However, the results suggest that the observed turnover is not primarily related to the direct effects of warmer climate. Compositional changes resulting in the larger turnover vary in different ecological contexts and are influenced by various nonclimatic drivers.
Many terrestrial endotherm food webs constitute three trophic level cascades. Others have two trophic level dynamics (food limited herbivores; plants adapted to tackle intense herbivory) or one ...trophic level dynamic (herbivorous endotherms absent, thus plants compete for the few places where they can survive and grow). According to the Exploitation Ecosystems Hypothesis (EEH), these contrasting dynamics are consequences of differences in primary productivity. The productivity thresholds for changing food web dynamics were assumed to be global constants. We challenged this assumption and found that several model parameters are sensitive to the contrast between persistently warm and seasonally cold climates. In persistently warm environments, three trophic level dynamics can be expected to prevail almost everywhere, save the most extreme deserts. We revised EEH accordingly and tested it by compiling direct evidence of three and two trophic level dynamics and by studying the global distribution of felids. In seasonally cold environments, we found evidence for three trophic level dynamics only in productive ecosystems, while evidence for two trophic level dynamics appeared in ecosystems with low primary productivity. In persistently warm environments, we found evidence for three trophic level dynamics in all types of ecosystems. The distribution of felids corroborated these results. The empirical evidence thus indicates that two trophic level dynamics, as defined by EEH, are restricted to seasonally cold biomes with low primary productivity, such as the artic–alpine tundra and the temperate steppe.
Disturbances related to geomorphological processes are frequent, widespread and often intense at high latitudes and altitudes, affecting the fine-scale distribution of many plant species. While the ...inclusion of physical disturbances into models of species geographic ranges is widely recommended, no studies have yet tested the utility of field-quantified geomorphological disturbances for terrestrial species distribution modelling. Here we apply generalized additive models and boosted regression trees to examine if the explicit inclusion of terrestrial and fluvial geomorphological variables alters species distribution models for 154 vascular plant, bryophyte and lichen species in north European mountain tundra. The inclusion of these disturbances significantly improved both the explanatory and predictive power of distribution models, with consistent results for all three species groups. Spatial distribution predictions changed considerably for some species after the inclusion of disturbance variables, with fluvial disturbances generating strongly linear features for species influenced by erosion or sediment deposition. As a consequence, models incorporating geomorphological variables produced markedly more refined distribution maps than simpler models. Predictions of species distributions will thus benefit strongly from the inclusion of fine-scale geomorphological variables, particularly in areas of active earth surface processes, enabling more accurate forecasting of future species ranges under changing conditions.
Anthropogenic nutrient enrichment and shifts in herbivory can lead to dramatic changes in the composition and diversity of aboveground plant communities. In turn, this can alter seed banks in the ...soil, which are cryptic reservoirs of plant diversity. Here, we use data from seven Nutrient Network grassland sites on four continents, encompassing a range of climatic and environmental conditions, to test the joint effects of fertilization and aboveground mammalian herbivory on seed banks and on the similarity between aboveground plant communities and seed banks. We find that fertilization decreases plant species richness and diversity in seed banks, and homogenizes composition between aboveground and seed bank communities. Fertilization increases seed bank abundance especially in the presence of herbivores, while this effect is smaller in the absence of herbivores. Our findings highlight that nutrient enrichment can weaken a diversity maintaining mechanism in grasslands, and that herbivory needs to be considered when assessing nutrient enrichment effects on seed bank abundance.
The importance of microclimate conditions is becoming increasingly recognised in ecological research, especially as they can differ widely from macro‐ and mesoclimate. Effective measurement of ...microclimate variability in heterogeneous field conditions requires measurements from a large number of sensors, ideally sampling across both small and large scales, which necessitates the development of cost‐effective sensor networks.
Here, we develop an environmental microcontroller (
EMU
) sensor network for measuring soil moisture and temperature with high spatiotemporal coverage. The system can easily be implemented in larger or smaller setups, though our study consisted of 40 plots distributed across 4 sites in northern Lapland. Using 40
EMUs
, each equipped with 10 soil temperature and 10 soil moisture sensors, we collected roughly 3.5 million unique soil temperature and moisture records over the course of about 2 months. We then compared these measurements to those from commercial temperature sensors (
iButtons
) and
TDR
soil moisture probes.
We show that our sensor network is able to successfully characterise microclimate variation at the site, plot and within‐plot scales with high accuracy and good reliability. Moreover, even including development costs, the total price per
EMU
unit was less than €100, yielding a much cheaper and higher resolution system than is currently available from commercial producers. For both temperature and soil moisture, we found a strong relationship between the sensor network measurement and those obtained from commercial systems. Roughly 10% of the overall spatial variation in temperature and moisture occurred within plots—that is. over the scale of 25–50 cm.
Our results show that accurate measurements of microclimate soil temperature and soil moisture can be obtained using low‐cost sensor networks. We also show that microclimate variability at small scales can make up a considerable fraction of total environmental variability. To this end, we discuss some of the difficulties encountered during the development process and suggest possible improvements for further studies. While the sensor network described here can be applied without any modifications for quantifying topsoil conditions, we note that with minor changes to our code and hardware, the system can be customised for other kinds of measurements.
The degree to which different taxonomic groups show congruence in diversity patterns has attracted increased attention, yet such studies on stream biota are lacking. We examined environmental ...correlates of and congruence in the species richness patterns of bryophytes, macroinvertebrates, and fish in 101 boreal streams in Finland. Congruence in species richness among the taxonomic groups was generally low, mainly because of their differing responses to major environmental gradients. Bryophytes and macroinvertebrates showed the strongest degree of congruence, but even this relationship had a relatively weak predictive power. Bryophyte diversity showed the strongest relationship with water colour, followed by habitat stability, and stream size. Macroinvertebrate diversity increased with stream size, and further variation was accounted for by water colour and acidity. Fish species richness showed a weak and complex relationship with geographical location, stream size, and in-stream habitat characteristics. The regression models explained 23, 45, and 26% of the variation in species richness of bryophytes, macroinvertebrates, and fish, respectively. Our results suggest that indicator taxa may be of limited value in stream biodiversity inventories. Habitat-based approaches are suggested as an alternative surrogate measure in the conservation evaluation of lotic biodiversity.PUBLICATION ABSTRACT
Biotic and abiotic factors interact with dominant plants—the locally most frequent or with the largest coverage—and nondominant plants differently, partially because dominant plants modify the ...environment where nondominant plants grow. For instance, if dominant plants compete strongly, they will deplete most resources, forcing nondominant plants into a narrower niche space. Conversely, if dominant plants are constrained by the environment, they might not exhaust available resources but instead may ameliorate environmental stressors that usually limit nondominants. Hence, the nature of interactions among nondominant species could be modified by dominant species. Furthermore, these differences could translate into a disparity in the phylogenetic relatedness among dominants compared to the relatedness among nondominants. By estimating phylogenetic dispersion in 78 grasslands across five continents, we found that dominant species were clustered (e.g., co‐dominant grasses), suggesting dominant species are likely organized by environmental filtering, and that nondominant species were either randomly assembled or overdispersed. Traits showed similar trends for those sites (<50%) with sufficient trait data. Furthermore, several lineages scattered in the phylogeny had more nondominant species than expected at random, suggesting that traits common in nondominants are phylogenetically conserved and have evolved multiple times. We also explored environmental drivers of the dominant/nondominant disparity. We found different assembly patterns for dominants and nondominants, consistent with asymmetries in assembly mechanisms. Among the different postulated mechanisms, our results suggest two complementary hypotheses seldom explored: (1) Nondominant species include lineages adapted to thrive in the environment generated by dominant species. (2) Even when dominant species reduce resources to nondominant ones, dominant species could have a stronger positive effect on some nondominants by ameliorating environmental stressors affecting them, than by depleting resources and increasing the environmental stress to those nondominants. These results show that the dominant/nondominant asymmetry has ecological and evolutionary consequences fundamental to understand plant communities.
We found a prevalent disparity between the dominant and nondominant species (measured as the standardized effect size of the mean nearest taxonomic distance), with the former more clustered than the latter, suggesting a disparity in the mechanisms organizing both groups. We also found several clades more likely to have nondominant species than dominant species, measured as the probability of finding a species of a given clade among the third less abundant species in the sites where that clade occurred. Unexpectedly, many nondominant clades have a large number of species, mainly were comprised of nonwoody species, and often appeared in the phylogeny. Together, these findings suggest dominance and nondominance are conserved and that their differences have ecological consequences.
The degree to which different taxonomic groups show congruence in diversity patterns has attracted increased attention, yet such studies on stream biota are lacking. We examined environmental ...correlates of and congruence in the species richness patterns of bryophytes, macroinvertebrates, and fish in 101 boreal streams in Finland. Congruence in species richness among the taxonomic groups was generally low, mainly because of their differing responses to major environmental gradients. Bryophytes and macroinvertebrates showed the strongest degree of congruence, but even this relationship had a relatively weak predictive power. Bryophyte diversity showed the strongest relationship with water colour, followed by habitat stability, and stream size. Macroinvertebrate diversity increased with stream size, and further variation was accounted for by water colour and acidity. Fish species richness showed a weak and complex relationship with geographical location, stream size, and in-stream habitat characteristics. The regression models explained 23, 45, and 26% of the variation in species richness of bryophytes, macroinvertebrates, and fish, respectively. Our results suggest that indicator taxa may be of limited value in stream biodiversity inventories. Habitat-based approaches are suggested as an alternative surrogate measure in the conservation evaluation of lotic biodiversity.
PDF
