Vegetation changes in Jasper National Park assessed from resampling of ecological land classification plots established in the 1970s

Twenty stands of uniform, mature, undisturbed Pseudotsuga menziesii var. glauca forest were selected in Banff and Jasper National Parks, using a combination of airphoto and ground surveys. Quantitative sampling methods were used to describe their floristic composition, vegetation structure, and physical habitats.Scattered trees of Pinus contorta, Picea glauca, and Populus tremuloides occurred in the Pseudotsuga forests. The poorly developed shrub strata contained Shepherdia canadensis, Rosa acicularis, Spiraea lucida, Juniperus communis. Major herb, dwarf shrub, bryophyte, and lichen species were Elymus innovatus, Calamagrostis rubescens, Fragaria virginiana, Astragalus decumbens, Aster conspicuus; Arctostaphylos uva-ursi, Linnaea borealis; Hylocomium splendens, Abietinella abietina, Tortula ruralis; Peltigera canina. A cyclical pattern of vegetation change is related to the death, replacement, and maturation of Pseudotsuga trees.Relations between vegetation and physical habitat were analyzed by simple correlation and multiple regression. Available potassium in soil, stand age, and slope exposure were most influential in regression equations for tree stratum development. Understory strata were primarily correlated with tree stratum development.A two-dimensional stand ordination based on the vegetational similarity of subordinate vascular strata showed a pronounced separation of Banff and Jasper Pseudotsuga forests, and prompted recognition of two new climax associations (sensu Daubenmire): Pseudotsuga / Elymus innovatus in Jasper; Pseudotsuga / Calamagrostis rubescens – Elymus innovatus in Banff. Habitat differences between the two associations include macroclimate, parent materials, and soil moisture.

Fire and herbivory are important determinants of nutrient availability in savanna ecosystems. Fire and herbivory effects on the nutritive quality of savanna vegetation can occur directly, independent of changes in the plant community, or indirectly, via effects on the plant community. Indirect effects can be further subdivided into those occurring because of changes in plant species composition or plant abundance (i.e., quality versus quantity). We studied relationships between fire, herbivory, rainfall, soil fertility, and leaf nitrogen (N), phosphorus (P), and sodium (Na) at 30 sites inside and outside of Serengeti National Park. Using structural equation modeling, we asked whether fire and herbivory influences were largely direct or indirect and how their signs and strengths differed within the context of natural savanna processes. Herbivory was associated with enhanced leaf N and P through changes in plant biomass and community composition. Fire was associated with reduced leaf nutrient concentrations through changes in plant community composition. Additionally, fire had direct positive effects on Na and nonlinear direct effects on P that partially mitigated the indirect negative effects. Key mechanisms by which fire reduced plant nutritive quality were through reductions of Na‐rich grasses and increased abundance of Themeda triandra, which had below‐average leaf nutrients.

Fire and herbivory are important determinants of nutrient availability in savanna ecosystems. Fire and herbivory effects on the nutritive quality of savanna vegetation can occur directly, independent of changes in the plant community, or indirectly, via effects on the plant community. Indirect effects can be further subdivided into those occurring because of changes in plant species composition or plant abundance (i.e., quality versus quantity). We studied relationships between fire, herbivory, rainfall, soil fertility, and leaf nitrogen (N), phosphorus (P), and sodium (Na) at 30 sites inside and outside of Serengeti National Park. Using structural equation modeling, we asked whether fire and herbivory influences were largely direct or indirect and how their signs and strengths differed within the context of natural savanna processes. Herbivory was associated with enhanced leaf N and P through changes in plant biomass and community composition. Fire was associated with reduced leaf nutrient concentrations through changes in plant community composition. Additionally, fire had direct positive effects on Na and nonlinear direct effects on P that partially mitigated the indirect negative effects. Key mechanisms by which fire reduced plant nutritive quality were through reductions of Na-rich grasses and increased abundance of Themeda triandra, which had below-average leaf nutrients.

Abiotic soil properties, plant community composition, and herbivory all have been reported as important factors influencing the composition of soil communities. However, most studies thus far have considered these factors in isolation, whereas they strongly interact in the field. Here, we study how grazing by vertebrate herbivores influences the soil nematode community composition of a floodplain grassland while we account for effects of grazing on plant community composition and abiotic soil properties. Nematodes are the most ubiquitous invertebrates in the soil. They include a variety of feeding types, ranging from microbial feeders to herbivores and carnivores, and they perform key functions in soil food webs. Our hypothesis was that grazing affects nematode community structure and composition through altering plant community structure and composition. Alternatively, we tested whether the effects of grazing may, directly or indirectly, run via changes in soil abiotic properties. We used a long-term field experiment containing plots with and without vertebrate grazers (cattle and rabbits). We compared plant and nematode community structure and composition, as well as a number of key soil abiotic properties, and we applied structural equation modeling to investigate four possible pathways by which grazing may change nematode community composition. Aboveground grazing increased plant species richness and reduced both plant and nematode community heterogeneity. There was a positive relationship between plant and nematode diversity indices. Grazing decreased the number of bacterial-feeding nematodes, indicating that in these grasslands, top-down control of plant production by grazing leads to bottom-up control in the basal part of the bacterial channel of the soil food web. According to the structural equation model, grazing had a strong effect on soil abiotic properties and plant community composition, whereas plant community composition was the main determinant of nematode community composition. Other pathways, which assumed that grazing influenced nematode community composition by inducing changes in soil abiotic properties, did not significantly explain variation in nematode community composition. We conclude that grazing-induced changes in nematode community composition mainly operated via changes in plant community composition. Influences of vertebrate grazers on soil nematodes through modification of abiotic soil properties were of less importance.

Background and aims Re-introduction of large grazers in the few remaining natural and semi-natural grasslands are thought to be an effective management tool to prevent dominance of late successional plant species and restoration of plant biodiversity. The main objective of this study was to test whether the introduction of large herbivores retard the succession by reducing the abundance of highly competitive tall species and whether it is accompanied with changes in plant community composition and spatial distribution of plant species. Methods In order to test this hypothesis, we studied the effect of grazing by large herbivores on vegetation at three hierarchical levels: individual plant species, emergent groups of functionally similar herbaceous plant species, and the main gradients of plant community composition. Study sites were thirteen spatially separated, dry coastal dune grasslands in western Belgium and north-western France. Key results Grazing had a predominantly negative effect on high competitive dominant species and led to changes in composition of emergent groups toward less competitive plant species. Additionally, these changes in plant community composition were accompanied with changes in spatial distribution patterns of individual plant species and community richness. Conclusions Our results suggest that the current grazing management applied in these nature reserves is able to prevent the expansion of dominant highly competitive species and establishment of functionally different plant species.

Biodiversity loss and changes in plant community composition induced by anthropogenic nitrogen (N) deposition exert profound effects on ecosystem functions. However, limited studies have considered the joint effects of plant community composition, plant species richness, plant functional diversity and soil biodiversity on the dynamics of soil autotrophic and heterotrophic respiration under extra N input. We addressed this issue by conducting a multilevel N‐manipulation experiment in a Tibetan alpine steppe. Based on soil respiration observations as well as biotic and abiotic measurements under this N addition experiment, we quantified the relative and interactive effects of above‐/below‐ground biodiversity, plant community composition and other explanatory variables (environmental factors, plant and microbial properties) on autotrophic and heterotrophic respiration. Our results showed that the effects of N enrichment via plant productivity, root amount, the proportion of sedge biomass and plant functional diversity explained 71% of the N‐induced variations in autotrophic respiration. With regard to heterotrophic respiration, the combination of N addition, soil pH, plant functional diversity and soil biota diversity accounted for 78% of its variations along the N addition gradient. Further analyses showed that above‐/below‐ground diversity loss and changes in plant community composition explained similar variation to that contributed by other factors in both autotrophic and heterotrophic respiration. The declined plant functional diversity and the increased proportion of sedge biomass promoted autotrophic respiration. Conversely, the loss of soil biodiversity together with the decreased plant functional diversity led to the decline of heterotrophic respiration along the experimental N gradient. Our results highlight that the indirect regulation of N input on ecosystem function through changes in plant community composition and above‐/below‐ground biodiversity loss should be considered for better understanding the responses of terrestrial ecosystems to atmospheric N deposition. A free Plain Language Summary can be found within the Supporting Information of this article.

Traditional approaches to ecological land classification (ELC) can be enhanced by integrating, a priori, data describing disturbances (natural and human), in addition to the usual vegetation, climate, and physical environment data. To develop this new ELC model, we studied an area of about 175,000 km2 in the Abies balsamea–Betula papyrifera and Picea mariana-feathermoss bioclimatic domains of the boreal forest of Quebec, in eastern Canada. Forest inventory plots and maps produced by the Ministere des Ressources naturelles du Quebec from 1970 to 2000 were used to characterize 606 ecological districts (average area 200 km2) according to three vegetation themes (tree species, forest types, and potential vegetation-successional stages) and four sets of explanatory variables (climate, physical environment, natural and human disturbances). Redundancy, cluster (K-means) and variation partitioning analyses were used to delineate, describe, and compare homogeneous vegetation landscapes. The resulting ELC is hierarchical with three levels of observation. Among the 14 homogeneous landscapes composing the most detailed level, some are dominated by relatively young forests originating from fires dating back to the period centered on 1921. In others, forest stands are older (fires from the period centered on 1851), some are under the influence of insect outbreaks and fires (southern part), while the rest are strongly affected by human activities and Populus tremuloides expansion. For all the study area and for parts of it, partitioning reveals that natural disturbance is the dominant data set explaining spatial variation in vegetation. However, the combination of natural disturbances, climate, physical environment and human disturbances always explains a high proportion of variation. Our approach, called “ecological land classification of homogeneous vegetation landscapes”, is more comprehensive than previous ELCs in that it combines the concepts and goals of both landscape ecology and ecosystem-based management.

Question: How strong are climate warming-driven changes within mid-elevation forest communities? Observations of plant community change within temperate mountain forest ecosystems in response to recent warming are scarce in comparison to high-elevation alpine and nival ecosystems, perhaps reflecting the confounding influence of forest stand dynamics. Location: Jura Mountains (France and Switzerland). Methods: We assessed changes in plant community composition by surveying 154 Abies alba forest vegetation releves (550-1,350 m a.s.l.) in 1989 and 2007. Over this period, temperatures increased while precipitation did not change. Correspondence analysis (CA) and ecological indicator values were used to measure changes in plant community composition. Releves in even- and uneven-aged stands were analysed separately to determine the influence of forest stand dynamics. We also analysed changes in species distribution to detect shifts along the elevation gradient by focusing on the lowest, central and highest positions of lowland and mountain species altitudinal ranges. Results: We found significant shifts along the first CA axis, which reflected a change in plant community composition towards a greater frequency of lowland species. Analyses of ecological indicator values indicated increases in temperature and light availability in A. alba stands, particularly in even-aged stands. However, no major changes in overall species distribution were found. Conclusions: The community-level changes are consistent with effects of climate warming and local stand dynamics. Changes in species distribution were small in comparison to observed local temperature increases, perhaps reflecting dispersal limitation, phenotypic plasticity or microclimatic buffering by the tree canopy. Causality cannot rigorously be inferred from such a descriptive study; however, we suggest that recent warming is now driving plant community change in the climatically more moderate mid-elevation forest setting.

Abstract. Peatlands are carbon (C) storage ecosystems sustained by a high water table (WT). High WT creates anoxic conditions that suppress the activity of aerobic decomposers and provide conditions for peat accumulation. Peatland function can be dramatically affected by WT drawdown caused by climate and/or land-use change. Aerobic decomposers are directly affected by WT drawdown through environmental factors such as increased oxygenation and nutrient availability. Additionally, they are indirectly affected via changes in plant community composition and litter quality. We studied the relative importance of direct and indirect effects of WT drawdown on aerobic decomposer activity in plant litter at two stages of decomposition (incubated in the field for 1 or 2 years). We did this by profiling 11 extracellular enzymes involved in the mineralization of organic C, nitrogen (N), phosphorus (P) and sulphur. Our study sites represented a three-stage chronosequence from pristine to short-term (years) and long-term (decades) WT drawdown conditions under two nutrient regimes (bog and fen). The litter types included reflected the prevalent vegetation: Sphagnum mosses, graminoids, shrubs and trees. Litter type was the main factor shaping microbial activity patterns and explained about 30 % of the variation in enzyme activities and activity allocation. Overall, enzyme activities were higher in vascular plant litters compared to Sphagnum litters, and the allocation of enzyme activities towards C or nutrient acquisition was related to the initial litter quality (chemical composition). Direct effects of WT regime, site nutrient regime and litter decomposition stage (length of incubation period) summed to only about 40 % of the litter type effect. WT regime alone explained about 5 % of the variation in enzyme activities and activity allocation. Generally, enzyme activity increased following the long-term WT drawdown and the activity allocation turned from P and N acquisition towards C acquisition. This caused an increase in the rate of litter decomposition. The effects of the short-term WT drawdown were minor compared to those of the long-term WT drawdown: e.g., the increase in the activity of C-acquiring enzymes was up to 120 % (bog) or 320 % (fen) higher after the long-term WT drawdown compared to the short-term WT drawdown. In general, the patterns of microbial activity as well as their responses to WT drawdown depended on peatland type: e.g., the shift in activity allocation to C-acquisition was up to 100 % stronger at the fen compared to the bog. Our results imply that changes in plant community composition in response to persistent WT drawdown will strongly affect the C dynamics of peatlands. The predictions of decomposer activity under changing climate and/or land-use thus cannot be based on the direct effects of the changed environment only, but need to consider the indirect effects of environmental changes: the changes in plant community composition, their dependence on peatland type, and their time scale.

AimsEnvironmental changes in Europe influence plant community composition, but the literature quantifying these changes often shows inconsistent trends, due mostly to heterogeneous survey methods. Here, we investigated temporal changes in plants over 12 years at the species and community level at a regional scale, using a standardized, plot‐based monitoring scheme.LocationData originated from 1,389 permanent plots of a standardized monitoring scheme targeting plant communities. Plots were distributed in the Burgundy region (France), initially grouped into 175 (2 km × 2 km) grid cells containing eight 10‐m2 plots each, that were surveyed in at least 2 years between 2009 and 2020.MethodsWe characterized changes in vascular plants in 10‐m2 plots by examining the temporal changes in the probability of occurrence of common species, changes in species diversity using species richness, Shannon–Wiener and Pielou's indices and changes in abundance‐weighted mean community ecological preferences using Ellenberg indicator values.ResultsAcross 198 common species, probability of occurrence in the region has shown a decline since 2009. This decline is associated with a general decrease by 13% of both species richness and the Shannon index between 2009 and 2020. This trend was stronger in annual crops and grasslands, whereas forest diversity remained relatively constant over time. Pielou's index diminished on average, except in natural forests. Mean community Ellenberg indicator values suggested slight changes in plant community composition, with an increasing preference for nutrient‐poor soils and Atlantic conditions over time.ConclusionsThe observed biodiversity loss in the Burgundy region is consistent with a widespread shift in community composition in response to environmental change. Existing conservation measures do not seem to compensate for the average losses, indicating that these measures are still inadequate to protect plant communities. Our approach also emphasizes the speed at which plant communities are changing and thus the need for better monitoring of the European flora.

AimAttempts over the past 30 years to explain geographical variation in the strength of herbivore pressure have given rise to ecological hypotheses like the latitudinal herbivory hypothesis. This hypothesis, however, has rarely been tested using community‐level data. Therefore, the aim of our study was to examine the patterns and potential mechanisms underlying geographical variation in community‐wide herbivory.LocationThe Qinghai‐Tibetan Plateau.Time PeriodJuly 2021.Major Taxa StudiedPlants.MethodsWe selected 43 grassland sites along a 1500‐km latitudinal gradient (c. 27°N to 39°N) and a 2698‐m elevational gradient (1886–4584 m) on the Qinghai‐Tibetan Plateau. We evaluated geographical patterns in invertebrate herbivory pressure at the population and community levels, while also evaluating the importance of geographical variation in mediating the effects of abiotic and biotic factors on intraspecific variation (through changes in herbivory on component species) and species turnover effects (through changes in plant community composition).ResultsCommunity‐wide herbivory decreased with latitude, mirroring intraspecific variation, while species turnover effects did not vary along any tested geographical gradients. Furthermore, we found that geographical variation in community‐wide herbivory was strongly positively correlated with soil nitrogen content. We also found a positive effect of soil nitrogen content on intraspecific variation and a negative effect of plant community biomass on species turnover effects.Main ConclusionsThe latitudinal gradient in community‐wide herbivory was primarily mediated by intraspecific variation, which was in turn associated with a gradient in soil nitrogen content. Our findings highlight the need for community‐wide assessments of geographical variation in plant–herbivore interactions, decomposing community‐wide herbivory into intraspecific variation and species turnover effects.

SummaryNutrient additions typically increase terrestrial ecosystem productivity, reduce plant diversity and alter plant community composition; however, the effects ofPadditions and interactions betweenNandPare understudied.We added bothN(10 g m−2) and three levels ofP(2.5, 5 and 10 g m−2) to a native, ungrazed tallgrass prairie burned biennially in northeasternKansas,USA, to determine the independent and interactive effects ofNandPon plant community composition and above‐ground net primary productivity (ANPP).After a decade of nutrient additions, we found few effects ofPalone on plant community composition,Nalone had stronger effects, andNandPadditions combined resulted in much larger effects than either alone. The changes in the plant community were driven by decreased abundance ofC4grasses, perhaps in response to altered interactions with mycorrhizal fungi, concurrent with increased abundance of non‐N‐fixing perennial and annual forbs. Surprisingly, this large shift in plant community composition had little effect on plant community richness, evenness and diversity.The shift in plant composition withNandPcombined had large but variable effects onANPPover time. Initially,NandNandPcombined increased above‐ground productivity ofC4grasses, but after 4 years, productivity returned to ambient levels as grasses declined in abundance and the community shifted to dominance by non‐N‐fixing and annual forbs. Once these forbs increased in abundance and became dominant,ANPPwas more variable, with pulses in forb production only in years when the site was burned.Synthesis. We found that a decade ofNandPadditions interacted to drive changes in plant community composition, which had large effects on ecosystem productivity but minimal effects on plant community diversity. The large shift in species composition increased variability inANPPover time as a consequence of the effects of burning. Thus, increased inputs ofNandPto terrestrial ecosystems have the potential to alter stability of ecosystem function over time, particularly within the context of natural disturbance regimes.

Hummocks, small earth or peat mounds, are widely distributed in the arctic and develop as a consequence of biomass accumulation and cryoturbation in the active layer. There is general agreement that the type of vegetation covering peat hummocks may alter the accumulation rate of organic material and thus hummock growth and local carbon sink dynamics. Studies on hummock plant community compositions from the arctic are very scarce. Here, I present results of a case study from the arctic tree-line near Churchill, Manitoba (Canada). Vegetation composition, hummock height and soil moisture content were recorded in 40 peat hummocks located along a tree-line gradient from open forest to tundra. Based on a cluster analysis I found three moss-dominated types of hummock vegetation, according to (1) a Tomenthypnum nitens (golden fuzzy fen moss) type on low hummocks, (2) a Hylocomium splendens (stair-step moss) type on medium-sized hummocks, and (3) a Pleurozium schreberi (red-stemmed feathermoss) type on hummocks higher than 60-70 cm. I found hummock height to increase towards the forest interior with decreasing water content of the upper organic layer on the hummock top. This is indicated by a significant change in vegetation composition towards drought resistant moss species on higher hummocks. Furthermore, species richness decreased with increase in hummock height. Based on evidence from historical tree-line invasion the overall results suggest that hummock height increases due to peat accumulation over the course of time resulting in a typical change in plant community composition.

Long‐term ecosystem development involves changes in plant community composition and diversity associated with pedogenesis and nutrient availability, but comparable changes in soil microbial communities remain poorly understood. In particular, it is unclear whether the diversity of plants and microbes respond to similar abiotic drivers, or become decoupled as resources change over long time‐scales. We characterized communities of archaea, bacteria and fungi in soils along a 2‐million‐year chronosequence of coastal dunes in a biodiversity hot spot in Western Australia. The chronosequence involves marked changes in soil pH and nutrient availability that drive major shifts in plant community composition and diversity as soils age. Patterns of α‐diversity for microbial groups differed along the chronosequence. Bacterial α‐diversity was greatest in intermediate‐aged soils; archaeal diversity was greater in young alkaline or intermediate‐aged soils, while fungal α‐diversity—like plant diversity—was greatest in old, strongly weathered soils where phosphorus is the limiting nutrient. Changes in microbial community composition along the chronosequence were explained primarily by the long‐term decline in soil pH, with a smaller influence of the relative abundance of plant nutrient‐acquisition strategies. However, changes between the prokaryote and fungal communities, and between fungal and plant communities, became increasingly decoupled along the chronosequence, demonstrating that the coordination of change in biological communities by abiotic drivers becomes weaker during long‐term ecosystem development. Several bacterial taxa, including DA101 (Verrucomicrobia), “Candidatus Solibacter” (Acidobacteria) and Gaiella (Actinobacteria), were particularly abundant on the oldest dunes, indicating that they are adapted to acquire phosphorus from extremely infertile soils. However, we cannot disentangle the influence of phosphorus from the long‐term decline in soil pH along the chronosequence. Synthesis. These results provide evidence for contrasting patterns of plant and microbial community composition and α‐diversity in response to acidification and nutrient depletion during long‐term pedogenesis.

Tundra vegetation is responding rapidly to on-going climate warming. The changes in plant abundance and chemistry might have cascading effects on tundra food webs, but an integrated understanding of how the responses vary between habitats and across environmental gradients is lacking. We assessed responses in plant abundance and plant chemistry to warmer climate, both at species and community levels, in two different habitats. We used a long-term and multisite warming (OTC) experiment in the Scandinavian forest–tundra ecotone to investigate (i) changes in plant community composition and (ii) responses in foliar nitrogen, phosphorus, and carbon-based secondary compound concentrations in two dominant evergreen dwarf-shrubs (Empetrum hermaphroditum and Vaccinium vitis-idaea) and two deciduous shrubs (Vaccinium myrtillus and Betula nana). We found that initial plant community composition, and the functional traits of these plants, will determine the responsiveness of the community composition, and thus community traits, to experimental warming. Although changes in plant chemistry within species were minor, alterations in plant community composition drive changes in community-level nutrient concentrations. In view of projected climate change, our results suggest that plant abundance will increase in the future, but nutrient concentrations in the tundra field layer vegetation will decrease. These effects are large enough to have knock-on consequences for major ecosystem processes like herbivory and nutrient cycling. The reduced food quality could lead to weaker trophic cascades and weaker top down control of plant community biomass and composition in the future. However, the opposite effects in forest indicate that these changes might be obscured by advancing treeline forests.