Vascular Plants Facilitated Bryophytes in a Grassland Experiment

In grassland communities vascular plants and bryophytes form two distinct layers. In order to understand the factors responsible for plant community structure, more information about interactions between these plant groups is needed. Often negative correlations between vascular plant and bryophyte covers have been reported, suggesting competition. Here we tested experimentally whether different grassland vascular plant species (Trifolium pratense, Festuca pratensis, Prunella vulgaris) had different influences on the cover of two bryophyte species (Rhytidiadelphus squarrosus, Brachythecium rutabulum). In a two-year garden pot experiment one bryophyte species and one vascular plant species were planted per pot. Bryophytes were planted at a constant density, vascular plants in four densities. The cover of both bryophyte species increased with increasing vascular plant cover, showing the facilitative effect of vascular plants through creating better microclimate, e.g., optimising temperature. Bryophyte responses to vascular plant species were species-specific. Festuca had significantly positive effects on both bryophyte species in the second year, and Trifolium on Brachythecium in both years, whereas Prunella had no significant effect on bryophytes. The facilitative effect of vascular plants was stronger at the second experimental year. In summary, the biotic effects between bryophytes and grassland vascular plants are species-specific and positive interactions are prevailing at low vascular plant densities.     

Ecosystem functions are resistant to extreme changes to rainfall regimes in a mesotrophic grassland

Aims

Major changes to rainfall regimes are predicted for the future but the effect of such changes on terrestrial ecosystem function is largely unknown. We created a rainfall manipulation experiment to investigate the effects of extreme changes in rainfall regimes on ecosystem functioning in a grassland system.

Methods

We applied two rainfall regimes; a prolonged drought treatment (30 % reduction over spring and summer) and drought/downpour treatment (long periods of no rainfall interspersed with downpours), with an ambient control. Both rainfall manipulations included increased winter rainfall. We measured plant community composition, CO₂ fluxes and soil nutrient availability.

Results

Plant species richness and cover were lower in the drought/downpour treatment, and showed little recovery after the treatment ceased. Ecosystem processes were less affected, possibly due to winter rainfall additions buffering reduced summer rainfall, which saw relatively small soil moisture changes. However, soil extractable P and ecosystem respiration were significantly higher in rainfall change treatments than in the control.

Conclusions

This grassland appears fairly resistant, in the short term, to even the more extreme rainfall changes that are predicted for the region, although prolonged study is needed to measure longer-term impacts. Differences in ecosystem responses between the two treatments emphasise the variety of ecosystem responses to changes in both the size and frequency of rainfall events. Given that model predictions are inconsistent there is therefore a need to assess ecosystem function under a range of potential climate change scenarios.     

Moisture conditions and the presence of bryophytes determine fescue species abundance in a dry calcareous grassland

Festuca ovina is the abundant matrix-forming species and F. rubra a subordinate species in shallow-soil calcareous grasslands. F. pratensis is a transient species, occurring sparsely in this community. We hypothesised that the different abundances of these three species are primarily due to the differential effect of moisture conditions on their germination and early establishment, and that the effect of the pattern of rainfall intensity depends on the presence or absence of a bryophyte layer. We studied the dependence of the germination and establishment of the three fescue species on the moisture conditions both in the laboratory and in the patches of intact grassland community (microcosms). In a laboratory germination experiment, F. pratensis showed the highest, F. rubra , the intermediate and F. ovina, the lowest drought tolerance. In microcosms, the establishment of F. ovina was the highest. At the same time, the annual mortality of seedlings of F. ovina was the lowest. All three species responded positively to an increasing irrigation level. Differently from F. ovina, F. rubra showed a positive response only in plots from which the bryophyte layer had been removed, while F. pratensis responded positively to both irrigation and bryophyte removal. We conclude that moisture conditions have a differential effect on the three fescue species mainly in the seedling establishment, not in the germination phase. For the successful establishment of F. rubra and F. pratensis, the coincidence of high rainfall and local disturbance, removing bryophytes, is required. The presence or absence of bryophytes had no effect on establishment in dry years, while in rainy years the removal of bryophytes has a clear positive effect.     

Vegetation responses in Alaskan arctic tundra after 8 years of a summer warming and winter snow manipulation experiment

We used snow fences and small (1 m²) open‐topped fiberglass chambers (OTCs) to study the effects of changes in winter snow cover and summer air temperatures on arctic tundra. In 1994, two 60 m long, 2.8 m high snow fences, one in moist and the other in dry tundra, were erected at Toolik Lake, Alaska. OTCs paired with unwarmed plots, were placed along each experimental snow gradient and in control areas adjacent to the snowdrifts. After 8 years, the vegetation of the two sites, including that in control plots, had changed significantly. At both sites, the cover of shrubs, live vegetation, and litter, together with canopy height, had all increased, while lichen cover and diversity had decreased. At the moist site, bryophytes decreased in cover, while an increase in graminoids was almost entirely because of the response of the sedge Eriophorum vaginatum. These community changes were consistent with results found in studies of responses to warming and increased nutrient availability in the Arctic. However, during the time period of the experiment, summer temperature did not increase, but summer precipitation increased by 28%. The snow addition treatment affected species abundance, canopy height, and diversity, whereas the summer warming treatment had few measurable effects on vegetation. The interannual temperature fluctuation was considerably larger than the temperature increases within OTCs (<2°C), however. Snow addition also had a greater effect on microclimate by insulating vegetation from winter wind and temperature extremes, modifying winter soil temperatures, and increasing spring run‐off. Most increases in shrub cover and canopy height occurred in the medium snow‐depth zone (0.5–2 m) of the moist site, and the medium to deep snow‐depth zone (2–3 m) of the dry site. At the moist tundra site, deciduous shrubs, particularly Betula nana, increased in cover, while evergreen shrubs decreased. These differential responses were likely because of the larger production to biomass ratio in deciduous shrubs, combined with their more flexible growth response under changing environmental conditions. At the dry site, where deciduous shrubs were a minor part of the vegetation, evergreen shrubs increased in both cover and canopy height. These changes in abundance of functional groups are expected to affect most ecological processes, particularly the rate of litter decomposition, nutrient cycling, and both soil carbon and nitrogen pools. Also, changes in canopy structure, associated with increases in shrub abundance, are expected to alter the summer energy balance by increasing net radiation and evapotranspiration, thus altering soil moisture regimes.     

Phenological Sensitivity of Early and Late Flowering Species Under Seasonal Warming and Altered Precipitation in a Seminatural Temperate Grassland Ecosystem

Shifts in flowering phenology of plants are indicators of climate change. The great majority of existing phenological studies refer solely to gradual warming. However, knowledge on how flowering phenology responds to changes in seasonal variation of warming and precipitation regimes is missing. We report the onset of 22 early (flowering before/within May) and 23 late flowering (flowering after May) species in response to manipulated seasonal warming (equal to + 1.2°C; last 100-year summer/winter warming), additional winter rainfall, and modified precipitation variability (including a 1000-year extreme drought event followed by heavy rainfall) over the growing season in two consecutive years for a species-rich temperate grassland ecosystem. The average onset of flowering (over 2 years) was significantly advanced 3.1 days by winter warming and 1.5 days by summer warming compared to control. Early flowering species responded to seasonal warming in both years, while late-flowering species responded in only 1 year to summer warming. The average onset of early flowering species was significantly advanced, 4.9 days by winter warming and 2.3 days by summer warming. Species-specific analysis showed that even within the early flowering community there were divergences. A positive correlation between plant height and shift in flowering onset was detected under winter warming (R² = 0.20, p = 0.005). The average onsets of early and late flowering community were affected by neither winter rain nor growing season precipitation variability. Seasonal differences in warming, and particularly winter warming, might alter community dynamics among early and late flowering species which can cause shifts in the seasonal performances of temperate ecosystems.     

Species richness of vascular plants, bryophytes and lichens in dry grasslands: The effects of environment, landscape structure and competition

We studied the relative importance of local habitat conditions and landscape structure for species richness of vascular plants, bryophytes and lichens in dry grasslands on the Baltic island of Öland (Sweden). In addition, we tested whether relationships between species richness and vegetation cover indicate that competition within and between the studied taxonomic groups is important. We recorded species numbers of vascular plants, bryophytes and lichens in 4 m² plots (n=452), distributed over dry grassland patches differing in size and degree of isolation. Structural and environmental data were collected for each plot. We tested effects of local environmental conditions, landscape structure and vegetation cover on species richness using generalized linear mixed models. Different environmental variables explained species richness of vascular plants, bryophytes and lichens. Environmental effects, particularly soil pH, were more important than landscape structure. Interaction effects of soil pH with other environmental variables were significant in vascular plants. Plot heterogeneity enhanced species richness. Size and degree of isolation of dry grassland patches significantly affected bryophyte and lichen species richness, but not that of vascular plants. We observed negative relationships between bryophyte and lichen species richness and the cover of vascular plants. To conclude, effects of single environmental variables on species richness depend both on the taxonomic group and on the combination of environmental factors on a whole. Dispersal limitation in bryophytes and lichens confined to dry grasslands may be more common than is often assumed. Our study further suggests that competition between vascular plants and cryptogams is rather asymmetric.     

A Bryophyte flora of Kent. II. Hepaticae

Abstract

The military training area on Salisbury Plain contains the largest area of chalk grassland in western Europe. The grassland swards, though relatively tall, are often rich in flowering plant species. The bryophyte flora of areas disturbed in five different ways (prehistoric earthworks, twentieth century rifle ranges, ant-hills, vehicle tracks and shell-holes) was compared to that of adjacent, relatively undisturbed grassland. There was no significant difference in bryophyte cover between quadrats on disturbed ground and the controls, but the disturbed sites supported more bryophyte species per quadrat. Of the 55 taxa recorded, 38 species were at least three times more frequent in the disturbed than the undisturbed sites, compared to four which were at least three times more frequent in the control sites. The species favouring disturbed conditions included several bryophytes characteristically associated with chalk soils in southern England, including some that fruit freely (e.g. Microbryum curvicollum, Tortula lanceola) and others that fruit very rarely (e.g. Abietinella abietina, Entodon concinnus). These results are discussed in relation to the conservation of bryophytes and other disturbance-tolerant and disturbance-dependent species on Salisbury Plain and in the wider context of the protection of the bryophytes of chalkland habitats.     

Mowing Reduces Exotic Annual Grasses but Increases Exotic Forbs in a Semiarid Grassland

Cheatgrass (Bromus tectorum) and other exotic winter‐active plants can be persistent invaders in native grasslands, growing earlier in the spring than native plants and pre‐empting soil resources. Effective management strategies are needed to reduce their abundance while encouraging the reestablishment of desirable native plants. In this 4‐year study, we investigated whether mowing and seeding with native perennial grasses could limit growth of exotic winter‐actives, and benefit growth of native plants in an invaded grassland in Colorado, United States. We established a split‐plot experiment in October 2008 with 3 mowing treatments: control, spring‐mowed, and spring/summer‐mowed (late spring, mid‐summer, and late summer), and 3 within‐plot seeding treatments: control, added B. tectorum seeds, and added native grass seeds. Cover of plant species and aboveground biomass were measured for 3 years. In March and June of 2010, 2011, and March of 2012, B. tectorum and other winter‐annual grasses were half as abundant in both mowing treatments as in control plots; however, cover of non‐native winter‐active forbs increased 2‐fold in spring‐mowed plots and almost 3‐fold in spring/summer‐mowed plots relative to controls. These patterns remained consistent 1 year after termination of treatments. Native cool‐season grasses were most abundant in spring‐mowed plots, and least abundant in control plots. There was higher cover of native warm‐season grasses in spring/summer‐mowed plots than in control plots in July 2011 and 2012. The timing of management can have strong effects on plant community dynamics in grasslands, and this experiment indicates that adaptive management can target the temporal niche of undesirable invasive species.     

Plant species richness in mountain forests of the Bavarian Alps

Abstract

Based on a stratified random sample of 93 vegetation plots (144 m²) from montane and subalpine climax forests in a representative section through the Bavarian Alps, spatial pattern and environmental correlates of species density of trees, vascular understorey and epigeic bryophytes were analysed. Detecting landscape scale patterns in beta- and gamma-diversity based on interpretation of rarefaction curves proved to be difficult in a sample that had been stratified by ecological criteria. In 144 m² plots tree species density (5 ± 2.0, max. 10) declined with elevation and increased with stand age (multiple R ² = 0.557). The latter effect can be attributed to the secular history of game management and browsing pressure, which has hindered the regeneration of species-rich tree stands since ca. 150 yr. Species density of the forest undergrowth reached remarkably high levels for vascular plants (42 ± 12.8, max. 69) and bryophytes (14 ± 6.0, max. 30) and strongly depended on cover of the respective layer in a unimodal pattern, suggesting to separate direct and indirect effects, mediated through the mass effect, in the subsequent construction of regression models. Multiple regression (R ² = 0.47) revealed that vascular species density is limited chiefly through low plant cover, which in turn decreases with tree cover, elevation and soil quality, and secondly by species pools that contain larger numbers of species requiring high pH and ample light. Cover and direct effects had roughly equal weight in controlling bryophyte species density (R ² = 0.57). Biomass depended on the proportion of conifers in the tree layer and on site quality, less fertile sites tending to have higher bryophyte cover. The increase of bryophyte species density with elevation was interpreted as an effect of a pool of largely boreal-subalpine species. The increase of species density with stand age suggests dispersal limitation and deserves further study.     

Production and microtopography of bog bryophytes: response to warming and water-table manipulations

Boreal peatlands, which contain a large fraction of the world's soil organic carbon pool, may be significantly affected by changes in climate and land use, with attendant feedback to climate through changes in albedo, fluxes of energy or trace gases, and soil carbon storage. The response of peatlands to changing environmental conditions will probably be dictated in part by scale-dependent topographic heterogeneity, which is known to interact with hydrology, vegetation, nutrients, and emissions of trace gases. Because the bryophyte community can contribute the majority of aboveground production in bogs, we investigated how microscale topography affects the response of bryophyte species production and cover to warming (using overhead infrared lamps) and manipulations of water-table height within experimental mesocosms. We removed 27 intact peat monoliths (2.1-m² surface area, 0.5-0.7 m depth) from a bog in northern Minnesota, USA, and subjected them to three warming and three water-table treatments in a fully crossed factorial design. Between 1994 and 1998, we determined annual production of the four dominant bryophyte taxa within three microtopographic zones (low, medium, and high relative to the water table). We also estimated species cover and calculated changes in topography and roughness of the bryophyte surface through time. Total production of all bryophytes, and production of the individual taxa Polytrichum strictum, Sphagnum magellanicum, and Sphagnum Section Acutifolia, were about 100% greater in low microtopographic zones than in high zones, and about 50% greater in low than in medium zones. Production of bryophytes increased along the gradient of increasing water-table heights, but in most years, total production of bryophytes was negatively correlated with height above the set water table only for the wettest water-table treatment. Although bryophyte production was unaffected by the warming treatments, the bryophyte surface flattened in proportion to the degree of warming. These results indicate that production of bryophytes is driven most strongly by the absolute and relative height of the bryophyte surface above the water table. Predicted changes in water-table height commensurate with changes in surface temperature may thus affect both production and superficial topography of bryophyte communities.     

Long-term vegetation change in the Juncus squarrosus grassland at Moor House,northern England

Data from the long-term experiment on sheep grazing versus zero sheep grazing (i.e. in an enclosure) on the composition of the Juncus squarrosus grassland at the Moor House NNR are presented. The data have been analysed to assess change in (1) the abundance of individual species, (2) higher plant and bryophyte communities, and (3) vegetation structure. The higher plant data suggested that both the enclosed-and grazed plots were changing in the same direction, but the enclosed plot was moving much faster. The general tendency was towards a blanket bog vegetation dominated by Eriophorum vaginatum and Calluna vulgaris. Juncus squarrosus has declined very quickly in the enclosed plot, but there has also been a slower decline in the grazed one. A significant increase in Calluna vulgaris has occurred only in the enclosed plot. In contrast, the bryophyte data showed completely different successional trajectories in the two treatment plots.The vegetation structure changed markedly after release from grazing, with a decrease in phytomass, but increase in necromass in the lowest height strata. There was no noticeable change in structure over the 18 year period in the grazed plot.Particular problems found in this study were that some species either fluctuated widely in response, or changed in a curvilinear manner.     

Predicted changes in vegetation structure affect the susceptibility to invasion of bryophyte-dominated subarctic heath

Background and Aims

A meta-analysis of global change experiments in arctic tundra sites suggests that plant productivity and the cover of shrubs, grasses and dead plant material (i.e. litter) will increase and the cover of bryophytes will decrease in response to higher air temperatures. However, little is known about which effects these changes in vegetation structure will have on seedling recruitment of species and invasibility of arctic ecosystems.

Methods

A field experiment was done in a bryophyte-dominated, species-rich subarctic heath by manipulating the cover of bryophytes and litter in a factorial design. Three phases of seedling recruitment (seedling emergence, summer seedling survival, first-year recruitment) of the grass Anthoxanthum alpinum and the shrub Betula nana were analysed after they were sown into the experimental plots.

Key Results

Bryophyte and litter removal significantly increased seedling emergence of both species but the effects of manipulations of vegetation structure varied strongly for the later phases of recruitment. Summer survival and first-year recruitment were significantly higher in Anthoxanthum. Although bryophyte removal generally increased summer survival and recruitment, seedlings of Betula showed high mortality in early August on plots where bryophytes had been removed.

Conclusions

Large species-specific variation and significant effects of experimental manipulations on seedling recruitment suggest that changes in vegetation structure as a consequence of global warming will affect the abundance of grasses and shrubs, the species composition and the susceptibility to invasion of subarctic heath vegetation.     

Small-Scale Wetland Restoration in the High Arctic: A Long-Term Perspective

Results are presented using vegetative shoots and bryophyte sods to restore floristically impoverished high arctic wet sedge-moss meadows that had suffered intense damage from vehicle activity during the period 1960–1967. Clonal transplants of Carex aquatilis var. stans, a native sedge, were planted with and without bryophyte sods in vehicle ruts in 1972. After nearly two decades, there was less Carex cover in the planted ruts with flowing water than in the contiguous controls. This pattern was slightly reversed in planted plots with standing water. Reinvasion of Eriophorum angustifolium occurred in treated ruts, but cover was less in both treatments than in controls in 1990. The unexpected recruitment of Eriophorum scheuchzeri from the seed bank in moss-sodded plots is discussed in terms of its local and regional importance. Total plant cover in restored ruts was nearly equal to that of controls, but biomass was somewhat less than that in control plots. Plots with bryophytes were environmentally distinct, due primarily to increases in organic mat depth relative to controls. After 18 years, restoration efforts resulted in increased plant cover in treated ruts compared to naturally recovering ruts.

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Bryophyte biomass and species richness on the Park Grass Experiment,Rothamsted, UK

The relationships between bryophyte biomass and species richness and soil pH, nutrient applications and vascular plant biomass and species richness were analyzed for the Park Grass Experiment (Rothamsted, UK). The study examined the abundance of bryophytes in relation to long-term fertilizer and lime application and to fertilizer treatments recently being ceased on some plots. The probability of bryophytes being present on a plot increased with increasing soil pH, and on plots at soil pH 3.3–4.5, the lowest values in this experiment, there were virtually no mosses present. Total bryophyte biomass decreased with increasing vascular plant biomass and vascular plant richness. Both bryophyte biomass and species richness showed a curvilinear response to soil pH. Bryophyte biomass was markedly increased on plots where nitrogen (N) fertilization had recently been ceased. The abundance of the common bryophyte species showed individualistic responses to treatments. N had a negative effect on the abundance of Brachythecium rutabulum. Increasing soil pH, and the application of phosphorus (P) and potassium (K) fertilizer together, had a positive effect on Eurhynchium praelongum. This species was also negatively affected by N, but tolerated larger amounts of it (100–150 kg ha^–1 N) than B. rutabulum. An ephemeral moss, Bryum subapiculatum, had a unimodal response to soil pH but showed no response to N, P, K or other explanatory variables.     

Association between bryophytes and seedlings in Nothofagus sub-Antarctic forests

Bryophytes, which include mosses, liverworts and hornworts, indeed play a significant role in the natural dynamics of native forests. They contribute to fundamental ecological processes such as tree regeneration. In this context, the objective was to analyse the association of bryophytes with Nothofagus seedlings, as well as whether the substrates where bryophytes grew influenced bryophyte-tree seedling association, in sub-Antarctic forests at two contrasting landscapes (coastal and mountain) of Tierra del Fuego (Argentina), to better understand their impacts on the natural regeneration processes. We hypothesized that bryophytes act as a substrate for seed germination and initial regeneration growth in pure and mixed forests of N. pumilio and N. betuloides, resulting in widespread tree seedlings–bryophyte associations in all landscapes. In each forest and landscape location, 60 transects were established (10 m in length) to evaluate bryophyte cover (by point intercept method) and substrate type (bare soil, decaying wood and litter cover) where they were growing. An adaptation of the relative interaction index (RII) based on tree seedling cover associated with bryophyte species (%) and tree seedling cover in the absence of bryophytes (%) was calculated and analysed to assess competition or facilitation between bryophytes and tree seedlings. Nothofagus pumilio seedlings were less abundant in bryophytes compared to other substrates, suggesting an inhibitory effect on the germination and/or survival of N. pumilio. In contrast, the seedlings of N. betuloides, in both pure and mixed forests, exhibited higher abundance on bryophyte substrates, particularly in mosses at mountain landscape (RII = 0.83 ± 0.08 in litter and 0.62 ± 0.11 in decaying wood). These findings suggest that bryophytes play a facilitating role for N. betuloides seedlings during germination and initial phases of growth, mainly in the mountain. Therefore, their conservation promotes N. betuloides forest continuity, both in pure and mixed structures.     

Press–pulse interactions: effects of warming,N deposition,altered winter precipitation,and fire on desert grassland community structure and dynamics

Global environmental change is altering temperature, precipitation patterns, resource availability, and disturbance regimes. Theory predicts that ecological presses will interact with pulse events to alter ecosystem structure and function. In 2006, we established a long‐term, multifactor global change experiment to determine the interactive effects of nighttime warming, increased atmospheric nitrogen (N) deposition, and increased winter precipitation on plant community structure and aboveground net primary production (ANPP) in a northern Chihuahuan Desert grassland. In 2009, a lightning‐caused wildfire burned through the experiment. Here, we report on the interactive effects of these global change drivers on pre‐ and postfire grassland community structure and ANPP. Our nighttime warming treatment increased winter nighttime air temperatures by an average of 1.1 °C and summer nighttime air temperature by 1.5 °C. Soil N availability was 2.5 times higher in fertilized compared with control plots. Average soil volumetric water content (VWC) in winter was slightly but significantly higher (13.0% vs. 11.0%) in plots receiving added winter rain relative to controls, and VWC was slightly higher in warmed (14.5%) compared with control (13.5%) plots during the growing season even though surface soil temperatures were significantly higher in warmed plots. Despite these significant treatment effects, ANPP and plant community structure were highly resistant to these global change drivers prior to the fire. Burning reduced the cover of the dominant grasses by more than 75%. Following the fire, forb species richness and biomass increased significantly, particularly in warmed, fertilized plots that received additional winter precipitation. Thus, although unburned grassland showed little initial response to multiple ecological presses, our results demonstrate how a single pulse disturbance can interact with chronic alterations in resource availability to increase ecosystem sensitivity to multiple drivers of global environmental change.     

Effects of experimentally imposed climate scenarios on flowering phenology and flower production of subarctic bog species

Climate scenarios for high‐latitude areas predict not only increased summer temperatures, but also larger variation in snowfall and winter temperatures. By using open‐top chambers, we experimentally manipulated both summer temperatures and winter and spring snow accumulations and temperatures independently in a blanket bog in subarctic Sweden, yielding six climate scenarios. We studied the effects of these scenarios on flowering phenology and flower production of Andromeda polifolia (woody evergreen) and Rubus chamaemorus (perennial herb) during 2 years. The second year of our study (2002) was characterized by unusually high spring and early summer temperatures. Our winter manipulations led to consistent increases in winter snow cover. As a result, average and minimum air and soil temperatures in the high snow cover treatments were higher than in the winter ambient treatments, whereas temperature fluctuations were smaller. Spring warming resulted in higher average, minimum, and maximum soil temperatures. Summer warming led to higher air and soil temperatures in mid‐summer (June–July), but not in late summer (August–September). The unusually high temperatures in 2002 advanced the median flowering date by 2 weeks for both species in all treatments. Superimposed on this effect, we found that for both Andromeda and Rubus, all our climate treatments (except summer warming for Rubus) advanced flowering by 1–4 days. The total flower production of both species showed a more or less similar response: flower production in the warm year 2002 exceeded that in 2001 by far. However, in both species flower production was only stimulated by the spring‐warming treatments. Our results show that the reproductive ecology of both species is very responsive to climate change but this response is very dependent on specific climate events, especially those that occur in winter and spring. This suggests that high‐latitude climate change experiments should focus more on winter and spring events than has been the case so far.     

Seasonal contrasting changes of foliar concentrations of terpenes and other volatile organic compound in four dominant species of a Mediterranean shrubland submitted to a field experimental drought and warming

To test the effect of forecasted drought and warming conditions for the next decades by GCM and ecophysiological models on foliar concentrations of volatile organic compounds (VOCs) and especially of volatile terpenes, we studied four typical Mediterranean woody plants (Pinus halepensis L., Pistacia lentiscus L., Rosmarinus officinalis L. and Globularia alypum L.) under a field experimental drought and warming generated using automatically sliding curtains. Terpenes were detected in the four studied species (R. officinalis L., P halepensis L., Pistacia lentiscus L. and G. alypum L.). In general, maximum concentrations of terpenes were found in the coldest periods and minimum concentrations in the summer. Their concentrations ranged between 0.003 mg g^?1 DM (eugenol) in G. alypum under drought conditions and 37 mg g^?1 DM in R. officinalis under control conditions. Main volatile terpenes found in all studied species except in G. alypum were α‐pinene, camphene, β‐pinene, β‐phellandrene and caryophyllene. In general, VOC leaf concentrations increased when soil moisture increased and decreased when air temperature increased. However, contrasting not consistent responses to the drought and warming treatments were found among species, seasons and years. For example, in P. halepensis, the concentrations decreased in response to drought in winter and instead increased in summer. Contrarily, drought decreased concentrations in summer and increased them in winter in Pistacia lentiscus. In any case, the data on seasonal VOC concentration in Mediterranean woody species provided here will add new knowledge of seasonal variation in essential oil contents of these species. These data might help in the study of flammability of Mediterranean ecosystems and in improving prediction algorithms, inventories and modelling of monoterpene emissions in response to climate change, which mostly do not consider the changes in concentration under drought stress. However, the lack of general and consistent response patterns to increasing drought and warming among species, seasons and years found here makes this task difficult.     

Vegetation change in Southeast Greenland? Tasiilaq revisited after 40 years

Questions: Are there changes in species composition of the oceanic, Low‐Arctic tundra vegetation after 40 years? Can possible changes be attributed to climate change? Location: Ammassalik Island near Tasiilaq, Southeast Greenland. Methods: Species composition and cover of 11 key vegetation types were recorded in 110 vegetation survey plots in 1968–1969 and in 11 permanent plots in 1981. Recording was repeated in 2007. Temporal changes in species composition and cover between the surveys were tested using permutation tests linked with constrained ordinations for vegetation types, and Mann–Whitney tests for individual species. Changes in vegetation were related to climate change. Results: Although climate became warmer over the studied period, most of the vegetation types showed minor changes. The changes were most conspicuous in mire and snowbed vegetation, such as the Carex rariflora mire and Hylocomium splendens snowbed. In the C. rariflora mire, species number and cover of vascular plants and cover of bryophytes increased, whereas in the H. splendens snowbed species numbers of vascular plants, bryophytes, and also lichens increased. Lichen richness increased in the Carex bigelowii snowbed and cover of bryophytes in the Salix herbacea snowbed. No such changes occurred in the Alchemilla glomerulans meadow, Alchemilla alpina snowbed and Phyllodoce coerulea heath. There was no change of species composition within the Salix glauca scrub, A. alpina snowbed, lichen grassland and the Empetrum nigrum and Phyllodoce coerulea heaths. Most changes resulted from increasing frequency or cover of some species; there were very few decreasing species. Most of the increasing species indicate drier substrate conditions. Conclusions: Only minor changes in species composition and cover were detected in the vegetation types studied. These changes were probably caused by milder winters and warmer summers during the years before the 2007 sampling. Climate warming may have reduced the duration of snow cover and soil moisture, particularly in snowbed and mire habitats, where species composition change was most pronounced. However, its magnitude was insufficient to cause a major change in species composition. Thus, on the level of plant community types, tundra vegetation near Tasiilaq was rather stable over the last 40 years.     

Physiological and antioxidant responses of <Emphasis Type="Italic">Erica multiflora</Emphasis> to drought and warming through different seasons

Climate change projections forecast a warming and an associated change in the distribution and intensity of rainfalls. In the case of the Mediterranean area, this will be reflected in more frequent and severe drought periods in the future. Within a long-term (9 years) manipulation experiment, we aimed to study the effect of the soil drought (15–20% decreased soil moisture) and warming conditions (+1°C warming) projected for the next decades onto photosynthetic rates and water relations, and onto the antioxidant and anti-stress defense capacity of Erica multiflora, a common species of the dry Mediterranean coastal scrublands, in two different seasons, spring and summer. Results indicated that none of the applied treatments was severe enough to induce a pronounced negative response of photosynthesis in this species well adapted to harsh Mediterranean conditions, but also highlighted important seasonal differences. Photosynthesis was limited by photoinhibition in spring and by stomatal closure in summer. Isoprenoid emission and the level of enzymatic and non-enzymatic antioxidants were lower in summer than in spring, whereas pigment and total phenolic contents were generally higher in summer. Volatile isoprenoid emissions were largely inhibited by drought and were not stimulated by warming. Drought and warming increased the oxidation state of ascorbate and reduced total glutathione levels in spring, but not in summer. It is concluded that E. multiflora plants can adapt to prolonged drought and warming, at least at the level simulated by our manipulative experiment, through changes in the seasonal physiological and antioxidant response of leaves.