Subalpine Grasslands Research Articles

Herbivory mediated by coupling between biomechanical traits of plants and grasshoppers

Summary Despite their potential to provide a mechanistic understanding of ecosystem processes, the functional traits that govern interaction networks remain poorly understood. We investigated the extent to which biomechanical traits are related to consumption in a plant–grasshopper herbivory network. Using a choice experiment, we assessed the feeding patterns of 26 grasshopper species for 24 common plant species from subalpine grasslands. We quantified shear and punch toughness for each plant species, while grasshopper incisive and molar strengths were estimated by a lever mechanics model, following the measurement of mandibular traits. Models incorporating co‐phylogenetic effects showed that the ratio between the grasshopper incisive strength and plant toughness, that reflects the cutting effort, is correlated with the mass of plant eaten. Moreover, a strong relationship between the incisive strength of the grasshoppers and the weighed mean toughness of the plants they eat was found. Our results suggest that biomechanical constraints imposed by plants influence the evolution of grasshoppers' mandibular traits. Such scaling relationships offer promising avenues towards the understanding of trait – function links in interaction networks.

Calcium Induces Long-Term Legacy Effects in a Subalpine Ecosystem

Human activities have transformed a significant proportion of the world’s land surface, with profound effects on ecosystem processes. Soil applications of macronutrients such as nitrate, phosphorus, potassium or calcium are routinely used in the management of croplands, grasslands and forests to improve plant health or increase productivity. However, while the effects of continuous fertilization and liming on terrestrial ecosystems are well documented, remarkably little is known about the legacy effect of historical fertilization and liming events in terrestrial ecosystems and of the mechanisms involved. Here, we show that more than 70 years after the last application of lime on a subalpine grassland, all major soil and plant calcium pools were still significantly larger in limed than in unlimed plots, and that the resulting shift in the soil calcium/aluminium ratio continues to affect ecosystem services such as primary production. The difference in the calcium content of the vegetation and the topmost 10 cm of the soil in limed vs. unlimed plots amounts to approximately 19.5 g m−2, equivalent to 16.3% of the amount that was added to the plots some 70 years ago. In contrast, plots that were treated with nitrogen-phosphorus-potassium fertilizer in the 1930s did not differ from unfertilized plots in any of the soil and vegetation characteristics measured. Our findings suggest that the long-term legacy effect of historical liming is due to long-term storage of added calcium in stable soil pools, rather than a general increase in nutrient availability. Our results demonstrate that single applications of calcium in its carbonated form can profoundly and persistently alter ecosystem processes and services in mountain ecosystems.

The allelopathic effects of Festuca paniculata depend on competition in subalpine grasslands

Allelopathy is recognized as an important process in plant–plant interactions, but how it affects plant communities growing in competitive conditions has not been assessed. This article investigates whether the allelopathic effect of Festuca paniculata is modified by competition between target plants in subalpine grasslands. We hypothesized that plants growing in mixed stands will be more affected by allelochemicals than the same species in monoculture. At Lautaret pass (Northern French Alps), a pot experiment was designed. We used leachates from donor pots (Treatments: 1. Bare soil, 2. F. paniculata clipped, and 3. F. paniculata unclipped) to water target pots (Treatments: 1. Control (soil only), 2. Dactylis glomerata, 3. Agrostis capillaris, and 4. D. glomerata and A. capillaris). Target plants were cultivated during one growing season. The effects of leachates from donor pots and interspecific competition in target pots were evaluated by measuring the final biomass of plants. Soil fertility was controlled in all target pots by measuring NO3 −, NH4 +, N, and C % of the soil. Effect of target treatment under bare soil : Both D. glomerata and A. capillaris grew better in monocultures than in mixture. Effect of donor treatment on monocultures : Under bare soil, D. glomerata grew better than under F. paniculata leachates. By contrast, A. capillaris did not respond to donor pot treatment. Effect of donor treatment on mixtures: However, when both species were cultivated together under F. paniculata leachates, the biomass of D. glomerata was similar to that in monoculture under bare soil. Differences in sensitivity to allelopathy reversed the impact of interspecific competition: A. capillaris facilitated D. glomerata under allelopathy, which made allelopathy of F. paniculata on D. glomerata inefficient. The complexity of overlapping mechanisms of plant–plant interactions are highlighted by this semi-natural experiment. In subalpine grasslands, allelopathy not only limits the growth of neighboring plants, but it may also modify community assembly by affecting other plant–plant interactions such as competition. This study contributes to explore the way allelopathy interacts with other plant–plant interactions in natural systems.

High diversity of small organic N observed in soil water

The pool of organic N molecules in the soil solution reflects the activity of plants, microbes and other biological processes, and thus is likely to provide information important for ecosystem N and C cycling (e.g. organic N uptake by plants). Amino acids in soil water have often been a target of study, but few previous studies have attempted to examine a broader range of organic N molecules. The aim of this study was to develop a capillary electrophoresis-mass spectrometry (CE-MS) procedure for profiling of those small (<250 Da) organic N molecules in soil water that are amenable to analysis by CE-MS (viz., cationic at low pH, ionisable by electrospray). Centrifugal extracts of soil water from a sub-alpine grassland contained approximately 100 non-redundant peaks of small organic cations, 58 of which have been identified. Consistent with earlier studies, protein amino acids and common non-protein amino acids were among the most abundant compounds. Soil water also contained large amounts of several quaternary ammonium compounds (e.g. carnitine, acetyl carnitine, betaine, choline, ergothioneine) with the pool of quaternary ammonium compounds approximately 25% of the size of the pool of common amino acids. The large amounts of quaternary ammonium compounds in soil probably reflects their dual roles in central metabolism and osmoprotection in plants and microbes. Other identified compounds included unusual amino acids (e.g. β-alanine, pipecolic acid), heterocyclic compounds derived from aromatic amino acids (e.g. 4-(hydroxymethyl)imidazole, urocanate, nicotinic acid), amines (ethanolamine, spermine), sugar amines (glucosamine), and additional putative osmolytes of microbial or plant origin (trimethylamine N oxide, ectoine). Results of this study indicate that the pool of small organic N in soil water is more diverse than generally appreciated and not necessarily dominated by protein amino acids and common non-protein amino acids.

Carbohydrate and nitrogen stores in Festuca paniculata under mowing explain dominance in subalpine grasslands

Cessation of traditional management threatens semi-natural grassland diversity through the colonisation or increase of competitive species adapted to nutrient-poor conditions. Regular mowing is one practice that controls their abundance. This study evaluated the ecophysiological mechanisms limiting short- and long-term recovery after mowing for Festuca paniculata, a competitive grass that takes over subalpine grasslands in the Alps following cessation of mowing. We quantified temporal variations in carbon (C) and nitrogen (N) content, starch, fructan and total soluble sugars in leaves, stem bases and roots of F.paniculata during one growth cycle in mown and unmown fields and related them to the dynamics of soil mineral N concentration and soil moisture. Short-term results suggest that the regrowth of F.paniculata following mowing might be N-limited, first because of N dilution by C increments in the plant tissue, and second, due to low soil mineral N and soil moisture at this time of year. However, despite short-term effects of mowing on plant growth, C and N content and concentration at the beginning of the following growing season were not affected. Nevertheless, total biomass accumulation at peak standing biomass was largely reduced compared to unmown fields. Moreover, lower C storage capacity at the end of the growing season impacted C allocation to vegetative reproduction during winter, thereby dramatically limiting the horizontal growth of F.paniculata tussocks in the long term. We conclude that mowing reduces the growth of F.paniculata tussocks through both C and N limitation. Such results will help understanding how plant responses to defoliation regulate competitive interactions within plant communities.

Nitrogen deposition effects on subalpine grassland: The role of nutrient limitations and changes in mycorrhizal abundance

To better understand how increasing atmospheric nitrogen (N) deposition may affect subalpine grassland, we carried out a nutrient addition experiment in the Swiss Alps.N addition (+N) was combined with phosphorus (P) addition (+P) to determine nutrient limitations in plant functional groups. To examine responses of arbuscular mycorrhizal fungi (AMF) and AMF effects on plant growth, in-growth cores containing local plant species (phytometers) were inserted, and in half of them the external mycelium was disrupted weekly to impede mycorrhizal functioning. At harvest, aboveground biomass and element concentrations of the established vegetation were measured, as well as phytometer shoot and root mass, and the percentage of root length colonized (%RLC) by AMF.Only productivity of grasses increased under +N and +P, while other groups showed no or negative growth responses. +P decreased %RLC in all phytometers, whereas +N increased %RLC in the most abundant grass species, and reduced the relative abundance of arbuscules to total intraradical mycelium in the other species. Weekly destruction of the external mycelium reduced %RLC in most species, but did not affect plant biomass.The results suggest that increased N deposition in such N- and P-co-limited grassland will lead to shifts in plant functional group composition due to differences in the plants’ nutrient demand, that +N will affect AMF abundance and mutualistic functioning, but that changes in AMF abundance may not considerably affect plant growth.

Vegetation Database of the Grassland Communities in Anatolia

In Turkey approximately 20,000 vegetation releves do exist. However, there is no central database for Turkish vegetation releves. We started building a vegetation database based on grassland vegetation releves from published and unpublished data from Turkey. The database contains dune, steppic, alpine and subalpine grassland vegetation. Approximately 1,878 releves have been entered in TURBOVEG format. Plots were georeferenced using the Google Earth plugin integrated in the TURBOVEG software. Typical header data were entered when available. Most of the releves belong to the classes Astragalo-Brometea and DaphnoFestucetea. This report describes the available content in the Vegetation Database of the Grassland Communities in Anatolia (GIVD ID AS-TR-001).

Remote sensing-based estimation of gross primary production in a subalpine grassland

Abstract. This study investigates the performances in a terrestrial ecosystem of gross primary production (GPP) estimation of a suite of spectral vegetation indexes (VIs) that can be computed from currently orbiting platforms. Vegetation indexes were computed from near-surface field spectroscopy measurements collected using an automatic system designed for high temporal frequency acquisition of spectral measurements in the visible near-infrared region. Spectral observations were collected for two consecutive years in Italy in a subalpine grassland equipped with an eddy covariance (EC) flux tower that provides continuous measurements of net ecosystem carbon dioxide (CO2) exchange (NEE) and the derived GPP. Different VIs were calculated based on ESA-MERIS and NASA-MODIS spectral bands and correlated with biophysical (Leaf area index, LAI; fraction of photosynthetically active radiation intercepted by green vegetation, fIPARg), biochemical (chlorophyll concentration) and ecophysiological (green light-use efficiency, LUEg) canopy variables. In this study, the normalized difference vegetation index (NDVI) was the index best correlated with LAI and fIPARg (r = 0.90 and 0.95, respectively), the MERIS terrestrial chlorophyll index (MTCI) with leaf chlorophyll content (r = 0.91) and the photochemical reflectance index (PRI551), computed as (R531-R551)/(R531+R551) with LUEg (r = 0.64). Subsequently, these VIs were used to estimate GPP using different modelling solutions based on Monteith's light-use efficiency model describing the GPP as driven by the photosynthetically active radiation absorbed by green vegetation (APARg) and by the efficiency (ε) with which plants use the absorbed radiation to fix carbon via photosynthesis. Results show that GPP can be successfully modelled with a combination of VIs and meteorological data or VIs only. Vegetation indexes designed to be more sensitive to chlorophyll content explained most of the variability in GPP in the ecosystem investigated, characterised by a strong seasonal dynamic of GPP. Accuracy in GPP estimation slightly improves when taking into account high frequency modulations of GPP driven by incident PAR or modelling LUEg with the PRI in model formulation. Similar results were obtained for both measured daily VIs and VIs obtained as 16-day composite time series and then downscaled from the compositing period to daily scale (resampled data). However, the use of resampled data rather than measured daily input data decreases the accuracy of the total GPP estimation on an annual basis.

Temperature and Moisture Controls of C Fluxes in Grazed Subalpine Grasslands

The aim of this research was to determine how changes in soil moisture and temperature influence ecosystem C fluxes in the context of changing grazing regimes in subalpine grasslands in the Pyrenees. We (i) measured CO2 fluxes in the field in cattle- and sheep-grazed areas, and (ii) compared responses of CO2 and CH4 fluxes from soil turf samples from cattle- and sheep-grazed areas to changes in soil temperature and moisture. The cattle-grazed area showed greater ecosystem respiration and gross ecosystem photosynthesis than the sheep-grazed areas. With respect to the temperature and moisture treatments, the two areas responded in a similar way: Soil moisture was the strongest driver of soil respiration rates; although temperature also increased CO2 effluxes from the soils, the effects were transient. The greatest effluxes of CO2 were found in soils incubated at elevated temperature and 80% soil moisture content. Methane fluxes were only influenced by the moisture treatment, with the greatest methane oxidation rates found at 40% soil moisture content. We conclude that regional changes in moisture availability resulting from climate change are likely to be the most important driver of soil respiration and methane fluxes in these grazed subalpine ecosystems.

Land‐use change in subalpine grassland soils: Effect on particulate organic carbon fractions and aggregation

AbstractAbandonment of mountain grassland often changes vegetation composition and litter quantity and quality, but related effects on labile soil organic matter (SOM) are largely unknown. The aim of this study was to investigate the impacts of grassland management and abandonment on soil carbon distribution in light (&lt; 1.6 g cm–3) particulate organic matter (POM) and aggregation along a gradient of management intensity including hay meadows, pastures, and abandoned grasslands. The reduction of management intensity is an interregional phenomenon throughout the European Alps. We therefore selected sites from two typical climate regions, namely at Stubai Valley, Austria (MAT: 3°C, MAP: 1097 mm) and Matsch Valley, Italy (MAT: 6.6°C, MAP: 527 mm), to evaluate effects of land‐use change in relation to climate. Free water‐floatable and free POM (wPOM, fPOM), and an occluded POM fraction (oPOM), were isolated from three water‐stable aggregate size classes (2–6.3 mm, 0.25–2 mm, &lt; 0.25 mm) using density fractionation. Aggregate mean weight diameter slightly decreased with decreasing management intensity. In contrast to absolute POM‐C, fPOM‐C increased in aggregates at both sites with abandonment. Because the oPOM‐C was less affected by abandonment, the ratio of oPOM‐C : fPOM‐C shifted from &gt; 1 to &lt; 1 from meadow to abandoned grassland in aggregates at both sites and thus independent of climate. This suggests that in differently managed mountain grasslands free and occluded POM are functionally different SOM fractions. In bulk soil, the oPOM‐C : fPOM‐C ratio is better suited as an indicator for the response of SOM to management reduction in subalpine grasslands than the total soil C, absolute or relative POM‐C content.

Decomposition of labelled roots and root-C and -N allocation between soil fractions in mountain grasslands

Given the high turnover of fine roots in mountain grasslands, knowledge of their decomposition rates and the capacity of mountain grassland soils to stabilize root-derived C are central to understand the role of these ecosystems as potential C sinks. Here we studied the decomposition of fine roots in mountain grasslands and estimated the rates at which root-C and -N incorporated into protected pools at two soil depths. For this purpose, we incubated standard 13C- and 15N-labelled wheat roots mixed with unlabelled soil at 5 and 20 cm depth in two mountain grassland sites. Particle size fractionation allowed the quantification of the labelled wheat root-C and -N allocated to each size fraction (coarse sand, fine sand and silt plus clay sized) as well as their incorporation rates into the finest fraction. Between 62% and 78% root-C remained in the soil after one year of field incubation, faster decomposition being registered at the warmest site. In the following two years, roots decomposed much more slowly. In contrast to reports in the literature, our results indicate that decay rates during the first year were highest in the deep layer. The incorporation of wheat root-derived organic matter into the silt plus clay size fraction was also much greater during the first year of decomposition than in the following two years and also slightly higher in the deep soil than in topsoil. The incorporation rates of root-13C and root-15N into this fraction also suggest that the wheat-derived organic matter associated with this fraction was N-enriched and less recalcitrant (i.e., less resistant to acid hydrolysis) than that recovered from the coarser fractions. Furthermore, recalcitrant organic matter incorporated much more slowly than labile organic matter did. We conclude that the conditions of the subalpine grassland subsoil are more favourable for root decomposition than the topsoil and that the organic matter that incorporates into the protected pool is characterised by a high N content and low biochemical recalcitrance.

Control of soil pH on turnover of belowground organic matter in subalpine grassland

Grasslands store substantial amounts of carbon in the form of organic matter in soil and roots. At high latitudes and elevation, turnover of these materials is slow due to various interacting biotic and abiotic constraints. Reliable estimates on the future of belowground carbon storage in cold grassland soils thus require quantitative understanding of these factors. We studied carbon turnover of roots, labile coarse particulate organic matter (cPOM) and older non-cPOM along a natural pH gradient (3.9–5.9) in a subalpine grassland by utilizing soil fractionation and radiocarbon dating. Soil carbon stocks and root biomass, turnover, and decomposability did not scale with soil pH whereas mean residence times of both soil organic matter fractions significantly increased with declining pH. The effect was twice as strong for non-cPOM, which was also stronger enriched in 15N at low pH. Considering roots as important precursors for cPOM, the weaker soil pH effect on cPOM turnover may have been driven by comparably high root pH values. At pH < 5, long non-cPOM mean residence times were probably related to pH dependent changes in substrate availability. Differences in turnover along the pH gradient were not reflected in soil carbon stocks because aboveground productivity was lower under acidic conditions and, in turn, higher inputs from aboveground plant residues compensated for faster soil carbon turnover at less acidic pH. In summary, the study provides evidence for a strong and differential regulatory role of pH on the turnover of soil organic matter that needs consideration in studies aiming to quantify effects of changing environmental conditions on belowground carbon storage.

The response of soil moisture to rainfall event size in subalpine grassland and meadows in a semi-arid mountain range: A case study in northwestern China’s Qilian Mountains

Summary Knowledge of soil moisture is critical to understanding many of the hydrological processes that are of interest in soil hydrology, meteorology, and ecology research. In the present study, we used rainfall and soil moisture data from 2003 to 2008 measured at grassland and meadow sites in the Qilian Mountains of northwestern China to analyze the response of soil moisture to rainfall event size during the growing season. The responses of soil moisture at the grassland and meadow sites to rainfall event size were similar, although total rainfall, the frequency of large rainfall events, and the vegetation types were different. Soil moisture at depths of 20 and 40 cm increased significantly after rainfall events larger than 15 and 20 mm, respectively, but the magnitude of these changes varied in response to differences in the duration of the dry interval preceding the rain. Soil moisture at depths from 60 to 80 cm in the grassland increased obviously with rainfall events larger than 40 mm or after two consecutive large rainfall events, but was not significantly correlated with rainfall event size in the meadow. Soil moisture at depths from 120 to 160 cm did not change significantly during the growing season at either site. The soil water storage at depths from 20 to 80 cm at both sites increased obviously after rainfall events larger than 20 mm. The present results suggest that large rainfall events (>20 mm) play a key role in increasing soil water storage in the grassland and meadow ecosystems of these semi-arid mountains.

Glacial history and local adaptation explain differentiation in phenotypic traits in the Alpine grassland herb Campanula barbata

Background: Quaternary glaciations have affected the phylogeographic structure of many widespread plant species of the European Alps. Survival of plants in isolated refugia on the fringes of the Alps has been proposed as a main driver for molecular differentiation within species across the Alps, and could also be responsible for phenotypic differentiation. Aims: To establish if phenotypic differentiation is in accordance with phylogeographic structure and if population differentiation reflects adaptive processes. Methods: In a common garden we measured vegetative and reproductive traits of plants from 15 populations of two phylogeographic lineages of Campanula barbata from subalpine grasslands across the Alps. Results: The two phylogeographic lineages were differentiated in plant height and number of inflorescences, suggesting that glacial history affected phenotypic differentiation, either through neutral processes or adaptation. Furthermore, negative correlations of number of leaves, plant height, number of flowers and above-ground biomass with altitude of population origin indicated that part of the observed differentiation among populations was due to adaptation to current altitude-related conditions either during or after recolonisation. Conclusions: Our results suggest that phenotypic differentiation across the investigated regions may be due to glacial history-related processes as well as due to more recent processes of local adaptation.

Assessing long-term land-use legacies in subalpine grasslands by using a plant trait-based generic modelling framework

Background: In European mountains, where semi-natural grasslands have high cultural and nature conservation value, land-use legacies from past ploughing are associated with distinct floristic compositions and ecosystem properties. It remains unknown if these differences are stable or if post-arable grasslands are only transient states that eventually follow a predictable successional pathway. Aims: We use a generic vegetation dynamics model based on plant traits to test these alternative hypotheses in subalpine grasslands of the central French Alps. Methods: We classified dominant graminoids into trait-based Plant Functional Types (PFTs) and simulated their long-term response to fertility, annual mowing and past ploughing. Results: Simulations demonstrated that a temporary dispersal limitation of long-lived tussock grasses could have allowed species-rich hay meadows to develop as alternative communities. We also show that when they are regularly mown, meadows are resistant to colonisation by long-lived tussock grasses. Conclusions: Our results thus support traditional management based on regular mowing, but also highlight the key role of landscape history through its effects on dispersal. Our study also demonstrates the usefulness of easy-to-measure plant traits and a widely applicable generic modelling framework for testing hypotheses on the long-term interactions of multiple drivers of vegetation dynamics.

Impact of wild ungulate grazing on Orthoptera abundance and diversity in subalpine grasslands

Abstract. 1. Grasslands cover approximately 40% of the Earth’s terrestrial landscape, supporting large communities of vertebrate and invertebrate herbivores. Orthoptera play an important role, consuming relatively large amounts of biomass. Their occurrence can be strongly affected by habitat diversity and structure, which can be shaped by large herbivores. Several studies have focused on the impact of livestock on Orthoptera communities, but little is known about how wild ungulates influence the abundance and diversity of these insects in grassland ecosystems.2. We studied Orthoptera abundance and diversity in subalpine grasslands in the Swiss Alps, where grazing by red deer and chamois has created a mosaic of short‐ and tall‐grass patches. Data on vegetation structure, habitat diversity and plant nitrogen (N) content allowed us to consider how these parameters affected the occurrence of Orthoptera at our study sites.3. We found a total of nine Orthoptera species with an average density of 2.6 individuals m−2. Neither Orthoptera abundance nor diversity differed between short‐ and tall‐grass patches created by large ungulates. Both Orthoptera abundance and diversity were, however, positively influenced by increasing vegetation height, but negatively by increasing habitat diversity within patches. Increasing plant N content promoted a more even spread of species within the insect assemblage on short‐ but not on tall‐grass patches.4. Large‐scale habitat alteration by wild ungulates had no direct effect on the abundance and diversity of Orthoptera. However, we observed that they indirectly affected Orthoptera abundance and diversity by altering plant N content and the structure of the habitat at small scales.

Influence of Topography on the Colonization of Subalpine Grasslands by the Thorny Cushion Dwarf Echinospartum horridum

In this study, we analyzed the effect of topography, particularly slope, on the expansion rates and population dynamics of Echinospartum horridum at small spatial and temporal scales in the grassland communities of Ordesa–Monte Perdido National Park (OMPNP) (NE Spain). E. horridum is a thorny cushion dwarf, endemic of Spain and south of France, forming dense mono-specific large patches difficult to be penetrated by other plants and large herbivores once it is established. Between 2005 and 2007, we collected demographic parameters from 300 marked plants of E. horridum that were distributed in the center and the edge of four patches. At the patch edge, two of the four patches had a high slope (≥10°) and two had a low slope (<10°), whereas at the patch centers the slope was high (18°–30°). To calculate invasion speed, we use aerial photographs from 1981 and 2003. Plants in the center of patches had lower growth rates, fewer flowers, and higher crown death rates than did the plants at edge of patches. Slope influenced significantly invasion rates: the speed of expansion was lowest on gentle slopes, probably because of competition with grass. The speed of diffusion from 1981 to 2003 varied from 2.09 m yr−1 on the steep slopes to 1.93 m yr−1 on the shallow slope. Plant dynamics at patch edges suggest that colonization by E. horridum will continue in the grasslands of the OMPNP.

Winter CO2 fluxes in a sub-alpine grassland in relation to snow cover, radiation and temperature

Carbon dioxide (CO2) emissions were measured over a period of 3 years at the sub-alpine Swiss CARBOMONT site Rigi Seebodenalp. Here we show, that winter respiration contributes larger than expected to the annual CO2 budget at this high altitude, rich in belowground organic carbon grassland (7–15% C by mass). Furthermore the contribution of winter emissions to the annual CO2 budget is highly dependent on the definition of “winter” itself. Cumulative winter respiration determined over a 6 month period from 15th of October until 15th of April contributed 23.3 ± 2.4 and 6.0 ± 0.3% to the annual respiration during the years under observation, respectively. The insulation effect of snow and a lowering of the freezing point caused by high concentrations of soil organic solutes prevented the soil from freezing. These conditions favored higher soil temperatures resulting in relatively high respiratory losses. The duration of snow cover and micrometeorological conditions determining the photosynthetic activity of the vegetation during snow-free periods influenced the size and the variability of the winter CO2 fluxes. Seasonal values are strongly influenced by the days at the end and the beginning of the defined winter period, caused by large variations in length of periods with air temperatures below freezing. Losses of CO2 from the snow-covered soil were highest in winter 2003/2004. These high losses were partially explained by higher temperatures in the topsoil, caused by higher air temperatures just before snowfall. Thus, losses are not a consequence of higher soil temperatures registered during the summer heat wave 2003. However, water stress in summer 2003 might have caused an increment in dead organic matter in the soil providing additional substrate for microbial respiration in the following winter. Although considerable day-to-day fluctuations in snow effluxes were recorded, no conclusive and generally valid relationship could be found between CO2 losses from the snow pack and snow depth, rate of snow melt, wind speed or air pressure. This suggests that time lags and hysteresis effects may be more important for understanding winter respiration than concurrent environmental conditions in most ecosystems of comparable type.

Syntaxonomic revision and floristic characterization of the phytosociological alliances corresponding to subalpine and alpine grasslands of the Pyrenees and Cantabrian Mountains (classes Caricetea curvulae, Carici-Kobresietea, and Festuco-Seslerietea)

In this study, we made a numerical revision of the eight phytosociological alliances belonging to the classes Caricetea curvulae Br.-Bl. 1948, Carici rupestris-Kobresietea bellardii Ohba 1974, and Festuco-Seslerietea Barbéro & Bonin 1969. This analysis was designed to reveal the significant alliances corresponding to alpine and subalpine grasslands, review the associated syntaxonomical hierarchy, and establish the diagnostic floras of these alliances. The study area comprised the subalpine and alpine vegetation belts of the Pyrenees and the Cantabrian Mountains (northern Spain and southern France). We used 2259 floristic relevés, downloaded from the “Sistema de Información de la Vegetación Ibérica y Macaronésica” database, for statistical treatment. First, we classified the dataset, using the K-means clustering technique, so as to reveal a syntaxonomical structure. Second, we calculated the fidelity index Ochiai in all classification partitions. Finally, we compared the obtained lists with community descriptions from four bibliographical references. As a result, we could provide a diagnostic flora for every alliance. Therefore, we reconstructed seven of the eight alliances described. The numerical and bibliographical lists of characteristic species were similar for most syntaxa. Moreover, we proposed some new diagnostic species. Some alliances were considered more statistically robust than others. Finally, syntaxonomical repercussions have been suggested.

Assessing the impacts of mountain biking and hiking on subalpine grassland in Australia using an experimental protocol

Mountain biking is an increasingly popular, but sometimes controversial, activity in protected areas. Limited research on its impacts, including studies comparing biking with hiking, contributes to the challenges for mangers in assessing its appropriateness. The impacts of mountain bike riding off trail were compared to those of hiking on subalpine grassland in Australia using a modification of a common trampling experimental methodology. Vegetation and soil parameters were measured immediately and two weeks after different intensities of mountain biking (none, 25, 75, 200 and 500 passes across slope, 200 pass up and down slope) and hiking (200 and 500 passes across slope). There were reductions in vegetation height, cover and species richness, as well as changes in species composition and increases in litter and soil compaction with riding. Riding up and down a moderate slope had a greater impact than riding across the slope. Hiking also affected vegetation height, cover and composition. Mountain biking caused more damage than hiking but only at high use (500 passes). Further research including other ecosystems, topography, styles of riding, and weather conditions are required, but under the conditions tested here, hiking and mountain biking appear to be similar in their environmental impacts.