Dwarf-shrubs dynamics in Mediterranean high mountain ecosystems

QuestionVegetation in the alpine and treeline ecotone faces changes in both climate and land use. Shrub encroachment is considered an effect of these changes, but it’s still unclear how this effect is mediated by environmental heterogeneity. Our goal is to determine which environmental factors shape the fine-scale spatial distribution and temporal trends of alpine dwarf shrub.LocationThree sites in the Central Apennine, Italy.MethodsWe used a comprehensive set of environmental factors across a broad temporal span to model, at a fine-scale, both (1) the current spatial distribution and (2) the change in shrub cover over the past 60 years.ResultsOur results show that dwarf shrubs have generally increased in our study sites over the past 60 years, yet their distribution is strongly shaped by the joint influence of the fine-scale topography, productivity, land use and micro-climate. In particular, shrubs have been locally favored in areas with harsher alpine environmental constraints and stronger resource limitation. Instead, contrary to expectations, at this fine scale, warmer temperatures and the decline in grazing have not favored shrub encroachment.ConclusionDwarf shrubs appear as a stress-tolerant, pioneer vegetation that is currently distributed mainly over areas that are otherwise sparsely vegetated. It appears that shrubs exhibit poor competitive ability to invade grasslands and, though they have increased overall, they remain restricted to the least productive areas. Fine-scale environmental heterogeneity may strongly influence future responses of dwarf shrubs in changing alpine ecosystems.

Revisiting the subalpine Mesolithic site Ullafelsen in the Fotsch Valley, Stubai Alps, Austria – new insights into pedogenesis and landscape evolution from leaf-wax-derived <i>n</i>-alkanes, black carbon and radiocarbon dating

Archaeological research in high mountain regions has gotten a lot more attention since the discovery of the copper age mummy called “Ötzi” in the Ötztaler Alps in 1991. In the Tyrolean Stubai Alps, the Mesolithic site Ullafelsen at 1869 m a.s.l. (above sea level) close to the recent upper timberline in the Fotsch Valley represents, on the one hand, a very important archaeological reference site and offers, on the other hand, intriguing research questions related to, amongst others, pedogenesis. Given that no biomarkers and stable isotopes have been hitherto investigated, we aimed at contributing with respective analyses and additional radiocarbon dating to a better understanding of the landscape evolution and pedogenesis on and around the Ullafelsen. Our results for modern vegetation suggest that leaf-wax-derived n-alkanes allow us to chemotaxonomically distinguish between subalpine deciduous trees (nC27 predominance) versus (sub)alpine grasses, herbs and dwarf shrubs (nC29, nC31 and/or nC33 predominance). Except for Juniperus, conifers produce no or extremely low n-alkane contents. Although no clear vegetation changes could be inferred from the n-alkane patterns of the investigated soil profiles, the total n-alkane content (TAC) was developed for the first time as an unambiguous proxy for distinguishing between buried (= fossil) topsoils (2Ahb horizons) and humus-enriched subsoils such as Bh horizons of podzols. Based on this leaf wax proxy, we can rule out that the 2Ahb?/Bh? horizons under question on the Ullafelsen are buried topsoils as suggested previously. Dating of the H2O2-pretreated soil samples yielded 14C ages for the podzol Bh horizons ranging from 6.7 to 5.4 cal kyr BP. This is clearly younger than the overlying Mesolithic living floor (LL) (10.9 to 9.5 cal kyr BP) but pre-dates the assumed intensification of alpine pasturing from the Bronze Age onwards. Both the LL and the directly overlying OAh3 horizon yielded black carbon maxima and benzene polycarboxylic acid patterns reflecting fire-induced human impact during the Mesolithic. The discrepancy between the Mesolithic charcoal 14C ages (ages of ≥ 9.5 cal kyr BP) versus the 14C ages obtained for bulk n-alkanes ranging from 8.2 to 4.9 cal kyr BP suggests that non-alkane-producing conifers predominated the vegetation on and around the Ullafelsen after the Mesolithic occupation. Only with the anthropo-zoological lowering of the timberline associated with alpine pasturing since the Neolithic and especially the Bronze Age has an n-alkane-producing vegetation cover (grasses, herbs or dwarf shrubs) started to predominate.

Ancient sedimentary DNA shows rapid post-glacial colonisation of Iceland followed by relatively stable vegetation until Landnám

&lt;p&gt;Understanding patterns of colonisation is important for explaining both the distribution of single species and anticipating how ecosystems may respond to global warming. Insular flora may be especially vulnerable because oceans represent severe dispersal barriers. Here we analyse two lake sediment cores from Iceland for ancient sedimentary DNA to infer patterns of colonisation and Holocene vegetation development. Our cores from lakes Torfdalsvatn and Nykurvatn span the last c. 12,000 cal. yr BP and c. 8600 cal. yr BP, respectively. With near-centennial resolution, we identified a total of 191 plant taxa, with 152 taxa identified in the sedimentary record of Torfdalsvatn and 172 plant taxa in the sedimentary record of Nykurvatn. The terrestrial vegetation at Torfdalsvatn was first dominated by bryophytes, arctic herbs such as Saxifraga spp. and grasses. Around 10,100 cal. yr BP, a massive immigration of new taxa was observed, and shrubs and dwarf shrubs became common whereas aquatic macrophytes became dominant. At Nykurvatn, all dominant taxa occurred already in the earliest samples; shrubs and dwarf shrubs were more abundant at this site than at Torfdalsvatn. There was an overall steep increase both in the local and regional species pool until 8000 cal. yr BP, by which time &amp;#190; of all taxa identified had arrived. In the period 4500-1000 cal. yr BP, a few new taxa of bryophytes, graminoids and forbs are identified. The last millennium, after human settlement of the island (Landn&amp;#225;m), is characterised by a sudden disappearance of Juniperus communis, but also reappearance of some high arctic forbs and dwarf shrubs. Notable immigration during the Holocene coincides with periods of dense sea-ice cover, and we hypothesise that this may have acted as a dispersal vector. Thus, although ongoing climate change might provide a suitable habitat in Iceland for a large range of species only found in the neighbouring regions today, the reduction of sea ice may in fact limit the natural colonisation of new plant species.&lt;/p&gt;

Dwarf Shrubs Impact Tundra Soils: Drier, Colder, and Less Organic Carbon

In the tundra, woody plants are dispersing towards higher latitudes and altitudes due to increasingly favourable climatic conditions. The coverage and height of woody plants are increasing, which may influence the soils of the tundra ecosystem. Here, we use structural equation modelling to analyse 171 study plots and to examine if the coverage and height of woody plants affect the growing-season topsoil moisture and temperature (< 10 cm) as well as soil organic carbon stocks (< 80 cm). In our study setting, we consider the hierarchy of the ecosystem by controlling for other factors, such as topography, wintertime snow depth and the overall plant coverage that potentially influence woody plants and soil properties in this dwarf shrub-dominated landscape in northern Fennoscandia. We found strong links from topography to both vegetation and soil. Further, we found that woody plants influence multiple soil properties: the dominance of woody plants inversely correlated with soil moisture, soil temperature, and soil organic carbon stocks (standardised regression coefficients = − 0.39; − 0.22; − 0.34, respectively), even when controlling for other landscape features. Our results indicate that the dominance of dwarf shrubs may lead to soils that are drier, colder, and contain less organic carbon. Thus, there are multiple mechanisms through which woody plants may influence tundra soils.

Ancient sedimentary DNA shows rapid post-glacial colonisation of Iceland followed by relatively stable vegetation until Landnám

Understanding patterns of colonisation is important for explaining both the distribution of single species and anticipating how ecosystems may respond to global warming. Insular flora may be especially vulnerable because oceans represent severe dispersal barriers. Here we analyse two lake sediment cores from Iceland for ancient sedimentary DNA to infer patterns of colonisation and Holocene vegetation development. Our cores from lakes Torfdalsvatn and Nykurvatn span the last c. 12,000 cal. yr BP and c. 8600 cal. yr BP, respectively. With near-centennial resolution, we identified a total of 191 plant taxa, with 152 taxa identified in the sedimentary record of Torfdalsvatn and 172 plant taxa in the sedimentary record of Nykurvatn. The terrestrial vegetation at Torfdalsvatn was first dominated by bryophytes, arctic herbs such as Saxifraga spp. and grasses. Around 10,100 cal. yr BP, a massive immigration of new taxa was observed, and shrubs and dwarf shrubs became common whereas aquatic macrophytes became dominant. At Nykurvatn, all dominant taxa occurred already in the earliest samples; shrubs and dwarf shrubs were more abundant at this site than at Torfdalsvatn. There was an overall steep increase both in the local and regional species pool until 8000 cal. yr BP, by which time ¾ of all taxa identified had arrived. In the period 4500-1000 cal. yr BP, a few new taxa of bryophytes, graminoids and forbs are identified. The last millennium, after human settlement of the island (Landnám), is characterised by a sudden disappearance of Juniperus communis, but also reappearance of some high arctic forbs and dwarf shrubs. Notable immigration during the Holocene coincides with periods of dense sea-ice cover, and we hypothesise that this may have acted as a dispersal vector. Thus, although ongoing climate change might provide a suitable habitat in Iceland for a large range of species only found in the neighbouring regions today, the reduction of sea ice may in fact limit the natural colonisation of new plant species.

Architecture of dwarf shrubs and dwarf subshrubs of the genus of Thymus L. and Scutellaria L. (Lamiaceae)

The structure of 24 species of Thymus and 12 species of Scutellaria was studied using the architectural approach. For the first time, an architectural unit was described, it is a branched sympodial axis. The architectural unit consists of sympodial axes n+1 order, formation shoots, branching shoots, ephemerous shoots. The wide distribution of species and development of species in contrasting habitat conditions is due to the diversity of sympodial axes and shoots that are part of the architectural unit. Depending on the type of branching and the spatial position of sympodial axes, six modifications of architectural unit were identified. It is established that the structure of mature individuals are formed due to the repetition one of the same modification of architectural unit or a combination different modifications of architectural unit. Each of the variants of the combination determines the type of life form (dwarf shrub or dwarf subshrub) and biomorph (monocentric, dense polycentric, sparse polycentric) and depends on the conditions of the ecotope. The identified modifications of the architectural unit and the variants of their combination determine the strategy for the development of dwarf shrubs and dwarf subshrubs in the development of Northern and Central Asia.

Shrub and dwarf shrub communities of Sangilen Plateau

The paper presents a detailed ecological and caenotic characteristic of dwarf shrub and shrub communities growing in the highmountain belt of the Sangilen Plateau. The communities investigated were referred to the class of Loiseleurio-Vaccinietea Eggler 1952. The dwarf birch thickets with prevalence of Betula rotundifolia and the high incidence of Caragana jubata, Juniperus pseudosabina, J. sibirica, Pentaphylloides fruticosa, Salix glauca, Spiraea alpina were referred to the union of Carici tristis–Betulion rotundifoliae Zibzeev et al. 2018 of the order of Betuletalia rotundifoliae Mirkin at al. ex Chytrý Pešout et Anenkhonov 1993. Communities with dominant calciphilous shrubs and dwarf shrubs, such as Rhododendron adamsii, Caragana jubata, Salix berberifolia, S. reticulata, were referred to the union of Saxifrago oppositifoliae–Rhododendrion adamsii Zibzeev et al. 2018 of the order of Rhododendro-Vaccinietalia Br.-Bl. ex Daniels 1994.

Effect of Vaccinium vitis-idaea L. and moisture on mountain-meadow soils

&lt;p&gt;Against the climate change there has been an overgrowing of phytocenoses of alpine lichen heath and arctic tundra with dwarf shrubs and shrubs over the past 40 years. Dwarf shrubs roots of &lt;em&gt;Vaccinium vitis-idaea&lt;/em&gt; L. forms symbiosis with ericoid mycorrhiza, which may lead to change of soil properties. Mycorrhizal fungi regulate nitrogen, phosphorus and carbon cycles by secretion of active enzymes which depolymerize and mineralize soil organic matter and increase available of mineral nutrition elements for vegetation and microorganisms.&lt;/p&gt;&lt;p&gt;Moreover, in the previous research it was found that moisture was greater under shrubs than under alpine lichen heath. It is known that moisture plays key role in microbial processes in the soil, affect on enzyme activity, nitrification, mineralization and so on. Therefore, the objective of this research is to evaluate the influence of both dwarf shrubs and moisture on the soil characteristics.&lt;/p&gt;&lt;p&gt;Research area is located around 2750 m a.s.l. in the alpine heath of Teberda Nature Reserve, North Caucasus, Karachay-Cherkess Republic where 3 areas with different moisture (15, 21 and 27%) were chosen. In each area samples of mountain-meadow soil were collected from under dwarf shrubs and alpine lichen heath without dwarf shrubs (control) during 10 days of the second part of July and then frozen until laboratory analysis. Firstly, there were analyzed chemical (soil pH, mineral P, organic N, C, inorganic N) and biological (C and N of microbial biomass, basal respiration, mineralization, nitrification and activity of glucosidase, phosphatase, chitinase and leucinaminopeptidase) properties of the soil samples. Furthermore, it was made statistical analysis in Statistica 8.0 program.&lt;/p&gt;&lt;p&gt;&amp;#160;It was found that increase in moisture is accompanied by increase in concentrations of inorganic forms of nitrogen, C and N of microbial biomass, basal respiration and nitrification activity in heath without shrubs, which indicates a growth of microbiota activity. However concentrations of labile organic carbon and nitrogen, and enzymatic activity decrease at the same conditions. Such changes indicate a shift from a community of heath with herbal vegetation to communities dominated by ericoid mycorrhizal plants.&lt;/p&gt;&lt;p&gt;The investigation also revealed that soil acidity is significantly higher under &lt;em&gt;V. vitis-idaea&lt;/em&gt; L., however, there is a noticeable decrease in nitrification activity, inorganic nitrogen concentrations, which indicates minor dependence of the dwarf shrubs on mineral compounds in nitrogen nutrition.&lt;/p&gt;&lt;p&gt;Thus, both the presence of &lt;em&gt;V. vitis-idaea&lt;/em&gt; L. and various moisture have a significant effect on the soil characteristics. Moreover, the moisture under control plays an essential role, while under the dwarf shrubs many soil properties remain unchanged, therefore, &lt;em&gt;V. vitis-idaea&lt;/em&gt; L. creates a microclimate in the soil among roots where moisture has no effect.&lt;/p&gt;