Modern pollen samples from alpine vegetation on the Tibetan Plateau.

1  A set of 316 modern surface pollen samples, sampling all the alpine vegetation types that occur on the Tibetan Plateau, has been compiled and analysed. Between 82 and 92% of the pollen present in these samples is derived from only 28 major taxa. These 28 taxa include examples of both tree (AP) and herb (NAP) pollen types. 2  Most of the modern surface pollen samples accurately reflect the composition of the modern vegetation in the sampling region. However, airborne dust-trap pollen samples do not provide a reliable assessment of the modern vegetation. Dust-trap samples contain much higher percentages of tree pollen than non-dust-trap samples, and many of the taxa present are exotic. In the extremely windy environments of the Tibetan Plateau, contamination of dust-trap samples by long-distance transport of exotic pollen is a serious problem. 3  The most characteristic vegetation types present on the Tibetan Plateau are alpine meadows, steppe and desert. Non-arboreal pollen (NAP) therefore dominates the pollen samples in most regions. Percentages of arboreal pollen (AP) are high in samples from the southern and eastern Tibetan Plateau, where alpine forests are an important component of the vegetation. The relative importance of forest and non-forest vegetation across the Plateau clearly follows climatic gradients: forests occur on the southern and eastern margins of the Plateau, supported by the penetration of moisture-bearing airmasses associated with the Indian and Pacific summer monsoons; open, treeless vegetation is dominant in the interior and northern margins of the Plateau, far from these moisture sources. 4  The different types of non-forest vegetation are characterized by different modern pollen assemblages. Thus, alpine deserts are characterized by high percentages of Chenopodiaceae and Artemisia, with Ephedra and Nitraria. Alpine meadows are characterized by high percentages of Cyperaceae and Artemisia, with Ranunculaceae and Polygonaceae. Alpine steppe is characterized by high abundances of Artemisia, with Compositae, Cruciferae and Chenopodiaceae. Although Artemisia is a common component of all non-forest vegetation types on the Tibetan Plateau, the presence of other taxa makes it possible to discriminate between the different vegetation types. 5  The good agreement between modern vegetation and modern surface pollen samples across the Tibetan Plateau provides a measure of the reliability of using pollen data to reconstruct past vegetation patterns in non-forested areas.

Impact of Holocene climate changes on alpine and treeline vegetation at Sanetsch Pass, Bernese Alps, Switzerland

In order to infer reactions of treeline and alpine vegetation to climatic change, past vegetation changes are reconstructed on the basis of pollen, macrofossil and charcoal analysis. The sampled sediment cores originate from the small pond Emines, located at the Sanetsch Pass (connecting the Valais and Bern, Switzerland) at an altitude of 2288 m a.s.l. Today's treeline is at ca. 2200 m a.s.l. in the area, though due to special pass (saddle) conditions it is locally depressed to ca. 2060 m a.s.l. Our results reveal that the area around Emines was covered by treeless alpine vegetation during most of the past 12,000 years. Single individuals of Betula, Larix decidua and possibly Pinus cembra occurred during the Holocene. Major centennial to millennial-scale responses of treeline vegetation to climatic changes are evident. However, alpine vegetation composition remained rather stable between 11,500 and 6000 cal. BP, showing that Holocene climatic changes of +/− 1 °C hardly influenced the local vegetation at Emines. The rapid warming of 3–4 °C at the Late Glacial/Holocene transition (11,600 cal. BP) caused significant altitudinal displacements of alpine species that were additionally affected by the rapid upward movement of trees and shrubs. Since the beginning of the Neolithic, vegetation changes at Sanetsch Pass resulted from a combination of climate change and human impact. Anthropogenic fire increase and land-use change combined with a natural change from subcontinental to more oceanic climate during the second half of the Holocene led to the disappearance of P. cembra in the study area, but favoured the occurrence of Picea abies and Alnus viridis. The mid- to late-Holocene decline of Abies alba was primarily a consequence of human impact, since this mesic species should have benefitted from a shift to more oceanic conditions. Future alpine vegetation changes will be a function of the amplitude and rapidity of global warming as well as human land use. Our results imply that alpine vegetation at our treeline pass site was never replaced by forests since the last ice-age. This may change in the future if anticipated climate change will induce upslope migration of trees. The results of this study emphasise the necessity of climate change mitigation in order to prevent biodiversity losses as a consequence of unprecedented community and species displacement in response to climatic change.

Factors Controlling Species Richness in Alpine Plant Communities: An Assessment of the Importance of Stress and Disturbance

This study explores whether the high variability of vascular plant diversity among alpine plant communities can be explained by stress and/or disturbance intensities. Species numbers of 14 alpine plant communities were sampled in the Swiss Alps. To quantify the intensity of 13 stress and 6 disturbance factors potentially controlling plant life in these communities, a survey was conducted by asking numerous specialists in alpine vegetation to assess the importance of the different factors for each community. The estimated values were combined in stress- and disturbance-indices which were compared with diversity according to the Intermediate Stress Hypothesis, the Intermediate Disturbance Hypothesis, and the Dynamic Equilibrium Model, respectively. Each of these theories explained a part of the variability in the species richness, but only the Dynamic Equilibrium Model provided a complete and consistent explanation. The last model suggests that community species richness within the alpine life zone is generally controlled by stress intensity. Disturbance and competition seem to play a secondary role by fine-tuning diversity in specific communities. As diversity is primarily limited by stress, a moderation of temperature-related stress factors, as a result of global warming, may cause a shift of the equilibrium between stress, disturbance, and competition in alpine ecosystems.

Impacts of climate change on vegetation distribution. No. 1: Climate change induced vegetation shifts in the palearctic region

Global average temperature has increased and precipitation pattern has altered over the past 100 years due to increases in greenhouse gases. These changes will alter numerous site factors and biochemical processes of vegetative communities such as nutrient and water availability, permafrost thawing, fire regime, biotic interactions and invasion. As a consequence, climate change is expected to alter distribution ranges of many species and communities as well as boundaries of biomes. Shifting of species and vegetation zones northwards and upwards in elevation has already been observed. Besides, several experiments have been conducted and simulations have been run all over the world in order to predict possible range shifts and ecological risks. In this paper, we review literature available in Web of Science on Europe and boreal Eurasia and give an overview of observed and predicted changes in vegetation in these regions. The main trends include advance of the tree line, reduction of the alpine vegetation belt, drought risk, forest diebacks, a shift from coniferous forests to deciduous forests and invasion. It is still controversial if species migration will be able to keep pace with climate change.

Distribution and species diversity of plant communities along transect on the Northeastern Tibetan plateau

The distribution and species diversity of plant communities along a 600 km transect through the northeastern Tibetan Plateau (32 degrees 42'-35 degrees 07' N, 101 degrees 02'-97 degrees 38' E) with altitudes from 3255 to 4460 m are described. The transect started from the Youyi Bridge of Banma through Dari, Maqin and Maduo to Zaling Lake. The data from 47 plots along the transect are summarized and analyzed. The mean annual temperature, the mean annual rainfall and the length of growing season decreases from 2.6 to -4.5 degrees C, from 767.2 to 240.1 mm, from 210 to 140 days, respectively, along the transect from the southeastern Banma to northwestern Zaling Lake. The number of vascular plant species recorded in 47 plots is 242 including 2 tree, 34 shrub, 206 herb species. Main vegetation types on the transect from southeast to northwest are: Sabina convallium forest, Picea likiangensis forest, Pyracantha fortuneana + Spiraea alpina shrub, Hippophae neurocarpu shrub, Sibiraea angustata + Polygonum viviparum shrub, Stellera chamaejasme herb meadow, Potentilla fruticosa + Salix obscura + Carex sp. Shrub, Kobresia capillifolia meadow, P. froticosa + Kobresia humilis shrub, Caragana jubata + S. obscura shrub, Kobresia tibetica meadow, Kobresia pygmaea meadow, K. pygmaea + Stipa purpurea steppe meadow, Stipa purpurea steppe. Plant richness and diversity index all showed a decreasing trend with increasing of elevation along transect from southeast to northwest. Detailed information on altitudinal ranges and distribution of the alpine vegetation, vascular flora and environments over the alpine zone at northeastern Tibetan Plateau provides baseline records relevant to future assessment of probable effects of global climate changes.

Descriptions and validation of the names of some high-rank syntaxa in the European Asplenietea trichomanis and Polypodietea

The paper presents the description of one new order (Asplenietalia septentrionalo-cuneifolii) and two new alliances (Arenarion bertolonii and Physoplexido comosae- Saxifragion petraeae). In addition, the syntaxon Asplenietalia lanceolato-obovati is here formally raised to the order level and the name Hypno-Polypodietalia vulgaris is validated.

A model-data comparison of Holocene timberline changes in the Swiss Alps reveals past and future drivers of mountain forest dynamics

Mountain vegetation is strongly affected by temperature and is expected to shift upwards with climate change. Dynamic vegetation models are often used to assess the impact of climate on vegetation and model output can be compared with paleobotanical data as a reality check. Recent paleoecological studies have revealed regional variation in the upward shift of timberlines in the Northern and Central European Alps in response to rapid warming at the Younger Dryas/Preboreal transition ca. 11700years ago, probably caused by a climatic gradient across the Alps. This contrasts with previous studies that successfully simulated the early Holocene afforestation in the (warmer) Central Alps with a chironomid-inferred temperature reconstruction from the (colder) Northern Alps. We use LandClim, a dynamic landscape vegetation model to simulate mountain forests under different temperature, soil and precipitation scenarios around Iffigsee (2065m a.s.l.) a lake in the Northwestern Swiss Alps, and compare the model output with the paleobotanical records. The model clearly overestimates the upward shift of timberline in a climate scenario that applies chironomid-inferred July-temperature anomalies to all months. However, forest establishment at 9800 cal. BP at Iffigsee is successfully simulated with lower moisture availability and monthly temperatures corrected for stronger seasonality during the early Holocene. The model-data comparison reveals a contraction in the realized niche of Abies alba due to the prominent role of anthropogenic disturbance after ca. 5000 cal. BP, which has important implications for species distribution models (SDMs) that rely on equilibrium with climate and niche stability. Under future climate projections, LandClim indicates a rapid upward shift of mountain vegetation belts by ca. 500m and treeline positions of ca. 2500m a.s.l. by the end of this century. Resulting biodiversity losses in the alpine vegetation belt might be mitigated with low-impact pastoralism to preserve species-rich alpine meadows.

Effects of elevation and land use on the biomass of trees, shrubs and herbs at Mount Kilimanjaro

The protection and sustainable management of forest carbon stocks, particularly in the tropics, is a key factor in the mitigation of global change effects. However, our knowledge of how land use and elevation affect carbon stocks in tropical ecosystems is very limited. We compared aboveground biomass of trees, shrubs and herbs for eleven natural and human-influenced habitat types occurring over a wide elevation gradient (866–4550 m) at the world's highest solitary mountain, Mount Kilimanjaro. Thanks to the enormous elevation gradient, we covered important natural habitat types, e.g., savanna woodlands, montane rainforest and afro-alpine vegetation, as well as important land-use types such as maize fields, grasslands, traditional home gardens, coffee plantations and selectively logged forest. To assess tree and shrub biomass with pantropical allometric equations, we measured tree height, diameter at breast height and wood density and to assess herbaceous biomass, we sampled destructively. Among natural habitats, tree biomass was highest at intermediate elevation in the montane zone (340 Mg ha−1), shrub biomass declined linearly from 7 Mg ha−1 at 900 m to zero above 4000 m, and, inverse to tree biomass, herbaceous biomass was lower at mid-elevations (1 Mg ha−1) than in savannas (900 m, 3 Mg ha−1) or alpine vegetation (above 4000 m, 6 Mg ha−1). While the various land-use types dramatically decreased woody biomass at all elevations, though to various degrees, herbaceous biomass was typically increased. Our study highlights tropical montane forest biomass as important aboveground carbon stock and quantifies the extent of the strong aboveground biomass reductions by the major land-use types, common to East Africa. Further, it shows that elevation and land use differently affect different vegetation strata, and thus the matrix for other organisms.

Mean cover and frequencies of vascular plant species during three decades around Abisko Scientific Research Station

Plant species distributions are expected to shift and diversity is expected to decline as a result of global climate change, particularly in the Arctic where climate warming is amplified. We have recorded the changes in richness and abundance of vascular plants at Abisko, sub-Arctic Sweden, by re-sampling five studies consisting of seven datasets; one in the mountain birch forest and six at open sites. The oldest study was initiated in 1977-1979 and the latest in 1992. Total species number increased at all sites except for the birch forest site where richness decreased. We found no general pattern in how composition of vascular plants has changed over time. Three species, Calamagrostis lapponica, Carex vaginata and Salix reticulata, showed an overall increase in cover/frequency, while two Equisetum taxa decreased. Instead, we showed that the magnitude and direction of changes in species richness and composition differ among sites.