The Caledonian mountains. Northern Europe, and their changing ecosystems

With the exception of solar conditions, the climate of the Caledonian Mountains, Northern Europe, is influenced more by the nearness to the Atlantic Ocean and the Gulf Stream than by altitude and latitude. The length of the photoperiod during the growing season increases with latitude, although the total solar influx decreases. Heaths composed of species with a boreal distribution are particularly characteristic at low altitudes and latitudes, whereas species with an arctic and arctic-alpine distribution dominate at high altitudes and latitudes. Periodic events in the population dynamics of certain plant and animal species distinguish the ecosystems at high latitudes from those at low latitude. The effects of global change are likely to become most pronounced in the north since the rate at which the ultraviolet-B (UV-B) absorbing ozone layer is being reduced and the increase in concentration of «greenhouse gases» in the atmosphere are both higher in the arctic than in regions further south. Changes in the ecosystems due to increased direct human impacts are also likely to occur in some areas.[fr] À l'exception des conditions solaires, le climat des montagnes dites «Caledonian», au Nord de l'Europe, est beaucoup plus influencé par la proximité de l'Océan Atlantique et le Goulf Stream que par l'altitude ou la latitude. La durée de la photopériode pendant la saison de végétation augmente avec la latitude, tandis que la radiation solaire total s'abaisse. À des altitudes et latitudes basses, les landes riches en espèces à distribution boréale deviennent caractéristiques, tandis que les espèces arctiques et artico-alpines dominent dans les hautes altitudes ou latitudes. Des événements périodiques dans la dynamique de la population de certains animaux ou plantes peuvent distinguer les écosystèmes des hautes latitudes de ceux de basse latitude. Les effets du changement climatique global seraient bien sûr plus prononcés au nord, car d'une part le taux d'absortion de Vultraviolet-B (UV-B) par la couche d'ozone devient plus bas et d'autre part la concentration de gaz à effet de serre est plus forte dans les régions arctiques que plus au sud. De plus, dans certaines régions, il y a de changements dans les écosystèmes dûs à un impact direct croissant des activités humaines. [es] Condiciones solares aparte, el clima de las montañas caledonianas, situadas en el N de Europa, viene condicionado por la cercanía del Océano Atlántico y la corriente del Golfo, más que por la latitud y la altitud. Es sabido que la duración del fotoperíodo en el período de crecimiento vegetativo se incrementa con la latitud, aunque el flujo total solar descienda. Los brezales en cuya composición entran especies de distribución boreal son muy característicos de las bajas altitudes y latitudes. Ahora bien, las perturbaciones periódicas que tienen lugar en la dinámica poblacional de ciertas plantas o animales distinguen los ecosistemas de latitudes elevadas de los que están situados a baja latitud. Sin duda, los efectos del cambio global serán más intensos en el Norte, por cuanto la tasa de absorción de rayos ultravioleta B (UV-B) por parte de la capa de ozono se aminora y el incremento de la concentración de los «gases-invernadero» es consecuentemente mayor en el Ártico que en las zonas más meridionales. Además, en los ecosistemas también se están notando cambios por causa de los crecientes impactos directos de las actividades humanas en ciertas áreas

Effects of Warming on Shrub Abundance and Chemistry Drive Ecosystem-Level Changes in a Forest-Tundra Ecotone

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

Quantitative importance of staminodes for female reproductive success in Parnassia palustris under contrasting environmental conditions.

The five sterile stamens, or staminodes, in Parnassia palustris act both as false and as true nectaries. They attract pollinators with their conspicuous, but non-rewarding tips, and also produce nectar at the base. We removed staminodes experimentally and compared pollinator visitation rate and duration and seed set in flowers with and without staminodes in two different populations. We also examined the relative importance of the staminode size to other plant traits. Finally, we bagged, emasculated, and supplementary cross-pollinated flowers to determine the pollination strategy and whether reproduction was limited by pollen availability. Flowers in both populations were highly dependent on pollinator visitation for maximum seed set. In one population pollinators primarily cross-pollinated flowers, whereas in the other the pollinators facilitated self-pollination. The staminodes caused increased pollinator visitation rate and duration to flowers in both populations. The staminodes increased female reproductive success, but only when pollen availability constrained female reproduction. Simple linear regression indicated a strong selection on staminode size, multiple regression suggested that selection on staminode size was mainly caused by correlation with other traits that affected female fitness. [ABSTRACT FROM AUTHOR

Experimental warming differentially affects vegetative and reproductive phenology of tundra plants

Rapid climate warming is altering Arctic and alpine tundra ecosystem structure and function, including shifts in plant phenology. While the advancement of green up and flowering are well-documented, it remains unclear whether all phenophases, particularly those later in the season, will shift in unison or respond divergently to warming. Here, we present the largest synthesis to our knowledge of experimental warming effects on tundra plant phenology from the International Tundra Experiment. We examine the effect of warming on a suite of season-wide plant phenophases. Results challenge the expectation that all phenophases will advance in unison to warming. Instead, we find that experimental warming caused: (1) larger phenological shifts in reproductive versus vegetative phenophases and (2) advanced reproductive phenophases and green up but delayed leaf senescence which translated to a lengthening of the growing season by approximately 3%. Patterns were consistent across sites, plant species and over time. The advancement of reproductive seasons and lengthening of growing seasons may have significant consequences for trophic interactions and ecosystem function across the tundra

Strong microsite control of seedling recruitment in tundra

The inclusion of environmental variation in studies of recruitment is a prerequisite for realistic predictions of the responses of vegetation to a changing environment. We investigated how seedling recruitment is affected by seed availability and microsite quality along a steep environmental gradient in dry tundra. A survey of natural seed rain and seedling density in vegetation was combined with observations of the establishment of 14 species after sowing into intact or disturbed vegetation. Although seed rain density was closely correlated with natural seedling establishment, the experimental seed addition showed that the microsite environment was even more important. For all species, seedling emergence peaked at the productive end of the gradient, irrespective of the adult niches realized. Disturbance promoted recruitment at all positions along the environmental gradient, not just at high productivity. Early seedling emergence constituted the main temporal bottleneck in recruitment for all species. Surprisingly, winter mortality was highest at what appeared to be the most benign end of the gradient. The results highlight that seedling recruitment patterns are largely determined by the earliest stages in seedling emergence, which again are closely linked to microsite quality. A fuller understanding of microsite effects on recruitment with implications for plant community assembly and vegetation change is provided

Conservation genetics of the annual hemiparasitic plant Melampyrum sylvaticum (Orobanchaceae) in the UK and Scandinavia

Melampyrum sylvaticum is an endangered annual hemiparasitic plant that is found in only 19 small and isolated populations in the United Kingdom (UK). To evaluate the genetic consequences of this patchy distribution we compared levels of diversity, inbreeding and differentiation from ten populations from the UK with eight relatively large populations from Sweden and Norway where the species is more continuously distributed. We demonstrate that in both the UK and Scandinavia, the species is highly inbreeding (global F IS = 0.899). Levels of population differentiation were high (F’ST = 0.892) and significantly higher amongst UK populations (F’ST = 0.949) than Scandinavian populations (F’ST = 0.762; P < 0.01). The isolated populations in the UK have, on average, lower genetic diversity (allelic richness, proportion of loci that are polymorphic, gene diversity) than Scandinavian populations, and this diversity difference is associated with the smaller census size and population area of UK populations. From a conservation perspective, the naturally inbreeding nature of the species may buffer the species against immediate effects of inbreeding depression, but the markedly lower levels of genetic diversity in UK populations may represent a genetic constraint to evolutionary change. In addition, the high levels of population differentiation suggest that gene flow among populations will not be effective at replenishing lost variation. We thus recommend supporting in situ conservation management with ex situ populations and human-mediated seed dispersal among selected populations in the UK

Reproductive Ecology and Severe Pollen Limitation in the Polychromic Tundra Plant, Parrya nudicaulis (Brassicaceae)

Pollen limitation is predicted to be particularly severe in tundra habitats. Numerous reproductive patterns associated with alpine and arctic species, particularly mechanisms associated with reproductive assurance, are suggested to be driven by high levels of pollen limitation. We studied the reproductive ecology of Parrya nudicaulis, a species with relatively large sexual reproductive investment and a wide range of floral pigmentation, in tundra habitats in interior montane Alaska to estimate the degree of pollen limitation. The plants are self-compatible and strongly protandrous, setting almost no seed in the absence of pollinators. Supplemental hand pollinations within pollinator exclusion cages indicated no cage effect on seed production. Floral visitation rates were low in both years of study and particularly infrequent in 2010. A diversity of insects visited P. nudicaulis, though syrphid and muscid flies composed the majority of all visits. Pollen-ovule ratios and levels of heterozygosity are consistent with a mixed mating system. Pollen limitation was severe; hand pollinations increased seed production per plant five-fold. Seed-to-ovule ratios remained low following hand pollinations, indicating resource limitation is likely to also be responsible for curtailing seed set. We suggest that pollen limitation in P. nudicaulis may be the result of selection favoring an overproduction of ovules as a bet-hedging strategy in this environmental context of highly variable pollen receipt